Accumulation and biotransformation dynamics of the neurotoxic complex, saxitoxin, in different life stages of Ostrea chilensis.

The neurotoxic complex saxitoxin, is a group of marine toxins that historically has significantly impacted human health and the ability to utilize marine resources. A steady increase in the distribution and intensity of Alexandrium catenella blooms in Chile, and around the world, has caused major ecological and socioeconomic impacts, putting this type of dinoflagellate, and its toxicity, in the spotlight. Ostrea chilensis is a commercially and ecologically important resource harvested from wild populations and farmed in centers of southern Chile, where it is exposed to large harmful algal blooms of the type that can cause paralysis in humans. This study contributes to our understanding about the transfer of toxins from A. catenella cells to juvenile and adult Ostrea chilensis by tracking transformations of the neurotoxic complex until it reaches its most stable molecular form in the intracellular environment of O. chilensis tissues. These biotransformations are different in O. chilensis juveniles and adults, indicating a differentiated response for these two life stages of this bivalve species. These studies can be used for similar analyses in other ecologically and commercially important species of filter feeding organisms, providing greater understanding of the specific interactions of bivalves in scenarios of toxic dinoflagellate proliferations (e.g. A. catenella blooms).

Brooding strategy in fluctuating salinity environments: oxygen availability in the pallial cavity and metabolic stress in females and offspring in the Chilean oyster Ostrea chilensis.

Organisms that encounter stressful situations in nature often cope using behavioral (e.g., avoidance) or physiological tactics. In sessile mollusks, the only available behavioral option in dealing with salinity stress is to "clam up", isolating their tissues from the environment. Though effective in the short term, prolonged isolation can have detrimental physiological consequences, particularly for females brooding embryos in a mantle cavity that is isolated from the external environment. In the Quempillén estuary, the Chilean oyster, Ostrea chilensis, spent nearly one-third of its brooding season at salinities low enough to cause female isolation. When females thus isolated themselves, the dissolved oxygen in their mantle cavity fluid dropped to hypoxic levels within 10 min. In females that were brooding embryos, this depletion of oxygen was not uniform: oxygen was depleted more quickly in the palp region (where embryos accumulate) than in the inhalant region. Additionally, oxygen was reduced even more quickly in the palp region when females were brooding late-stage embryos, which consumed oxygen significantly more quickly than embryos in earlier developmental stages. Finally, O. chilensis used anaerobic metabolism to cope with the hypoxia induced by isolation, as lactate accumulated in the tissues of both females (brooding > non-brooding) and embryos (late stage > early stage). Our findings demonstrate the trade-off between an adaptive avoidance behavior (clamming up) and the potentially detrimental consequences brought on by such a behavior (hypoxia). Cycling of embryos throughout the mantle cavity by deliberate female pumping keeps them from accumulating in the area between the palps, forestalling the creation of hypoxic conditions there. In addition, the capacity for anaerobic metabolism by both females and their embryos should help them tolerate the low oxygen levels that do eventually arise when the pallial cavity is isolated from the surrounding environment during long periods of reduced ambient salinity.

Contrasting physiological responses of two populations of the razor clam Tagelus dombeii with different histories of exposure to paralytic shellfish poisoning (PSP).

This study describes the physiological performance of two populations of the razor clam Tagelus dombeii from two geographic areas with different histories of exposure to paralytic shellfish poisoning (PSP) linked to the toxic dinoflagellate Alexandrium catenella. Clams from Melinka-Aysén, which are frequently exposed to PSP, were not affected by the presence of toxins in the diet. However, clams from Corral-Valdivia, which have never been exposed to PSP, exhibited significantly reduced filtration activity and absorption, affecting the energy allocated to scope for growth (SFG). Ammonia excretion and oxygen uptake were not affected significantly by the presence of A. catenella in the diet. Measurements of energy acquisition and expenditure were performed during a 12-day intoxication period. According to three-way repeated measure ANOVAs, the origin of the clams had a highly significant effect on all physiological variables, and the interaction between diet and origin was significant for the clearance and absorption rates and for the scope for growth. The scope for growth index showed similar positive values for both the toxic and non-toxic individuals from the Melinka-Aysén population. However, it was significantly reduced in individuals from Corral-Valdivia when exposed to the diet containing A. catenella. The absence of differences between the physiological response of the toxic and non-toxic clams from Melinka-Aysén may be related to the frequent presence of A. catenella in the environment, indicating that this bivalve does not suffer negative consequences from PSP. By contrast, A. catenella has a negative effect on the physiological performance, primarily on the energy gained from the environment, on T. dombeii from Corral-Valdivia. This study supports the hypothesis that the history of PSP exposure plays an important role in the physiological performance and fitness of filter feeding bivalves.