Biological Bulletin最新文献

AbstractPeriodic episodes of low oxygen (hypoxia) and elevated CO₂ (hypercapnia) accompanied by low pH occur naturally in estuarine environments. Under the influence of climate change, the geographic range and intensity of hypoxia and hypercapnic hypoxia are predicted to increase, potentially jeopardizing the survival of economically and ecologically important organisms that use estuaries as habitat and nursery grounds. In this review we synthesize data from published studies that evaluate the impact of hypoxia and hypercapnic hypoxia on the ability of crustaceans and bivalve molluscs to defend themselves against potential microbial pathogens. Available data indicate that hypoxia generally has suppressive effects on host immunity against bacterial pathogens as measured by in vitro and in vivo assays. Few studies have documented the effects of hypercapnic hypoxia on crustaceans or bivalve immune defense, with a range of outcomes suggesting that added CO₂ might have additive, negative, or no interactions with the effects of hypoxia alone. This synthesis points to the need for more partial pressure of O₂ × low pH factorial design experiments and recommends the development of new host∶pathogen challenge models incorporating natural transmission of a wide range of viruses, bacteria, and parasites, along with novel in vivo tracking systems that better quantify how pathogens interact with their hosts in real time under laboratory and field conditions.

AbstractThe copepods of coastal seas are experiencing warming water temperatures, which increase their oxygen demand. In addition, many coastal seas are also losing oxygen because of deoxygenation due to cultural eutrophication. Warming coastal seas have changed copepod species' composition and biogeographic boundaries and, in many cases, resulted in copepod communities that have shifted in size distribution to smaller species. While increases in ambient water temperatures can explain some of these changes, deoxygenation has also been shown to result in reduced copepod growth rates, reduced size at adulthood, and altered species composition. In this review we focus on the interactive effects of temperature and dissolved oxygen on pelagic copepods, which dominate coastal zooplankton communities. The uniformity in ellipsoidal shape, the lack of external oxygen uptake organs, and the pathway of oxygen uptake through the copepod's integument make calanoid copepods ideal candidates for testing the use of an allometric approach to predict copepod size with increasing water temperatures and decreasing oxygen in coastal seas. Considering oxygen and temperature as a combined and interactive driver in coastal ecosystems will provide a unifying approach for future predictions of coastal copepod communities and their impact on fisheries and biogeochemical cycles. Given the prospect of increased oxygen limitation of copepods in warming seas, increased knowledge of the physiological ecology of present-day copepods in coastal deoxygenated zones can provide insights into the copepod communities that will inhabit a future warmer ocean.

AbstractOxygen levels in the atmosphere and ocean have changed dramatically over Earth history, with major impacts on marine life. Because the early part of Earth's history lacked both atmospheric oxygen and animals, a persistent co-evolutionary narrative has developed linking oxygen change with changes in animal diversity. Although it was long believed that oxygen rose to essentially modern levels around the Cambrian period, a more muted increase is now believed likely. Thus, if oxygen increase facilitated the Cambrian explosion, it did so by crossing critical ecological thresholds at low O₂. Atmospheric oxygen likely remained at low or moderate levels through the early Paleozoic era, and this likely contributed to high metazoan extinction rates until oxygen finally rose to modern levels in the later Paleozoic. After this point, ocean deoxygenation (and marine mass extinctions) is increasingly linked to large igneous province eruptions-massive volcanic carbon inputs to the Earth system that caused global warming, ocean acidification, and oxygen loss. Although the timescales of these ancient events limit their utility as exact analogs for modern anthropogenic global change, the clear message from the geologic record is that large and rapid CO₂ injections into the Earth system consistently cause the same deadly trio of stressors that are observed today. The next frontier in understanding the impact of oxygen changes (or, more broadly, temperature-dependent hypoxia) in deep time requires approaches from ecophysiology that will help conservation biologists better calibrate the response of the biosphere at large taxonomic, spatial, and temporal scales.

AbstractOrganisms in coastal waters experience naturally high oxygen variability and steep oxygen gradients with depth, in addition to ocean deoxygenation. They often undergo diel vertical migration involving a change in irradiance that initiates a visual behavior. Retinal function has been shown to be highly sensitive to oxygen loss; here we assess whether visual behavior (photobehavior) in paralarvae of the squid Doryteuthis opalescens and the octopus Octopus bimaculatus is affected by low oxygen conditions, using a novel behavioral paradigm. Larvae showed an irradiance-dependent, descending photobehavior after extinction of the light stimulus, measured through the change in vertical position of larvae in the chamber. The magnitude of photobehavior was decreased as oxygen was reduced, and the response was entirely gone at <6.4 kPa partial pressure of oxygen (<74.7 μmol kg^-1 at 15.3 °C) in D. opalescens paralarvae. Oxygen also affected photobehavior in O. bimaculatus paralarvae. The mean vertical velocity of paralarvae was unaffected by exposure to reduced oxygen, indicating that oxygen deficits selectively affect vision prior to locomotion. These findings suggest that variable and declining oxygen conditions in coastal upwelling areas and elsewhere will impair photobehavior and likely affect the distribution, migration behavior, and survival of highly visual marine species.

AbstractDespite the global ecological importance of climate change, controversy surrounds how oxygen affects the fate of aquatic ectotherms under warming. Disagreements extend to the nature of oxygen bioavailability and whether oxygen usually limits growth under warming, explaining smaller adult size. These controversies affect two influential hypotheses: gill oxygen limitation and oxygen- and capacity-limited thermal tolerance. Here, we promote deeper integration of physiological and evolutionary mechanisms. We first clarify the nature of oxygen bioavailability in water, developing a new mass-transfer model that can be adapted to compare warming impacts on organisms with different respiratory systems and flow regimes. By distinguishing aerobic energy costs of moving oxygen from environment to tissues from costs of all other functions, we predict a decline in energy-dependent fitness during hypoxia despite approximately constant total metabolic rate before reaching critically low environmental oxygen. A new measure of oxygen bioavailability that keeps costs of generating water convection constant predicts a higher thermal sensitivity of oxygen uptake in an amphipod model than do previous oxygen supply indices. More importantly, by incorporating size- and temperature-dependent costs of generating water flow, we propose that oxygen limitation at different body sizes and temperatures can be modeled mechanistically. We then report little evidence for oxygen limitation of growth and adult size under benign warming. Yet occasional oxygen limitation, we argue, may, along with other selective pressures, help maintain adaptive plastic responses to warming. Finally, we discuss how to overcome flaws in a commonly used growth model that undermine predictions of warming impacts.

AbstractSea star wasting-marked in a variety of sea star species as varying degrees of skin lesions followed by disintegration-recently caused one of the largest marine die-offs ever recorded on the west coast of North America, killing billions of sea stars. Despite the important ramifications this mortality had for coastal benthic ecosystems, such as increased abundance of prey, little is known about the causes of the disease or the mechanisms of its progression. Although there have been studies indicating a range of causal mechanisms, including viruses and environmental effects, the broad spatial and depth range of affected populations leaves many questions remaining about either infectious or non-infectious mechanisms. Wasting appears to start with degradation of mutable connective tissue in the body wall, leading to disintegration of the epidermis. Here, we briefly review basic sea star biology in the context of sea star wasting and present our current knowledge and hypotheses related to the symptoms, the microbiome, the viruses, and the associated environmental stressors. We also highlight throughout the article knowledge gaps and the data needed to better understand sea star wasting mechanistically, its causes, and potential management.

AbstractThe calyptraeids Crepidula adunca and Crepidula norrisiarum, both direct developers, are abundant in the shallow waters of the northeastern Pacific. They have long been considered as two allopatric species that live on different hosts and differ in body size. In this study, we rigorously test this historical hypothesis by assessing molecular taxonomy, museum records, new morphological and host observations, and population genetic structure along the northeast Pacific coast. Results show that, contrary to previous understanding, the distributions of the two species largely overlap and that size does not effectively distinguish them, especially in the northern part of the range where the nominal "C. adunca" has been studied. Newly recognized northern occurrences of C. norrisiarum demonstrate that both species have similar, disrupted distributions that range from British Colombia through southern California. Neither species is reported to occur on the outer shores of southern Washington or Oregon, the exception being records of C. adunca at Cape Arago, Oregon. Despite this apparent geographic gap, neither species shows appreciable genetic differentiation between the northern and southern parts of its ranges. Despite body size having been used to distinguish these species, our observations do not support body size as a species-specific trait; rather, they support a new hypothesis that body size variation reflects regional differences in host use and host availability.

AbstractMost organisms are faced with daily cyclic changes in a suite of environmental conditions, including temperature. In shallow marine waters, populations of the same species may experience either intertidal or subtidal conditions, such that some individuals experience extreme daily fluctuations as the tide ebbs and flows, while others only a few meters away experience less pronounced or less frequent fluctuations or almost constant thermal conditions. This study used a fully factorial combination of three thermal treatments and two diet treatments to test the hypotheses that (1) individuals experiencing fluctuating temperatures perform more poorly than those experiencing the same mean temperature under constant conditions and that (2) the negative impact of fluctuating temperatures is greater under food-limiting conditions. Five life-history components of the slipper snail Crepidula cf. marginalis were used as response variables. We found that temperature fluctuations impacted size at hatching and time to hatching, as well as growth rate, to some extent. Diet treatments impacted growth rates, clutch sizes, time to first brood, and time to hatching. There were no statistically significant interactions between the two factors. These results show that fluctuations between two temperatures that are typically experienced by these animals in the field can significantly affect fitness-related characters and, therefore, suggest the tidal height at which larvae settle can significantly impact individual fitness. This is one of the first studies to demonstrate that differences in the frequency of fluctuations, in the absence of differences in the magnitude or the mean, can have significant impacts on invertebrate life histories.

AbstractThe Atlantic slipper limpet, Crepidula fornicata, is a sequential hermaphrodite whose size at sex change is plastic with respect to social and population cues. As an organism allocates energy between growth, reproduction, and maintenance, the increased cost of one process may affect another. Thus, C. fornicata affected by a stressor might have to alter the balance of energy allocation, potentially leading to changes in the timing of sex change. One such biotic stressor, the boring sponge Cliona celata, has been demonstrated to affect growth and condition of numerous molluscs. In this study, we explored whether the presence of the boring sponge affected the rate of sex change for C. fornicata, using both field surveys and an in situ manipulation. Population surveys suggested that while boring sponges may reduce tissue condition of slipper limpets, this relationship is highly variable and likely confounded by site variables. Using population metrics (size at sex, L₅₀), the presence of a boring sponge did not appear to affect sex change. Likewise, during the in situ experiment where we manipulated stack sex ratios, we did not find any differences in the timing of sex change between male-male and male-female stacks, even though C. fornicata without sponges grew significantly faster. Thus, results from field surveys and our in situ experiment suggest that sex change in this species appears robust to biotic stressors. This study suggests that C. fornicata will undergo sex change when conditions dictate, even if it is experiencing some level of biotic stress, a strategy that likely allows it to maximize lifetime reproductive output.