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Abstract

Eurytemora americana and Acartia tonsa are two of the most important copepods from the Bahía Blanca estuary plankton. In this study 30 females from each species were sorted from seasonal and recently preserved zooplankton samples. Prosome length (PL), width (PW) and height (PH) and urosome length (UL) and width (UW) were measured and subsequently the following ratios determined: PL:PW, PL:PH, PW:PH and PL:UL. Individual volumes for E. americana and A. tonsa females were estimated following the morphometric method in order to obtain individual biomass values for rapid application in the future. The formula for individual volume was: V (mm 3 )= π (PL PW PH)/6 + π (UL UW 2 )/4. Regression tests were conducted for both species utilizing individual volume vs prosome length or width as independent variables and fitting data to a power model. Covariance analysis and single comparison between regression lines were used in order to evaluate the temporal behavior of these relationships. PL:UL was the best ratio for separating one species from the other, being 1.46 for E. americana and 3.53 for A. tonsa. Average individual volume and std. error estimated for E. americana and A. tonsa were 0.0749 (± 0.0097) mm 3 and 0.0399 (± 0.0049) mm 3 , respectively. Despite their similar size, strong differences between

Reproductive trade-off of the copepod Acartia tonsa in a hypersaline estuary of the Southwestern Atlantic. Temporal variations in the morphology of eggs

“…This trend could be translated as a metabolic balance in favour of body mass with resting egg production during the Sabatini 1995). The seasonal variations in female size could be attributed to the seasonal variations in temperature and in the typical food conditions in BBE (Hoffmeyer & Torres 2001). Lower temperatures lead to a less-costly metabolism as well as a lower reproductive activity (Gaudy et al 2000;Hansen et al 2010a).…”

“…This copepod is found in the water column throughout the year, with maximal abundance during the warm season (austral summer: December to March) and minimal abundance during the cold season (austral winter: June to August), when temperature decreases and the environment becomes unfavourable for the species (Sabatini 1989;Hoffmeyer 1994Hoffmeyer , 2004. Although females in BBE have shown seasonal variation in their body size (Sabatini 1989;Hoffmeyer & Torres 2001), the relationship between body size and reproductive traits has not yet been addressed. Likewise, although the production of subitaneous eggs with different spine lengths in this estuary has also been reported (Diodato et al 2006), its relationship with the size of females, the production of morphotypes relative to embryogenesis and resting stages has not yet been elucidated.…”