Peter Mumby on Herbivorous Parrotfish
The Role of Parrotfishes and Other Herbivorous Fishes
Dr. Peter Mumby is a Professor of Coral Reef Ecology at the University of Exeter in the United Kingdom. His research group (www.ex.ac.uk/msel) carries out applied research into the factors determining the resilience of coral reefs. Much of the research is used to generate new tools for use in conservation planning such as marine reserve design algorithms and remote sensing methods.
Dr. Mumby’s paper “Thresholds and the resilience of Caribbean coral reefs”, which was published in November 2007 in the journal Nature, presented, according to Mumby, the first concrete evidence that herbivorous fishes are essential to the health of coral and, in turn, the tropical reefs built by coral. In his spare time, Dr. Mumby maintains the coral reef video web resource at www.reefvid.org, which is a potentially great resource for marine aquarists.
Dr. Mumby agreed to site down with Blue Zoo News to discuss herbivorous fishes and, in particular, the parrotfish.
BZN: Thank you Dr. Mumby for taking the time to speak with Blue Zoo News about your research dealing with herbivorous fishes. To begin, what is the role of herbivorous fishes on the world's reefs?
PM: Herbivorous fish, chiefly parrotfish and surgeonfish, are the major herbivores on coral reefs (though urchins predominate in many parts of the world that have been subjected to heavy fishing). The diet of parrotfish and surgeonfish is mostly focused on fine algal turfs that provide a highly-productive and rapidly-replaced food source. A number of parrotfishes will also consume small amounts of live coral and, in some cases, significant amounts of fleshy macroalgae or seaweed.
Experimental and comparative studies have shown that removal of all herbivores leads to a prolific bloom of algae, which, of course, isn't terribly surprising. In the Caribbean, we have shown that prevention of fishing—which mostly affects the largest fishes—can have a sufficiently large impact as to reduce the amount of seaweed in marine reserves.
ZN: Why is reducing the amount of seaweed through grazing important?
PM: The role of grazing is important because seaweed can prevent coral populations from recovering effectively. Seaweed prevents new corals from settling on the reef, and those that do manage to settle suffer reduced growth rate, reduced fecundity and, in some cases, direct overgrowth and mortality by algae. Thus, it is important to maintain a surplus of herbivores in order to facilitate coral recovery after disturbance.
BZN: What are your thoughts about the marine aquarium trade insofar as it concerns herbivorous fishes?
PM: One of the weaknesses I've observed of the marine aquarium trade and collection of fishes for aquariums is the lack of guidelines on sustainable levels of fish removal. By sustainable, I don't mean that the fishes are prevented from becoming locally-extinct; I mean sustainable from an ecosystem perspective. In order to do this we need to know how much grazing, or herbivory, is needed in order to maintain a healthy reef and then ensure that sufficient grazing is carried out on the reef after fish are removed for food or the aquarium trade. This would require a moderately small investment in research. On the positive side, however, the same research could also add ecological value to the aquarium trade. For example, it would be useful to list the ecological importance of each species as one of its key attributes. We've started doing this for parrotfishes in the Pacific. The outcome would be a boost in education and appreciation of the role these fishes play.
BZN: Are marine reserves the answer?
PM: Marine reserves definitely play an important role in protecting marine biodiversity. However, we urgently need to adapt fisheries policies to ensure that adequate grazing is maintained outside of marine reserves. Failure to do so will result in a loss of coral structure which will reduce the abundance of reef fishes where people fish. In other words, failure to maintain a high-quality reef habitat will have negative effects on fisheries production and human welfare.
BZN: Are you concerned about the populations of other herbivorous fishes that are very popular in the marine aquarium trade (I'm thinking specifically of yellow tangs, rabbitfishes and Centropyge angels)? Also, do you have any specific thoughts on the parrotfishes most commonly imported for the aquarium trade such as Cetoscarus bicolor, Scarus taeniopterus, Scarus vetula, and Sparisoma aurofrenatum?
PM: Tangs and rabbitfishes can both be important herbivores on reefs so the same issues apply. All of the parrotfish species you list are important grazers, particularly Scarus vetula, which has an extremely high bite rate and is probably the most important herbivore on many Caribbean reefs.
BZN: What would be the best management strategy for these herbivorous fishes until the research to which you refer can be carried out?
PM: It's hard to recommend management strategies without estimates of the current extraction rates of these species for the aquarium trade. In general, it would be best to limit extraction of these species as much as possible and only take juveniles rather than adults. It'd be very interested if anyone had estimates of their current extraction rates.
Do you think it best that marine aquarium industry attempt to voluntarily self-regulate collection practices? Or do you think it should be left to politicians and fisheries management folks?
PM: I think self-regulation is always preferable and we as scientists have a responsibility for providing appropriate advice on collection practices. I'd like to see collaboration between the marine aquarium industry and scientists to generate practical advice that could then be implemented by the industry.
BZN: As would we. Thank you very much for sharing your thoughts with us, Dr. Mumby. We think the willingness of marine scientists such as yourself to sit down and talk with hobbyists in forums such as this goes a long way toward promoting that collaboration. If our readers are interested in reading your excellent article in the journal Nature, where can they get a copy?
PM: Your readers can e-mail me at email@example.com for a free copy.
Be sure to see Blue Zoo News’ three part article series on Herbivorous Fishes, the first of which (titled “Queen of Green”) discusses Dr. Mumby’s research and is archived in the Resources section of the Blue Zoo Aquatics website.
Published 4 June 2008. © Blue Zoo Aquatics