Tautogolabrus Research Articles

Climate-induced reduction in metabolically suitable habitat for U.S. northeast shelf marine species

The U.S. northeast shelf (USNES) has been experiencing rapid ocean warming, which is changing the thermal environment that marine species inhabit. To determine the effect of current and future ocean warming on the distribution of five important USNES fish species (Atlantic cod [Gadus morhua], black sea bass [Centropristis striata], cunner [Tautogolabrus adspersus], spiny dogfish [Squalus acanthias], summer flounder [Paralichthys dentatus]), we applied species-specific physiological parameters from laboratory studies to calculate the Metabolic Index (MI). The MI for each species was calculated across a historical (1972–2019) and contemporary (2010–2019) climatology for each season. Broadly, the oceanic conditions in the winter and spring seasons did not limit metabolically suitable habitat for all five species, while portions of the USNES in the summer and fall seasons were metabolically unsuitable for the cold water species (Atlantic cod, cunner, spiny dogfish). The warmer water species (black sea bass, summer flounder) experienced little metabolically suitable habitat loss, which was restricted to the most southern portion of the distribution. Under a doubling of atmospheric CO2, metabolically suitable habitat is projected to decrease substantially for Atlantic cod, restricting them to the Gulf of Maine. Cunner are projected to experience similar habitat loss as Atlantic cod, with some refugia in the New York Bight, and spiny dogfish may experience habitat loss in the Southern Shelf and portions of Georges Bank. In contrast, black sea bass and summer flounder are projected to experience minimal habitat loss restricted to the southern inshore portion of the USNES. The utility of using MI for co-occurring fish species in the USNES differed, likely driven by species-specific physiology and whether the southern edge of a population occurred within the USNES.

Among-individual variation in thermal plasticity of fish metabolic rates causes profound variation in temperature-specific trait repeatability, but does not co-vary with behavioural plasticity.

Conspecifics of the same age and size differ consistently in the pace with which they expend energy. This among-individual variation in metabolic rate is thought to influence behavioural variation, since differences in energy requirements should motivate behaviours that facilitate energy acquisition, such as being bold or active in foraging. While there is evidence for links between metabolic rate and behaviour in constant environments, we know little about whether metabolic rate and behaviour change together when the environment changes-that is, if metabolic and behavioural plasticity co-vary. We investigated this using a fish that becomes dormant in winter and strongly reduces its activity when the environment cools, the cunner (Tautogolabrus adspersus). We found strong and predictable among-individual variation in thermal plasticity of metabolic rates, from resting to maximum levels, but no evidence for among-individual variation in thermal plasticity of movement activity, meaning that these key physiological and behavioural traits change independently when the environment changes. The strong among-individual variation in metabolic rate plasticity resulted in much higher repeatability (among-individual consistency) of metabolic rates at warm than cold temperatures, indicating that the potential for metabolic rate to evolve under selection is temperature-dependent, as repeatability can set the upper limit to heritability. This article is part of the theme issue 'The evolutionary significance of variation in metabolic rates'.

Thermal constraints on exercise and metabolic performance do not explain the use of dormancy as an overwintering strategy in the cunner (Tautogolabrus adspersus).

Winter cold slows ectotherm physiology, potentially constraining activities and ecological opportunities at poleward latitudes. Yet, many fishes are winter-active, facilitated by thermal compensation that improves cold performance. Conversely, winter-dormant fishes (e.g. cunner, Tautogolabrus adspersus) become inactive and non-feeding overwinter. Why are certain fishes winter-dormant? We hypothesized that winter dormancy is an adaptive behavioural response arising in poleward species that tolerate severe, uncompensated constraints of cold on their physiological performance. We predicted that below their dormancy threshold of 7--8°C, exercise and metabolic performance of cunner are greatly decreased, even after acclimation (i.e. shows above-normal, uncompensated thermal sensitivity, Q10>1-3). We measured multiple key performance metrics (e.g. C-start maximum velocity, chase swimming speed, aerobic scope) in cunner after acute exposure to 26-2°C (3°C intervals using 14°C-acclimated fish) or acclimation (5-8 weeks) to 14-2°C (3°C intervals bracketing the dormancy threshold). Performance declined with cooling, and the acute Q10 of all six performance rate metrics was significantly greater below the dormancy threshold temperature (Q10,acute8-2°C=1.5-4.9, mean=3.3) than above (Q10,acute14-8°C=1.1-1.9, mean=1.5), inferring a cold constraint. However, 2°C acclimation (temporally more relevant to seasonal cooling) improved performance, abolishing the acute constraint (Q10,acclimated8-2°C=1.4-3.0, mean=2.0; also cf. Q10,acclimated14-8°C=1.2-2.9, mean=1.7). Thus, dormant cunner show partial cold-compensation of exercise and metabolic performance, similar to winter-active species. However, responsiveness to C-start stimuli was greatly cold-constrained even following acclimation, suggesting dormancy involves sensory limitation. Thermal constraints on metabolic and exercise physiology are not significant drivers of winter dormancy in cunner. In fact, compensatory plasticity at frigid temperatures is retained even in a dormant fish.

ECR Spotlight – Lauren Rowsey

ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Lauren Rowsey is an author on ‘ Thermal constraints on exercise and metabolic performance do not explain the use of dormancy as an overwintering strategy in the cunner (Tautogolabrus adspersus)’, published in JEB. Lauren is a PhD candidate in the lab of Ben Speers-Roesch at University of New Brunswick Saint John, Canada, investigating physiological performance of fishes in challenging environments.

Whole-genome sequencing reveals fine-scale environment-associated divergence near the range limits of a temperate reef fish.

Environmental variation is increasingly recognized as an important driver of diversity in marine species despite the lack of physical barriers to dispersal and the presence of pelagic stages in many taxa. A robust understanding of the genomic and ecological processes involved in structuring populations is lacking for most marine species, often hindering management and conservation action. Cunner (Tautogolabrus adspersus) is a temperate reef fish with both pelagic early life-history stages and strong site-associated homing as adults; the species is also of interest for use as a cleaner fish in salmonid aquaculture in Atlantic Canada. We aimed to characterize genomic and geographic differentiation of cunner in the Northwest Atlantic. To achieve this, a chromosome-level genome assembly for cunner was produced and used to characterize spatial population structure throughout Atlantic Canada using whole-genome sequencing. The genome assembly spanned 0.72 Gbp and 24 chromosomes; whole-genome sequencing of 803 individuals from 20 locations from Newfoundland to New Jersey identified approximately 11 million genetic variants. Principal component analysis revealed four regional Atlantic Canadian groups. Pairwise FST and selection scans revealed signals of differentiation and selection at discrete genomic regions, including adjacent peaks on chromosome 10 across multiple pairwise comparisons (i.e. FST 0.5-0.75). Redundancy analysis suggested association of environmental variables related to benthic temperature and oxygen range with genomic structure. Results suggest regional scale diversity in this temperate reef fish and can directly inform the collection and translocation of cunner for aquaculture applications and the conservation of wild populations throughout the Northwest Atlantic.

Oyster aquaculture cages provide fish habitat similar to natural structure with minimal differences based on farm location

Oyster aquaculture gear may augment natural seafloor by providing structured habitat for economically important fish species. Underwater video census was used to assess fish abundance and community composition on eastern oyster (Crassostrea virginica) shelf and bag style aquaculture off-bottom cages and within natural rock reef habitat. During 2018, underwater cameras were mounted on four study cages at a dense shellfish farm of 40-100 commercial cages (dense cage farm), on four single cages interspersed on low relief seafloor (sparse cage farm), and amongst four boulders on a rock reef (rock reef), within an embayment off Milford, Connecticut, which is part of Long Island Sound, in the United States. In 2019, cameras were similarly deployed on two study cages per farm at each of three shellfish farms off Milford, Norwalk and Westport, CT. Video was recorded hourly in eight-minute segments from 7 am to 7 pm. Data loggers monitored seawater temperature, light intensity, and current speed. Fish abundance (MaxN) was calculated for all videos. We compared fish abundance and community composition between May and September, on cage and boulder habitat, on cages at dense and sparse farms and on cages across farm locations. In 2018, abundance of black sea bass (Centropristis striata), scup (Stenotomus chrysops) and tautog (Tautoga onitis) was significantly higher on cages than boulders, regardless of cage number. Cunner (Tautogolabrus adspersus) abundance was significantly higher on boulders than cages when cage sites were grouped. However pairwise comparisons indicated that cunner were significantly higher at the sparse cage farm versus the rock reef but cunner abundance on the dense cage farm and rock reef sites was not significantly different. Abundance of black sea bass, scup, tautog, and cunner were not significantly different across 2019 farm locations. Young-of-the-year fish occurred episodically at all sites during both years, with black sea bass and scup most abundant. Fish abundance corresponded to seasonal changes in seawater temperature and was highest at the warmest temperatures. Light intensity and current speed explained less variation in fish abundance relative to temperature, and relationships were inconsistent across habitats and farm locations Our results suggest that multi-tiered oyster aquaculture cages contribute structure to seafloor environments that provide habitat for temperate reef fish similar to natural rock reefs.

Impacts of thermal acclimatization on fish skeletal muscle

Thermal acclimation allows ectotherms to maintain physiological homeostasis while occupying habitats with constantly changing temperatures. This process is especially important in skeletal muscle which powers most movements necessary for life. We aimed to understand how fish skeletal muscle is impacted by acclimatization in the laboratory. To accomplish this, we compared muscle contraction kinetics of four-week lab acclimatized fish (at 20 °C) to fish taken directly from the field when sea surface temperatures were similar to lab treatment temperature (ocean temperature ranged from 17.7 to 19.9 °C in the four weeks prior to collection at 20 °C). To examine these effects, we chose to study tautog (Tautoga onitis) and cunner (Tautogolabrus adspersus) from Long Island Sound. We found that timing of contraction kinetics in cunner and tautog did not differ from the lab acclimatized and field acclimatized groups. However, lab acclimatized cunner produced greater contraction force than fish taken directly from the field. This increased force production allowed lab acclimatized cunner to produce greater power when compared to cunner from the field treatment. Furthermore, laboratory acclimatized cunner did not express any slow myosin heavy chain, suggesting that their muscle had transitioned to mostly fast twitch fibers after being held at a constant temperature in the lab. None of these effects were seen in tautog. In this work we highlight the importance of considering the impacts laboratory conditions have on experimental conditions.

Size Differences in Personality Profiles of the Cunner Wrasse (Tautogolabrus adspersus)

Individual animals, including fish, often differ consistently in their behaviours, which is known as personality. An individual’s values on the five axes of personality, which are activity, aggression, anxiety, boldness, and sociality, come together and form syndromes. The major syndromes, proactive or reactive, characterize an individual’s expected behaviour. The cunner wrasse, (Tautogolabrus adspersus), is the only warm-water cleaner fish for removal of sea lice from Atlantic salmon in Eastern Canada. Developing behavioural assay of the syndromes is important for industry to use to improve aquaculture because they are linked to species’ growth, cleaning efficiency, and welfare. I explored if the proactive and reactive syndromes exist in cunners and how their size influences the syndromes. The research was conducted with different sizes of cunners (n=43) in the Hagen Aqualab for three months, starting from January 2020. An open field test, scoring anxiety, and a swimming test, scoring activity, were conducted, followed by a mirror test measuring sociality and aggression. Then, a replica test was conducted to score boldness, followed by a novel object test also measuring boldness. Then, a shelter-seeking test was conducted to score anxiety. I found that cunners of all size-classes showed proactivity and reactivity. However, there was a significant difference in which components of the five axes of personality determined the two syndromes between large and small-medium cunners. These findings may develop a behavioural assay for industry to use when they breed cleaner fish to use for their desired traits, such as better growth and higher cleaning efficiency.

Habitat and trophic niche overlap among juvenile black sea bass, tautog, and cunner: interspecific interactions amid a species geographic range expansion

Juvenile black sea bass Centropristis striata populations are increasing in southern New England estuaries of the northeastern USA with possible trophodynamic effects on labrid species: tautog Tautoga onitis and cunner Tautogolabrus adspersus. In this study, we examined the abundance, size-structure, and feeding ecology of juvenile sea bass and labrids in Narragansett Bay (Rhode Island, USA) from June to October in 2018 and 2019 and evaluated potential interspecific competition using habitat, diet, and isotopic niche overlap indices. Juveniles (age-0+) of each fish species spatiotemporally co-occurred in shallow, polyhaline habitats throughout the estuary. Age-0 cohorts were numerically dominant across species and initially recruited to the study area in July (minimum total length, TL = 15-20 mm), reached peak abundances in mid- to late summer (maximum abundances = 12-140 fish 100 m-2), and emigrated from field sites in October (maximum TL = 85-96 mm). Stomach content and stable isotope (δ15N and δ13C) analyses determined that focal fishes were generalist carnivores that foraged in bentho-pelagic food webs. Fishes also overlapped in their respective ambit and core isotopic niche space, but interspecific dietary overlap was size-dependent. Dietary overlap was most pronounced between sea bass ≤49 mm TL and labrids ≤59 mm TL due to their mutual reliance on gammarid and caprellid amphipods. Ontogenetic dietary shifts then resulted in food niche segregation, such that sea bass 50-139 mm TL consumed decapod crustaceans and fish, whereas labrids 60-181 mm TL mainly fed on amphipods, worms, bivalves, and turf-associated biota, i.e. bryozoans, hydroids, and seaweeds. Habitat and trophic niche overlap between early juvenile sea bass and labrids purportedly have not caused opposite population trajectories or food resource limitation in Narragansett Bay, indicating an absence of exploitative competition. Alternatively, realized competition between species may be too spatiotemporally restricted to alter their population dynamics. Continuous monitoring of the sea bass’s bio-ecological effects in southern New England estuaries is warranted, however, given their recent range expansion and increasing abundances at northern latitudes.

Cold-induced metabolic depression in cunner (Tautogolabrus adspersus): A multifaceted cellular event.

Metabolic depression and dormancy (i.e., stopping/greatly reducing activity and feeding) are strategies used by many animals to survive winter conditions characterized by food shortages and cold temperatures. However, controversy exists on whether the reduced metabolism of some fishes at cold temperatures is due to dormancy alone, or also involves active metabolic depression. Thus, we acclimated winter-dormant cunner [Tautogolabrus adspersus, a north temperate wrasse which in Newfoundland is at the northern limit of its distribution] and winter-active Atlantic salmon (Salmo salar) to winter (0°C; 8h light: 16h dark) and summer (10°C; 16h light: 8 h dark) conditions, and measured the thermal sensitivity of ATP-producing and O2-consuming processes in isolated liver mitochondria and hepatocytes when exposed in vitro to temperatures from 20 to 0°C and 10 to 0°C, respectively. We found that: 1) liver mitochondrial State 3 respiration and hepatocyte O2 consumption in cunner were only ~ one-third and two-thirds of that measured in salmon, respectively, at all measurement temperatures; 2) cunner mitochondria also have proton conductance and leak respiration (State 4) values that are only approximately one-third of those in salmon; 3) the mitochondria of cunner show a dramatic reduction in respiratory control ratio (from ~ 8 to 3), and a much greater drop in State 3 respiration, between 10 and 5°C (Q10 values in 10- and 0°C-acclimated fish of 14.5 and 141.2, respectively), as compared with salmon (3.9 and 9.6, respectively); and 4) lowering temperature from 5 to 0°C resulted in ~ 40 and 30% reductions in hepatocyte O2 consumption due to non-mitochondrial respiration and Na+-K+-ATPase activity, respectively, in cunner, but not in salmon. Collectively, these results highlight the intrinsic capacity for metabolic depression in hepatocytes and mitochondria of cunner, and clearly suggest that several cellular processes play a role in the reduced metabolic rates exhibited by some fishes at cold temperatures.

Growth and Mortality as Causes of Variation in Metabolic Scaling Among Taxa and Taxonomic Levels.

Metabolic rate (MR) usually changes (scales) out of proportion to body mass (BM) as MR=aBMb, where a is a normalisation constant and b is the scaling exponent that reflects how steep this change is. This scaling relationship is fundamental to biology, but over a century of research has provided little consensus on the value of b, and why it appears to vary among taxa and taxonomic levels. By analysing published data on fish and taking an individual-based approach to metabolic scaling, I show that variation in growth of fish under naturally restricted food availability can explain variation in within-individual (ontogenetic) b for standard (maintenance) metabolic rate (SMR) of brown trout (Salmo trutta), with the fastest growers having the steepest metabolic scaling (b≈1). Moreover, I show that within-individual b can vary much more widely than previously assumed from work on different individuals or different species, from -1 to 1 for SMR among individual brown trout. The negative scaling of SMR for some individuals was caused by reductions in metabolic rate in a food limited environment, likely to maintain positive growth. This resulted in a mean within-individual b for SMR that was significantly lower than the across-individual ("static") b, a difference that also existed for another species, cunner (Tautogolabrus adspersus). Interestingly, the wide variation in ontogenetic b for SMR among individual brown trout did not exist for maximum (active) metabolic rate (MMR) of the same fish, showing that these two key metabolic traits (SMR and MMR) can scale independently of one another. I also show that across-species ("evolutionary") b for SMR of 134 fishes is significantly steeper (b approaching 1) than the mean ontogenetic b for the brown trout and cunner. Based on these interesting findings, I hypothesise that evolutionary and static metabolic scaling can be systematically different from ontogenetic scaling, and that the steeper evolutionary than ontogenetic scaling for fishes arises as a by-product of natural selection for fast-growing individuals with steep metabolic scaling (b≈1) early in life, where size-selective mortality is high for fishes. I support this by showing that b for SMR tends to increase with natural mortality rates of fish larvae within taxa.

Inactivity and the passive slowing effect of cold on resting metabolism as the primary drivers of energy savings in overwintering fishes.

ABSTRACTWinter dormancy is a seasonal survival strategy common among temperate ectotherms, characterized by inactivity, fasting and low metabolic rates. Previous reports of metabolic rate depression (MRD) in winter-dormant ectotherms, including many fishes, may have resulted from confounding influences of temperature-dependent variation in activity on metabolic rate measurements. We hypothesize that, as demonstrated recently in the winter-dormant cunner (Tautogolabrus adspersus), inactivity and the passive physicochemical (Arrhenius) effect of cold on standard metabolic rate (SMR) are the common primary mechanisms underlying the low metabolic rates among winter-dormant fishes. Using automated video tracking, we investigated threshold temperatures for winter dormancy onset (major reductions in activity, increased sheltering and fasting) in four phylogenetically diverse teleost species reported to be winter dormant: cunner, pumpkinseed sunfish (Lepomis gibbosus), American eel (Anguilla rostrata) and mummichog (Fundulus heteroclitus). All species showed large activity and feeding reductions, but the magnitude of change and dormancy threshold temperature was species-specific. We propose that a continuum of overwintering responses exists among fishes from dormant to lethargic to active. The relationship between activity and metabolic rate was then measured using video-recorded automated respirometry during acute cooling and following cold acclimation in pumpkinseed, mummichog and eel. In all species, activity and metabolic rate were strongly correlated at all temperatures, and cooling caused reduced activity and metabolic rate. When variation in activity was controlled for across temperatures spanning the dormancy thresholds, the thermal sensitivity of metabolic rate including SMR indicated the predominance of passive physicochemical influences (mean Q10<3.5), rather than active MRD. Activity reductions and physicochemical slowing of metabolism owing to cold appear to be the primary energy-saving mechanisms in overwintering fishes.

A Novel Marine Pathogen Isolated from Wild Cunners (Tautogolabrus adspersus): Comparative Genomics and Transcriptome Profiling of Pseudomonas sp. Strain J380.

Cunner (Tautogolabrus adspersus) is a cleaner fish being considered for utilized in the North Atlantic salmon (Salmo salar) aquaculture industry to biocontrol sea lice infestations. However, bacterial diseases due to natural infections in wild cunners have yet to be described. This study reports the isolation of Pseudomonas sp. J380 from infected wild cunners and its phenotypic, genomic, and transcriptomic characterization. This Gram-negative motile rod-shaped bacterium showed a mesophilic (4–28 °C) and halotolerant growth. Under iron-limited conditions, Pseudomonas sp. J380 produced pyoverdine-type fluorescent siderophore. Koch’s postulates were verified in wild cunners by intraperitoneally (i.p.) injecting Pseudomonas sp. J380 at 4 × 103, 4 × 105, and 4 × 107 colony forming units (CFU)/dose. Host-range and comparative virulence were also investigated in lumpfish and Atlantic salmon i.p. injected with ~106 CFU/dose. Lumpfish were more susceptible compared to cunners, and Atlantic salmon was resistant to Pseudomonas sp. J380 infection. Cunner tissues were heavily colonized by Pseudomonas sp. J380 compared to lumpfish and Atlantic salmon suggesting that it might be an opportunistic pathogen in cunners. The genome of Pseudomonas sp. J380 was 6.26 megabases (Mb) with a guanine-cytosine (GC) content of 59.7%. Biochemical profiles, as well as comparative and phylogenomic analyses, suggested that Pseudomonas sp. J380 belongs to the P. fluorescens species complex. Transcriptome profiling under iron-limited vs. iron-enriched conditions identified 1159 differentially expressed genes (DEGs). Cellular metabolic processes, such as ribosomal and energy production, and protein synthesis, were impeded by iron limitation. In contrast, genes involved in environmental adaptation mechanisms including two-component systems, histidine catabolism, and redox balance were transcriptionally up-regulated. Furthermore, iron limitation triggered the differential expression of genes encoding proteins associated with iron homeostasis. As the first report on a bacterial infection in cunners, the current study provides an overview of a new marine pathogen, Pseudomonas sp. J380.

Strike a pose: Does communication by a facultative cleaner fish, the cunner wrasse (Tautogolabrus adspersus), facilitate interaction with Atlantic salmon (Salmo salar)?

Tropical dedicated cleaner fishes communicate with client fishes to enable cooperative parasite removal, however, the ability of temperate facultative cleaner fishes to elicit cooperation through communication has yet to be fully investigated. Understanding the wider dynamics of communication in cleaning mutualism is particularly important for the salmon farming industry, because it uses temperate facultative cleaner fishes to control parasitic salmon-lice. To investigate whether cleaner-client communication might benefit parasite removal by facultative cleaners used in aquaculture, we observed interactions between cunner wrasse (n = 42) and their Atlantic salmon (n = 59) clients, which were either infected or non-infected by chalimus stage salmon-lice. We found that expression of two behavioural cues, cunners posing towards salmon and cunner making body-contact with salmon: (1) was higher when cunners were alongside infected salmon rather than non-infected salmon, (2) reduced the average distance between the cunner and trios of infected salmon, (3) increased the time cunner spent visually inspecting infected salmon, but, (4) did not decrease antagonistic interaction between the cunner and the salmon. Behavioural variation was high among individuals, nevertheless larger cunners (> 100 g) showed significantly higher rates of desirable mutualistic (e.g. inspection, pecking) and communicative (e.g. posing, contact) behaviours than smaller cunners. These findings imply this facultative cleaner wrasse displayed behavioural cues to infected clients which increased proximity and resulted in higher rates of mutualistic behaviours. If these two behavioural cues are subsequently shown to be correlated with delousing performance, then they could be used to identify high-performing elite cleaners for use in sea-farms and in selective breeding programs.

Distribution and structure of coastal ichthyoplankton communities of the Bay of Fundy in southern New Brunswick, Canada

Ichthyoplankton communities from Saint John Harbour and Passamaquoddy Bay on the New Brunswick shore of the Bay of Fundy, Canada, were sampled seasonally between 2011 and 2014. Saint John Harbour is an industrialised port whereas Passamaquoddy Bay is less developed, with a focus on aquaculture. In total, 32 species of fish eggs and larvae were recorded: 26 species in Saint John Harbour and 25 in Passamaquoddy Bay. Nineteen species were common to both areas. The dominant species in Passamaquoddy Bay were Enchelyopus cimbrius, Urophycis sp., Scophthalmus aquosus, and Tautogolabrus adspersus. In Saint John Harbour, E. cimbrius, Urophycis sp., Clupea harengus, and Pseudopleuronectes americanus were most abundant. The communities of the two areas were significantly different. This was most pronounced in summer when Saint John Harbour had a much higher proportion of C. harengus and much lower overall abundances, relative to Passamaquoddy Bay. Saint John Harbour demonstrated higher taxonomic diversity than Passamaquoddy Bay, attributable to the wider variety of salinity regimes present within the harbour. In both areas, the ichthyoplankton communities were strongly seasonal with the highest abundance and diversity in summer. Surface temperature was the best predictor of community composition. Given its industrialisation, Saint John Harbour had a surprisingly diverse ichthyoplankton community, comparable to the less impacted Passamaquoddy Bay. The strong flushing in the harbour by high riverine output and tidal exchange may diminish industrial impact. We strongly recommend incorporating ichthyoplankton into the long-term monitoring of Saint John Harbour and provide guidance to this end.

Thermal acclimation leads to variable muscle responses in two temperate labrid fishes.

Temperature can be a key abiotic factor in fish distribution, as it affects most physiological processes. Specifically, temperature can affect locomotor capabilities, especially as species are exposed to temperatures nearing their thermal limits. In this study, we aimed to understand the effects of temperature on muscle in two labrids that occupy the Northwest Atlantic Ocean. When exposed to cold temperatures in autumn, cunner (Tautogolabrus adspersus) and tautog (Tautoga onitis) go into a state of winter dormancy. Transitions into dormancy vary slightly, where tautog will make short migrations to overwintering habitats while cunner overwinter in year-round habitats. To understand how muscle function changes with temperature, we held fish for 4weeks at either 5 or 20°C and then ran muscle kinetic and workloop experiments at 5, 10 and 20°C. Following experiments, we used immunohistochemistry staining to identify acclimation effects on myosin isoform expression. Muscle taken from warm-acclimated cunner performed the best, whereas there were relatively few differences among the other three groups. Cunner acclimated at both temperatures downregulated the myosin heavy chain, suggesting a transition in fiber type from slow-oxidative to fast-glycolytic. This change did not amount to a detectable difference in muscle power production and kinetics. However, overall poor performance at cold temperatures could force these fishes into torpor to overwinter. Tautog, alternatively, retained myosin heavy chains, which likely increases locomotor capabilities when making short migrations to overwintering habitats.

Effects of overwintering temperatures on the escape response in cunner (Tautogolabrus adspersus).

Cunner (Tautogolabrus adspersus) are a temperate labrid species that inhabit the Western Atlantic and experience temperatures ranging from 0°C to 25°C. During autumn, once temperatures drop below 10°C in Long Island Sound, cunner find shelter and enter a state of quiescence. Previous work has shown that acclimation to low temperatures limits the performance of locomotor musculature, which significantly lowers steady swimming capabilities. We aimed to understand how the escape response (C-start) might be impacted by temperatures experienced by cunner in Long Island Sound over the course of a year. Escape responses were recorded at 250 frames/s at 20°C, 15°C, 10°C, and 5°C. Average peak velocities and accelerations were faster in fish acclimated to 20°C than to 5°C and 10°C. Despite taking a similar turn angle to 10°C and 15°C fish, the 5°C treatment group took longer to complete the C-start, which might make them more susceptible to predation at this temperature. Based on these results it appears that the escape response is reduced at cold temperatures. Previous research has shown that locomotor musculature performance is significantly reduced at cold temperatures, which could explain the results seen here. The decrease in escape performance at cold temperatures could explain their state of extended torpor as the slowed C-start at these cold temperatures might make them more susceptible to predation.

A temperate labrid fish demonstrates compensatory mechanisms to feed at torpor‐inducing temperatures

AbstractTemperature can have profound impacts on fitness‐related activities in fishes. Feeding is an ecologically relevant task which is controlled by muscle function. Consequently, in ectotherms, muscle function and feeding kinematics can be altered by temperature. This study investigated the effect of decreasing temperature on the feeding kinematics of the northern most labrid in the Western Atlantic. During winter, cunner (Tautogolabrus adspersus) enter a state of extended torpor in order to conserve energy when water temperatures drop below ~10°C. We hypothesized that feeding kinematics would be slower at lower temperatures especially those associated with torpor (≤10°C). Additionally, we hypothesized that prey type will elicit different feeding behaviors. Feeding events on sandworms and Asian shore crabs were recorded at 5, 10, 15 and 20°C. Fish held at 5°C had slower opening and closing jaw velocities while using more ram than the other temperature treatments. No differences were detected between prey types. For both prey types, the temperature treatment which consistently induced torpor (5°C) slowed oral jaw movements, which likely forced cunner to rely more on ram than suction to capture prey. Torpor temperatures appeared to have less of an effect on feeding than on metabolic rate, steady swimming capabilities and muscle function, suggesting some compensatory mechanisms of feeding musculature in cunner.

The benefit of being still: energy savings during winter dormancy in fish come from inactivity and the cold, not from metabolic rate depression.

Winter dormancy is used by many animals to survive the cold and food-poor high-latitude winter. Metabolic rate depression, an active downregulation of resting cellular energy turnover and thus standard (resting) metabolic rate (SMR), is a unifying strategy underlying the persistence of organisms in such energy-limited environments, including hibernating endotherms. However, controversy exists about its involvement in winter-dormant aquatic ectotherms. To address this debate, we conducted simultaneous, multi-day measurements of whole-animal oxygen consumption rate (a proxy of metabolic rate) and spontaneous movement in a model winter-dormant marine fish, the cunner (Tautogolabrus adspersus). Winter dormancy in cunner involved a dampened diel rhythm of metabolic rate, such that a low and stable metabolic rate persisted throughout the 24 h day. Based on the thermal sensitivity (Q10) of SMR as well as correlations of metabolic rate and movement, the reductions in metabolic rate were not attributable to metabolic rate depression, but rather to reduced activity under the cold and darkness typical of the winter refuge among substrate. Previous reports of metabolic rate depression in cunner, and possibly other fish species, during winter dormancy were probably confounded by variation in activity. Unlike hibernating endotherms, and excepting the few fish species that overwinter in anoxic waters, winter dormancy in fishes, as exemplified by cunner, need not involve metabolic rate depression. Rather, energy savings come from inactivity combined with passive physico-chemical effects of the cold on SMR, demonstrating that thermal effects on activity can greatly influence temperature-metabolism relationships, and illustrating the benefit of simply being still in energy-limited environments.

Seaweed structure shapes trophic interactions: A case study using a mid-trophic level fish species

Biogenic habitat structure, such as that created by foundation macrophytes, shapes the interactions of higher trophic level organisms by creating three-dimensional refuge spaces. In recent decades, many kelp habitats have transformed into turf-dominated communities. This represents a fundamental change in the overall habitat structure in these communities, with an unknown impact on upper trophic level organisms. We investigated how macroalgae morphology affects a common residential mid-trophic level wrasse, Tautogolabrus adspersus (cunner), which utilizes macroalgae for both refuge and foraging. Three studies were conducted: in situ behavioral video observations, a refuge choice experiment, and a foraging efficiency experiment. Video observations revealed that in kelp-dominated and mixed habitat types cunner use macroalgae more often for refuge than for foraging, but in turf-dominated habitats refuge and foraging events were equal. In these habitats, refuge-seeking was more often associated with a tall, morphologically simple kelp. The refuge choice experiment supported our video observations with cunner preferentially seeking refuge beneath taller but less morphologically complex algae instead of shorter filamentous forms. In predation trials, macroalgae complexity did not significantly affect the number of prey the fish captured. Our results provide evidence that the refuge-seeking behavior of this residential mid-trophic level fish may be impacted by the ongoing shifts in macroalgae dominance in the Gulf of Maine. Loss of its preferred refuge (tall, canopy-forming kelps) may force it to use the less-preferred introduced turf algae instead. However, whether turf provides sufficient protection for this species remains unclear. With the ongoing loss of kelp in temperate coastal ecosystems worldwide, it is important to understand the potential indirect effects that changes in habitat structure will have on the trophic interactions of upper level organisms.