27-May-2020:  Invasive mussel is spreading rapidly in Kerala’s backwaters

An invasive mussel native to the South and Central American coasts – the Charru mussel (Mytella strigata) is spreading quickly in the backwaters of Kerala.

The Charru mussel is elbowing out other mussel and clam species. It is threatening the livelihoods of fishermen engaged in molluscan fisheries. The potential of Charru mussel to outcompete the lucrative clam fishery is a serious concern that urgently needs to be addressed. Though this smaller mussel is edible, the overall economic loss and impact on biodiversity is much bigger.

The rapid spread of the Charru mussel (Mytella strigata) may have been triggered by Cyclone Ockhi which struck the region in 2017.

Surveys show the presence of the Charru mussel in the Kadinamkulam, Paravur, Edava-Nadayara, Ashtamudi, Kayamkulam, Vembanad, Chettuva and Ponnani estuaries/backwaters. Ashtamudi Lake, a Ramsar site in Kollam district, remains the worst-hit.

With a population as high as 11,384 per sq metre here, it has replaced the Asian green mussel (Perna viridis) and the edible oyster Magallana bilineata (known locally as muringa).

The Charru mussel resembles the green and brown mussels but is much smaller in size. Its colour varies from black to brown, purple or dark green. In many areas, this invasive species has smothered beds of the short-neck clam. The short-necked clam fisheries in the lake had obtained an eco-label from the Marine Stewardship Council and about 3,000 people are dependent on fisheries here. In such a scenario, the fast-breeding Charru mussel could be seen as a ‘pest,’ the authors state.

2-Jan-2020: Kerala for steps to curb alien plants’ growth in NBR

The Forest and Wildlife Department is planning to adopt steps to arrest the rampant growth of invasive plants, especially Senna spectabilis, in the forest areas of the Nilgiri Biosphere Reserve (NBR), including the Wayanad Wildlife Sanctuary.

The spread of invasive plants, especially Senna spectabilis , is posing a major threat to the forest areas of the reserve, owing to its quick growth and coppicing character.

The tree species was found in nearly 10 sq km area of the 344.44 sq km sanctuary around five years ago. Now, it had invaded to more than 50 sq km of the sanctuary. A recent study of the Ferns Nature Conservation Society recorded the presence of the plant in 78.91 sq km area of the sanctuary.

The plant has started to invade the adjacent Bandipur and Nagarhole tiger reserves in Karnataka and the Mudumalai tiger reserve in Tamil Nadu.

Earlier, the plant species was planted as avenue trees in Wayanad. Due to mass flowering and drying of bamboo species in Wayanad, lots of open spaces were created which had been occupied by Senna spectabilis .

An adult tree grows up to 15 to 20 metres in a short period of time and every year distributes thousands of seeds after gregarious flowering. The thick foliage arrests the growth of other indigenous tree and grass species and causes food shortage for the wildlife population, especially herbivores. Moreover, wildlife will not feed on the leaf of the tree as it is not palatable for them.

The vayal ecosystem (marshy land) of the forest area now has this plant in large numbers. The allelochemicals produced by this plant adversely affect the germination and growth of the native species.

The Kerala Forest Research Institute (KFRI) has developed some physical and chemical measures to tackle the threat of the plant. Though we have been following the physical method to tackle the issue for the past five years, it is yet to have any desired effect.

Hence, forest departments are planning to adopt an integrated method combining physical as well as chemical measures to address the issue.

With the adjacent tiger reserves also under threat, managers of these reserves had agreed to follow similar steps to address the issue. The issue would be discussed at interstate meetings.

19-Sep-2019: Invasive species may soon wipe out Shola vegetation from Nilgiris

Expanding plantains like tea and eucalyptus along with exotic and invasive species in the Nilgiris can wipe out Shola vegetation, according to a report filed by an expert committee formed by the Madras High Court. This change in vegetation will result in loss of water sources and is already leading to massive landslides.

The Shola vegetation has become relict in Ooty Nilgiris and may vanish soon as a result of exotics and tea plantations. The committee recognises the deleterious impact of invasive species like eucalyptus, tea plantations and wattle and naturalised alien species like Lantana camara, Opuntia stricta, Chromolaena odorata, Parthenium hysterophorus and Senna spectabilis on the Shola forest and grasslands.

The wattle is replacing grasslands and Shola forests. The plantations of Eucalyptus, pines and cupressus have virtually wiped out grasslands and sholas. The massive tea gardens also replaced the vegetation.

The Shola vegetation are tropical montane forests found in the Western Ghats separated by rolling grasslands in high altitudes.

The expert committee visited the Mudumalai Tiger Reserve on August 21, 2019. Around 60 per cent (690 square kilometres) of the entire core and buffer area of the reserve is under invasion, found the committee. Three petitions were filed in the Madurai bench of the high court in 2014, 2016 and 2017 to draw the court’s attention to this invasion. The petitions were later moved to the Madras High Court, which, on January 11, formed an expert committee to look into the issue.

The domination of invasive species in the Western Ghats was between 65 and 75 per cent. No secondary or fresh growth of indigenous trees, plants or grass, which serve as food for elephants, was seen in areas occupied by invasive species.

Moreover, the attempts made by the forest department to manage the invasive alien species has had little or no success. Removal of exotics and invasive alien species and subsequent ecological restoration of weed-free landscapes requires well-knitted management structure and resources.

The committee recommended that there is an urgent need to map the extent of exotic plantations, spread of invasive alien species and loss of grasslands in each forest division of the Nilgiris.

20-Apr-2019: Indian bullfrogs take to invasive behaviour early in Andamans

Indian bullfrogs introduced in the Andaman islands are invasive, and eat native wildlife including fish and lizards. Now, experiments reveal that the frogs take to this invasive behaviour early in their lives. Even in the developmental stages, the large bullfrog tadpoles eat other native frog tadpoles.

The Indian bullfrog Hoplobatrachus tigerinus (native to the Indian subcontinent) has rapidly invaded the Andaman islands after it was introduced there in the early 2000s. In human-dominated areas, it now shares space with other native (and often endemic) frog species. The bullfrogs are prolific breeders: they have short breeding seasons, and each egg clutch can contain up to 5,750 eggs. Its tadpoles are carnivorous and eat other tadpoles (including their own species).

To discern the impacts that bullfrog tadpoles have on native frog tadpoles, researchers used a series of experiments. They first collected egg clutches (four each) of Indian bullfrogs, and native endemic frogs Microhyla chakrapanii and Kaloula ghoshi. Once the tadpoles emerged, they mixed the clutches and randomly assigned individuals to seven different ‘treatments’ or combinations in circular plastic pools containing 30 tadpoles each. One treatment contained equal numbers of all three species, three treatments comprised tadpoles of two species and three consisted of tadpoles of a single-species. The team replicated these experiments for up to four times for different treatments, observing 25 pools in total. They monitored the pools daily to detect metamorphosing tadpoles and recorded the survival of tadpoles in each pool every week.

Their results, published in Biological Invasions, reveal that Indian bullfrog tadpoles – which grew to be the largest (around 20 millimetres) – also grew the fastest. The survival of both endemic frog tadpoles reduced to zero when bullfrog tadpoles were present. In the three-species treatment too, all individuals of the endemic frog tadpoles in most pools were eaten by bullfrog tadpoles within the first week itself. The proportion of bullfrog tadpoles surviving was greater in the presence of both endemic frog tadpoles. This is worrying because other native frog species – many of which are only being described – could also be affected. Humans play a huge role in the invasive success of these frogs and urgent management actions including screening at ports of entry could help prevent their spread to other islands.

17-Dec-2017: Biodiversity under attack by invasive species

Zoological Survey of India (ZSI) has for the first time compiled a list of alien invasive animal species, totalling 157. This number excludes invasive microbe species. Of the 157 species, 58 are found on land and in freshwater habitats, while 99 are in the marine ecosystem.

Just as alien plant species such as Parthenium hysterophorus (cotton grass) and Lantana camara (Lantana) are known to harm agriculture and biodiversity, invasive animal species pose a threat to biodiversity and human well-being.

According to experts, alien species become ‘invasive’ when they are introduced deliberately or accidentally outside their natural areas, where they out-compete the native species and upset the ecological balance. Of the 58 invasive species found on land and in freshwater, there were 31 species of arthropods, 19 of fish, three of molluscs and birds, one reptile and two mammals.

Paracoccus marginatus (Papaya Mealy Bug), which belongs to Mexico and Central America but is believed to have destroyed huge crops of papaya in Assam, West Bengal and Tamil Nadu. Phenacoccus solenopsis (Cotton Mealybug) is a native of North America but has severely affected cotton crops in the Deccan. Among the invasive fish species, Pterygoplichthys pardalis (Amazon sailfin catfish) has been destroying fish populations in the wetlands of Kolkata.

Achatina fulica (African apple snail) is said to be most invasive among all alien fauna. It is a mollusc and was first reported in the Andaman and Nicobar Islands. But today it is found all across the country and is threatening the habitats of several native species.

Among the alien invasive marine species, the genus Ascidia accounts for the maximum number of species (31), followed by Arthropods (26), Annelids (16), Cnidarian (11), Bryzoans (6), Molluscs (5), Ctenophora (3), and Entoprocta (1).

Experts point to the example of Tubastrea coccinea (Orange Cup-Coral), which originated in Indo-East Pacific but has now been reported in the Andaman and Nicobar Islands, the Gulf of Kutch, Kerala and Lakshadweep.

This compilation was announced on the sidelines of the National Conference on the Status of Invasive Alien Species in India, organised by the ZSI and the Botanical Survey of India (BSI).