Perforated trapezoidal artificial reefs can augment the benefits of restoration of an island and its marine ecosystem

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.