6:15 PM - 7:30 PM
[BBG21-P01] Diversity index of coral distributions and its relation to physical variables in Amitori Bay, Iriomote Island, Japan.
Keywords:Coral, Diveristy index, Wave height, Soil particle, Intermediate disturbance hypothesis
Field observations were conducted to obtain data on coral distributions, sea temperature, sea salinity, wind speed, and river flow rate [Shimokawa et al., 2014]. Ocean and wave model numerical simulations and soil particle tracking analysis were conducted to obtain the spatial and temporal distributions of wave height and the numbers of soil particles with the observed physical data. Our results showed that the life forms and sizes of corals significantly varied depending on their locations in the bay, because the physical variables differed significantly among these locations.
From the results of the above observations and simulations, we calculated diversity index of coral distributions and its relation to physical variables. The diversity index, DI [Shannon, 1948; MacArthur and MacArthur, 1961, Clark & Warwick, 2001, McCune and Grace, 2002] is defined as
DI=-∑ ci log2 ci,
where ci is the ratio of i-th type coverage to total coverage. DI is a quantitative measure for the degree in which a dataset includes different types and is related closely to entropy concept in Thermodynamics. The value of DI increases when both the number of types and the evenness increase. For a given number of types, the value of DI is maximized when all types are equally abundant.
The results show that Averages of diversity index of the coral types at the mouth and inner parts of the bay are lower than average of the whole region, but average of diversity index at the intermediate part of the bay with the intermediate physical disturbances is higher than it. This seems to support the intermediate disturbance hypothesis demonstrated by Connell  which states species diversity in local area is maximized when environmental disturbances is neither too weak not too strong.
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