Survival under chronic stress from sediment load: Spatial patterns of hard coral communities in the southern islands of Singapore

Abstract

Six reef sites were chosen along the west coast of the southern islands of Singapore, at an increasing distance from the densely populated metropolitan area, to study the spatial patterns of coral reef communities on the upper reef slope ( approximately 4m) and the associated environmental conditions. Chronic exposure to high sediment load was the most obvious form of anthropogenic stress. Recruitment rates on ceramic tiles were low (1.4+/-1.0-20+/-14.7 recruits m(-2) yr(-1)) but decreased towards the main island of Singapore as did hard coral cover and coral density. Coral fauna consisted of genera generally found in deeper waters (e.g., fungiids, foliose Oxypora, Leptoseris, and Echinopora) or those well-adapted to turbid waters (e.g., Porites, Pectinia, Leptastrea, Montipora). Light extinction coefficient (K) and % live coral cover (%LCC) showed a strong and inverse curvilinear relationship (%LCC=13.60 *K(-3.40)). Similarly, the rate of sediment deposition (DFSPM) (RR=1.51-0.17 *DFSPM) and water clarity (RR=3.56-2.92 *K) exhibited strong and inverse relationships with recruitment rates (RR). Although measured levels of the downward flux of suspended particulate matter and suspended solids were well within "normal" levels recorded in the literature, it was the proportion of benthic space, generic coral composition, and site history that offered compelling evidence of chronic exposure to increased sediment load. Clearly a reduction in both water clarity and live-coral cover has taken place since monitoring efforts began in the early 1970s, in fact coral cover has more than halved at all sites examined since the 1980s and benthic space was predominantly occupied by dead corals covered with sediment and filamentous algae.

Augmenting the Post-Transplantation Growth and Survivorship of Juvenile Scleractinian Corals via Nutritional Enhancement

“…Clearly, size was a key determinant of post-transplantation survival. However, the average post-transplantation mortality rate of all P. damicornis juveniles in this study (46%) was higher than that reported from other studies (11–34%) [10], [11], [17], likely due to the high sediment levels in Singapore waters, which have been estimated to limit scleractinian recruitment to two individuals m −2 [45]. As was observed during monthly visits to the study site, most juvenile colonies were smothered by fine particulate sediment, with obvious damage to the coral tissue.…”

Impacts of Sediments on Coral Energetics: Partitioning the Effects of Turbidity and Settling Particles

“…In the mid-1970s much of the reef flat surrounding Pulau Hantu was destroyed following a reclamation project which increased the island's land area from 0.024 to 0.12 km 2 [2]. Today, approximately 2.21 km 2 of intertidal reef flat remains [47]. Sedimentation rates on the reef slope often exceed 10 mg cm −2 d −1 [6], [48], [49], levels considered to be detrimental to the more sensitive species of coral [40].…”

Land Use Impacts on Coral Reef Health: A Ridge-to-Reef Perspective

“…A study in Palau refined this perspective: Acropora transplants (at least one year old) survived equally well near and far from land, yet naturally occurring adult Acropora were rare near land, suggesting that the first year of life may be the most vulnerable for Acropora (Golbuu et al, 2011). Juvenile assemblages differed but adults did not after high flooding in the Great Barrier Reef (Thompson et al, 2014), while reefs in Singapore demonstrate an opposite pattern (Dikou and van Woesik, 2006). Additional research may reconcile these findings and assist restoration efforts by suggesting species and lifehistory stages when outplants are most likely to survive nearshore (Ng et al, 2016).…”