30. Lipid Use in the Lecithotrophic Larvae of Laternula elliptica under pH and Temperature Stress

Christine H. Bylenga (1), Vonda J. Cummings (2)*, Ken G. Ryan (1)

1 School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand 6140
2 National Institute of Water and Atmospheric Research (NIWA), Private Bag 14901, Wellington, New Zealand 6021

Background
Ocean change may impact larval development due to the increased energetic costs of acid-base regulation under ocean acidification and the maintenance of higher metabolic rates. This may strain energetic reserves, which are limited in lecithotrophic larvae, reducing larval response capacity or diverting energy from somatic growth or calcification.

Methods
The lecithotrophic larvae of the Antarctic bivalve, Laternula elliptica were raised under elevated temperature (-0.5, 0.5 and 1.5°C) and reduced pH conditions (pH 7.65). Primary lipid classes were identified and quantified in the larvae using a Thin Layer Chromatography/Flame Ionization Detection system. The use of lipids during development and under stress was determined by measuring the concentrations of different lipid classes and total lipids in newly fertilised and late stage larvae. Effects of temperature and pH conditions on D-larval metabolic rates were determined from oxygen consumption measurements.

Findings
The primary lipid classes in L. elliptica larvae were triacylglycerols and phospholipids, comprising over 85% of the total lipid content. Despite considerable depletion of both of these lipid classes during development, significant reserves remained for metamorphosis. However, lipid utilisation was not significantly different between treatments. In contrast, metabolic rates significantly increased in elevated temperature treatments, but were not affected at reduced pH.

Conclusions
Larvae of L. elliptica are well provisioned for development to the D-larval stage, with significant lipid reserves remaining for metamorphosis under end of century temperature and pH projections. The lack of significant treatment effects on lipid depletion was surprising given the increased metabolic rates. Furthermore, a companion study shows negative effects on larval growth, suggesting diversion of energetic resources away from larval development. However, increased energetic costs to maintaining acid-base balance may be met by sources other than lipids. Examination of the impacts of stressors on protein reserves is pending and those results will also be presented.