Bioinvasion of Kappaphycus alvarezii on corals in the Gulf of Mannar, India.

Kappaphycus alvarezii (Doty) Doty (Rhodophyta: Solieriaceae) is a Philippine-derived macroalga introduced into the Gulf of Mannar Marine Biosphere Reserve, South India for mariculture in 2000. Here we report its bioinvasion on branching corals (Acropora sp.) in the Kurusadai Island. Qualitative data collected using underwater photography clearly indicated its invasion and establishment on live and dead corals as well as coral rubbles and pavements. It specifically invaded Acropora sp. as monospecific beds with extraordinary phenotypic plasticity in the form of thallus, thickness of its major axis and lateral branching. It shows remarkable shadowing and smothering effects over the coral colonies. The primary and secondary branches are much reduced in the invaded algal colonies. Quantitative data on its live cover on corals and biomass production are also reported. These observations are discussed with available limited information on bioinvasion of K. alvarezii on coral reefs. Our findings disprove all arguments and misapprehensions reported earlier about this species as coral-friendly and as a safe candidate for mariculture for the production of carrageenan under wild conditions in the Gulf of Mannar. Our observations underscore the need for urgent reconsideration of its cultivation in a biologically diverse ecosystem, the Gulf of Mannar.