MARINE ECOLOGIST Dr Anjani Ganase explains the benefits of parrotfish for healthy coral reefs; and urges a ban on parrotfish harvesting. Better yet, we should choose to eat lionfish, and pass on the parrotfish.
While coral reefs are major habitat providers to an array of marine organisms, the ability of corals to continue to grow and provide their important functions is governed by a number of physical and biological parameters. Over the last fifty years, when coral reefs have suffered some of the worst degradations, scientists have discovered an important ally in keeping corals on coral reefs, the parrotfish. Parrotfish are common on coral reefs around the world. As herbivores, they spend their days grazing the reef surfaces for algae. A school of parrotfish can clear large tracts of the reef surface of algae. This action is crucial for new coral larvae to settle and grow to form new reef structure and is vital in the recovery of reefs following any disturbance that results in coral mortality and the replacement by fast-growing algae.
Parrotfish actually refer to a family of fish species with very distinctive traits. The most characteristic trait of parrotfish is their prominently fused teeth that resemble the beak of a bird or in my opinion, a badly designed set of dentures. The fused teeth allow them to scrape the surfaces of reef rock and even grind bits of coral to be passed out as sand. Examples of common parrotfish species found in the Caribbean and TT include the rainbow parrotfish (Scarus guacamaia), princess parrotfish (scarus taeniopterus) and stoplight parrotfish (sparisoma viride).
Individual species of parrotfish are easily differentiated by their colour patterns and the shape of their teeth, if one gets close enough to look. During different stages of development, parrotfish also undergo significant changes in their colourations. While most parrotfish in the Caribbean feed on algae, some also feed on coral, and less in-depth research has been done on whether parrotfish species may have a preference to the type of algae they feed on and how much. The stoplight parrotfish, for instance, tends to graze on seagrass and algae, but they are also known to feed on one of the major hard corals in the Caribbean, orbicella annularis, a major reef builder.
The importance of parrotfish in facilitating coral reef growth and the buildup of hard coral has even been traced back to prehistoric and historical times by comparing the abundance of parrotfish teeth to the coral growth rates, both taken from reef cores. Times of high parrotfish abundance correlated with high coral reef growth rates. Other major algae grazers, such as sea urchins, did not show such correspondence; the sea urchin may have played a role in reef coral maintenance, yet it was not sufficient enough to promote hard coral growth (Cramer et al 2017).
Regionally, parrotfish have been over exploited in over 70 per cent of the reefs monitored across the Caribbean, and the presence of large adult parrotfish are few and far between on the coral reefs around Tobago. While the importance of parrotfish has become more apparent throughout the Caribbean, the will to protect continues to lag. Several campaigns in recent years have been embarked upon in specific countries, such as the Pass on Parrotfish Campaign run by The Nature Conservancy in Haiti, Jamaica and St Vincent and the Grenadines. Despite this, many Caribbean countries do not actively protect parrotfish. Except for areas where there are active marine parks or through the banning of non-selective fishing methods (fish traps), this leads to unprotected reefs vulnerable to algae overgrowth after disturbance events.
Since Caribbean islands and their marine habitats – coral reefs – are especially vulnerable to the devastation of climate change that will increase thermal stress events, sea-level rise and more severe hurricanes, it is important to safeguard as many opportunities for resilience as possible. One study emphasised the importance of parrotfish when it came to the threat of climate change. Prediction models showed that if less than 10 per cent of parrotfish were harvested on a reef, the reef may be significantly more resilient, that is able to resist or recover quickly, from disturbances related to climate change, simply because there are more fish to prevent algae overgrowth and more clean surfaces were available for successful coral recruitment.
Another study showed that more beneficial to reefs is not just the number of parrotfish, but the size of the parrotfish. The study revealed that the relationship between high parrotfish biomass and low algae on the reef breaks down when the fish are small in size (even though they may be more abundant) (Schantz et al 2019). It is theorised that smaller parrotfish are less efficient at cleaning compared to the adults, as large parrotfish do a better job of cleaning reefs and aiding successful coral recruitment (Schantz et al 2019). Unfortunately, over-exploitation through overfishing typically results in the loss in larger fish first (Valles and Oxenford 2014).
While the role of the parrotfish is crucial for healthy reefs, they are not the lone saviour for coral reefs. There are other components that also need improving in tandem to the protection of the parrotfish. This includes the presence and health of hard corals on the reef or neighbouring reefs to continue to reproduce. Other factors that drive algal blooms on the reefs include nutrient pollution as a result of run off from agricultural lands or wastewater contaminations. Under these conditions, algal blooms may persevere despite a healthy parrotfish population.
Parrotfish protection does not occur in TT, and in recent time, the appetite for parrotfish has increased. Parrotfish has been seen in market stands and in the grocery. If TT takes the step to ban harvesting parrotfish, we can curb the loss of our parrotfish and therefore reduce the vulnerability of our reefs to future disturbances. We can drive the conservation of parrotfish by actively avoiding the purchase of parrotfish. Even better, let’s choose to feed on lionfish, a known invasive predator on Caribbean reefs.
Bozec, Y. M., O'Farrell, S., Bruggemann, J. H., Luckhurst, B. E., & Mumby, P. J. (2016). Tradeoffs between fisheries harvest and the resilience of coral reefs. Proceedings of the National Academy of Sciences, 113(16), 4536-4541.
Cramer, K. L., O’Dea, A., Clark, T. R., Zhao, J. X., & Norris, R. D. (2017). Prehistorical and historical declines in Caribbean coral reef accretion rates driven by loss of parrotfish. Nature Communications, 8(1), 1-8.
Shantz, A. A., Ladd, M. C., & Burkepile, D. E. (2020). Overfishing and the ecological impacts of extirpating large parrotfish from Caribbean coral reefs. Ecological Monographs, 90(2), e01403.
Valles, H., & Oxenford, H. A. (2014). Parrotfish size: a simple yet useful alternative indicator of fishing effects on Caribbean reefs?. PLoS One, 9(1), e86291.