Effects of ocean acidification and warming on the specific dynamic action of California Grunion (Leuresthes tenuis) larvae

Abstract

Ocean acidification (OA) and Ocean Warming (OW) are ongoing environmental changes that present a suite of physiological challenges to marine organisms. Larval stages may be especially sensitive to the effects of climate change because the larval phase is a time of critical growth and development. Of particular importance to growth is Specific Dynamic Action (SDA) – the energy used in digestion, absorption, and assimilation of food. Relatively little is known about the energetics of SDA for larval fishes and even less is known about how SDA may be affected by climate change. In this study we used feeding experiments and respirometry assays to characterize the functional form of SDA for California Grunion (Leuresthes tenuis). In a second set of experiments, we tested the independent and combined effects of ocean acidification and warming on SDA. Our first experiment revealed that an elevated metabolic rate was detectable within an hour of feeding, peaked at 3–6 h post feeding, and lasted about 24 h in total. Experiments testing the effects of acidification and warming revealed that temperature generally increased the maximum rate of postprandial respiration and the total amount of energy expended via SDA. In an experiment where feeding level was the same for fish held at different temperatures, elevated pCO2 increased the maximum rate of postprandial respiration and shortened the SDA response. However, in an experiment that allowed fish to consume more food at high temperatures, effects of pCO2 on SDA were minimal. The effects of OA on SDA may depend on a combination of temperature and food availability, and the disruption of SDA with OA may be part of a chain of events where digestion and assimilation efficiency are impaired with potential consequences for growth, survival, and population replenishment.