Numerical
analysis : The
similarity between the atolls and the
relationships between the type of atoll and
the fish population.
Here
again, the results obtained with the MDS
method (Fig. 8) were similar to
those of the PCA (Fig.9, B): on the
one hand we have Reka
Reka, the smallest lagoon, and on the other hand, Kauehi,
the largest of the lagoons on which the variables
relating to the fish were collected. Taiaro, the most
enclosed atoll, is set apart from the others.
Fig
8
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Fig.
8
- Multi Dimensional Scaling of
the atolls in terms of their fish.
AM
= Amanu, HA = Haraiki, HI = Hiti, HK = Hikueru,
KA = Kauehi, MA = Marokau, NI = Nihiru, OC = ocean,
RR = RekaReka, TA = Taiaro, TE = Tekokota, TI =
Tikehau, TK = Takapoto, TS = Tepoto Sud, TU =
Tuanake.
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Fiig
9
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Fig.
9
-
Principal components analysis of 10
atolls, 4 forced
variables and 6 trophic categories of fish. A)
correlations between the variables in the space
of the two main components. The
circle shows balanced contributions, which
correspond to the hypothetical case where the
total variability of the IVs and FVs is randomly
associated with the two main components. The
variables which extend beyond the circle of
balanced contributions therefore make large
contributions to the first two main axes. Here
we must look at the angle between these two
descriptors and the angles they form with the
main axes. The more obtuse each of these angles
is, the closer the correlation will be, and
right angles indicate a complete lack of
dependence. B) Position of the atolls in
the system of reduced axes.
AM
= Amanu, HA = Haraiki, HI = Hiti, HK = Hikueru,
KA = Kauehi, MA = Marokau, NI = Nihiru, OC = ocean,
RR = RekaReka, TA = Taiaro, TE = Tekokota, TI =
Tikehau, TK = Takapoto, TS = Tepoto Sud, TU =
Tuanake.
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-
Herbivorous,
piscivorous, planktonophagic and carnivorous
fish were all found to be associated with
the area of the atolls, as was the total
biomass of the fish (Fig.
7A). This is quite a logical finding,
since these four trophic categories account
for 82 to 99% of the total biomass in
question. Coral-eaters were more closely
associated with the log of the porosity (Fig.
9A), as was the abundance of the coral (Fig.
7A).
-
The
above findings can be summarised as follows:
-
The
more widely open the atolls are to the
surrounding ocean, the more abundant the
coral and the corallivorous fish will be
in their lagoons (Figs. 7A
et 9A).
-
The
larger the lagoons are, the greater the
biomass of the macrophytes and the
herbivorous fish they contain will be (Figs.
7A et
9A).
-
The
larger the lagoons are, the greater the
biomass of the fish and the piscivorous
fish they contain will be (Figs. 7A
et 9A).
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References :
Dufour
P. and M. Harmelin-Vivien (1997). A research program for
a typology of atoll lagoons: strategy and first results.
Proc. 8th Int. Coral Reefs Symp. Panama, H.A. Lessios (ed.),
Allen Press, N.Y., 1: 843-848.
Dufour
P., Andréfouët S, Charpy L., Garcia N. (2001) Atolls
morphometry controls nutrient regime in their lagoons. Limnology
and Oceanography 46 (2): 456-461
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Atoll_site_