Early post-settlement habitat and diet shifts and the nursery function of tidepools during Sillago spp. recruitment in Moreton Bay, Australia

Knowledge of settlement and recruitment processes is crucial for the conservation and sustainable management of commercial fish stocks, yet for some species such information is limited. We investigated the length-frequency distribution and feeding activity of 0-group Sillago whiting on mudflats in Moreton Bay, Australia, and evaluated whether permanent intertidal residence is (1) an integral component of recruitment and (2) related to the suitability of temporary microhabitats (tidepools) as primary nursery refuges. A total of 399 whiting, comprising the 3 commercially and/or recreationally important species S. analis, S. ciliata and S. maculata, were collected from intertidal pools and adjacent subtidal waters during low tide. Newly settled metamorphic larvae dominated whiting assemblages in tidepools (>80%) and fed almost exclusively on meiofaunal copepods and nematodes. It was only once metamorphosis was complete that new settlers joined the main juvenile population—i.e. they commenced tidal migrations, or they took up permanent residence in subtidal seagrass beds (>90% juveniles), and shifted their diet towards macrofaunal decapods and polychaetes. During the critical first weeks after settlement, occupation of intertidal pools seemed likely to increase fitness of whiting. Specifically, the pools may provide shelter from predation, temperature-induced increases in growth and temporally extended access to intertidal meiofauna. The latter, however, appeared to vary depending on whether copepods or nematodes were the preferred prey, and whether occupied pools were isolated or interconnected. Resource and conservation managers should consider largely structureless mud- and sandflats as primary nursery zones for Sillago populations throughout their range in the Indo-Pacific.