Marine Political Ecology Collective

The temperature–size rule predicts that rising temperatures lead to smaller
adult sizes with important consequences for fitness, but how this response
interacts with temperature-driven changes in food quality remains unclear.
Fatty acids are critical indicators of good food quality and hold the
potential to unravel these interactions, while stable isotopes can reveal
metabolic responses. In a fully crossed factorial design, the benthic copepod
Tachidius discipes was grown at 15 and 24°C and fed with fatty acid
content varying diatoms resulting from culturing Nitzschia sp. at these
respective temperatures. Our results show temperature and food quality
impacted synergistically on copepods: body and clutch size decreased by
10% and 40%, respectively, at 24°C, with good-quality food alleviating the
body size effect and increasing clutch size at 15°C. Increased copepod
Δ13C, reflecting increased metabolic demands, was found at elevated
temperatures and when fed with poor-quality food. Multiple regression
models highlighted the importance of specific ω-3 and ω-6 fatty acids
for body and clutch size, supporting our conclusion that metabolic and
food quality-mediated responses to temperature rise resulted in energetic
imbalances that mediated the interaction between food quality and the
temperature–size rule with negative consequences for reproductive output.