Numerical
analysis : The
similarity between the atolls and the
relationships between the type of atoll and
the sediments,
the benthos and the fish
Here
again, the results obtained with the MDS method (Fig.
6) were similar to those of the Principal Components
Analysis (Fig. 7B). The large
atolls Kauehi and Marokau are opposed here to the
smaller atolls of South Tepoto and Reka Reka. Taiaro,
the most tightly closed atoll, is set apart from the
others.
Fig
6
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Fig.6
-
Multi Dimensional Scaling of
the atolls in terms of the sediments, the fish
and the benthos.
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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Fig
7
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Fig.
7
- Principal
components analysis on 10 atolls, 3 forced
variables and 7 internal variables relating to
the fish, the benthos and the sediments. The
projections onto the two main axes account for
29 and 26% of the total variability of the 10
atolls under consideration. A) correlations between the variables in
the space defined by the two main axes. 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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-
Two
main variables were positively associated with the area
of the lagoons: the macrophyte biomass and the fish
biomass (Fig. 7A).
-
The
organic carbon levels (%C) in the sediments
were found to decrease with the size of the
lagoons. Mollusca seem to be more abundant
on the more tightly closed atolls, whereas coral
is more abundant on the more widely open
atolls.
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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_