Asian Scientist 14 Nov 16;
AsianScientist (Nov. 14, 2016) - Although Singapore’s reefs have suffered extensive damage over the last 27 years, they have proven to be more resilient than expected, according to a study published in Scientific Reports.
In the past 200 years, Singapore has been transformed from a forest-covered island to a highly urbanized city-state of more than 5.4 million. Extensive coastal construction, dredge spillage and land reclamation have resulted in high sedimentation rates, turbidity and pollution, putting immense pressure on the surrounding coral reefs.
Analyzing surveys conducted between 1986 to 2012, researchers from the National University of Singapore, Nanyang Technological University, Singapore’s National Parks Board, the University of New South Wales and the Sydney Institute of Marine Science found that coral cover declined at all sites, particularly in the first decade.
In 1998, a major bleaching event occurred as the result of high water temperatures associated with an El Nino.
However, corals at shallower reef sites were remarkably resilient to this event, showing signs of recovery within a decade. By 2008 coral cover had increased to about 1993 levels.
“It is remarkable that diverse shallow coral communities can persist in such adverse conditions,” says study first author Dr. James Guest, formerly of UNSW and now at the Hawai’i Institute of Marine Biology.
“Undoubtedly, Singapore’s reefs have suffered as a result of human activities, but the recovery of corals at shallow sites is really surprising given how impacted this environment is. It really shows how tough corals can be.”
However, the study also showed that corals at deeper sites were less resilient, with coral cover at these sites continuing to decline.
The lack of recovery at deeper sites may be due to low light levels or a lack of unsuitable substratum for new corals to settle and survive.
Reefs in Singapore appear to have undergone substantial bleaching again this year, which is likely to test whether the resilience to bleaching observed in previous decades is still present on these reefs.
The article can be found at: Guest et al. (2016) 27 Years of Benthic and Coral Community Dynamics on Turbid, Highly Urbanized Reefs Off Singapore.
Singapore’s coral reefs proving resilient in the face of challenges
Today Online 17 Nov 16;
SINGAPORE — The Republic’s coral reefs have proven to be more resilient than expected despite the impact from human activity such as dredging and warming sea waters, concluded an international group of researchers after analysing surveys of reefs conducted over nearly three decades.
In an article published in Scientific Research on Nov 8, the authors, which included scientists from the National University of Singapore, Nanyang Technological University, and the National Parks Board, reported that while coral cover has declined, reefs in shallower waters have recovered at a rapid rate, even after a major bleaching episode in 1998.
The data, which came from 15 sites south of the main island, found that coral cover at all sites between 1986 and 2012 declined by about 12 per cent at shallower depths of 3m to 4m, and by about 30 per cent at the deeper depths of 6m to 7m.
But shallow reef crest sites showed recovery of about 16 per cent between 1998 and 2008, although coral cover at deep sites declined until 2003 and has not recovered to historical levels.
“Our data support the notion that coral reefs will change rather than disappear entirely due to coastal land use changes, and provide a glimmer of hope that some heavily disturbed Indo-Pacific reefs can remain in a coral-dominated state,” said the research team, which was led by scientists from the University of New South Wales and also included scientists from the Sydney Institute of Marine Science.
The study described the “human disturbances” that have been affecting Singapore’s ecosystems for decades. The majority of the southern coastline and islands, where Singapore’s coral reefs are located, have undergone reclamation, and many intertidal flats have made way for petrochemical plants, as well as military and recreational areas.
“Extensive coastal construction, dredge spillage and modified hydrodynamics have resulted in sedimentation rates and levels of total suspended solids exceeding those considered optimal for tropical reefs,” said the authors.
Underwater visibility, thought to have been about 10m in the 1960s, decreased to about 2m in the late 1980s, and remains at around this level. “Eutrophication is thought to have increased at least 30-fold in the last 60 years, although measured nutrient concentrations are relatively low,” they said. There were also two major thermal coral bleaching events in 1998 and 2010.
Despite the “clear, significant, negative impacts on both marine and terrestrial biodiversity”, diverse coral communities of more than 250 coral species remain on the fringing reefs around most of Singapore’s southern islands, said the researchers.
These are restricted to depths of about 8m due to very high light attenuation — loss of light intensity from seawater — and comprise “stress-tolerant taxa typical of heavily sedimented and turbid waters”.
Average coral cover at the shallow reef crest was about 36 per cent, above the current average of about 22 to 27 per cent for the Indo-Pacific, although similar to estimated averages for reefs in the South China Sea region (about 40 per cent).
The lack of recovery at deeper sites may be due to low light levels or a lack of unsuitable terrain for new corals to settle and survive on.
But the authors stressed that while the shallow reefs have retained relatively high coral cover for almost three decades, it “does not mean that they will remain this way indefinitely”.
“Furthermore, despite high coral cover, we do not know if these altered shallow coral communities are providing any of the functions and ecological services normally associated with reef ecosystems (for instance, reef building, productive fisheries, diving tourism),” they said.
Future monitoring programmes should consider incorporating other metrics such as net accretion, structural complexity and herbivory rates to assess reef health more broadly, they added.
Study senior author Professor Peter Steinberg said in a report by UNSW: “This is by no means a cause for complacency regarding the state of our reefs, but rather highlights that if we can reduce local stressors, reefs are more likely to be able to rebound from the effects of global stressors such as climate change.”
Singapore is experiencing what could be its worst coral bleaching episode to date, with preliminary assessments showing that it could be more severe than the previous two major bleaching events.
Dive trails at the Sisters’ Islands Marine Park have been closed since June to minimise additional stress to the reefs.
