Goatfish Foraging Relationships

This article is written by Andy Lewis of Tevene'i Marine based in Australia. Tevene'i Marine is a Coral Reef Ecology Consultancy and Ecotourism business established by Dr. Andrew Lewis and Daniela Lewis, graduates of the Department of Marine Biology at James Cook University.

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This image  is part of a stereo pair, shot on Lizard Island, Australia. It  shows Parupeneus barberinus engaged in feeding,  being watched by a species of Labrid, Cheilinus chlorurus. All goatfish (Family Mullidae) have barbels, and they use them to sense and smell out small invertebrates from under the sediment. This is what the Parupeneus barberinus in the above shot is doing with its head buried down in the sand.


Biological Background
The images of the month illustrates an example of what marine biologists call a "multi-species foraging association". As the name
suggests, these associations consist of individuals from more than one species, which come together and simultaneously engage in feeding behaviour. These associations can be seen frequently on coral reefs, and there is considerable variation in the size and composition of the feeding schools.


The smallest associations just consist of a pair of fishes, and usually both species are benthic carnivores, such as the goatfish and the wrasses illustrated in this months images. Often, one member of the pair is the "leader" and seems to decide the direction and precise feeding locations, while the other member is the "follower" and just feeds wherever the leader does. In some cases both the leader and follower have similar diets, whereas in other associations, the follower has a different diet and often feeds opportunistically on prey disturbed by the leader. An example of the latter we have studied at Orpheus Island is the moon wrasse (Thalassoma lunare) following large parrotfish (Chlorurus microrhinos) and picking at boring invertebrates exposed when the parrotfish disturbs the reef surface as it bites algae with its powerful jaws. We found that the moon wrasses feed up to three times faster when they are in association with the parrotfish, compared to when they are feeding alone.


Other associations consist of groups of fishes from many different species. In some associations, the fishes may all share a similar diet (i.e. carnivores like Chaetodontids, Mullids, Labrids all feeding together), or consist of fishes from widely different trophic groups (i.e. carnivores and herbivores). Some of the biggest associations form when carnivores join large roving schools of herbivorous fishes - a typical school may consist of 50 parrotfish (Scaridae), 10 rabbitfish (Siganidae), 10 surgeonfish (Acanthuridae), and 2-5 individuals of goatfish, butterflyfish, wrasses, and angelfish. The whole school swims along in unison, and then at some particular place (often decided by the herbivores), the school descends to the bottom and begins to feed within a relatively small area. The interesting aspect of this behaviour is that once feeding commences, each different species adopts its particular feeding mode, with the herbivores nipping algae, the goatfish sifting sediment with their barbels, the butterflyfish eating live corals, etc. After a short time (30 seconds to 1 minute), the school ascends en masse and moves again to another location.

The composition of these multi-species foraging associations is quite flexible, with fishes entering and leaving the schools over time. At some locations, there seems to be a daily pattern - for example at Watson's Bay at Lizard Island, the rabbitfishes usually forage in pairs in the morning, but in the afternoon, form large schools of several hundred individuals (mainly Siganus doliatus, S. puellus, & S. corallinus), which also include butterflyfishes, wrasses, and goatfish.

There are several possible reasons why fishes may form these foraging groups instead of feeding alone. First, they may get access to more food, particularly in cases like the moon wrasse and the parrotfish, where the parrotfish disturbs food items that can be consumed by the smaller wrasse. Second, there is the obvious minimisation of individual predation risk that comes through schooling behaviour.

Finally, fishes may use these larger schools to reduce aggressive encounters with the territorial damselfishes which defend algal turfs over much of the reef surface. The latter can be very aggressive to single fishes (herbivores and non-herbivores) that enter their territory, but when 40 or 50 fishes enter at once to feed, the damselfish is overwhelmed and often "gives up the fight"!

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