Miss Alexia Graba-Landry1, Prof. Morgan Pratchett1, Dr. Andrew Hoey1
1ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Australia
Coral reefs are threatened by climate change as they are sensitive to increasing ocean temperatures. Herbivorous fishes play a key ecological role on coral reefs by cropping algae, allowing for recruitment and growth of corals, largely contributing to resilience. Asynchronies in responses of algal processes (growth) and herbivore processes (consumption) to increasing temperature may cause coral reefs to shift, but the direction/magnitude of this shift is unknown. It was hypothesized that algae would be more robust to increasing temperature than herbivores as photosynthesis is more thermally robust than cellular respiration, leading to potential algal overgrowth as temperatures increase.
We investigated natural feeding rates of eight herbivore species and production of algal turfs across seasonal and latitudinal temperature gradients. Next, we investigated the effect of experimental temperature (summer minimums to +1C above summer maximums) to growth and palatability of Sargassum spp., and individual herbivore consumption and metabolism of Siganus doliatus.
Across latitude, season and in tank experiments, we found no difference in feeding rates when temperatures ranged between 26C-32C. During winter months (23-24C) feeding rates slowed. There was no change to the biomass of algal turfs across all seasons. There were however, strong negative effects of increasing temperature to macroalgal survival, growth, and palatability. These results are novel as herbivore consumption exceeded macroalgal production at higher temperatures (30-32C), contrary to our hypothesis. Understanding thermal limits across trophic levels is imperative to predicting future community structure of coral reefs, and the drivers that may cause range shifts of primary producer and consumer.
Alexia is a current PhD student at the ARC Centre of Excellence for Coral Reef Studies at James Cook University. She is a Canadian native with a Bachelor of Science from the University of Winnipeg. She obtained her Honours in Marine Science and Management at Southern Cross University, Australia where she investigated the effects of ocean acidification and warming to subtropical seaweeds. Her PhD thesis focusses on the effect of increasing temperature on marine plant-herbivore (seaweed-fish) interactions on coral reefs. Specifically, as the oceans warm, how consumption by herbivores will scale with growth/primary production by primary producers.