Beyond a single patch: local and regional processes explain diversity patterns in a seagrass epifaunal metacommunity

Abstract

Ecological communities are jointly structured by dispersal, density-independent responses to environmental conditions, and density-dependent biotic interactions. Metacommunity ecology provides a framework for understanding how these processes combine to determine community seagrass meadows along the British Columbia coast. We tested the hypothesis that eelgrass Zostera marina L. epifaunal invertebrate assemblages are influenced by local environmental conditions but that high dispersal rates at larger spatial scales dampen the effects of environmental differences. We used hierarchical joint species distribution modelling to understand the contribution of environmental conditions, spatial distance between meadows, and species co-occurrences to epifaunal invertebrate abundance and distribution across the region. We found that patterns of taxonomic compositional similarity among meadows were inconsistent with dispersal limitation, and meadows in the same region were often no more similar to each other than meadows over 1000 km away. Abiotic environmental conditions (temperature, dissolved oxygen) explained a small fraction of variation in taxonomic abundance patterns across the region. We found novel co-occurrence patterns among taxa that could not be explained by shared responses to environmental gradients, suggesting the possibility that interspecific interactions influence seagrass invertebrate abundance and distribution. Our results suggest that biodiversity and ecosystem functions provided by seagrass meadows reflect ecological processes occurring both within meadows and across seascapes and that management of eelgrass habitat for biodiversity may be most effective when both local and regional processes are considered.

A Biophysical Model and Network Analysis of Invertebrate Community Dispersal Reveals Regional Patterns of Seagrass Habitat Connectivity

“…In the absence of direct estimates of connectivity that can include oceanographic currents, these studies have inferred dispersal limitation from comparisons of community composition over Euclidean distances. Stark et al (2020) found low turnover in community composition over 1,000 km of coastline which suggests that dispersal is not limiting the presence of species in seagrass meadows in this region and that most meadows are likely connected by dispersal at least often enough to rescue populations from stochastic extinction. While our results show low probabilities for long distance connections, we found a large number of possible short-distance connections and few completely isolated meadows.…”

“…While our results show low probabilities for long distance connections, we found a large number of possible short-distance connections and few completely isolated meadows. Therefore, much of the Salish Sea could be connected through multi-generational steppingstone dispersal to connect distant meadows, which could explain the community composition patterns found in Stark et al (2020). Additionally, Stark et al (2020) found that the subset of taxa present in all sampled meadows represented multiple dispersal strategies, and no one strategy dominated cosmopolitan taxa.…”

“…Therefore, much of the Salish Sea could be connected through multi-generational steppingstone dispersal to connect distant meadows, which could explain the community composition patterns found in Stark et al (2020). Additionally, Stark et al (2020) found that the subset of taxa present in all sampled meadows represented multiple dispersal strategies, and no one strategy dominated cosmopolitan taxa. Our results are consistent with this finding in that any species that can disperse as larvae or rafting on debris for at least 1+ days could connect most of the Salish Sea through stepping-stone dispersal, and generalists utilizing other habitat types could potentially accomplish this even more efficiently.…”

“…species that were identified in biodiversity surveys of meadows along the coast of BC (Whippo et al, 2018;Stark et al, 2020). We considered the potential pelagic propagule duration (PD) and a daily mortality rate in the biophysical model.…”

“…These species may move as larvae, juveniles or adults through mostly passive transportation in ocean currents and settle on distant meadows of seagrass (Boström et al, 2010). Dispersal and connectivity have been suggested as one of the important drivers of local and regional biodiversity patterns in eelgrass-associated communities (France and Duffy, 2006;Yamada et al, 2014;Whippo et al, 2018;Stark et al, 2020). These inferences were based on spatial biodiversity patterns and in the absence of oceanographically informed estimates of potential connectivity.…”