Benthic habitat properties can delay settlement in an estuarine fish (Sciaenops ocellatus)

Settlement is the last stage of high mortality in the life cycle of demersal marine fishes, making the number of larvae that successfully settle to a benthic habitat a predictor of future population size. Habitat selection is an active settlement process for coral reef fishes, however, there has been less research about settlement in other ecosystems. This study used laboratory and field experiments to examine the relationship between size and settlement over various substrates in red drum Sciaenops ocellatus, a temperate and subtropical estuarine species. In the laboratory, vertical position of fish (4.3 to 40.0 mm standard length [SL]) was recorded in the presence of sand, oyster shells, or seagrass to determine median settlement size. Median settlement size was 12.9 mm SL for seagrass, 15.8 mm SL for sand, and 20.5 mm SL for oyster shells. To determine the size at which fish settle in the wild, vertically partitioned field enclosures were used to separate individuals (5.2 to 37.3 mm SL) in the water column (>16 cm from the sediment) from those in the seagrass (<16 cm from the sediment). Larvae in the water column were smaller than in the seagrass (9.3 vs. 14.3 mm SL). Previous studies reported that red drum reach nursery habitats at 4 mm SL, but this study suggests that they do not use structured habitats at first. Instead, this fish settles at different sizes to various habitats, which can be interpreted as evidence for active settlement.