Epifaunal diversity patterns within and among seagrass meadows suggest landscape‐scale biodiversity processes

Abstract

Coastal seascapes can support high animal diversity and secondary productivity that attracts conservation interest and provides ecosystem services. Though the importance of spatial structure in marine habitats is well known, determining the dominant spatial scale for biodiversity patterns is an often‐overlooked dimension of the ecological and conservation value of seagrass meadows. We estimated biodiversity patterns at fine (0.28 m2), meadow and seascape scales to explore whether seagrass‐associated biodiversity patterns are consistent with spatial processes such as abiotic habitat filtering or metacommunity dynamics in a northeast Pacific seascape. In Barkley Sound, British Columbia, we quantified epifaunal biodiversity on eelgrass (Zostera marina) to test three hypotheses: Taxonomic diversity and composition (1) vary randomly within meadows but (2) vary systematically among meadows reflecting meadow location or environmental conditions, and (3) spatial patterns are stable over time. We sampled epifaunal invertebrates in a systematic spatial grid within nine eelgrass meadows. We found that epifaunal community composition varied as much over a few meters within the same meadow as among meadows separated by kilometers and of different sizes and wave exposures. In each meadow, we observed less than three‐quarters of the species in the regional species pool, and we observed non‐random spatial aggregation within many species. Even with spatial turnover, assemblages were more similar than predicted by null models based on random species distributions, suggesting that some species tend to co‐occur in high abundance. These spatial biodiversity patterns were not clearly explained by meadow location, area, or abiotic conditions, except that there were differences in clusters of meadows distinguished by their salinity (more marine vs. more fresh). Our results indicate that effective conservation and understanding of how seagrass can support high biodiversity and ecosystem function may require consideration of spatial connections among meadows, and not just the condition of the meadows themselves.

Temporal variation in dispersal modifies dispersal-diversity relationships in an experimental seagrass metacommunity

“…Spatial and temporal variability in dispersal, as well as variation in dispersal intensity, are likely primary drivers of alpha and beta diversity in seagrass ecosystems. There is, however, no direct evidence yet for how dispersal patterns could contribute to the spatial biodiversity patterns observed across seagrass meadows within regions (Carr et al 2011, Barnes & Ellwood 2012, Yamada et al 2014, Whippo et al 2018. Our study builds on previous work by Lee & Bruno (2009), which demonstrated that intensity and variability of grazer dispersal has a strong influence on grazer abundance, alpha diversity, and species composition.…”

“…Hereafter, we use 'dispersal' synonymous with the grazer additions. Although the spatial scale at which grazer dispersal occurs remains an active research question, grazer density does vary at the scale of both meters and kilometers (Whippo et al 2018), which is likely a product of both grazer movement and grazer reproduction. However, we note that large pulses of grazers may also occur in seagrass communities due to local grazer blooms (Whippo et al 2018).…”

“…Although the spatial scale at which grazer dispersal occurs remains an active research question, grazer density does vary at the scale of both meters and kilometers (Whippo et al 2018), which is likely a product of both grazer movement and grazer reproduction. However, we note that large pulses of grazers may also occur in seagrass communities due to local grazer blooms (Whippo et al 2018). Therefore, while we concentrate on how this experiment mimics different levels of dispersal from one isolated patch to another, the experimental results could also be interpreted as the biodiversity impacts of grazer blooms within a patch.…”

The effect of environmental gradient on biodiversity and similarity of invertebrate communities in eelgrass (Zostera marina) beds

“…Previous studies also showed some redundancy in presence/absence of the observed species among the study sites in Akkeshi (Momota & Nakaoka, ; Yamada et al, ) and other places (e.g., Whippo et al, ) as patches of eelgrass meadows are interconnected within a given system. Site‐specific community compositions can be determined not only by presence/absence of species but also by abundance of dominant species (Whippo et al, ). Therefore, the results for both abundance‐based and presence‐absence‐based RDA should be considered and that both salinity gradient and the amount of eelgrass habitats are the important components for determining the identities of species and their relative abundance.…”

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

“…While research in past decades has found evidence for direct and indirect influences of local characteristics such as habitat complexity (Orth et al 1984), primary biomass (Cébrian andDuarte 1998, Gullström et al 2012), and nutrient availability (Virnstein and Howard 1987) on faunal diversity and abundance, recent studies have focused more on regional scale or multimeadow processes such as dispersal (Whippo et al 2018, Lefcheck et al 2016, Stier et al 2019, Yeager et al 2019, and have found that the influence of local-scale factors are often overriden by regional patterns of inter-meadow connectivity (Lefcheck et al 2016, Stier et al 2019, Yeager et al 2019. This pattern has been attributed to relatively rapid life histories and high intermeadow dispersal in seagrass-associated organisms (Lefcheck et al 2016).…”