AME 30:49-56 (2002)  -  doi:10.3354/ame030049

ABSTRACT: Habitat, seasonality and species distribution of the marine fungoid protists, thraustochytrids, were investigated in a coastal area of the Ligurian Sea (NW Mediterranean). Three habitats (the sandy surf area, the middle of a 5 m seawater column, and its underlying sandy sea bottom) were monitored monthly for 1 yr. Thraustochytrids in the surf and sea bottom sandy samples yielded average densities of 4.4 ± 4 and 6.1 ± 5.3 x 10⁴ cells l^-1, respectively. In both sandy habitats, a similar seasonal trend was observed: the highest densities were recorded in late spring, while a significant drop in densities occurred during the autumn-winter period. In the water column, the density of thraustochytrids was much lower, 1.3 ± 1 x 10² cells l^-1 and did not show significant seasonal variations. A positive relationship between organic matter and thraustochytrid densities occurred in the sandy sea bottom. Among the nutrients assessed in the water column, only total phosphorus was related to variations of thraustochytrid densities. The 3 habitats analyzed showed marked differences in species number and assemblage. A higher number of species were found in the sandy sea bottom than in the sandy surf area and in the seawater column. The genus Thraustochytrium was the most abundant in the sandy bottom habitat. Among Thraustochytrium species, those characterized by sporangia with proliferation bodies were dominant. Species of the genus Schizochytrium, typically forming a cluster of sporangia, were dominant in the sandy surf area. Here, the possible ecological significances of these species¹ features are discussed.

KEY WORDS: Thraustochytrid protists · Abundance · Seasonal variations · Species assemblages · Mediterranean coasts