PARENT SESSION
OOS 1: Genetic Explorations of the Seascape: Using Molecules and Experiments to Understand Marine Biodiversity.
Organized by: E Sotka and R Thacker
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room E 141 .

Changing by degrees: Adaptive response of reef coral symbioses to climate change.

Baker, Andrew¹, ¹ Wildlife Conservation Society, New York, New York, USA

ABSTRACT- Reef-building corals worldwide are increasingly threatened by acute exposure to high temperature stress, leading to recurrent episodes of mass coral bleaching and mortality. However, many coral communities around the world experience chronic exposure to extremely high temperatures without apparent harmful effect. Conventional explanations for these unusually tolerant corals assume local acclimatization or adaptation, but the mechanisms underlying this capability are under-investigated. One potential mechanism by which reef corals might respond to temperature extremes is by hosting genetically distinct algal symbiont communities that differ in their thermal optima and resistance to bleaching. To test this hypothesis, molecular surveys were undertaken of algal symbionts from reef corals in extreme high temperature environments (Saudi Arabia) and from the latitudinal limits of coral distribution in three oceans (Japan, Madagascar, Israel, Brazil, Bermuda). Results showed that reef corals from high temperature environments were dominated by an unusual Symbiodinium in clade D, while corals at high latitudes (that experience cooler mean temperatures and higher seasonal variability) were dominated by a diversity of symbionts in clades A and B. These data indicate that: (1) the ability of reef coral species to associate with a diversity of algal symbionts may be important in understanding how they acclimatize and/or adapt to chronic temperature stress; and (2) flexibility in coral-algal symbiosis may help mitigate the detrimental effects of climate change by elevating bleaching thresholds and buffering coral species from extinction. This adaptive response may already be occurring: the clade D symbiont found in chronic high temperature environments appears to be increasing in abundance on other reefs worldwide, particularly those devastated by the 1997-98 El Niño. Consequently, while reefs may continue to experience mass bleaching and mortality as their symbiont communities are slowly replaced, the long-term prospects for their ultimate survival may be better than assumed.

Key words: Reef, Climate Change, Coral, Symbiosis