Comparison of populations of Tanais dulongii (Tanaidacea) in pristine and impacted coastal environments of Argentina

CARLOS E. RUMBOLD; SANDRA OBENAT; EDUARDO SPIVAK

Mar del Plata

Congreso; Coastal and estuarine research federation 2012; 2012

Coastal and estuarine research federation, Universidad Nacional de Mar del Plata

Animal populations are influenced by the change in space and time of environmental factors such as salinity, temperature, availability of shelter and feeding sites, presence of competitors and predators, and organic matter of sediment. These factors have a great influence on population dynamics, affecting for example density and sex-ratio. The aim of this study was to compare two populations of Tanais dulongii, in natural and impacted coastal environments of Mar del Plata. Five replicate samples were collected seasonally in the intertidal La Estafeta (natural area: 38° 09´ S - 57° 38´ W) and Mar del Plata Harbor (impacted area: 38° 02´ S - 57° 32´ W) during 2011. The material was fixed in 70% alcohol. In the laboratory, samples were weighed and tanaid specimens were counted and sexed. Density was expressed as number of individuals per 100 gr (wet weight) of sample and was higher in La Estafeta (382 ± 82 ind/100 gr; mean ± SE) than in Mar del Plata Harbor (5 ± 2 ind/100 gr). In the latter, density remained unchanged, whereas in La Estafeta maximum values were recorded during autumn (787 ± 176 ind/100 gr) and winter (455 ± 37 ind/100 gr), which differed significantly from Harbor results. Mean densities of males, ovigerous females, pre-ovigerous females (in all groups: 1 ± 1 ind/100 gr) and non-reproductive individuals (mean: 5 ± 2 ind/100 gr) did not differ seasonally in Mar del Plata Harbor. In La Estafeta, instead, males reached their maximum density in winter (15 ± 2 ind/100 gr), non-reproductive individuals in autumn (721 ± 170 ind/100 gr), pre-ovigerous females in autumn and winter (55 ± 12 and 71 ± 7 ind/100 gr; respectively), and ovigerous females did not showed seasonal variation (mean: 8 ± 2 ind/100 gr). Finally, the sex ratio (males / males + females) was always female biased in both populations (mean Harbor: 0.15; mean La Estafeta: 0.16). The analyzed population parameters varied between pristine and human impacted habitats.