The effects of eutrophication-related alterations to coral reef communities on agents and rates of bioerosion (Reunion Island, Indian Ocean)

Abstract

This study investigated the variation of bioerosional processes in relation to disturbances of reefal communities due to eutrophication. La Saline fringing reef (Reunion Island) is subjected to nutrient inputs from the adjacent land. Bioerosion by grazers, microborers, and macroborers was measured using experimental substrata exposed for 1 year in three sites characterized by different levels of nutrient input and benthic community response. The relationship between bioerosion and epilithic algal cover of hard substrata and the interactions between the various agents of bioerosion were analyzed with parametric statistics. Significant variations in bioerosion were found among sites, ranging from 1.63 to 3.52 kg CaCO 3 m -2 year -1 for grazing rates, from 6.73 to 32.25 g m -2 year -1 for macroboring rates, and from 43.78 to 67.56 g m -2 year -1 for microboring rates. One of the major factors controlling these variations appeared to be changes in the epilithic algal cover on substrata in response to changes in reefal water chemistry. In low nutrient areas, where dead corals were colonized mainly by algal turfs, erosion by microorganisms was low (43.78 g m -2 year -1 ) due to intense grazing (3.52 kg m -2 year -1 ). In reef zones receiving high nutrient inputs, the development of encrusting calcareous algae and macroalgae was associated with the lowest grazing (1.63 kg m -2 year -1 ) and macroboring (6.73 g m -2 year -1 ) rates recorded among sites. In contrast, high microboring rates (57.54 and 67.56 g m -2 year -1 ) were found in enriched areas in association with high macroalgal cover.

Swell impact on reef sedimentary processes: A case study of the La Reunion fringing reef

“…In the present study, the sampling depth, around 2 to 5 cm, could be associated with a time scale of one week to one month. Hence, the vectors computed before the swell event would be related to several previous transport processes, combined with the overprinting of biological activity (Chazottes et al, 2002). The vector trends computed after the swell event would be representative of contemporaneous transport processes, strictly related to this event.…”

“…In addition, this fringing reef shows a low coral diversity and a small area of live coral associated with increasing algal cover (Naïm et al, 2000). The few studies that have focussed on the sedimentology of the Ermitage-La Saline fringing reef described the compositional and grain-size characteristics of the sedimentary deposits (Montaggioni, 1978;Gabrié & Montaggioni, 1982;Chazottes et al, 2002Chazottes et al, , 2008. Despite these previous studies, there is still a lack of knowledge on the distribution and dynamics of sediments in the back-reef areas of the fringing reefs around La Reunion.…”

Heterozoan carbonates from the equatorial rocky reefs of the Galápagos Archipelago

“…In Panama, episodic eutrophication (via upwelling) determines distinct heterozoan biofacies resembling cool-water associations (Reijmer et al, 2012). Nutrient enrichment also leads to shallowing of deeper-water facies (Hallock, 2005), drowning events (Betzler et al, 1997(Betzler et al, , 2009Blomeier & Reijmer, 1999;Mallarino et al, 2002) and an increase of calcareous bioerosion (Chazottes et al, 1995;Glynn, 1997;Peterh€ ansel & Pratt, 2001;Radtke et al, 2011) that, in turn, alter or reduce carbonate buildups (Hallock, 1988;Chazottes et al, 2002Chazottes et al, , 2008Sch€ afer et al, 2011;Triollet & Golubic, 2011). In addition, nutrient levels are a key factor influencing reef recovery after mass mortality, with mean nutrient levels being almost as important in determining recovery speed as mean temperature .…”

Temperate bioerosion: ichnodiversity and biodiversity from intertidal to bathyal depths (Azores)

“…Only few studies have focused on community succession of bioerosion agents and the impact of changes in community on rates of bioerosion (Chazottes et al, , 2002Hassan, 1998;Tribollet et al, 2002;Tribollet & Golubic, 2005). Improving knowledge on communities of bioeroders, their succession over time and particularly their distribution along environmental gradients such as bathymetrical or latitudinal transects in modern carbonate ecosystems will allow us to better understand the dynamic of bioerosion in the past and will help reconstructing palaeoclimate and palaeoenvironments.…”