Abstract

Within the coastal zone, oceanographic features, such as fronts, can have major effects on the abundance and distribution of larval fish. We investigated the effects of fronts on larval fish assemblages by jointly collecting physical (ADCP and CTD) and biological (larvae) data in the nearshore waters of the south coast of South Africa, on four separate neap-tide occasions. Accumulation of fish larvae at predominantly internal wave-associated fronts was observed, with higher larval densities inshore of and within the front than farther offshore. On each occasion, larvae of coastal species with pelagic eggs (Mugillidae and Sparidae) were numerically dominant at the front itself, while inshore of the front, larvae of coastal species with benthic eggs (Gobiesocidae and Gobiidae) were more abundant. Offshore catches mainly comprised Engraulidae (pelagic species with pelagic eggs) larvae, which were generally restricted to the bottom, where current velocities were onshore on each occasion. On the occasion when fast (>100 cm/s) currents prevailed, however, accumulation of the larvae of coastal species occurred offshore of the front, and larvae were mixed throughout the water column. Thus, larval occurrence at these coastal frontal systems was strongly affected by the degree of mixing by currents, which on most occasions resulted in onshore retention. The results underline the importance of frontal systems in determining the nearshore distributions of fish larvae, particularly by retaining coastal fish species in the inshore region. The environmental variability observed at these frontal systems has potential implications for larval connectivity of fish populations.

Highlights

  • The early life history of coastal marine fishes is complex, and most species have a dispersive pelagic larval stage that is followed by a settlement phase when juveniles seek suitable habitats (Moser et al, 1984; Leis, 1991a; Lecchini et al, 2005)

  • We investigated the role of coastal fronts as potential transport and accumulation mechanisms for fish larvae in nearshore habitats of the eastern Agulhas Bank along the temperate south coast of South Africa, a region that is influenced by both the largescale effects of the Agulhas Current, a major ocean current, and the more local effects of winds and tides (Schumann, 1998, 1987)

  • Our findings highlight the important contributions that life history traits and hydrodynamics play in larval transport and coastal retention associated with fronts

Read more

Summary

Introduction

The early life history of coastal marine fishes is complex, and most species have a dispersive pelagic larval stage that is followed by a settlement phase when juveniles seek suitable habitats (Moser et al, 1984; Leis, 1991a; Lecchini et al, 2005). A dispersal phase has major implications for population dynamics as it is during the pelagic larval stage that the spatial scales for adult connectivity and the. Understanding the mechanisms that influence the distribution and transport of pre-settlement larvae remains, a major challenge given the dynamic coastal environment in which dispersal takes place. Limited dispersal may be driven by oceanographic circulation and/or active larval behaviour, which can potentially serve to reduce spatial displacement (Kingsford, 1990; Cowen and Castro, 1994)

Methods
Results
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call