Abstract
This study examined echinoderm assemblages from nearshore rocky habitats for large-scale distribution patterns with specific emphasis on identifying latitudinal trends and large regional hotspots. Echinoderms were sampled from 76 globally-distributed sites within 12 ecoregions, following the standardized sampling protocol of the Census of Marine Life NaGISA project (www.nagisa.coml.org). Sample-based species richness was overall low (<1–5 species per site), with a total of 32 asteroid, 18 echinoid, 21 ophiuroid, and 15 holothuroid species. Abundance and species richness in intertidal assemblages sampled with visual methods (organisms >2 cm in 1 m2 quadrats) was highest in the Caribbean ecoregions and echinoids dominated these assemblages with an average of 5 ind m−2. In contrast, intertidal echinoderm assemblages collected from clearings of 0.0625 m2 quadrats had the highest abundance and richness in the Northeast Pacific ecoregions where asteroids and holothurians dominated with an average of 14 ind 0.0625 m−2. Distinct latitudinal trends existed for abundance and richness in intertidal assemblages with declines from peaks at high northern latitudes. No latitudinal trends were found for subtidal echinoderm assemblages with either sampling technique. Latitudinal gradients appear to be superseded by regional diversity hotspots. In these hotspots echinoderm assemblages may be driven by local and regional processes, such as overall productivity and evolutionary history. We also tested a set of 14 environmental variables (six natural and eight anthropogenic) as potential drivers of echinoderm assemblages by ecoregions. The natural variables of salinity, sea-surface temperature, chlorophyll a, and primary productivity were strongly correlated with echinoderm assemblages; the anthropogenic variables of inorganic pollution and nutrient contamination also contributed to correlations. Our results indicate that nearshore echinoderm assemblages appear to be shaped by a network of environmental and ecological processes, and by the differing responses of various echinoderm taxa, making generalizations about the patterns of nearshore rocky habitat echinoderm assemblages difficult.
Highlights
Biodiversity assessments in marine systems are of great interest from ecological, public and management standpoints
Within intertidal assemblages collected with 16x quadrats, highest abundances were found in the Variable Natural Macroalgal biomass Substrate category
Echinoderm diversity is typically higher in coastal regions than deeper waters [34,59]; while echinoderms typically are a conspicuous and abundant component within intertidal and shallow subtidal habitats, they often are not overly diverse compared to other phyla [37,60,61,62]
Summary
Biodiversity assessments in marine systems are of great interest from ecological, public and management standpoints. It has long been postulated that diversity in marine species or communities may follow latitudinal gradients with diversity peaking at the equator and declining towards higher latitudes [5], with evolutionary, historical and ecological mechanisms suggested as drivers [6] Support for this trend is evident from shallow waters to the deep-sea [7,8,9,10] and a recent meta-analysis suggests that the trend can be viewed as a generalized pattern in marine taxa [11]. As intriguing as the idea of a generalized diversity pattern in marine communities may be, it is important to better understand large-scale diversity patterns for individual taxa and habitat types This will allow for the development and further hypothesis testing needed to explain latitudinal and other large-scale marine biodiversity patterns [11,18,19,20]
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