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Coastal habitats in India are especially prone to invasion by alien species, and the major avenues for the invasion are through ballast water, natural calamities or through accidental introduction/escape during unscientific coastal aquaculture and seaweed culture informs this report titled 'A review on the impacts of invasive alien species on Indian coastal ecosystems' by The National Biodiversity Authority .
An Invasive Alien Species (IAS) is any plant or animal that is introduced into an environment where it does not naturally belong. The plant or animal survives and gradually establishes itself in the new environment and multiplies rapidly, replacing the original native species that normally thrive in that environment leading to biotic homogenisation, replacement of native species and reduction in biodiversity of the region.
India has a coastline of 7,516 km of which the mainland accounts for 5,422 km while Lakshadweep, Andaman and Nicobar coasts extend 132 km and 1,962 km, respectively. Nearly 250 million Indians live within a distance of 50 km from the coastal areas of India. Several major cities of India are on/near the coastal zone and provide livelihood to several million people.
Coastal ecosystems are varied and support unique habitats such as estuaries, lagoons, mangroves, backwaters, salt marshes, mud flats, rocky shores and sandy stretches that house a number of endemic and IUCN threat category species. Indian coastal systems also support three Gulfs (Gulf of Mannar (East coast), Gulf of Kachchh and Gulf of Khambat (West coast), and three major reefs atoll, fringing and barrier which support rich coral and fish diversity and several endemic and endangered species.
The plants and animals that live in these habitats vary according to environmental factors such as salinity and temperature fluctuations. Indian coastal systems are highly biodiverse and support 844 species of marine alga (seaweeds), 14 species of sea grasses, 69 species of mangroves and 451 floral species. Animals include 5 species of sea turtles, 26 species of sea snakes, 30 species of marine mammals, 47 species of tunicates, 200 species of corals and bryozoans, 451 species of sponges, 765 species of echinoderms, 1300 marine fish, 2900 species of crustaceans and 3370 species of marine molluscs. However, much still remains to be known in terms of marine biodiversity.
Ballast water discharge can have the most deleterious impacts on marine diversity than intentional introduction and natural calamities. Shipping transfers over 80 percent of the world’s cargo and about 12 billion tonnes of ballast water throughout the global oceans each year. Ballast is defined as any solid or liquid that is brought on board ship to increase the draft and regulate the stability or to maintain stress loads.
Ballast water mainly helps in submergence of propeller and rudder for friendly steerage of the cargo ships. In earlier days, materials like rocks and metals were used as ballast, but modern ships use sea water for ballasting. Normally, when a ship unloads the cargo, it takes marine water as ballast for the return trip in order to maintain the ship’s stability and structural integrity. Whenever it again loads cargo, the ballast water is discharged into the adjacent place/port where it is going to load the cargo.
The marine/ocean water loaded for ballast purposes contains a variety of organisms starting from microorganisms to smaller chordate and aquatic plants. Many of the aquatic species die before they reach their destination because of the stressful ballasting and de-ballasting processes and the environmental conditions prevailing inside ballast tanks that are unfriendly for the survival of the species. However, some of the individuals/ species are able to survive and slowly establish themselves in these new habitats and evolve as an invasive species in due course of time and often outcompete native species and disturb the ecological balance of the native habitats thus threatening the livelihoods of the coastal communities.
While natural disasters such as tsunamis and cyclones also play an important role in introducing invasive species in marine habitats, there is very little information and documentation on the modes in which this happens.
A number of marine algae (seaweed) have turned into invasive species after being introduced into coastal ecosystems such as K. alvarezii, a native of Philippines that was introduced in India in the Gulf of Mannar Biosphere Reserve for cultivation in the mid-1990s and in the sea waters of North of Palk Bay and South of Tuticorin coast. But in due course of time K. alvarezii escaped from cultivation sites and successfully established its colony in the neighbouring areas, which has paved the way for its invasion into the coral reef ecosystem of Kurusadai Island of Gulf of Mannar.
Due to this high commercial worth, the invasion impacts of K. alvarezii on coastal ecosystems were not recognised by policy makers and park managers, but it was found that it smothered corals of this island and led to the degradation of the native corals.
Invasion of snowflake coral (Carijoa riisei) in the Indian coastal system was found to lead to degeneration of coral reefs which support 25 percent of total marine biodiversity and contribute to 10 percent of total fishery production. A number of exotic corals that have invaded Indian coastal habitats have been found to accelerate the degeneration process of native corals.
During the 1980s prawn and shrimp culture highly depended on the native species Macrobrachium rosenbergii and Penaeus monodon. But after the introduction of exotic shell fish, L. vannamei, the native species slowly faded out from the culture and natural habitats in India. The entry of L. vannamei attracted farmers because of its fast growth, low incidence of native diseases, specific pathogen-free nature, ability to tolerate high density and low salinity, availability of domesticated strains. However, outbreak of new diseases has now reduced the value of shell fish in the market.
Studies also show that many invasive species such as algae can cause red tides, and most of the species produce toxins which are harmful to marine organisms and humans. If organisms infected by the toxins are eaten by humans , it can cause severe health impacts.
Invasive alien species can also disrupt the ecological balance of ecosystems where they reside and gradually replace the existing native species not only affecting the health of marine ecosystems, but also posing a threat to livelihoods of people who depend on the ecosystems for their livelihoods.
Thus, direct economic losses can be caused by a number of marine invasive species due to reductions or complete collapse in fisheries production due to competition, predation and displacement of the commercially important fish species through invasion.
Very little or no knowledge is available on coastal habitat biodiversity before and after the bio invasions due to non-availability of detailed studies on coastal habitats as well as due to non-availability of experts (Taxonomists / Ecologists) for identifying marine invasive species.
The Subsidiary Body on Scientific, Technical and Technological Advice (SBSTTA) has pointed out some of the important areas to be addressed by the CBD signatories:
The SBSTTA (2003) has also recommended developing useful conceptual models to undertake experimental research, prevention, management, monitoring and control of invasive species in wetland ecosystems.
Other areas of intervention include: