Relative influence of processes structuring fjord deep-water macrofaunal communities across multiple spatial scales

We examined the processes that maintain spatially subdivided deep-basin macrobenthic communities in a New Zealand fjord. Based on previously reported quantitative taxa distribution data, we measured physical and biological processes acting at the sample scale (physical and nutritional sediment characteristics, predation), basin scale (disturbance, productivity, local connectivity) and the fjord scale (connectivity to the regional species pool). Using partial redundancy analysis (RDA), we partitioned their effects on community variability. Direct gradient analysis revealed that previously reported high-, medium- and low-diversity communities are similarly grouped according to their position along measured biotic and abiotic gradients, where 36% of community variation in niche space (i.e. after effects of distance along the fjord were removed) was explained by the full model. Variance partitioning showed that basin-scale factors explained the highest amount of variation in basin communities, followed by sample-scale and fjord-scale factors. Sample-and basin-scale factors were correlated. Examination of the residual component of community variation showed that further investigation into basin-scale processes is warranted. These data support the notion of multi-scaled control of community dynamics. Fjords may be unique in representing an 'ecotone' type habitat demonstrating processes at similar scales to those maintaining shallow soft-sediment communities, and those of deep-sea systems. Furthermore, this analysis may understate the importance of connectivity to the regional species pool (fjord-scale process) in such habitats where local extinctions may be relatively frequent.