Salp and pyrosomid blooms and their importance in biogeochemical cycles

Abstract

Abstract The importance of salps and pyrosomas in biogeochemical cycles is related to their well-known periodical occurrence in vast swarms and to the way that they feed on phytoplankton. During the last 30 years, a large effort has been devoted to understanding the nutritional ecology of salps, revealing their high grazing impact on phytoplankton populations and their role in the downward flux of matter. In contrast, little attention has been paid, until recently, to the nutritional ecology of pyrosomas. However, they also have an important grazing impact while swarming, and produce very large numbers of faecal pellets. Estimation of the ecological and biogeochemical importance of salps has given rise to different types of models. Salps and pyrosomas are found periodically in dense swarms in various areas of the world oceans. The nutritional ecology of salps is characterized by: (1) very high filtration rates; (2) removal of minute particles and microorganisms with high efficiency; (3) high defaecation rates; and (4) production of large faecal pellets which sink rapidly. Moreover, the faecal material is enriched in several elements (e.g. carbon, nitrogen, calcium, and aluminium) compared to the salp itself, and degradation of the faecal pellets of oceanic salps is very slow (Yoon, 1995; see Yoon et al., 1996).