Dissertation - HQ

Chapter 2
Detection and quantification of
marine larvae orientation in the
pelagic environment
J.-O. Irisson, C. Guigand, C. Paris
Submitted to Limnology & Oceanography: Methods
2.1 Introduction
The previous chapter highlighted that many behaviours of larval fishes
are potentially important but still very poorly described. In fact, most
information concerns coral reef fishes in their late larval stage. It also
pointed out the inclusion of oriented swimming as the natural next step
for models of the early-life of history of fish. Indeed, if larvae swim
randomly, their movement would only add noise around the passive
drifting trajectories. In contrast, modelling studies have shown that
oriented horizontal swimming greatly influences dispersal outcomes 87 .
Modelling experiments also suggested that the nature of the orientation
cue influences larval trajectories and that the sensory threshold is the
key factor determining the supply rate of larvae onto the reef 82,143 .
Therefore, to understand the dynamics of the pelagic phase, it is critical
to be able to measure the orientation of larvae throughout ontogeny
and gain further insight in the cues involved in this behaviour.
Orientation behaviour and related cues have been studied using
three methods: in situ visual observations by scuba divers 90 , in situ
fixed experiments using light traps or patch reefs where cues are manipulated
144,145 , and laboratory observations in choice chambers 103,112,115 .
These methods have shown that fish larvae orient and that cues such as
sound and chemical plumes originating from reefs can be detected and
might be used for navigation. These findings were consistent among
the studies and were the subject of recent reviews 25,58,101,146 . However,
Orientation is little
known but important
Three study
methods exist
47