Changes in mesozooplankton community structure during Trichodesmium erythraeum bloom in the coastal waters of southwestern Bay of Bengal

Abstract

Present study addresses variability in mesozooplankton community structure (size ranges from 0.2-20 mm) during the appearance of diazotrophic marine cyanobacterium Trichodesmium erythraeum bloom in the coastal waters southeastern part of India. Zooplankton density (individuals per 10 m3) was the maximum during pre-bloom period (5.5 x 105) followed by bloom (4.9 x 105) and post-bloom period (4.3 x 105). Copepods contributed ~ 64 % of the zooplankton abundance during pre-bloom period in which calanoids were dominant (41%). Carnivore copepods (25%) (Cyclopoids and Poicilostomatoids) dominated over herbivore (23%) (Paracalanidae) during the peak bloom. Non-copepod holoplankters and meroplankters were dominant during pre-bloom period. The cladoceran, Evadne tergestina (35% of total non-copepod crustacean holoplankton) was found to be the most important species during bloom period. Among the meroplankters, cirripede nauplii (59% of the total meroplankton) were dominant form during bloom period. Co-occurrence of Trichodesmium bloom with high abundance of Penilia avirostris & Evadne tergestina and association of Acartia spinicauda and Oithona spp., in large numbers during bloom were the interesting features of this study.