Faced with environmental stress, the females of many marine invertebrate species can isolate their brood chambers from the external environment for prolonged periods. Although brood chambers have therefore typically been assumed to protect the brooded embryos, the effects of continued isolation on conditions within brood chambers have not been examined. In the present research, we investigated the effects of external stress on conditions in the brood chambers for 2 sympatric species, the gastropod Crepipatella dilatata and the bivalve Ostrea chilensis. Both species incubate their embryos in the pallial cavity for at least 4 wk before the young emerge as larvae (oyster) or juveniles (gastropod). Brooding and non-brooding females were stimulated to isolate the pallial cavity from the external environment by exposing them to water of reduced salinity (<22 to 24 psu). We then recorded subsequent changes in salinity, dissolved oxygen, pH, and ammonium ion concentration within the pallial fluid. Although salinity within the pallial cavity remained high for both species, oxygen availability for brooding females of C. dilatata and O. chilensis dropped to hypoxic levels (<1.5 mg O2 l-1) within 12 h and 20 min, respectively. In addition, pH of the intrapal- lial fluid dropped substantially with prolonged maternal isolation, suggesting a possible impact on shell formation for brooded veligers. Indeed, in the case of C. dilatata, the pH of pallial fluid initially fell to 6.4, but then tended to become more basic after 6 h of maternal isolation, a possible conse- quence of shell dissolution. On the other hand, ammonium ion concentration increased progressively with prolonged maternal isolation. Our data show that, whereas initially the isolation mechanism protected incubated embryos from exposure to low salinity stress, continued isolation from the exterior transformed the brood cavity from a protective environment to an oppressive one, i.e. from a protective nursery to more of a prison.

Shallow-water coastal areas suffer frequent reductions in salinity due to heavy rains, potentially stressing the organisms found there, particularly the early stages of development (including pelagic larvae). Individual adults and newly hatched larvae of the gastropod Crepipatella peruviana were exposed to different levels of salinity stress (32(control), 25, 20 or 15), to quantify the immediate effects of exposure to low salinities on adult and larval behavior and on the physiological performance of the larvae. For adults we recorded the threshold salinity that initiates brood chamber isolation. For larvae, we measured the impact of reduced salinity on velar surface area, velum activity, swimming velocity, clearance rate (CR), oxygen consumption (OCR), and mortality (LC50); we also documented the impact of salinity discontinuities on the vertical distribution of veliger larvae in the water column. The results indicate that adults will completely isolate themselves from the external environment by clamping firmly against the substrate at salinities ≤24. Moreover, the newly hatched larvae showed increased mortality at lower salinities, while survivors showed decreased velum activity, decreased exposed velum surface area, and decreased mean swimming velocity. The clearance rates and oxygen consumption rates of stressed larvae were significantly lower than those of control individuals. Finally, salinity discontinuities affected the vertical distribution of larvae in the water column. Although adults can protect their embryos from low salinity stress until hatching, salinities <24 clearly affect survival, physiology and behavior in early larval life, which will substantially affect the fitness of the species under declining ambient salinities.