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S’pore’s coral reefs proving resilient in the face of challenges

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.

A clownfish swimming among bleached sea anemone. Singapore is experiencing what could be its worst coral bleaching episode to date, with assessments showing that it could be more severe than the previous two major bleaching events in 1998 and 2010. PHOTO: National Parks Board

A clownfish swimming among bleached sea anemone. Singapore is experiencing what could be its worst coral bleaching episode to date, with assessments showing that it could be more severe than the previous two major bleaching events in 1998 and 2010. PHOTO: National Parks Board

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 Reports 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.

Correction: An earlier version of this report said the study report was published in Scientific Research. This is incorrect. It was published in Scientific Reports. We are sorry for the error.

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