Littoral Fish Assemblages Research Articles

Comparing beach seine and gillnet sampling methods in fish assemblages from Southern Brazilian shallow coastal lakes

The aim of this study was to compare littoral zone fish assemblage richness, composition, dominance and size patterns between beach seine and gillnets sampling methods in coastal lakes at Tramandaí river, Southern Brazil. Monthly samples were taken in the littoral zones of six coastal shallow lakes (Itapeva, Quadros, Malvas, Fortaleza, Rondinha and Barros). Dominance and similarity analyses showed differences in species composition, numerical abundance and biomass among the sampling methods. Eleven species were dominant, but only one (Psalidodon aff. fasciatus) was dominant to both sampling methods. Beach seines sampled individuals with a total length ranging from 20 to 80 mm, while gillnets sampled individuals with a total length over 100 mm. An assemblage with high species richness, dominated by small fishes was found in the lake’s margins. In contrast, an assemblage with lower species richness comprised of larger fishes was found in inner areas. The methods are complementary in accessing species richness. Beach seine is a better alternative for monitoring programs as it provides reliable data at lower cost. These results may be useful in the sample design of future research or in the monitoring of ichthyofauna.

Spatial and seasonal variation in littoral fish assemblages of four estuarine lagoons on the Mexican Pacific coast

The shallowest zones of coastal lagoons are particularly appropriate nursery habitat for many fish species by providing refuge from predators and abundant food, among other benefits. However, little is known about the characteristics of fish assemblages and their relationship with environmental factors in these areas. The main objective of this study was to investigate the abundance and composition of the fish assemblages in the shallow zones (≤1 m) of four coastal lagoons in the Central Mexican Pacific and determine the correlation of their spatial and seasonal variations with selected abiotic variables. Fish samples were taken with a beach seine in the months of May and December during two consecutive years. Simultaneously, the physical and chemical variables of the water were measured, and the particle size of the sediment and content of organic matter were determined. A total of 26016 fish belonging to 60 species were collected, but only eight species (Poeciliopsis turrubarensis, Lile stolifera, Poecilia butleri, Eucinostomus currani, Anchoa sp, Gerres simillimus, Atherinella guatemalensis and Mugil setosus) accounted for more than 80% of the specimens. Significant differences in the composition of the fish assemblages between lagoons were found. The changes were principally related to the type of communication with the ocean, second to physical and chemical variables, primarily salinity, followed by size of the sediment particles (% of mud or sand). Observed seasonal changes could have been related to environmental and biological factors (e.g. recruitment) acting synergistically. No evidence was found that the state of eutrophication of the lagoons is severe and could be affecting the composition of the fish assemblages.

Seasonal variation and drivers of zooplankton, macroinvertebrate and littoral fish communities from irrigation ponds in a semi-arid region in the Eastern Cape (South Africa)

Irrigation ponds are increasingly abundant globally, particularly in water-stressed countries with limited natural surface waters, yet knowledge of their ecology is limited. Here, we assessed zooplankton, macroinvertebrate, and littoral fish communities from irrigation ponds located in the Sundays River Valley in South Africa. This study assessed the seasonal community patterns in response to physico-chemical and biotic components. Water temperature, water depth, Secchi depth, and ammonium concentrations differed significantly across seasons. Similarly, Chlorophyll-a concentrations differed seasonally, with water transparency identified as the main driver. Zooplankton was dominated by Rotifera, Copepoda and Cladocera. Seasonal changes in temperature and subsequent fluctuations in water levels resulted in changes in zooplankton community. Macroinvertebrates were dominated by insects, notably the families Corixidae and Naucoridae. The littoral fish community comprised of Glossogobius callidus, Oreochromis mossambicus and Gambusia affinis. Zooplankton, macroinvertebrates and littoral fish abundances, species richness, diversity and assemblage composition differed significantly across seasons with temperature identified as the main driver of these differences. This study demonstrates that bottom-up processes are the dominant drivers of the irrigation pond communities in the Sundays River Valley and highlights the relevance of seasonal abiotic drivers in structuring these communities, particularly G. callidus and G. affinis.

The species–area relationship for a highly fragmented temperate river system

AbstractDespite the importance of species–area relationships (SARs) to conservation, SARs in human‐fragmented rivers have received little attention. Our aim was to test for the presence and strength of SARs for littoral fish assemblages of an extensively dammed river in south‐central Ontario, Canada, and to examine long‐running hypotheses for the drivers of SARs. Twenty‐six navigational dams with locks built between 1837 and 1913 occur along the 160 km length of the Trent River examined in this study. We evaluated the relationship between richness and fragment area, and then used linear models to test whether the area per se, habitat diversity, or other hypotheses were best supported by the data. A power–function relationship with area explained 46% of the variation in fish species richness, and the slope (z = 0.4) was high compared with SARs reported from other ecosystems, indicating that species accumulated rapidly with an increase in fragment area. Multi‐predictor models suggested that area was significantly related to richness, but that vegetation cover diversity had a stronger relative effect. The slope of our SAR may indicate that there is a high degree of isolation between populations in different fragments, even though the lock system reportedly allows some passage of organisms. Our findings also suggest that mitigating against local extinction due to small population sizes (i.e., area effects), and enhancing aquatic vegetation cover may be viable strategies for promoting species diversity in the study river. Studies of SARs in fragmented rivers may offer additional benefits to supporting restoration planning where efforts are being made to increase species diversity.

Experience of the monitoring of the littoral fish assemblages at reserved waters (on the example of the Karadag Nature Reserve aquatory, Crimea)

Feasibility of monitoring of the littoral fish assemblages at the reserved water areas (Karadag Nature Reserve, Crimea) by methods of visual estimation and video recording involving data of fish catch statistics of fishing companies and recreational fishermen providing fishing in the waters adjacent to the reserved aquatory is discussed. At the water area of the reserve 18 species (35%) were identified exclusively by visual recording and video recording methods, 13 more species were identified by the mentioned contactless methods and simultaneously as a result of the analysis of information from recreational fishermen and fish catch statistics. As a result, 31 species of fish (or 61 % of the identified species) were identified visually or by video recording. The contactless methods were detected mostly sedentary (15) and nomad (11) species. Migratory species in the majority (9 species vs. 6) were identified only as a result of the analysis of information from recreational fishermen and fish catch statistics.

Connection promoted by annual floods shaping the response community attributes of shallow lakes fish inhabit the upper Paraná River floodplain

The temporal variability of the hydrological cycle plays a key role in shaping the diversity of the biotic components in floodplains. However, species respond differently to this cycle, and therefore, lakes can function as natural laboratories to test hypotheses about the interactions between the mechanisms involved in this dynamic. Here, we evaluate whether and how the level of the Parana River affects the structure of fish assemblages in the littoral region of lakes (with and without permanent connection to the Parana River), using taxonomic richness and species similarity data from a time series of 14 years. Our main working hypothesis was that the ecological descriptors (species richness, abundance, and spatial vs. temporal distribution) of fish assemblages, among lakes with different degrees of connection to the main river of the floodplain, may respond differently to the variation in the hydrological level. The results showed a significant difference in the composition of fish assemblages among the studied lakes, but the trends depended on the year considered (2002, 2006, 2012, and 2013). Therefore, despite of the artificial regulation promoted by dams upstream, the hydrological cycle still is the main driver of beta-diversity in littoral fish assemblages from shallow lakes in this floodplain. In addition, the variability of the composition of these assemblages is also straightly dependent on the features of the floods. Our results highlight the importance of seasonal variability in the hydrological level of this river for non-stochastic assembly rules of fish communities across spatial and temporal scales.

Free-diving underwater fish photography contests: a complementary tool for assessing littoral fish communities

Characterizing fish communities must be a priority to safeguard resources and determine critical changes. Here, species richness and the spatial and temporal evolution in the structure of fish assemblages were analysed based on photos taken in underwater free-diving contests. A total of 29 contests held from 2008 to 2015 at four different locations along the northeastern Spanish coast, including a marine protected area were analysed. Contests reward the number of species per participant and photographic quality. Species image frequency from each tournament were standardized to catch image rate. A total of 88 taxa were recorded, including 32 cryptobenthic species, the highest number recorded in the Mediterranean littoral system so far. Cluster analyses yielded four major groups. Catch image rates in the marine protected area were significantly higher for seven species of high commercial interest and for two big labrids of recreational interest, including an endangered species (Labrus viridis). Overall, the study showed that photographic free-diving contest data are a potential tool for determining species richness in littoral systems since contest rules promote competition between participants to obtain maximum fish diversity. We believe that this type of cost-effective data can be applied worldwide as a complementary way of monitoring littoral fish assemblage.

Restructuring of littoral fish assemblages after drought differs in two lakes at the terminus of a heavily regulated river

AbstractDrought significantly shifts the mix of functional groups present in river ecosystems and abundances of many aquatic fauna decline. The consequences of drought for fish often include the decline of ecological specialists and the predominance of generalist species. However, factors influencing the restructuring of littoral fish assemblages following prolonged drought in heavily regulated rivers are poorly understood. We compared the restructuring of littoral fish assemblages in 2 large connected lakes, which differ in hydrology and habitat availability, after 15 years of drought in their catchment. The once‐abundant and diverse fish assemblages showed limited signs of postdrought recovery after 5 years. There were differences between the 2 lakes related to the species present, their abundances, and the functional groups within fish assemblages. The functional groups present also shifted through time from alien‐dominated to freshwater generalist‐dominated. Only 2 of 5 native fish functional groups (freshwater generalist and diadromous) had increasing abundances (used as a proxy for recovery) following the drought, and these increases only occurred in the lake with the greater connectivity and diversity in habitat and hydrology. In contrast to patterns observed for natives, abundances of alien fishes in the littoral zone of the lakes declined after an initial spike in numbers associated with substantial river flows immediately following drought. This study shows that the recovery of native fish populations following prolonged drought in a heavily regulated semiarid river occurs over a time scale of years and recovery of some extant ecological specialists was incomplete after as many as 5 years.

A littoral fish index that responds to eutrophication in boreal lakes

Littoral fish assemblages were sampled by electrofishing at 70 nearshore sites in the Kitka lake group (lakes Ala-Kitka, Yli-Kitka and Posionjärvi) in northeastern Finland. Fish assemblages were usually dominated by littoral fish species, especially minnow (Phoxinus phoxinus) and alpine bullhead (Cottus poecilopus). Young individuals (mainly 0+ and 1+) of other fish species, such as burbot (Lota lota) and perch (Perca fluviatilis) were also recorded frequently. A littoral fish index (LiFI) was developed to respond to the degree of eutrophy. Of the candidate metrics, three were chosen for the index: (1) proportion of minnow and alpine bullhead individuals in the electrofishing catch, (2) density of perch, and (3) average weight of all individual fish in the catch. The index value responded to the extent of eutrophy; total phosphorus explained 55.3% of the variation in LiFI index values. A test of the index with data from other Finnish lakes suggested that the index is feasible for use in a broader context. Finally, the index values from the Kitka lakes were classified from bad to high in assessing the ecological status of the littoral sites around the studied lakes. We recommend the use of littoral electrofishing and LiFI index in lakes where detailed, bay-specific information is needed about the ecological status, and in all situations where the littoral zone is in focus.

Impacts of fishing and environmental factors driving changes on littoral fish assemblages in a subtropical oceanic island

The structure of demersal fish assemblages of commercial interest was studied at 51 sites on La Palma Island (Canary Islands, northeastern Atlantic). On this island, demersal fish populations are limited and independent from other islands. As deep water separates the islands and the shallow sublittoral platforms are not continuous, adult inter-island migrations are not possible except between the islands of Lanzarote and Fuerteventura. Otherwise, each island functions as a closed system, and the status of an island fish assemblage depends on local environmental conditions and activities performed in situ by the islanders. These circumstances provide a unique opportunity to test the intrainsular variability of fish assemblages. With this background, environmental parameters, fishing pressure and distance to the MPA were considered to identify the main factors explaining the spatial variation of fish assemblages off La Palma Island. Twenty-six fish species were recorded, but 60% of the total fish biomass was represented by only five species (Sparisoma cretense, Pomadasys incisus, Canthidermis sufflamen, Diplodus cervinus cervinus and Bodianus scrofa). However, the structure of assemblages was heterogeneous in response to different variables and showed substantial spatial variation. The assemblages were strongly modified by the presence of upright seaweed cover, fishing activities, and certain environmental variables. Differences were more pronounced in species that occupied the higher trophic levels. The most disturbed assemblages were those located in areas with lower upright seaweed cover and with higher fishing pressure, whereas the best-preserved assemblages corresponded to sites with controlled fishing activities, located within the MPA.

Sampling Glacial Lake Littoral Fish Assemblages with Four Gears

AbstractLittoral zone fish assemblages are important components of freshwater lakes. Monitoring of littoral fish assemblage structure is important because littoral fishes often comprise the majority of the entire fish assemblage, and fluctuations in the structure and abundance of the littoral fish assemblage can influence trophic interactions and fishery yields at the ecosystem level. Single‐gear sampling designs, however, may only capture a subset of the fish assemblage, resulting in a skewed representation of fish assemblage structure. Use of multiple gears can be justified if they provide complementary fish assemblage information. Our objective was to compare glacial lake fish assemblage structure as represented by four gears and to assess whether the gears provide redundant or complementary fish assemblage information. Two northeastern South Dakota glacial lakes were sampled with a beach seine, benthic sled, drop net, and push trawl in August 2011. Results indicated that fish assemblage structure did not differ significantly among gears. However, fish assemblage descriptors (metrics of species richness, diversity, dominance, and evenness) and rates of species accumulation did differ among gears; in comparison with the drop net, the beach seine, benthic sled, and push trawl collected more individuals with qualitatively greater species richness and diversity at a faster rate. The beach seine collected the most individuals representing the greatest number of species with the least amount of sampling effort (i.e., fastest rate of species accumulation); thus, we recommend the use of beach seines for monitoring and assessment of littoral fish assemblages in glacial lakes.Received March 16, 2012; accepted August 16, 2012

Structure of the littoral fish assemblage in an impounded tributary: the effects of macrophytes presence (subtropical region, Brazil)

To evaluate the effects of macrophytes presence in the structure of littoral fish assemblages in the littoral zone, monthly samples were collected from September, 2006 to August, 2007 in an impounded tributary of the Itá Reservoir, the Fragosos River, located in the Upper Uruguay River Basin. Fish were collected using a beach seine and sampling was conducted in the littoral zone inside a macrophyte stand and in an area with no macrophytes. A total of 5,191 fish were captured during the study period. Fish assemblage attributes (fish abundance, species richness, and diversity) varied significantly between sampling months and areas. The abundance of Astyanax cf. bimaculatus, Astyanax fasciatus, Geophagus brasiliensis, and Gymnotus carapo also varied significantly between sampling months and areas. Detrended Correspondence Analysis showed a clear spatial segregation at the first axis and a slight temporal segregation at the second axis. These results were confirmed by Multiple Response Permutation Procedure analysis. Apparently, the presence of the aquatic macrophytes is not the only factor influencing the distribution of littoral fish assemblages in the Fragosos River. Littoral fish seem to be taking advantage of low- to medium-sized macrophyte stands, but few species used maximum-sized stands.

The black scorpionfish, Scorpaena porcus (Scorpaenidae): Could it serve as reliable indicator of Mediterranean coastal communities’ health?

Status of coastal fishery organisms, which are exposed to a wide range of stressors throughout their lives, can be indicative of various pressures. The black scorpionfish, Scorpaena porcus, is ubiquitous in Mediterranean coastal waters where it has ecological and economic importance and thus may qualify as suitable indicator of status of littoral fish assemblages. To test this, we analysed spatial and temporal variability in the abundance, biomass, size and weight of this scorpaenid species. Between 1993 and 2009, investigated population was monitored by experimental trammel net fishing, within the warm period (May to September) and at multiple areas along the eastern Adriatic coast with the aim of testing for the consistency of patterns of change across a large spatial scale (∼600km). We hypothesized that if S. porcus could serve as a reliable indicator of Mediterranean coastal communities’ health, then reduction in its abundance and biomass and decrease in its size and weight should be observed, as a consequence of the constant fishing pressure. The results revealed that the pattern of variability in NCPUE and BCPUE through time followed an increasing trend at all the areas, except for one where the slope of regression analysis was positive but not significant. On the other hand, length and weight structure fluctuated irregularly from year to year. Non-significant decrease in size of S. porcus was still observed across the studied region. However, we conclude that investigated Adriatic population did not go through profound changes and we briefly explore the possible reasons why this species did not clearly match the concept of indicator organisms.

Long-term trends in the structure of eastern Adriatic littoral fish assemblages: Consequences for fisheries management

Long-term interannual changes in abundance, biomass, diversity and structure of littoral fish assemblages were examined between 1993 and 2009 by experimental trammel net fishing up to six times per year, within the warm period – May to September, at multiple areas along the eastern Adriatic coast with the aim of testing for the consistency of patterns of change across a large spatial scale (∼600 km). The results revealed spatially consistent increasing trends of total fish abundance and biomass growing at an average rate of 15 and 14% per year, respectively. Of the diversity indices analysed, the same pattern of variability was observed for Shannon diversity, while Pielou evenness and average taxonomic distinctness measures Δ ∗ and Δ + showed spatial variability with no obvious temporal trends. Multivariate fish assemblage structure underwent a directional change displaying a similar pattern through time for all the areas. The structural change in fish assemblages generally involved most of the species present in trammel net catches. A large pool of fish species responsible for producing the temporal pattern of assemblage change was relatively different in each of the areas reflecting a large geographic range covered by the study. An analysis of 4 fish species ( Symphodus tinca, Pagellus erythrinus, Mullus surmuletus, Scorpaena porcus) common to each of the study areas as the ones driving the temporal change indicated that there were clear increasing trends of their mean catches across the years at all the study areas. A common pattern among time trajectories across the spatial scale studied implies that the factor affecting the littoral fish assemblages is not localised but regional in nature. As an underlying factor having the potential to induce such widespread and consistent improvements in littoral fish assemblages, a more restrictive artisanal fishery management that has progressively been put in place during the study period, is suggested and discussed.

Assessment of the ecological status of regulated lakes: stressor-specific metrics from littoral fish assemblages

Following the European Water Framework Directive (WFD), the ecological status of lakes should be classified based mainly on biota, including fish fauna. In Finnish regulated lakes, littoral fish assemblages may be especially vulnerable to winter drawdown in water level. In this study, we sampled littoral fish assemblages by electrofishing in 14 regulated and 9 reference lakes, and developed three stressor-specific metrics based on total fish density, proportion of disturbance-sensitive species, and occurrence of juveniles. Ecological status was classified from bad to high in regulated lakes, whereas standard WFD assessment based on NORDIC gillnet sampling indicated high status and no response to water level regulation. We suggest that stressor-specific metrics should be integrated into the assessment of the ecological status of regulated lakes in the WFD.

The influence of diel period on fish assemblage in the unstructured littoral of reservoirs

Abstract Diel changes in littoral fish assemblage were studied in four reservoirs in the Czech Republic (Central Europe). The sampling was performed by beach seining in an unstructured littoral zone. Perch, Perca fluviatilis L., roach, Rutilus rutilus (L.), bream, Abramis brama (L.), carp, Cyprinus carpio L., ruffe, Gymnocephalus cernua (L.), pikeperch, Sander lucioperca (L.), eel, Anguilla anguilla (L.) and A. brama × R. rutilus hybrids exhibited higher densities at night. Only bleak, Alburnus alburnus (L.) exhibited higher densities during the day. The number of species was higher in night hauls, and mean body size of roach and bleak was also higher at night. Diel changes in fish densities resulted in the change in species composition between day and night. The study has implication for the sampling design to assess littoral fish assemblages using beach seine netting and recommends night sampling for a representative assessment or sampling during both diel periods for a robust assessment.

Dietary Segregation of Pelagic and Littoral Fish Assemblages in a Highly Modified Tidal Freshwater Estuary

AbstractEstuarine food webs are highly variable and complex, making identification of their trophic pathways difficult. Energy for the food web of the San Francisco Estuary is thought to be based largely on in situ phytoplankton production, but little attention has been paid to littoral habitats, where other energy sources may be important. We analyzed the stomach contents of over 960 juvenile fishes and the stable carbon and nitrogen isotope ratios of these fishes and their potential food resources in pelagic and littoral habitats from the tidal freshwater area of the estuary. The mixing model IsoSource was used to examine energy sources important to consumers. Our results show evidence of two predominant food web pathways. Pelagic fishes and some littoral fishes showed strong dependence on a zooplankton–phytoplankton trophic pathway. However, the majority of fishes in littoral habitats had diets and carbon isotope ratios consistent with energy arising from submerged aquatic vegetation and epiphytic macroalgae. IsoSource revealed that the overall majority of nutrition of littoral fishes originated from consumption of grazer amphipods. Examining both stable isotopes and stomach contents allowed us to identify a food web with contributions to resident fishes that had been previously underestimated in the estuary. This study provides insight to how estuarine food webs have changed over the last few decades and highlights why the functions of habitats must be understood for effective restoration planning.

Zonation and spatial distribution of littoral fish communities from the southwestern Finnish coast (Archipelago and Bothnian Sea, Northern Baltic Sea)

The aim of our study was to test whether the distribution of littoral fish assemblages would reflect both their immediate environment with reference to local underwater vegetation, including larger scale geographic archipelagial zonation. A total of 62 locations were sampled using beach seine and underwater video along the southwestern Finnish coastline in summer 2001. At all locations, water temperature, water transparency and benthic vegetation patterns (depth ranges of plant species or taxa) were recorded. Using correspondence analysis, our results showed a clear division of the Archipelago Sea into three separate zones based on littoral fish species assemblages. Overall, fish assemblages formed three distinct site groups, being dominated by pike and cyprinids, by percids and gobies, or by gasterosteids, and showed clear inner, middle and outer archipelago zones respectively, within the study area. Our results suggest that while vegetation in the study sites was diverse, it failed to express the zonation reflected by the littoral fish assemblages, which showed a definite zonation pattern which broadly reflected previous reports using both physical and biological parameters. We interpret our results to show that littoral vegetation is better in expressing small-scale differences between study sites, while littoral fish communities are more robust in detecting changes over a larger geographical scale.

Is the Cape Roux marine protected area (Saint-Raphaël, Mediterranean Sea) an efficient tool to sustain artisanal fisheries? First indications from visual censuses and trammel net sampling

In recent decades, marine reserves have been established either to protect ecosystem structure and biolog- ical diversity or to serve as management tools to counter the overexploitation of fish stocks. The Cape Roux marine protected area (MPA), in the Mediterranean Sea, was established in December 2003 for the management of artisanal fisheries and enhancement target fish stocks. Monitoring of littoral fish assemblages (0-30 m depth) in this zone began one year after the MPA was set up. The survey was conducted at 6 stations, located inside and outside the MPA, using three methods: underwater visual cen- sus (UVC) on transects, UVC using a new fish assemblage survey technique (FAST), and experimental net fishing performed by a fisherman. The FAST indices were derived from visual censuses, performed along a random pathway, scoring species on a presence/absence basis and size on a 2-class basis. Indices were calculated seasonally, by applying weights according to species and size. This study presents results obtained between October 2005 and June 2007. In the protected area, the experimental fishing yielded significantly higher abundance and species richness, and the FAST method highlighted a decrease in seasonal fluctuations. These two complementary methods (UVC and experimental fishing) revealed the early changes in fish assemblages in response to protection. The FAST method employed here seems to be relevant for the study of artisanal fishery target fishes, as a low-cost and sensitive UVC method.

Food resource use in a tropical eastern Pacific tidepool fish assemblage

An understanding of the trophic organization patterns of tropical littoral fish assemblages can contribute to the knowledge of key ecosystem processes while simultaneously assisting to validate large-scale biogeographic patterns (i.e. latitudinal patterns in fish herbivory). In the present study, the diets of eight fish species inhabiting the tide pools of a rocky shore on the western coast of Colombia (tropical eastern Pacific) are documented. A total of 17 prey items were identified, with a major representation (average percent by weight) of crabs and macroalgae items in the guts of all species. Small crustacean prey items (crabs, shrimps, copepods and amphipods) dominated the diets of most species, but consumption of macroalgae and diatoms by a significant number of species was also observed. We identified four significant trophic guilds within the assemblage using multivariate techniques (cluster analysis and nMDS): an omnivorous guild, consisting of Malacoctenus zonifer and the smallest size class of Bathygobius ramosus; a small-prey carnivorous guild, consisting of the intermediate size classes of B. ramosus and the smallest size class of Gobiesox adustus; a large-prey carnivorous guild, consisting of both largest size classes of B. ramosus and G. adustus; and an herbivorous guild consisting of Abudefduf concolor, A. troschelii and Chaenomugil proboscideus. The diet of two species slightly overlapped those of the rest of the assemblage and did not conform to any guild (Echidna nocturna and Halichoeres aestuaricola). It is hypothesised that guild formation may be a consequence of aggregation of species at abundant resources in the intertidal zone rather than a direct consequence of inter-specific competition. Ontogenetic changes in diets were observed in two resident species of the assemblage (B. ramosus and G. adustus). The latitudinal trend for herbivory inside this tropical assemblage is discussed in comparison with similar temperate studies in the eastern Pacific.