Where were young snapper most abundant: in weak, moderate or strong currents?

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Nursery habitats support higher survival and growth for the organisms associated with them and are important during early life for many fishes and invertebrates. How they provide these benefits is often unclear.

In New Zealand, researchers assessed potential explanations for the nursery function of structurally complex habitats for post-settlement snapper, Chrysophrys auratus. They deployed Artificial Seagrass Units (ASUs), combining video observation, netting and diet analysis of associated post-settlement snapper with descriptions of potential prey in the microhabitats surrounding the ASUs.

The researchers observed no predation attempts and few potential predators, suggesting that structurally complex habitats do not serve as predation refuges for these snapper. Their diet consisted mostly of calanoid and cyclopoid copepods, which were most commonly sampled from the water column. Nearly all suspected feeding events were also observed in the water column.

Considering water velocity at each ASU, plankton sampling showed that copepods were more available as current strength increased, while netting and video observation showed that snapper abundance was highest at sites with intermediate water velocity. The researchers suggest that the interaction between water flow and food availability may present an important trade-off between energy expenditure and food intake for post-settlement snapper. Structurally complex habitats may mediate this relationship, letting snapper access sites with more food while reducing swimming costs. This proposed mechanism may also help explain the importance of estuarine nursery habitats for other species.