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Exploring Australia’s northern boundary: larval fish and krill assemblages of the complex Kimberley pelagic ecosystem

Holliday, D., Beckley, L.E. and Sutton, A.L. (2011) Exploring Australia’s northern boundary: larval fish and krill assemblages of the complex Kimberley pelagic ecosystem. In: 48th Annual Conference of the Australian Marine Science Association, 3 - 7 July, Fremantle, Western Australia.


Coastal and shelf waters off the Kimberley coast, north-western Australia, experience large-amplitude tides (>10 m) which are considered to be the primary forcing mechanism driving regional circulation and influencing the ecology of the pelagic ecosystem. This study presents an examination of variability in macro-zooplankton, particularly euphausiid (krill), and larval fish assemblages, concurrent with the physical oceanography, as part of a collaborative investigation of physical forcing of productivity on the Kimberley shelf during the austral autumn. Variability was examined at a regional cross-shelf scale and at temporal scales over tidal cycles (hrs) and a spring-neap cycle (week). Both larval fishes and euphausiid assemblages were diverse (110 families and 20 species, respectively) and displayed strong cross-shelf patterns. Larval fish assemblages showed a much greater diversity and abundance in coastal waters. The high abundance of euphausiids in coastal waters was dominated by larval stages whereas the diversity of adults was highest in outer shelf and oceanic waters. There did not appear to be any evidence of frontal structures over the shelf or at the shelf break which could explain the observed cross-shelf structuring. PERMANOVA analyses revealed weak variability between assemblages associated with subsequent tides suggesting minimal net change in response to transport over a tidal cycle. Furthermore, there was no significant difference in these assemblages between spring and neap tides. An additional sampling station was occupied for 24 hrs to examine differences over a tidal cycle. High tide, which corresponded with deeper vertical mixing due to an influx of cooler, less saline water was characterised by significantly higher concentrations and diversity of larval fishes, particularly the larvae of coastal and reef-dwelling taxa (e.g. Lutjanidae, Serranidae). Furthermore, the increase in abundance of larvae of oceanic teleost taxa (e.g. Myctophidae) reflected shoreward transport with the incoming tide. This study contributes new information regarding the ecology of the Kimberley pelagic ecosystem, specifically macro-zooplankton and larval fishes, which can be used to evaluate future changes to this ecosystem related to anthropogenic disturbance.

Item Type: Conference Item
Murdoch Affiliation: School of Environmental Science
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