Abstract
Gastropod assemblages from nearshore rocky habitats were studied over large spatial scales to (1) describe broad-scale patterns in assemblage composition, including patterns by feeding modes, (2) identify latitudinal pattern of biodiversity, i.e., richness and abundance of gastropods and/or regional hotspots, and (3) identify potential environmental and anthropogenic drivers of these assemblages. Gastropods were sampled from 45 sites distributed within 12 Large Marine Ecosystem regions (LME) following the NaGISA (Natural Geography in Shore Areas) standard protocol (www.nagisa.coml.org). A total of 393 gastropod taxa from 87 families were collected. Eight of these families (9.2%) appeared in four or more different LMEs. Among these, the Littorinidae was the most widely distributed (8 LMEs) followed by the Trochidae and the Columbellidae (6 LMEs). In all regions, assemblages were dominated by few species, the most diverse and abundant of which were herbivores. No latitudinal gradients were evident in relation to species richness or densities among sampling sites. Highest diversity was found in the Mediterranean and in the Gulf of Alaska, while highest densities were found at different latitudes and represented by few species within one genus (e.g. Afrolittorina in the Agulhas Current, Littorina in the Scotian Shelf, and Lacuna in the Gulf of Alaska). No significant correlation was found between species composition and environmental variables (r≤0.355, p>0.05). Contributing variables to this low correlation included invasive species, inorganic pollution, SST anomalies, and chlorophyll-a anomalies. Despite data limitations in this study which restrict conclusions in a global context, this work represents the first effort to sample gastropod biodiversity on rocky shores using a standardized protocol across a wide scale. Our results will generate more work to build global databases allowing for large-scale diversity comparisons of rocky intertidal assemblages.
Highlights
It has been long and generally recognized that the diversity of coexisting species has a fundamental influence on many ecological processes, including those processes that determine the stability of the community itself [1,2]
Carnivorous gastropods were rare in all Large Marine Ecosystem regions (LME) (,5% when present), and a considerable number (30%–40%) of gastropods species with unknown trophic preferences were found in the Kuroshio Current, Mediterranean Sea and Caribbean Sea LMEs
It has been suggested that patterns of marine species over large spatial scales are not explained by one single factor but by the combination of several causes and mechanisms [65,66]
Summary
It has been long and generally recognized that the diversity of coexisting species has a fundamental influence on many ecological processes, including those processes that determine the stability of the community itself [1,2]. Any understanding of this relationship has to depart from a proper description of the distribution patterns of diversity across different spatial and temporal scales [3,4,5,6,7,8,9]. It has been shown, that the shape of the relationship might be subjected to anthropogenic influences operating at different spatial scales [10]. The impacts of global change range from climate effects on community structure, productivity and nutrient cycling to human-induced effects such as fishing pressure and the introduction of non-native species, the latter can occur through the extension of species distribution range in response to climate (e.g., [11,12,13,14,15])
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