Dissertation - HQ

Acknowledgements 91
This evidence and the lack of correlation with physical variables,
except for a possible accumulation in the atoll’s lee or in eddies, suggest
that larval distribution was determined by the combined effects of advection
by currents, spawning time (because it determines which currents
the larvae will be subjected to), and family-specific swimming strategies
interacting with the current. Indeed larvae did not seem to position
themselves in areas of specific hydrographic or feeding conditions, so
their swimming was probably more related to the interaction with, and
exploitation of, flow structures. And at least some larvae probably swam
because some Pomacentridae larvae, for example, were found more
than 20 km away from the nearest shore (while species with demersal
eggs were thought to stay close to shore 162,168 ). If those larvae were to
recruit, Tetiaroa was the nearest opportunity, and it would demand
some significant swimming to get there.
. . . and this is
a behaviourally
driven process
In a nutshell, no strong biophysical correlates could actually be
detected between the overall distribution of coral reef fish larvae and
hydrographic factors such as temperature, phytoplankton richness, or
local current speed. No general “law” regarding the spatial position of
larval aggregations was obvious either (close or far from shore, on the
windward or leeward side of land masses, etc.). This lack of evidence
could be caused by the limitations of currently available sampling
methods which do not resolve both metre and kilometre scale structures
at once. Such limitations will only be overcome by instruments allowing
both high frequency and large scale sampling, such as towed video
recording systems 188 . Alternatively, the spatial distribution could be the
result, seemingly random and probably chaotic, of advection by currents
together with behaviour by fish larvae. The only way to predict the
distribution of larvae in such a situation is probably that used in Paris
& Cowen 71 : small temporal and spatial scale modelling with immediate
feedback from observations. Only by progressing in small time steps is it
possible to resolve such non-linear interactions between behaviour and
currents. While the advances in physical oceanography are promising,
predicting larval advection accurately will remain impossible until we
gain, at least, a clear understanding of the behaviour of fish larvae
throughout ontogeny.
4.A Acknowledgements
The authors are grateful to the captain and crew of the N. O. Alis who
showed unweary enthusiasm and ingenuity, to the rest of the scientific
crew (C. Guigand, L. Carassou, D. Lecchini, P. Ung), to R. K. Cowen
for accepting to lend his equipment and let go some of his best crew
members for a month, to P. Torres for his help with the sorting of
MOCNESS samples, to A. Fukui, D. Johnson, J. M. Leis, M. J. Miller,
D. Richardson, and A. Suntsov for their advice on the identification of
fish larvae, and to the staff of the CRIOBE, in Moorea, for pre- and post-