How is Herbivory Impacting Algal Assemblage at Rottnest Island, Western Australia with the Ongoing Climate Change?
Climate change can negatively impact temperate reefs by introducing tropical herbivores and adding top-down trophic pressure to the primary producers. Tropical herbivores are thought to be more diverse and abundant than their temperate counterparts, so the influx of macroalgae-eating herbivores into the temperate reefs raises concerns about how temperate reefs will be impacted. By using herbivore exclusion cages, the author studied if fish and urchin herbivory impacted the algal community on Rottnest Island, Western Australia. Experimental tiles were left in situ for four months from February to July 2016 at both shallow platforms and deeper tidal sea beds. Herbivory was measured by identifying the fish species in the area, filming fish feeding behavior, calculating the relative abundance of each species filmed, and using quadrats to count urchin abundance on shallow platforms. After confirming a high herbivory rate in the area, permutational multivariate analysis of variance was performed to isolate the key variables in determining fish, algae, and urchin community. Site-specific variation was identified as the key driver, and while depth played a role, it did not have as much explanatory power. Caging treatment did not produce any detectable changes. These results suggest a high degree of neutrality and randomness in determining the community structure and composition of intertidal platforms and tidal beds.