Specific plasticity of the anemone Anthopleura hermaphroditica to intertidal and subtidal environmental conditions of the Quempillén estuary.

The cellular capacity of marine organisms to address rapid fluctuations in environmental conditions is decisive, especially when their bathymetric distribution encompasses intertidal and subtidal zones of estuarine systems. To understand how the bathymetric distribution determines the oxidative damage and antioxidant response of the estuarine anemone Anthopleura hermaphroditica, individuals were collected from upper intertidal and shallow subtidal zones of Quempillén River estuary (Chile), and their response analysed in a fully orthogonal, multifactorial laboratory experiment. The organisms were exposed to the effects of temperature (10°C and 30°C), salinity (10 ppt and 30 ppt) and radiation (PAR, > 400-700 nm; PAR+UV-A, > 320-700 nm; PAR+UV-A+UV-B, > 280-700 nm), and their levels of lipid peroxidation, protein carbonyl and total antioxidant capacity were determined. The results indicated that the intertidal individuals of A. hermaphroditica presented higher levels of tolerance to the stressful ranges of temperature, salinity, and radiation than individuals from the subtidal zone, which was evident from their lower levels of oxidative damage to lipids and proteins. These results were consistent with increased levels of total antioxidant capacity observed in subtidal organisms. Thus intertidal individuals could have greater plasticity to environmental variations than subtidal individuals. Future studies are needed to understand the mechanisms underlying stress adaptation in individuals from this estuarine anemone subjected to different environmental stressors during their life cycles.

Growing Safe: Acute Size Escape from Desiccation in Juvenile Crepipatella peruviana (Mollusca: Gastropoda).

Desiccation is an important limiting factor in the intertidal zone. Generally decreasing seaward, desiccation stress can also be alleviated in wet microhabitats. Juvenile snails are generally more susceptible to desiccation than adults, and, for some species, juveniles must therefore hide in microhabitats to survive emersion. The transition from hiding in safe microhabitats to being able to survive fully exposed for the duration of low tide is not well documented. In this study, we investigated the influence of size on desiccation tolerance in juveniles of the calyptraeid gastropod Crepipatella peruviana to determine the size at which they can first survive exposure to air. Juveniles 2-13 mm long were exposed to 75% or 100% relative humidity for 0.5-6.5 hours. Juveniles smaller than 5 mm in shell length did not survive emersion at 75% relative humidity for even 0.5 hours; surprisingly, most also perished after short exposures to air at 100% relative humidity, suggesting that something other than desiccation stress may also be at play. In marked contrast, 82% of juveniles larger than 6 mm in shell length survived exposure to 75% relative humidity for the full 6.5 hours. In a field survey, no juveniles smaller than 9 mm were found on exposed rock but rather were found only in wet microhabitats. We suggest that the clearly defined size escape from desiccation may reflect a change in gill functioning or a newfound ability to retain water more effectively within the mantle cavity at low tide.

Role of the Substrate in Feeding and Growth of the Marine Suspension-Feeding Gastropods Crepidula fornicata and Crepipatella peruviana.

Unlike lamellibranch bivalves, suspension-feeding calyptraeid gastropods lack siphons and paired shell valves to regulate water inflow. This study was designed to determine if calyptraeid gastropods use the solid surface to which they attach to facilitate food particle capture. Juveniles of both Crepidula fornicata and Crepipatella peruviana were maintained with phytoplankton for 3 to 6 wk in the laboratory, either attached to solid substrate or without solid substrate. Individuals of C. fornicata and C. peruviana that were reared on solid substrate grew about five to ten times more, or two times more, respectively, than those deprived of solid substrate. Final tissue weights were also significantly greater for individuals of both species that had been reared on solid substrate. For the two species, phytoplankton clearance rates were about two to three times higher for individuals attached to solid substrate than for those without solid substrate; rates of food cord production from the gills were also significantly higher. About 50% of C. peruviana that were deprived of solid substrate died during the first 3 wk of observation, and about 60% were dead by 6 wk. In contrast, most individuals of C. peruviana that were attached to solid substrate survived for the entire 6-wk study period, and all of the C. fornicata survived whether or not they were attached to solid substrate. The solid substrate to which calyptraeid gastropods attach clearly plays an important role in their feeding biology, although the precise role remains to be explored.

Brooding in the Chilean oyster Ostrea chilensis: unexpected complexity in the movements of brooded offspring within the mantle cavity.

Brooding in invertebrates serves to protect embryos from stressful external conditions by retaining progeny inside the female body, effectively reducing the risk of pelagic stages being exposed to predation or other environmental stressors, but with accompanying changes in pallial fluid characteristics, including reduced oxygen availability. Brooded embryos are usually immobile and often encapsulated, but in some Ostrea species the embryos move freely inside the female pallial cavity in close association with the mother's gills for as long as eight weeks. We used endoscopic techniques to characterize the circulation pattern of embryos brooded by females of the oyster, Ostrea chilensis. Progeny at embryonic and veliger stages typically circulated in established patterns that included the use of dorsal and ventral food grooves (DFG, VFG) to move anteriorly on the gills. Both embryos and veligers accumulated around the mother's palps, and remained there until an active maternal countercurrent moved them to the gill inhalant area. Both food grooves were able to move embryos, veligers, and food-particle aggregates anteriorly, but the DFG was more important in progeny transport; early embryos were moved more rapidly than veligers in the DFG. A microcirculation pattern of embryos was apparent when they were moved by gill lamellae: when they were close to the VFG, most embryos lost gill contact and "fell" down to the DFG. Those that actually reached the DFG moved anteriorly, but others came into contact with the base of the lamellae and again moved towards the VFG. The circulation pattern of the progeny appears well-suited for both cleaning them and directing them posteriorly to an area where there is more oxygen and food than in the palp region. This process for actively circulating progeny involves the feeding structures (gill and palps) and appears to be energetically costly for the female. It also interferes with feeding, which could explain the poor energy balance previously documented for brooding females of this species.