Modelling the effects of food limitation and temperature on the growth and reproduction of the krill Nyctiphanes australis. (5th May 2022) - Lagos, Paulo F.
Abstract: The krill Nyctiphanes australis is the most abundant and ecologically important euphausiid in southern Australia and New Zealand coastal and shelf waters. The species lives in coastal environments which are currently susceptible to shifts in temperature and productivity. Due to its abundance, it sustains many inshore fisheries and, for this reason, determining the potential outcome of future changes in sea temperature and productivity for Nyctiphanes is important. The temperature- and food-dependence of growth and reproduction of Nyctiphanes species can be made through Dynamic Energy Budget models (DEB), developed here to quantify how temperature and food availability affects growth, fecundity, egg size, and the energetic content of the eggs throughout the krill life-span. The DEB model predictions are in good agreement with measured life-history traits for the species and show that krill grows slower during winter while females do not always reach sexual maturity when temperatures are below 8 °C and food levels are low. We found that higher temperatures and low food levels decrease the energetic content and diameter of the eggs by ∼20%, affecting the length and age at which N. australis commence reproduction. Under current scenarios of future ocean warming, these results indicate that populations of N. australis are likely to decline, with potential knock-on effects on coastal marine ecosystems and inshore fisheries. Highlights: Under current ocean warming and primary productivity scenarios for the region is likely that populations of N. australis would decline. N.australis is susceptible to a reduction in food availability and higher temperatures, from developmental stages as early as the egg. Higher temperatures in combination with low food levels decrease the energetic content and diameter of the eggs by ∼20%. N.australis undergo slow growth periods during winter, time when food is scarce and temperatures are below 10 °C in Otago and below 12 °C in Tasmania.