Bio-Invasion

The exotic seaweed, Kappaphycus alvarezii was introduced in Gulf of Mannar in 2005. The K. alvarezii is red seaweed native to Phillippines and is an invasive species in the non-native environs of Gulf of Mannar.
The alga spreads mainly by fragmentation (pieces of seaweed float to new locations) and can overgrow and kill coral by smothering, shading it from sunlight and abrasion. It causes shifts from diverse coral reef to a seaweed-dominated, low-diversity reef and changes the bottom structure of the reef, reduces access to crevices and holes.

In 2007, bioinvasion of K. alvarezii was observed on branching corals of Acropora sp. in Krusadai island of Gulf of Mannar.

In October 2008, Tamil Nadu Forest Department along with SDMRI Reef Research Team observed the invasion in three islands of GoM viz. Shingle, Krusadai and Poomarichan in a minimal area of about 10 m2.

In November 2008, a team of scientists from Indian Institute of Science visited the area and confirmed the invasion and destruction to corals and seagrass beds.

The monitoring data available with SDMRI for over 5 years clearly indicate the bio-invasion by K. alvarezii in the coral reef areas of over 2.0 km2, destroying over 800 branching and massive coral colonies of Acropora cytherea, A. formosa, A. nobilis, Montipora digitata and Porites solida, size ranging from small (< 20 cm) to larger (> 80 cm) colonies.

The Government of Tamil Nadu issued orders in December 2005 [G.O. Ms. No.229, E & F (EC.3) Department dated 20.12.2005] that K. alvarezii can be cultivated by Self Help Groups (SHGs) in the seawaters North of Palk Bay and South of Tuticorin coast. The very purpose of the G.O. is to protect the key coastal habitats like corals reefs and seagrass beds and also the associated biodiversity in Gulf of Mannar and Palk Bay. However, the cultivation is practiced on the luxuriant seagrass beds on the South Palk Bay which is very near to coral reef areas of Gulf of Mannar and the algal fragments invade into reef areas.

The Ramanathpuram District Collector initiated the manual removal of invaded exotic seaweed from the coral colonies in Krusadai Island on 21.07.2010 along with officials from Forest Department, District Administration, Scientists, media and local fisher men. Thereafter, the Forest Department continued the manual removal in limited reef area invaded by K. alvarezii. However, re-growth of the algae following their removal is also be rapid due to the ability of the algae to re-grow from minute attachment points and also the low palatability of the algae to native herbivorous fishes.

A regular manual removal system is essential to save all invaded coral colonies and further monitoring of affected reef areas, which is a tremendous task with high financial implications.

Presently, MoEF sanctioned a 3 year project to SDMRI to assess the impact of exotic seaweed, K. alvarezii on corals and associated biodiversity. This is the first long term comprehensive study aiming to develop appropriate management plan to protect the affected coral and seagrass areas.