Tuesday, 2 December 2014

Suspended Sediment as Coral Stressors

Coral reefs are complex and important features of the marine environment. They have the highest biodiversity of any marine ecosystem. Coral reefs are often referred to as the “rainforest of the sea” due to their rich in biodiversity.  Reefs provide important ecosystem services such as feeding and breeding ground for large number of fish, invertebrates and marine mammals.  Apart from that, coral reefs also protect shorelines from erosion by becoming natural breakwater which minimize wave impacts from storms and hurricanes in coastal areas. However, the coral reefs coverage around the world is in decline. Worldwide declines in coral coverage and overall reef degradation can be attributed to a variety of anthropogenic and natural causes. These include climate changes, coral bleaching, diseases and biological infestation, coral mining, tourism, habitat loss from development and suspended sediment. Human intervention is still seen as the major causes of corals death. The anthropogenic impacts might be caused by near shore dredging and the unplanned human occupation of the coastal zone. 

Coral reef ecosystem under siege of various stress 

One of the most prominent stressor in coral decline is suspended sediment. Suspended sediment is very fine soil particles which suspended in the water as a result of erosion in streams or on beaches, or from wave-induced re-suspension of particles from the bottom. These fine particles can smother the coral mucus surface which can reduce larval replenishment and impede their ability to persist. Corals can be additionally stressed due to the allocation of energy required to remove sediment particles, sites for new coral recruitment can be eliminated, and coral colonies can be buried under conditions that permit sediment accumulation. Thus, it can be justified that suspended sediment is indeed a vital factor which may inhibit the growth and survival of corals.
At the moment, the rate of suspended sediment or sedimentation rate in coral reef areas has increased due to human activities such as coastal development and tourism. Sediment accumulation rate or sedimentation rate of 10mg.cm-2.day-1 seems to be critical limit for coral to grow. It is reported that up to a rate of sedimentation deposition of 15mg.cm-2.day-1, the reefs start to decline. Hence, continuous monitoring of sedimentation rate and other threatening factors should be done in order to assess the health of the coral reef. 

High concentration of suspended sediment may results in coral death