Abstract
The tropical north-west of Australia boasts a marine environment with a diverse array of biota as well as highly dynamic oceanography because of large tidal fluctuations, seasonal monsoons, tropical cyclones and El Niño influences.
Krill, as part of the holoplankton, are influenced by such oceanographic conditions. An investigation off the Kimberley coast during the austral autumn of 2010 revealed 20 species of krill, of which three, Euphausia fallax, Euphausia sibogae and Nematoscelis gracilis, were identified as new records for the region.
Although the number of species increased from shelf to oceanic waters, concentrations of krill decreased.
Pseudeuphausia latifrons was the most abundant species off the Kimberley coast, with concentrations highest in shelf waters sampled during the night (2.84 ± 1.95 m-3). This species was also the most abundant at the 100 m and 200 m isobaths, but Stylocheiron carinatum dominated in the deeper waters (500 m, 1000 m and 2000 m stations).
In terms of environmental influences on the krill assemblages, together mean seawater density, zooplankton settled volume and depth provided the highest correlation with krill assemblages (r2=0.69, P=0.002).
Mean seawater density was used as an indicator for water masses, and two distinct water masses were identified in the study area, a warmer (300°C), higher salinity (>34.7 psu) surface layer overlayed a cooler, less saline layer.
The Kimberley coast is one of the least studied marine environments of Australia, particularly for zooplankton, and this study improves the understanding of oceanographic influences on krill diversity and distribution in this highly dynamic environment.