Dissertation - HQ

Results 85
Figure 4.10 Concentration of reef fish larvae (as in Figure 4.6) plotted over the
mean intensity of current speed within 0-90 m, as determined by the objective
analysis (see Figure 4.4 for a representation of speeds, in the surface layer only).
continuous variable in a GLM (p = 0.001, variance explained = 9.5%).
These results are related to the two regions of high abundances which
are both to the West of the atoll (Figure 4.6 or 4.4). Assuming that
the general direction of the flow is from the South-East to the North-
West, as deduced from the objective analysis, the opposite diagonal,
passing through stations 1, 11, 15, 21, 29 and 31, separates windward
stations from leeward stations (see Figures 4.1 and 4.4). Among these
three groups (windward, leeward, and middle), the abundances are not
significantly different (Kruskal-Wallis χ 2 = 4.16, df = 2, p = 0.13). When
groups were restricted to strictly wind- and leeward stations, closer to
the island, the difference became significant (Wilcoxon rank sum test,
W = 278, p = 0.035). But the effect is still weaker than the longitudinal
gradient and may actually just be a by-product (leeward stations are,
on average, more westerly than windward ones).
Distance from shore was shown to influence the abundance of fish
larvae. Larvae of species with demersal eggs were more abundant close
to shore while larvae hatching from pelagic eggs peaked farther away
from shore 162,168 . However, at the scale of this study (from 500 m to
25 km away from the reef), distance from shore was never significantly
influencing the abundance of larvae, whether it was tested on the
total abundance or for specific groups (e.g. Gobiidae or Pomacentridae
Distance from shore
has no influence