Considerations about Coscinodiscus wailesii (Diatomeae) on the Santa Catarina island coast, Brazil

Abstract

Universidade Federal Fluminense - Instituto de Biologia Programa de Pos-graduacao em Biologia Marinha (Caixa Postal 100.644 Niteroi, RJ, Brasil) *Corresponding author: daviamt@gmail.com Coscinodiscus wailesii Gran et Angst, first described in the Pacific Ocean by Hasle and Lange (1992) but which has since been occupying oceans and coastal seas all over the world, is considered an invasive species. It is frequently found in high concentrations as the dominant organism with densities higher than 90% (DURSELEN; RICK, 1999; EDWARDS et al., 2001). In Brazil it has only been registered in recent studies such as those undertaken by Valente-Moreira (1987), Moreira-Filho et al. (1990), Souza-Mosimann et al. (1993), Fernandes et al. (2001) and Tenenbaum et al. (2004). It is likely that the species was introduced by the discharge of ballast water (FERNANDES et al., 2001). The register of C. wailesii in Brazilian waters only as recently as 1987 may also be due to a misidentification as it is very similar to C. concinnus Wm. Smith. As Wiltshire and Durselen (2004) emphasize, both species co-exist in the North Sea and have similar dimensions. It suggests that this confusion might have arisen in studies conducted in Brazil. There exists, therefore, the possibility that the occurrence of C. wailesii in Brazilian waters anteceded any existing publication on it. As an invasive organism C. wailesii replaces the native phytoplankton by competition, decreasing biodiversity (EDWARDS et al., 2001). The success of the species is related to its resistance to different temperatures and salinities, higher tolerance to heavy metals than is shown by native species and the large size of its cells, unpalatable to planktonic herbivores (DURSELEN; RICK, 1999). Coscinodiscus wailesii is considered a potentially harmful species due to its production of insoluble mucilage which adversely affects fishing activities (EDWARDS et al., 2001). These organisms develop high biomass leading to oxygen and nutrient depletion, adversely affecting mussel and seaweed cultivation (FERNANDES et al., 2001; PROENCA; FERNANDES, 2004). The depletion of inorganic nitrogen in areas cultivated with the seaweed Porphyra (Nori) causes talus whitening and consequent economic loss (NISHIKAWA; YAMAGUCHI, 2008). It is important to consider the potential economic impact of C. wailesii in estuaries and coastal areas, especially in the Santa Catarina State where large mariculture projects are undertaken. This study presents the cell characterization and aspects of the distribution of C. wailesii in the Santa Catarina Island coastal waters. The samples analyzed were collected at three sites on Santa Catarina Island, South-Western Atlantic, Brazil (Fig. 1): the Ratones Grande Station (RGS) (27o28’30.52”S - 48o33’27.27”W) and Guarazes Station (GS) (27o33’20.09”S - 48o33’27.50”W) on the central-west coast and Pantano do Sul Station (PSS) (27o47’24.97”S - 48o30’39.31”W) in the south-east. The RGS and GS stations receive the influence of the rivers and mangrove swamps of Ratones and Itacorubi mainly as regards their nutrient contribution, which includes phosphorus and nitrogen, and of the fresh water draining from the adjacent continental areas (PAGLIOSA et al., 2005; PAGLIOSA et al., 2006). The PSS station is located in an area open to the sea. Sampling was carried out monthly from January 2007 to January 2008. Water was collected from the surface. Temperature and salinity were measured in situ , with an Arba thermometer and a Shibuya refractometer. Coscinodiscus wailesii cells were quantified using an inverted microscope and following Utermohl (1958). A complete 5 ml chamber was counted for each sample. Ten to thirty transects in a 1ml chamber were counted for total phytoplankton.