A REVIEW ON IMPACTS OF INVASIVE ALIEN SPECIES ON INDIAN COASTAL ECOSYSTEMS

According to the Convention on Biological Diversity (CBD), an alien species is a species, sub-species or lower taxon, introduced outside its natural past or present distribution, which includes any part, gametes, seeds, eggs or propagules of such species that might survive and subsequently reproduce (CBD, 2002).

Invasive Alien Species (IAS) have been identified as one of the significant drivers of global biodiversity, which resulted in species and habitat loss worldwide (Sandilyan, 2016). Ever-increasing globalization and the ongoing environmental changes have facilitated the dissemination of invasive species significantly (Early et al., 2016).

All major groups including virus, fungi, algae, mosses, ferns, higher plants, invertebrates, fishes, amphibians, reptiles, birds and mammals have been recognized for their invasion potential in different habitats including wetlands. However, plants, insects and mammals comprise the most common types of invasive alien in terrestrial environment (Rejmanek and Richardson, 2000; Sujay et al., 2010), whereas in aquatic habitats, molluscs, fishes, algae, floating and submerged plants are the predominant taxa (Anil et al., 2002; Sandilyan, 2016). In general, invasive species are widely distributed in all kinds of ecosystems. Recent survey highlighted that 17% of the global land area is highly prone to invasion (except Antarctica and glaciated Greenland) (Early et al., 2016). The report also stated that 16% of globally important biodiversity-sensitive areas are highly vulnerable to bioinvasion (Early et al., 2016). I. IntroductionCentre for Biodiversity Policy and Law (CEBPOL)

Studies have well established that invasive species can influence the species composition, community structure and functions of ecosystems by repressing or excluding native species, either directly by outcompeting them for resources or indirectly by changing the way that nutrients are cycled through the bio-geo system. Most of the time the whole ecosystem may be placed at risk through knock-on effects due to invasion, which results in irretrievable loss to native species that depends on the ecosystem (GISP, 2004; Levine et al., 2003).

Wetland habitats are highly prone to invasion, especially the coastal habitats which naturally provide several avenues for the invasion (Anil et al., 2002; Sandilyan, 2016). The major pathway for coastal invasion is through ballast water (e.g. Karenia brevis), natural calamity (e.g. Lion fish Pterois volitans) accidental introduction/escape during unscientific coastal aquaculture (e.g. Litopenaeus vannamei) and seaweed culture (e.g. Kappaphycus alvarezii) (Figure 1) (Anil et al., 2002; Brigg et al., 2004). However, a number of studies highlighted about the ballast water issues. Annually, 1 2 billion tonnes of ballast w a t e r is being exchanged throughout the world. A single bulk cargo ship of 200,000 tonnes can carry up to 60,000 tonnes of ballast water (Ibrahim and Manal, 2012; Raghunathan et al., 2013). Every day, nearly 7,000 marine and coastal species travel across the world’s oceans by cargo ships, which silently carry more than 4,500+ different species including microbes, plants and small animals i n t h e i r ballast water tanks. Among them some of the species can evolve as invasive species and cause deleterious impacts to the coastal ecosystem and lead to huge economic loss (WWF, 2009; Ibrahim and Manal, 2012).

A number of studies have pointed out that marine invasion is highly harmful to ecosystem functions, native species and human health, which may also cause huge economic and biodiversity loss (Anil et al., 2002). For instance, studies highlighted that death of a large number of fishes, sea turtle, sea birds and marine mammals was reported due to harmful algal blooms (HABs) as Impacts of Invasive Alien Species on Indian coastal Ecosystem a result of untreated ballast water discharge (Pierce and Henry, 2008). The HABs, commonly known as ‘Red Tides’, have been identified as a major health hazard. More than 300 algal species which cause red tides have been identified so far, and most of the species produce toxins that are harmful to marine organisms and human. For instance, the microscopic algae Karenia brevis can kill large numbers of fish and other marine organisms including dolphins (Pierce and Henry, 2008). During blooming K. brevis produces/liberates a collection of polyether neurotoxins called brevetoxins. This substance can easily dissolve in the environment and adversely affect the habitat and wildlife of the region. A study in southern Florida disclosed the large-scale mortality of fish, marine turtle, sea birds and mammals due to brevetoxins produced by K. brevis (Pierce and Henry, 2008).

Researchers clearly state that it is very difficult to control and eradicate the aquatic invasive species that have established themselves in open waters. Only few successful examples are available pertaining to eradication, especially if the invading species was detected at a very early stage inside enclosed areas such as an island or small bay. Using biocides to eradicate the invasive species is the only viable option recommended by experts (Ibrahim and Manal, 2012). On the other hand, prevention and management have been identified as an environmentally friendly way to manage the invasive species.

Obviously, the need of the hour is for scientific planning to find an early detection and eradication of invasive species in Indian coastal habitats. A group of experts (inter- and intra-science) including taxonomists, ecologists and resource managers should be established for better prevention and effective management of marine invasion. Formulating new strategies and action plans with updated technology will be highly helpful for better management