[Coral-List] Coral range expansion with global warming (Thomas Goreau)

[Riccardo Rodolfo-Metalpa]

Dear Pr Goreau,
I just would like to report a few precisions about the effects of temperature increase on the marginal Mediterranean corals. As you correctly wrote, the average sea surface temperature in the Mediterranean Sea is increasing. Prior to this increase, the temperature ranged from 13 to 24°C due to the marked seasonality - below the optimum for calcification. Therefore, it was not warm enough to build “real” reefs. However, during the last decade, the average summer temperature reached 25-26°C and remained at this level for several weeks. Furthermore, peaks of 28°C are not unusual and more and more recurrent.
As a consequence, native coral species such as Cladocora caespitosa, Balanophyllia europaea and the temperate introduced Oculina patagonica are suffering from this temperature increase and show mass mortality events as well as other benthic species. Therefore, without a quick adaptation of these species to high temperatures, this phenomenon can be only harmful and increase the mortality events of shallow water corals in the Mediterranean.
Paradoxically, in the Middle to Late Pleistocene ages, when the seawater temperatures are thought to have been higher than present, Cladocora caespitosa were very abundant as it has been revealed by the presence of several fossil reefs. In contrast, the present geographical occurrence of C. caespitosa bioherms and true reefs (only few existing in the Adriatic and Aegean seas) in the Mediterranean Sea has decreased with respect to their fossil distribution, suggesting that the current environmental conditions are not favorable to its growth.

For more details, several papers investigated the effect of increasing temperature on Mediterranean coral species:
Cerrano C, Bavestrello G, Bianchi CN, Cattaneo-Vietti R, Bava S, Morganti C, Morri C, Picco P, Sara G, Schiaparelli S, Siccardi A, Sponga F (2000). A catastrophic mass-mortality episode of gorgonians and other organisms in the Ligurian Sea (NW Mediterranean), summer 1999. Ecol. Letters 3, 284-293.

Rodolfo-Metalpa R, Richard C, Allemand D, Ferrier-Pagès C (2006b) Growth and photosynthesis of two Mediterranean corals Cladocora caespitosa and Oculina patagonica under normal and elevated temperatures. J Exp Biol 209, 4546-4556

Regards

Riccardo

Riccardo Rodolfo-Metalpa PhD
Marine Biology and Ecology Research Centre
University of Plymouth
6th floor Davy Building
PL4 8AA, UK


At 08:45 PM 1/13/2008, Thomas Goreau wrote:
>> Dear Allen,
>>
>> I don't have references handy, but here are some leads.
>>
>> With regard to range expansion:
>>
>> Mexican researchers have been following northward expansion of corals
>> in the Sea of Cortez for some years, and I hope they can point to
>> papers on this. Surveys at Sodwana reef in South Africa show that
>> live coral cover and diversity have been steadily increasing. It
>> would be most interesting to see if the corals are expanding
>> northward on Honshu, Japan, and there may be studies on this by
>> Japanese researchers. Australia should be seeing the same.
>>
>> In SE Florida the local dive groups I work with there, Cry of the
>> Water in Broward County, and Reef Rescue in Palm Beach County, are
>> seeing expansion of the now rare Acropora cervicornis and Acropora
>> palmata northwards. But they are severely threatened by dredging
>> projects and algal blooms around the offshore sewage outfalls, which
>> we have now finally convinced the Governor, after years of appeals,
>> to shut down.  If we can get these reefs protected (which they are
>> not now),  clean up the water, and stop the new dredging projects,
>> which killed almost all the live reefs of the area in the 1960s and
>> 1970s, we should see significant northward coral expansion since
>> there is a good supply of coral and fish larvae swept out of the
>> Caribbean by the Gulf Stream.
>>
>> Thanks to above average sea surface temperature rise, the
>> Mediterranean is now warm enough for reef building corals, but the
>> two local species with zooxanthellae don't build up large
>> aggregations, and there would be reluctance to introducing non-native
>> species. However, a few million years ago the Mediterranean area was
>> the global center of coral diversity.
>>
>> But dreams of coral reef marching poleward, which have been proposed
>> by some in the past as a benefit of global warming, are probably
>> fiction. The reason is that the coastal areas of North America, Asia,
>> and Australia that they could expand to are densely populated and the
>> sewage and agricultural nutrients are way too high for coral reefs
>> even if the temperatures were acceptable.
>>
>> With regard to the time it takes to form framework coral reef
>> structures that creates sheltered habitats, as opposed to coral reef
>> communities that are sparse veneers on non growing coral substrate,
>> that can take a long time since reefs (as opposed to corals)
>> typically grow millimeters a year.
>>
>> Best wishes,
>> Tom