Clearance rates of sand-burrowed and laterally pressed unburrowed Pismo clam Tivela stultorum (Mawe 1823) in a laboratory open-flow system.

Pismo clam extraction is currently banned in Mexico to help the recovery of natural populations. Thus, the primary objective of this study was to gain insight on its basic biology and husbandry protocols. Growth and clearance rate (CR) of sand-burrowed and sediment-free, laterally pressed adult Pismo clams were quantified in the laboratory as a function of burrowing condition, flow, temperature, and microalgal concentration using open-flow chambers. After 40 days, clams remained healthy regardless of burrowing condition and showed a hyperbolic CR response pattern to increased flow, with CR directly proportional to flows lower than 1000 ml min-1. Maximal asymptotic CR values (300 to 400 ml min-1 org-1) were observed from 1000 to 2000 ml min-1. No significant CR differences were observed between burrowed and laterally pressed clams, yet microalgal concentration effects were detected, with constant maximal CRs of ∼250 ml min-1 in the range of 50 to 200 cells µl-1 and decline at higher concentrations. Maintenance protocols of laterally pressed organisms were validated in the laboratory with both weight and CR data. To our knowledge, this is the first study providing whole-body physiological data translated into effective husbandry protocols for Pismo clams. This approach represents a fresh perspective to traditional research areas, opening the possibility for continued experimentation under controlled conditions.

Trace Metal Residues in Marine Mussels: A Global Survey.

Pressures from anthropogenic activities are causing degradation of estuarine and coastal ecosystems around the world. Trace metals are key pollutants that are released and can partition in a range of environmental compartments, to be ultimately accumulated in exposed biota. The level of pressure varies with locations and the range and intensity of anthropogenic activities. The present study measured residues of trace metals in Mytilus mussel species collected from a range of locations around the world in areas experiencing a gradient of anthropogenic pressures that we classified as low, moderate, or high impact. The data showed no grouping/impact level when sampling sites in all countries were incorporated in the analysis, but there was significant clustering/impact level for most countries. Overall, high-impact areas were characterized by elevated concentrations of zinc, lead, nickel, and arsenic, whereas copper and silver were detected at higher concentrations in medium-impact areas. Finally, whereas most metals were found at lower concentrations in areas classified as low impact, cadmium was typically elevated in these areas. The present study provides a unique snapshot of worldwide levels of coastal metal contamination through the use of Mytilus species, a well-established marine biomonitoring tool. Environ Toxicol Chem 2021;40:3434-3440. © 2021 SETAC.

Acidification stress effect on umbonate veliger larval development in Panopea globosa.

Ocean acidification generates a decrease in calcium carbonate availability essential for biomineralization in organisms such as mollusks. This effect was evaluated on Panopea globosa exposing for 7 days umbonate veliger larvae to two pH treatments: experimental (pH 7.5) and control (pH 8.0). Exposure to pH 7.5 affected growth, reducing larval shell length from 5.15-13.34% compared to the control group. This size reduction was confirmed with electron microscopy, also showing shell damage. The physiological response showed an increase in oxygen consumption in larvae exposed to low pH with a maximum difference of 1.57 nmol O2 h-1 larvae-1 at day 7. The gene expression analyses reported high expression values for nicotinamide adenine dinucleotide (NADH) dehydrogenase and Perlucin in larvae at pH 7.5, suggesting a higher energetic cost in this larval group to maintain homeostasis. In conclusion, this study showed that acidification affected development of P. globosa umbonate veliger larvae.

Thermal Physiological Performance and Thermal Metabolic Scope of the Whelk Kelletia kelletii (Forbes, 1850) (Gastropoda: Neptuneidae) Acclimated to Different Temperatures.

nvestigations of thermal limits are crucial to understanding climate change ecology because it illuminates how climate will shape future species distributions. This work determined the preferred temperature, critical threshold limits represented by the Critical Thermal Maximum (CTMax) and (CTMin), thermal window, oxygen consumption rate and thermal metabolic scope of Kelletia kelletii acclimated to 13, 16.0, 19.0 and 22.0 ± 1°C to determine if this species is sensitive to global warming. The preferred temperature (PT) of Kellet's whelk was determined using the acute method. The acclimation temperature significantly affected the thermal preference of the marine snail (P < 0.05) and increased from 13.2 to 24.2°C as the acclimation temperature increased from 13.0 to 22.0°C. The PT was 13.4°C. The acclimation temperature did not significantly affect the CTMax (P > 0.05), obtaining a range of 29.2 to 30.2°C. The CTMin had an interval of 9.2°C, at acclimation temperatures of 13 to 16°C, and increased significantly (P < 0.05) at 12.3°C in the acclimation interval of 19-22°C. The thermal window for the different acclimation temperatures was 163.5°C2. The oxygen consumption rate of the snails increased significantly (P < 0.05) when the acclimation temperature increased from 13.0 to 22.0°C, peaking at 63.6 mg of O2 kg-1 h-1 w.w. in snails maintained at the highest acclimation temperature. The thermal metabolic scope increased significantly (P < 0.05) when the acclimation temperature was 13.0°C, with values of 68.7 mg O2 h-1 kg-1 w.w., then decreased significantly (P < 0.05) to 27.9 mg O2 h-1 kg-1 w.w at 32°C. Therefore, the thermal aerobic scope was highest at the temperatures that K. kelletii preferred. These results may partially explain their pattern of distribution on the Baja California coast.

Transcriptomic and metabolic response to chronic and acute thermal exposure of juvenile geoduck clams Panopea globosa.

The Cortes geoduck Panopea globosa is a large bivalve with a high commercial value distributed from the southern Pacific coast of the Baja California Peninsula to the northern Gulf of California, inhabiting a wide range of subtropical temperatures. A new record of this species in shallower waters suggests that it can tolerate a warmer environment than previously thought. To better understand the whole-body and molecular response mechanisms to different temperatures, we assessed the metabolic rate of juvenile individuals exposed to chronic and acute thermal conditions and analyzed the transcriptomic response in ctenidial tissues. Whole-body metabolic rate measurements showed that juveniles were able to acclimate at least partially within three weeks from 20 °C (C20) to 29 °C (C29), while organisms acutely exposed to 29 °C (A29) significantly increased their metabolic rate. This was coincident with transcriptomic results, as similar gene expression patterns were found in clams chronically exposed to C29 and C20, but different from those acutely exposed to 29 °C (A29) and 31 °C (A31). High degree of expression of genes involved in DNA repair and transcription regulation were found in C29 juveniles, whereas protective genes against oxidative stress were highly expressed in A29 organisms. A high expression of genes involved in protein re-folding was also observed in A31 juveniles. In conclusion, the combined results of whole-body metabolism and transcriptomic expression patterns suggest that P. globosa juveniles have a high physiological plasticity and are well adapted to inhabit an environment with broad temperature fluctuations.

Diagnosis of trace metal contamination in sediments: the example of Ensenada and El Sauzal, two harbors in Baja California, Mexico.

Total metal concentrations in sediments from within Ensenada and El Sauzal Harbors are generally higher than at the mouths. Grain-size analyses suggested that this enrichment could be due to the presence of fine-grained sediments in the inner part of the harbors rather than to anthropogenic perturbations. The (Me/Al)sample ratios for Pb, Co, Ni and Fe were significantly higher for Ensenada Harbor relative to El Sauzal Harbor, whereas the ratios for Cd, Mn, Zn and Cu were statistically equivalent for both harbors. Calculated enrichment factors [EFMe=(Me/Al)sample/(Me/Al)shale] indicated that the metals showing slight enrichment were those associated with anthropogenic contamination (Pb, Zn), or probably related to primary productivity in the water column (Cd, Co). The levels of most of the metals were not greatly enriched, a consideration that is of the utmost importance when contamination issues are at stake.

Metabolic depression and whole-body response to enforced starvation by Crassostrea gigas postlarvae.

Physiological and biochemical measurements were performed on six oyster (Crassostrea gigas) cohorts, in order to: (a) investigate the whole-body response (growth, energy content, metabolic and excretion rates) of 2-week-old postlarvae (spat) to enforced (0-8 days) starvation, and (b) test the potential use of three aerobic enzyme systems as indices of physiological condition. Starvation resulted in exponential reduction of postlarval metabolic and excretion rates, as well as a linear decrease in enzyme activity. These response mechanisms effectively limited the loss of endogenous reserves after 2 days of starvation and maintained the oyster's functional integrity over prolonged (8 days) starvation. Proteins appeared to be selectively conserved during short-term (2 days) starvation, as suggested by a decrease in total protein content, while maintaining constant weight-specific enzyme activity. Postlarvae starved for 2 days exhibited relatively higher lipid losses, lower mortality and lower metabolism than metamorphosing stages, thus suggesting a greater buffering capacity to starvation in the former. The activity of the electron transport system may be a useful indicator of long-term stress or developmental condition of oyster postlarvae, while citrate synthase and cytochrome oxidase could be used as indicators of growth rate. None of these enzyme systems is recommended as an index of aerobic metabolism during short-term starvation.