The role of fishes as food: A functional perspective on predator-prey interactions

Every animal dies. In nature, mortality usually occurs due to predation by
other animals. One of the fundamental consequences of mortality is the
transfer of energy and nutrients from one organism (prey) to another
(predator). On coral reefs, these key interactions and processes, that are
essential for ecosystem functioning, are primarily mediated by fishes; up
to 53% of fishes on coral reefs can be regarded as piscivorous. To date,
piscivory on coral reefs has been primarily studied with regards to the
species piscivores feed on, and how piscivores control populations.
Consequently, understanding prey selectivity by piscivorous fishes has
been a major goal. However, prey functional traits may also be important
in understanding these ‘energy transactions’, especially in complex
ecosystems such as coral reefs. Our goal, therefore, was to quantify - at
a community level - functional traits of prey that have been shown to
influence predator-prey interactions. We found that, on average,
deep-bodied, social fishes occupy higher positions in the water column,
whereas solitary species are usually elongate and more closely associated
with the benthos. On closer examination, we found that solitary species
have a size-dependent relationship, with substratum associations shifting
to water column associations, at approximately 50 mm body length. Our
results reveal three distinct prey functional groups: cryptobenthic
substratum dwellers, solitary epibenthic, and social fishes. These groups
display significant differences in their morphologies and behaviours.
Furthermore, based on a meta-analysis of published mortality rates of
small-bodied (< 100 mm TL) reef fishes, we show that the three
groups display different mortality rates, possibly due to differential
exposure to, and potential to be captured by, different predator types.
Although fishes are widely available on coral reefs, they may not be
equally available as prey to all piscivore types. Prey are not simply
victims; they are capable of influencing potential predation through
functional traits.