Immunoecology of the short neck clam Paphia malabarica (Chemnitz, 1782) in a tropical monsoon-influenced estuary

Abstract

Understanding the variability in organism's immunological response is crucial for predicting changes at population or community level. The present study investigated the immunoecology of a commercially valuable clam Paphia malabarica in a tropical monsoon-influenced estuary. Clams were collected monthly during a year cycle, which coincided with pre-monsoon (February–May), monsoon (June–September) and post-monsoon seasons (October–January). For assessment of immune functioning, selected hemocyte parameters (total hemocyte concentration, hemocyte mortality, lysosomal content, esterase activity, reactive oxygen species production, and phagocytic activity) were analyzed using flow cytometry. Simultaneously, clam's condition index, nutrients, chlorophyll a, dissolved oxygen, pH, temperature and bacterial density were also measured at the sampling site. Our results exhibited seasonal patterns in hemocyte functioning with the highest activity during the pre-monsoon season (suggestive of a suitable harvesting period) and lowest during monsoon (suggestive of a critical biological period). The critical biological period for P. malabarica was marked with compromised immune parameters inflicted by low salinity, food availability, and possibly high bacterial abundance. Also, the involvement of reproductive stress altering the hematological functioning in P. malabarica cannot be ruled out. Nutrients, dissolved oxygen, pH and temperature could not explain much of the hemocyte variability. The present study has further validated the usefulness of hemocyte as a suitable marker for understanding immunoecology of P. malabarica which is of prime importance, especially in a monsoon-influenced tropical estuarine environment. The findings of our research will be constructive in monitoring natural as well as cultivated bivalve populations of economic and ecological relevance.