Impact of the changing ecology on intertidal polychaetes in an anthropogenically stressed tropical creek,India

Polychaete assemblages and associated environment of 12 strategically selected intertidal stations along the extremely polluted Thane creek on the west coast of India were studied monthly for a year and compared with past available data to investigate changes in the creek ecology due to various anthropogenic activities like industrial, domestic, and solid waste disposal along with land reclamation. Shannon’s index (H′) varied spatially from 0.4 to 1.5, Margalef richness index (d) from 0.4 to 1.1, and evenness index (J) from 0.3 to 0.7 indicating poor polychaete diversity. Ceratonereis burmensis and Lycastis indica were the most abundant and omnipresent polychaetes in the creek indicating their tolerance and adaptability to various degrees of pollution. Hydro-sedimentological investigations revealed enhancement of total nitrogen (TN) and organic carbon (C_org) load and hypoxic levels of dissolved oxygen (DO) over the years. Silt component of sediment was increasing, with proportionate decrease in clay due to various anthropogenic disturbances. Species richness was correlated positively with clay and negatively with silt. The BIO-ENV analyses indicated the strong influence of NO₃ ⁻-N, clay and TN on the distribution patterns of polychaetes. Pollution-tolerant polychaetes like Lycastis ounaryensis and Polydora tentaculata were getting replaced by more pollution-resistant species like C. burmensis in the creek due to changing sediment texture, reduced oxygen levels, and increased C_org and TN.