The biological oceanography of Western Rock Lobster larvae

• Main Authors: Waite, A., Beckley, L.E., Thompson, P.A., Saunders, M., Sawstrom, C., Sachlikidis, N., Caputi, N., DeLestang, S., Jeffs, A., Barnard, R.
• Format: Conference Object
• Language: English
• Published: 2011
• Subjects: Indian; Ocean acidification
• Online Access: https://researchrepository.murdoch.edu.au/id/eprint/6659/

We examine in detail, for the first time, the biological oceanographic mechanisms affecting nutrition, growth and survival of larvae of the Western Rock Lobster while they undergo their planktonic phyllosoma phase in the Eastern Indian Ocean. The Western Rock Lobster is the most valuable single-species fishery in Australia, representing about 20% of the total value of Australia’s fisheries. Variability in settlement of puerulus stage and catch of adults has been shown to be highly correlated with the strength of the Leeuwin Current (in turn impacted by El Nino events) and westerly wind conditions. The below-average puerulus settlement for five years, including the two lowest on record, triggered a profound re-examination of mechanisms driving year class strength of larval settlement, since such fluctuations can pose a serious risk to a sustainable rock lobster industry. Here we present outcomes from the first research voyage (July 2010) of a 3-year study of the biological oceanography of the Western Rock Lobster larvae. We present a new understanding of the feeding of late-stage phyllosoma in the wild, and describe its oceanographic context. We show evidence that the phyllosoma have a preference for key prey with specific nutritional attributes, and suggest that this is directly related to the need to accumulate substantial nutritional reserves before they can metamorphose into the puerulus stage, cross the continental shelf, and settle to form the next generation of fishable adult lobsters. We propose that the autumn phytoplankton bloom within the Leeuwin Current, as identified by satellite ocean colour, is a key food resource driving production of healthy phyllosoma, and thus a strong year class. We speculate that the “Abrolhos Front” is a seasonally important feature supporting shoreward fluxes of phyllosoma. Our study directly addresses the hypothesis that productivity of the oceanic planktonic ecosystem offshore is a critical variable driving phyllosoma health and therefore recruitment success. These water masses have been shown directly to impact the ecological function of Ningaloo Reef and other iconic coastal habitats downstream. In particular, we investigate the alignment of dissolved oxygen and nitrate profiles with ocean carbonate chemistry in three dimensions on and off the continental shelf. We speculate on the origins and impacts of these signatures including the implications for ocean acidification. These are the first measurements of their kind in this region.