Influence of commercial farming of Kappaphycus alvarezii (Rhodophyta) on native seaweeds of Gulf of Mannar, India: Evidence for policy and management recommendation

Seemingly unabated global demands for raw materials of red seaweeds for k-carrageenan have expanded commercial cultivation of Kappaphycus alvarezii in the extended areas of the tropics. However, this has also increased speculations of negative environmental effects of K. alvarezii cultivation on the native marine biota. In the present investigation the native seaweed diversity was studied from 2018–2019 in four months interval within the intertidal regions of 19 islands of the Gulf of Mannar. Data gathered were divided in to two categories, i.e. islands near to cultivation sites (2–8 km away) and far from cultivation sites (30–70 km away) revealed occurrence of 113 and 122 seaweed species respectively. Significance differences were observed only in percentage cover (F = 6.505; p = 0.013) and species richness (F = 10.312; p = 0.002) in between the two group of islands. Simpson diversity and Shannon Weaver indices were in the range of 0.870—0.884 and 2.554—2.707 respectively and no significant differences recorded between the two group of islands (p > 0.05). A Bray–Curtis Similarity index (95%) indicated a homogenous distribution of seaweed diversity. Dictyota dichotoma, Halimeda gracilis, Padina pavonica, Sargassum polycystum and Turbinaria ornata were the most common species in both groups of islands. The present study confirmed that commercial farming of K. alvarezii did not affect the native seaweeds diversity in the islands of the Gulf of Mannar.