Functional and energetic consequences of climate change on a predatory whelk

The increasing rise in sea surface temperature caused by human activities currently represents the major threat to biodiversity and natural food webs. In this study we used the Lessepsian mussel Brachidontes pharaonis, one of the most recent invaders of the Mediterranean Sea, as a model to investigate the effect of a novel prey and a chronic increase in temperatures on functional parameters of local consumers, compared to the native mytilid species Mytilaster minimus. In particular we focused on the whelk Stramonita haemastoma, a widespread Mediterranean intertidal predator that actively preys on bivalves, barnacles and limpets, by studying the direct effects of such multiple stressors on feeding and growth rate, projected into a future climate change scenario (RCP8.5) relative to 2046-2065 with higher hypothesized temperatures of 2 °C. Gastropods showed a significantly higher feeding rate (ADFR) on M. minimus at high (6.45 ± 0.43) vs low temperatures (5.15 ± 0.33) compared to B. pharaonis (2.84 ± 0.37 vs 2.48 ± 0.27). Ingestion rate (ADIR), however, recorded higher values for B. pharaonis at high (1.71 ± 0.22) and low (1.49 ± 0.16) temperatures, compared to M. minimus (0.17 ± 0.01 vs 0.14 ± 0.01). Prey significantly influenced growth rate, condition index and the length-weight relationship (LWR) of whelks, while only ADFR seemed to be influenced by higher temperatures. In conclusion the extra amount of energy from the novel prey, together with temperature side effects, successfully influenced growth rates and reproductive events, positively affecting the global fitness of whelks.