Morphology and total lipids in Thysanoessa macura from the southern part of the Indian Ocean during summer. Spatial and sex differences

Abstract

Samples obtained during austral summer (February) were utilized to study the morphological differences of Thysanoessa macrura and the total lipid content, in relation to sex and geographic location. This species shows an evolution in morphometry, its carapace length increases slightly with sexual maturation, and its second thoracic leg becomes bigger and stronger, as well as its dactylus and especially the setae in the dactylus, which are stronger in a bigger animal allowing them to feed on other lipid-rich zooplankton. All these characteristics seem to support the hypothesis that animals change their diet during this period, allowing them to grow faster during summer, and accumulate lipids as a reserve material. This hypothesis is supported by a steeper slope in the length-weight regression during summer and an even steeper slope of the regression between carapace length and total lipids, especially adults. Great differences in lipid content were found between subadults and adults during this season, being higher in adults and, especially females. Lipids were higher in the northern stations in frontal area. A significant difference in lipid content was found among the stations sampled. Also a significant difference in lipid content was found between subadults, males and females. The species has a longer reproductive season than previously thought, which could depend on local conditions. Its development is accelerated during the summer bloom. Life history strategies of subadults and adults are apparently quite different, according to our lipid results and morphometrics data. Lipids reserves in subadults are not accumulated during summer, thus, T. macrura must accumulate massive amounts of lipids during autumn or late summer as a survival strategy of the species, as proposed for other species.