The impact of industrial and urban sewage outflows off tropical high islands is an important environmental problem. This problem is yet more acute when there are coral reefs. For Mauritius Island the effects of the main sewer outflow was studied. Dispersion of the plume was modelized using a bidimensional code. Seawater physical and chemical classic parameters, plus fecal bacteriological ones, were also recorded and used for the modeling of oceanic waters and reefal ones. Sediment parameters of the inner reef flat were analyzed for grain-size indices and silt ratio, living and detrital organic matter contents, and then trace metals composition. ACP statistical analyzes performed allow to map the sewage outflow influences, showing a clear decreasing gradient from this point. Qualitative analyzes of the distribution of macrobenthic species living of the reef mainly those known in the SW Indian Ocean as biologic indicators of some edaphic conditions, were also done. The main edaphic facies induced by the sewage outflow plume was the growth of a high and dense carpet of the green algae creating anoxic conditions at the sediment-wafer interface. High densities of sea urchins seem more the consequences of an overfishing on the reef flat, destroying the carnivorous fishes. Nevertheless these sea urchins outbreaks are characteristic of degraded stages of the coral reef communities as it is well known in the SW Indian Ocean.

The spatial distribution of ciguateric dinoflagellates was investigated in the coral reef lagoon of the island of Mayotte at the end of the dry season of (1992). Both oceanic and lagoonal waters were oligotrophic. Different substrates were investigated (algae, algal turfs and dead corals) in two areas. One area consisted of a transect between an alluvial coastal bay and the outer barrier reef, through lagoonal patch-reefs, and a second area comprised a lagoonal complex. On nearly all the substrates, the dinoflagellates Gambierdiscus toxicus Adachi and Fukuyo, Ostreopsis spp. and Promcentrmn spp., generally exhibited the following relative abundances: Ostreopsis spp. > Prorocemnim spp. > G. toxicus. Highest abundances of all species of dinoflagellales, particularly G. toxicus, occurred on dead corals, more especially on the inner slope of the barrier reef and on lagoonal patch-reefs, but not at the back of the bay nor on the barrier reef outer slope. On macroalgal substrates, dinoflagellates were moderately abundant, but some substrates, such as several red algae, supported higher abundances suggesting a stimulation. Experimental bio-assays to compare growth in seawatcrs previously incubated with macroalgae, showed pre-conditioned seawaters could be either stimulatory or inhibitory. The red alga, Halymeniu floresia (Cryptonemiaceae), inhibited growth of G. toxicus, while Portieria hornemanii stimulated it. Growth was also slightly stimulated by the brown algae Turbinaria ornatu and Surgassum cf. turbinatifolium (Sargassaceae). Both red algae stimulated the growth of Ostreopsis ovatu to a similar degree.

Other| November 01, 1989 La sedimentation actuelle dans le lagon de Mayotte (ile volcanique a recif-barriere, SW ocean indien) et son evolution recente en liaison avec les apports terrigenes B. A. Thomassin; B. A. Thomassin Author Stn. Mar. Endoume, Marseilles 13007, France Search for other works by this author on: GSW Google Scholar A. Arnoux; A. Arnoux Author Search for other works by this author on: GSW Google Scholar J. Coudray; J. Coudray Author Search for other works by this author on: GSW Google Scholar C. Froget; C. Froget Author Search for other works by this author on: GSW Google Scholar B. Gout; B. Gout Author Search for other works by this author on: GSW Google Scholar G. Kouyoumontzakis; G. Kouyoumontzakis Author Search for other works by this author on: GSW Google Scholar J. P. Masse; J. P. Masse Author Search for other works by this author on: GSW Google Scholar Y. Reyre; Y. Reyre Author Search for other works by this author on: GSW Google Scholar J. P. Reys; J. P. Reys Author Search for other works by this author on: GSW Google Scholar E. Vacelet E. Vacelet Author Search for other works by this author on: GSW Google Scholar Author and Article Information B. A. Thomassin Author Stn. Mar. Endoume, Marseilles 13007, France A. Arnoux Author J. Coudray Author C. Froget Author B. Gout Author G. Kouyoumontzakis Author J. P. Masse Author Y. Reyre Author J. P. Reys Author E. Vacelet Author Publisher: Société Géologique de France First Online: 03 Mar 2017 Online Issn: 1777-5817 Print Issn: 0037-9409 GeoRef, Copyright 2012, American Geosciences Institute. Reference includes data from PASCAL, Institute de l'Information Scientifique et Technique, Vandoeuvre-les-Nancy, France Bulletin de la Société Géologique de France (1989) V (6): 1235–1251. https://doi.org/10.2113/gssgfbull.V.6.1235 Article history First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation B. A. Thomassin, A. Arnoux, J. Coudray, C. Froget, B. Gout, G. Kouyoumontzakis, J. P. Masse, Y. Reyre, J. P. Reys, E. Vacelet; La sedimentation actuelle dans le lagon de Mayotte (ile volcanique a recif-barriere, SW ocean indien) et son evolution recente en liaison avec les apports terrigenes. Bulletin de la Société Géologique de France 1989;; V (6): 1235–1251. doi: https://doi.org/10.2113/gssgfbull.V.6.1235 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin de la Société Géologique de France Search Advanced Search This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.