No abstract

The Gulf of Mannar (GoM) is located along the southeast coast of India. It has a chain of 21 low‐lying uninhabited islands extending from Rameswaram to Tuticorin. These islands are endowed with coral reefs, beds of seagrasses, and other associated marine life. Growing human population has led to accelerated coral mining and destructive fishing practices and this has brought about changes in the bio‐geomorphology of the islands, altered the hydrodynamic conditions, and resulted in severe erosion of the islands. The area of Vaan Island had decreased from 20.8 ha in 1969 to 2.33 ha in 2015. While hard measures have proven successful in preventing erosion, ecosystem‐based measures taking into account the resilience of the flora and fauna yield greater and more natural benefits. A total of 10,600 perforated trapezoidal artificial reef (AR) modules were deployed in clusters along two rows on the windward side of Vaan Island. ARs of 1 and 2 m height were placed respectively along contours of 2 and 3 m depth. The shape and arrangement of the ARs dissipated wave energy through the shoaling effect. As a result, a spit appeared and the area increased to 3.15 ha. The ARs also support epibenthic communities, benthic macrofauna, corals, and fishes. The deployment of an ecosystem‐based multipurpose perforated trapezoidal AR model has been successful not only in restoring the sinking island but also in enhancing the species richness, and it can be adopted as a tool in the restoration of islands and their marine ecosystems.

Intensive underwater surveys have been conducted to assess the extent of coral bleaching and subsequent mortality in the Gulf of Mannar between March and October 2016. The extent of bleaching was 23.92%  10.55% during the period between March and June 2016, and the live coral cover was drastically reduced to 22.69  9.07% during October 2016 with a mortality of 16.17  8.46%. Fast-growing coral forms, including the genera Acropora, Montipora and Pocillopora were most affected, not only by bleaching but also by severe mortality. Boulders, including the genera Porites, Favia and Favites were found to be resistant to bleaching. During the bleaching period, water temperature was between 31.2C and 32.6C. The current bleaching is in alignment with the third global coral bleaching event which occurred between 2014 and 2017. Management interventions, including protection and rehabilitation using the native resistant coral species will not only help in the recovery process, but also increase the live coral cover.