On the habitat and isolation of Gymnocharacinus bergi (Osteichthyes: Characidae)

Synopsis Gymnocharacinus bergi is a rare Paranensean fish which is the only characiform almost lacking scales in the adult. It is endemic and the only species in a peculiar spot — a tributary of the Valcheta creek — in the Somuncurá plateau in northern Patagonia, Argentina, over 300 km from the nearest place with a paranensean fish fauna. Besides its geographical isolation, G. bergi occurs within an area with climatic features drastically different from those currently associated with fishes from Neotropical temperate zones. We tested the assumption that water temperature in the naked characin habitat do not agree with the northern Patagonia climate. We also considered the isolation of G. bergi within the framework of an increasing inpoverishment of the paranensean ichthyofauna along a NE-SW axis in the Buenos Aires province. For this we applied a decrement equation used in island biogeography. Our findings demonstrate that the existence of G. bergi in its isolated habitat is possible because of the thermal traits of the water at the sources of the creeks, its temperature being independent of the climate of the area. The chemical composition of water was found to be within the range of common environments in the Buenos Aires pampas inhabited by several species of Paranensean fishes. Geographically, G. bergi lives in the last of a series of habitats which show a decreasing number of species correlated with the increasing distance from the La Plata River. Conservation status of the species is briefly discussed.     

Changes in rocky reef fish assemblages throughout an estuary with a restricted inlet

Rocky reef habitat is common in many estuaries, yet its role as a habitat for fishes is poorly understood. There is also limited understanding of how access of coastal species into estuaries and habitat quality can affect the distribution of rocky reef fishes within estuaries. This study used baited remote underwater video stations to determine spatial patterns in fish assemblages associated with rocky reef habitat throughout a barrier estuary with a permanently open but restricted inlet. Estuarine rocky reefs provided habitat for a diverse assemblage of fishes, many of which were large juveniles and subadults. In the absence of a pronounced salinity or temperature gradient, a clear transition in fish assemblages occurred from coastal waters, through the inlet channel, to the central estuary, and into the inner estuary. The inlet channel, notably its narrowness and length, limits tidal input into this estuary, which acts as a significant impediment to the dispersal of many coastal fishes, and insufficient habitat excludes many coastal rocky reef species from the inner estuary. This study highlights the need to recognise estuarine rocky reefs as providing habitat for diverse fish assemblages and the role inlets play in restricting access of coastal species.     

Temperature Tolerances of North American Freshwater Fishes Exposed to Dynamic Changes in Temperature

Traditionally lower and upper temperature tolerances of fishes have been quantified in the laboratory via three different experimental approaches: the Fry or incipient lethal temperature (ILT), critical thermal (CTM) and chronic lethal (CLM) methodologies. Although these three experimental laboratory approaches generate endpoints which are quantitatively expressed as a temperature, are determined experimentally with random samples of fish acclimated to specific temperatures, and involve both time and temperature as major test variables, they do not quantify the same response. All three approaches generate valuable, albeit different, information concerning the temperature tolerance of a species. In this review we have summarized published research concerning the tolerance of North American freshwater fishes to dynamic changes in temperature, i.e., tolerance is tested by methods that gradually change temperatures until biological stress is observed. We found more than 450 individual temperature tolerances listed in 80 publications which present original dynamic temperature tolerance data for 116 species, 7 subspecies and 7 hybrids from 19 families of North American freshwater fishes. This total represents about 1/3 of the families and 1/6 of the known North American freshwater species. Temperature tolerance data were partitioned by experimental approach, i.e., critical thermal method (CTM) and chronic lethal method (CLM), and direction of temperature change. Although both CTM and CLM expose fish to dynamic changes in water temperature, these two methods differ in temperature change rates and test endpoints, and hence measure different aspects of thermal stress. A majority of the 80 studies employed CTM to assess temperature tolerance, in particular determination of CTmaxima. One or more CTmaxima has been reported for 108 fishes. Twenty-two fishes have reported highest CTmaxima of 40°C or higher. Several species in the family Cyprinodontidae have generated some of the highest CTmaxima reported for any ectothermic vertebrate. For a variety of reasons, data concerning tolerance of low temperatures are less plentiful. Low temperature tolerance quantified as either CTminima or CLminima were found for a total of 37 fishes. Acclimation temperature exerts a major effect on the temperature tolerance of most North American fish species and it is usually strongly linearly related to both CTmaxima and CTminima. Although we uncovered dynamic temperature tolerance data for 130 fishes, only a single dynamic, temperature tolerance polygon has been published, that for the sheepshead minnow, Cyprinodon variegatus.     

Subregional differences in groundfish distributional responses to anomalous ocean bottom temperatures in the northeast Pacific

Although climate‐induced shifts in fish distribution have been widely reported at the population level, studies that account for ontogenetic shifts and subregional differences when assessing responses are rare.In this study, groundfish distributional changes in depth, latitude, and longitude were assessed at different size classes by species within nine subregions. We examined large, quality‐controlled datasets of depth‐stratified‐random bottom trawl surveys conducted during summer in three large regions—the Gulf of Alaska and the west coasts of Canada and the United States—over the period 1996–2015, a time period punctuated by a marine “heat wave.” Temporal biases in bottom temperature were minimized by subdividing each region into three subregions, each with short‐duration surveys. Near‐bottom temperatures, weighted by stratum area, were unsynchronized across subregions and exhibited varying subregional interannual variability. The weighted mean bottom depths in the subregions also vary largely among subregions. The centroids (centers of gravity) of groundfish distribution were weighted with catch per unit effort and stratum area for 10 commercially important groundfish species by size class and subregion. Our multivariate analyses showed that there were significant differences in aggregate fish movement responses to warm temperatures across subregions but not among species or sizes. Groundfish demonstrated poleward responses to warming temperatures only in a few subregions and moved shallower or deeper to seek colder waters. The temperature responses of groundfish depended on where they were. Under global warming, groundfish may form geographically distinct thermal ecoregions along the northeast Pacific shelf. Shallow‐depth species exhibited greatly different distributional responses to temperature changes across subregions while deep‐depth species of different subregions tend to have relatively similar temperature responses. Future climate studies would benefit by considering fish distributions on small subregional scales.     

马鞍列岛岩礁生境鱼类群落生态学.Ⅰ.种类组成和多样性

为了解潮下带岩礁生境的鱼类区系特征,于2009年对马鞍列岛岩礁生境进行了12个月的多网目组合刺网采样,从分类学和生态型组成等方面,结合多样性和相对重要性指数,对该生境的鱼类组成和多样性特征进行了分析。全年共采集鱼类87种,隶属2纲14目50科73属。其中鲈形目鱼类51种,占58.6%;趋礁性鱼类49种,占56.3%;放流鱼类7种,占8%。所有鱼类个体中,幼鱼的总比例为67.4%。暖水种、暖温种和冷温种分别为50、36和1种;底层、近底层和中上层鱼类各为19、46和22种,其中褐菖鲉(Sebasti scus marmoratus)、黄姑鱼(Nibea albiflora)和赤鼻棱鳀(Thryssa kammalensis)分别为各水层的绝对优势种;定居种、季节性洄游种和偶见种各为32、55和11种。岩礁生境鱼类多样性呈现明显的季节变化特征,2月份最低,9月份最高。研究结果表明,马鞍列岛岩礁生境是以趋礁鱼类为特征群体、暖水性和暖温性鱼类共同主导、各个类型的幼鱼在夏秋季集群出现、同时也分布了一定量放流种的高鱼类多样性栖息地,它为各种鱼类提供了优良的摄食、避敌和繁殖场所,是近岸海洋生态系统中相当重要的生境。然而相比过去,该生境的鱼类多样性已经大大降低,因此需对其保护工作予以更多关注。     

Heat tolerance and its plasticity in Antarctic fishes

The adaptive radiation of the Antarctic notothenioid ancestral benthic fish stock within the chronic freezing waters of the Southern Ocean gave rise to five highly cold adapted families. Their stenothermy, first observed from several high-latitude McMurdo Sound species, has been of increasing recent interest given the threat of rising polar water temperatures from global climate change. In this study we determined the heat tolerance in a geographically diverse group of 11 Antarctic species as their critical thermal maximum (CTMax). When acclimatized to their natural freezing water temperatures, environmental CTMaxs ranged from 11.95 to 16.17 °C, well below those of fishes endemic to warmer waters. There was a significant regional split, with higher CTMaxs in species from the more northerly and thermally variable Seasonal Pack-ice Zone. When eight of the Antarctic species were warm acclimated to 4 °C all showed a significant increase over their environmental CTMaxs, with several showing plasticity comparable in magnitude to some far more eurythermal fishes. When the accrual of heat tolerance during acclimation was followed in three high-latitude McMurdo Sound species, it was found to develop slowly in two of them, which was correlated with their low metabolic rates.     

Will northern fish populations be in hot water because of climate change?

Predicted increases in water temperature in response to climate change will have large implications for aquatic ecosystems, such as altering thermal habitat and potential range expansion of fish species. Warmwater fish species, such as smallmouth bass, Micropterus dolomieu , may have access to additional favourable thermal habitat under increased surface-water temperatures, thereby shifting the northern limit of the distribution of the species further north in Canada and potentially negatively impacting native fish communities. We assembled a database of summer surface-water temperatures for over 13 000 lakes across Canada. The database consists of lakes with a variety of physical, chemical and biological properties. We used general linear models to develop a nation-wide maximum lake surface-water temperature model. The model was extended to predict surface-water temperatures suitable to smallmouth bass and under climate-change scenarios. Air temperature, latitude, longitude and sampling time were good predictors of present-day maximum surface-water temperature. We predicted lake surface-water temperatures for July 2100 using three climate-change scenarios. Water temperatures were predicted to increase by as much as 18 °C by 2100, with the greatest increase in northern Canada. Lakes with maximum surface-water temperatures suitable for smallmouth bass populations were spatially identified. Under several climate-change scenarios, we were able to identify lakes that will contain suitable thermal habitat and, therefore, are vulnerable to invasion by smallmouth bass in 2100. This included lakes in the Arctic that were predicted to have suitable thermal habitat by 2100.     

Gametogenesis and Development of Gymnocharacinus Bergi (Pisces, Characidae): Reproductive Mode Relative to Environmental Stability

Gymnocharacinus bergi (Pisces, Characidae) is classified as 'endangered' (IUCN 1996). It has been given particular attention among Patagonian fishes due to the reduction of some of its morphological structures, particularly scales, its extreme southern distribution among the Characiformes and its strong adaptation to a thermal environment in northeastern Patagonia. This paper describes the main aspects of gametogenesis, induced breeding, spawning and development of G. bergi, whose life history traits are related to the peculiar characteristics of its restricted environment. The temperature and flow stability of the Valcheta Stream make many of the environmental variables predictable. Other variables related to photoperiod undergo predictable fluctuation during the year. Gymnocharacinus bergi has synchronous gametogenesis and a rather short breeding season, which is earlier than for Paranensean characids. Its reproductive mode, courtship and spawning behaviour, and the absence of sexual dimorphism are common to other small characins from lotic environments. Gymnocharacinus bergi is a sedentary species with precocial characters, such as low fecundity and slightly adhesive, yolk-rich oocytes which are large in relation to the small size of the female. Larvae are robust, development is indirect and adulthood prolonged. These peculiar characteristics indicate a reproductive style very different from that of the main groups of Patagonian fish fauna.     

Thermal response of demersal and pelagic juvenile fishes from the surf zone during a heat‐wave simulation

Experimental measurements were collected in the laboratory to evaluate the maximum thermal limit and thermal plasticity of Neotropical juvenile fish with different life habitats (demersal and pelagic) from surf zone in response to a “heat‐wave experiment”. Trials were conducted using two temperature acclimations (T_a), including the current average temperature of Southeastern Brazil (T_a: 14 days at 25°C) and the “heat‐wave experiment” (T_a: 14 days at 30°C), simulating a heat‐wave event that occurs when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5°C. Typical species of the surf zone were used: the demersal White sea catfish (Genidens barbus) and Gulf kingcroaker (Menticirrhus littoralis), and the pelagic fishes Great pompano (Trachinotus goodei) and Long‐fin mullet (Mugil brevirostris). The thermal range and plasticity values for the both life‐habitats species were verified through current and heat‐wave acclimation. The thermal tolerance at high temperatures (CT_max) of these species differed between T_a, habitat and species. Fish showed a species‐specific response to temperature increase, regardless of their habitat even under similar abiotic conditions. However, at the heat‐wave simulation, the demersal fish presented a greater thermal plasticity in relation to the pelagic fish. Despite the higher thermal tolerance when exposed to heat‐wave simulation, all fish species displayed a lower thermal edge safety that is markedly close to their maximum thermal limits.     

Temporal plasticity in thermal‐habitat selection of burbot Lota lota a diel‐migrating winter‐specialist

In this study, animal‐borne telemetry with temperature sensors was coupled with extensive habitat temperature monitoring in a dimictic reservoir, to test the following hypotheses: behavioural thermoregulation occurs throughout the year and temperature selection varies on a diel and seasonal basis, in a winter‐specialist diel‐migrating fish. Burbot Lota lota demonstrated nightly behavioural thermoregulation throughout the year, with a large seasonal shift between selection for very cold temperatures (<2° C) optimal for reproduction during the spawning period and selection for warmer temperatures (12–14° C) optimal for hunting and feeding during non‐reproductive periods. During daylight hours, while L. lota avoided habitats warmer than optimal for reproduction and feeding during the spawning and non‐reproductive periods, respectively, active selection was limited to selection for 4–6° C habitat during the prespawning period. Although behavioural thermoregulation explained the night‐time migration, behavioural thermoregulation only partially explained daytime behaviour, indicating that diel migration is best explained by a combination of factors. Thus, thermal‐habitat selection was a good predictor of night‐time habitat occupancy in a diel‐migrating species. Together, these results show that thermal‐habitat selection by fishes may be important throughout the year and a more seasonally plastic behaviour than previously recognized.     

Local distribution and thermal ecology of two intertidal fishes

Geographic variability in the physiological attributes of widely distributed species can be a result of phenotypic plasticity or can reflect evolutionary responses to a particular habitat. In the field, we assessed thermal variability in low and high intertidal pools and the distribution of resident fish species Scartichthys viridis and transitory Girella laevifrons along this vertical intertidal gradient at three localities along the Chilean coast: Antofagasta (the northernmost and warmest habitat), Carrizal Bajo (central coast) and Las Cruces (the southernmost and coldest habitat). In the laboratory, we evaluated the thermal sensitivity of fish captured from each locality. The response to temperature was estimated as the frequency of opercular movements and as thermal selectivity in a gradient; the former being a indirect indicator of energy costs in a particular environment and the latter revealing differential occupation of habitat. Seawater temperature in intertidal pools was greatest at Antofagasta, and within each site was greatest in high intertidal pools. The two intertidal fish species showed opposite patterns of local distribution, with S. viridis primarily inhabiting the lower sectors of the intertidal zone, and G. laevifrons occupying the higher sectors of the intertidal zone. This pattern was consistent for all three localities. Locality was found to be a very important factor determining the frequency of opercular movement and thermal selectivity of both S. viridis and G. laevifrons. Our results suggest that S. viridis and G. laevifrons respond according to: (1) the thermal history of the habitat from which they came, and (2) the immediate physical conditions of their habitat. These results suggest local adaptation rather than plasticity in thermoregulatory and energetic mechanisms.     

Effects of temperature acclimation on the critical thermal limits and swimming performance of <Emphasis Type="Italic">Brachymystax lenok tsinlingensis</Emphasis>: a threatened fish in Qinling Mountain region of China

Brachymystax lenok tsinlingensis is an endangered teleost fish species that occurs in the Qinling Mountain region of China. It also happens to represent the southernmost distribution of an endemic Salmonid fish worldwide. Recently, the habitat of this species shifted towards a higher altitude presumably because of climate change, indicating that this species might be suffering from thermal stress. However, information on the thermal physiology of this species is extremely limited. Accordingly, we investigated the effects of acclimation temperature (6, 12, and 18 °C) on ecologically relevant end points such as critical thermal limits, swimming performance and metabolic rate. Our results showed that elevated acclimation temperatures resulted in increased thermal tolerance and decreased swimming efficiency. High temperature (i.e., 18 °C) did not have a marked effect on the critical swimming speed and the maximum metabolic rate but caused an increase in the energetic cost of transport compared with the results at 12 °C. Interestingly, we found that both the acclimation response ratio and the critical thermal maxima of B. lenok tsinlingensis were higher than that of many other Salmonidae fishes, suggesting that this species responds plastically to temperature changes and has a high thermal tolerance. These characteristics are hypothesized to be related to the southernmost distribution of this species.     

Aggressive Behaviour Between Gymnocharacinus Bergi (Pisces, Characidae) And Other Neotropical Fishes From A Thermal Stream In Patagonia

Gymnocharacinus bergi is a stenothermal endangered fish only found in the headwaters of a thermal stream within the temperate Somuncurá Plateau (Patagonia, Argentina). In spite of the presence of other fish species in the Valcheta Stream basin, none of these has been found at the headwaters. Temperature and salinity cannot account for the absence of extremely eurytopic Cnesterodon and Jenynsia. In addition, there is no evidence of diet overlapping or territory defence between these species and G. bergi. Therefore, we hypothesise that agonistic behaviour might be related to G. bergi's isolation. Experiments were performed in order to analyse interspecific interaction between G. bergi and individuals of the other two species. Cnesterodon decemmaculatus showed a submissive behaviour while Jenynsia multidentata was clearly aggressive. G. bergi decreased its aggressive behaviour towards C. decemmaculatus throughout the experiment. However, when placed with J. multidentata, its aggressive behaviour did not diminish. We suggest that the characteristics of the agonistic behaviour displayed by J. multidentata, opposite from those displayed by C. decemmaculatus, might account for the absence of J. multidentata in G. bergi's present habitat. With respect to C. decemmaculatus, other factors such as its low counter current swimming ability might play a major role in this phenomenon.     

牛山湖两种不同生境小型鱼类的种类组成、多样性和密度

研究了2003年春季浅水草型湖泊牛山湖小型鱼类空间分布（种类组成、多样性和密度等）与生境异质性之间的关系.根据水生植被状况、离岸距离和水深,选择了两种差异较大且有代表性的生境类型,即近岸沉水植物茂密的生境A和远岸沉水植物稀疏的生境B.使用围网（180 m²）在这两种生境中进行小型鱼类的采样,采用多次标志回捕法和Zippin去除法估算了围网内小型鱼类的密度.结果表明,两种不同生境中小型鱼类的种类组成、多样性度量值和密度估算值均存在一定程度的差异：1）生境A中的渔获物由5科14种小型鱼类组成,优势种类为生活在中、下水层的高体鳑鲏、彩副鱊和麦穗鱼;生境B中的渔获物由3科9种小型鱼类组成,优势种类为生活在湖底的子陵吻鰕虎鱼和小黄黝鱼.2）生境A和生境B小型鱼类群落间的Bray-Curtis指数为0.222,结构相似性较低;但二者的物种等级丰度分布则无显著差异,均属于对数级数分布.3）生境A中高体鳑鲏、彩副鱊、麦穗鱼等9种小型鱼类的总密度值为8.71 ind·m^-2,生境B中子陵吻鰕虎鱼、小黄黝鱼等5种小型鱼类的总密度值只有3.54 ind·m^-2.小型鱼类在这两种不同生境中的空间分布差异可能与其逃避捕食、觅食和繁殖等生态习性的生境需求有关,因此,水生植被生境对小型鱼类资源合理开发和多样性保护具有重要意义.     

Metabolic responses to low temperature in fish muscle

For most fish, body temperature is very close to that of the habitat. The diversity of thermal habitats exploited by fish as well as their capacity to adapt to thermal change makes them excellent organisms in which to examine the evolutionary and phenotypic responses to temperature. An extensive literature links cold temperatures with enhanced oxidative capacities in fish tissues, particularly skeletal muscle. Closer examination of inter-species comparisons (i.e. the evolutionary perspective) indicates that the proportion of muscle fibres occupied by mitochondria increases at low temperatures, most clearly in moderately active demersal species. Isolated muscle mitochondria show no compensation of protein-specific rates of substrate oxidation during evolutionary adaptation to cold temperatures. During phenotypic cold acclimation, mitochondrial volume density increases in oxidative muscle of some species (striped bass Morone saxatilis, crucian carp Carassius carassius), but remains stable in others (rainbow trout Oncorhynchus mykiss). A role for the mitochondrial reticulum in distributing oxygen through the complex architecture of skeletal muscle fibres may explain mitochondrial proliferation. In rainbow trout, compensatory increases in the protein-specific rates of mitochondrial substrate oxidation maintain constant capacities except at winter extremes. Changes in mitochondrial properties (membrane phospholipids, enzymatic complement and cristae densities) can enhance the oxidative capacity of muscle in the absence of changes in mitochondrial volume density. Changes in the unsaturation of membrane phospholipids are a direct response to temperature and occur in isolated cells. This fundamental response maintains the dynamic phase behaviour of the membrane and adjusts the rates of membrane processes. However, these adjustments may have deleterious consequences. For fish living at low temperatures, the increased polyunsaturation of mitochondrial membranes should raise rates of mitochondrial respiration which would in turn enhance the formation of reactive oxygen species (ROS), increase proton leak and favour peroxidation of these membranes. Minimisation of mitochondrial oxidative capacities in organisms living at low temperatures would reduce such damage.     

Linking ecology with parasite diversity in Neotropical fishes

A comparative analysis was performed to seek large-scale patterns in the relationships between a set of fish species traits (body size, type of environment, trophic level, schooling behaviour, depth range, mean habitat temperature, geographical range, ability to enter brackish waters and capability of migration) and the diversity of their metazoan parasite assemblages among 651 Neotropical fish species. Two measurements of parasite diversity are used: the species richness and the taxonomic distinctness of a fish's parasite assemblage, including all metazoan parasites, ectoparasites only, or endoparasites only. The results showed that, on this scale, the average taxonomic distinctness of parasite assemblages was clearly more sensitive to the influence of host traits than parasite species richness. Differences in the taxonomic diversification of the parasite assemblages of different fish species were mainly related to the fish's environment (higher values in benthic–demersal species), trophic level (positive correlation with increasing level), temperature (positive correlation with temperature in marine ectoparasites, negative in endoparasites; positive for all groups of parasites in freshwater fishes) and oceanic distribution (higher values in fish species from the Pacific Ocean than those of the Atlantic). The results suggest that, among Neotropical fish species, only certain key host traits have influenced the processes causing the taxonomic diversification of parasite assemblages.     

Water temperature fluctuations and territoriality in the intertidal zone: two possible explanations for the elevational distribution of body size in Graus nigra

On the central coast of Chile, distribution of body size in Graus nigra varied with tidal pool height. With the objective of determining whether environmental temperature is one of the possible causes which explains the observed distribution pattern, two behavioural responses were analysed during an experimental period of increasing water temperature: number of opercular movements (an indirect measure of energy expenditure) and activity levels. The interactions of temperature × time and body size × time had a significant effect on the number of opercular movements. At low temperatures (13–15° C), large fish reached a maximum number of opercular movements, while small fish reached a maximum only at high temperatures (23–25° C). The interaction temperature × time had a significant effect on activity levels of different body sizes. In general, large fish appeared to be less active than small fish, however, at very high temperatures (24–26° C) all individuals increased their activity levels. These data indicate that small fish are acclimatized to live in a wider range of temperatures (13–23° C), and, for fish of all body sizes, the highest temperatures (23–26° C) probably constitute a suboptimal microhabitat. Strong territoriality was observed, with large individuals displacing smaller individuals. These data suggest that temperature is an important factor in explaining why large individuals are not present in high tidal pools (high temperatures), whereas territoriality explains why small individuals are not in low tidal pools (habitat of large individuals).     

Adapt,move or die – how will tropical coral reef fishes cope with ocean warming?

Previous studies hailed thermal tolerance and the capacity for organisms to acclimate and adapt as the primary pathways for species survival under climate change. Here we challenge this theory. Over the past decade, more than 365 tropical stenothermal fish species have been documented moving poleward, away from ocean warming hotspots where temperatures 2–3 °C above long‐term annual means can compromise critical physiological processes. We examined the capacity of a model species – a thermally sensitive coral reef fish, Chromis viridis (Pomacentridae) – to use preference behaviour to regulate its body temperature. Movement could potentially circumvent the physiological stress response associated with elevated temperatures and may be a strategy relied upon before genetic adaptation can be effectuated. Individuals were maintained at one of six temperatures (23, 25, 27, 29, 31 and 33 °C) for at least 6 weeks. We compared the relative importance of acclimation temperature to changes in upper critical thermal limits, aerobic metabolic scope and thermal preference. While acclimation temperature positively affected the upper critical thermal limit, neither aerobic metabolic scope nor thermal preference exhibited such plasticity. Importantly, when given the choice to stay in a habitat reflecting their acclimation temperatures or relocate, fish acclimated to end‐of‐century predicted temperatures (i.e. 31 or 33 °C) preferentially sought out cooler temperatures, those equivalent to long‐term summer averages in their natural habitats (~29 °C). This was also the temperature providing the greatest aerobic metabolic scope and body condition across all treatments. Consequently, acclimation can confer plasticity in some performance traits, but may be an unreliable indicator of the ultimate survival and distribution of mobile stenothermal species under global warming. Conversely, thermal preference can arise long before, and remain long after, the harmful effects of elevated ocean temperatures take hold and may be the primary driver of the escalating poleward migration of species.     

Physiological correlates of habitat association in East African sunbirds (Nectariniidae)

East African sunbirds (Nectariniidae) vary in the degree to which they use open habitats and forest habitats. Species that use open habitats may experience more extreme temperatures and greater exposure to solar radiation than those in forest habitats. Basal rates of metabolism, body temperature and thermal conductance were compared for open habitat- and forest-associated sunbirds from Kibale National Park, Uganda. Variation in basal rate of metabolism was associated with body mass, but there was no difference between forest and open habitat species. Variation in body temperature was not associated with body mass or habitat. Variation in thermal conductance was associated with body mass and habitat; open habitat species were characterized by significantly lower thermal conductances than forest species. Because reduced thermal conductance may decrease energy expenditure at low ambient temperatures and reduce exogenous heat gain at high ambient temperatures, this difference may optimize energy expenditure when temperatures are highly variable. This suggests a mechanism by which physiological characteristics may influence energetic consequences of habitat selection.     

Temperate macroalgae impacts tropical fish recruitment at forefronts of range expansion

Warming waters and changing ocean currents are increasing the supply of tropical fish larvae to temperature regions where they are exposed to novel habitats, namely temperate macroalgae and barren reefs. Here, we use underwater surveys on the temperate reefs of south-eastern (SE) Australia and western Japan (~33.5°N and S, respectively) to investigate how temperate macroalgal and non-macroalgal habitats influence recruitment success of a range of tropical fishes. We show that temperate macroalgae strongly affected recruitment of many tropical fish species in both regions and across three recruitment seasons in SE Australia. Densities and richness of recruiting tropical fishes, primarily planktivores and herbivores, were over seven times greater in non-macroalgal than macroalgal reef habitat. Species and trophic diversity (K-dominance) were also greater in non-macroalgal habitat. Temperate macroalgal cover was a stronger predictor of tropical fish assemblages than temperate fish assemblages, reef rugosities or wave exposure. Tropical fish richness, diversity and density were greater on barren reef than on reef dominated by turfing algae. One common species, the neon damselfish (Pomacentrus coelestis), chose non-macroalgal habitat over temperate macroalgae for settlement in an aquarium experiment. This study highlights that temperate macroalgae may partly account for spatial variation in recruitment success of many tropical fishes into higher latitudes. Hence, habitat composition of temperate reefs may need to be considered to accurately predict the geographic responses of many tropical fishes to climate change.