Catastrophic mortality on inshore coral reefs of the Florida Keys due to severe low-temperature stress

Abstract

Coral reefs of the Florida Keys typically experience seasonal temperatures of 20-31°C. Deviation outside this range causes physiological impairment of reef-building corals, potentially leading to coral colony death. In January and February 2010, two closely spaced cold fronts, possibly driven by an unusually extreme Arctic Oscillation, caused sudden and severe seawater temperature declines in the Florida Keys. Inshore coral reefs [e.g., Admiral Reef (ADM)] experienced lower sustained temperatures (i.e., < 12°C) than those further offshore [e.g., Little Grecian Reef (LG), minimum temperature = 17.2°C]. During February and March 2010, we surveyed ADM and observed a mass die-off of reef-building corals, whereas 12 km away LG did not exhibit coral mortality. We subsequently measured the physiological effects of low-temperature stress on three common reef-building corals (i.e., Montastraea faveolata, Porites astreoides, and Siderastrea siderea) over a range of temperatures that replicated the inshore cold-water anomaly (i.e., from 20 to 16 to 12°C and back to 20°C). Throughout the temperature modulations, coral respiration as well as endosymbiont gross photosynthesis and maximum quantum efficiency of photosystem II were measured. In addition, Symbiodinium genotypic identity, cell densities, and chlorophyll a content were determined at the beginning and conclusion of the experiment. All corals were significantly affected at 12°C, but species-specific physiological responses were found indicating different coral and/or Symbiodinium cold tolerances. Montastraea faveolata and P. astreoides appeared to be most negatively impacted because, upon return to 20°C, significant reductions in gross photosynthesis and dark respiration persisted. Siderastrea siderea, however, readily recovered to pre-treatment rates of dark respiration and gross photosynthesis. Visual surveys of inshore reefs corroborated these results, with S. siderea being minimally affected by the cold-water anomaly, whereas M. faveolata and P. astreoides exhibited nearly 100% mortality. This study highlights the importance of understanding the physiological attributes of genotypically distinct coral-Symbiodinium symbioses that contribute to tolerance, recovery, and consequences to an environmental perturbation. These data also document effects of a rarely studied environmental stressor, possibly initiated by remote global climate events, on coral-Symbiodinium symbioses and coral reef communities.

Recent decade of growth and calcification of Orbicella faveolata in the Florida Keys: an inshore-offshore comparison

“…Recent mortality was 14.2% when Cheeca Rocks was surveyed in February 2010 (FRRP 2014). Offshore reefs did not experience cold enough conditions to cause bleaching, mortality, or significant reductions in the physiological function of O. faveolata , Kemp et al 2011, Colella et al 2012.…”

“…The long-term growth dynamics of O. annularis and O. faveolata on the FRT were previously investigated (Hudson 1981, Helmle et al 2011, but these studies did not address growth from 1997 onward. The period we examine incorporates the Caribbean-wide 2005 mass coral bleaching event, the 2009−2010 cold-water bleaching, and localized warm-water bleaching in 2011 (Manzello et al 2007b, Kemp et al 2011, Colella et al 2012. These multiple thermal stress events provide an opportunity to measure the growth response of this threatened species across sites with differing disturbance histories and environmental conditions.…”

Calcification rates of the massive coral Siderastrea siderea and crustose coralline algae along the Florida Keys (USA) outer-reef tract

“…Records of a recent cold event, for example, illustrate this point. In January 2010, massive mortality of corals on nearshore patch reefs occurred along the length of the upper Keys (where there are few tidal passes) due to a cold front that cooled nearshore waters to below 16°C for multiple days (Kemp et al 2011;Lirman et al 2011;Colella et al 2012).…”

Tenacious D: Symbiodinium in clade D remain in reef corals at both high and low temperature extremes despite impairment

“…Cold stress appears physiologically similar to heat stress in corals, as both cause reduced photosystem II (PSII) quenching, leading to photodamage and symbiont loss (Saxby et al, 2003;Thornhill et al, 2008;Kemp et al, 2011;Roth et al, 2012). Like heat stress, bleaching from cold stress is also light dependent (Saxby et al, 2003), implicating a common mechanism associated with photodamage to PSII (Wicks et al, 2010).…”