Detecting the effects of natural disturbances on coral assemblages in French Polynesia: A decade survey at multiple scales

Abstract

Coral reefs in French Polynesia, just like many others throughout the world, have been subjected to several natural disturbances including 15 cyclones, seven major bleaching events, and several Acanthaster planci outbreaks since the 1980s. In order to document the effects of these perturbations on coral assemblages, we initiated a long-term monitoring program that extended over both local and regional scales. Coral cover was quantified at 20 sites situated on the outer reef slope of 13 islands. The results from the first decade (1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002) are analyzed and the adequacy of our approach is discussed in the context of identifying potential indicators of coral reef health. Among 13 islands in French Polynesia, only two were unaffected by natural disturbances. We found important local and regional variation in the impacts of coral bleaching and cyclones, and three major temporal trends were distinguished: 1) 10 sites where coral cover decreased in relation to the occurrence of major disturbances; 2) nine sites where coral cover increased, despite the occurrence of disturbances affecting seven of them; and 3) a site where no significant variation in coral cover was found. The responses to perturbations were different among coral genera: Acropora species were particularly susceptible to bleaching events, whereas physical damages induced by cyclones concerned mainly branching species of Acropora and Pocillopora. Thus, monitoring surveys could be improved by selecting different and complementary indicators (one on the variation in diversity, one estimating changes in the abundance/cover, and one estimating the potential for recovery), by integrating several spatial scales, and by including at least the most informative species. High frequency recordings of environmental parameters (e.g. sea surface temperature) may be also a complementary tools for identifying causal relationships between changes in coral reef community structure and the factors causing the changes.

Comparative Effects of Different Disturbances in Coral Reef Habitats in Moorea, French Polynesia

“…To explore long-term changes in coral cover and community structure at Moorea, quantitative data were compiled from 15 studies conducted at Tiahura [16,33,49,58,[62][63][64][65][66][67][68][69][70] and/ or Vaipahu [16,62,71,72], located 2 kilometres apart on the north coast of Moorea [62]. Most of these studies (11 studies) directly compared changes in coral cover and composition through time, sampling coral assemblages between 2-17 years.…”

“…Areas in which coral reef degradation is most pronounced (the Caribbean, SE Asia, and the western Indian Ocean) are characterized by a long history of heavy exploitation of coral reef resources and other chronic disturbances [9], which may have increased vulnerability to recent acute disturbances, such as severe tropical storms [16][17][18][19][20], El Niño Southern Oscillation (ENSO) events [21,22], coral bleaching events [23][24][25][26][27][28], high and low temperature extremes, freshwater plumes from heavy rainfall and runoff events [29], coral diseases [30], and outbreaks of coral predators (mainly, the corallivorous sea star Acanthaster planci in the Indo-Pacific, [31][32][33][34][35][36][37][38][39], and 2 Journal of Marine Biology tidal fluctuations [40]). More importantly, coral loss and associated degradation of coral reef habitats is expected to worsen over the next 2-3 decades, due to climate related increases in temperature [41] and ocean acidification [42].…”

“…• C [16,26,58,61]. Then, cyclones have been reported to occur in Moorea during two El Nino events in 1983 and 1991, but in general are rare in French Polynesia (Table 1).…”

A boom–bust phylum? Ecological and evolutionary consequences of density variations in echinoderms

“…This sea star generally occurs in low densities of ;0.06 individuals/ha (Endean 1974), but apparently sustainable populations of ;26 individuals/ha have been observed in Panama (Glynn 1973). The earliest reports of massive population increases were from the Great Barrier Reef in 1957; subsequently, outbreaks were reported across the IndoPacific including Japan (Yamaguchi 1986), Hawaii (Branham et al 1971), Micronesia (Colgan 1987), French Polynesia (Adjeroud et al 2005), the Andaman Sea (Chansang et al 1987), and the Red Sea (Ormond and Campbell 1974).…”

Recovery from disturbance of coral and reef fish communities on the Great Barrier Reef, Australia

“…Disturbances on coral reefs range from local physical disturbances such as storm waves, which have differential effects on sections of the same reef and usually last a few days (Cheal et al 2002, Halford et al 2004, Adjeroud et al 2005 to larger scale and longer term phenomena such as outbreaks of the crown-of-thorns starfish Acanthaster planci and coral bleaching, which affect numerous reefs within a sector and persist for weeks to years (Moran 1986, Sano et al 1987, Berkelmans & Oliver 1999, Marshall & Baird 2000, Sano 2000, Wilkinson 2004. The major impact ABSTRACT: Coral reefs are consistently and increasingly subject to acute disturbance events that often lead to a reduction in live coral cover with concomitant effects on the diversity and abundance of coral reef fishes.…”