MANGALURU: The production of bivalves, a class of marine and freshwater molluscs, along the Karnataka coast has declined by a whopping 71% in the last 15 years, which is an indicator of the fast-deteriorating water quality in the sea, a study has revealed.
While the total production of bivalves like clams, mussels and oysters was 12,952 tonnes in the year 2002, it declined to 3,845 tonnes in 2015. The sharp decline could have been due to multiple factors such as declining nutrient flow, over-extraction of shells, sand mining and impact of surface water temperature, said the study, lead-authored by Ramachandra Bhatta, former ICAR-Emeritus scientist. He is part of a committee constituted by state government’s Planning Department to conduct a study for Niti Aayog’s Goal 14: Conserve and sustainably use the oceans, seas and marine resources for sustainable development.
Bhatta said bivalves have almost vanished in Dakshina Kannada and, at present, are available to some extent in Aghanashini of Uttara Kannada district. He said bivalve is a very good indicator of water quality and production of bivalves is directly related to the nutrient flow in river valley. Construction of dams which has reduced freshwater flow into the sea has seriously hurt the productivity of the sea by starving it of vital nutrients, thus affecting marine life.
The study suggests that the decline in oyster and other freshwater bivalve catch could be addressed through farmed bivalves by borrowing technology from other parts of the country/world. Farmed bivalves could be explored and encouraged in Karnataka under the ICZM project. Also, research and development institutes could introduce technology extension services and infrastructure for culturing of bivalves in the region, he felt.
In another startling revelation, the study said that many commercial fish species, including sardine and mackerel, have almost vanished in the sea between Mangaluru and Surathkal because of industrial pollution in the recent years. The study on physical, chemical and biological aspects of seawater and sediments of the coastal belt from New Mangalore Port to Surathkal reveals high ammonia off Surathkal, high nitrite and nitrate in the near-shore waters off Kulai and high nitrite and ammonia in the harbour area. Similarly, it says high petroleum hydrocarbon (PHc) values were observed near the harbour, while phenols remained high in the near-shore waters of Kulai and Surathkal.
Significantly, high concentration of cadmium and mercury were observed off Kulai and harbour regions, respectively. A recent study by National Institute of Oceanography (NIO 2007) for the Mangalore Special Economic Zone (MSEZ) found high concentrations of heavy metals in the coastal water of Thannirubhavi- Chitrapura area. The study also points out to deteriorating levels of dissolved oxygen (DO2). In these waters, DO2 ranged from 2.52ml/ltr to 3.7ml/l, whereas 4ml/ltr to 6ml/ltr are considered healthy.