The biogeography and community structure of kelp forest macroinvertebrates

Understanding species distributions and their community structure is increasingly important when taking an ecosystem‐based approach to conservation and management. However, knowledge of the distribution and community structure of species in mid‐range trophic levels (e.g. macroinvertebrates) is lacking in most marine ecosystems. Our study aimed to examine the spatial distribution and community‐level biogeographic patterns of common kelp forest–rocky reef macroinvertebrates in Southern California and to evaluate the effects of environmental gradients on these communities. Quantitative SCUBA surveys were used to estimate macroinvertebrate densities at 92 sites from 2008–2012. Non‐metric multidimensional scaling was used to evaluate spatial patterns of macroinvertebrate communities among Regions. We found that kelp forest–rocky reef macroinvertebrate communities are distinct among different island and mainland regions, and their community patterns exhibited a strong relationship with an environmental gradient (i.e. sea surface temperature) even after controlling for geographic distance between sites. High abundances of urchin species (Strongylocentrotus purpuratus and Strongylocentrotus franciscanus) were strong drivers of regional differences. Macroinvertebrate community patterns were driven by characteristic species that were typically more prevalent at warmer or colder sites. Our results provide the first quantitative analysis of macroinvertebrate community structure within the California kelp forest ecosystem. We also describe the distribution and abundance of 92 conspicuous kelp forest‐rocky reef macroinvertebrates among nine pre‐defined Regions. This study provides important preliminary information on these macroinvertebrate species that will be directly useful to inform management of invertebrate fisheries and spatial protection of marine resources.     

The Brittlestar Amphiodia urtica; A Candidate Bioindicator?

Abstract. The ophiuroid Amphiiodia urtica L yman is presently under study as a potential wastewater discharge indicator species from ocean outfalls in the Southern California Bight. On the San Pedro Shelf, the maximum abundance of A. urtica was found at depths from 30 to 100 m, and in sediment with a median grain size of 0.085 nim, 60–80% sand. 15–30% silt, 0–37% clay, and 0.2–0.5% TOC. The mean abundance of A. urtica fluctuated annually with a slight increase from 1977 through 1993.
The hypothesis was posed that the distribution and abundance of A. urtica is not influenced by an ocean outfall and its operation on the San Pedro Shelf. Based on long-term (1977–1994) and intensive (2860 samples) sampling. the hypothesis was rejected. However, the effect of the outfall is not clear because sediment bioassays from test stations and controls produced no significant differences in survivorship and growth of juveniles. Amphiodia presently occupies areas within the Zone of Initial Dilution (ZID) where it was not found during the mid-1970s and early 1980s. While recognizing that A. urtica abundance responds to proximity to the outfall, the mechanism for this response is still unclear. The application of a single species as a bioindicator is not recommended, and most certainly not without fully essing its role in community structure and function.     

Polychaete Assemblages in the San José Gulf (Chubut, Argentina), in Relation to Abiotic and Biotic Factors

Abstract. The composition and distribution of the polychaete assemblages of the San José Gulf (Chubut, Argentina) are described in relation to environmental variables using indicator species (TWINSPAN) and canonical correspondence analysis (CCA). The polychaetes were collected during a benthic cruise in October 1984. Sediments were collected at 110 sampling sites using a 0.25 m² van Veen bottom grab or by divers in near-shore areas and sieved with 1 mm mesh. A total of 73 polychaete taxa were collected and identified. Both analyses revealed the presence of four main assemblages distributed according to depth as well as bivalve and seaweed abundance gradients: ' Syllis-Eunice ' and ' Harmothoe-Eunice ' assemblages occurred at the same depths (0 –­ 185 m) and substrata (poorly sorted rock and coarse sand), but were separated by bivalve and seaweed abundance, wherby the highest abundances of bivalves and the minimum abundances of seaweeds corresponded to the ' Syllis-Eunice ' association. The ' Ninoe-Glycera ' and ' Aglaophamus- Fabriciinae indet. 6' assemblages also occurred at similar depths (0 – 60 m) and substrata (very well-sorted medium-fine sand), but differed in their composition of bivalves and seaweed abundances; the ' Aglaophamus- Fabriciinae indet. 6' association corresponded with minimum bivalve and maximum seaweed abundances.     

Horizontal spatial and temporal distribution patterns of nearshore larval fish assemblages at a temperate rocky shore

There have been no previous studies of the composition of nearshore larval fish assemblages along the coast of Portugal. We aimed to describe the composition and horizontal distribution patterns of larval fish assemblages and their temporal dynamics near a rocky reef at depths shallower than 13 m (inshore) and at two miles (3.70 km) from shore (offshore), as well as along transects perpendicular to the shoreline, from the reef to 10 miles offshore (18.52 km). Samples were taken using 5 min sub-surface trawls at the rocky shore of the Arrábida Marine Park (W Portugal). A total of 1021 larvae were collected, belonging to 61 taxa inshore and to 29 taxa offshore. Along transects, 626 larvae of 52 taxa were collected. Most larvae belonged to coastal species associated with rocky reefs. Total larval abundance and diversity were higher from May to July, which is consistent with the spawning activity of adults. Diversity and total larval abundance decreased significantly with increasing distance from shore, both in the inshore/offshore comparison and in the transects, where this decrease was evident at a very small spatial scale (within the first mile from the reef). Species assemblages differed in the pattern of distribution, with most species clearly associated to the extreme nearshore. The distribution patterns obtained were independent of the spawning mode of species. Results are discussed in the light of the possible physical mechanisms that can potentially act at the Arrábida Marine Park to facilitate larvae retention and the role of larval behaviour.     

Anthropogenic factors and habitat complexity influence biodiversity but wave exposure drives species turnover of a subtropical rocky inter‐tidal metacommunity

Coastal ecosystems are complex and species rich, but are vulnerable to degradation from a variety of anthropogenic activities. Nevertheless, information on inter‐tidal community composition in the Caribbean Basin and at other oceanic sites is lacking. Such information is essential to developing a more comprehensive understanding of rocky inter‐tidal systems and their responses to global change. The goals of this study were to determine the relative importance of environmental (wave power density, wave height), habitat (e.g. algal cover, slope, complexity of rock surfaces) and anthropogenic (distance to roads, population density) factors associated with the structure of local assemblages at multiple shore heights and the regional metacommunity of mobile invertebrates on oceanic rocky inter‐tidal habitats. Environmental characteristics associated with habitat complexity (algal cover, rock surface complexity) and human population density were most strongly associated with abundance and biodiversity of invertebrates. Species richness was positively correlated with surface complexity, but abundance was negatively correlated with both surface complexity and per cent algal cover. By contrast, abundance of invertebrates was positively correlated with human population density, and diversity was negatively correlated with human population density. Abundance of invertebrates was greatest in the mid inter‐tidal zone, whereas diversity was greatest in the lower inter‐tidal zone. Metacommunity structure was Gleasonian, but the gradient along which species turnover occurred was correlated with measures of wave exposure, rather than anthropogenic activity. Unlike in previous studies, mostly at mainland sites, human activity primarily altered dominance patterns of communities, while having relatively little effect on species richness or composition.     

Seasonal and Between-Substrate Variation in Mobile Epifaunal Community in a Multispecific Seagrass Bed of Otsuchi Bay, Japan

Abstract. A seagrass bed in Otsuchi Bay, northeastern Japan, consists of three seagrass species ( Zostera marina, Z. caulescens and Z. caespitosa ) that differ in morphology and phenology. We studied the mobile epifaunal community in the seagrass bed to examine (1) whether seasonal and between-substrate variation in the epifaunal community agrees with variation in seagrass abundance and morphological complexity, and (2) whether patterns of seasonal and between-substrate variation vary among epifaunal species. We collected mobile epifauna from each of Z. marina and Z. caulescens on 11 occasions between October 1995 and November 1996 (at 1 – 1.5 month intervals) using a hand-closing net. A total of 9 842 individuals of mobile epiphytic animals were collected and they were classified into 80 taxa. Abundance and species richness of the epifaunal community were high in summer to autumn and low in winter to spring, and diversity index and evenness were higher in Z. marina than Z. caulescens . However, patterns of seasonal and between-substrate variation in these parameters did not parallel those in seagrass abundance and complexity. Most of the dominant epifaunal species showed significant seasonal and between-substrate variation in abundance, although their patterns varied greatly among individual species. A cluster analysis recognized several distinct groups of animals showing similar seasonal and between-substrate variation. Our findings suggest that the observed variation in the epifaunal community is not determined by a single or some strong external factors but by complex interactions of multiple factors operating differently for each component species.     

Depth-stratified community zonation patterns on Gulf of Alaska rocky shores

Vertical zonation patterns have been considered ubiquitous in intertidal ecosystems but questions remain about their generality for individual taxonomic groups and over broad spatial scales, and whether they continue into adjacent shallow subtidal habitats. Taxon richness, invertebrate abundance, and macroalgal biomass were examined in the summer of 2003 along a vertical gradient in the rocky intertidal and shallow subtidal habitats around Kodiak Island, Kachemak Bay, and Prince William Sound, all within the Gulf of Alaska. Replicate samples of benthic organisms were taken in the high (～ 7 m), mid (～ 4 m) and low (～ 0 m) intertidal (relative to MLLW), and at 1, 5, 10 and 15 m water depths at three sites in each region, and identified to the lowest possible taxonomic level. Our primary goals were to assess (1) how estimates of taxon richness, invertebrate abundance, and macroalgal biomass vary among intertidal heights and subtidal depths and (2) how general these patterns are when considered across the Gulf of Alaska. Our results show that when all invertebrates were considered together, most of the variation in taxon richness was accounted for by differences among depths (i.e. intertidal heights and subtidal depths) (～ 51%), and among replicate samples within each depth (～ 26%). Little to none of the variation was accounted for by differences among sites within each region (～ 1%) or among regions themselves (～ 0%). When considered across the Gulf of Alaska, total taxon richness and organism abundance were greatest in the low intertidal/shallow subtidal and decreased with increasing height/depth. When separated by phylum and examined together with macroalgae, variation in abundance and/or biomass among depths was significant and accounted for most of the variability. Differences among regions and sites within each region were not significant and accounted for little to none of the variance. Because the pattern of zonation varied among sites within each region, it reduced the generality of a single zonation pattern for the Gulf of Alaska. Likewise, when community composition was compared among depths, geographic regions and sites within each region using multivariate analyses, vertical zonation patterns were evident at a regional scale, but high variability in these patterns among sites within each region reduced the generality of these patterns.     

Structure et variabilité de I'ichtyofaune d'une zone rocheuse protégée en Méditerranée (Pare national de Port-Cros, France)

Abstract. A Mediterranean fish assemblage has been visually censused over a period of two years from two permanent, rocky, infralittoral stations (10–15 m) which display a high habitat complexity and are located in a protected area. Six home-range categories were defined for a better understanding of the community structure which was analyzed through qualitative and quantitative data. The respective roles of different sources of variability in species composition and numerical abundance were evaluated.     

Habitat use of inter‐tidal chitons – role of colour polymorphism

This study presents a new approach to examining European chiton habitat use according to morphological characteristics. Time‐search transects were conducted on four Portuguese rocky shores at two shore levels. The chiton species, abundance and individual morphometric features were recorded and related to the substratum dominant epiphytes and surface roughness. The chiton Lepidochitona cinerea (Linnaeus 1767) was the dominant species (77%), followed by Leptochiton algesirensis (Capellini 1859) (15%) and Acanthochitona crinita (Pennant 1777) (8%). Species abundance did not vary significantly with shore level or amongst shores. Six colour morphs were considered for Lepidochitona cinerea, four for A. crinita and one for Lepidochiton algesirensis. Substratum characteristics significantly explained the variation in species and colour morph distribution. There was a high correlation between the presence/absence and type of epiphytic algae and the substratum surface roughness level. We hypothesize that three mechanisms operating either independently or in interaction may explain the non‐random distribution of colour polymorphisms according to their habitat characteristics: (i) presence of algae that are part of their diet; (ii) use of rock as shelter – for instance, crevices and cover resulting from algae fronds and; (iii) morph–rock colour matching as a camouflage mechanism to reduce predation pressure.     

Diel vertical migration of medusae in the open Southern Adriatic Sea over a short time period (July 2003)

Diel vertical migration (DVM) of medusae was investigated at a fixed station in the oligotrophic Southern Adriatic Sea at several depths during summer (July) 2003. We hypothesized that medusan DVM is considerably influenced by environmental variables such as hydrographic features, light intensities, and potential prey densities. We used short-term repetitive sampling as an approach to detail these relationships. Of the 26 species collected, the highest abundance was in the layer between the thermocline (15 m) and 100 m depth, where Rhopalonema velatum predominated, reaching the maximum count of 93 individuals per 10 m³. Seven species were observed over a wide depth range: Solmissus albescens (15–1200 m), R. velatum (0–800 m), Persa incolorata (50–1200 m), Octophialucium funerarium (200–1200 m), Arctapodema australis (200–1200 m), Amphinema rubra (100–800 m), and Rhabdoon singulare (15–600). According to the medusan weighted mean depth (WMD) calculations, the longest DVMs were noted for the deep-sea species S. albescens , O. funerarium , and A. australis . The shallowest species, Aglaura hemistoma , was primarily non-migratory. Certain medusan assemblages were associated consistently with a particular depth layer characterized by a particular light intensity. The interplay of environmental factors and trophic relationships explains some of the features of medusan migratory patterns. These findings thus contribute to understanding the variables that determine patterns of medusan vertical migratory behavior.     

Variability in the structure of epiphytic assemblages of the Mediterranean seagrass Posidonia oceanica in relation to depth

The aim of the present study was to evaluate whether the variability in the structure of the epiphytic assemblages of leaves and rhizomes of the Mediterranean seagrass Posidonia oceanica differed between depths at a large spatial scale. A hierarchical sampling design was used to compare epiphytic assemblages at two different depths (10 and 20 m) in terms of both species composition and abundance and patterns of spatial variability in the Tuscan Archipelago (North Western Mediterranean Sea, Italy). Results showed significant differences in the structure of assemblages on rhizomes and leaves at different depths. These differences were related to species composition and abundance; differences were not significant for total biomass, total percentage cover and percentage cover of animals and algae. Whereas the higher variability was observed among shoots in all the studied systems, patterns of spatial variability at the other spatial scales investigated differed between the two studied depths. Moreover, in the present study, analogous patterns between depths resulted for both the assemblages of leaves and rhizomes, suggesting that factors that change with depth can be responsible for the spatial variability of both the assemblages (leaves and rhizomes), and operate regardless of the microclimatic conditions and the structure of assemblages.     

Community structure of bathyal decapod crustaceans off South-Eastern Sardinian deep-waters (Central-Western Mediterranean)

Community structure and faunal composition of bathyal decapod crustaceans off South-Eastern Sardinian deep-waters (Central-Western Mediterranean) were investigated. Samples were collected during 32 hauls between 793 and 1598 m in depth over the 2003–2007 period. A total of 1900 decapod specimens belonging to 23 species were collected. Multivariate analysis revealed the occurrence of three faunistic assemblages related to depth: (i) an upper slope community at depths of 793–1002 m; (ii) a middle slope community at depths of 1007–1212 m and (iii) a lower slope community at depths greater 1420 m. In the upper and middle slopes the benthic ( Polycheles typhlops ) and epibenthic–endobenthic feeders (mainly Aristeus antennatus and Geryon longipes ), which eat infaunal prey, were dominant, followed by the macroplankton–epibenthic feeders such as Acanthephyra eximia and Plesionika acanthonotus . In the deepest stratum, the most remarkable feature was the prevalence of macroplankton–epibenthic feeders ( A. eximia and P. acanthonotus ). A small percentage of the benthic deep-sea lobster Polycheles sculptus was also present. The biomass presented higher values in the middle slope and declined strongly in the lower slope. There was no general pattern of mean individual weight/size versus depth among decapods, and the changes seemed to be species-specific with different trends.     

Community structure and functional traits of mollusks associated with coastal reef macroalgae in Northeastern Brazil

This study investigated the community structure and functional traits of the mollusk fauna associated with macroalgae with different thallus morphologies in a reef environment in Northeastern Brazil. A total of 15 individuals of each species of macroalgae adhered to natural substrate and 15 individuals of Padina gymnospora detached from the substrate were collected. The structural complexity of algal habitats was measured and the associated malacofauna screened and identified. All three macroalgae differed significantly in the complexity of their habitat, with Sargassum polyceratium being the most complex. A total of 823 specimens of mollusks belonging to 22 species and 11 families were recorded, of which Columbellidae was the most represented with six species. The functional trait “size” revealed that micromollusks smaller than 10 millimeters were predominant in the community; however, individuals of larger sizes (up to 24.54 millimeters) belonging to young stages of other species were also present. Eight functional trophic groups were identified, of which “carnivorous” stood out with seven species. Six functional groups of microhabitats were identified, with intra‐specific variation in habitats, while habitat expansion was documented for species not yet recorded in association with macroalgae. The structure of the molluskan community differed among the three algae species with the greatest richness, abundance, and diversity of mollusks and functional traits occurring with S. polyceratium. Community structure differed between algae adhered to natural substrate and detached algae, with the latter having lower mollusk richness and diversity, but with greater abundance of some species that remained on algal fronds after release from the reef environment. This study reinforces the importance of algal habitat for marine invertebrate fauna, especially for micromollusks that spend their entire life cycle, or part of it, in association with macroalgae.     

Habitat modification in tidepools by bioeroding sea urchins and implications for fine‐scale community structure

By creating novel habitats, habitat‐modifying species can alter patterns of diversity and abundance in marine communities. Many sea urchins are important habitat modifiers in tropical and temperate systems. By eroding rocky substrata, urchins can create a mosaic of urchin‐sized cavities or pits separated by exposed, often flat surfaces. These microhabitats appear to harbor distinct assemblages of species. We investigated how a temperate rocky intertidal community uses three small‐scale (<100 cm²) microhabitats created by or adjacent to populations of the purple sea urchin (Strongylocentrotus purpuratus): pits occupied by urchins, unoccupied pits, and adjacent flat spaces. In tidepools, flat spaces harbored the highest percent cover of algae and sessile fauna, followed by empty pits and then occupied pits. The Shannon diversity and richness of these sessile taxa were significantly higher in flat spaces and empty pits than in occupied pits. The composition of these primary space holders in the microhabitats also varied. Unlike primary space holders, mobile fauna exhibited higher diversity and richness in empty pits than in flat spaces and occupied pits, although results were not significant. The protective empty pit microhabitat harbored the highest densities of most trophic functional groups. Herbivores, however, were densest in flat spaces, concordant with high algal coverage. These results suggest the habitats created by S. purpuratus in addition to its biological activities alter community structure at spatial scales finer than those typically considered for sea urchins.     

Succession patterns of polychaetes on algal‐dominated rocky cliffs (Aegean Sea,Eastern Mediterranean)

Ecological succession has been scarcely investigated on sublittoral rocky cliffs. The few relevant studies deal with the structure of the developing community and are limited to higher taxa or sessile forms. The objective of the present study was to examine succession patterns on algal‐dominated rocky cliffs both at the structural (species composition) and functional (feeding guild composition) level, using Polychaeta, a dominant taxon in this marine habitat, as a reference group. Cement panels were seasonally installed on the rocky substratum (25–30 m depth) and sampled every 3 months over a 1‐year period. Twenty‐nine polychaete species were recorded, previously reported from the surrounding benthic community, and classified into eight feeding guilds. Most species were assigned as sessile filter‐feeders; this guild dominated in abundance and biomass. A strong effect of the length of immersion and of the seasonal onset of succession on the developed communities was assessed: species composition analyses suggested convergence into a similar organization as succession proceeds, whereas the impact of starting season on succession was stronger when analysing feeding guilds. In both cases succession was faster on panels installed in winter. The main emerging patterns were in agreement with relevant surveys of the entire benthic fauna, thus supporting the efficacy of polychaetes as a surrogate group for studying ecological succession in the benthic marine environment.     

Spatio-temporal variability and vertical distribution of a low rocky subtidal assemblage in the north-west Mediterranean

Natural assemblages show large variability at multiple scales in space and time as a consequence of several abiotic and biological factors. This study was conducted in conditions of high turbidity of the water and examined the spatio-temporal variability and the vertical distribution at two different depths of a low rocky subtidal assemblage. Algal and invertebrate organisms were sampled at a range of spatial scales extending from meters to a few kilometers, over a period of 21 months. Results indicated that patterns of distribution and abundance of organisms differed between the two depths and at the smallest spatial scales examined. These differences were due to differences in relative abundance rather than differences in composition of taxa. Results showed that assemblages varied largely among dates of sampling, suggesting that temporal variability of these organisms may be more important than previously stated. The patchy distribution and the peculiar life traits of most taxa of these assemblages allowed the concept of metapopulation and metacommunity to be applied to this system. This might have implications for predictions of the responses of subtidal assemblages to environmental changes due to anthropogenic activities.     

[已撤稿] 三亚珊瑚礁珊瑚藻种类及其空间特征与环境因子的关系

珊瑚藻是珊瑚礁生态系统中重要的功能性群体。2010年通过水肺潜水分析了三亚珊瑚礁区的珊瑚藻种类组成和丰度, 以及群落空间特征与环境因子的关系。共鉴定出3科10属25种珊瑚藻, 其中珊瑚藻科占优势地位。三亚珊瑚礁区的珊瑚藻优势种分别为叉节藻Amphiroa ephedraea、拟中叶藻Mesophyllum simulans、串胞新角石藻Neogoniolithon fosliei、中叶藻M. mesomorphum、圆锥呼叶藻Pneophyllum conicum、孔石藻Porolithon onkodes和布氏水石藻Hydrolithon boergesenii。基于多元统计的分析结果, 将调查采样站位分为近岸型和离岸型2个主要集群, 其中近岸型的珊瑚藻种类以浊度、沉积速率(0~63μm)和悬浮物耐受种类为主, 离岸型则以光依赖-沉积物敏感种类为主。以珊瑚藻种类组成和丰度为基础的群落相似性分析结果表明, 其空间变异处于显著性水平。生物与非生物变量的相关分析结果表明, 最佳两变量组合(浊度和盐度)显著影响三亚珊瑚礁区2种类型调查站位中的珊瑚藻集合。在同一个研究站位, 因受干扰程度不同, 深水处的珊瑚藻的覆盖率比浅水处高。分析结果表明, 在三亚独特的珊瑚礁区中, 自然或人为的物理干扰因素都对调节珊瑚藻群落结构非常重要。     

Relationships Between Community Structure of the Intertidal Macroinfauna and Sandy Beach Characteristics Along the Chilean Coast

Abstract. Eight sandy beaches were seasonally sampled along the coast of Chile, from ca. 21 to 42° S (about 3000 km) to study the relationship between community structure of the intertidal macroinfauna and beach characteristics. Sediment samples (0.1 m², 30 cm deep) were collected (July – September 1998 and December 1998 – January 1999) with plastic cylinders at 15 equally spaced levels along three replicated transects extending from above the drift line to the swash zone. The sediment was sieved through a 1 mm mesh and the organisms collected stored in 5 % formalin. To define beach types, Dean's parameter (Ω) was calculated from wave heights and periods, and fall velocity of sand particles from the swash zone. Crustaceans (mainly peracarids) were the most diverse group with 14 species, followed by polychaetes with 5 species. The talitrid amphipod Orchestoidea tuberculata , the cirolanid isopods Excirolana braziliensis and E. hirsuticauda and the anomuran decapod Emerita analoga were the most widely distributed and common species. Regression analyses between species richness, abundance and biomass of the whole macroinfauna versus sediment characteristics, beach face slopes and morphodynamic beach states showed no significant relationships. Thus, macroinfaunal community characteristics did not increase linearly from lower intermediate to higher intermediate or dissipative beach states as had been found before in Chile or in other coasts. A comparative analysis with data from sandy beaches of other world regions showed that the number of species inhabiting Chilean sandy beaches was generally lower, whereas total population abundances were generally higher compared with values reported elsewhere.     

Diversity of decapod crustaceans at the interface of unconsolidated seabed areas and rocky shores in tropical/subtropical Brazil

The decapod crustacean assemblages from unconsolidated seabed areas located near rocky shores in the Ubatuba region on the south-east coast of Brazil were analysed by investigating the abundance, richness, diversity and dominance of species. The relationships of the sediment and bottom-water temperature to total species abundance, richness and diversity were also evaluated. Monthly samples were taken from January 1998 through December 1999 at sites in Ubatumirim and Mar Virado. At each locality, three areas were defined as either ‘exposed’, ‘sheltered’ or ‘island’. The highest species abundance was found in the sheltered area of Ubatumirim and the exposed area of Mar Virado, and during autumn. At Ubatumirim, the highest richness occurred in the exposed area and the highest diversity near the island. At Mar Virado, the highest richness and diversity were found near the island. Autumn and winter collections yielded the highest richness but the lowest diversity. The higher diversities, which were measured near the islands and during spring and summer, were consequences of the greater evenness of the data. The areas with the highest diversity also had the most heterogeneous sediment composition, thus reinforcing the hypothesis that areas with more complex substrata support more diverse faunas.