Spatial and temporal distributions of epiphytic diatoms growing on Thalassia testudinum Banks ex König: relationships to water quality

The spatial and temporal distributions of the epiphytic diatom flora on Thalassia testudinum was described within the Florida Bay estuary and at one Atlantic site east of the Florida Keys over a 1-year period. Species of the genus Mastogloia dominated the epiphytic diatom flora (82 out of 332 total species). Nonmetric Multidimensional Scaling (NMDS) and Analysis of Similarity (ANOSIM) revealed four distinct spatial assemblages and two temporal assemblages. Eastern and western Florida Bay assemblages were identified within the estuary. The eastern diatom assemblage was characterized by high relative abundances of Brachysira aponina and Nitzschia liebetruthii, while the western assemblage was characterized by the abundance of Reimerothrix floridensis, particularly during summer. Two diverse and distinct marine assemblages, one located in the Gulf of Mexico along the western edge of Florida Bay and the other behind the Florida reef tract in the Atlantic Ocean, were also identified. Analysis of the spatial distribution of diatoms and water quality characteristics within Florida Bay suggest that these assemblages may be structured by salinity and nutrient availability, particularly P. The Gulf of Mexico and the western Florida Bay assemblages were associated with higher water column salinities and TP concentrations and lower DIN concentrations and TN:TP ratios relative to the eastern Florida Bay assemblage. The temporal variation in diatom assemblages was associated with water temperature, though temporal indicator species were few relative to the number of spatial indicators. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Effects of fishing on parasitism in a sparid fish: contrasts between two areas of the Western Mediterranean

This study addressed the impacts of fishing on the rates of parasitism using the sparid Boops boops as a model fish species. Using a large suite of parasite species in B. boops, with different life histories, transmission pathways and host specificity, we compared parasite diversity, prevalence, abundance and community structure at two Mediterranean localities in the Balearic Sea, Santa Pola Bay and the Gulf of Oran, that are characterised by a contrasting pattern of fishing of B. boops. A total of 360 fish were examined comprising nine distinct samples collected during the warm and the cold weather months. A total of 29 parasite species were identified, with eight species in common for the two localities. Parasite component communities at Santa Pola Bay were more species rich and abundant than those at the Gulf of Oran and exhibited a different community structure. Of the eight common taxa used in the quantitative comparisons, five exhibited significant difference for prevalence between the two localities, four having substantially higher prevalence at Santa Pola and only one being more prevalent at the Gulf of Oran. Two specialist trematodes and the sparid generalist monogenean exhibited consistently higher prevalence and abundance at Santa Pola Bay than at the Gulf of Oran; the two specialists were also identified as key species for assigning individual fish to their locality of origin. The consistent differences in the richness, abundance and structure of parasite communities in B. boops from Santa Pola Bay and the Gulf of Oran may reflect the contrasting patterns of exploitation of the populations of this fish host at the two localities.     

Epibenthic gastropods of the middle Florida keys: the role of habitat and environmental stress on assemblage composition

A survey of epibenthic prosobranch gastropods was undertaken in both seagrass and hard substratum (coral or old reef rock) habitats on opposite sides of the Florida Keys (Florida Bay and Hawk Channel) to compare faunal differences attributable to differences in the above two habitats and environments. Additionally, two data sets (26 continuous months) of daytime dissolved oxygen, surface salinity and water temperature from Florida Bay (Long Key) and Hawk Channel (Key Largo) environments were compared to determine differences that might constitute environmental stresses likely to affect the fauna. The above data were collected to determine if several hypotheses concerning effects of stress on organisms, assemblage, community and faunal composition were consistent with data on assemblage structure. These hypotheses were that: (1) stress should reduce the average size of organisms; (2) shorten food chains; (3) reduce predation intensity; (4) reduce species richness and diversity; and (5) increase the relative abundance of predator-susceptible ancestral species (i.e. Archaegastropoda). Water quality data suggest that the two most likely forms of stress in deeper (>1 m) areas of Florida Bay adjacent to the Keys are cold water temperatures associated with winter cold fronts and low predawn oxygen associated with warm summer temperatures, high salinity, and periodic algal and seagrass drift buildups. Seagrass sites had high population densities and low diversity due to the dominance of Astraea americana Gmelin (American star shell) in Florida Bay and Modulus modulus L. in Hawk Channel seagrass habitats. Florida Bay sites had high species richness on a small spatial scale, but Hawk Channel sites had more species and greater encounter rates of new species on a larger scale. Predawn oxygen measurements taken during July in four habitats were positively correlated with prosobranch species richness and diversity. Faunal data, analysed on a population density basis, fit the above hypotheses of body size, trophic level, and evolutionary age of the species. Attempts to measure predation on an experimental prosobranch (A. americana) were unsuccessful but a tethering experiment with a sea urchin (Echinometra lucunter L.) indicated higher predation in the less stressful Hawk Channel than Florida Bay hard substratum sites. Stress appears to reduce the abundance of higher trophic levels (both prosobranch and finfish predators) resulting in the dominance of ancestral forms not adapted to predation but tolerant of environmental stress. Eutrophication or increased oxygen demands in Florida Bay could result in further species richness and diversity declines.     

Ben Franklin temperate reef and deep sea `Agassiz Coral Hills' in the Blake Plateau off North Carolina

This paper deals with two deep water coral ecosystems off the North Carolina coast, both under the depositional, erosional, and biological influence of the Gulf Stream and its eddies and episodic upwelling processes. The first coral community, Ben Franklin temperate reef, is located at 20 meters in Onslow Bay and is characterized by the ahermatypic coral Oculina arbuscula Verrill and unusually high abundance of the small predatory isopod Eurydice bowmani George and Longerbeam. The deep sea coral community, Agassiz Coral Hills, is located over the Blake Plateau at 650 meters, dominated by the fossilized, dead and living coral Bathypsammia tintinnabulum, with rare occurrence of the deep sea solitary coral Flabellum goodei. The deep sea coral sites were sampled with an otter trawl, outfitted with `Benthos' flotation spheres. The results suggest that the fish and shrimp fauna exhibits high species richness in the Agassiz Coral Hills off North Carolina in comparison with a control site over the Blake Plateau off Florida. Species richness may be linked to episodic upwelling events along the Gulf Stream meanders. The fish fauna in the Agassiz Coral Hills includes the following two commercially important deep sea fish species: the wreck fish Polyprion americanus and the eel Synaphobranchus koupi. The Ben Franklin reef and the Agassiz Coral Hills are recommended as Marine Protected Areas.     

Possible Ballast Water Transfer of Lionfish to the Eastern Pacific Ocean

The Indo-Pacific Red Lionfish was first reported off the Florida coast in 1985, following which it has spread across much of the SE USA, Gulf of Mexico, and Caribbean Sea. Lionfish negatively impact fish and invertebrate assemblages and abundances, thus further spread is cause for concern. To date, the fish has not been reported on the Pacific coast of North or Central America. Here we examine the possibility of ballast water transfer of lionfish from colonized areas in the Atlantic Ocean to USA ports on the Pacific coast. Over an eight-year period, we documented 27 commercial vessel-trips in which ballast water was loaded in colonized sites and later discharged untreated into Pacific coast ports in the USA. California had the highest number of discharges including San Francisco Bay and Los Angeles-Long Beach. A species distribution model suggests that the probability of lionfish establishment is low for the western USA, Colombia and Panama, low to medium for Costa Rica, Nicaragua, El Salvador and Guatemala, medium to high for mainland Ecuador, and very high for western Mexico, Peru and the Galapagos Islands. Given the species’ intolerance of freshwater conditions, we propose that ballast water exchange be conducted in Gatún Lake, Panama for western-bound vessels carrying ‘risky’ ballast water to prevent invasion of the eastern Pacific Ocean.     

Do Tropical Cyclones Shape Shorebird Habitat Patterns? Biogeoclimatology of Snowy Plovers in Florida

Background

The Gulf coastal ecosystems in Florida are foci of the highest species richness of imperiled shoreline dependent birds in the USA. However environmental processes that affect their macroecological patterns, like occupancy and abundance, are not well unraveled. In Florida the Snowy Plover (Charadrius alexandrinus nivosus) is resident along northern and western white sandy estuarine/ocean beaches and is considered a state-threatened species.

Methodology/Principal Findings

Here we show that favorable nesting areas along the Florida Gulf coastline are located in regions impacted relatively more frequently by tropical cyclones. The odds of Snowy Plover nesting in these areas during the spring following a tropical cyclone impact are seven times higher compared to the odds during the spring following a season without a cyclone. The only intensity of a tropical cyclone does not appear to be a significant factor affecting breeding populations.

Conclusions/Significance

Nevertheless a future climate scenario featuring fewer, but more extreme cyclones could result in a decrease in the breeding Snowy Plover population and its breeding range. This is because the spatio-temporal frequency of cyclone events was found to significantly affect nest abundance. Due to the similar geographic range and habitat suitability, and no decrease in nest abundance of other shorebirds in Florida after the cyclone season, our results suggest a common bioclimatic feedback between shorebird abundance and tropical cyclones in breeding areas which are affected by cyclones.     

A comparison between aquatic birds of lakes and coastal rivers in Florida

Aquatic birds were counted on five Gulf coast Florida rivers to determine if these river systems supported densities, biomass and species richness similar to those found on Florida lakes. Forty-two species were identified and for the species that were found on both Florida streams and lakes similar densities and biomass were encountered. As with Florida lakes, stream bird abundance and species richness were higher in winter months than in summer months, a consequence of migratory bird populations. Total bird abundance, biomass per unit of phosphorus, and species richness per unit of area were similar to data collected on Florida lakes. Thus, Florida rivers are capable of supplying sufficient resources to maintain bird densities, biomass and species richness values similar to lakes of equal size and nutrient concentrations and are therefore important habitats for aquatic bird populations. An examination of individual habitat characteristics indicates that water depth was inversely correlated and submersed aquatic vegetation was positively correlated with bird density, biomass and species richness within the river systems. While both habitat characteristics are important they are also inversely related making it difficult to separate the individual significance of each characteristic.     

Taxonomy and biogeography of the fiddler crabs (Ocypodidae: Genus Uca) of the Atlantic and Gulf coasts of eastern North America

Fifteen species of fiddler crabs are reported for eastern North America between Massachusetts and Quintana Roo, Mexico. Thirteen occur in the United States and 11 in Mexico, with eight in common to the two countries. Of 13 species in the Gulf of Mexico, five are endemic and a sixth is restricted largely to the peninsulas of Florida and Yucatan. The status of U. rapax in the northern Gulf remains to be resolved. Range limits of most species approximate one or the other of two sets of intersecting thermal and geological boundaries that subdivide the Gulf of Mexico along north-south and east-west axes. Species belonging to subgenus Minuca tend to replace one another at the thermally-controlled Carolinian-Caribbean marine biotic boundary across the Florida peninsula and northern Gulf. However, only U. minax of all the North American fiddler crabs exhibits the classical disjunct Carolinian distribution, and this appears basically to reflect the discontinuous distribution of temperate salt marshes that are the habitat of the species. Distributions of species belonging to subgenus Celuca adhere for the most part to the subdivision of the Gulf into western terrigenous and eastern carbonate sedimentary provinces. The northern transition occurs in the vicinity of Apalachee Bay and the southern at Laguna de Terminos. A third distributional pattern is shown by U. subcylindrica , a specialized endemic species of the hypersaline Laguna Madre system of the western Gulf. The level of endemism in the fiddler crabs is relatively high in comparison with that of other marine groups within the Gulf of Mexico. This may be a consequence of the adaptations of fiddler crabs as specialized deposit feeders to regional differences in climatic and edaphic characteristics of a marginally marine upper shore habitat. The distributional patterns of the endemics could prove useful in reconstructing palaeoecological events of evolutionary significance within the Gulf of Mexico.     

Red mangrove life history variables along latitudinal and anthropogenic stress gradients

Mangroves migrate northward in Florida and colonize marshes historically dominated by salt marsh species. In theory, this migration should be facilitated by greater numbers of propagules stemming from increased reproductive activity and greater genetic variability caused by outcrossing. We aimed to determine if stand reproduction and % outcrossing were affected by cold stress (stress increases with latitude), anthropogenic stress (human population density as a proxy), and years since a major hurricane. Further, we wished to determine if mutation rate varied with the stressors and if that affected stand reproduction. Both coasts of Florida from the southern Florida Keys to Tampa Bay on the Gulf of Mexico coast, and Merritt Island on the Atlantic coast. We conducted field surveys of frequency of reproducing trees (104,211 trees surveyed in 102 forested stands), incidence of trees showing albinism in propagules, and% outcrossing estimated from the ratio of albino:normal propagules. Structural equation modeling (SEM) was used to test a conceptual model that served as a multivariate hypothesis. Reproductive frequencies varied by site and increased with latitude although more strongly on the Gulf coast. Our SEM results indicate that outcrossing increases in this predominately selfing species under conditions of cold and anthropogenic stress, and that this increases reproductive output in the population. Further, we find that increased mutation rates suppress stand reproductive output but there is no significant relationship between outcrossing and mutation rate. Tree size responded to stressors but did not affect stand reproduction. Reproduction increased with years since major hurricane. Potential for colonization of northern Florida salt marshes by mangroves is enhanced by increased reproductive rates that provides more propagules and outcrossing that should enhance genetic variation thereby promoting adaptation to novel environmental conditions. Natural (cold) stress reduced mutation rate and increased stand reproductive output but anthropogenic stress did the opposite.     

Latitudinal variation in spongivorous fishes and the effectiveness of sponge chemical defenses

It has been proposed that predation pressure declines with increasing latitude and a positive correlation exists between predation intensity and the investment into chemical defenses. However, little direct evidence supports the idea that tropical species are better defended chemically than their temperate counterparts. Temperate reefs of the South Atlantic Bight (SAB) off Georgia, USA, provide a unique opportunity to study tropical sponges in a temperate environment. We documented sponge species richness and abundance, sponge predator density, and examined the ability of eight sponge species to chemically deter predation by fishes on two reefs in the SAB. We used rarefaction analysis and ANOVA to compare our results for sponge species richness and density, respectively, with similar published studies conducted on reefs of the sub-tropical Atlantic (i.e., Florida Keys). These analyses were combined with similar statistical comparisons for spongivorous fish species richness and density. Results showed that sponge species richness was lower, but sponge density was higher, on the temperate SAB reefs than on the subtropical reefs. Both spongivorous fish diversity and density were lower on the SAB reefs. The greater abundance of sponges and lower density of predators on SAB reefs suggest a lower frequency of predation on sponges on SAB reefs. Of the eight sponge species assayed from the SAB reefs, five possessed chemical extracts that were significantly less deterrent to fish predators than their tropical/subtropical conspecifics. When the results were combined across all sponge species, the chemical deterrence of fish predators was significantly lower for extracts obtained from the temperate sponge community as compared to the tropical/subtropical assemblage. These results support the more general hypothesis that a lower density and diversity of sponge predators occurs at high as compared to low latitudes in the western Atlantic and may contribute to decreased investment in chemical defenses.     

Genetic diversity within a threatened,endemic North American species, <Emphasis Type="Italic">Euphorbia telephioides</Emphasis> (Euphorbiaceae)

The southeastern United States and Florida support an unusually large number of endemic plant species, many of which are threatened by anthropogenic habitat disturbance. As conservation measures are undertaken and recovery plans designed, a factor that must be taken into consideration is the genetic composition of the species of concern. Here we describe the levels, and partitioning, of genetic diversity in 17 populations of the rare and threatened Florida endemic, Euphorbia telephioides (telephus spurge). Species-wide genetic diversity was high (P_s = 91%, AP_s = 3.81, A_s = 3.57 and H_es = 0.352) as was mean population genetic diversity (P_p = 81%, AP_p = 2.98, A_p = 2.59 and H_ep = 0.320) which ranks it among the highest 10% of plant species surveyed. Partitioning of genetic variation (G_st = 0.106) was low compared to other herbaceous outcrossing perennials indicating high historical gene flow across its limited geographic range. Among population G_st values within the three Florida counties in which it occurs, Gulf (0.084), Franklin (0.059) and Bay Counties (0.033), were also quite low. Peripheral populations did not generally have reduced genetic variation although there was significant isolation by distance. Rarefaction analysis showed a non-significant relationship between allelic richness and actual population sizes. Our data suggest that E. telephioides populations were probably more continuously distributed in Bay, Gulf and Franklin Counties and that their relative contemporary isolation is a recent phenomenon. These results are important for developing a recovery plan for this species.     

Fish species richness evaluation in Mexican coastal lagoons: a case study in the Gulf of Mexico

We analyze the origin of knowledge about fish species richness in the Tuxpan-Tampamachoco estuarine system, in Veracuz, México. A complete inventory of the fish species known to date for this system (N = 179) was elaborated from published lists and from sampling seagrass meadows of Tampamachoco Lagoon, which yielded 14 previously unknown species. When compared, the different lists showed a low similarity that may reflect differences in sampling methods and collecting strategies. Current data suggest that fish species richness in Mexican coastal lagoons (Gulf of Mexico) is not related with lagoon surface area, as has been suggested, but with the number of inventories available for each lagoon, being these a reflection of the sampling effort. A sampling design for the assessment of fish species richness in estuarine systems should consider: a) using the highest possible variety of sampling fishing gears, b) collecting in all microhabitat types and c) the preference of bimonthly or quarterly samplings for two or more years over monthly samplings in a single year.     

Fish reduce anuran abundance and decrease herpetofaunal species richness in wetlands

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Community structure and biogeography of shore fishes in the Gulf of Aqaba,Red Sea

Shore fish community structure off the Jordanian Red Sea coast was determined on fringing coral reefs and in a seagrass-dominated bay at 6 m and 12 m depths. A total of 198 fish species belonging to 121 genera and 43 families was recorded. Labridae and Pomacentridae dominated the ichthyofauna in terms of species richness and Pomacentridae were most abundant. Neither diversity nor species richness was correlated to depth. The abundance of fishes was higher at the deep reef slope, due to schooling planktivorous fishes. At 12 m depth abundance of fishes at the seagrass-dominated site was higher than on the coral reefs. Multivariate analysis demonstrated a strong influence on the fish assemblages by depth and benthic habitat. Fish species richness was positively correlated with hard substrate cover and habitat diversity. Abundance of corallivores was positively linked with live hard coral cover. The assemblages of fishes were different on the shallow reef slope, deep reef slope and seagrass meadows. An analysis of the fish fauna showed that the Gulf of Aqaba harbours a higher species richness than previously reported. The comparison with fish communities on other reefs around the Arabian Peninsula and Indian Ocean supported the recognition of an Arabian subprovince within the Indian Ocean. The affinity of the Arabian Gulf ichthyofauna to the Red Sea is not clear. Received in revised form: 2 November 2001 Electronic Publication     

Fish species richness decreases with salinity in tropical coastal lagoons

Aim To analyse the relationship between fish species richness and salinity, and to provide a simple linear model for fish diversity trends across salinity gradients in a tropical coastal lagoon that can be compared with other similar ecosystems and other communities. To reinforce our conclusions, the salinity–fish richness relationship was investigated at different spatial scales (sampling station, set of stations and whole lagoon) and for two different periods, separated by 18 years. Location The Terminos coastal lagoon, a shallow tropical lagoon (mean maximum depths ranging between 3.5 and 4.5 m), is located in the southern Gulf of Mexico (18.5–18.8° N, 91.3–91.9° W). The lagoon is 70 km long and 30 km wide, with a surface area of 1700 km². Methods Fish sampling, individual identification to the species level, and environmental variable measurements were carried out monthly at 17 sampling points. Multiple regression analysis with a backward selection procedure was used to relate fish species richness to environmental variables. Other statistical techniques, including cluster analysis and ancova , were applied to experimental data surveys. Results Among the different environmental variables, salinity was significantly and consistently related to fish species richness, whatever the period and the scale of observation. We found mainly significant negative correlations (P < 0.05) between fish species richness and salinity when sampling stations were analysed individually, and particularly for the river runoff zones with high variation in salinity throughout the year. For the entire lagoon, robust negative linear models were observed when fish species richness was organized into salinity ranges, with salinity explaining c. 8% of the variation in mean fish species richness (in a multiple regression analysis; 63–93% when considered in isolation). Main conclusions In the Terminos lagoon the relationship between fish species richness and salinity is mainly negative on any spatial scale. This result may be due partially to the penetration of freshwater fishes into estuarine areas following freshwater discharges, and partially to the dominance of estuarine taxa more able to tolerate low than high salinity values. Finally, we suggest that the ‘realized’ ecotone, where species from different origins really mix, is situated between 5 and 10‰, corresponding to the highest fish richness.     

北部湾秋季底层鱼类多样性和优势种数量的变动趋势

根据1992年、2001年和2006年秋季在北部湾进行的底拖网调查数据,对该海域鱼类的种类组成、物种多样性、优势种及其数量的变动趋势进行分析。1992年共记录鱼类171种,隶属17目77科;2001年记录鱼类156种,隶属18目71科;2006年记录157种,隶属17目67科。3个年代记录的鱼类均以鲈形目的种类数最多,其中1992年为96种(占56.14%)、2001年90种(占57.69%)和2006年89种(占56.69%)。鱼类的Pielou均匀度指数(J')和Shannon-Wiener多样性指数(H')的变化趋势一致:以2001年最高,为0.72和3.64;其次为1992年,为0.64和3.27;2006年最低,分别为0.52和2.64。丰富度指数(D)呈逐年下降的趋势:为1992年的21.03,2001年的20.74和2006年的19.61。建立非线性回归模型对北部湾3个年代出现的6种共有优势种(发光鲷Acropoma japonicum、带鱼Trichiurus haumela、二长棘鲷Parargyrops edita、黄斑鲾Leiognathus bindus、竹荚鱼Trachurus japonicus和黄带绯鲤Upeneus sulphureus)的数量变化趋势进行分析。结果表明:北部湾鱼类中的经济价值较高的优势种逐渐被低值和小型的鱼类所替代,但繁殖力较强和寿命较短的鱼类变动较小。在6种共同优势种中,黄斑鲾和发光鲷的渔获率呈上升趋势;带鱼和黄带绯鲤的渔获率呈下降趋势;而二长棘鲷和竹荚鱼的渔获率基本保持不变。研究结果表明,北部湾鱼类的优势种更替明显,总体变化趋势是k选择种类(以红笛鲷和黑印真鲨等为代表)逐渐被r选择种类(发光鲷、鲾科和天竺鱼科等为代表)所替代,即寿命长、个体大和营养级高的鱼类数量减少,寿命短、个体小和营养级较低的种类增多。     

Polychaete assemblages of a sub-arctic Newfoundland fjord: habitat, distribution, and identification

This study explores the association of 24 polychaete species with sandy and muddy habitats located in a sub-arctic fjord, and across Atlantic Canada including Labrador, Newfoundland, and the Gulf of St. Lawrence. Key characters used to facilitate species identification are also summarized. Within Bonne Bay, distinctive polychaete assemblages were associated with specific sediment types and polychaete species richness and density were significant both predictors of corresponding total (infaunal) density and species richness. Polychaetes were denser and more diverse in sandy sediments, partly because sandy locales were associated with the outer portion of the bay, and therefore were closer to the more productive and diverse Gulf of St. Lawrence. In general, species that occupied both sediment types were more widely distributed within Bonne Bay and across the region. The biogeography of most species also suggests that the Bonne Bay fauna is transitional between Labrador and Acadian biogeographic provinces.     

Quantitative assessment of fish assemblages on artificial reefs using acoustic and conventional netting methods,in Xiangshan Bay,Zhejiang Province,China

Artificial reefs are often deployed by many countries for the purpose of enhancing fishing after a period of several years. The objective of this study was to analyze the effect of a pilot artificial reef system deployment in enhancing the demersal fish assemblages, investigated using both acoustic methods and bottom trammel nets, during four years between 2011 and 2017, in Xiangshan Bay, Zhejiang Province, China. Comparisons of community indices, including fish biomass, species richness and species diversity, indicated relatively consistent trends between the control sites and the artificial reefs following their deployment in 2012. Fish density, represented by the value of the nautical area scattering coefficient, and fish biomass were significantly higher on the artificial reefs than at the control sites in 2015 and 2017, and species richness and diversity were significantly greater at the reefs from 2013 to 2017. Blackhead seabream (Acanthopagrus schlegelii) and false kelpfish (Sebastiscus marmoratus) were the dominant fishes on the artificial reefs, and the average body lengths of these two species were significantly greater 40 and 64 months after deployment. Thus, construction of the artificial reefs appears to have achieved their primary purpose as fish-attraction devices, thereby contributing to ecological restoration in Xiangshan Bay.     

Sea star (Asteroidea) association structures on the rocky reef in the Gulf of California, Mexico

Sea stars are invertebrates that play relevant roles in rocky and coral reefs: they occupy different levels in food webs and may act as top predators. There are numerous studies on taxonomy and biogeography of the class in the eastern tropical Pacific, but information about the attributes and composition of its assemblages is scant. The objectives of this study were the examination and comparison of asteroid community structure from four regions of the Gulf of California, Mexico, characterized by the presence of rocky reefs, and the search for possible associations between pairs of species. In August 2004 we visited four locations in the western gulf: Bahia de Los Angeles (29 degrees N), Santa Rosalia (27 degrees N), Loreto (26 degrees N) and La Paz (24 degrees N), and censuses sea stars using 50 m2 belt transects (N=93). Abundance and species richness was estimated, as well as diversity (H'), evenness (J') and taxonomic distinctness (delta*); then, all variables were compared among regions with analysis of variance. In addition, an ordination analysis was run looking for groups of locations with similar faunistic composition. Our results showed that Loreto Bay had the highest richness and abundance of asteroids, probably because it presents a large number of habitats and multiple food sources; these conditions seem to favor the occurrence of rare species and of detritivores. However, there were no significant interregional differences among ecological indices, nor we detected groups of locations singled out because of its species composition. Thus, community structure of sea stars in rocky areas of the Gulf of California is quite homogeneous and do not change with latitude. This is a consequence of the fact that all regions under analysis had the species Phataria unifascialis and Pharia pyramidatus as dominant in number. There were significant positive associations between three pairs of species: apparently competition is not particularly relevant to control sea star community structure in the Gulf.