Detecting growth under environmental extremes: Spatial and temporal patterns in nucleic acid ratios in two Antarctic bivalves

Growth of Antarctic benthic organisms is very slow due to temperature and food availability, and subtle differences in growth rate may be difficult to detect. Nucleic acid ratios (RNA/DNA, RNA/protein or total RNA concentration) are measures of protein synthesis potential and may be used to assess short-term growth rate in a range of marine organisms. We quantified nucleic acid ratios in the scallop Adamussium colbecki and the clam Laternula elliptica at five locations in the Ross Sea, Antarctica. We were able to detect species-specific, habitat-specific, and seasonal differences in nucleic acid ratios and related these to associated differences in primary productivity. By using nucleic acid ratios, future studies could relatively easily obtain a measure of growth rate from a multitude of locations with contrasting habitat characteristics, food availability and temperature regimes around the Antarctic continent. This would yield a unique understanding of spatial and temporal patterns in bivalve growth in this extreme environment.     

Physiological Condition of Juvenile Wading Birds in Relation to Multiple Landscape Stressors in the Florida Everglades: Effects of Hydrology,Prey Availability,and Mercury Bioaccumulation

The physiological condition of juvenile birds can be influenced by multiple ecological stressors, and few studies have concurrently considered the effects of environmental contaminants in combination with ecological attributes that can influence foraging conditions and prey availability. Using three temporally distinct indices of physiological condition, we compared the physiological response of nestling great egrets (Ardea alba) and white ibises (Eudocimus albus) to changing prey availability, hydrology (water depth, recession rate), and mercury exposure in the Florida Everglades. We found that the physiological response of chicks varied between species and among environmental variables. Chick body condition (short-term index) and fecal corticosterone levels (medium-term) were influenced by wetland water depth, prey availability, region, and age, but not by mercury contamination. However, mercury exposure did influence heat shock protein 70 (HSP70) in egret chicks, indicating a longer-term physiological response to contamination. Our results indicate that the physiological condition of egret and ibis chicks were influenced by several environmental stressors, and the time frame of the effect may depend on the specialized foraging behavior of the adults provisioning the chicks.     

Testing local and global stressor impacts on a coastal foundation species using an ecologically realistic framework

Despite the abundance of literature on organismal responses to multiple environmental stressors, most studies have not matched the timing of experimental manipulations with the temporal pattern of stressors in nature. We test the interactive effects of diel‐cycling hypoxia with both warming and decreased salinities using ecologically realistic exposures. Surprisingly, we found no evidence of negative synergistic effects on Olympia oyster growth; rather, we found only additive and opposing effects of hypoxia (detrimental) and warming (beneficial). We suspect that diel‐cycling provided a temporal refuge that allowed physiological compensation. We also tested for latent effects of warming and hypoxia to low‐salinity tolerance using a seasonal delay between stressor events. However, we did not find a latent effect, rather a threshold survival response to low salinity that was independent of early life‐history exposure to warming or hypoxia. The absence of synergism is likely the result of stressor treatments that mirror the natural timing of environmental stressors. We provide environmental context for laboratory experimental data by examining field time series environmental data from four North American west coast estuaries and find heterogeneous environmental signals that characterize each estuary, suggesting that the potential stressor exposure to oysters will drastically differ over moderate spatial scales. This heterogeneity implies that efforts to conserve and restore oysters will require an adaptive approach that incorporates knowledge of local conditions. We conclude that studies of multiple environmental stressors can be greatly improved by integrating ecologically realistic exposure and timing of stressors found in nature with organismal life‐history traits.     

Interacting environmental mosaics drive geographic variation in mussel performance and predation vulnerability

Although theory suggests geographic variation in species' performance is determined by multiple niche parameters, little consideration has been given to the spatial structure of interacting stressors that may shape local and regional vulnerability to global change. Here, we use spatially explicit mosaics of carbonate chemistry, food availability and temperature spanning 1280 km of coastline to test whether persistent, overlapping environmental mosaics mediate the growth and predation vulnerability of a critical foundation species, the mussel Mytilus californianus. We find growth was highest and predation vulnerability was lowest in dynamic environments with frequent exposure to low pH seawater and consistent food. In contrast, growth was lowest and predation vulnerability highest when exposure to low pH seawater was decoupled from high food availability, or in exceptionally warm locations. These results illustrate how interactions among multiple drivers can cause unexpected, yet persistent geographic mosaics of species performance, interactions and vulnerability to environmental change.     

The sources and distribution of carbon (DOC,POC, DIC) in a mangrove dominated estuary (French Guiana,South America)

Improved quantification of the factors controlling soil organic matter (SOM) stabilization at continental to global scales is needed to inform projections of the largest actively cycling terrestrial carbon pool on Earth, and its response to environmental change. Biogeochemical models rely almost exclusively on clay content to modify rates of SOM turnover and fluxes of climate-active CO₂ to the atmosphere. Emerging conceptual understanding, however, suggests other soil physicochemical properties may predict SOM stabilization better than clay content. We addressed this discrepancy by synthesizing data from over 5,500 soil profiles spanning continental scale environmental gradients. Here, we demonstrate that other physicochemical parameters are much stronger predictors of SOM content, with clay content having relatively little explanatory power. We show that exchangeable calcium strongly predicted SOM content in water-limited, alkaline soils, whereas with increasing moisture availability and acidity, iron- and aluminum-oxyhydroxides emerged as better predictors, demonstrating that the relative importance of SOM stabilization mechanisms scales with climate and acidity. These results highlight the urgent need to modify biogeochemical models to better reflect the role of soil physicochemical properties in SOM cycling.     

Phenotypic Plasticity of Early and Late Successional Forbs in Response to Shifts in Resources

We compared the phenotypic plasticity of two early successional forbs of nutrient-poor mobile dunes (Agriophyllum squarrosum and Corispermum macrocarpum) and two later successional forbs (weeds) of stabilized, higher nutrient dunes and cropland (Chenopodium acuminatum and Salsola collina) to variations in environmental factors. A controlled (including soil nutrients, water, and population density) greenhouse experiment was conducted in Horqin sandy land, China. Late successional species had high plasticity in growth response to nutrients and water or high performance in high soil nutrients and water, reflecting their higher nutrient habitat. In contrast, the early successional species have low plasticity, reflecting their adaptation to resource-poor early successional soil. Late successional species did not always have higher reproductive effort than early successional species. Plants did not have a uniform strategy of increasing reproductive effort with any environmental stressors. Reproductive effort increased with increasing water availability and decreasing nutrient levels, while density had no effect. Patterns of plasticity traits for late successional species exhibited a complex of Master-of-some and Jack-of-all-trades. Late successional species had higher performance or higher plasticity than early successional species.     

The clam Neilonella sulculata in San Jorge Gulf (Argentina,Southwest Atlantic): spatial distribution pattern and inverse relationship between size and density

Neilonella sulculata is a dominant bivalve on muddy bottoms of the continental shelf and gulfs off Argentina (Southwest Atlantic). Two benthic surveys performed in 2007 and 2009 in San Jorge Gulf, a depositional area characterized by silt/clay sediments, gave us the opportunity to test whether the population of this clam displays a significant spatial structure and to analyse if there is an inverse relationship between size and density. Density, biomass and size–frequency distribution displayed significant spatial structure, being positively autocorrelated at the smallest spatial scales (c. 1.7–14/17?km). Biomass also showed spatial contagion at scales of 25–33?km. A substantial increase in density and biomass occurred between 2007 and 2009. Empty valves in the sediment showed that the maximum size attained by the species may exhibit considerable variation at relatively short temporal scales. Regardless of temporal changes in density and biomass, the spatial structure of these variables remained stable. In densely populated areas, shell size decreased with increasing density, suggesting a density-dependent control of growth. A clear north–south increase in density and biomass was detected, which might be related to a gradient in food availability caused by a thermohaline frontal system associated with wind-related upwelling.     

Assessing the sensitivity of bivalve populations to global warming using an individual‐based modelling approach

Climate change exposes benthic species populations in coastal ecosystems to a combination of different stressors (e.g., warming, acidification and eutrophication), threatening the sustainability of the ecological functions they provide. Thermal stress appears to be one of the strongest drivers impacting marine ecosystems, acting across a wide range of scales, from individual metabolic performances to geographic distribution of populations. Accounting for and integrating the response of species functional traits to thermal stress is therefore a necessary step in predicting how populations will respond to the warming expected in coming decades. Here, we developed an individual‐based population model using a mechanistic formulation of metabolic processes within the framework of the dynamic energy budget theory. Through a large number of simulations, we assessed the sensitivity of population growth potential to thermal stress and food conditions based on a climate projection scenario (Representative Concentration Pathway; RCP8.5: no reduction of greenhouse gas emissions). We focused on three bivalve species with contrasting thermal tolerance ranges and distinct distribution ranges along 5,000 km of coastline in the NE Atlantic: the Pacific oyster (Magallana gigas), and two mussel species: Mytilus edulis and Mytilus galloprovincialis. Our results suggest substantial and contrasting changes within species depending on local temperature and food concentration. Reproductive phenology appeared to be a core process driving the responses of the populations, and these patterns were closely related to species thermal tolerances. The nonlinear relationship we found between individual life‐history traits and response at the population level emphasizes the need to consider the interactions resulting from upscaling across different levels of biological organisation. These results underline the importance of a process‐based understanding of benthic population response to seawater warming, which will be necessary for forward planning of resource management and strategies for conservation and adaptation to environmental changes.     

Physiological community ecology: variation in metabolic activity of ecologically important rocky intertidal invertebrates along environmental gradients

Rocky intertidal invertebrates live in heterogeneous habitatscharacterized by steep gradients in wave activity, tidal flux,temperature, food quality and food availability. These environmentalfactors impact metabolic activity via changes in energy inputand stress-induced alteration of energetic demands. For keystonespecies, small environmentally induced shifts in metabolic activitymay lead to disproportionately large impacts on community structurevia changes in growth or survival of these key species. Herewe use biochemical indicators to assess how natural differencesin wave exposure, temperature and food availability may affectmetabolic activity of mussels, barnacles, whelks and sea starsliving at rocky intertidal sites with different physical andoceanographic characteristics. We show that oxygen consumptionrate is correlated with the activity of key metabolic enzymes(e.g., citrate synthase and malate dehydrogenase) for some intertidalspecies, and concentrations of these enzymes in certain tissuesare lower for starved individuals than for those that are wellfed. We also show that the ratio of RNA to DNA (an index ofprotein synthetic capacity) is highly variable in nature andcorrelates with short-term changes in food availability. Wealso observed striking patterns in enzyme activity and RNA/DNAin nature, which are related to differences in rocky intertidalcommunity structure. Differences among species and habitatsare most pronounced in summer and are linked to high nearshoreproductivity at sites favored by suspension feeders and to exposureto stressful low-tide air temperatures in areas of low wavesplash. These studies illustrate the great promise of usingbiochemical indicators to test ecological models, which predictchanges in community structure along environmental gradients.Our results also suggest that biochemical indices must be carefullyvalidated with laboratory studies, so that the indicator selectedis likely to respond to the environmental variables of interest.     

Nature versus nurture: Structural equation modeling indicates that parental care does not mitigate consequences of poor environmental conditions in Eastern Bluebirds (Sialia sialis)

How organisms respond to variation in environmental conditions and whether behavioral responses can mitigate negative consequences on growth, condition, and other fitness measures are critical to our ability to conserve populations in changing environments. Offspring development is affected by environmental conditions and parental care behavior. When adverse environmental conditions are present, parents may alter behaviors to mitigate the impacts of poor environmental conditions on offspring. We determined whether parental behavior (provisioning rates, attentiveness, and nest temperature) varied in relation to environmental conditions (e.g., food availability and ectoparasites) and whether parental behavior mitigated negative consequences of the environment on their offspring in Eastern Bluebirds (Sialia sialis). We found that offspring on territories with lower food availability had higher hematocrit, and when bird blow flies (Protocalliphora spp.) were present, growth rates were reduced. Parents increased provisioning and nest attendance in response to increased food availability but did not alter behavior in response to parasitism by blow flies. While parents altered behavior in response to resource availability, parents were unable to override the direct effects of negative environmental conditions on offspring growth and hematocrit. Our work highlights the importance of the environment on offspring development and suggests that parents may not be able to sufficiently alter behavior to ameliorate challenging environmental conditions.     

Herbivore Impacts on Marsh Production Depend upon a Compensatory Continuum Mediated by Salinity Stress

Plant communities are disturbed by several stressors and they are expected to be further impacted by increasing anthropogenic stress. The consequences of these stressors will depend, in part, upon the ability of plants to compensate for herbivory. Previous studies found that herbivore impacts on plants can vary from negative to positive because of environmental control of plant compensatory responses, a.k.a. the Compensatory Continuum Hypothesis. While these influential studies enhanced our appreciation of the dynamic nature of plant-herbivore interactions, they largely focused on the impact of resource limitation. This bias limits our ability to predict how other environmental factors will shape the impact of herbivory. We examined the role of salinity stress on herbivory of salt marsh cordgrass, Spartina foliosa, by an herbivore previously hypothesized to influence the success of restoration projects (the scale insect, Haliaspis spartinae). Using a combination of field and mesocosm manipulations of scales and salinity, we measured how these factors affected Spartina growth and timing of senescence. In mesocosm studies, Spartina overcompensated for herbivory by growing taller shoots at low salinities but the impact of scales on plants switched from positive to neutral with increasing salinity stress. In field studies of intermediate salinities, scales reduced Spartina growth and increased the rate of senescence. Experimental salinity additions at this field site returned the impact of scales to neutral. Because salinity decreased scale densities, the switch in impact of scales on Spartina with increasing salinity was not simply a linear function of scale abundance. Thus, the impact of scales on primary production depended strongly upon environmental context because intermediate salinity stress prevented plant compensatory responses to herbivory. Understanding this context-dependency will be required if we are going to successfully predict the success of restoration efforts and the ecological consequences of anthropogenic disturbances.     

Differences in demographic traits of four butterflyfish species between two reefs of the Great Barrier Reef separated by 1,200?km

Many species demonstrate variation in life history attributes in response to gradients in environmental conditions. For fishes, major drivers of life history variation are changes in temperature and food availability. This study examined large-scale variation in the demography of four species of butterflyfishes (Chaetodon citrinellus, Chaetodon lunulatus, Chaetodon melannotus, and Chaetodon trifascialis) between two locations on Australia’s Great Barrier Reef (Lizard Island and One Tree Island, separated by approximately 1,200 km). Variation in age-based demographic parameters was assessed using the re-parameterised von Bertalanffy growth function. All species displayed measurable differences in body size between locations, with individuals achieving a larger adult size at the higher latitude site (One Tree Island) for three of the four species examined. Resources and abundances of the study species were also measured, revealing some significant differences between locations. For example, for C. trifascialis, there was no difference in its preferred resource or in abundance between locations, yet it achieved a larger body size at the higher latitude location, suggesting a response to temperature. For some species, resources and abundances did vary between locations, limiting the ability to distinguish between a demographic response to temperature as opposed to a response to food or competition. Future studies of life histories and demographics at large spatial scales will need to consider the potentially confounding roles of temperature, resource usage and availability, and abundance/competition to disentangle the effects of these environmental variables.     

Regulation of a truncated isoform of AMP-activated protein kinase α (AMPKα) in response to hypoxia in the muscle of Pacific oyster Crassostrea gigas

AMP-activated protein kinase α (AMPKα) is a key regulator of energy balance in many model species during hypoxia. In a marine bivalve, the Pacific oyster Crassostrea gigas, we analyzed the protein content of adductor muscle in response to hypoxia during 6 h. In both smooth and striated muscles, the amount of full-length AMP-activated protein kinase α (AMPKα) remained unchanged during hypoxia. However, hypoxia induced a rapid and muscle-specific response concerning truncated isoforms of AMPKα. In the smooth muscle, a truncated isoform of AMPKα was increased from 1 to 6 h of hypoxia, and was linked with accumulation of AKT kinase, a key enzyme of the insulin signaling pathway which controls intracellular glucose metabolism. In this muscle, aerobic metabolism was maintained over the 6 h of hypoxia, as mitochondrial citrate synthase activity remained constant. In contrast, in striated muscle, hypoxia did not induce any significant modification of neither truncated AMPKα nor AKT protein content, and citrate synthase activity was altered after 6 h of hypoxia. Together, our results demonstrate that hypoxia response is specific to muscle type in Pacific oyster, and that truncated AMPKα and AKT proteins might be involved in maintaining aerobic metabolism in smooth muscle. Such regulation might occur in vivo during tidal intervals that cause up to 6 h of hypoxia.     

Short-term regrowth responses of four steppe grassland species to grazing intensity, water and nitrogen in Inner Mongolia

Inner Mongolia steppe grasslands are widely used for livestock farming and the regrowth ability of grassland species is therefore strongly influenced not only by water and nutrient availability but also quite heavily by grazing. However, little is known on how grazing, water and nitrogen interactively affect the dominant C3 species (Leymus chinensis, Stipa grandis, Agropyron cristatum) and the C4 species (Cleistogenes squarrosa). Therefore in the 2007 and 2008 growing seasons, a field experiment was carried out to test the hypothesis that under different grazing intensities the dominant species show different short-term regrowth response to simultaneous variation in the availability of water and nitrogen. Single factor and interaction effects of the addition of water (rainfed vs. simulated wet-year) and nitrogen (0 or 25 kg N ha^?1) were analysed along a gradient of four grazing intensities (ungrazed, lightly, moderately and heavily grazed) after one month of grazing exclusion. Water and nitrogen addition affected short-term regrowth of all species in a similar way whereas species responded differently to grazing. Simulated wet-year water availability consistently resulted in higher standing biomass, relative growth rate and cellulase digestible organic matter yield. Supplementary nitrogen promoted standing biomass and crude protein concentration. The nutritive value of all species’ standing biomass showed a similar increase with more intensive grazing. However, heavy grazing led to a clear shift in the relative biomass of the species, i.e. mainly a promotion of the C4 grass, C. squarrosa. In contrast to our hypothesis, there were no differences among species in their response to water or nitrogen addition, whereas, heavy grazing induced the expected species-specific response. Our results suggest that heavy grazing rather than nitrogen or water determine short-term shifts in species composition of the investigated steppe ecosystem. Furthermore, differences in the species-specific growth response to grazing may increase the proportion of the C4 grass C. squarrosa in steppe communities, whereas higher availability of nitrogen and water may lead to higher forage biomass and nutritive value of all investigated species but in short-term cannot compensate for the grazing induced changes in species composition.     

Plasticity of Noddy Parents and Offspring to Sea-Surface Temperature Anomalies

Behavioral and/or developmental plasticity is crucial for resisting the impacts of environmental stressors. We investigated the plasticity of adult foraging behavior and chick development in an offshore foraging seabird, the black noddy (Anous minutus), during two breeding seasons. The first season had anomalously high sea-surface temperatures and ‘low’ prey availability, while the second was a season of below average sea-surface temperatures and ‘normal’ food availability. During the second season, supplementary feeding of chicks was used to manipulate offspring nutritional status in order to mimic conditions of high prey availability. When sea-surface temperatures were hotter than average, provisioning rates were significantly and negatively impacted at the day-to-day scale. Adults fed chicks during this low-food season smaller meals but at the same rate as chicks in the unfed treatment the following season. Supplementary feeding of chicks during the second season also resulted in delivery of smaller meals by adults, but did not influence feeding rate. Chick begging and parental responses to cessation of food supplementation suggested smaller meals fed to artificially supplemented chicks resulted from a decrease in chick demands associated with satiation, rather than adult behavioral responses to chick condition. During periods of low prey abundance, chicks maintained structural growth while sacrificing body condition and were unable to take advantage of periods of high prey abundance by increasing growth rates. These results suggest that this species expresses limited plasticity in provisioning behavior and offspring development. Consequently, responses to future changes in sea-surface temperature and other environmental variation may be limited.     

Till Death Do Us Part: Stable Sponge-Bacteria Associations under Thermal and Food Shortage Stresses

Sporadic mass mortality events of Mediterranean sponges following periods of anomalously high temperatures or longer than usual stratification of the seawater column (i.e. low food availability) suggest that these animals are sensitive to environmental stresses. The Mediterranean sponges Ircinia fasciculata and I. oros harbor distinct, species-specific bacterial communities that are highly stable over time and space but little is known about how anomalous environmental conditions affect the structure of the resident bacterial communities. Here, we monitored the bacterial communities in I. fasciculata (largely affected by mass mortalities) and I. oros (overall unaffected) maintained in aquaria during 3 weeks under 4 treatments that mimicked realistic stress pressures: control conditions (13°C, unfiltered seawater), low food availability (13°C, 0.1 µm-filtered seawater), elevated temperatures (25°C, unfiltered seawater), and a combination of the 2 stressors (25°C, 0.1 µm-filtered seawater). Bacterial community structure was assessed using terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA gene sequences and transmission electron microscopy (TEM). As I. fasciculata harbors cyanobacteria, we also measured chlorophyll a (chl a) levels in this species. Multivariate analysis revealed no significant differences in bacterial T-RFLP profiles among treatments for either host sponge species, indicating no effect of high temperatures and food shortage on symbiont community structure. In I. fasciculata, chl a content did not significantly differ among treatments although TEM micrographs revealed some cyanobacteria cells undergoing degradation when exposed to both elevated temperature and food shortage conditions. Arguably, longer-term treatments (months) could have eventually affected bacterial community structure. However, we evidenced no appreciable decay of the symbiotic community in response to medium-term (3 weeks) environmental anomalies purported to cause the recurrent sponge mortality episodes. Thus, changes in symbiont structure are not likely the proximate cause for these reported mortality events.     

Under a neighbour's influence: public information affects stress hormones and behaviour of a songbird

Socially acquired information improves the accuracy and efficiency of environmental assessments and can increase fitness. Public information may be especially useful during unpredictable food conditions, or for species that depend on resources made less predictable by human disturbance. However, the physiological mechanisms by which direct foraging assessments and public information are integrated to affect behaviour remain largely unknown. We tested for potential effects of public information on the behavioural and hormonal response to food reduction by manipulating the social environment of captive red crossbills (Loxia curvirostra). Red crossbills are irruptive migrants that are considered sensitive to changes in food availability and use public information in decision making. Here, we show that public information can attenuate or intensify the release of glucocorticoids (i.e. stress hormones) during food shortage in red crossbills. The observed modulation of corticosterone may therefore be a physiological mechanism linking public information, direct environmental assessments and behavioural change. This mechanism would not only allow for public information to affect individual behaviour, but might also facilitate group decision making by bringing group members into more similar physiological states. The results further suggest that stressors affecting entire populations may be magnified in individual physiology through social interactions.     

An environmentally induced tidal periodicity of microgrowth increment formation in subtidal populations of the clam Ruditapes philippinarum

The periodicity of increment formation in the shell of the Manila clam Ruditapes philippinarum was investigated in the subtidal zone of the Auray River estuary (South Brittany, France). Calcein markings were performed at different periods between May and October 2007 using in situ benthic chambers tented by scuba divers. This study shows that shell microgrowth increments were well-defined and deposited with a tidal periodicity in the subtidal zone, providing the calendar base for high-resolution ecological studies and environmental reconstruction from these R. philippinarum shells. Endogenous rhythmicity in shell microgrowth increment formation and oxygen consumption was previously documented in this species from intertidal flats. Our study suggests that, in the subtidal zone, Manila clams' rhythmic activity may be controlled by such an endogenous process, synchronized by tidal cues. As in other bivalves, R. philippinarum is an osmoconformer euryhaline bivalve. The tidal rhythmicity of shell microgrowth increments in subtidal specimens of this species could be explained by a behavioral adaptation of valve closure at low tide to protect the clam from low salinities and/or to synchronize with food availability. Finally, large inter-individual variability in tidally associated growth rates and asynchronous growth breaks were observed, and could be due to genetic variability between individuals, asynchronous partial spawning events or predation.     

Sex-specific plasticity in body phosphorus content of Hyalella amphipods

Understanding the evolution of sexually dimorphic traits requires knowledge of the genetic and environmental sources of variation. However, we know surprisingly little about how the sexes differ in their responses to environmental nutrient supply. Here, we investigated how phosphorus (P) availability, a key metric of eutrophication, affects body composition in each sex of two Hyalella amphipod species. We also examined whether differences in food preference and acquisition are responsible for observed variation in body P. We discovered environmentally-driven changes in body P that were dependent on both species and sex. In both species, males contained less P when raised in low-P laboratory conditions compared to high-P field environments, while females exhibited no significant differences. Importantly, this difference was greater in the species that is known to have larger sexual traits and higher growth rates. Variation in P content was not due to differences in acquisition of P because both sexes preferred high-P food and consumed it at a similar rate. Our study illuminates potentially important sex- and species-specific evolutionary consequences of rapid alterations to P availability due to cultural eutrophication.     

Vertical Migrations of a Deep-Sea Fish and Its Prey

It has been speculated that some deep-sea fishes can display large vertical migrations and likely doing so to explore the full suite of benthopelagic food resources, especially the pelagic organisms of the deep scattering layer (DSL). This would help explain the success of fishes residing at seamounts and the increased biodiversity found in these features of the open ocean. We combined active plus passive acoustic telemetry of blackspot seabream with in situ environmental and biological (backscattering) data collection at a seamount to verify if its behaviour is dominated by vertical movements as a response to temporal changes in environmental conditions and pelagic prey availability. We found that seabream extensively migrate up and down the water column, that these patterns are cyclic both in short-term (tidal, diel) as well as long-term (seasonal) scales, and that they partially match the availability of potential DSL prey components. Furthermore, the emerging pattern points to a more complex spatial behaviour than previously anticipated, suggesting a seasonal switch in the diel behaviour mode (benthic vs. pelagic) of seabream, which may reflect an adaptation to differences in prey availability. This study is the first to document the fine scale three-dimensional behaviour of a deep-sea fish residing at seamounts.