Temporal changes in benthic assemblages on Florida Keys reefs 11 years after the 1997/1998 El Niño

Abstract

Disturbances that result in the mass mortality of reef-building corals are changing the appearance of reefs worldwide. Many reefs are transitioning away from scleractinian-coraldominated assemblages to benthic communities composed primarily of non-scleractinian taxa. This study evaluated recovery patterns of reef communities in the Florida Keys following the mortality associated with the 1997/1998 El Niño. We examined temporal trends among the 5 most spatially abundant reef taxa and stony coral species from 1999 to 2009 at 3 spatial scales, and applied a Principal Coordinate Analysis (PCoA) to determine whether changes in their cover resulted in a shift in community structure. Trends of decreasing stony coral cover were not identified Keys-wide between 1999 and 2009, but 2 of the 3 habitats examined -shallow and deep forereefs -did show a significant decline in cover. Concomitantly, octocoral cover significantly increased Keys-wide and in all 3 habitats. The transition to octocorals was most evident on shallow forereefs, where octocoral cover significantly increased at 9 of 12 reefs and overwhelmingly influenced the PCoA. On deep forereefs, octocoral and sponge cover did significantly increase, but did not impart a clearly defined shift in community structure like that observed on shallow forereefs. Community composition at patch reefs was relatively consistent during the study, but the increase in octocoral cover may accelerate further following a cold-water mortality event in 2010. These results demonstrate that octocorals are emerging as the predominant benthic taxa in the Florida Keys. Although the transition to octocorals may have started long ago, their apparent resilience to present-day stressors will likely allow this shift to continue into the foreseeable future.

Cryptic regime shift in benthic community structure on shallow reefs in St. John, US Virgin Islands

“…These alternative transitions include changeovers from scleractinians to corallimorpharians or soft corals in the Indo-Pacific (Work et al 2008), and to sponges (Loh & Pawlik 2014) or gorgonian soft corals (Ruzicka et al 2013, Lenz et al 2015 in the Caribbean. Transitions in community structure favoring octocorals are particularly interesting, be cause octocorals have long been recognized as im portant constituents of coral reef faunas (Kinzie 1973), even though ecological studies of this ecosystem rarely give them much attention.…”

“…In the Caribbean, octocoral populations historically have been recorded over large areas of reef with their colonies interspersed at low densities among scleractinians (Kinzie 1973). Recent analyses indicate that octocorals may be becoming more common throughout the region (Ruzicka et al 2013, Lenz et al 2015, including in habitats formerly dominated by scleractinians (Ruzicka et al 2013). These changes may reflect a widespread and gradual transition in benthic community structure to favor octocorals, which has im portant implications for the structure and function of coral reefs.…”

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

“…This most recent decline was driven by mortal-ity of the Orbicella (formerly Montastraea) annularis species complex (Ruzicka et al 2013, Toth et al 2014. The loss of the O. annularis species complex has occurred across the Caribbean (Bruckner & Bruckner 2006, Edmunds & Elahi 2007, Bruckner & Hill 2009).…”

“…Coral cover on the FRT has been ≤5% since the 1997/98 El Niño on offshore reefs and has continued to decline (Somerfield et al 2008, Ruzicka et al 2013). This most recent decline was driven by mortal-ity of the Orbicella (formerly Montastraea) annularis species complex (Ruzicka et al 2013, Toth et al 2014.…”

“…An exception to this trend is the inshore patch reefs that are located between the islands of the Florida Keys and the offshore reefs. Since the 1997/98 El Niño, average coral cover on the patch reefs has ranged from 15 to 35%, with some reefs having values > 40% (Lirman & Fong 2007, Ruzicka et al 2013). This high coral cover is enigmatic because inshore sites experience greater thermal variability, increased turbidity/depressed light, increased sedimentation, and elevated nutrients (Shinn 1966, Hudson 1982, Lirman & Fong 2007.…”