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Spatial organization of species distributions: hierarchical and scale-dependent patterns and processes in coastal seascapes

Final Report Summary - BAYESIANMETAFLATS (Spatial organization of species distributions: hierarchical and scale-dependent patterns and processes in coastal seascapes)

Understanding how the plants and animals that live in the seafloor vary in their spatial patterns of diversity and abundance is fundamental to improving knowledge of ecological processes that underpin communities, as well as advance the modelling of species distributions under realistic assumptions. Such critical knowledge, which was gathered during this project, informs both our fundamental understanding of ecosystem processes and community ecology, ecological monitoring, as well as the role of biodiversity in maintaining ecosystem functioning in coastal ecosystems.
1200 macrobenthic samples were collected.

(Objective 1) in Manukau, Tauranga, and Kaipara Harbour, New Zealand, following a pre-determined sampling scheme. We identified over 145 species, mostly bivalves, polychaetes, and crustaceans living beneath the surface of the intertidal sands, and counted 73813 individuals. In addition, 960 Chlorophyll a samples as a proxy for food availability were analysed, 960 sediment samples to caption habitat variability were processed, and 960 photo-quadrats of the sampling locations were used to describe cover of seasgrass (Zostera), shellhash, and bare sand.
Using recent multivariate spatial models (Moran’s Eigenvector Mapping; MEM), we found that benthic communities were distinctly spatially structured at four spatial scales, but there was no clear separation of the importance of environmental vs. biotic factors at these scales.

(Objective 2). A broad selection of environmental variables contributed to the large-scale variation, whereas a much-limited set explained part of the fine-scale community structure. Our results emphasize there is no prevailing scale to which environmental factors drive biodiversity and stress the importance of dissecting variation across scale to advance an understanding of processes structuring species communities and inform conservation measures.

Also, we used recently developed so-called Joint Species Distribution Models (Objective 3), to accommodate both spatial correlations within and between locations and give full inference about model parameters and the characteristics of unobserved spatially structured factors. Key is that such models enable to separate shared habitat preferences from co-occurrence patterns due to interactions, such as competition. We demonstrated the utility of these models in defining the role of species interactions across large spatial scales. Our results show the presence of species interactions beyond scales generally amenable to manipulative studies and provide a new approach allowing conservation research and measures to acknowledge and assess important ecological phenomena.

Furthermore, it is well recognized that the functional performance of individual species is affected by abundance and distribution, but the implication for multiple species that share traits influencing functional redundancy and resilience to stressors has not been resolved. Therefore, we assessed the degree of sharing of specific functional traits in these communities. We defined functional groups, based on biological traits that relate to how macrofauna modify sediment biogeochemistry and stability, and their resilience to disturbance. Results show clear spatial gradients and boundaries of abundance and distributions separating function. Our findings emphasise the importance of not only within functional group species richness, but also abundance and occurrence as a framework to investigate functional diversity and resilience of benthic seafloor communities.