Introduction

The multimillionaire market of ornamental marine species (OMS henceforth) depends almost totally on capture and export of live specimens inhabiting coral reefs at the Indo-Pacific and Caribbean-Antilles (Lango-Reynoso et al. 2012; Moorhead and Zeng 2010; Olivotto et al. 2011). Since traditional fishing often provokes considerable harm to fragile ecosystems and poorly known usually endangered wild stocks, many scientists have addressed research towards key species. However, the literature includes just a small number of species that are current in the market and inhabit elsewhere the West American coast, broadly the Panamic marine biogeographic province. Little is known about the potential of OMS in this region although they have not gone unperceived, particularly in the Gulf of California (Guerrero-Izquierdo 2014; Lango-Reynoso et al. 2012).

One of the targeted species in this region is the yellow-arrow spider crab, Stenorhynchus debilis (Smith, 1871) (Brachyura: Inachidea) (Fig. 1). The alluring long-legged crab is a conspicuous member of communities that colonize cultivation artifacts at La Paz (Monteforte 2005) and Loreto bays (Murtaugh and Hernández 2014). The four species known in the genus Stenorhynchus (S. lanceolatus, east Atlantic-Mediterranean; S. seticornis/S. yangi Caribbean-Antillas region, and S. debilis itself), are frequent items on sale tagged by diameter (leg span) generally between 140 and 180 mm. By browsing the internet for size data or pictures having dimensional reference (e.g. someone’s hand or a known object), Fig. 1 indicates that S. debilis can grow to 180 mm of leg span and even larger, and definitely it owns excellent attributes to become a pricey OMS. Therefore, we investigated this species as experimental actor, principally seeking patterns linked with land-based live management and cultivation.

Fig. 1
figure 1

Specimen of yellow-arrow spider crab Stenorhynchus debilis (male) measuring more than 180 mm of leg span. The specimen was captured in 2015 on an artificial reef that had been installed a few months earlier near our study site at 10 m of depth. Since this system was placed adjacent to the rocky-coralline reef, we might suppose the specimen was not original dweller therein

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Two objectives were established: (1) Find the species’ profile into selected tests. Data included: anesthetic therapies, temperature-salinity thresholds, functional and behavioral responses to: food and feeding, density, sex-ratio, size, shelters, and handling in general, and practical aims on ovigerous females, eggs, and larvae, and (2) Evaluate outputs in seek of explanations for growth, survival and general performances of individuals as a function of species-dependent profiles related to S. debilis particular biogeography, distribution and zonation in the tropical-temperate Panamic-Gulf of California bioecological range, and in account of small-crab criteria,

Analytical comparisons of our data at the light of allied crabs and commercial decapods in general (edible and ornamental, Stenorhynchus spp. included) are discussed by the relevance of such objectives. Species-dependent incognitos were implicit because S. debilis is one of the few Panamic-Gulf of California species that show longest latitudinal continuity in this already long band, roughly from the 28° N (west coast of the Baja California peninsula) and upper Gulf of California, to the Galápagos archipelago. Many species of fish and invertebrates exhibit low, mild, or strong affinity (north-south expansion and/or submergence) to transitional zone phenomena provoked by Niño-Niña events that are customary in this region (e.g. Garth 1958, 1991; Keen 1971; Miller and Lea 1972). The crab belongs to a short list of species with strong affinity, thus it presents temporary incidence as far as California and Oregon, and Chile (Engle and Richards 2001; García-Guerrero and Hendrickx 2004; Garth 1958, 1991; Montagne and Cadien 2001; Wicksten 2012). Besides, S. debilis has been recorded from low intertidal to ~200 m of depth and in oceanic islands like Revillagigedo, Clipperton, and Galápagos (Crane 1937; Garth 1958, 1991). These features would entail hypothesis of compatibility within the traditional OMS market which is principally based on tropical stenotopic ambient i.e. reef-system aquaria.

Further motivations for the present study concern the evaluation of growth, performance and behavior because many Brachyura display singular facets in captivity and/or cultivation conditions; for example, molting delay after sexual maturity or as a result of stress has been reported among the Majoidea and Cancridea (Cruz-Castaño and Campos 2003; Matson and Spaziani 1985; Olmi and Bishop 1983). In addition, females can store sperm which leads to molting delays and/or rhythm displacement of maturation and eggs release (McLay and López-Greco 2011). In consequences, some hindrances to assess growth patterns were expected in our experiments. Mating events and/or harvesting ripe eggs at the correct moment –indispensable sprockets to start cultivation—were compromised by these facets as well. Moreover, claw-bearing decapods demand extra care in confinement conditions like cultivation tanks or domestic aquaria. In consequence, intra and inter-specific dynamics were important perspectives to ponder on the scope of OMS.

Experimental Structure in Real Conditions

The collection site was a pearl oyster farm (Pteria sterna) located in La Paz bay, southwest Gulf of California. Live specimens of S. debilis were extracted from the farm’s off-shore cultivation artifacts (15–18 mm mesh). Previous studies on pearl oysters farming in La Paz bay (Monteforte 2005) anticipated that collection into the artifacts could be meager and probably would consist of small specimens since workers in the farm carry monitoring and cleaning routines in a 3 months schedule. We planned 4–5 visits to the farm distributed between May and August 2015 in order to comply with the design of five experiments: four of them related to live management overall (Table 1), and the fifth one to study the characteristics of ovigerous females aiming at cultivation.

Table 1 Array of Experiments carried out on Stenorhynchus debilis between May and August 2015, focus on ovigerous females excluded. Data logging of Indicators in each individual (Number of Crabs per Parameter) was evaluated as a function of time (minutes, hours or days) in accordance to Tested Parameters and the type of Indicator in scrutiny. The Real Sequence of Experiments was pre-established by practical reasons assuming an appropriate step-by-step acquaint to our subject crab as potential OMS. The collection effort varied consequently (e.g. number of cultivation artifacts manipulated in order to fill the N crabs needed for each experimental design)
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About 230 cultivation artifacts were examined across the four expeditions and 470–480 specimens of S. debilis (25 ovigerous females included) were effectively counted and collected. The colonizing community in the artifacts and over pearl oyster shells was quite diversified, it had similar number and types of brachyuran species as reported by Monteforte (2005), Murtaugh and Hernández (2014), and Wright López (1997), but as expected, they showed low abundance and most of the specimens of “large” species (e.g. Portunus xanthusi, Eriphia squamata, Pilumnus towsendi, Panopeus purpuratus) were small. For S. debilis, the average frequency was 2–4 individuals per artifact and a maximum of six happened seldom.

To identify what crabs were suitable for the experimental designs, three leg span categories were established since the first collecting session: small (less than 20 mm), medium (20–40 mm) and large from 40 mm to the largest observed (50–60 mm). Later on, these ranges remained constant even if three or four big males between 60 and 70 mm of leg span were found. Although artifacts without S. debilis always stayed into 18 to 20%, many were manipulated (hauled aboard, transported during 15–20 min to the farm’s dock, disassembled, and hand-picking) to obtain medium to large-sized specimens in number enough for each experiment. Crabs in the small leg span category or smaller were not abundant; probably a proportion was washed out when bringing artifacts aboard or during the transport. To some extent, the choice of medium and large crabs would justify much of the applicability of our study since the mechanic vernier resulted tough a tool for the very small ones who had fragile rostrum and flexible carapace on the width axis. In occasions, the balance was not sensible enough for specimens weighing less than 0.001 g (smaller than 10–15 mm of leg span). Sex was indistinct in at least 30 out of the 40–45 crabs collected in total for the small category. Crabs bearing missing appendages, broken rostrum and/or cracked carapace, and/or smaller than 20 mm of diameter were freed (~30% of the total collection), still a handful of healthy crabs of mixed sizes and sex and some ovigerous females were kept in formalin-alcohol.

The selected crabs (about 365 along the four expeditions, 25 ovigerous females in total included) were transported to our laboratory into 100-L portable coolers loaded with plastic yarn and netting to provide protection and avoid fights. No relaxant substances were added and 40–45 crabs was the maximum total allowed in a single cooler. Trips to the laboratory took about 45 min on paved road in vehicle with running air-conditioner while conventional 12 V air-pumps connected to the dashboard sockets supplied aeration into the coolers. At arrival to facilities, they were pre-acclimatized by leaving them 3–3.5 h in a quiet fresh place indoors (no fed), under slow flow of filtered and UV sanitized seawater at 24–25 °C of temperature and 36–37 ‰ of salinity (summer average conditions in La Paz bay at 8–12 m of depth) and mild aeration with electric air-pumps and bubbling stones. Natural mortality always remained between 2 and 4% whilst fights and agonistic events (autotomy, self-damage) had low frequency.

Ovigerous females appeared sporadically in the artifacts. Sixteen out the 25 collected in total were in the small leg span category and practically all (19/25) were collected in the visit devoted to temperature-salinity tests which needed 140 suitable crabs at best (section 2.1.3). These females were extremely sensible to handling (autotomy, agonistic tearing and eating eggs, and prompt death). When present, they were placed into the coolers in individual plastic boxes profusely drilled and furnished with yarn and netting. None of them took part in the experiments except six in a first pre-sale management trial (section 2.1.5) and the main stock reserved for cultivation practices.

Experimental Designs: Organization and Procedures

Reference Measurements for the Experimental Crabs

Wet weight (W in g) was recorded with electronic balance (± 0.001 g), and carapace size components with mechanical vernier (± 0.01 mm). These components were the following:

  • Total length (TL): distance between rostrum tip and posterior margin of carapace. Since the rostrum is fragile, the handling with vernier was done with great care.

  • Carapace length (CL): distance between posterior margin of carapace and rostrum base (an imaginary line over the distal edge of both ocular cavities).

  • Carapace width (CW): distance between the lateral-branchial margins.

Anesthetic Therapies

Clove-oil extract Eugenol 99% (Sigma-Aldrich®) was tested in two related experiments. Three concentrations (100, 200 and 300 μL L−1) were used in the first one to investigate effects of exposure time (relax-recovery). In the second experiment, crabs were stored in non-anesthetized and anesthetized conditions, this time in Eugenol at a concentration of 100 μL L−1, based in the results of the previous experiment.

Three tanks of 25-L were used in the first experiment (Table 1). A total of 30 crabs were placed in individual square cages (~10 cm across) and distributed by 10 cages/crabs in each tank keeping sex-ratio close to 1:1 (non-ovigerous females). The desired amount of Eugenol was pre-dissolved in 1-L flasks (strong agitation, no alcohol) and poured into each tank while gently stirring to facilitate diffusion. Relaxation and recovery were timed in the corresponding cases by recording sequential events of unresponsiveness (phase I: decrease of activity in maxilippeds and antennas, and loss of equilibrium; phase II grip release and jellyfish-like rolling-floating, and phase III: immobility at approach or poking), and return to normal behavior in the recovery pans. Mortality was monitored throughout.

In the second treatment, 15 crabs were introduced each in a 250 mL plastic bag containing polypropylene yarn and filled half-and-half with filtered and UV sanitized seawater and compressed natural air (SCUBA tank). Eugenol was pre-dissolved at a concentration of 100 μL L−1 and slowly added to 10 bags, the other five bags were not treated. The 15 bags with their respective crab were sealed with rubber bands and distributed in three groups of five bags, and packed in three transparent plastic containers. Crabs exposed to 100 μL L−1 of Eugenol were retrieved at 5 h (first container) and 8 h (second container), and induced to recovery in 1-L pans with clean running seawater and aeration. The five bags of the third container (clean controls) were just visually examined and mortality was recorded until last dead (~ 46 h). Measurements of pH and dissolved oxygen (DO) were taken when a crab had died in its corresponding bag. To isolate the effect of Eugenol upon mortality, a reference was registered in a 500 mL jug filled with clean filtered and UV sanitized seawater previously aerated for oxygen saturation (pH = 7.8 at 7.5–8.0 mL L−1 of DO). Witnesses of pH and DO were also recorded in six sealed 250 mL bags (without crabs) half-and-half filled with natural SCUBA air and seawater containing Eugenol at 100 μL L−1. Measurements of pH and DO were taken after opening two of these bags respectively at 6, 12 and 24 h, finding that both parameters had remained stable except for one of the bags stored for 24 h, whose DO decreased to 6.8 mL L−1.

Response to Temperature and Salinity

Thresholds of temperature and salinity were analyzed by subjecting crabs to shock by thermo-regulated bayonets and laboratory quality natural salt without returning to La Paz bay averages imitated in laboratory. Fourteen 25-L tanks were prepared, seven of them at seven salinities from 15 to 50‰ and fixed temperature of 24.5 °C, and the other seven were at seven temperatures from 5 to 42 °C and fixed salinity of 36–37‰ (Tables 1, and 2A, B). A total of 122 crabs were placed in individual square cages and immersed into the 14 experimental tanks so that each tank had eight crabs at sex ratio close to 1:1 (non-ovigerous females). Observations were recorded every hour. Accumulated mortality (% h−1) was used to calculate median lethal temperature (MLT50) and salinity (MLS50) (Akhila et al. 2007; Finney 1985).

Table 2 (A, B) Percent accumulated mortality of Stenorhynchus debilis submitted to shock of Temperature (A) and Salinity (B). The initial number of crabs in each parameter mark was N = 8
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Growth and Survival by Diet

Large body of research focused on stomach contents of many Decapoda coincide on correlating a series of internal and external morphologic features with functions and behavior related to species’ expressions such as feeding habits (e.g. degree of omnivourism and/or specialization like algae-cutters, bottom-sweepers, scavengers, shell-breakers, stalk-jumpers, predator-swimmers) and other specific aspects (e.g. movement patterns like speed and agility, dwelling strategies, mating, and large variety of courtships and fighting displays) (Allardyce and Linton 2010; Claverie and Smith 2007; Creswell and Mardsen 1990; Dahdouh-Guebas et al. 1999; Huber et al. 2000; Mariappan et al. 2009; Monteforte 1987; Nunes and Parsons 1998, 2000; Squires 2003; Vermeij 1978; Williams 1981, 1982). Therefore, the punctual picture of S. debilis in context of these correlations (e.g. photos of buccal parts and chelae in supplementary material) certainly underlined a definite framework within management in live conditions, whether experimental or commercial.

Although we dissected a few specimens of S. debilis in –unsuccessful—search of identifying stomach contents, still Crane (1937, p. 50) describes a meticulous diet consisting of “..algae, minute crustaceans probably amphipods, some anemones, and sea urchin”. It was not pragmatic to copy this menu in laboratory and/or recommend it for pre-sale management or use in aquaria. In fact, the list of possible food items out of small fish, invertebrates, seaweeds, etc. that colonize cultivation artifacts and pearl oyster shells may reach several hundred (Monteforte 2005; Monteforte and García-Gasca 1994; Wright López 1997).

The commercial market offers ample choices to feed edible and ornamental decapods. Actually, members of marine aquaria social networks (some of them owning Stenorhynchus spp. or other ornamental decapods) describe time-taking home-made recipes. We wanted our food pieces to be small, sinkable, soft but compact enough to withstand manipulations (e.g. first approach, pinching, tasting), and attractive somehow (odorant?). Finely chopped fresh scallop muscle (Argopecten ventricosus) and surimi (crab-meat imitation), and 35% protein commercial pellets for juvenile white-legged shrimp were inexpensive and easy to obtain. These three types of food were tested in this experiment.

Twenty-four crabs (11 males and 13 non-ovigerous females) were weighed and measured, placed in individual 300-mL flat transparent plastic boxes profusely perforated (~3 mm drill) and roughened inside to provide cling-on surface, and distributed into a 100-L tank (Table 1) by three groups of eight boxes (1 crab/ 1 box/ 1 type of food) keeping sex ratio close to 1:1. Weight and carapace measurements were recorded every 17 days until completing 68 days, thus four measuring sessions were realized after the initial one. All of the handlings proceeded under anesthesia by exposing the crabs to 200 μL L−1 of Eugenol in 1-L pans (based on our results) until they started to show less activity and body oscillations (2–3 min), then they were delicately dried with cotton dabs, measured and weighed, and rinsed into clean seawater before placing them back into their respective boxes. Crabs fed once daily following a shrimp protocol which starts by serving 10–12% of the subject biomass and then the amount is adjusted depending on consumption (Akiyama and Dominy 1989; Amaya et al. 2007). Dead crabs were retired and logged for size and weight as occurring. Unconsumed food was daily removed by siphoning and 50% of the water was replaced during the procedure. The experiment stopped at day 68 because accumulated mortality had exceeded the limit of acceptability (Catacutan 2002).

Behavior and Performance in pre-Sale Conditions

We used a 500-L tank with up-lift system built on a 3 mm mesh plastic board placed 4–5 cm over the tank bottom. A substrate layer ~5 cm thick made of flat pebble, gravel and rough sand was arranged over the board. Needle-perforated tubing supplied mild aeration from underneath. Shelters were provided using PVC tubes (5.5 cm diameter × 15 cm length) to simulate cryptic habitat, and ballasted bouquets of polypropylene ribbon (30-35 cm long × 1 cm width) to simulate seaweeds.

Sixty-four crabs entered a first trial (28 males and 36 females, six of them ovigerous). This amount was arbitrarily set as imitation of a ‘profitable’ tank, but instead, it became a fierce battleground that led us to install a second trial with 19 males and 19 non-ovigerous females. In both cases, shelters (PVC tubes and bouquets) were distributed over an imaginary grid (2.04 m2, the tank bottom area), placing a different one in each cell so that each crab would have two sheltering options in each trial. Scallop muscle, surimi and pellets were offered together by spreading equal composites at random in the grid (~ 0.8 g per crab, that is, starting with 50–53 g daily in the first trial and 25–27 g in the second trial). Dead crabs –a lot during both trials—were retired after leaving them in the tank not more than 3 h when possible (assessing cannibalism). The amount of food was gradually adjusted for the number of survivors. Unconsumed food was removed by siphoning and 1/3 of water volume was replaced during the procedure.

Observations on Ovigerous Females and the Cultivation Practice

Nineteen healthy ovigerous females were collected in a focus expedition to the farm (July 2015). Three (the smallest, the largest, and a medium-sized) were sacrificed to observe morphology of eggs and pre-Zoea, and calculate fecundity, and 16 were used in a cultivation trial. They were placed in individual transparent plastic boxes of 250 mL profusely perforated and covered with nylon netting 300 μm mesh, each box containing one PVC tube and one bouquet. The boxes with their corresponding female were deposed into a 200-L square tank, pre-acclimatized and fed the three food items for 72 h at the averages of temperature and salinity, and then induced to release their eggs. We chose the customary cooling-warming regime used for tropical Decapoda (Arana and Ortega 2004; Cripe 1994; Pillai et al. 1988): lowering to 20 °C (demanded about 3 h), slowly re-raise (the maximum summer average at La Paz bay 30-31o C would be near the limit for S. debilis), and stabilize at 24–25 °C after the expected hatching. This temperature is the current one to cultivate tropical crabs and also recommended for traditional tropical home aquaria.

Data Treatment and Statistical Background

The planning for factorial experiments i.e. based in counting and measuring inputs over a gradient, was meant to identify key Indicators in real scenarios where experimental replications were limited by the scarce number of suitable individuals. Seeking to minimize the virtual incertitude, an individual code (carapace components and weight) was assigned. We used CSS-Statistica 8.0 (StatSoft, Tulsa, USA) to probe these codes and evaluate probable patterns by means of statistical inferences accordingly the structure of databases (Siegel and Castellan 2009; Zar 1999). However, the coding approach was not as useful in terms of spatial repartition within shelter and/or food grids in the pre-sale tank. It will be seen in section 3.4 that the particular aftermaths resulting from this experiment concerned fast-paced behavioral events where crabs were difficult to follow individually. On the contrary, the code applies for live and periodically dying crabs during the short experiments of anesthesia and temperature-salinity in which mortality was the main factor under scrutiny. Since handling un-anesthetized crabs to record initial measurements may introduce biases when testing single parameters, the individual code was assigned to crabs gradually dying and to survivors at the end. The fact was implicit in the interpretation of results in these short experiments (sections 3.1 and 3.2) because the recording logs were realized at close intervals whilst the diet experiment had longer intervals (17 days), thus dead crabs received attention principally on the basis of weight. There was a question of timing, for corpses usually remained overnight in place and we are unsure as to how much decaying would alter the original weight and/or the proportion of eventual gain. Besides, the recording time along the 17 days schedule varied ±3 h. Some dead crabs had consumed some food, others did not. Some tended to float, others rolled on the bottom. Comparisons of individual weight between the last live record and the expiration one (day 34 and on) generally yielded negligible differences and coincided with evidence of low or no feeding. It seemed that post-handling mortality time tended to shorten after day 34, hence the underlying structure of the diet experiment relied on live crabs that were supposed to grow or die across accumulated phases of 17 days. That is why the individual code continued being active in the database until the last live record. Nevertheless, other kinds of improvisation were needed later (section 3.3).

Results

Anesthetic Therapies

In the first experiment, none of the 10 crabs exposed to 100 μL L−1 showed relaxation before 40 min of exposure. Then they gradually lost balance and phase III was reached at 55–60 min. Recovery took 10–15 min and mortality was none. At 200 μL L−1, 8/10 crabs showed phase III in less than 7 min and 9/10 crabs in 10 min. They took 5 to 10 min to recover. The 10th specimen, a small female, was still reactive after 25 min. Survival at 96 h in both therapies was the same (9/10 crabs) included the reactive female who died within 24 h. In the contrary, the 10 crabs exposed to 300 μL L−1 rapidly underwent phase III in the first 4–5 min of exposure but none of them got fully recovered and died 2–3 h later.

Consecutive Mann-Whitney U tests between 100 and 200 μL L−1 (phases I to III and recovery timing, the aforementioned female excluded) suggest that smaller individuals reached relaxation before the larger ones and also needed longer time to recover, but the significance level was not conclusive (p from 0.048 to 0.062 throughout). No differences by sex were detected.

In the second experiment, the five crabs stored 5 h in 100 μL L−1 took 30–35 min to recover. One small male died 23 h later; the other four crabs were alive and apparently healthy at 96 h, behaving and feeding normally. Two of the five crabs stored for 8 h at this concentration were dead. The other three showed recovery in less than 40 min and were alive and stable 96 h later. No influence by sex was detected. The five untreated crabs survived fairly well until 39–40 h and then mortality increased to three specimens in the next hour. The last crab, a medium-sized female, died at 46 h.

Measurements of pH and dissolved oxygen (DO) taken in the bags whose crab had died showed that pH had lean to the acid range (7.4 at 5 h and 7.0 at 8 h) while likely some DO had been consumed (7.0 and 6.6 mL L−1; respectively). Records in the bag when the last –untreated—crab died (a large male about 50 mm of leg span), were pH = 6.4 and DO = 5.5 mL L−1.

Thresholds of Temperature and Salinity

The eight crabs exposed to 5 °C immediately ceased to move but later some of them slowly moved their limbs. All showed autotomy, at least two and up to five appendages (legs in most cases) in the first 30 min. Survival still was 80% at 1 h, but rapidly fell to 10% at 6 h; total mortality was registered at 8 h (Table 2A).

The eight crabs exposed to temperatures between 10 and 30 °C seemed in good shape at 96 h. The eight crabs at 33 °C showed slow but constant mortality, reaching 100% at 70 h. Crabs exposed to temperatures of 35 °C and higher, had high frequency of autotomy and all died in less than 2 h. Calculations for MLT50 marked the low extreme in 7.5 °C at 12 h and the high one in 32.8 °C at 3 h (Table 2A). Crabs exhibited trembling movements, contractions and autotomy when dying by lethal high or low temperature and it seemed that small/light crabs were affected earlier than the large/heavy ones.

The eight crabs exposed to salinity of 25‰ were intermittently active and inactive during the first nine hours without apparent harm. Then the activity diminished along a rapid increase of mortality that reached 70% at 12 h and 100% at 21 h (Table 2B). The eight crabs exposed to 15 and 20‰ gradually got inactive and lost equilibrium, and died in 2.5–3 h. At salinities of 30 and 40‰, survival was 100% at 96 h. The eight crabs exposed to 45‰ presented constant mortality from the first hour; the last one survived 18–19 h only. The lowest extreme of MLS50 was detected at 21 h in 26.4‰ and highest in 42.6‰ (Table 2B). The response of crabs to lethal of high or low salinity turned to relaxation, thus autotomy had moderate incidence. As it happened in the temperature test, small/light crabs apparently were more sensible in this experiment.

In general, the results of this experiment suggest that the proper ranges of temperature and salinity to maintain specimens of S. debilis in good health are close to the standards of home (tropical) aquaria (24–28 °C and 34–37‰).

Effect of Diet

The evaluation of growth in commercial crabs is based on pre- and post-molt measurements of carapace size and weight using stepwise methods (Brylawski and Miller 2006; Fumis et al. 2006; Moksnes et al. 2014), but we could not applied them because only one small female underwent incomplete molting near the end of the experiment and died few minutes later. However, the 24 participant crabs in this experiment showed dimensional increase (Fig. 2), therefore we needed to verify if heavy/light crabs corresponded or not to large/small carapace size components, or assume machine or person errors.

Fig. 2
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Plot of dimensional changes measured in 24 specimens of Stenorhynchus debilis during 68 days in the dietary experiment (17 days tick mark). Three groups of crabs numbered 1 to 8 were fed one of the three items (1 crab/ 1 box/1 item). Each live crab collects four measurements or black dots (W, TL, CL, and CW) from an initial set (day 0) and then in sessions every 17 days. Individuals were ranked by weight in the day 0 dataset of each food item just for graphical purposes. The tag “M” in this plot is a female (#8) fed scallop muscle that started to molt at day 57–61 but died without completion. Blank in any row 1 to 8 indicates a dead individual counted in each measurement session (+17 days and on)

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First, a non-parametric Shapiro-Wilks W test was applied to evaluate normality in the measuring sessions. Table 3 shows that crabs had narrower range in carapace measurements than in weight at day zero. At days 17 and 34, non-normality values increased in all records because some individuals had gained weight and size, notably in carapace width (Fig. 2). Normality turned up at days 51 and 68 (Table 3) due to the influence of mortality and little dimensional changes in most individuals (Fig. 2); nevertheless, the number and bias of empty cells (dead crabs, principally in surimi) was already weakening the sensibility of the inference. As a consequence, the next exploration was realized by means of a non-parametric Kendall matrix (pooled food item) (Table 4). Note that Fig. 2 was ranked by weight at day zero for each food item; this was intended for graphical purposes and does not affect the structure of Table 4. Since weight was the only data having bias from normality at day zero (significant, but not exceedingly far from p = 0.05) (Table 3), we supposed this dimension could be more effective to appraise the crabs’ initial state and provide a visual monitor of performance during the experiment.

Table 3 Output of the non-parametric Shapiro–Wilk W test to detect variations of normality in carapace size components and weight of Stenorhynchus debilis within each measurement session during the dietary experiment. The effect of food item is pooled. N is the number of live crabs in each schedule form day 0 and every 17 days
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Table 4 Output of Kendall (T) to test presence and concordance of rank permutation in individual dimensions as a function of time for Stenorhynchus debilis in the dietary experiment. To simplify visual analysis, non-significant coefficients were deleted
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So far, Table 4 shows that rank concordance of measurements within each dataset was generally significant, meaning that the correspondence of heavy/light crabs to large/small carapace was acceptable. As a corollary, the permutation of rank order among individuals at days 17 and 34 was affected by increase in weight and carapace size components, particularly evident in some individuals (Fig. 2). In fact, finding significant coefficients clustered within days 34, 51 and 68 (Table 4) indicates that individual rank variation of weight and carapace size components remained regular throughout the experiment because most individuals had little dimensional changes (Fig. 2). Mortality from day 17 and on (empty data) contributed to this situation.

To explain these dimensional changes as a function of time and food item, a Size Index (SI) was coded for each crab. This index consisted of a triangular area (TL minus CL in order to exclude the rostrum) of Log transformed carapace size components multiplied by weight. The strategy should compensate the influence of non-normality detected in some of the measurements (Table 3).

$$ \mathrm{SI}=\left(\left(\mathrm{Log}\;\mathrm{CW}\times \left(\mathrm{Log}\;\mathrm{TL}\hbox{-} \mathrm{Log}\;\mathrm{CL}\right)\right)\left./2\right)\right)\times \mathrm{Log}\;\mathrm{W} $$

—SI is the individual Size Index and Log of each CW, TL, CL, and W are transformed data of the individual. Log transformation usually is the recommended strategy when data are positive numbers and have a trend to vary at higher values (Zar 1999, p. 275). Other standardization or normalization methods make the transformed data dimensionless, thus comparative criteria to locate and scale the original data may be lost, particularly when these data are few.

A tridimensional surface plot of SI was traced (Fig. 3) using the distance-weighed least square procedure at the minimum stiffness to graphically exaggerate peaks and valleys, which is recommended when datasets have few records and/or categories, and especially if any or all axis contain transformed data (CSS-Statistica manual). Figure 3 confirmed evidences of growth from scallop muscle in first place and surimi in second. The influence of scallop muscle became stronger from day 17 until the end of the experiment, while pellets had earned second place.

Fig. 3
figure 3

Plot of combined effect of time and food item in the dimensional changes of Stenorhynchus debilis expressed as individual Size Index variations from 0 (start) to 68 days with 17 days tick marks. The tridimensional surface was fitted to a Size Index (SI) using Log transformed data in order to smooth biases from normality detected in some cases (Table 3), and the distance-weighed least squares procedure with minimal stiffness to visually exaggerate the effect (see section 3.3)

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We evaluated SI using one-way bi-factorial ANOVA. Differences in the magnitude of SI were significant in terms of food item (F = 4.367, p = 0.016) but not in terms of time (F = 1.455, p = 0.224). The combination of both factors was not significant (F = 0.962, p = 0.472), still a post-hoc Tukey test detected a group of low SI in days 0 and 17, and another group of high SI in days 51 and 68, with the dataset of day 34 at shorter distance to the high SI group than to the former. Although the non-significance level of this pattern as a function of time was sensible in all cases (p from 0.064 to 0.082), the data showed that crabs likely grew more from day 0 to 34 than from 34 to 68, and differences of SI were imprinted from day 17 in favor of scallop muscle. At day 68 (end of the experiment) crabs had higher SI in scallop muscle and pellets (Fig. 3) but significant differences were detected only when comparing scallop muscle vs surimi (p = 0.032).

Total mortality in this experiment was 42% (10/24), which is higher than what is considered acceptable in crustacean studies (20–25%, Catacutan 2002). It seems that survival was affected more likely by manipulations and anesthesia than by diet. Figure 2 shows the progress of mortality (blanks in rows 1 to 8 of corresponding food item). Survival was satisfactory until day 34 in the three items, falling to ~50% at day 68. Post-handling mortality tended to occur every time earlier. Survivors were concentrated in muscle and pellet whilst only one small female survived on surimi (#2, it had little dimensional changes).

Behavior in pre-Sale Conditions

Results in both trials (64 and 38 crabs) suggested that overcrowding was the reason of the ferocious violence observed within the first 3 to 5 h in both cases (e.g. big vs small, male vs male, pursuits, and ‘gang’ attacks in several occasions). Although S. debilis normally is a slow-walker, they moved actively into the tank and fatal conflicts were immediate. Threatening stances and combats (erected position, pushing the opponent with rostrum and first legs, chelae thrusting and interlocking, short rapid displacements) resulting in short chasing/retreat or death, generally occurred at the entrance of PVC tubes or near the base of bouquets, and also involved food pieces.

The frequency of fights and degree and magnitude of lethality (severity of mutilations and mortality rate) gradually diminished likely coinciding with evidences of harem formation when nearly 65% of the crabs were dead or badly mutilated (~8–10 h). The event seemed to trend at a sex proportion of 1 or 2 males and at least 4 controlled or non-controlled non-ovigerous females for each male. Surviving males worked to herd non-ovigerous females toward the shelters. They tried to control two or three females placing themselves at the entrance to PVC tubes or at the base of bouquets. Wandering in the tank (for shelter, females, or feeding) was opportune moment for males to gather more females so lethal encounters did not stop.

Calm states were observed when crabs remained sheltered, which was the preferred location most of the time. Larger males controlling up to three females showed noticeable propensity for bouquets. Small males usually were solitary in PVC tubes; a few of them had harem of one or two females therein. Cannibalism after combats or on corpses did not happen although it is a common habit in many decapods (Huber et al. 2000; Marshall et al. 2005). We tried to assess spatial repartition of crabs related to shelter and/or food grids but this was not clear, yet sexual/size spatial segregation seemed likely because the decrease of frantic violence entailed gradual allotment, insofar within the shelter grid. Differential predilection to bouquets or PVC tubes was detected as a probable result of male sizes and number of females in the harem over what appeared to be territories sited well apart in the tank.

Solitary males and solitary non-ovigerous females displayed more activity than crabs grouped in harems. They covered more area and realized intermittent incursions in empty or occupied shelters whether bouquets or PVC tubes. Although non-ovigerous females generally preferred being solitary usually in a PVC tube, encounters with males (after the high violence phase) often resulted in herding toward a shelter nearby, haremized or in course. Females rarely opposed to courtship but copulation was not detected in any case. No molting events were visible in these trials.

During steady states after the frenzy situation, in occasion up to three non-ovigerous females shared a single shelter without conflicts, usually a PVC tube. Fights among females frequently exploded over a single food item. Males did not attack females of their own harem, but displayed shepherd vigilance during feeding migrations. We saw, just once, a male bringing food to the first female successfully herded to his harem, a bouquet actually. We do not know if it happened again, after or before this observation. Female-female conflicts in male-controlled shelters were uncommon. Newcomer females, when successfully herded to the harem, got adapted easily.

The six ovigerous females in the first trial showed propensity to segregate and remain hidden, usually in a PVC tube. They survived unharmed the first exploration and appropriation of shelter and a good part of the battle (~2 h). Fatal encounters concurred with feeding time. These females were highly reactive to threats or attacks. Threatening approaches from males and/or non-ovigerous females compelled them to quickly retreat and hide, but direct attacks triggered egg-tearing and eating and prompt death. It looked like males usually were the main attackers.

Competition for food could be reserved. The three food items were spread more or less in equal proportion in the tank and fresh food was permanently available. Competition for a single piece was likely accidental. The mechanism was: approach, grab (or snatch from other crab if possible), and retire toward the nearest empty shelter which implied a risky exploration. Similarly to the Brachyura, handling the item (inspection and taste?) was also the ordinary behavior for S. debilis. Items were consumed until finish (or almost), especially if other crabs were in the neighborhood. We did not detect preference for the type of food in this experiment. Crabs seemed to go for the nearest piece.

These trials were enough to confirm the behavior of S. debilis into the well-known aggressiveness of claw-bearing Decapoda (Huber 1987; Huber et al. 2000; Mariappan et al. 2009; Ueno and Nagayama 2012). The results indicate that one large male and three medium-sized females could be the convenient amount, size structure, and sex-ratio to maintain specimens in comfortable pre-sale conditions or as potential breeders. We believe this arrangement may be the recommended one for normal domestic aquaria, say 250 to 300-L polyspecific reef system tanks. Probably a 500-L tank or larger would admit two harems, certainly taking in consideration the bioarchitecture of reef systems i.e. trophic structure, shelter network, and overall intra- and inter-specific relationships, plus equipment, accessories, maintenance routines, among other elements.

Ovigerous Females, Eggs, Larvae, and Cultivation Practices

Stenorhynchus debilis is a small crab; its ovigerous females carry small eggs in small numbers, but the parameters are subjective (e.g. Gourney 1942 p. 55; Okamori and Cobo 2003; Reid and Corey 1991; Strathmann 1985; Van Dover et al. 1985). In our samples (Table 5) eggs of S. debilis had spherical shape (380 to 450 μm of diameter, similar to Crane 1937 p. 37, and García-Guerrero and Hendrickx 2004). Eggs of individual ovigerous females showed several stages of division and pre-Zoea. It seems that ovigerous females of S. debilis would be able to carry more eggs than the amounts depicted in Table 5, for tearing off some during collection and/or transport was suspected.

Table 5 Individual relative fecundity (number of eggs g−1), measurements (weigth, total carapace length and diameter), and egg count of three Stenorhynchus debilis ovigerous females (largest, medium, smallest). Eggs were clustered in four paired racemes, a characteristic morphologic feature found for the species probably shared by its co-generics and other inachid crabs as well
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Two details are worth mention:

  1. (1)

    The smallest ovigerous female in Table 5 had 7.0 mm of carapace width (CW), 13.6 mm of total length (TL), and hardly 20 mm of leg span. This female is smaller than reported by García-Guerrero and Hendrickx (2004) in Mazatlán (southeast Gulf of California), and the third smallest individual collected in our expeditions. The other two were a male and a female both having less than 20 mm of leg span.

  2. (2)

    The largest ovigerous female in Table 5 was also the largest of the 19 collected in the special expedition (July 2015). The second in size –just slightly smaller —was among the six ovigerous females that were introduced in the first behavioral trial in August 2015 (section 2.1.5). These two ovigerous females corresponded to small-medium non-ovigerous females (~30 mm of leg span).

Sixteen of the 25 ovigerous females collected in total, barely had 20–25 mm of leg span. Since cultivation artifacts are cleaned every 3 months, this feature denotes that puberty occurs at very early size/age. It also applies for several “large” species of crabs that were studied into pearl oysters cultivation artifacts placed years ago near the location wherein specimens of our subject crab were collected (Monteforte 2005; Wright López 1997).

Eleven of the 16 ovigerous females survived the 72 h acclimatization and nine finished the cooling-warming induction alive. Seven of them commenced to release almost all of their eggs sometimes using the chelae. Intermittent, yet partial egg-eating happened at least once in four females. About 3000 eggs were retrieved and placed in a 30-L cylinder-conical container made of white fiber-glass. Eggs rested on 300 μm mesh netting fitted to a circular frame on the conic edge. Tubing and air stones provided mild bubbling from underneath this structure. Water temperature was slowly stabilized in 24.5–25.5 °C.

Ten eggs were sampled every 24 h for observation and photography. Since the first sample we noted some eggs had been damaged probably during cropping. Eggs tended to float and/or become opaque when decayed. They appeared frequently in the next samples but kept low amount in general. We obtained a total of 900–950 Zoea I between 9 and 13 d later; however, no food was available and they all died before the sixth day of living. Unexpected failures in several of the old buildings at CIBNOR due to cumulated use and sequels of Odile hurricane in September 2014, stopped our laboratory area for months and still now is not fully functional. So, no morphological evidence of Zoea II was detected.

Our album contains microphotographs of eggs in different division stages and instars of pre-Zoea and Zoea I (see supplementary material). Visual characteristics and measurements were annotated and compared with pictures, drawings and descriptive information available for allied species (Paula and Cartaxana 1991; Cházaro-Olvera et al. 2013; Gourney 1942; Goy et al. 1981; Guinot 2012; Medellín-Mora et al. 2009; Paula 1987; Rhyne et al. 2005; Sandifer and Van Engel 1972; Santana et al. 2003; Yang 1976). Size of S. debilis Zoea I looked similar to other small species of Brachyura. Morphologic correlations within the genus Stenorhynchus underscored the presence/absence, distribution and shape of ornaments (e.g. protuberances, spines, and setae), characteristics of somites and other appendages, telson structure, and the amount, shape, size, color, and distribution of chromatophores. The S. debilis Zoea I exhibited a rather conservative morphology in comparison to its co-generics. Many inachid Zoea I have well-defined mandibles and display swimming aptitude, which indicate planktotrophic forms probably having predatory and food selection skills. Zoea I of S. debilis own similar characteristics.

Management procedures related to hatchery and larval development could be contrasted with majid crabs Mithrax and Mithraculus (Calado et al. 2003a, 2007, 2008; Goy et al. 1981; Rhyne et al. 2005; Sandifer and Van Engel 1972; Santana et al. 2003) and S. seticornis (Hernández et al. 2012). We believe S. debilis may compile similar requirements in general.

Discussion

Stenorhynchus debilis occupies a distinctive compartment in the Panamic-Gulf of California region. Only four species of Brachyura, S. debilis included, have been recorded up to California and Oregon, USA (Engle and Richards 2001; Montagne and Cadien 2001; Wicksten 2012). Incidentally, Pteria sterna is also present in the list of species having strong affinity to transitional zone phenomena. Our findings in regards to thresholds of salinity and temperature converged on these observations, for S. debilis tolerated cooler temperature and higher salinity than the average ranges measured at La Paz bay. In this context, the pertinence of species-dependent identity is attached to a vast rationalization (e.g. Anger 2003; Brylawski and Miller 2006; Calado et al. 2005a; Portner 2002; Ravaux et al. 2012; Strathmann 1985; Tomanek 2010). Prospecting the species situation by reference to MLT50 and MLS50 should logically yield consistent interpretations as small tropical-temperate crab (Table 2A, B). From practical viewpoints, temperature, rather than salinity, defines the performance of S. debilis during packing and transport while home aquaria usually deal with stenotopic coral reef communities where many water parameters and technical aspects are critical. Ranges of 24–28 °C and 34–37‰ are generally recommended, thus the values obtained on MLT50 and MLS50 suggest that S. debilis is compatible with stenotopic reef systems. These ranges are also the standards to cultivate small tropical decapods (Calado et al. 2003a, 2007a, 2008; Goy et al. 1981; Hernández et al. 2012; Rhyne et al. 2005; Sandifer and Van Engel 1972; Santana et al. 2003) but fine points are yet to calibrate to achieve full-cycle production of S. debilis.

We are still unsure about which is the best temperature regime to induce egg release and hatching on S. debilis, considering its biogeography and zonation. The cooling-warming procedure applied in this experiment apparently worked well since it is standard for tropical decapods (Arana and Ortega 2004; Cripe 1994; Pillai et al. 1988), but we did not try warming-cooling instead. Actually, the spawning of some commercial bivalves whose wild stock inhabits both the Gulf of California and the western Peninsula (e.g. Pteria sterna, Nodipecten subnudosus, Argopecten ventricosus, Anadara tuberculosa, Atrina maura) is launched by cooling in the Gulf side (winter), and warming in the Pacific side (summer) (Barrios-Ruiz et al. 2003; García-Domínguez 2002; Maeda-Martínez 2002; Monteforte 2005). A seasonal monitoring has to be carried out on S. debilis.

We confirmed that S. debilis must be treated with care. Crabs did react to Eugenol at specific doses and exposure-recovery time. The concentration of 200 μL L−1 worked well and seems recommendable to handle crabs in experimental conditions. However, only descriptive aspects could be discussed to compare anesthetic therapies in known species (effective or ineffective in species A vs B, C, etc., and combining big vs small, young vs old, female vs male, etc.) (Cowing et al. 2015; Coyle et al. 2004); unless we had investigated metabolic issues and/or biochemical histology (e.g. Parodi et al. 2012) with proper equipment and enough individuals to do it.

Traditionally, OMS are transported in separate recipients filled 1/3 to 1/2 of seawater and insufflated with compressed natural air or pure oxygen, and sealed. Silva et al. (2015) used 1-Lt bags finding that oxygen, ammonia and pH are key variables in long periods of pack/transport of some Mediterranean ornamental marine fish. Adding anti-ammonia, pH buffers, bits of food, and/or drops of commercial antibiotic/sanitary substance are common practices among micro-enterprises (Silva et al. 2015). The results of the packing-transport trial convey that S. debilis may not stand more than 36 h in untreated conditions (without anesthesia). Crabs could probably tolerate 8–10 h in Eugenol at a concentration of 100 μL L−1, preferably even less. Although these time lapses should allow long travels, it could be longer in real conditions (Silva et al. 2015). Our bags were smaller (250 ml, 50/50 seawater and natural SCUBA air) than those used by Silva et al. (2015), and we did not use chemical controllers in the water. Data of dissolved oxygen DO and pH taken before and after 46 h of storage (untreated crabs) gave consistent results in respect of mortality (oxygen depletion-acid pH). Eugenol might be necessary only to prevent uncontrolled transport-export trips of particularly cherished stock. Using yarn of polypropylene ribbon and soft netting is recommended to transport decapods having long and fragile appendages. This material provides cling-on structure and protection against brusque handling, and helps to avoid fights.

Stenorhynchus debilis posed other challenges. Claw-bearers are not easy creatures to maintain in breeding groups and they are complicated tenants to introduce in aquaria communities whether built from scratch or already functioning. Actually, our ‘profitable’ pre-sale tank resulted in frantic self-thinning leading to territory allotment probably related to courtship/harem dynamics and repartition of shelters. The natural aggressiveness was exacerbated at high density (Huber et al. 2000; Mariappan et al. 2009; Ueno and Nagayama 2012). Competition for food and shelters apparently was accidental. The results in this point suggest that haremization was a dynamic process of female swapping principally associated to feeding time in first instance, and victories against other males in second instance. Sex-ratio of 3 females and 1 male seemed to be the equilibrium state. Shelters are mandatory to promote protective harems and probably may help crabs to feed properly. PVC tubes and bouquets were adequate to maintain breeding groups or ovigerous females with production in mind, and to arrange convenient conditions in pre-sale tanks. In the other hand, cultivation may succeed using current methods to maintain potential breeders in good shape and able to procreate, and ensure full-cycle production.

Choosing food and feeding schedules are decisions connected to behavioral issues. S. debilis was likely to be selective in its diet (Crane 1937 p. 50). Members of the genus Stenopus, Lysmata, Mithraculus, Thor, Clibanarius and Stenorhynchus are symbiotic cleaning crews so part of their diet could be naturally provided in the aquarium (Medeiros et al. 2011; Wirtz et al. 2009). In fact, the criteria to choose artificial fed for opportunistic omnivorous crabs should consider that even a minor morphologic variation can open to additional food choices and/or modify behavior (Allardyce and Linton 2010; Claverie and Smith 2007; Creswell and Mardsen 1990; Dahdouh-Guebas et al. 1999; Huber et al. 2000; Mariappan et al. 2009; Monteforte 1987; Nunes and Parsons 1998, 2000; Squires 2003; Vermeij 1978; Williams 1981, 1982).

Trial and error feeding tests are needed when meeting a new species, that is, offering different food to measure palatability, growth, survival and performances overall, by choosing what is handy or recommended for benthic crustaceans (Calado et al. 2005a, 2005b; Cunha et al. 2008; Nunes and Parsons 1998, 2000; Huo et al. 2014; Simoes 2004). Besides, the youth of crabs in the artifacts was propitious to study growth patterns based on the diet because short intermolt phases were expected (Brylawski and Miller 2006; Fumis et al. 2006; Ng et al. 2008; Olmi and Bishop 1983), even if molt delays and changes in reproduction timing could arise (Olmi and Bishop 1983; Cruz-Castaño and Campos 2003; Matson and Spaziani 1985; McLay and López-Greco 2011).

Surprisingly, none of the crabs in the dietary experiment showed molt signs until the activity was more or less perceptible in one small female only, nevertheless, the results showed trends of periodical increment of size and weight. Personal or machine errors were discarded.

Molt, shortly described, occurs when individuals engorge with seawater and tissue buildup, then a fracture develops along the cephalothorax molt line, and the crab backs out of its old carapace through the posterior margin. This behavior may explain why the increase in weight corresponded to increase in carapace length (CL) and width (CW) (Fig. 2). Some small crabs gained some size and weight over time, probably because they engorged faster than the larger ones. Scallop muscle promoted this trend (Figs. 2 and 3). The Size Index (SI) seemed suitable approach to evaluate events of dimensional growth in terms intermolt stages and ideally to appraise the development of molt. Scallop muscle and pellets may partially fulfill nutritional requirements, but surimi is highly processed food whose components and quality vary depending on manufacturer, age of the package, and market place. Crabs fed surimi had low survival and inconsistent growth. So far, the diet experiment showed that scallop muscle and pellet had been consumed better than surimi, yet no clear preference was confirmed by the two pre-sale management experiments where crabs just went for the nearest piece and kept it until consumption, or close. Therefore, the validity of dietary factors must be analyzed from the stance of omnivorous crabs and the environment where they are managed in laboratory, pre-sale maintenance and aquaria. Although the bioenergetic aspect of nutritional contents is speculative at this point, many references to commercial decapods and allied species provide useful guidelines. We still want to try homemade vegetable-hashed meat gelatine balls as advised in internet special-interest groups.

The last piece of identity for S. debilis would consist of multiple comparisons related to ovigerous females, eggs, and larvae. The general morphology agreed with taxonomic levels (Anger 2001, p.109–115; Crane 1937; García-Guerrero and Hendrickx 2004; Hines 1986; Okamori and Cobo 2003; Reid and Corey 1991; Van Dover et al. 1985). Species-dependent aspects stood out; for example, we collected smaller ovigerous females than reported before and also found that egg-carrying capacity could be higher. Larval development certainly accounts for large part of species-dependent differences, mainly morphologic (e.g. Anger and Nair 1979; Paula and Cartaxana 1991; Cházaro-Olvera et al. 2013; Clark et al. 1998; Cobo 2002; Goy et al. 1981; Hines 1986; Ng et al. 2008; Okamori and Cobo 2003; Paula 1987; Santana et al. 2003; Van Dover et al. 1985; Yang 1976). It is very unlikely that S. debilis could develop a Zoea III instar. We still even ignore how Zoea II looks like. The behavioral and technologic meaning of uniqueness of larval development and cultivation is yet to investigate. This last piece of identity may be useful to assess further factors that are determinant in building protocols of full-cycle cultivation dedicated to S. debilis on the basis of what is known for commercial decapods and ornamental marine crabs (e.g. Calado et al. 2003a, 2007a, 2008; Goy et al. 1981; Hernández et al. 2012; Rhyne et al. 2005; Sandifer and Van Engel 1972; Santana et al. 2003). Unfortunately, this objective was not accomplished for the moment.

Conclusions

The experimental role of S. debilis was probed onto bio-benchmarks pertaining allied species to investigate what species-dependent factors are critical to achieve practical objectives related to land-based management and cultivation. We found interesting updates, and also correlations with edible and ornamental crabs were confirmed. Differences or similarities of profile analysis and performances were coherent with the expected cadre for S. debilis, being itself a special Panamic species with affinity to cool better than warm seawater. The customary temperature and salinity for tropical OMS in laboratory and domestic aquaria –typically tropical stenotopic systems—should be compatible. Anesthesia and manipulations were the main factors affecting survival in the diet test, yet we believe the Size Index (SI) was a reliable approach to interpret dimensional changes in terms of intermolt efficiency as a function of nutritional contents and willingness to consume the offered food. Relationships between structure and function of feeding parts, type of food, and feeding behavior were logical when choosing inexpensive food. Stenorhynchus debilis showed strong territorial behavior; aggressiveness and agonistic reactions were exacerbated at high density. It seemed that one large male and three medium-sized non-ovigerous females is the recommended unit to safely keep potentially breeding groups or tenants in pre-sale tanks or home aquaria up to 300-L. The crab may live long in well-maintained aquaria; some members of hobbyist social networks report 7 years or more for S. lanceolatus and S. seticornis, but recommend paying attention to density and combinations of claw-bearing tenants with other species of fish and/or invertebrates. Our study ended by reiterating the need for further effort to understand the requirements of S. debilis and improve cultivation and management strategies in order to achieve full-cycle certified technology. At the closure of this work, many questions on technical and management adjustments to meet livelihood requirements still remain pending.