Pulau Hantu - A celebration of marine life

Secret lives and secret worlds hidden in Singapore's most popular coral reef.

Tuesday, April 18, 2006

Can Reefs Exist In Murky Waters?

Coral reefs can also flourish in naturally turbid waters ...

"Coral reefs can also flourish in naturally turbid waters to at least 10 m depth (Yentsch et al. 2002), supporting unique and diverse communities that are not found in clearer offshore waters.

Reefs in coastal and inshore waters experience naturally more variable conditions, including higher levels of dissolved and particulate nutrients and siltation and hence reduced water clarity, and more fluctuating salinity, than reefs in oceanic waters, where water clarity is high, siltation is low, and nutrient levels are generally low except during periods of upwelling (Furnas 2003).

Coral reef communities naturally change along gradients from terrestrially influenced to oceanic conditions. These natural gradients contribute to the diversity of types of coral reefs found.

Large volumes of freshwater and sediment discharges kill corals and prevent coral reef growth, even when systems are unaltered by humans; hence no coral reefs are found tens to hundreds of kilometres downstream of large rivers such as the Amazon (Brazil) or Fly River (Papua New Guinea). Smaller streams can alter reef communities at the scale of hundreds of meters to a few kilometres downstream of their mouths (West and Van Woesik 2001).

Reefs vary greatly in their susceptibility to damage by poor water quality.

Existing field observations from around the world indicate that reefs in poorly flushed semi-enclosed bays or lagoons, and reefs surrounded by a shallow sea floor, are at greatest risk of degradation, probably because materials are retained for prolonged periods of time, extending the period of exposure to more 'chronic' conditions.

In contrast, reefs along well-flushed coastlines surrounded by deep water, where terrestrial pollutants are washed out within days to weeks, appear more resistant and resilient against degradation by exposure to high sediment and nutrient loads."

International Society for Reef Studies, ISRS (2004) The effects of terrestrial runoff of sediments, nutrients and other pollutants on coral reefs. Briefing Paper 3, International Society for Reef Studies, pp: 18.

full paper (PDF)

Reefs growing in murky waters can be special?

"Coral reefs in the Golfo de Guacanayabo in southeastern Cuba are unique in many respects--shape, structure, builders, biodiversity, endemic forms and origin.

Observed from the air, they exhibit complex reticulated contours. These 20- to 25-metre-high reefs have grown vertically in murky, stagnant waters in a muddy bottom bay.

Here, the usual Caribbean reef-building Scleractinia (Acropora palmata, Montastraea annularis complex, M. cavernosa, Diploria spp.) are not present. Instead, there exist abundant small branchy colonies of non-reef-building Oculina spp., Cladocora arbuscula and Porites porites f. divaricata; very delicate A. cervicornis; the strictly endemic Eusmilia fastigiata f. guacanayabensis; and a rare form of the Hydrozoa Millepora alcicornis f. delicatula.

These small bushy stony corals, together with numerous sponges, combine to form unusual reefs such that some reef parts appear almost 'gelatinous'.

It has not been shown that the Guacanayabo reefs developed on top of older positive structures. Instead, their origin may be understood as arising from delicate branchy coral colonies that have grown on soft bottom together with sponges, gradually compensating for the submergence of the sea floor.

A survey performed west of the Golfo de Guacanayabo found incidences of coral branches with sponges and other invertebrates providing a base for buildups on soft bottom, showing how this unusual construction can develop in various locales.

By studying the Guacanayabo reefs, we can learn how to work more effectively toward their sustainability and the protection of their unique biodiversity.

The preservation of these unusual reefs requires public education and the putting into place of special restrictions. The positive experience of the adjacent park, a protected part of the Archipelago Jardines de la Reina reefs, suggests extending that park eastward to include the Guacanayabo reefs.

The Guacanayabo reefs are not only intriguing in terms of understanding a rare type of 'marginal' reef, but also provide a model for understanding fossil reefs in analogous conditions."

The reticulated reefs in Golfo de Guacanayabo, Cuba and bioconstructions in the 'Urgonian', Bulgaria, by Vassil N. Zlatarski 131 Fales Rd., Bristol, RI 02809, USA vzlatarski@yahoo.com International Society for Reef Studies, Abstracts Volume, European Meeting Cambridge, 4-7 th September, 2002 111

full abstract