ABSTRACT
For sessile intertidal organisms, periods of low tide impose both cellular and physiological challenges that can determine bathymetric distribution. To understand how intertidal location influences the cellular response of the bivalve Perumytilus purpuratus during the tidal cycle (immersion-emersion-immersion), specimens from the upper intertidal (UI) and lower intertidal (LI) of bathymetric distribution were sampled every 2 h over a 10-h period during a summer tidal cycle. Parallelly, organisms from the UI and LI were reciprocally transplanted and sampled throughout the same tidal cycle. Levels of oxidative damage (lipid peroxidation and protein carbonyls) as well as total antioxidant capacity and total carotenoids were evaluated as cellular responses to variations in environmental conditions throughout the tidal cycle. The results indicate that both the location in the intertidal zone (UI/LI), the level of aerial exposure, and the interaction of both factors are determinants of oxidative levels and total antioxidant capacity of P. purpuratus. Although oxidative damage levels are triggered during the low tide period (aerial exposure), it is the UI specimens that induce higher levels of lipid peroxidation compared to those from the LI, which is consistent with the elevated levels of total antioxidant capacity. On the other hand, organisms from the LI transplanted to the UI increase the levels of lipid peroxidation but not the levels of protein carbonyls, a situation that is also reflected in higher levels of antioxidant response and total carotenoids than those from the UI transplanted to the LI. The bathymetric distribution of P. purpuratus in the intertidal zone implies differentiated responses between organisms of the lower and upper limits, influenced by their life history. A high phenotypic plasticity allows this mussel to adjust its metabolism to respond to abrupt changes in the surrounding environmental conditions.
ABSTRACT
Many invertebrates enclose their embryos within egg capsules, from which the offspring hatch. In marine gastropods that brood their egg capsules, hatching could involve radular activity by the mother or by unhatched stages, increased osmotic concentration of the intracapsular fluid, or production of hatching enzymes. The present research sought to determine whether mechanical action by the brooding female or by the encapsulated embryos was involved in the hatching for two sympatric and closely related species of calyptraeid: Crepipatella dilatata, which exhibits direct development without free-living larvae, and Crepipatella peruviana, which releases free-living veliger larvae. We also considered the role that enzymatic action or osmotic changes in the intracapsular fluid might play in hatching. Using scanning electron micrograph analyses, we found no evidence that the well-developed, pre-hatching juvenile radula of C. dilatata played any role in the hatching process and that the radula of C. peruviana did not even develop until long after hatching; so there was no evidence of radular activity involved in the hatching of either species. For C. peruviana, the intracapsular fluid osmolality was always higher than that of the surrounding seawater, suggesting that there is a strong natural water inflow during development. Moreover, when egg capsules of C. peruviana were exposed to lower ambient salinities, the substantial entry of water correlated well with high percentages of hatching, particularly for egg capsules containing advanced veligers, suggesting that an osmotic mechanism may be involved in the hatching process of this species. In contrast, hatching in C. dilatata appeared to be enzymatically mediated.
