It is important to know the ultimate role of small copepods in structuring mesozooplankton community pattern and diversity on an estuary-coastal gradient. Here multivariate analyses were used to elucidate this in the Godavari estuary, on the east coast of India. During May 2002, corresponding to the spring intermonsoon, mesozooplankton were sampled from 4 GPS fixed stations in the estuarine reaches of River Godavari and 19 in the coastal waters where Godavari enters the Bay of Bengal. There were 91 mesozooplankton taxa represented by 23 divergent groups. Copepods were by far the most prominent in terms of species richness, numerical abundance, and widespread distribution followed by appendicularians. Small copepods of families Paracalanidae, Acartiidae, Oithonidae, Corycaeidae, Oncaeidae, and Euterpinidae dominated. There were differing regional mesozooplankton/copepod communities, that segregated the estuary-coastal sites into different biotic assemblages: Group-I representing the estuary proper, Group-II estuary mouth and near shore, Group-III the intermediate coastal stations and Group-IV the coastal-offshore waters. Alpha (SRp, H', J', ?*) and beta diversity (MVDISP, ß, ß-dissimilarity) measures varied noticeably across these assemblages/areas. The significant correlation of small copepod abundance with total mesozooplankton abundance and biomass (mgDM.m-3) in the estuarine (r: 0.40) and coastal (r: 0.46–0.83) waters together with a regression analysis of diversity measures have revealed the importance of small copepods in the overall mesozooplankton/copepod community structure. There were ‘characterizing’ and ‘discriminating’ species, responsible for the observed assemblage patterns. Mesozooplankton/copepod community structure and the size-spectra observed during this study indicate an estuarine-coastal gradient in plankton tropho-dynamics that may shift between a microbial dominated system inside the estuary and mixotrophy in the coastal waters. The functional diversity of copepods revealed features of an effective niche sharing and efficient utilization of the coastal resources by the resident zooplankton some of which are brought out for the first time showing a tropical estuary under the influence of monsoons. The present study also illustrates the importance of, and advocates the need for, incorporating complementary or additional biodiversity measures while describing biotic communities vis-à-vis environmental gradients. |
