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F  I S H B  I T E R  AT E S

F1 4

What

What Is It?

BENCHMARK

Fish bite rates measure how many times herbivorous

To be developed.

fish bite a defined area of reef substrate during some

specified length of time, or how many times they

TA R G E T

bite on algal assays that are set out on the reef for a

specified time period.

To be developed.

The key functional role of herbivorous fishes on reefs,

through their grazing activity, is to keep non-encrusting

RED FL AG

algae in check, so algae do not outcompete corals for

space. High levels of grazing are necessary if corals

To be developed.

are to retain a competitive advantage.

Why Do We Measure It?

Why

Fish bite rates give an indication of the intensity

Usefulness

of herbivory -- which is probably the single most

important  process  influencing  reef  community

The feasibility of using this indicator needs to be

structure. Herbivorous fishes, through their grazing and

assessed across the MAR. If a standardized method

scraping, help constrain the growth of non-encrusting

can be agreed upon, this indicator has high potential

algae and influence algal distribution, abundance and

value as a more direct indicator of herbivory than just

species richness. Their ability to keep algae cropped

measuring the abundance of herbivores.

provides better habitat for corals to recruit and grow.

Herbivorous fish guilds are categorized according to

The fish bite rate method can be used to gauge the

how they graze. Scaridae (parrotfish) are scrapers;

effect of herbivorous fishes on algal composition.

Acanthuridae (surgeonfish) and Microspathodon

This fish-bite indicator should not be confused with

chrysurus (yellowtail damselfish) are browsers; and

Indicator F11 ­ Herbivorous Fish Abundance. That

other Pomacentridae (damselfish) are denuders. The

indicator measures fish abundance and biomass as

bite of one species can thus have quite a different

a proxy for herbivory. Measurements of bite rate more

effect than that of another species (in terms of grazing

directly assess the actual process of herbivory.

efficiency, etc.). The observation method should

capture all of these groups, provided they are in the

How

How Do We Measure It?

sample area.

This indicator can be measured in two different ways:

The herbivory assay method is biased towards

macroalgal feeding species, underestimates herbivory

(1) Observation: A diver visually counts the number

by some groups such as scraping and excavating

of fish bites during a specified time and area (e.g., 5

parrotfish and sea urchins. It also does not measure

min in a 1-m plot). Grazing rate measurements need

herbivory for some sucking and scraping species such

to be standardized for the time of day (usually made

as grazing surgeonfish.

between 10:00 a.m. and 2:00 p.m.)46.

Some researchers have noted the importance of

(2) Assays: A diver sets out a number of algal assays

consistently using neutrally colored lines, clothespins

for a specified period of time (usually 24 hrs) and

and such to avoid varying the visual attractiveness of

measures the number of bites on each assay45.

the sampling gear for fish.

Assays should contain a common, palatable species

of macroalgae and/or Thalassia (turtle grass) as a

A combination of the two metrics would provide a

common reference species. At least one such study

more balanced measure of total fish herbivory.

has occurred in the MAR, although the method has

not yet been standardized or widely used in monitoring

programs.

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