According to researchers at the ARC Centre of Excellence for Coral Reef Studies at James Cook University and the Australian Institute of Marine Science, seaweed- and algae-eating reef fish play a vital role in the health of coral reefs. Healthy coral reefs in turn help to bolster a host nation’s jobs and ecotourism industries.
The paper, “Diversity and stability of herbivorous fishes on coral reefs,” was published in the journal Ecology and analyzes 15 years of surveys across the Great Barrier Reef. It details how a diverse group of herbivorous fish ensures that seaweed and algae are kept in check on the reefs. The researchers call the collection of fish the “portfolio effect,” akin to a stock owner choosing a diverse set of stocks to ensure against losses. If one species experiences a decline, other species can prevent the algae and seaweed from multiplying and smothering the coral reef. The study points to overfishing on Caribbean reefs during the 1980s that led to an overabundance of seaweed that choked the life of the reefs. A single urchin species was all that was left to keep the seaweed in check, and when that urchin experienced a population collapse, there were no species left to control the seaweed. This in turn had negative effects on the tourism industry.
“In this research, we measured how strong the ‘portfolio effect’ was in different reef locations. We found that high biodiversity makes seaweed control twice as stable as it would be if we relied on one super-abundant species, like the sea urchin in the Caribbean,” co-author Sean Connolly said in a prepared statement. “Biodiversity reduces the risk that environmental fluctuations will push overall herbivory below the threshold that might trigger a regime shift toward seaweed-dominated reefs.”
The researchers identified three types of herbivorous fishes: territorial grazers that are attached to a specific site on the reef and bite the algae; roving grazers that move around the reefs eating algae; and scrapers, which can be found all over the reef eating algae back to the limestone surface of the reef where the algae is attached, which clears the area for corals to establish. All types of these herbivorous fish are important to the health of the reefs.
The paper “Diversity and stability of herbivorous fishes on coral reefs” by Loïc M. Thibaut, Sean R. Connolly and Hugh P.A. Sweatman is published in the latest issue of Ecology. An abstract is available here.