Bottom Habitats Research Articles

Fish-habitat associations on a subsea pipeline within an Australian Marine Park

Subsea pipelines have been installed in all major hydrocarbon basins across the globe to support the offshore Oil & Gas (O&G) industry. These artificial structures provide hard substratum that can be colonised and utilised by sessile and mobile organisms. The present study utilises industry-collected remotely operated vehicle (ROV) video to assess fish species richness and abundance, and marine growth type, extent and complexity along sections of a subsea gas pipeline, in 56–82 m depth, that traverses the Australian Commonwealth Montebello Marine Park (MMP). A total of 7493 fish from 81 species and 33 families were recorded from 606 analysed 10 m transects spaced across sections of the pipeline. Of these 81 species, 27 are considered fishery-target species in the Pilbara Demersal Scalefish fishery (PDSF), with select commercial fishing activities permitted with authorisation within the Marine Park. A moderate abundance (175) of sub-adult red emperor (Lutjanus sebae), a fishery-indicator species, were observed along the pipeline. Eleven different categories of marine growth habitat were observed, with the pipeline possessing quite uniform coverage of encrusting marine growth (coralline algae, bryozoans, ascidians, etc.) with patchy occurrences of more structurally complex sponges and black/octocoral forms. Fish species richness and abundance of the commercially targeted Moses’ snapper (Lutjanus russellii) were correlated positively with increasing cover of sponges. The pipeline itself had very few spans and was never more than fractionally buried. Despite the somewhat homogenous habitats, depths, and position of the pipeline relative to the seafloor, presence of a field joint indent had a positive influence on the abundance of some common and commercially important fish species. This study demonstrates the ecological value of ROV footage obtained during industry inspection operations that were conducted for reasons unrelated to the determination of ecological information. The pipeline offers a corridor of hard bottom habitat within a marine park that facilitates epibiotic growth and the presence of reef-associated species in a region characterised by sandy sediments. Results indicate the potential importance of subsea O&G infrastructure as a habitat for fish, and in consequence, potentially also as structures with value to fisheries.

Occurrence and habitat use of European eel (Anguilla anguilla) in running waters: lessons for improved monitoring, habitat restoration and stocking

To improve the management of the European eel (Anguilla anguilla) in freshwater, it is essential to define important lotic habitats. Electrofishing data from 289 wadeable, hard-bottom sites in 69 Swedish coastal rivers and streams, originally surveyed for salmonid monitoring, were used to evaluate the effects of sampling- and habitat-related factors on eel occurrence. Probability of eel occurrence, as influenced by sampling procedure (sampled area, number of consecutive runs and ambient water temperature) and habitat characteristics (size of catchment, dominating bottom substrate, shade, water velocity, mean depth), was evaluated for small (total length ≤ 150 mm) and large (> 150 mm) yellow eels. Data were analysed in a mixed presence/absence generalized linear model with dispersal (distance to mouth from sampled site), habitat and sampling-related variables as covariates. The two models explained variation in occurrence to 81.5% for small eel and 76.2% for large eel. Probability of eel occurrence decreased with distance from the river mouth, and increased with sampled area, number of runs, water temperature, coarser substrate and size of river. We suggest that future eel habitat restoration should focus on lower reaches of larger rivers with suitable coarse bottom habitats. Stocking of young eel should be carried out in comparable accessible habitats in the upper reaches where eel densities are low. The results also strongly indicate that eel may be sampled together with young salmonids with DC electrofishing in wadeable habitats.

Ecological and population characteristics of the seashell Conus princeps on the Pacific coast of central Mexico

Marine snails of the genus Conus have acquired remarkable biomedical importance because of the high number of toxins they produce for feeding and self-defense. One of these toxins gave way to a new medication and two other are under development for clinical and cosmetic purposes. Nevertheless, there is little basic knowledge about this group of species, particularly in Mexico. This study aimed to determine the relative abundance, spatial distribution, bathymetric distribution, and habitat preference of the snail Conus princeps along the southern coast of Jalisco (Mexico). To achieve this goal, we conducted direct samplings by snorkeling or scuba diving at 13 beaches, covering the intertidal, shallow subtidal, and deep subtidal zones. Relative density was between 0.021 and 0.418 snails per 100 m2, with an average value of 0.152 snails per 100 m2. The population showed an aggregated spatial distribution pattern according to the nearest neighbor index. Snails had shells that measured between 23.1 mm and 52.2 mm long, with an average shell size of 39.7 mm. Conus princeps was mainly distributed in the intertidal and shallow subtidal zones. The smaller organisms were present at shallower depths, while the larger organisms were distributed throughout the sampled depth habitats. In general, snail abundance decreased as depth increased. From the underwater photography analysis, we determined that Conus princeps snails prefer rocky bottom habitats covered with brown seaweed.

Comparative Analysis of Mollusc Assemblages from Different Hard Bottom Habitats in the Central Tyrrhenian Sea

Composition, trophic structure, and species-substrate relationships of molluscan assemblages inhabiting different hard bottom habitats (Sabellaria alveolata reef, photophilic bottoms, Phyllophora crispa sciaphilic assemblage, and coralligenous bioconstruction) were studied in two different sites of the Tyrrhenian Sea. In particular, molluscs from the Sabellaria alvevolata (Linnaeus, 1767) reef and coralligenous concretion were investigated, testing the hypothesis that bioconstructions increase the diversity and abundance of associated biota compared to the surrounding habitats. A total of 3134 individuals belonging to the classes of Polyplacophora (5 species, 24 individuals), Bivalvia (39 sp., 2734 ind.), and Gastropoda (53 sp., 376 ind.) were identified. These three taxonomic groups showed different distribution patterns in the studied habitats. Multivariate analyses revealed significant inter-habitat differences in the composition of mollusc assemblages, especially between bioconstructions and the other habitats. S. alveolata and coralligenous host the highest rich molluscan fauna when compared to the neighboring hard bottom habitats characterized by photophilic and sciaphilic assemblages. The first ones were dominated by bivalve suspension feeders, mainly represented by sessile and sedentary organisms, which act as bio-constructors, bio-eroders, or simply inhabit the several microhabitats provided by the bioconstructions, while the second ones host a rich molluscan fauna dominated by gastropod grazers and predators. The present study increases the comparative knowledge of molluscan assemblages inhabiting habitats of littoral plans of the Mediterranean Sea, providing pivotal information regarding biodiversity of coastal zones.

Characterizing the benthic community in Maryland's offshore wind energy areas using a towed camera sled: Developing a method to reduce the effort of image analysis and community description.

Offshore wind farms are a crucial component for the improvement of renewable energy in the United States. The Bureau of Ocean Energy Management (BOEM) designated ~170 km2 of shelf area for wind energy development off the coast of Maryland, USA. In order to understand potential environmental impacts of wind turbine installation on the benthic ecosystem within the designated area, we conducted a study to visually characterize bottom habitats and epibenthic communities in the Mid-Atlantic Outer Continental Shelf blocks of the Maryland wind energy area. Seven 5 km long transects were sampled using a towed camera sled with a downward-facing digital camera that captured images at 5 frames·s-1s. Additional small-mesh beam trawling was also conducted at selected locations complementary for species identification. Image data were analyzed using two image selection methods, random and systematic (i.e. video frames were selected at various intervals). For both methods, estimates of community diversity (Hill’s N2) stabilized with sample sizes ranging from 316 to 398 frames. Our results allowed us to define distinct epibenthic communities and bottom habitats that are associated with offshore wind energy sites and to develop a sampling technique for digital images that can be applied to other research programs.

Three new diatom species of the genus Diploneis (Bacillariophyta) from Lake Baikal

We present three new species, Diploneis implicatus, Diploneis lacustris and Diploneis pumicosus, from the littoral zone of Lake Baikal. Descriptions of these species are based on light and scanning electron microscopical features that distinguish them from other taxa. Diploneis implicatus exhibits external openings of each stria areola flanked by short siliceous thickenings of the vimenes and virgae forming a regular pattern on the external valve that is unique for the genus. Similar structures have previously been reported only in the distantly related and ecologically different Craticula citroides. Diploneis lacustris possesses a conopeum, uncommon in Diploneis and known only in Diploneis aokiensis from Japan. In our species, the conopeum is variable in structure and only developed in the apical quarter of the valve. The third species, Diploneis pumicosus, has a distinctive raphe system morphology similar to that in the single valve of Diploneis conopeospongiosa from Lake Baikal. All three species inhabit silty bottom habitats at depth of 20 m or more, and have so far been found in the southern basin of Lake Baikal. The diversity of Diploneis species in Lake Baikal is a rich resource for further understanding the genus.

Environmental drivers of habitat use by a marine fish on a heterogeneous and dynamic reef flat

Intertidal and subtidal zones consist of heterogeneous habitats and dynamic environmental conditions, providing diverse options for fish to take advantage of marine resources. We explored how various environmental factors affected habitat use of an ecologically and economically important tropical marine fish, bonefish (Albula vulpes), on a fringing reef flat in Culebra, Puerto Rico, using a fine-scale acoustic telemetry positioning system. Machine learning algorithms and Bayesian inference via integrated nested Laplace approximation indicated diel period was the most important predictor of bonefish habitat use; bonefish occupied seagrass and mixed bottom (seagrass, macroalgae, sand) habitats most often at night, a deep-water soft sediment lagoon during the day, and infrequently used a shallow coral rubble reef crest. Zero-truncated (presence only) positioning frequency revealed more constrained utilization distributions during daytime and periods of higher water temperatures. Bonefish occupancy was highest in seagrass and mixed bottom habitats at lower water temperatures, and declined rapidly throughout the flat above 30 °C, which is consistent with temperature-mediated physiological constraints on performance (i.e. collapse of aerobic scope). Other factors including lunar phase, tidal state, and tide height had limited influence on bonefish habitat use. Building on a body of research, we propose several drivers of bonefish habitat use patterns amongst the diverse regions and habitats occupied, including predation risk, angling pressure, tidal variations, and temperature-related physiological performance. Our results emphasise the importance of conserving important seagrass foraging habitat through management and restoration.

Bacteria defend carrion from scavengers

AbstractCarrion in the form of dead seal pups and algal mats placed on soft bottom habitats at Explorers Cove and Salmon Bay, McMurdo Sound, attract scavenging invertebrates that are driven away by hydrogen sulphide produced by sulphate-reducing bacteria sequestered below a layer of Beggiatoa/Thioploca-like filamentous bacteria. This system is usually found for lipid-rich marine mammal carrion, but also occurred with natural algal mats.

Experiment on growth response and Feed Conversion Ratio (FCR) of fishes by feeding BR Sludge from distillery spent wash at distillery factory in Yangon, Myanmar

The two freshwater fishes, the catfish Pangasius pangasius (Hamilton, 1822) and the catla fish Catla catla (Hamilton, 1822)were experimented in small culture ponds for growth response and feed conversion ratio during the study period from October 2018 to January 2019. The Pangasius pangasius fish growth rates of test and control ponds were almost equal. The control growth rates of Catla catla fish were higher than the test pond. Among these fishes, the fish Catla catla was the soft bottom habitat and they preferred mud bottom sediments. Among them, the growth rates of fish Catla catla was less than other species. The FCR values of the test ponds are 12.7 of Pangasius pangasius fish and 21.5 of Catla catla fish. The FCR values of the control ponds are 14.9 of Pangasius pangasius fish and 23.8 of Catla catla fish. In the present study, the results of FCR values are very useful for BR Sludge from Distillery Spent Wash. The feeding ratio (FCR) of test ponds is less than control ponds that is very good useful for these culture fishes.

Between a Rock and Soft Bottom: Evaluating the Use of Rod and Reel to Monitor Tautog in Southern Massachusetts

AbstractFishery‐independent trawl surveys are commonly used to monitor the status and trends of marine finfish species. Although bottom trawls are powerful sampling tools, they are limited to surveying relatively featureless bottom habitats and, as a result, may not accurately represent the trends in the relative abundance of fish species associated with structured and complex habitats. We evaluated the feasibility of rod and reel as an alternative fishery‐independent survey methodology to monitor the abundance of Tautog Tautoga onitis, a recreationally and commercially important structure‐dwelling reef fish, in the coastal waters of Massachusetts. Results suggest that a rod‐and‐reel survey is an effective, low‐cost approach to monitor the structured habitats inaccessible to trawl gears. Using a generalized linear mixed modeling framework we were able to identify important predictor variables influencing catch rates; variables that would be important in the design of a continued long‐term monitoring program and in the standardization of these data as an index of relative abundance. Variables retained in the top model included year, month, depth strata, bottom water temperature, tidal phase, fishing vessel, angler avidity, and random effects that accounted for the repeated measures survey design. Power analyses revealed that the directed rod‐and‐reel survey had far greater power to detect changes in Tautog abundance than the extant trawl survey, which had very little power to detect even large shifts in abundance. The results of this pilot study suggest that the continued use of rod and reel as a complementary survey tool would be warranted to further compare the trends in Tautog abundance generated using the two different survey methodologies, to reduce uncertainty in the stock assessment, and to improve the information upon which Tautog management is predicated in Massachusetts waters.

Multimarker response to salinity stress in two estuarine bivalves of different genetic diversity: Mya arenaria and Limecola balthica from the Gulf of Gdańsk (southern Baltic Sea)

AbstractThe estuarine bivalves Limecola balthica and Mya arenaria are common inhabitants of marine soft bottom habitats in the Northern Hemisphere. Both species are able to live under a wide range of environmental conditions including variable salinity. However, in L. balthica there is high genetic variability, and populations are often genetically adapted to local conditions. By contrast, genetic diversity in M. arenaria is low across the species’ geographic range, which attests to acclimatization to different conditions. We hypothesized that individuals of M. arenaria should perform better under osmotic stress. We tested this hypothesis by performing a 5‐week experiment that exposed individuals of both clam species to hypo‐ and hyperosmotic conditions. A multiple biomarker approach that included physiological, biochemical, and histological markers was used to assess bivalve performance. Exposure to the different salinities induced biological responses that particularly affected respiratory activity in both species tested, but these responses were much more pronounced in individuals of L. balthica. The results confirmed the hypothesis that the phenotypic plasticity of M. arenaria was more pronounced and reflected a different strategy of adapting to heterogeneous habitats.

Habitat assessment of a restored oyster reef in South Texas

Oyster reefs are important foundational habitats and provide many ecosystem services. A century of habitat degradation has resulted in substantial reductions in the extent and quality of oyster reefs in many estuaries, thus spurring restoration efforts. In this study, a 1.5 ha oyster reef complex was constructed in Copano Bay, Texas to restore habitat for oysters and associated fauna. Oysters and resident and transient fishes and crustaceans were monitored at the restored reef as well as at nearby natural oyster reef and unrestored bottom (i.e., dense mud with shell hash) habitats for two years following reef construction. The restored reef had substantial oyster recruitment and growth, with oyster abundance and size comparable to nearby habitats within the first year. Resident and transient fauna communities recruited to the restored reef within six months post-construction, and abundance and diversity were comparable to nearby habitats. Significant changes observed in oyster densities between the first and second year post-restoration demonstrate the importance of monitoring over multiple years to capture multiple recruitment cycles and growth to market size. Nekton densities did not change significantly after the first year, but changes in community assemblages were observed through the end of the study. The high densities of oysters and resident nekton relative to other studies indicate that this restoration project was successful in restoring suitable habitat. The design of the reef complex, consisting of relatively high-relief reef mounds and deeper corridors, likely contributed to the relatively high oyster and nekton densities observed in this study. Overall, the restored reef in this study showed tremendous near-term success in providing important ecological functions associated with habitat provision and oyster production.

Plastic litter transfer from sediments towards marine trophic webs: A case study on holothurians

This study estimates for the very first time plastic litter levels in sea cucumbers (Echinodermata, Holothuroidea) sampled in situ and their intakes from sediments in three different rocky bottom habitats (slides, cliff, banks) settled in Salina Island (Aeolian Archipelago). Macroplastic were never recorded while meso- and microplastics were identified in all sediment (81–438 items/kg d.w.) and animal samples (1.8–22 items/ind.). Plastic intakes by sea cucumbers resulted frequently associated to the size range included within 100–2000 μm. Over than 70% of ingested plastic litter is represented by the size fraction >500 μm. Sediment/animals ratios % are included 2.7 ± 2.0% in studied habitats with a selective intake of fragments occurring in slides. Furthermore, results support the occurrence of selective ingestion of plastic litter by holothurians in natural environments underlining the role of these species in microplastic transfer from abiotic towards biotic compartments of the marine trophic web.

Uncovering cryptic diversity of Lyngbya: the new tropical marine cyanobacterial genus Dapis (Oscillatoriales).

Cyanobacteria comprise an extraordinarily diverse group of microorganisms and, as revealed by increasing molecular information, this biodiversity is even more extensive than previously estimated. In this sense, the cyanobacterial genus Lyngbya is a highly polyphyletic group composed of many unrelated taxa with morphological similarities. In this study, the new genus Dapis was erected from the genus Lyngbya, based on a combined molecular, chemical, and morphological approach. Herein, two new species of cyanobacteria are described: D.pleousa and D.pnigousa. Our analyses found these species to be widely distributed and abundant in tropical and subtropical marine habitats. Seasonally, both species have the ability to form extensive algal blooms in marine habitats: D.pleousa in shallow-water, soft bottom habitats and D.pnigousa on coral reefs below depths of 10m. Electron microscopy showed that D.pleousa contains gas vesicles, a character not previously reported in Lyngbya. These gas vesicles, in conjunction with a mesh-like network of filaments that trap oxygen released from photosynthesis, provide this species with an unusual mechanism to disperse in coastal marine waters, allowing D.pleousa to be present in both benthic and planktonic forms. In addition, both D.pleousa and D.pnigousa contained nitrogen-fixing genes as well as bioactive secondary metabolites. Several specimens of D.pnigousa biosynthesized the secondary metabolite lyngbic acid, a molecule that has also been isolated from many other marine cyanobacteria. Dapis pleousa consistently produced the secondary metabolite malyngolide, which may provide a promising chemotaxonomic marker for this species.

Defining soft bottom habitats and potential indicator species as tools for monitoring coastal systems: A case study in a subtropical bay

The definition of habitats and indicator species is a prerequisite for monitoring and conservation programs. Nonetheless, defining habitats in marine soft-bottom environments is challenging given their spatiotemporal dynamics and apparent homogeneity. The selection of indicator species is also complicated given the large number of occasional species usually presented in benthic communities. This study aims to elaborate a framework based on well-established analytical methodologies to identify soft-bottom habitats and select indicator species to support monitoring and conservation programs. The proposed framework consists of four steps: 1) perform a Redundancy Analysis (RDA) on the community data to identify the community structure response to environmental gradients; 2) conduct a kernel density analysis on the RDA biplot to determine the habitats; 3) use the indicator values analyses (IndVal) to select indicator species of each habitat; 4) run polynomial quantile regression analysis to find the optimum distribution of each indicator species. Such framework allows the determination of habitats based on the association of environmental and biological datasets, instead of relying solely on abiotic surrogates. As a case study, we used data of macro and meiofauna of a biodiverse coastal ecosystem in Southeast Brazil which is under anthropogenic pressure. Three main habitats were identified in the bay, and macro and meiofaunal assemblages were influenced by similar environmental variables. Nevertheless, macrofauna was more sensitive to changes in sediment composition, whereas meiofauna responded strongly to changes in total organic content and water depth. Macro- and meiofauna indicator taxa showed high specificity and fidelity values to each habitat, supporting their use in monitoring and conservation programs. The spatio-temporal organization of each habitat and the optimum distribution of each indicator species provide baseline knowledge to be used to monitor environmental changes in the study area and help in its conservation.

Large interannual variation in spawning in San Diego marine protected areas captured by molecular identification of fish eggs

Author(s): Duke, Elena | Advisor(s): Burton, Ron S | Abstract: Marine protected areas have become an important management tool that can provide data regarding human impacts on the ocean while protecting exploited species, enhancing biodiversity and protecting ecosystems. Long-term monitoring of reserves is critical to assess how global processes such as natural environmental variation and climate change affect marine populations. We conducted fish egg surveys in both soft bottom habitat and kelp forest and identify fish eggs using DNA barcoding. We compared these data to baseline spawning data established by Harada et al 2015. We documented large inter-annual variability in fish egg abundance associated with climatic fluctuations, including an El Nino event captured during our sampling years. Interestingly, we observed a phenological shift of peak spawning activity during 2017. We found inter-annual fish egg abundance may be linked with upwelling regimes and winter temperatures. We found no distinct differences in community composition between habitats we sampled. Through long-term monitoring of fish spawning we can understand how natural environmental variation such as El Nino events affect fish populations which will help us predict how temperature increases associated with climate change will affect marine fish populations. Furthermore, long-term monitoring can help track trends in marine resource availability and evaluate marine reserve efficacy.

Modeling dispersal and spatial connectivity of macro-invertebrates in Danish waters: An agent-based approach

Marine organisms with planktonic life stages are subjected to extensive transport that results from the interactions between ocean currents and their behavioral responses to environmental changes in the course of their life. Questions remain on the identification of key drivers of dispersal and connectivity in marine populations as they can have multiple uses in the conservation and management of marine ecosystems. Here we investigate whether the open Kattegat, at the entrance to Baltic Sea, is the main source of recruitment to the benthos in associated estuaries and coastal sites through export of planktonic invertebrate larvae. We couple a 3D hydrodynamic ocean model (MIKE3FM) to an agent-based model and simulate the dispersal of macro-invertebrate populations in Danish waters. We use characteristic dispersal traits of the larval community (pelagic larval duration, spawning season, and settling behavior) and simulate dispersal processes within the muddy bottom habitats to derive recruitment rates and potential donor populations leading to population connectivity patterns on each site, one bay and two Danish fjords. We then use our recruitment results in the bay to compare them with field data on species diversity in the same area. A total of 48 different combinations of pelagic larval durations and spawning seasons of macro-invertebrates are simulated in two years 2004 and 2010. From these results, we conclude that the central and southern parts of the Danish waters are identified as important spawning grounds whereas the Kattegat does not seem to be the main provider of larvae into the selected sites. The model also predicts higher abundance and recruitment rates of macro-invertebrate larvae in 2010 compared to 2004. These results are supported by comparable species distribution data collected in the study area. Our results show the importance of an integrated modeling tool combining ocean circulation and biological traits to obtain a detailed description of dispersal and connectivity of macro-invertebrate community in the area, which can provide a more accurate baseline to manage marine biodiversity.

Habitat features not water variables explain most of fish assemblages use of sandy beaches in a Brazilian eutrophic bay

The influence of water variables and the availability of complex bottom habitats in the sublittoral zone on surf-zone fish assemblages of sandy beaches in a Brazilian eutrophic bay were assessed. In total, 64 seine hauls were carried out bimonthly between October 2012 and September 2013 in two beaches located within a marine-estuarine transitional zone in Guanabara Bay and <1 km apart to each other. These beaches share very similar geomorphological and hydrodynamic conditions, but the sublittoral zone of Urca Beach is more structurally-complex because of the presence of artificial structures made of concrete and beds of seagrass and drifting macroalgae, in contrast to the more homogeneous sandy substrate found in Dentro Beach. A total of 1257 fish were caught, with H. clupeola (N = 640), A. brasiliensis (N = 161), T. carolinus (N = 123) and T. goodei (N = 91) accounting for the dominant species. Urca and Dentro beaches shared few similarities in terms of fish species composition, and no seasonal or spatial difference was found for fish richness, abundance, and biomass. Except for the pelagic and planktivorous H. clupeola, which were more abundant in the seine hauls performed in Dentro Beach, the other dominant fish species were more abundant in the hauls conducted in Urca Beach. These findings confirmed the hypothesis that the availability of complex habitats in the nearby sublitoral zones of sandy beaches may lead to positive effects on their associated fish assemblages probably by the increased availability of feeding and spawning sites. Our paper also revealed that water variables were also important, but their effects only explained partially the seasonal variations of few species, agreeing however with the broad consensus of the function of sandy beaches as nursery grounds. Despite the interesting applied potential for fish management, the role of complex habitats in sandy beaches should be better investigated before any measure toward habitat manipulation and enrichment were carried out.

Seasonal variability of phytoplankton in the shallow waters of the southern Baltic Sea

The Baltic Sea is characterized by seasonal variation of phytoplankton structure. These organisms are particularly sensitive to changes in various environmental factors. Because of annually repeated changes, turnover of species composition, abundance and biomass of phytoplankton is observed. Spatial and temporal variability of individual phytoplankton groups is diversified in a district parts of the Baltic Sea. Therefore, of three different coastal areas were chosen: Ustka – estuary habitat, Poddąbie – sandy habitat and Rowy – rocky bottom habitat. The aim of this paper is to determine temporal and spatial structure of phytoplankton occurrence chosen coastal areas between November 2014 and September 2016. All three studies regions the same dominants, abundance and biomass were observed. Only in Ustka region increase of the diatoms was observed. Which could see the cause of river waters wave. Seasonal phytoplankton studies in three selected habitats revealed, that in those areas that abundance and biomass is similar (75%-80%). Based on this evaluation it is can be stated that conducting phytoplankton more frequently is more important than number of research stations.

A review of the biology, ecology, behavior and conservation status of the dusky grouper, Epinephelus marginatus (Lowe 1834)

The dusky grouper is a large-bodied marine species usually associated with rocky substrates and reefs currently experiencing increasing anthropogenic pressures. Here, we critically evaluate studies conducted during the last few decades on this endangered species, focusing on its biology, ecology, behavior, stock structure and fisheries, and identify future research directions to fill current knowledge gaps. This species plays an important functional role in the rocky bottom habitats in which it lives, usually occupying the highest trophic levels and with the potential role as a keystone species in some ecosystems. It has a complex life cycle characterized by a high longevity, a slow growth rate and a monandric protogynous hermaphroditic mode of reproduction. The species also exhibits spawning aggregation behavior, which makes it more vulnerable to fishing activity. Aside from its ecological importance, this species has high commercial value for professional fishers and is also highly prized by recreational spearfishers. These biological features, associated with increasing fishing pressures throughout most of its geographical distribution, have led to Epinephelus marginatus being included since 2004 in the IUCN Red List of Threatened Species as Endangered. Despite a large amount of research being conducted on this species over the last five decades or so, using a number of different tools and techniques, key questions regarding its biology still remain unanswered. In terms of conservation and management plans designed to safeguard this endangered species, we identified the crucial need to improve fisheries landing statistics for the species and to increase the number of marine protected areas within its distribution beyond the Mediterranean Sea.