7 PM | Cleaning Mumbai’s coastal water, naturally | 24th August, 2019

Context: artificial reefs and their significance in coastal areas

• Submerged shipwrecks are the most common form of artificial reef. Oil and gas platforms, bridges, lighthouses, and other offshore structures often function as artificial reefs.
• Marine resource managers also create artificial reefs in underwater areas that require a structure to enhance the habitat for reef organisms, including soft and stony corals and the fishes and invertebrates that live among them.
• Materials used to construct artificial reefs have included rocks, cinder blocks, and even wood and old tires. Nowadays, several companies specialize in the design, manufacture, and deployment of long-lasting artificial reefs that are typically constructed of limestone, steel, and concrete.

Need for artificial reefs in coastal areas:

• Industrialization: Rapid industrialization has taken place along the coastline of India. Among the coastlines, industrial pollution is recorded high on coast of West Bengal, Tamil Nadu, Gujarat, Maharashtra and Andhra Pradesh.
• Municipal solid waste: Municipal waste consists of degradable and non-degradable waste which comprises of plastic, rubber, glass, heavy metals and so on. The discarded plastic waste leads to entanglement, suffocation and ingestion of aquatic life.
• Consumption of plastic by the marine animals causes disruption of the endocrine system and reduction in reproduction rate. Heavy metals such as mercury, lead, nickel, arsenic, and cadmium, could also accumulate in the tissues of many species in a bio accumulation process.
• Complexity:The human impacts on climate, habitats, species and the air and water quality are complex inter-connected problems. This means there are never any simple solutions or silver bullets.
• Being a coastal state, Maharashtra is bestowed with a coast line of about 720 kms. Thane, Mumbai, Raigad, Ratnagiri and Sindhudurg districts are all located along the coastal front in Maharashtra.
• The coastal and creeks water quality is deteriorating due to disposal of partially treated sewage, open drains water as well as industrial wastewater which is today’s major environmental concern.
• Water quality: The Mumbai and Thane saline coastal waters have remained steady in the water quality for over a decade, but unfortunately have hovered within the ‘polluted’ grade of the Water Quality Index.
• It is estimated that nearly 250 million people live within area of 50 km from the coastline of India. This coastline supports a huge human population, which is dependent on the rich coastal and marine resources for economic growth. So with increasing population increases pollution in general and particularly marine pollution.

Types of Artificial reefs:

• Wrecks and large steel structures: Coral reef organisms grow well on steel structures, despite the concerns of some that iron and other limiting nutrients will favor algal or bacterial growth. India
• In addition to wrecks, but along the same lines, are the use of decommissioned oil platforms as artificial reefs, providing that proper environmental preparations are completed first, these structures can provide amazing ‘islands of biodiversity’ in otherwise barren seascapes.
• Concrete structures: Concrete is the favorite material to use for most reef managers for many reasons. It is a material that is very close in composition to natural coral limestone, and also it is strong, heavy, cheap, and readily available all over the world. Concrete can be made into nearly any shape or size, and lasts a long time under the ocean

Significance of artificial reefs:

• Bivalves: Bivalve reefs tend to be biodiversity hotspots, which adds value to local artisanal fisheries and also makes for attractive sites for snorkeling, diving, and eco-tourism with underwater marine observatories.
• One can even imagine the line of eateries serving delicious mussel dishes along the coast, providing alternative livelihoods for fishermen.
• Marine biodiversity: Marine biodiversity can be greatly enhanced by combining the bivalve restoration with seaweed and sea grass, which can absorb nutrients and reduce eutrophication, revive oxygen levels and a multitude of habitats while also serving as a natural defense against cyclones and storm surges.
• Coastal erosion will also be reduced by the combination of reefs, seaweed and sea grass. As most solid structures in ocean waters tend to do, reefs can also be designed to be fish aggregating devices.
• Intestines of coastal system: Bivalves are known as nutrient capacitors and the ‘intestines’ of coastal ecosystems because of their ability to ingest and release nutrients.
• Their lifespan can range from 2-100 years, which, along with their ability to withstand disturbances from terrestrial runoff, cyclones and waves, can make them a worthy investment as natural coastal water cleansers.
• Fish stock enhancement: Improving populations of aquatic organisms by providing shelter for juvenile and mature individuals as well as for adults during delicate life stages (e.g. moulting season for crustaceans).
• Other purposes:Purposes for artificial reefs include increasing the efficiency of artisanal, commercial, and recreational fisheries, producing new biomass in fisheries and aquaculture, boosting underwater recreation and ecotourism opportunities, preserving and renewing coastal habitats and biodiversity, and advancing research.

Way forward:

• Considering the growing population closer to the coasts and some of the inevitable development activities such as the coastal highway, environmental-friendly economic development must consider as many natural solutions as possible.
• Artificial reefs and bivalves with seaweed and sea grass offer a well-tested natural solution with many benefits. Mumbai is an ideal test-bed for a pilot experiment in this natural solution. Replicating it along the extensive coastline of India can follow with the lessons learned in Mumbai coasts.

Source:https://www.thehindubusinessline.com/opinion/columns/a-natural-solution-to-help-tackle-mumbais-coastal-water-pollution/article29224390.ece.