7thISS - Book - Porifera Research.pdf - Porifera Brasil - UFRJ

Porifera Research: Biodiversity, Innovation and Sustainability - 2007Reading the code of coral reef sponge communitycomposition and structure for environmental biomonitoring:some experiences from CubaPedro M. AlcoladoInstituto de Oceanología, Ave. 1ra, No. 18406, Playa, La Habana, Cuba. alcolado@ama.cuAbstract: The structure of exposed (non-cryptic) coral reef sponge communities could be considered as a potentially readablecoded message reflecting their physical environment. The present paper describes explorations in Cuba of the potential use ofsponge communities as bio-indicators. Clathria venosa is the sponge that most consistently has proved to be a bioindicator ofurban based pollution in Cuban coral reefs due to its stenotopic character with regard to this stress source. Iotrochota birotulataforma musciformis was abundant close to the polluted Havana Bay, but not in other polluted sites, making it inconsistent asindicator. It has been quite rare in non-polluted waters. Cliona delitrix was represented in an area with great sewage influence.However it did not appear in some polluted sites probably because corals were extremely scarce and small. Scopalina ruetzleriwas well represented close to bays with different degrees of urban based pollution. Cliona varians was well represented onlyin one polluted place. Multivariate analyses (cluster analysis, non-metric multidimensional scaled analysis) have proved to bevery useful tools to clearly segregate sites with regard to level of pollution, and to identify factors and interactions determiningcommunity structure and composition. Abundance or dominance of Tectitethya crypta and Cliona vesparia (alpha stage) weretypical of heavy sedimentation conditions; while Aplysina cauliformis tended to dominate in sites affected by both hurricanesand sedimentation (abundance increased by fragmentation). Meta-analysis of Shannon’s heterogeneity index H’ and Pielou’sequitability index J’ is proposed as a useful tool to classify and compare sites with regard to the way that sponges interprettheir environment (degree of severity and predictability). Meta-analysis by means of a scatter graph with ranges of H’ atdifferent depths provides a spatial framework for comparing and classifying sponge communities with regard to environmentseverity.Keywords: sponges, bio-indicators, coral reefs, CubaIntroductionMany papers have dealt with the factors and interactions thatdetermine sponge distribution and community characteristics(partly reviewed by Sarà and Vacelet 1973, Bergquist1978, Wulff 2006), but few have been explicitly devoted toexploring the potential usefulness of sponge communities asbio-indicators for environmental bio-monitoring purposes.In the last few decades, the search for bio-indicatorshas become an urgent need in a world environment that ischanging at an unprecedented rate. According to Alcolado(1984; with some added arguments), sessile taxa are suitableas potential environmental bio-indicators because:- They must be adapted to the environment due to theirimmobility. Thus, their abundance or their presence (or evenabsence) must reflect the average ecological conditions, orvery recent strong stressful events.- Their composition and community structure are not affectedby migrations or local displacements.- The exposed (non-cryptic) sponge communities, havingpassed the fish predation filter thanks to deterrence (Wulff1997), are influenced more by the physical environmentthan by ecological interactions within themselves (sensuBradbury 1977). Cooperation rather than competitionseems to be the rule among sponge populations (Sarà 1970)and, according to Rützler (1970), sponges are able to solvecompetition by entering into complex epizoic relationships,without detriment to their pumping and filtering activities.Reiswig (1973) adds that small sponge individuals (duringthe first year after settlement) are subject to severe mortalityby competition with other sessile organisms, but whensponges reach greater volume competitors have little furthereffect. On the other hand, sponges overgrow corals muchmore frequently than the reverse, although when the reverseoccurs, the sponge tissue shows no adverse effect (Jacksonand Buss 1975).- The absence of food partitioning mechanisms influencingcommunity structure.Such features favor sponges over many other zoologicalgroups as potential indicators. That does not mean thatthere could not be some degree of influence of biologicalinteractions, but apparently to a much lower extent than thephysical environment (light, waves, sediments, pollution) inbuilding up the community structure and composition. This