![]() Moreover, it provides additional ecosystem services, such as habitat for fish and resident invertebrates 28– 30, 45, 46, improve water quality and enhance primary production 24, 47, 48. Oyster reefs form persistent, three-dimensional structures which can attenuate waves 27, 42, trap sediment 7, 9, 43, 44, and are resilient growing with sea level rise 22, 23. The succession and growth of other vegetation types, such as salt marshes varies with season and is becoming less efficient in trapping sediments due to incoming erosive waves during high energy periods in the monsoon season (see Supplementary Fig. Moreover, mangroves were being deforested due to construction of aquaculture ponds and salt pans in many intertidal areas 41. However, only 60 km out of a total of 957 km sea facing embankments are protected by a forest belt, which is gradually degrading due to ever increasing cyclones 40. Mangroves have proven to be cost effective in dissipating wave energy and reducing hydraulic load on embankments during storm surges 39. Mangroves, salt marshes and oyster reefs, which form part of the biotic environment of the coastal ecosystems in Bangladesh have the ability to provide coastal protection through trapping sediments and promoting accretion. This is particularly severe in offshore (island) areas, such as in the islands of Kutubdia and Sandwip that are frequently impacted by storm surges, increasing astronomical tides and erosive waves associated with southwest monsoon winds 35. Shoreline erosion is increasingly threatening coastal communities and their livelihoods 37, forcing thousands of people to migrate to the mainland 38. Until 2015, a total of 1,576 km 2 area was lost due to shoreline erosion at an annual rate of 6.3 km 2 in 1985–1995 and 11.4 km 2 in 2005–2015, respectively 35. The coastline of Bangladesh has changed rapidly over the last few decades 35, 36. It provides opportunities to combine engineering principles with ecological processes to reduce environmental impacts of man-made infrastructure 34. The use/design of sustainable ecosystems that integrate human society with related natural habitats for the benefit of both is called ecological engineering 31– 33. Moreover, they offer additional ecosystem services including: (1) water quality regulation 24, 25 (2) ecosystem succession 26, 27 and (3) fisheries production 28– 30. They have the capacity to reduce flow and dampen wave energy through their physical structures and by doing so, they trap and stabilize sediments, allowing to keep pace with sea-level rise by natural accretion and growth 13, 19– 23. ![]() These habitats include coral reefs 5, reef-forming bivalves 6– 9, dense vegetation of kelps and seagrasses 10, 11, salt marsh vegetation 12– 14 and mangroves 15– 18. This study showed that breakwater oyster reefs can reduce erosion, trap suspended sediment, and support seaward saltmarsh expansion demonstrating the potential as a nature-based solution for protecting the subtropical coastlines.Ĭoastal habitats play a critical role in coastal adaptation strategies as they can reduce the vulnerability of coastal communities to natural hazards like flooding, eroding shorelines and sea level rise 1– 4. The changes caused by the deployed reefs also facilitated seaward expansion of the salt marsh. On the lee side of the reefs, there was accretion of 29 cm clayey sediments with erosion reduction of 54% as compared to control sites. Waves were totally blocked by the vertical relief of the reefs at water levels <0.5 m. The reefs were able to dissipate wave energy and act as breakwaters for tidal water levels between 0.5–1.0 m. The observed wave heights in the study area ranged 0.1–0.5 m. This was done over four seasons, including the rainy monsoon period. ![]() Data were collected on wave dissipation by the reef structures, changes in shoreline profile, erosion-accretion patterns, and lateral saltmarsh movement and related growth. Three breakwater reefs with recruited oysters were deployed on an eroding intertidal mudflat at Kutubdia Island, the southeast Bangladesh coast. A field experiment was undertaken to assess the benefit of oyster breakwater reefs to mitigate shoreline erosion in a monsoon-dominated subtropical system. Oyster reefs have the potential as eco-engineers to improve coastal protection.
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