Green2009-herbivore monitoring

Monitoring Functional Groups of Herbivorous Reef Fishes
Assigning Species to Functional Groups
The practical application of monitoring key functional groups of herbivores requires assigning each
species to a functional group in each geographic area. The following is an example of how to assign
species to functional groups, based on a case study for the Asia Pacific Region.
This study focuses on six families of herbivorous reef fishes that each play important roles in coral reef
resilience: Acanthuridae, Ephippidae, Kyphosidae, Pomacanthidae, Labridae (Tribe Scarini) and
Siganidae (see Key Families and Their Feeding Modes). Other herbivorous reef fishes are not
included because:
• Small, cryptic families (blennies and gobies) are not amenable to visual census techniques,
and are unlikely to make a significant contribution in terms of ecosystem resilience.
• Damselfishes are small, and hard to identify. They also comprise a wide variety of diets
(herbivores, detritivores, algae grazers and planktivores), and it is a complex and difficult task
to assign them to functional groups. Species that are herbivorous also tend to be small and
contribute less in terms of ecosystem resilience, because they are territorial and farm algae
for their own consumption (see Territorial Behaviour).
• While some filefishes, triggerfishes and a wrasse (Pseudodax mollucanus: Cowman et al in
press) may be herbivores, their trophic status has not been confirmed (Myers 1999, Randall et
al 1996, G.P Jones unpubl. data).
A species list for each family in the Asia Pacific Region was provided by Dr. Gerry Allen (Allen et al
2003). Each species was assigned to a functional group (see Functional Groups above) based on the
best available literature, and expert opinion (Table 1). Species that did not belong to one of these
functional groups were deleted, including species that feed exclusively on detritus (Ctenochaetus
species) or plankton (some Acanthurus and Naso species: see Key Families and Their Feeding
Modes).
Ontogenetic changes in diet were taken into account for some species (see Ontogenetic Changes in
Feeding Modes). For example, only juveniles of some species of unicornfishes were included,
because they undergo an ontogenetic change from browsers to planktivores at around 20cm SL.
However, ontogenetic changes in parrotfishes from carnivory to herbivory were not considered,
because this change occurs at such a small size (32mm SL: Bellwood 1988) that juvenile parrotfishes
that are still carnivores would not be counted using underwater visual census methods (see Monitoring
Methods below).
These species will provide the basis of a monitoring program for key functional groups of herbivores
on reefs in the Asia Pacific Region.
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