Reproductive strategy and egg morphology of the copepod Acartia tonsa in a temperate estuary, Argentina

BERASATEGUI, A. A; HOFFMEYER, M.S; BIANCALANA F.; DUTTO, M. S.

Pucon

Simposio; 5th International Zooplankton Production Symposium; 2011

PICES-ICES-COPAS

The warm-water species Acartia tonsa has a wide distribution in estuarine areas, showing variation in morphological and physiological characteristics of its subitaneous and resting eggs. This work aims to evaluate the temporal variability in female size (PL prosome length), egg production (EP), egg hatching success (HS) and egg morphology of Acartia tonsa in the Bahia Blanca estuary. Experimental incubations were conducted with field females simulating in situ environmental conditions. Non-parametric tests were used to analyze the relationships among all variables. Three morphological types of eggs (I, II, III) were described according to their spine length (SL) by optic microscopy and SEM (SL I: 2.55 µm; SL II: 3, 25 - 7.95 µm; SL III: 8.5 -16.15 µm). Low egg production was recorded during the winter period (6.56 eggs. f-1.d-1) in which the presence of the three morphotypes was observed. However, the chorion morphology was independent of the hatching response, being the three morphological types, resting eggs with delayed hatching. Eggs differed significantly in diameter (D) and SL during winter from the eggs that were laid during summer. Negative correlations between SL- temperature (- 0.95) and between D-temperature (-0.75), were found. On the other hand, a positive correlation (0.74) between D (including spines) and PL was detected. During the summer period smaller females, higher egg production of subitaneous type I eggs (12.95 eggs. f-1.d-1) and higher hatching success, were observed. Temporal variability in the reproductive A. tonsa strategy, would allow it to remain in the plankton throughout the year.