Mucilage impact on gorgonians in the Tyrrhenian sea.

The mucilage phenomenon has affected the Tuscan Archipelago since its first appearance (1991) in the Tyrrhenian Sea (Mediterranean Sea) [Innamorati M, Raddi E, Buzzichelli A, Melley S, Demoulin M. Le mucillaggini nel Mar Tirreno. Biol Mar Suppl Notiz 1992;1:23-26; Sartoni G, Sonni C. Tribonema marinum J. Feldmann e Acinetospora crinita (Carmichael) Sauvageau nelle formazioni mucillaginose bentoniche osservate sulle coste toscane nell'estate 1991. Inf Bot Ital 1991;23:23-30; Sartoni G, Cinelli F, Boddi S. Ruolo di Tribonema marinum J. Feldmann ed Acinetospora crinita (Carmichael) Sauvageau negli aggregati mucillaginosi bentonici delle coste toscane. Biol Mar Suppl Notiz 1993;1:31-34]. Seasonally, these mucous aggregates become very common in the benthic domain. The gorgonians are the most exposed organisms because they provide the best support for mucilage growth; indeed, their long branches positioned in orthogonally with respect to the current so as to capture plankton, also trap the filamentous mucilage present in the water. A 3-year monitoring programme at Capo Calvo (Island of Elba) was carried out in order to study the appearance of the mucilage phenomenon and its impact on three species of gorgonians (Eunicella cavolinii, Eunicella singularis, and Paramuricea clavata). The composition of mucilage and the gorgonian recovery capacity, when damaged, were investigated. During the first year of study (1999), no relevant interactions between gorgonians and mucilages were recorded. Instead, massive presence of mucilages causing different types of damage to the different gorgonian species investigated was recorded during the second (2000) and third year (2001). The type and the extent of the impact of mucilages also depend on the season. Three species of algae (Nematochrysopsis marina, Chrysonephos lewisii and Acinetospora crinita) constitute the principal components of the mucilaginous aggregates. In general, the first two species occur during the spring season, down to 20 m, while A. crinita occurs at greater depths. In July, when the mucilages reach their maximum development, C. lewisii is the predominant species. This species mainly affects E. cavolinii and E. singularis while A. crinita mainly affects P. clavata, which colonizes greater depths.