Keywords

1 Introduction

The open sea area of the Montenegrin coast is characterized by diverse geological and morphological conditions. The length of the coast is approximately 300 km: the Bay of Kotor represents about 100 km of this, while the rest belongs to the open sea, including both steep rocky areas and sandy areas (beaches) such as the 12 km long Velika Plaža that are especially pronounced in the southern part [1]. The very steep limestone rocks descend more or less vertically up to 20–30 m in depth and continue as mosaics of gravel, sand, and silt. The narrow part of the coastal area represents an important economic resource and the main development zone of Montenegro [2]. Consequently, there are significant pressures on the marine ecosystem along the entire coast, with fishing and tourism as well as maritime transport making a major impact. The open coast is relatively poorly rugged with several bays and inlets and a small number of islands and cliffs. The largest part on the coast is open and exposed to the effects of the Mediterranean Sea. In addition, this part of the coast is affected by the freshwater inflow of the Bojana River.

The majority of living organisms in the Adriatic Sea belong to the littoral or coastal system. On the sea floor in the infralittoral zone are many types of substrates that predominantly define the community constituted by various organisms. In general, the marine ecosystems are divided into free water zone and seabed zone, that is, benthic and pelagic areas. Most of the living organisms belong to the phytal (littoral) or coastal system, occupying the sea bed or shelf to approximately 200 m in depth. This is characterized by the presence of benthic chlorophyll plants and dynamic connections between the plant and animal components of the benthic biocenoses [3]. With increasing depth in the seabed system, the following can be distinguished:

  1. (a)

    The supralittoral zone, in which organisms that tolerate or require permanent emergence can be found. This is the zone of seawater wetting.

  2. (b)

    The mediolittoral zone or tidal zone, which requires the organisms living there to undergo shifts between emersion and immersion.

  3. (c)

    The infralittoral zone, which can be found between the lower boundary of the low tide towards the mediolittoral zone and the depth of the zone of sea grasses and photophilic algae. In the Mediterranean this zone reaches to a depth of about 20 m, although in some tropical regions it can extend to approximately 80 m.

  4. (d)

    The circalittoral zone, which extends from the lower limit of the sea grasses or photophilic algae, to an extreme depth that is only inhabited by the algal vegetation most tolerant to low light, i.e. the most sciophilous.

Thus, these four zones whose names all contain the suffix “littoral” make up the littoral or coastal system, or given the presence of benthic chlorophyll algae, the phytal system. The underwater living world in these zones is determinated by the types of substrates present as well as the depth (i.e., the combination of the environment’s physicochemical parameters suitable for life). Accordingly, appropriate biocenoses have developed over time [4].

The investigation of benthic biocenoses in the open sea area of the Montenegrin coast is of greater academic interest in the last decade. At the same time, given Montenegro’s obligation to define marine protected areas, more detailed marine biodiversity research is necessary. Most data refer to the areas of Platamuni, Katiči, and Stari Ulcinj, which have been defined as three future protected zones [5,6,7,8]. In addition, data are available from other sites although they are mostly point-type and related to a narrow research area [9,10,11].

This paper is the first attempt to collect all existing data on the occurrence of the macrozoobenthos within the benthic biocenoses on the open sea of the Montenegrin coast in order to create a new database.

2 Material and Methods

The data presented in the paper were compiled from all available literature data, supplemented with recent personal research. Relevant historical data are contained within the reports of the Institute of Marine Biology (IBM), scientific papers, and unpublished documents. A total of 30 literature sources were reviewed for information collection purposes. The data include 54 localities along the open coast (Fig. 1, Table 1). Recent personal research on the species inventory information of macrozoobenthos was mainly performed by the scuba diving. The taxa were checked for their present valid nomenclature and the classification was arranged according to the WoRMS (http://www.marinespecies.org/) database.

Fig. 1
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An open sea area of the Montenegrin coast with designated localities

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Table 1 Names of sites indicated on Fig. 1
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3 Results and Discussion

At about 200 km long, the open part of the Montenegrin coast represents a relatively small section of the Adriatic, but it is characterized by rich biodiversity and the presence of different types of biocenoses. Habitats of particular interest under the European Union (EU) Habitats Directive – such as Posidonia oceanica meadows (Fig. 2), coralligenous habitats (Fig. 3), and marine caves (Fig. 4) – are all represented here.

Fig. 2
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Meadows of Posidonia oceanica (source: S. Petović)

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Fig. 3
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Coralligenous habitat (source: S. Petović)

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Fig. 4
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Marine cave (source: S. Petović)

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On the hard bottom in the upper infralittoral zone extends a community of photophilic algae (Fig. 5), while in areas characterized by overfishing, a large number of the urchins Paracentrotus lividus and Arbacia lixula can be found. Therefore, in these zones one can identify very well-developed “barren” community types (Fig. 6).

Fig. 5
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Biocoenoses of photophilic algae in the upper infralittoral zone (source: S. Petović)

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Fig. 6
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Barren communities on the rocky substrate (source: S. Petović)

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Beyond the rocky surface are fine sand and silt areas inhabited by faunistic organisms typical of such environmental conditions (Fig. 7).

Fig. 7
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Sandy-muddy substrate (source: S. Petović)

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The compilation of the available data reveals that in the benthic biocenoses in the open sea area of the Montenegrin coast live 489 species of invertebrates (Appendix). Of the total number of species recorded, the group of sponges contains 64 species, cnidarians 49 species, molluscs 193 species, annelids 27 species, arthropods 16 species, bryozoans 49 species, echinoderms 63 species, and tunics 29 species. The species identified can be grouped into a total of 240 families, 22 classes, and 8 phyla.

The biocenosis of the photophilic algae includes the part of the littoral zone in which light varies in terms of both amount and intensity from the upper to the lower limit of the infralittoral zone [4]. Within the algae layer are numerous representatives of macrozoobenthos. Moreover, within this biocenosis we can find representatives of all invertebrate phyla. For instance, the sponges group contains an abundant population of Chondrosia reniformis, including species from order Ircinia, Spongia officinalis, Aplysina aerophoba, Antho (Antho) inconstans, Spirastrella cunctatrix. In the cnidarians group the dominant representatives are Aiptasia mutabilis, Anemonia viridis, Balanophyllia europea. Among annelids, common species include Serpula vermicularis and Sabella spallanzanii. Molluscs and echinoderms represent the most abundant phyla. From the molluscs group, Bolinus brandaris, Cerithium vulgatum, Hexaplex trunculus, Haliotis tuberculata, Patella caerulea, Rocellaria dubia, and Mytilus galloprovincialis all frequently appear, while the most numerous echinoderms are species from order Holothuria, Echinaster sepositus, Marthasterias glacialis, Coscinasterias tenuispina, Paracentrotus lividus, Arbacia lixula, and Sphaerechinus granularis. Furthermore, on the rocky bottom, sea urchins Paracentrotus lividus and Arbacia lixula are common. Given the associated role of overfishing (as fish are predators of sea urchins), these dynamics have led to the regression of algal surfaces, the spread of bare rocky substrates, and the formation of barrens.

On the seafloor along the Montenegrin coast, meadows of the seagrasses Posidonia oceanica are mostly found on sandy substrate. Within these meadows, many species of sponges, molluscs, echinoderms, and tunicates are present. There are a large number of epiphytes on the grass leaves, dominated by hydrozoans and bryozoans. Of the macrozoobenthic species, Chondrosia reniformis, Clathria (Clathria) compressa, Clathrina clathrus, Crambe crambe, Ircinia spp., Sarcotragus spinosulus, Spirastrella cunctatrix, Aglaophenia pluma, Alicia mirabilis, Cladocora caespitosa, Balanophyllia (Balanophyllia) europaea, Hermodice carunculata, Protula sp., Sabella spallanzanii, Serpula sp, Arca noae, Bolinus brandaris, Bolma rugosa, Aporrhais pespelecani, Thracia phaseolina, Tonna galea, Turritella communis, Venus verrucosa, Marthasterias glacialis, Paracentrotus lividus, Arbacia lixula, Astropecten sp., Echinaster sepositus, Holothuria tubulosa, Sphaerechinus granularis, Ascidia sp., and Halocynthia papillosa can all be found.

Coralligenous biocenoses are mainly developed on the hard substrate of the circalittoral step. They are characterized by both calcified and non-calcified algae with an abundance of invertebrate species. The characteristic builders of coralligenous communities from the animal groups are sponges, anthozoans, and bryozoans. The predominant sponge species are Chondrilla nucula, Axinella damicornis, Petrosia (Petrosia) ficiformis, Phorbas tenacior, Chondrosia reniformis, Agelas oroides, Sarcotragus spinosulus, Cliona celata, Cliona viridis, Dysidea fragilis, Antho (Antho) incostans, Axinella cannabina, Axinella verrucosa, Axinella polypoides, Spongia (Spongia) officinalis, Pleraplysilla spinifera, Spirastrella cunctatrix, Clathria (Clathria) compresa, Haliclona poecillastroides, and Clathrina clathrus. Common cnidarians comprise Madracis pharensis, Cerianthus membranaceus, Eudendrium racemosum, and Cladocora caespitosa. Of the annelidas group, Hermodice carunculata is very common, while the bryozoans group includes Pentapora fascialis, Myriapora truncata, Cellaria salicornioides, and Reteporella grimaldii. Among echinoderms, Echinaster sepositus, Holothuria (Holothuria) tubulosa, Sphaerechinus granularis, Ophidiaster ophidianus, Paracentrotus lividus, Arbacia lixula, Centrostefanus longispinus, Cidaris cidaris are very frequent, while the most common ascidian is Halocynthia papillosa.

Soft substrates consist of different mud and sand fractions. They are disadvantageous to sessile organisms because they do not allow them to become attached to the seabed. They represent a rich world of infauna as well as epifauna, that is, species that inhabit and move on the surface. Such substrates are largely represented at depths greater than 30 m where the rocky coast is finished, while in areas where beaches are present, soft substrate starts from the coastline and descends deeper and deeper. Among animal species we can find soft coral species (Alcyonium palmatum, Veretillum cynomorium, Pennatula sp.), Condylactis aurantiaca, Actinia sp, Cerianthus membranaceus, Chamelea gallina, Ruditapes decussatus, Venus verrucosa, Callista chione, Tonna galea, Aporrhais pespelecani, Cerithium vulgatum as well as many annelids and arthropods. Also numerous are the irregular sea urchins Spatangus purpureus, Echinocyamus pusillus, Echinocardium cordatum, and Ova canaliferus, starfish from order Astropecten, sea cucumbers from order Holothuria as well as Eostichopus regalis.

Marine caves are very specific habitats. Given their lack of light, only sciafilic organisms can survive the environmental conditions they provide. Moreover, typical macrozoobenthic species include Acanthella acuta, Agelas oroides, Aplysina cavernicola, Axinella damicornis, Axinella verrucosa, Chondrosia reniformis, Clathrina clathrus, Haliclona fulva, Haliclona mucosa, Dysidea fragilis, Dysidea avara, Ircinia sp., Petrosia ficiformis, Phorbas tenacior, Scalarispongia scalaris, Spirastrella cunctatrix, Terpios fugax, Sarcotragus foetidus, Leptopsammia pruvoti, Polycyathus muellerae, Madracis pharensis, Eudendrium sp., Serpulorbis arenarius, Filograna, Protula sp, Hermodice carunculata, Serpula vermicularis, Rocellaria dubia, Adeonella calveti, Reteporella sp., Pentapora fascialis, Schizobrachiella sanguinea, Myriapora truncata, Crisia sp., Smittina cervicornis, Ophidiaster ophidianus, Hacelia attenuata, Holothuria sanctori, and Halocynthia papillosa.

Within the invertebrate species inhabiting the seabed of the Montenegrin shelf are 30 species protected by national and international regulations. Among these, the Pinna nobilis shell has been mentioned in the literature, although recent studies have confirmed the extinction and therefore loss of this protected species from the study area.

In addition to native species extending within their ecological niches, alien species introduced here have been recorded, some of which have already become established with large populations.

4 Threats to Zoobenthic Diversity and Protection

The benthic biocenoses of the open part of the Montenegrin coast are influenced by anthropogenic impacts, albeit to differing degrees depending on the area and the depth. Considering that along the coast there are three cities (Budva, Bar, and Ulcinj) as well as many smaller towns, it is unsurprising that the impact from the land to the sea is considerable. Most of the populated area lacks a centralized sewer system, so large quantities of household wastewater are discharged into the sea. Furthermore, even where a sewer system does function, very often the drainage pipes do not meet the technical requirements, i.e. they do not finish at the adequate distance and depth from the shore. The impact of wastewater is especially evident during the summer period, when the population in the coastal area is several times higher than during the rest of the year. The increase in wastewater brings a large amount of nutrients, leading to the greater development of micro and macro algae, which are indicators of the state of the marine environment.

Due to its beauty, the coastal area is attractive for real estate investment, leading to excessive urbanization in this part of the country. This is resulting in damage to the natural coastline and the creation of large amounts of waste, which ultimately reaches the sea owing to investor neglect. Consequently, the benthic communities in the area are under threat.

The development of tourism along the coast is occurring alongside the accelerated development of maritime tourism. Greater maritime traffic is exacerbating the threats faced by the marine ecosystem. Waste water, fuel, noise, and often solid waste accompany yachts, boats, and other vessels. Anchoring on the seafloor physically endangers benthic communities, whether these be Posidonia meadows or the coralligenous habitats that have developed here.

In addition, there is an international port in Bar that accommodates ships from all over the world, so its environmental impact is evident in terms of vector inputs for new non-native species [12]. Along the coast there are also many marinas both big and small that provide berths to a large number of vessels, whose activity affects the quality of the sea environment.

Marine organisms in demersal communities are also greatly affected by overfishing. Moreover, the harvesting of the protected species (Lithophaga lithophaga) is also present, while the use of prohibited fishing tools exacerbates the situation [2].

5 Conclusions

The Montenegrin coast lies on the south-eastern part of the Adriatic Sea. It is a link between the Mediterranean and the Adriatic and is strongly influenced by Mediterranean water. The 200 km long coastline is characterized by a variety of geomorphological features. Indeed, its coastline is adorned by steep cliffs rising to 50 m in depth, while to the south lies the Velika Plaža, a 12 km long beach. The coast is poorly rugged, so it is characterized by smaller bays and several little islands.

The coastal seabed is characterized by zones in the littoral area. Where the coast slightly enters into the sea, these zones are more evident and take up a wider belt, while where steep rocks vertically descend into the sea, the shift from one zone to another is less pronounced. Regarding to existing data we can conclude that littoral zone is well studied. Montenegro’s obligation to define marine protected areas has resulted in increased study of the marine ecosystem, primarily in the areas designated for protection. Therefore, most information pertains to the benthic biocenoses and dominant species for the areas of Platamuni, Katič, and Stari Ulcinj. Data are also available from other sites, although they are mostly point-type and related to a narrow research area.

Along the Montenegrin coast, habitats of particular interest under the EU Habitats Directive – such as Posidonia oceanica meadows, coralligenous habitats, and marine caves – can be found. In the shallower part on hard substrate, biocenoses of photophilic algae are present. In areas where the illegal fishing of the shellfish L. lithophaga and the use of illegal fishing gear remain ongoing, environmental damage can be observed. As a consequence of these activities, the degradation of the present biocenoses and the multiplication of sea urchins P. lividus and A. lixula are contributing to the creation of the so-called barren communities.

Our analysis of the macrozoobenthos in this area has revealed the presence of 489 species grouped into eight phyla, 22 classes, and 240 families. Of the invertebrate species inhabiting the seabed of the Montenegrin shelf, 27 are protected by national and international regulations. In addition to native species extending within their ecological niches, the presence of introduced alien species has been recorded, some of which have already become established with widespread populations.

This very rich marine life is exposed daily to various pressures from the land and the sea. Sewage inflows, coastal erosion, concreting the coast, anchoring, overfishing, and maritime transport are just some of the negative impacts on the marine ecosystem.