Morphological variability, spatial distribution and abundance of Helicostomella species (Ciliophora, Tintinnina) in relation to environmental factors (Argentine shelf; 40-55º

LUCIANA SANTOFERRARA .; ALDER VA

SCIENTIA MARINA

INST CIENCIAS MAR BARCELONA

Lugar: ESPAÑA; Año: 2009 vol. 73 p. 701 - 716

0214-8358

For first time a taxonomic and ecological study of species belonging to Helicostomella were performed over a mesoescale by examining ca. 3000 loricae collected in Argentine shelf waters during austral autumn. Microscopic and statistical analysis revealed that the general shape and the oral diameter remained practically constant, despite a continuous length fluctuation of ca. 300 µm which includes the entire range present in eight previously reported species. Consequently, we consider that the genus maybe represented only by H. subulata, whose strong fluctuations in length (mostly attributed to an increase in the collar length), density and biomass seem to respond to temperature, food availability and front-related processes. Buenos Aires coastal waters associated with a quasi permanent estuarine front (40-40.5°S), mixed conditions would favour moderate abundances of long loricae, whereas in northern (42.5-45.5°S) and southern (46-54.5°S) Patagonian waters, high (103 ind. L-1 ) and low (<5 ind. L-1) densities of short loricae seem to be a consequence of stratification and encystment, respectively. The non-occurrence of the species at 41-42°S, together with a three-fold reduction in length-related parameters between specimens from Buenos Aires and Patagonian waters, suggests a disjunct distribution. Keywords: tintinnids, genus Helicostomella, lorica polymorphism, abundance, shelf dynamics, fronts, environmental factors. Running title: Taxonomy and ecology of genus Helicostomella.