Seasonal and spatial variation of species toxicity in Mediterranean seaweed communities: correlation to biotic and abiotic factors

Abstract

The toxicity of crude extracts of 32 seaweed species from the western Mediterranean was analysed by Microtox ® assay in spring and autumn of 1996 and 1997. The species analysed represented more than 76% of seaweed coverage in the 3 algal communities studied: photophilic and sciaphilic communities from the Cabrera Archipelago (Balearic Islands), and a hemisciaphilic community from the Medes Archipelago (northeastern Iberian Peninsula). Most species showed seasonal variation of toxicity, which was greater in species from Cabrera than in those from Medes. Both, intra and interspecies variation of toxicity were found. Moreover, comparison of mean toxicity of these communities showed that toxicity was higher in November than in June in all cases, and that the photophilic community had both the highest number and the most toxic species. To make an ecologically relevant interpretation of the toxicity detected by Microtox ® , we compared the toxicity of extracts analysed by the Microtox ® test and those analysed by the commonly used sea urchin embryo assay. In addition to seaweeds, some species of invertebrates (sponges and ascidians) were compared to ascertain whether the relationship between the 2 tests was applicable to species belonging to different phyla. These comparisons allowed us to establish that 0.5 gamma units in Microtox ® assay is the threshold value between toxic and non-toxic species. Following a light gradient from the photophilic to the sciaphilic communities, the seaweed species that were occasionally toxic increased while the always-toxic seaweeds decreased. Rhodophyta and Phaeophyta had a higher percentage of toxic species than Chlorophyta. Non-encrusting seaweed forms were more toxic than the encrusting ones, and in contrast to most other seaweeds, the non-encrusting calcareous species that increased coverage from June to November simultaneously displayed a marked decrease in toxicity. We conclude that the temporal variation of toxicity observed in the seaweeds studied may be partially explained by intrinsic factors of the species (growth rates and growth shapes).

The Seasonal Fluctuation of the Antimicrobial Activity of Some Macroalgae Collected from Alexandria Coast, Egypt

“…These results are in accordance with those obtained from Atlantic samples by Hornsey and Hide (1974), from Mediterranean samples by Khaleafa et al (1975) and Stirk and Reinecke (2007) who reported that seasonal variation in antibacterial activity was observed with extracts which have antibacterial activity in late winter and early spring. This is in contrast to studies carried out by Rao and Parekh (1981), and Arun, Kumar and Rengasamy (2000) using Indian samples, and from Mediterranean samples by Martí et al (2004) who demonstrated the most active season was autumn. Salvador et al (2007), nevertheless, demonstrated that autumn and spring were the seasons with the highest percentage of active taxa against at least one test microorganism (69% and 67% respectively), followed by winter (56%) and summer (50%).…”

Chemical bioactivity of sponges along an environmental gradient in a Mediterranean cave

“…This significant negative correlation between sponge bioactivity and the number of positively associated species indicates that bioactivity may play an important role in the micro-structuring of animal-dominated benthic communities, as was found for algal-dominated communities from the same cave (Martí et al, 2004a). it has also been reported that allelochemical production plays a role in interference interaction between sponges in Caribbean communities Pawlik, 2000, 2005a,b).…”

“…although there are a few studies on the community structure and dynamics of Mediterranean caves (e.g. Gili et al, 1986;Bibiloni et al, 1989;zabala et al, 1989), to our knowledge chemically mediated interactions in invertebrate assemblages of caves have never been investigated (but see Martí et al, 2004a, for a study on seaweeds).…”

“…a threshold of 0.5 gamma units/mg sample was found to be appropriate to separate non-toxic from toxic species, because all the samples that reached this value had detrimental effects on sea urchin embryos (see Martí et al, 2004a, for a more detailed explanation).…”

“…The bioactivity measure used was a continuous variable and we did not know at which level the sponges had potentially noxious effects on other species; therefore, we established a criterion based on the relationship between the Microtox ® assay and the sea-urchin test (Martín and uriz, 1993;Martí et al, 2004a) to classify species into either a bioactive (toxic) or non-bioactive category. a threshold of 0.5 gamma units/mg sample was found to be appropriate to separate non-toxic from toxic species, because all the samples that reached this value had detrimental effects on sea urchin embryos (see Martí et al, 2004a, for a more detailed explanation).…”