A reef growing on a hot spring


Image: On location in St Vincent & The Grenadines

 

Tobago Cay Marine Park

We have reached the southern most islands on the Grenadines, and in the distance we can see Grenada, the next country south along the Lesser Antilles.  Today we surveyed within the Tobago Cay Marine Park (TCMP), established in 1997, to preserve the reefs around these isles that serve as foraging grounds and refuge for reef fish and juvenile turtles, in an area where both are fished.

We surveyed a sheltered reef near the island of Mayreau located within the marine park. While most of the reefs we’ve surveyed only extend to 10 -15 m in depth, this unique reef extends to 23 m, but still has a high diversity of coral and sponge life.  It is unique because the reef grows along an underwater hot spring.

 

A reef on a hot spring

As we dived along the reef, narrow streams of bubbles could be seen seeping out through the sand and local divers state that the water column undergoes rapid temperature fluctuations. They also believe that the gas bubbles provide nutrients to the reef and help them to grow. However, to me it sounds like these gas bubbles (which typically contain CO2) and rapidly changing temperatures would have a more negative impact. Researchers have carried out studies on coral reef ecosystems that occur naturally in areas with elevated carbon dioxide levels in the water column, due to volcanic seeps at sites in Papua New Guinea. These special ecosystems give us insight on how climate change and ocean acidification affects coral reef communities (Fabricius et al. 2011). Since the addition of carbon dioxide in the water column lowers its pH, making it more acidic, locations of high seeps have a much lower diversity and abundance of coral species (Fabricius et al. 2011).

 

Mystery bubbles

From our first observation, the hard coral life appeared to be typical but the sponge abundance and diversity was far higher compared to other reefs surveyed in the Grenadines. It would be interesting to find out what gas is being produced and how this gas as well as the temperature changes impacts this coral community.

 

Reference:

Fabricius, K. E., Langdon, C., Uthicke, S., Humphrey, C., Noonan, S., De’ath, G., Okazaki, R., Muehllehner, N., Glas, M. S., Lough, J. M. (2011), Losers and winners in coral reefs acclimatized to elevated carbon dioxide concentrations. Nature Climate Change, Vol 1.

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