Larval fish assemblages and water mass structure off the oligotrophic south-western Australian coast

Larval fish assemblages were sampled using replicated oblique bongo net tows along a five-station transect extending from inshore (18 m depth) to offshore waters (1000 m depth) off temperate south-western Australia. A total of 148 taxa from 93 teleost families were identified. Larvae of Gobiidae and Blenniidae were abundant inshore, while larvae of pelagic and reef-dwelling families, such as Clupeidae, Engraulidae, Carangidae and Labridae were common in continental shelf waters. Larvae of oceanic families, particularly Myctophidae, Phosichthyidae and Gonostomatidae, dominated offshore assemblages. Multivariate statistical analyses revealed larval fish assemblages to have a strong temporal and spatial structure. Assemblages were distinct among seasons, and among inshore, continental shelf and offshore sampling stations. Inshore larval fish assemblages were the most seasonal, in terms of species composition and abundance, with offshore assemblages the least seasonal. However, larval fish assemblages were most closely correlated to water mass, with species distributions reflecting both cross-shelf and along-shore oceanographic processes and events. Similarity profile (SIMPROF) analysis suggested the presence of twelve distinct larval fish assemblages, largely delineated by water depth and season. The strength and position of the warm, southward flowing Leeuwin Current, and of the cool, seasonal, northward flowing Capes Current, were shown to drive much of the variability in the marine environment, and thus larval fish assemblages.