Seasonal oceanographic phenomenon promotes hitchhiking among the plankton in a coastal marine ecosystem: A tropical perspective

Abstract

Epibiosis among plankton communities and the role of environmental forcing therein are discussed in this study. We hypothesized that a sub-surface thermal inversion phenomenon and associated hydrographical changes during winter monsoon promoted group/species-specific epibiosis among the plankton in the western Bay of Bengal. Plankton samples were collected from discrete depths along five transects placed perpendicular to the coast. Water column profiling revealed thermal inversion below the mixed layer depth along three southern transects (APB, APV and APK) and its absence along the two northern transects (ODP and ODG). Multivariate analysis revealed a significant difference in hydrographical properties between these areas. The warmer, highly saline waters of the thermal inversion layer, sandwiched at 10–20 m, between the colder, less saline waters of surface and bottom, supported higher density and diversity of epibionts on copepods and diatoms. The density of epibionts and intensity of epibiosis were significantly lower outside the thermal inversion layer and in the northern transects. Epibionts preferred copepods over diatoms and carnivorous/omnivorous copepods over herbivorous copepods of comparable size. These results suggest that hydrographical variability associated with thermal inversion during winter monsoon support epibiosis among the plankton in the coastal waters of the western Bay of Bengal (BoB). The present investigation is the first-ever study from a coastal marine ecosystem connecting hydrographical features with epibiosis among the plankton. Further studies are warranted to explore the higher frequency of epibiosis in the thermal inversion layer, the nutrient preference and indicator properties of epibionts, and their ecological role in the coastal and open ocean ecosystems.