Substrate preference and delayed settlement in northern rock sole larvae Lepidopsetta polyxystra

Abstract

We addressed the hypothesis that larval flatfish have behavioral control over the timing and habitat in which they settle. Annual and seasonal settlement patterns of northern rock sole Lepidopsetta polyxystra were characterized across varying depths and sediments in 2 nursery areas around Kodiak, Alaska, USA. These data were compared to experimental data from the laboratory, where northern rock sole larvae were reared and exposed to varying sediment sizes to determine: (1) the earliest ontogenetic stage of habitat selection, and (2) whether settlement was delayed when preferred sediment sizes were unavailable. Field data indicated that newly settled rock sole were not selecting habitat based on sediment characteristics. Rather, rock sole settled in shallow-water regions (∼5 m depth) of the nursery, where sediments were indistinguishable from surrounding sediment types and notably coarser than those in the deepest areas of the nursery. At 1 to 2 mo post-settlement, the distribution of juvenile rock sole shifted to deeper regions of the nursery, as predicted by habitat selection experiments from the laboratory. However, laboratory experiments indicated that habitat selection occurs earlier at the time of settlement, with preference for fine sediment sizes. Rock sole larvae in the laboratory also delayed settlement when exposed to coarse sediments, resulting in a significant increase in both the size- and condition-at-settlement. Therefore, despite evidence of behavioral control at settlement, biological or larger-scale physical processes may ultimately regulate quality and access to preferred benthic habitat in juvenile northern rock sole.