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Fishing & Ecosystems

Ecosystem Loss - Links from Dr. Kamal
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1.1 Conference Papers
1.1.28 Emerging coral reefs in young man-made structures: Does age really matter?

Abstract

 

Due to rapid coastal developments, in order to protect coasts from erosion and dissipate waves, submerged man-made structures such as breakwaters, groins and seawalls are widely extended into marine waters in Sri Lanka. Such structures may alter the composition of local benthic and associated fauna by reducing the complexity of habitats initially. However, these structures may become novel habitat open to colonization of marine biota and establishing diverse communities eventually in locations that would never be otherwise successfully colonized due to unstable substrates like sand, mud, and rubble. The construction of Hambantota port was commenced in 2008. The West and East breakwaters which are of 988 meters and 312 meters long, constructed to support a 230 meter entrance channel. Breakwaters are built mainly with concrete armor blocks or ‘Chinese pods” which weigh above 12 tonnes each together with few natural rocks. Present study was conducted between September 2013 and January 2014 in relatively calm and less turbulent conditions prevailing, in order to monitor the status of the environment after the completion of first phase of the Hambantota port development work. In order to identify and classify major marine habitats, underwater visual surveys were carried out through diving and snorkeling. Percent cover was estimated using belt transect method. Minimum of five quadrate samples were obtained randomly along the 50 m transect. In each sampling site, each coral encountered were recorded and only the specimens unable to identify were preserved for identification. Underwater video transects and photo-quadrates were also obtained along the line transect for permanent visual record of the data. The remarkable finding is that there were developing solitary and reef forming corals attached to the rocks and boulders in the submerged west breakwater and along the seawall of the west bank. Most of the corals observed were in the early development stage with some well-developed coral colonies.

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Corals communities represented 29 species belong to family Acroporidae (14 species of genus Acropora, 3 species of genus Montipora), Family Pocilloporidae (5 species of Pocillopora), family Faviidae (Favites abdita, Favia lizardensis, Favia sp, Porites solida and Porites stephensoni) and family Agariciidae (Coeloseris mayeri and Gardineroseris planulata). Corals were settled more on concrete blocks compared to natural rocks. Highest coral cover recorded was 92% in west breakwater whereas lowest recorded was 6% from west bank. All the corals observed were live and except for very few physical damages, there were no dead corals. Together with emerging corals, divers group of vivid colored reef associated fishes and other invertebrates provided one of the spectacular underwater ecosystems on this man-made structure. Although, there can be such coral developments in a mature breakwaters (i.e. old breakwaters < 20yrs), but this is not the case in a very young breakwater within five years of construction. This is a very rare and unique feature to observe in such a disturbed coastal environment while heavy excavations and constructions are still underway.

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The developer must pay fullest attention to protect these astonishing reefs. A silt curtain should be used as a measure during construction work and other dredging events likely to degenerate huge amount of sediments. Understanding the connectivity between corals on man-made structures and natural reefs may suggest the possibility of man-made structures act as surrogates of natural coral reefs and a potential source of coral larvae for increasing the resilience against the global coral crisis and recovery of local coral reefs.

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