Fine-scale habitat use and behavior of a nearshore fish community: nursery functions, predation avoidance, and spatiotemporal habitat partitioning

We have a limited understanding of habitat use and behavior in nearshore fish communities because they are rarely observed in situ. Consequently, ecologists recommend a process-based conceptualization of nursery habitats, but lack knowledge of nursery processes on fine scales along shore, and studies in controlled settings suggest that context-dependent behaviors allow fish to balance predation avoidance with other objectives, but there is little observational corroboration of these behaviors in situ. We used a long-term dataset of underwater observations to quantify the fine-scale habitat use and behavior of a shallow estuarine fish community. We asked, 'Within species, how does behavior vary with habitat context and developmental stage?' and 'Do species partition habitats in space and time?' We found that smaller fish occupied shallower depths where predators were less abundant; smaller fish schooled in larger groups; pelagic fish schooled in larger groups in deeper water; demersal fish schooled in larger groups when occupying the water column; and species partitioned habitats by depth and season. Additionally, smaller fish were proportionally less abundant along deep shorelines created by intertidal armoring. Overall, habitat use was suggestive of nursery functions, including ontogenetic habitat shifts, provision of predator refuge, and appropriate food/predation risk tradeoffs. Additionally, fish behaved in a manner consistent with adaptive decision-making to avoid predation, and time and space may be important axes on which transient juveniles partition habitats. Some nursery functions appeared to be mediated by a shallow depth gradient, which may be compromised by shoreline infrastructure and rising sea levels along built shorelines.