Fish Community Structure Research Articles

Cage transplant experiment shows weak transport effect on relative abundance of fish community composition as revealed by eDNA metabarcoding

Protection of freshwater fish diversity is a global conservation priority in face of its alarming decline in the last decades. A crucial step to protect freshwater fish diversity is the production of prompt and precise evaluation of community composition and spatial distribution. Metabarcoding of environmental DNA (eDNA metabarcoding) generally surpasses traditional methods for documenting diversity and community composition in aquatic environments. Nevertheless, empirical evidence evaluating how eDNA transportation in water affect community composition and structure via eDNA metabarcoding data remains scarce. Using a brown trout (Salmo trutta) cage transplant experiment in the St. Lawrence River (Canada), a large fluvial system, we tested the detection and relative abundance of species’ eDNA along 15 sampling locations. We detected brown trout eDNA in five localities up to 5,000 m from the cage, but only one sampling location situated 10 m downstream and in the direct line of the cage was affected at the community composition level. This locality showed a relative abundance of brown trout eDNA of 13.1%, while the four others showed a relative abundance under 1.0%. K-means cluster analysis confirmed the impact of brown trout eDNA on community composition by separating this locality from all others. Based on species loading of a redundancy analysis, we showed that this different k-means group was associated with the high relative abundance of brown trout. No evidence of transport effect of brown trout eDNA on fish community composition was observed in any other sampling locations. Together, our results support the view that eDNA metabarcoding can be both a conveyor belt of biodiversity information and a precise tool to study the composition and structure of fish communities in river.

Limited human access is linked to higher effectiveness in a marine sanctuary

Marine Protected Areas (MPAs) are a widely used tool for coral reefs conservation, but massive tourism activities inside MPAs worldwide can challenge their effectiveness. This study investigated the role of different levels of protection strictness (no-entry, low and high tourism-allowed zones) set for a marine sanctuary in shaping benthic cover and reef fish community structure in the richest and largest coral reef system of the Southwestern Atlantic. Reef fish community structure and benthic cover differed between protection levels. No-entry zones showed significant higher coral coverage and biomass of piscivores and herbivores than tourism-allowed zones. Highest differences were found between no-entry and high tourism intensity zones. Despite the fact that protection from fishing by itself can ensure conservation benefits, we show here that the establishment of no-entry zones improve MPAs effectiveness.

Fish diversity patterns along coastal habitats of the southeastern Galapagos archipelago and their relationship with environmental variables

Coastal habitats are essential for ecological processes and provide important ecosystem services. The Galapagos archipelago has a wide diversity of ichthyofauna which preservation guarantees the functioning of the marine ecosystem. In this study, we used ecological and taxonomic indices as well as multivariate analysis to identify spatiotemporal changes in fish community structure in coastal habitats of San Cristóbal Island in the southeastern Galapagos archipelago. We analyzed how the patterns of variability were related to the abiotic conditions (substrate, sea temperature and depth) of each habitat. Nine sites affected by anthropogenic influence (fishing and tourism) representing different habitats/substrates were sampled. Underwater surveys were conducted during the warm and cold seasons in 2010 and 2011 at transects that varied in depth according to site. Artificial habitat, followed by coral and rocky habitats, had the highest diversity, evenness, and taxonomic distinctness, while mangrove habitats had the lowest values. This was related to the habitat complexity and possible anthropogenic influences. While the diversity patterns were more strongly related to the type of substrate, followed by the combination of substrate and depth, and the sea temperature had less influence. These findings were related to the ecological traits of the fish communities and their mobility between habitats. Temporal changes in fish community diversity and composition were not detected at all sites, suggesting that these species have high fidelity to their habitats and a high environmental tolerance that allows them to persist in their habitats despite strong changes in sea temperature on the Galapagos archipelago.

Multidecadal changes in the demersal community structure in an urban bay: Shift from a bottom- to a top-heavy pyramid

Fish community structures in urban bays have changed over time as a result of anthropogenic activities, leading to changes in species richness, diversity, fish assemblage composition, and abundance. Tokyo Bay is one of the most eutrophic urban bays in Japan, and hypoxia occurs every summer in the bottom water of the bay. Accordingly, the demersal community in the bay has undergone drastic changes in taxonomic composition over the past several decades. We analyzed data from a bottom trawl survey spanning 35 years to characterize multidecadal changes in the slopes of body size spectra of the demersal community in Tokyo Bay, as a reliable index to represent shifts in community structure. We found that the community shifted from bottom-heavy pyramids in the past (1977–1995) to top-heavy pyramids in recent years (2003–2019) due to a decrease in the biomass of small-sized crustaceans and an increase in the biomass of large-sized elasmobranchs. Human-induced hypoxia can promote the formation of top-heavy pyramids, as it decimates the number of small-sized individuals. The existence of energy subsidies to large-sized individuals from the inner-shallow and outer bay areas as well as the pelagic community provides a possible explanation for the persistence of top-heavy pyramids.

Poor nutritional quality of primary producers and zooplankton driven by eutrophication is mitigated at upper trophic levels.

Eutrophication and rising water temperature in freshwaters may increase the total production of a lake while simultaneously reducing the nutritional quality of food web components. We evaluated how cyanobacteria blooms, driven by agricultural eutrophication (in eutrophic Lake Köyliöjärvi) or global warming (in mesotrophic Lake Pyhäjärvi), influence the biomass and structure of phytoplankton, zooplankton, and fish communities. In terms of the nutritional value of food web components, we evaluated changes in the ω‐3 and ω‐6 polyunsaturated fatty acids (PUFA) of phytoplankton and consumers at different trophic levels. Meanwhile, the lakes did not differ in their biomasses of phytoplankton, zooplankton, and fish communities, lake trophic status greatly influenced the community structures. The eutrophic lake, with agricultural eutrophication, had cyanobacteria bloom throughout the summer months whereas cyanobacteria were abundant only occasionally in the mesotrophic lake, mainly in early summer. Phytoplankton community differences at genus level resulted in higher arachidonic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) content of seston in the mesotrophic than in the eutrophic lake. This was also reflected in the EPA and DHA content of herbivorous zooplankton (Daphnia and Bosmina) despite more efficient trophic retention of these biomolecules in a eutrophic lake than in the mesotrophic lake zooplankton. Planktivorous juvenile fish (perch and roach) in a eutrophic lake overcame the lower availability of DHA in their prey by more efficient trophic retention and biosynthesis from the precursors. However, the most efficient trophic retention of DHA was found with benthivorous perch which prey contained only a low amount of DHA. Long‐term cyanobacterial blooming decreased the nutritional quality of piscivorous perch; however, the difference was much less than previously anticipated. Our result shows that long‐term cyanobacteria blooming impacts the structure of plankton and fish communities and lowers the nutritional quality of seston and zooplankton, which, however, is mitigated at upper trophic levels.

Seasonal and interannual variation in high-latitude estuarine fish community structure along a glacial to non-glacial watershed gradient in Southeast Alaska

Along the Gulf ofAlaska, rapid glacier retreat has driven changes in transport of freshwater, sediments, and nutrients to estuary habitats. Over the coming decades, deglaciation will lead to a temporary increase, followed by a long-term decline of glacial influence on estuaries. Therefore, quantifying the current variability in estuarine fish community structure in regions predicted to be most affected by glacier loss is necessary to anticipate future impacts. We analyzed fish community data collected monthly (April through September) over 7 years (2013–2019) from glacially influenced estuaries along the southeastern Gulf of Alaska. River delta sites within estuaries were sampled along a natural gradient of glacial to non-glacial watersheds to characterize variation in fish communities exposed to varying degrees of glacial influence. Differences in seasonal patterns of taxa richness and abundance between the most and least glacially influenced sites suggest that hydrological drivers influence the structure of delta fish communities. The most glacially influenced sites had lower richness but higher abundance overall compared to those with least glacial influence; however, differences among sites were small compared to differences across months. Two dominant species—Pacific staghorn sculpin and starry flounder—contributed most to spatial and temporal variation in community composition; however, given only small interannual differences in richness and abundance over the period of the study, we conclude that year-to-year variation at these sites is relatively low at present. Our study provides an important benchmark against which to compare shifts in fish communities as watersheds and downstream estuaries continue to transform in the coming decades.

Deep demersal fish communities respond rapidly to warming in a frontal region between Arctic and Atlantic waters.

The assessment of climate impact on marine communities dwelling deeper than the well‐studied shelf seas has been hampered by the lack of long‐term data. For a long time, the prevailing expectation has been that thermal stability in deep ocean layers will delay ecosystem responses to warming. Few observational studies have challenged this view and indicated that deep organisms can respond exceptionally fast to physical change at the sea surface. To address the depth‐specific impact of climate change, we investigated spatio‐temporal changes in fish community structure along a bathymetry gradient of 150–1500 m between 1998 and 2016 in East Greenland. Here, the Arctic East Greenland Current and the Atlantic Irminger Current meet and mix, representing a sub‐Arctic transition zone. We found the strongest signals of community reorganizations at depths between 350 and 1000 m and only weak responses in the shallowest and deepest regions. Changes were in synchrony with atmospheric warming, loss in sea ice and variability in physical sea surface conditions both within our study region and North of the Denmark Strait. These results suggest that interannual variability and long‐term climate trends of the larger ecoregion can rapidly affect fish communities down to 1000‐m depth through atmospheric ocean coupling and food web interactions.

Community Structure of Kepe-Kepe Fish in Liang Beacg Coral Ref Area Bunaken Island North Sulawesi

This research was carried out in the coral reef Liang Beach area of Bunaken Island in July 31st 2021 by using the visual cencus method on 5 meters depth. The result of the research showed that there were about 12 species of indicator fish Chaetodontidae are found in the coral reefarea.

Movement Shapes the Structure of Fish Communities Along a Cross-Shore Section in the California Current

Pelagic fish communities are shaped by bottom-up and top-down processes, transport by currents, and active swimming. However, the interaction of these processes remains poorly understood. Here, we use a regional implementation of the APex ECOSystem Model (APECOSM), a mechanistic model of the pelagic food web, to investigate these processes in the California Current, a highly productive upwelling system characterized by vigorous mesoscale circulation. The model is coupled with an eddy-resolving representation of ocean currents and lower trophic levels, and is tuned to reproduce observed fish biomass from fisheries independent trawls. Several emergent properties of the model compare realistically with observations. First, the epipelagic community accounts for one order of magnitude less biomass than the vertically migratory community, and is composed by smaller species. Second, the abundance of small fish decreases from the coast to the open ocean, while the abundance of large fish remains relatively uniform. This in turn leads to flattening of biomass size-spectra away from the coast for both communities. Third, the model reproduces a cross-shore succession of small to large sizes moving offshore, consistent with observations of species occurrence. These cross-shore variations emerge in the model from a combination of: (1) passive offshore advection by the mean current, (2) active swimming toward coastal productive regions to counterbalance this transport, and (3) mesoscale heterogeneity that reduces the ability of organisms to return to coastal waters. Our results highlight the importance of passive and active movement in structuring the pelagic food web, and suggest that a representation of these processes can help to improve the realism in simulations with marine ecosystem models.

Composition and structure of the mangrove fish and crustacean communities of Vanga Bay, Kenya

Mangroves support coastal fisheries, particularly by providing nurseries for juvenile fish. However, much remains unknown about the fish and crustacean communities in mangroves and about the lifecycles and behaviours of individual species. This study is the first to describe the fish and crustacean communities in the Vanga mangrove ecosystem, the largest mangrove forest and the most important marine fisheries landing site in southern Kenya. Using fyke nets, 14 mangrove creek sites were sampled once every 3 months during spring tides, between September 2015 and September 2017. The sampling period covered the north east (NEM) and south east (SEM) monsoon seasons. A total of 1,879 fishes and 1,132 crustaceans were caught, represented by 59 and 16 species, respectively. Over 95 % of the fishes caught were juveniles with 50 % of both fish and crustacean species being of commercial importance. About 70 % of the catch was dominated by only 6 fish species with Yarica hyalosoma and Acropoma japonicum contributing 44 % of the total abundance. Penaeus semisulcatus and Penaeus indicus dominated the crustaceans. Fish abundances differed significantly between seasons, with the SEM catches almost three times higher than those in the NEM, while crustaceans displayed no clear seasonality. The study documents for the first time the fish and crustacean communities in Vanga mangroves and confirms their importance as juvenile habitat for commercial species. The importance of mangrove and near mangrove habitat as nursery habitat for both fish and crustaceans emphasizes the need for conservation particularly of seaward edges

Underwater drones reveal different fish community structures on the steep slopes of a tropical reservoir.

A new approach for visual fish survey in reservoirs using underwater drones (remotely operated vehicle- ROV) is presented. The ROV was applied to identify abiotic gradients and to compare fish assemblages on the steep slopes in a tropical reservoir. The tested hypothesis is that fish are concentrated in the littoral zone due to the better physicochemical and habitat conditions, compared to deep and hypoxic layers. Twelve species were recorded (seven native, five exotic), with all species occurring in the littoral zone, seven species in the transition, and four in the profundal zone. A greater fish abundance and richness was found in the littoral zone corroborating the main hypothesis. The littoral zone was dominated by exotic cichlids (Cichla spp., Coptodon rendalli), while native catfish (Loricariichthys castaneus, Pimelodella lateristriga) occupied deeper areas. The fish distribution seems to be driven by local factors, such as oxygen availability and habitat structure. The preference for the littoral zone by alien cichlids may have led to the extirpation/decrease of native characids and induced catfishes to occupy deep habitats. Underwater drones can be a valuable tool for the simultaneous collection of abiotic/biotic data, especially in deep reservoirs with complex habitats, resulting in advances in the environmental monitoring.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10750-021-04790-9.

Barrier removal and dynamics of intermittent stream habitat regulate persistence and structure of fish community

Barrier effects observed in the presence of weirs are exacerbated by low water levels. We conducted a 10-year study to assess the ecological effects of stream restoration while analysing the possibility of a seasonal lack of hydrological continuity, with multiple measurements before and after restoring stream structural continuity. The research hypothesis assumes that in intermittent streams, there would be little or no change in the fish community downstream the barrier before vs. after barrier removal, and a significant change upstream the barrier before vs. after. Our results indicate, that by removing small barriers, their detrimental effects on the longitudinal passage of riverine fishes and fish assemblages can be rehabilitated. In the wet season, fish migrants from the mainstem river appeared in the downstream section of the stream. Stream intermittency, however, placed a habitat filter over the assemblage. Thus, after barrier removal, only two small-bodied fish species that tolerate periodic oxygen deficiencies and rising water temperatures gradually shifted upstream and formed stable populations. We emphasize, that we should not refrain from restoring the longitudinal continuity of intermittent streams, because they periodically provide fish valuable refugia and can also be a source of new generations and strengthen fish populations in mainstem river.

Combined Use of eDNA Metabarcoding and Bottom Trawling for the Assessment of Fish Biodiversity in the Zhoushan Sea

With the increase in fishing intensity and the intensification of marine pollution, the fishery resources in the Zhoushan Sea are seriously degraded, and the difficulty of censusing fish diversity hampers effective management in marine fishes. Environmental DNA metabarcoding and bottom trawl methods were used to determine the ability of the methods to distinguish fish assemblages in the Zhoushan Sea. The species composition and diversity of the Zhoushan Sea were assessed via high-throughput sequencing analysis of eDNA coupled with bottom trawl fishery survey data, after which the two methods were compared. eDNA screening identified 38.2% more fish species than bottom trawls. Combining these two methods, 33 orders, 65 families, and 130 species of fishes were identified. Perciformes and Clupeiformes, the most abundant orders in the catch, represented 31.5 and 10.0% of the total fish abundance, respectively. The results of ANOSIM and redundancy analyses indicated that the fish community structure varied significantly between summer and winter, however depth and temperature being the main environmental factors influencing fish distribution. The biodiversity index was higher in summer than in winter. Thus, our work provides more detailed seasonal data on biodiversity in the Zhoushan Sea, which is essential for the long-term management and conservation of coastal biodiversity. Compared with traditional survey methods, eDNA determination is highly sensitive, accurate, cost-efficient, and suitable for fish diversity studies in relevant sea areas. Although this approach cannot completely replace traditional methods, our findings demonstrate that it provides a reliable complementary method for assessing fish diversity in marine ecosystems.

Reef Fish in the Mudflats of Kaledupa Island in Wakatobi National Park, Indonesia

Although frequently described as low-fertility or low-productivity habitat, coastal mudflats serve as important feeding grounds for fish. Many fish species from adjacent coral reefs, seagrass beds, or mangroves foraging periodically in mudflats. Because of this foraging behaviour, some local fishermen are known to utilize the mudflats to catch fish. However, the impact of this catching activities to the ecosystem has not been fully discovered. An examination of the fish community structure and levels of environmental stress had carried out in the mudflat ecosystem of the coast of Kaledupa Island in Wakatobi National Park (WNP), Indonesia. Two mudflat study sites were selected from the shore of Balasuna and Tampara villages located between mangroves and coral reefs. Data were sampled from the fish catch of local fishermen using fish fences (sero) installed in each mudflat area. Fish community structure was analyzed using diversity index and index of relative importance (IRI). ABC curves and species exploitation rate were used to assess the local environmental pressure. A total of 74 fish species were recorded from the mudflats of Kaledupa, which was found to be dominated by reef-associated fish species, comprising 63 species and accounting for 85% of the total catch. Additionally, although both sites had relatively high reef fish diversity, the obtained Clarke’s W-statistic values were approximately 0, indicating that the local fish communities presented moderate levels of disturbance. Three out of five fish species with the highest IRI values were found to be over-exploited, namely Siganus canaliculatus, Lethrinus ornatus, and Lethrinus variegatus.

Characterization of fish community structure and an estuarine fish community index for temporarily closed estuaries (TCEs) from India's south-western coast.

We present for the first time, data on fish assemblage structure for ten temporarily closed estuaries (TCEs) along the south-western coast of India. Fish community structure differed significantly between TCEs based on species presence/absence, estuarine use and feeding mode. Marine migrant and freshwater stragglers dominated the 'fish guilds', while piscivores and zoobenthivores were the major feeding guilds, in all estuaries. We used the Estuarine Fish Community Index (EFCI) and a Combined Anthropogenic Pressure Index (CPI) to determine the ecological quality of TCEs. The application of functional guilds and EFCI successfully represented the use of TCEs by fish communities, and also the functional similarities existing between fish assemblages of these estuaries, despite considerable taxonomic, physical and chemical differences. EFCI indicated that the ecological health of TCEs in south-western India ranges from 'poor' to 'good'. We also established a significant relationship between CPI, EFCI and ecological quality in various TCEs using the Generalized Linear Model (GLM).

Trait groups as management entities in a complex, multispecies reef fishery.

Localized stressors compound the ongoing climate-driven decline of coral reefs, requiring natural resource managers to work with rapidly shifting paradigms. Trait-based adaptive management (TBAM) is a new framework to help address changing conditions by choosing and implementing management actions specific to species groups that share key traits, vulnerabilities, and management responses. In TBAM maintenance of functioning ecosystems is balanced with provisioning for human subsistence and livelihoods. We first identified trait-based groups of food fish in a Pacific coral reef with hierarchical clustering. Positing that trait-based groups performing comparable functions respond similarly to both stressors and management actions, we ascertained biophysical and socioeconomic drivers of trait-group biomass and evaluated their vulnerabilities with generalized additive models. Clustering identified 7 trait groups from 131 species. Groups responded to different drivers and displayed divergent vulnerabilities; human activities emerged as important predictors of community structuring. Biomass of small, solitary reef-associated species increased with distance from key fishing ports, and large, solitary piscivores exhibited a decline in biomass with distance from a port. Group biomass also varied in response to different habitat types, the presence or absence of reported dynamite fishing activity, and exposure to wave energy. The differential vulnerabilities of trait groups revealed how the community structure of food fishes is driven by different aspects of resource use and habitat. This inherent variability in the responses of trait-based groups presents opportunities to apply selective TBAM strategies for complex, multispecies fisheries. This approach can be widely adjusted to suit local contexts and priorities.

Nilai Ekologis dan Ekonomi Kawasan Sisen Ekosistem Lamun Kampung Syoribo dan Dafi di Pulau Numfor, Papua

Sisen or Sasisen is a tradition of closing the sea by indigenous Biak tribes in Biak Numfor and Raja Ampat. The purpose of this study is: (1) assessing the chemical chemical quality of the waters of the seagrass ecosystem sisen region, (2) reviewing the ecological index of the sisen area of seagrass ecosystems; a) diversity of seagrass species, b) the structure of seagrass fish communities, (3) examine the role of sisen in the management of seagrass ecosystems, and (4) analysis of the economic value of seagrass sisen areas. The research methods used are surveying and data collection through interview techniques (questionnaires and FGD), direct analysis, line transect, quadrat plot and VES. The results of the research obtained are: (1) the chemical chemical quality of the waters of the seagrass ecosystem sisen area in Kampung Syoribo and Dafi, Numfor Island is in good condition and suitable for marine life; (2) the diversity of seagrass species is classified as moderate with a value of H' = 1.44; (3) the structure of the seagrass fish community consists of a) diversity of 2.62, b) density of 14.89 individuals/m2, c) uniformity of 0.81, and d) dominance of 0.02; (3) the role of sisen systems in the management of seagrass ecosystems is: a) excellent understanding of sisen (93%), b) awareness of the benefits of sisen is very good (100%), c) knowledge of the sisen area is very good (100%), d) very good in the application of sisen (97%), e) very good in complying with sisen regulations (90%), and f) participation rates keep the sisen area very good (93%); (4) the economic value of sisen seagrass area for: a) fishing activities IDR 116,192,104, b) Siganus spp fish farming IDR 103,185,055, c) seaweed cultivation IDR 17,152,021, d) beach tourism IDR 13,562,671, and e) snorkeling tourism to IDR 10,356,852. The application of sisen in seagrass ecosystem areas provides excellent ecological and economic benefits.Key Words: Ecology's Value; Economics Value; Sisen Areas; Numfor Island

Effects of hydrological, environmental and spatial factors on fish diversity and community structure in oxbow lakes from the Amazon floodplain

Effects of flood pulses on lakes are mediated by the hydrological connectivity between environments in floodplain systems. Thus, hydrological connectivity along with other environmental filters are essential for structuring aquatic communities. Besides, it can also drive ecological changes in local diversity and species composition of numerous organisms. In this context, we characterize the hydrological connectivity in oxbow lakes to evaluate the influence of connectivity on alpha and beta diversity, as well as the local and spatial factors on the structure of fish metacommunities in different hydrological periods (flood, ebbing and drought). The study was conducted in oxbow lakes located in the Middle Purus River, western Amazon. The dynamics of hydrological periods was the primary factor in the variation of alpha diversity, and the different connectivity levels determined the increase in fish beta diversity. We found that even during biotic homogenization stemming from increased water levels, the beta diversity of fish remained high, since a region with varied connectivity levels between environments may contribute to the variation in species composition. In terms of metacommunities, the importance of connectivity was reduced during the flood, where the environment mainly structured metacommunities, which is consistent with species sorting. Thus, the contribution of connectivity increased during the disconnection of some lakes in the drought, especially for the most common and intermediate species, which may have influenced the dispersal and environmental pressures on these communities. For rare fish species, space and connectivity were the factors determining community structure, being influenced by factors of dispersal limitation during the flood and mass effect during the ebbing. Thus, the present study showed important processes that can lead to the structuring of fish communities in floodplains. This process induced different connectivity levels between rivers and lakes, and the action of environmental and spatial factors on species distribution, providing important information to encourage efforts for conservation and restoration of these ecosystems.

Assessment of fish communities from biotic type 6 in Black Sea Basin in Bosnia and Herzegovina

Fish are very sensitive to changes in damming of rivers, fragmentation and destruction of habitats, and changes in physical and chemical parameters. Changes in species diversity are a signal indicating that a significant and, as a rule, long-term change in one or more factors has occurred in the aquatic ecosystem. This in long term could lead to reduction of diversity and significant changes in the structure and dynamics of aquatic ecosystems. Biomonitoring of ichthyofauna is a very important element in the ecological assessment of water quality since changes in the structure of the fish community reflect changes in the quality of water in freshwater systems. The grouping of fish into ecological guilds has greatly improved our understanding of the impact of anthropogenic activities on fish and their communities. Therefore, the fish guilds represent the basis for ecological assessment based on the preferences of each recorded species in relation to tolerance, habitats, nutrition, reproduction and migrations. The results of the analyses of the structure of fish communities at 166 sites in biotic type 6 in the waters from the Black Sea Basin in Bosnia and Herzegovina have shown that the greatest influence on the distribution of different fish species has water temperature, flow, dissolved oxygen, and pH value. Obtained results clearly indicate an inverse relationship between altitude and the level of fish biodiversity. Values of applied diversity indices stress that fish communities in a river system usually follow a pattern of increasing species richness and diversity from upstream to downstream.

Determination of the Fish Community Structure of an Intertidal Rocky Zone of the Pacific Coast of Baja California Sur

The intertidal zone (also known as seashore) are transition areas between land and sea, that are greatly influenced by the tide cycle, therefore, environmental parameters, such as temperature and salinity, oscillate according to the periods in which these areas are exposed to air. Intertidal zones are highly diverse, which makes them key ecosystems for the development of sea life (both flora and fauna) exposed to drastic environmental change. The 59 visual censuses campaigns were carried out during the full moon of each month from 2015 to 2019. Temperature, salinity and dissolved oxygen were recorded during each visual census and showed variations between years. Temperature showed two distinct seasons, warm and cold. A total of 14,995 organisms were recorded, belonging to 30 species, 28 genera, 15 families, five orders and one class. Ecological indices like species richness (SR), Shannon-Wiener’s diversity (H') and Fisher’s alpha (α-Fisher) showed significant differences between years, 2015 and 2016 recorded as the most diverse years, while the lowest values were recorded in 2019. Therefore, fish communities of tide pools showed to be highly diverse, with 30 species recording similar relative abundances, and according to the BVI, only 11 species were dominant. Spatio-temporal variations of temperature, salinity and dissolved oxygen were highly correlated to changes in fish community structure, and the dominance of certain species, which are of great importance for the structure and dynamic of the tide pool communities. Therefore, the aim of the present study was to determine the fish community structure of tide pools during the low tide in the intertidal zone of a locality known as El Faro, on the west coast of La Paz, B. C. S., Mexico.