Fringing Reefs of Reunion Island and Eutrophication Effects - Part 1: Long-Term Monitoring of Two Shallow Coral Reef Communities

Abstract

No . 5 9 6 P AR T 1 : L o n g -T e r m Mo n i t o r i n g o f T wo S h a l l o w Co r a l Re e f Co mmu n i t i e s C a t h e r i n e T o u r r a n d , Od i l e N a i m, L i o n e l B i g o t , C h r i s t o p h e C a d e t , B r u c e C a u v i n , S t u a r t S e mp l e , L u c i e n F . Mo n t a g g i o n i , P a s c a l e C h a b a n e t a n d He n r i c h B r u g g e ma n nNo . 5 9 7 No . 5 9 7 P AR T 2 : L o n g -T e r m Mo n i t o r i n g o f P r i ma r y P r o d u c e r s Od i l e N a i m, C a t h e r i n e T o u r r a n d , E n r i c B a l l e s t e r o s , S t u a r t S e mp l e , L i o n e l B i g o t , B r u c e C a u v i n , P a s c a l e C u e t , a n d L u c i e n F . Mo n t a g g i o n i No . 5 9 8 P AR T 3 : L o n g -T e r m Mo n i t o r i n g o f L i v i n g Co r a l s Od i l e N a i m, C a t h e r i n e T o u r r a n d , Ge r a r d F . F a u r e , L i o n e l B i g o t , B r u c e C a u v i n , S t u a r t S e mp l e a n d L u c i e n F . Mo n t a g g i o n iA T OL L R E S E AR C H B UL L E T I N NOS . 5 9 6 -5 9 8 FRINGING REEFS OF REUNION ISLAND AND EUTROPHICATION EFFECTS ABSTRACTThis study assesses changes in subtidal benthic communities on the largest reef flat in Reunion, Saint-Gilles La Saline, using several types of surveys. Temporal and spatial trends are documented over a 22 year period , thus spanning the 1998 and 2000s bleaching events. The most plausible explanations for the observed trends are proposed. We chose two sites that are characterized by two types of community and metabolism: (1) an oligotrophic site dominated by Acropora corals (Site-Toboggan), where sea-urchins are numerous and macroalgae rare and (2) a dystrophic site dominated by non-Acropora corals, mostly massive and submassive, where macroalgae abound and sea-urchins are almost absent (Site-Planch'Alizés). Results are presented in three parts : Part 1 : general trends of the communities, part 2 : primary producers, part 3 : living corals.Part 1 presents three surveys. Survey 1 reports status and trends across the reef flats in 1993, 1996, and 2002, with all attached benthic components reported at the level of the species where possible. Survey 2 reports composition and changes in associated sedentary organisms such as sea urchins, holothurids, and the Pomacentridae fish Stegastes. Survey 3 focuses on the period 1998 to 2009 on permanent transects established in 1987 and monitored periodically, partly as a contribution to the Global Coral Reef Monitoring Network (GCRMN). In general, community structures at both locations remained stable, with primary producer coverage around 5% at Toboggan (T) and around 60% at Planch'Alizés (P). Living coral coverage averaged around 17% at both sites, but it was dominated by Acropora on Site-T (68%) and by massive corals on Site-P (88%). Regular echinoids were very abundant at T but almost absent from P, while the opposite was true for holothurids. The territorial damselfish Stegastes was of comparable abundance at both sites (<1 individuals per m 2 ). There were large changes in...

Fringing Reefs of Reunion Island and Eutrophication Effects - Part 2: Long-Term Monitoring of Primary Producers

“…However, at Site-P, upward-growing blades were also observed on vertical walls of coral cavities. As in Tourrand et al (2013), the monitoring time was divided into 3 periods: 1987-98, 1999-2003, 2004-2009. At T180, the permanent transect on Site-T (Table 1), the turfs increased significantly from 1987-98 to 2004-09 (Fig.…”

“…were previously described in details in Tourrand et al (2013). At "Toboggan" and "Planch'Alizés" sites, the inner parts of the fringing reef extend over 330 m from the shoreline seawards.…”

“…As far as we know, on the three sites of La Saline reef, labelled "Planch'Alizés" (Site-P), "Club Med", and at "south of the Hermitage pass" (see Fig.1, Tourrand et al, 2013), macroalgae were extremely abundant (Naim, 1993 and unpublished). In 1980's, in summer, perennial Gracilaria canaliculata populations were observed overgrowing and as a result, killing living coral colonies at Site-P and Site-Club Med (Photograph 1).…”

“…Mioche & Cuet (2002) regarded then MAS as an altered stage of ACR in a nutrientenriched environment. The increase of biomass of primary producers, especially of macroalgae, as well as productivity, may negatively impact stenoecious organisms, such as Acropora as well as the sea urchins, Echinometra mathaei and the Diadematidae, Diadema spp and Echinothrix diadema, by exposing them to elevated respiration rates, these genera and/or species being rare or completely absent in MAS (Semple, 1997;Tourrand et al, 2013). Table 6 gives the dominant facies at both sites in the 1980's, when the primary producers were the lowest at Site-T and the highest at Site-P. at low tide SiO 2 < 5 µM (Cuet, 1989b) at low tide 10 µM < SiO 2 < 50 µM (Cuet, 1989b) back reef water concentrations:…”

Fringing Reefs of Reunion Island and Eutrophication Effects - Part 3: Long-Term Monitoring of Living Corals

“…Reunion, Mauritius and Rodrigues), although far away from major pollution hotspots, are no longer pristine: over-nutrification, hypersedimentation and overfishing are major causes of stress Turner & Klaus, 2005). Coral bleaching has had a medium impact to date, although anomalies in subsurface water temperatures have increased (McClanahan et al, 2007;Tessier et al, 2008;Tourrand et al, 2013).…”