Introduction

The world macroalgae market is dominated by only a few species. For carrageenophytes, production is largely concentrated in Eucheuma spp. and Kappaphycus spp., based on marine farming, with the exception of Chondrus crispus Stackhouse and Gigartina skottsbergii Setchell et Gardner harvested from natural populations (Hurtado et al. 2017; FAO 2020a). However, the demand for species diversification has increased in the last decade, driven mainly by the development of the phycocolloid industry, an increase in direct consumption, and the use of nutraceutical and pharmaceutical products (Shannon and Abu-Ghannam 2019).

According to the FAO (2020a), 91.7% of the world’s macroalgae production in 2018 was obtained through aquaculture. In Brazil, although phycology is relatively well advanced and has a wide sea coast and good diversity of macroalgae, commercial aquaculture is embryonic with an estimated production of 730 t in 2018 (FAO 2020b). As a consequence, Brazil still depends on the import of fresh biomass and several of its products (Simioni et al. 2019). Even if Brazil does not have good floristic and climatic conditions for the production and processing of brown macroalgae for food and/or alginates, the country could become a producer of red algae to obtain agar and carrageenan or even for in natura consumption (Hayashi et al. 2014). In view of this, several studies have been carried out with native macroalgae showing promising results (Pereira and Silva 2021; Carneiro et al. 2021); however, these have never reached a significant commercial level so far (Simioni et al. 2019). As regards the carrageenophytes production, promising native species include Hypnea pseudomusciformis Nauer, Cassano & M.C.Oliveira and Chondracanthus teedei (Mertens ex Roth) Kützing (de Oliveira 1997; Simioni et al. 2019). For H. pseudomusciformis, the studies carried out to date have not shown results that would stimulate the sector by coming up against technical difficulties (Reis et al. 2006). With C. teedei, only studies related to taxonomy, reproduction, and ecology have been carried out (Braga 1985,  1990).

Although seaweed aquaculture technologies have developed dramatically in recent decades, there is a growing need for predictability and control over production processes and, hence, calls for intensified search for strains with the desired characteristics and high yields (Levy et al. 1990). Genetics and the development of new production techniques have led to improvements in obtaining strains in terrestrial agricultural plants in recent decades. However, strain selection of macroalgae is still an embryonic field (Robinson et al. 2013). Some programs for selecting macroalgae strains have been implemented over the past few years. The main target characteristics have been growth rate (Paula et al. 1999), more attractive morphology (Li et al. 1999), more resistance to breakage (Mollion and Braud 1993), tolerance to abiotic variation (Yan et al. 2010), tolerance to disease (Park and Hwang 2014), and high phycocolloid production (Hayashi et al. 2007).

Studies related to strain selection usually involve a pool of individuals from one or more populations. Experiments are then carried out in natural and/or laboratory conditions in order to express the desired phenotypes (Bulboa et al. 2008). Recently, new techniques have been used to improve strains, including protoplast fusion (Reddy et al. 2008), mutagenesis (Charrier et al. 2015), and genetic modification (Robinson et al. 2013). However, these techniques are difficult to perform and costly, in addition to the challenges of public acceptance owing to genetically modified organisms and environmental risks (Robinson et al. 2013). However, spore selection, although little used, has shown good results allowing high genetic variability and continuous selective breeding (Paula et al. 1999; Yan et al. 2010).

Macroalgae release an enormous number of spores that become part of the plankton. This reproductive effort is necessary due to losses during the development of germlings. Among the numerous sources of failure in recruiting spores are grazing, displacement to aphotic zones or to unfavorable surfaces, and limiting abiotic conditions (Maggs and Callow 2006). Temperature plays an important role as it regulates spore fixation, germination, and germling growth determining the patterns of biogeographic distribution (Yokoya and Oliveira 1993). This results in the introduction of complex reproductive mechanisms that often involve syngamy, mitospores, meiospores, and parthenogenetic development of unfertilized gametes (Liu et al. 2017). This complexity, in turn, results in high genetic diversity and contributes to the maintenance of populations in relation to environmental pressures (Coleman et al. 2020). Thus, strains with stress-tolerant genotypes are selected owing to environmental pressures, replacing less resistant individuals in the population or expanding the biogeographic distribution (Coleman et al. 2020). Some studies have been carried out to test the possibility of selecting strains from spores. Paula et al. (1999) and Bulboa et al. (2007), for instance, obtained more robust strains with high morphological differences and satisfactory growth rates using tetraspore progeny from Kappaphycus alvarezii (Doty) Doty ex P. C. Silva and K. striatus (Schmitz) Liao, respectively. Yan et al. (2010) obtained temperature-tolerant strains of Neoporphyra haitanensis (T.J. Chang & B.F. Zheng) J. Brodie & L.-E.Yang (formerly Porphyra haitanensis) by exposing germlings from conchospores at elevated temperatures.

In recent years, interest in macroalgae of the genus Chondracanthus has grown as a result of their economic potential for extraction of carrageenan, use in cosmetics, and direct consumption (Contador et al. 2020; Pereira and Silva 2021). Chondracanthus teedei is a cosmopolitan species found in Brazil from the state of Ceará (3° 42′ 24.30″ S and 38° 28′ 7.75″ W) to Rio Grande do Sul (31° 54′ 42.27″ S and 51° 35′ 23.09″ W) with Uruguay as its southern limit in the western Atlantic (34° 57′ 53.54″ S and 54° 56′ 22.98″ W) (Coutinho 1982; Joventino et al. 1998; Coll and Oliveira 1999) and is considered promising for carrageenan production (Pereira and van de Velde 2011). The life cycle is isomorphic triphasic (Pereira and Silva 2021) and differences in carrageenan composition are observed between the stages with gametophytes producing kappa/iota hybrid carrageenan and tetrasporophytes produces xi-theta hybrid carrageenan (Pereira and Mesquita 2003, 2004; Pereira et al. 2009). Zinoun et al. (1993b) show that it is possible to manipulate the metabolism of C. teedei by varying the temperature of the medium which results in changing the composition of carrageenan and its yield. The first studies with C. teedei in Brazil were carried out by Braga (1985) who demonstrated a tendency of biomass increase in the winter and decrease in the summer for southeast populations. In the laboratory, the author also observed that the species survives at temperatures between 18 and 26 °C, with greater growth rate at 22 and 26 °C without influence of the photoperiod. These results indicate that the species could be used for biomass production and carrageenan extraction in places where the amplitude of annual temperatures becomes a problem in cultivation, especially for tropical species such as K. alvarezii introduced in the south of Brazil. Thus, the present work aimed to evaluate the potential for strain selection using tetraspore and carpospore progeny from wild fronds of C. teedei to obtain strains with high growth rates, tolerance to temperature, and high yield of native carrageenan in view of the economic potential of this species for the phycocolloid production, functional food, and nutraceuticals.

Material and methods

Progenitors and spore release

Fronds of Chondracanthus teedei were collected in the northern part of Praia das Caravelas (27° 21′ 26.57″ S and 48° 32′ 12.69″ W) in Santa Catarina State, Brazil. After collection fronds were stored in plastic bags with seawater and transported inside coolers to the Laboratory of Phycology at Universidad de Santa Catarina (LAFIC-UFSC). In the laboratory, the fronds were separated by life cycle phase by visual inspection looking for cystocarps and tetrasporangial sori. Five female gametophytes with cystocarps and five sporophytes with tetrasporangial sori were selected at random. These progenitors were represented with the letters being A, B, C, D, and E for female gametophytes with cystocarps, and F, G, H, I, and J for sporophytes with tetrasporangial sori (Fig. S1 in the on-line Supplementary material). From each progenitor, four frond fragments containing reproductive structure (cystocarp or tetrasporangial sori) were removed and placed individually in Petri dishes with slides for microscopic observation and 50 mL of culture medium (Fig. 1). This totaled four Petri dishes for each progenitor (Fig. 1). After 24 h, the frond fragments were removed, and spores cultured for 30 days at 25 °C, photosynthetically active radiation (PAR) of 20 μmol photons m−2 s−1 with 2 fluorescent lamps (Osram 30 W Daylight), 12-h photoperiod, and salinity of 35. The culture medium consisted of sterilized seawater and von Stosch solution (8 mL L−1). Seawater was sterilized with a mechanical filter (5 and 10 μm) and exposed to UVC light in a slow continuous flow. In the first 7 days, 6 mL of GeO2 (3 μg L−1) was added to control possible contamination by diatoms, and potassium penicillin (0.2 mg mL−1) was added to inhibit cyanobacterial growth (Oliveira et al. 1995; Garcia-Jimenez et al. 1999). Culture medium was renewed weekly.

Fig. 1
figure 1

Sequence of strain selection process. (1) Gametophytic or tetrasporophytic progenitors with reproductive structures. (2) Petri dishes containing a frond fragment with reproductive structure. (3) Germlings after 30 days. (4) Selected strains grown in isolation. (5) Cross between strains from sporophytic progenitors to identify female gametophytes

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Initial isolation of strains

For strain selection one germling per Petri dish was randomly removed and cultivated in isolation for 60 days (Fig. 1). This totaled four germlings for each progenitor, resulting in 40 selected strains (20 from gametophytic progenitors and 20 from tetrasporophytic progenitors). After selection germlings were kept in Erlenmeyers with 50 mL of culture medium for 15 days, and then moved to Erlenmeyers with 250 mL of culture medium under constant aeration and 80 μmol photons m−2 s−1 (Fig. 1). One Erlenmeyer was used for each selected strain. Culture medium was renewed weekly and every 15 days the fronds were weighed with an analytical balance (BioPrecisa FA-2104N) and photographed. The strains are represented with the letter S of strain followed by a strain number and letter that indicates their progenitor. Example: S23H—Strain 23 originated from tetrasporophytic progenitor H. After 60 days of isolated cultivation, crosses were performed in the gametophytic strains to identify the female gametophyte by the formation of cystocarps (Fig. 1). To this end, the gametophytic strains were labeled and kept in the same container (aquarium with 3 L of culture medium) for 15 days. After this period, the strains were cultivated again isolated to increase biomass for subsequent experiments. The parameters were kept the same as previously described.

Effects of temperature on growth rate and native carrageenan yield in selected strains

To evaluate the effect of temperature on the growth rate and production of native carrageenan of the selected strains, a gradient table as described by Oliveira et al. (1995) was used. The conditions were those described above, varying only temperature (15, 25, and 30 °C). For this, 2 g of each strain selected previously was placed in Erlenmeyer with 500 mL of culture medium under constant aeration for 28 days. The culture medium was renewed weekly and the fronds were weighed. The experiment was carried out using three Erlenmeyers for each strain. The growth rate was calculated using the initial and final fresh biomass. Growth rate was calculated as Gr (% day−1) = [(Wt/Wi)1/t − 1] × 100, where Wi = initial fresh biomass, Wt = fresh biomass after 28 days, and t = experimental time in days.

Native carrageenan yield in selected strains was extracted according to Pereira and Mesquita (2004) with modifications. Fronds were washed with distilled water, dried at 60 °C until constant weight, and ground with liquid nitrogen. The dry material was rehydrated with distilled water (50 mL g−1) and the solution was kept at 85 °C for 3 h under constant agitation. Afterwards, the solution was centrifuged (3500×g for 15 min) and the supernatant separated. Native carrageenan was precipitated by adding twice the volume of ethanol (98° GL) in the warm supernatant, then centrifuging at 3500×g for 15 min. The precipitate was dried at 60 °C until constant weight and weighed. Native carrageenan yield is given as % of dry weight.

Statistical analysis

The data obtained in the strain selection were analysed with descriptive statistics while the data of the growth rate and native carrageenan yield resulting from the temperature experiment were analysed using parametric statistics. After evaluating normality, growth rate and native carrageenan yield data were tested for homogeneity of variances by the Cochran test. Since assumptions were obtained, two-way ANOVA was performed to evaluate the performance of the strains submitted to different temperatures. For that, temperatures and strains were used as independent factors, and growth rate and native carrageenan yield as dependent factors. The analyses were carried out between the strains referring to the progenitors of each life cycle stage. Analyses were not carried out between the life cycle stages. When significant differences were observed (p < 0.05), the Student-Newman-Keuls (SNK) multiple post hoc comparison test was applied. Statistical analyses were performed using STATISTICA 12 software (StatSoft, Inc. 2011).

Results

Strain selection

Tetraspores and carpospores in large numbers were obtained from fronds enabling the selection of 20 strains of female gametophytes and 20 strains of tetrasporophytes. However, six strains (two from progenitor A, two from progenitor B, and two from progenitor E) did not survive the first 15 days after selection. On the other hand, 34 strains survived, 14 from gametophytic progenitors and 20 from tetrasporophytic progenitors, and these were kept in the laboratory for at least 2 years.

Heterogeneity of morphologies, colors, sizes, and growth was observed in these strains. These differences were observed right from the early stages of development, resulting in individuals with more than one characteristic different from the others, even though they came from the same progenitor (Figs. 2 and 3; Fig. S2 to S11 in the on-line Supplementary material). The color ranged from dark crimson and red black to greenish throughout strain development (Fig. S2 to S11 in the on-line Supplementary material), with greenish being more prominent at 90 days (Figs. 2 and 3). Strains from gametophytic progenitors showed few ramifications (S06C, S10D, and S11D) (Fig. 2), while strains from tetrasporophytic progenitors showed dense ramifications (S17F, S27I, and S30I) (Fig. 3).

Fig. 2
figure 2

Strains obtained from carpospore progeny of Chondracanthus teedei after 90 days in laboratory culture. Arrow in S07C indicates cystocarps

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Fig. 3
figure 3

Strains obtained from tetraspore progeny of Chondracanthus teedei after 90 days in laboratory culture. Arrow in S24H indicates cystocarps

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Reproductive structures were observed in some strains. Tetrasporangial sori were observed releasing viable spores in practically all strains from gametophytic progenitors 30 days after selection. S04B, S05C, and S08C did not show reproductive structures, even after 90 days (Fig. 2). Strain S07C showed cystocarps 45 days after selection and release of viable carpospores after 90 days (Fig. 2). Reproductive structures were observed in only one strain from tetrasporophytic progenitors while kept isolated. Cystocarps were observed in S24H after 30 days, and release of viable carpospores was noted 45 days after selection (Fig. 3). Fifteen days after contact between gametophytic strains, cystocarps were observed in 12 strains (Table 1). Ninety days after selection, the strains differed in their final fresh weight, ranging from 0.02 to 0.27 g in strains from gametophytic progenitors and 0.05 to 0.74 g in strains from tetrasporophytic progenitors (Table 1). Moreover, GR ranged from 0.57 to 5.13% day−1 in strains from gametophytic progenitors with the highest value recorded for S07C, which presented cystocarps (Table 1). For strains from tetrasporophytic progenitors, GR values ranged from 2.16 to 6.79% day−1 with the highest value recorded for S17F (Table 1).

Table 1 Final fresh weight, growth rate, and reproductive structure observed in carpospore and tetraspore progeny of Chondracanthus teedei in laboratory culture for 90 days
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Effects of temperature on growth rate and native carrageenan yield in selected strains

Growth rate (GR) results of the selected strains exposed to different temperatures are shown in Figs. 4 and 5. All strains demonstrated positive growth throughout the experiment with significant differences between temperatures and strains selected from gametophytic (two-way ANOVA: F(26) = 40.307, p < 0.001) and tetrasporophytic (two-way ANOVA: F(38) = 35.240, p < 0.001) progenitors. A heterogeneous response was observed at different temperatures between strains, including those belonging to the same progenitor (Figs. 4 and 5). Higher GR values were observed, on average, at 25 °C for both stages of the life cycle. In comparing the GR of strains from the gametophytic progenitors, we observed the highest values of GR for S07C (5.61 ± 0.20% day−1) at 25 °C, followed by S12D (4.76 ± 0.21% day−1) at 15 °C and S05C and S07C (4.42 ± 0.16% day−1 and 4.54 ± 0.75% day−1, respectively) at 30 °C (Fig. 4). For these GR values, only S07C at 25 °C is significantly different (two-way ANOVA, SNK; p < 0.007) (Fig. 4 and Tab S1 in the on-line Supplementary material). On the other hand, strains from tetrasporophytic progenitors demonstrated the highest GR values for S21G and S27I (7.11 ± 0.36% day−1 and 6.53 ± 0.49% day−1, respectively) at 30 °C, followed by S30I, S17F, and S27I (6.79 ± 0.53% day−1, 6.56 ± 0.39% day−1 and 6.39 ± 0.27% day−1, respectively) at 25 °C and S27I (6.45 ± 0.53% day−1) at 15 °C (Fig. 5). These results have no significant differences (two-way ANOVA, SNK; p > 0.100) between them (Tab S1 in the on-line Supplementary material).

Fig. 4
figure 4

Growth rates (GR % day−1) of strains obtained from carpospore progeny of Chondracanthus teedei exposed to three temperatures (15, 25, and 30 °C). Bars represent mean ± SD for n = 3

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Fig. 5
figure 5

Growth rates (GR % day−1) of strains obtained from tetraspore progeny of Chondracanthus teedei exposed to three temperatures (15, 25, and 30 °C). Bars represent mean ± SD for n = 3

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Native carrageenan

Native carrageenan yield present in C. teedei strains was significantly influenced by temperature (gametophytic progenitor: two-way ANOVA: F(26) = 7.68, p < 0.001; tetrasporophytic progenitor: two-way ANOVA: F(38) = 8.79, p < 0.001), demonstrating heterogeneous responses at different temperatures between strains, including those belonging to the same progenitor (Figs. 6 and 7). In comparing the native carrageenan yield, we observed no significant differences among temperatures used in 12 strains, 4 strains from gametophytic progenitors (two-way ANOVA, SNK; p > 0.100) and 8 strains from tetrasporophytic progenitor (two-way ANOVA, SNK; p > 0.200) (Figs. 6, 7, and Tab S1 in the on-line Supplementary material). On the other hand, 4 strains, 1 strain from gametophytic progenitors and 3 strains from tetrasporophytic progenitors, showed higher levels of native carrageenan when kept at 15 °C, and 5 strains, 2 strains from gametophytic progenitors and 3 strains from tetrasporophytic progenitors, showed their highest values when kept at 30 °C. Among the strains from gametophytic progenitors, the highest carrageenan yield was observed in S07C at 30 °C (72.43 ± 3.11% DW), followed by 25 °C (67.60 ± 2.00% DW) and 15 °C (63.60 ± 2.78% DW) (Fig. 6). For these carrageenan values, only S07C at 30 °C is significantly different (two-way ANOVA, SNK; p < 0.031) (Fig. 6 and Tab S1 in the on-line Supplementary material). Meanwhile, from the strains of tetrasporophytic progenitors, the highest carrageenan yield was observed in S27I at 15 °C (74.3 ± 2.5% DW), 25 °C (73.7 ± 1.5% DW), and 30 °C (72.7 ± 1.5% DW) (Fig. 7). However, among these results, no significant differences (two-way ANOVA, SNK; p > 0.600) were noted (Fig. 7 and Tab S1 in the on-line Supplementary material).

Fig. 6
figure 6

Native carrageenan yield (% DW) of strains obtained from carpospore progeny of Chondracanthus teedei exposed to three temperatures (15, 25, and 30 °C). Bars represent mean ± SD for n = 3

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Fig. 7
figure 7

Native carrageenan yield (% DW) of strains obtained from tetraspore progeny of Chondracanthus teedei exposed to three temperatures (15, 25, and 30 °C). Bars represent mean ± SD for n = 3

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Discussion

Our results showed the feasibility of selecting strains through the release of spores from wild gametophytic and tetrasporophytic fronds of C. teedei in southern Brazil. Differences were observed among the various strains obtained, even when they originated from the same progenitor. We noted heterogeneity in morphology, color, size, biomass, growth rates, and yield of native carrageenan along development and different temperatures tested. These phenotypic differences may be the result of intraspecific genotypic differences and thus, eventually, express variations existing in the population of origin of the progenitors. Thus, we believe that populations of C. teedei may have intrinsic genetic diversity at the genotypic origin or heterosis. Accordingly, populations of C. teedei could serve as a source of individuals for strain selection from spores or matrices for crossbreeding aimed at a greater biomass production and/or carrageenan yield.

In general, strains obtained in this study visually showed morphological and color variability, with gametophytic strains more branched in relation to the tetrasporophytic strains, although differences were noted between strains at the same stage of the life cycle and those from the same progenitor (on-line Supplementary material). Although studies indicate that C. teedei is a promising species for carrageenan production (Pereira and van de Velde 2011), our results show that the morphologies found here meet the requirements for the Asian food market as well (see Figs. 2 and 3; Fig. S2 to S11 in the on-line Supplementary material) (Macchiavello et al. 2018). It is unlikely that this market could be sustained only by harvesting from natural populations (Contador et al. 2020). Therefore, it would be necessary to bolster production with preselected strains with the specific characteristics desired and maintained throughout development, as we observed for C. teedei in this study. Another reason for promoting strain selection is phycogastronomy directed toward the European food market. This species has already attracted a certain level of interest based on its use in small Italian villages and it has also recently gained interest from purveyors of haute cuisine (Palmieri and Forleo 2020).

Another important characteristic observed in this study was deviation in the sequence of the life cycle. Among the strains obtained from gametophytic progenitor C, cystocarp formation and release of viable carpospores in S07C were observed after 45 days of isolation, indicating that this is a monoic gametophytic strain, originating from carpospores (Fig. 2). The formation of a gametophyte from spores originating from cystocarps is commonly reported as apomictic and found in only a few macroalgae genera (West et al. 2001; Fierst et al. 2010), but so far, not reported to Chondracanthus. Although well documented for terrestrial plants (Majeský et al. 2017), little is known about the formation of apomictic individuals and the ecological implications in macroalgae. For Mastocarpus papillatus (C. Agardh) Kützing, for example, it is known that they are essential for the maintenance of some populations, mainly in their distribution limit (Fierst et al. 2010). This could be a basis for our finding once the C. teedei population that provided progenitor fronds is close to the southern limit of its distribution (Coll and Oliveira 1999). According to West et al. (1992), an apomictic system in red algae, similar to that in angiosperms, likely leads to the evolution of a greater genetic diversity. This has been understudied and explored but could reduce time and effort in future strain selection and maintenance.

We also observed the occurrence of self-fertilization in a strain obtained from tetrasporophytic progenitor H. Strain S24H showed cystocarps after 30 days of isolation and release of viable carpospores after 45 days. Self-fertilization in gametophytes is well documented for red algae (Rueness and Fredriksen 1998; Sano et al. 2020), as well as for some species of Chondracanthus spp. (Contador et al. 2020), although for C. teedei it is considered rare (Guiry et al. 1987; Braga 1990). Monoic individuals are considered a problem in breeding programs since self-fertilization hinders the hybridization process. On the other hand, they can help to maintain phenotypes obtained over generations (Meer 1990).

During this study, which included strain selection and temperature effects, the growth rates (GR) obtained in some strains of C. teedei showed values consistent with, or even higher than, those found for the species (Table 1) (see Bermejo et al. 2019) or for other economically important red algae (Bulboa et al. 2008; Ventura et al. 2020). When exposed to the temperature gradient, most strains (24 of 34) showed optimal GR values at the intermediate temperature used (25 °C) or without significant differences between 25 °C and one of the other temperatures used. These results corroborate the findings of Zinoun et al. (1993a) who identified an optimum temperature for growth between 20 and 25 °C for this species (formerly Gigartina teedii (Roth) Lamouroux). Thus, the breadth of growth performance would be related to the local temperature regime, as a reflection of adapting to these conditions (Eggert 2012). On the other hand, we obtained strains with responses different from the expected. Four strains showed optimal GR values only at the extreme temperatures used (S12D and S16F for 15 °C; S05C and S21G for 30 °C), and, interestingly, two gametophytic strains maintained their GR values without significant differences, irrespective of temperatures used, with a higher mean value for S27I (6.46 ± 0.07% day−1). These results demonstrate a possible strategy for maintaining the species in environments with wide thermal amplitude or a reflection of adaptation to the extensive geographic distribution (Pereira and Silva 2021). Optimum growth rates for temperatures different from the environmental average were also recorded for C. chamissoi (Bulboa and Macchiavello 2001) and other economically important red algae (Yokoya and Oliveira 1992).

The native carrageenan yield varied among strains and temperatures (see Figs. 6 and 7). Among the 34 selected strains, 12 showed higher yield of native carrageenan at the intermediate temperature used (25 °C) or without significant differences between 25 °C and one of the other temperatures used, with a maximum value of 69% DW for S30I. However, 4 strains showed higher yield when kept at 15 °C (maximum value 67% DW for S26H) and 5 when kept at 30 °C (maximum value 72% DW for S07C). On the other hand, 11 strains showed no temperature effect on the yield of native carrageenan, presenting a maximum value for S27I (74% DW for 15 °C and 25 °C; 73% DW for 30 °C). These values corroborate those found by Saito and Oliveira (1990) (76% DW) and Zinoun et al. (1993a, 1993b) (70% DW) for this species. Although our data corroborate the findings of Zinoun et al. (1993b) demonstrating a strong temperature influence on native carrageenan yield in C. teedei, it must be noted that these responses do not represent a clear pattern for this strains in relation to the temperatures used. As we demonstrate here, both intraspecific and intra-progeny variability was noted and should be explored to obtain strains with higher native carrageenan yield, but less effect of temperature on GR. Additionally, a more in-depth analysis becomes necessary since carrageenan can be influenced by temperature, both in its yield and in its composition and physical properties (Pereira and Silva 2021).

We concluded that this study demonstrates the efficiency of strain selection in C. teedei using tetraspore and carpospore progeny once a variety of strains demonstrated satisfactory values of GR and yield of native carrageenan under different temperature conditions. In practice, this could help in biomass production in places where the amplitude of annual temperatures becomes a problem in cultivation, especially for tropical species such as K. alvarezii. It could even help in the selection of strains resistant to the effects of climate change or short climate events like heatwaves. Thus, our results demonstrate that intraspecific and intra-progeny differences do exist in C. teedei. This not only is of academic interest, helping to explain the distribution of species that occupy a variety of environments with characteristics of tropical and subtropical climates (Pereira and Silva 2021), but may also have implications for the practice of selecting strains of this or other genera of red algae of economic interest. Accordingly, we see that strains S12D and S16F could be grown in the winter months and strains S21G and S05C during the summer in southern Brazil. Strains S17F and S30I obtained good results at 25 °C, and S27I maintained its GR and native carrageenan yield high at all temperatures. Thus, we believe that a combination of strains in different seasons could provide greater stability in biomass production and native carrageenan to, in turn, provide economically viable production.