Size and stage-dependent vertical migration patterns in reef-associated fish larvae off the eastern coast of Australia

Abstract

Larval fish have been shown to vertically migrate with ontogeny, a behaviour that influences their dispersal by exposing the larvae to currents with different velocities at different stages of development. Most studies have focused on studying the vertical migration of tropical reef fishes, that have been shown in general to migrate downwards with ontogeny. Here we investigated if similar ontogenetic vertical migration patterns also occur for seven families of temperate reef fish along the eastern coast of Australia, sampling at three depth ranges (0–1 m, 5–50 m, 51–100 m) across sixteen stations along the continental shelf, and eight within cold-core eddies. Larval fish were identified to the lowest taxonomic level possible, their standard length measured, and ontogenetic stage classified to preflexion, flexion or postflexion. Generalised linear models were used to determine if the larval fish exhibited patterns of vertical migration with ontogeny and length. Four families (Labridae, Serranidae, Scorpaenidae, and Synodontidae) exhibited a downwards migration with ontogeny similar to vertical distribution patterns seen in tropical reef fish studies, Mullidae displayed different vertical migration patterns within eddies compared to coastal waters, and two families showed no ontogenetic vertical migration (Pomacentridae and Scaridae). For all families other than Scaridae, the larvae inside an eddy were longer suggesting larval retention. The vertical migration patterns observed, while varying among taxa, show that reef-associated larval fish off the eastern Australian coast do change their depth with ontogeny. The results of this study will be useful in parameterising connectivity modelling studies for these temperate reef-associated families.