Settlement pattern of ascidians in harbour waters of Mumbai, west coast of India

The study was carried out in Mumbai (Bombay) harbour during 1995-96 by exposing perspex coupons at two study sites, namely south break waters and tidal basin. Though the ascidian species, solitary or colonial, settle throughout the year, their prevalence however, varies considerably from month to month. As many as ten species of ascidians were recorded from the two sites. Out of these, seven species, namely Symplegma reptans, S. brakenbielmi, S. viride, Diplosoma macdonaldi, Botrylloides magnicoecum, B. chevalense and Ecteinascidia sp. are colonial ascidians and Styela bicolor, Ascidia indica and Ascidia sydneiensis are solitary forms. Of these, the species namely A. sydneiensis, B. magnicoecum, B. chevalense, S. viride, D. macdonaldi and A. indica are reported for the first time from this region. Amongst these, S. reptans, B. magnicoecum and A. sydneiensis are of common occurrence. The species S. reptans and A. sydneiensis occurred throughout the year. During monsoon (June-September), the settlement of ascidians at cleaner south break waters is notably reduced, whereas, at tidal basin the colonies recorded were around 110/m super(2). At south break waters, during post-monsoon period, when water temperature reduced to 27 degree C and sea conditions are normal, the ascidians appeared in large number (max.1776/m super(2)). During pre-monsoon period, though the population density varied, the species composition remained high at both the sites. The non-monsoon month of October to May is the favourable period for ascidian settlement in Mumbai harbour.