Seasonal changes in biotic diversity and in Margalef's pigment ratio in a small pond

Summary

Although MARGALEF'S pigment ratio would be a very useful ecological tool if it accurately reflected the biotic diversity of an ecosystem, very few data have been presented in the literature to substantiate that it actually does so. In the present study, changes in the pigment ratio did not agree well with changes in biotic diversity of either total or metazoan plankton as measured by Simpson's or Shannon's indices of diversity. Pigments from dead plankters would accumulate and persist in the water column for some considerable period of time. As a consequence, changes in the pigment composition of the water column might lag behind the actual pigment composition of the plankton community. Even if pigment composition does reflect species diversity, as proposed by Margalef, measurement of the pigments within living plankters would be essential in computing the pigment ratio. The acetone extract method does not differentiate between functional pigments and pigments released from or retained within dead cells. Furthermore, changes in the diversity of total and metazoan plankton were not in agreement. It would seem that further data, from a variety of ecosystems, are needed before the value of Margalef's pigment ratio as an ecological tool can be determined.