Somatic Growth Rate Research Articles

Green turtle (Chelonia mydas) population demographics at three chemically distinct foraging areas in the northern Great Barrier Reef

The catchments of the Great Barrier Reef (GBR) have experienced significant modifications in recent decades, leading to increases in sources of pollutants and declines in coastal water quality. As coastal waters of the GBR support some of the highest density green turtle (Chelonia mydas) foraging populations in the western Pacific Ocean, understanding the effects of contaminants on GBR green turtle populations is a priority. In 2012, elevated strandings of green turtles in the Upstart Bay region instigated the WWF's collaborative Rivers to Reef to Turtles (RRT) project to investigate if coastal pollutants are compromising green turtle health. Important to interpreting these investigations into toxicology and health is understanding the demographics of the green turtle populations being investigated. In three green turtle foraging grounds, Cleveland Bay (CLV), Upstart Bay (UPB) and the Howick Group of Reefs (HWK), this study explored population size, age class structure, sex ratio, growth rates, body condition and diet, as well as indices of turtle health, such as plastron barnacle loads and eye lesions. The three foraging populations had similar age class structure and adult sex ratios to other green turtle foraging populations in the GBR. Somatic growth rate was nonlinear, peaking in immature turtles, and was much slower in turtles foraging at HWK compared to the other two sites. This may have been due to differences in food source, which was supported by the observed dietary shifts between seagrass and algae in HWK turtles, compared to a consistently seagrass diet in CLV and UPB turtles. There were also small differences in body condition between sites, as well as differences in barnacle loads, eye lesions and occurrence of fibropapilloma tumors. This study provides important information on green turtle foraging ground population dynamics in the northern GBR, and context for the other papers in this special issue.

Fractionation of otolith nitrogen stable isotopes measured by peroxodisulfate oxidation-bacterial conversion and isotope ratio mass spectrometry.

Otoliths are usually used to estimate the age of fish and the chemical composition such as nitrogen stable isotope ratios (δ15 N values) may record environmental information and ecological role of the fish. However, the isotopic fractionation of δ15 N values between diets and otoliths has rarely been investigated and remains unclear. Nitrogen isotopic fractionation between five different diets (δ15 Ndiet values) and otoliths (δ15 Noto values) were elucidated in tilapia Oreochromis mossambica reared in controlled feeding experiments. The otoliths were dissolved with hydrogen chloride and peroxodisulfate was used to oxidize the total organic materials to nitrate, which was further converted into N2 O gas by denitrification bacteria before the measurement of δ15 Noto values by isotope ratio mass spectrometry. The δ15 N values of muscles, gills, scales and livers of the tilapias were also measured by isotope ratio mass spectrometry. The peroxodisulfate oxidation-bacterial conversion method reduced the minimum mass of the otoliths required for analysis to as low as 2 mg, unlike past methods, which have required masses of 8-155 mg. The δ15 Noto values were not significantly different from the δ15 Ndiet values of the five diets. Furthermore, the somatic growth rate had no effect on the δ15 Noto values. Nevertheless, the δ15 N values of metabolically active tissues were significantly different from each other and higher than the δ15 Ndiet values, due to the deamination of these tissues. These results suggest that diet was the main source of amino acids for the otolith organic matrix and there was no biochemical transamination during the assimilation of dietary amino acids to otoliths. The δ15 Noto value can be used as a proxy of nitrogen sources of fishes and may have potential application in ecological studies such as the detection of diet shift, migration, trophic levels and environmental changes experienced by the fish population.

Geographic Variation in Somatic Growth Rate of Wood Turtles (Glyptemys insculpta)

Life history traits, such as body size and age at maturity, display intraspecific variation across a species' geographic range. Previous studies that examined body size variation among conspecific populations of turtles found that body size generally increases with increasing latitude, with the exception of Wood Turtles (Glyptemys insculpta) and Spotted Turtles (Clemmys guttata), which follow a non-linear relationship with larger body sizes at the two range extremes. Similarly, growth rates are influenced by climatic variables and should display geographic patterns reflective of different environments. The objectives of our study were to a) quantify somatic growth in a northern population of Wood Turtles, and b) determine if the observed geographic variation in body size was the result of interpopulation variation in somatic growth rates. In the northern population, as turtles approached maturity, somatic growth increments varied between the sexes such that on average males grew to larger mean carapace le...

Food Web Structure Informs Potential Causes of Bimodal Size Structure in a Top Predator

Background: Assemblages of fishes in lakes and reservoirs in the western USA are dominated by non-native, large-bodied, piscivorous fishes that lack a shared evolutionary history. Top predators in these crowded systems are often characterized by unstable population dynamics and poor somatic growth rates. One such assemblage is in Fish Lake, located in southern Utah, USA, in which introduced lake trout (Salvelinus namaycush, Walbaum) exhibit a bimodal growth pattern. A few lake trout in Fish Lake grow rapidly to large size typical of the species; whereas, most never grow beyond 600 mm total length. Objective: To inform competitive interactions in this evolutionarily novel fish assemblage that might cause the low recruitment to large body size in lake trout, we characterized trophic niche (from stable isotope analysis of C and N) of all fishes in the lake. Methods: We used a Bayesian mixing model to describe the trophic niche and infer diet of lake trout and their potential prey, and we used Bayesian ellipse analysis to identify potential areas of high competition within the food web. Large lake trout feed mostly on small lake trout and splake (Salvelinus namaycush, Walbaum x Salvelinus fontinalis, Mitchill) despite availability of abundant yellow perch. (Perca flavescens, Mitchill). Small lake trout and splake feed mostly on zooplankton and exhibit substantial overlap of their trophic niche implying competition for food. Yellow perch and Utah chub (Gila atraria, Girard; formerly an important food item for lake trout in Fish Lake) exhibit extreme overlap of their trophic niche implying strong competitive interactions. Results: Our data suggest that lack of recruitment to large body size in lake trout may result from a reduction in availability of Utah chub resulting from competitive interactions with yellow perch, and increased competition from introduced splake for available prey. Conclusion: Management actions that may help ameliorate the poor somatic growth rates of most lake trout include efforts to reduce perch populations or increase vulnerability of perch to predation by lake trout, and removal of splake as a competitor of small lake trout.

The Chronic Effects of Copper and Cadmium on Life History Traits Across Cladocera Species: A Meta-analysis

The effect of sublethal concentrations of heavy metals on cladoceran growth and reproduction is a cornerstone of modern ecotoxicology. However, the literature contains assays across numerous concentrations, on numerous species and genotypes, and conditions are far from consistent. We undertook a systematic review of the sublethal effects of copper and cadmium concentrations on Cladocera spp. life history (reproduction, maturation age, and somatic growth rate). Using meta-analysis, we tested the hypothesis that the effects of increasing Cu and Cd concentrations on traits may vary by species. We also evaluated where possible whether the effect of metal concentrations on traits vary by water hardness, exposure duration, or whether the metals were delivered in aqueous solution or via food. We surveyed > 200 papers, resulting in a set of 32 experimental studies representing 446 trials where the results were presented compared with Daphnia magna—the most commonly assayed species. We found qualitatively similar effects of Cu and Cd on life history traits that included reduction in reproduction and somatic growth rate and delay of maturation. Cladocera species showed marked variations in their susceptibility to metals, and D. magna was found to be the least sensitive species to sublethal changes in reproduction. The effects were largely consistent for aqueous vs. dietary food. Water hardness, where data were available, had no detectable effect. Available data indicate that exposure duration had no effect on the toxicity of Cu but did for D. magna reproductive response to Cd. Our study highlights the importance of including species identity when considering toxicological testing and regulation development.

Erratum - Daphnia magna fitness during low food supply under different water temperature and brownification scenarios

This corrects the article entitled “Daphnia magna fitness during low food supply under different water temperature and brownification scenarios" by the authors Andrea Gall, Martin J. Kainz and Serena Rasconi, published with DOI 10.4081/jlimnol.2016.1450. The data on somatic growth rates reported in the results section, paragraph "Life history traits", page 165, were incorrect and the rectified data are presented. Figure 4 has also been corrected accordingly.

No trade-offs in interspecific interference ability and predation susceptibility in newt larvae.

Coexistence of species with similar requirements is allowed, among others, through trade‐offs between competitive ability and other ecological traits. Although interspecific competition is based on two mechanisms, exploitation of resources and physical interference, trade‐off studies largely consider only species’ ability to exploit resources. Using a mesocosm experiment, we examined the trade‐off between interference competition ability and susceptibility to predation in larvae of two newt species, Ichthyosaura alpestris and Lissotriton vulgaris. In the presence of heterospecifics, L. vulgaris larvae slowed somatic growth and developmental rates, and experienced a higher frequency of injuries than in conspecific environments which suggests asymmetrical interspecific interference. During short‐term predation trials, L. vulgaris larvae suffered higher mortality than I. alpestris. Larvae of the smaller species, L. vulgaris, had both lower interference and antipredator performance than the larger I. alpestris, which suggests a lack of trade‐off between interference competition ability and predator susceptibility. We conclude that interference competition may produce a positive rather than negative relationship with predation susceptibility, which may contribute to the elimination of subordinate species from common habitats.

Dynamic Energy Budget theory predicts smaller energy reserves in thyasirid bivalves that harbour symbionts

Dynamic Energy Budget (DEB) theory describes the ecophysiology of individuals and distinguishes between the biomass of an organism that functions as an energy reserve and as a structure. DEB theory offers a robust framework to infer and contrast energy allocation patterns, even in data-poor species. We used this approach to compare two thyasirid bivalves that have scarce data: Thyasira cf. gouldi and Parathyasira sp., which co-occur in a seasonal environment, show similar life history features, and are both particulate feeders. However, T. cf. gouldi hosts chemosymbiotic bacteria that are digested as an additional resource, and how this mixotrophy affects the energy budget of these chemosymbiotic thyasirids is unknown. We used allometric and life history data to parameterize a DEB model for each species and found that symbiotic T. cf. gouldi has a smaller fraction of its biomass as an energy reserve relative to Parathyasira. A smaller energy reserve, in turn, implies reduced energy assimilation and mobilization fluxes, lower somatic maintenance costs and growth rate, and larger energy allocation to maturity and reproduction in symbiotic T. cf. gouldi. For a thyasirid inhabiting an environment with seasonal forcing, these life history traits may represent an evolutionary strategy where the symbionts function as a partial energy reserve. Our results elucidate a potential role of the chemosymbiotic bacteria in the ecophysiology of a bivalve host, and highlight how the symbiotic association is likely to alter the energy budget of a mixotrophic thyasirid.

Faster or slower: has growth of eastern Baltic cod changed?

ABSTRACTRecent environmental changes have influenced the ecology and biology of eastern Baltic cod. Declining somatic condition, maturation at smaller size and restricted size distribution of the population suggest that growth rates have decreased between the early 2000s and the 2010s. Extensive age estimation problems have until now precluded testing of this hypothesis. This study presents evidence for a decrease in somatic growth rate of Baltic cod. Temporal patterns of growth, condition and maturation were analysed based on two complementary analyses: length frequency mode progression derived from DATRAS bottom trawl survey data and known-age samples, where size at age was back-calculated from daily otolith growth patterns. In the known-age samples, growth was positively related to somatic condition at capture with maturity dependent differences. Immature individuals had experienced significantly lower growth and were in lower condition at capture than mature individuals. Growth rates in the known-age samples were estimated at 9.5, 7.8 and 5.7 cm per year for age classes 1, 2 and 3 respectively. Growth between age 2 and 3 decreased significantly from 8.8 cm in the 1997 year class to 7.6 cm in the 2010 year class. While the 2001 and 2004 known-age samples were representative for the population, the 2013 sample was biased towards individuals with a higher condition and growth. Complementary length frequency analysis following the length mode of fish from age 2 to age 3 confirmed growth estimates from the early 2000s, while suggesting a 37.5% lower growth in 2013 compared with 2005.

Sex-Specific Differences in Essential Lipid Requirements of Daphnia magna

Sex-specific differences in nutritional requirements may crucially influence the performances of the sexes, which may have implications for sexual reproduction and thus is of great ecological and evolutionary interest. In the freshwater model species Daphnia magna, essential lipid requirements have been extensively studied. Dietary deficiencies in sterols and polyunsaturated fatty acids (PUFA) have been shown to constrain somatic growth and parthenogenetic reproduction of female Daphnia. In contrast, nutrient requirements of male Daphnia have not been studied yet. Supplementation experiments were conducted to investigate differences in sterol (cholesterol) and PUFA (eicosapentaenoic acid, EPA) requirements between female and male D. magna. Thresholds for sterol-limited juvenile growth were higher in females than in males, suggesting that females are more susceptible to dietary sterol deficiencies than males. Sex-specific differences in maximum somatic growth rates were evident primarily in the presence of dietary EPA; females could not exploit their generally higher growth potential in the absence of dietary PUFA. However, the thresholds for EPA-limited growth did not differ between sexes, suggesting that both sexes have similar dietary EPA requirements during juvenile growth. During a life history experiment, the gain in body dry mass was higher in females than in males, irrespective of food treatment. In both sexes, the gain in body dry mass increased significantly upon EPA supplementation, indicating that both sexes benefited from dietary EPA supply also later in life. However, the positive effects of EPA supplementation were most pronounced for female reproduction-related traits (i.e. clutch sizes, egg dry masses, and total dry mass investment in reproduction). The high maternal investment in reproduction resulted in a depletion of nutrients in female somata. In contrast, the comparatively low paternal investment in reproduction allowed for the accumulation of nutrients in male somata. We conclude that males are generally less susceptible to dietary nutrient deficiencies than females, because they can rely more on internal body stores. Our data suggest that the performances of the sexes are differentially influenced by lipid-mediated food quality, which may have consequences for sexual reproduction and thus the production of resting eggs and the maintenance of Daphnia populations.

Global Warming: Testing for Direct and Indirect Effects of Temperature at the Interface of Primary Producers and Herbivores Is Required

In aquatic food webs, global warming may affect higher trophic levels by increased surface water temperatures and by changing the biochemical composition of phytoplankton. Correlations have suggested that growth of Daphnia, a major consumer of phytoplankton in freshwaters, is limited by a low content of the polyunsaturated fatty acid eicosapentaenoic acid (EPA) in natural phytoplankton and thus by food quality. Here we used the EPA-free green alga Chlamydomonas klinobasis and Daphnia magna to test for such food quality effects. The alga was grown in continuous cultures at 15°C, 20°C and 25°C and, different from other studies, dilution rates accounted for the effects of temperature on algal growth. This resulted in a maximum content of total fatty acids, of total PUFAs, of n-3 PUFAs and of α-linolenic acid when grown at 20°C, whereas at 15°C the lowest content of n-6 PUFAs and a threefold higher n-3/n-6 ratio than at 20°C and 25°C were observed. Unexpectedly the PUFA content did not show a maximum at 15°C. Growth experiments with D. magna were performed at 15°C, 20°C, and 25°C. With C. klinobasis grown at 20°C, Daphnia somatic growth rates increased with temperature. When the alga was raised at the same temperature as Daphnia, somatic growth rates of Daphnia increased with temperature, and supplementation indicated EPA-limitation at 15°C only. At 15°C and at 25°C, Daphnia growth was significantly higher on C. klinobasis raised at the respective temperature than on the same alga grown at 20°C. Hence, estimation of temperature effects on Daphnia growth requires to grow the food at the same temperature. At 15°C Daphnia newly built biomass had the highest content in total PUFAs and in α-linolenic acid, whereas the EPA-content was highest at 20°C. The content of n-6 PUFAs increased with temperature, which lead to the highest ratio of n-3/n-6 PUFAs at 15°C. This reflects increased PUFA-assimilation but decreased EPA-synthesis in Daphnia at lower temperatures. The results indicate that only if both algal food and consumer are grown at the same temperature, food quality effects of global warming can be more precisely predicted.

An empirical test for a zone of canalization in thermal reaction norms.

Theoretical models on the evolution of phenotypic plasticity predict a zone of canalization where reaction norms cross, and genetic variation is minimized in the environment a population most frequently encounter. Empirical tests of this prediction are largely missing, in particular for life-history traits. We addressed this prediction by quantifying thermal reaction norms of three life-history traits (somatic growth rate, age and size at maturation)of a Norwegian population of Daphnia magna and testing for the occurrence of an intermediate temperature (Tm ) at which genetic variance in the traits is minimized. Size at maturation changed relatively little with temperature compared to the other traits, and there was no genetic variance in the shape of the reaction norm. Consequently, age at maturation and somatic growth rate were strongly negatively correlated. Both traits showed a strong genotype-environment interaction, and the estimated Tm was 14°C for both age at maturation and growth rate. This value of Tm corresponds well with mean summer temperatures experienced by the population and suggests that the population has evolved under stabilizing selection in temperatures that fluctuate around this mean temperature. These results suggest local adaptation to temperature in the studied population and allow predicting evolutionary trajectories of thermal reaction norms under changing thermal regimes.

Extrinsic Factors Influencing Somatic Growth of Lake Sturgeon

AbstractVariation in somatic growth of Lake SturgeonAcipenser fulvescenshas primarily been attributed to temperature (latitude), but recent studies have suggested additional complexities. Based on populations in Manitoba, Canada, a multivariate analysis was conducted to reevaluate the extrinsic factors influencing growth of Lake Sturgeon. Length at ages 3, 6, 9, and 12 and the following six explanatory variables were examined: latitude, mean annual air temperature,pH, conductivity, juvenile Lake Sturgeon density (gill‐netCPUE), and water velocity. Length‐at‐age variables were highly correlated, but considerable variation for fish of a given age was observed along the flow axes of individual rivers (and even within multibasin reservoirs). For example, fork length at age 12 ranged from 520 to 906 mm. After dropping latitude due to colinearity with both temperature andpH, a redundancy analysis based on the remaining five explanatory variables explained 79.9% of the variation in the four length‐at‐age variables. Lake Sturgeon growth was negatively correlated with bothCPUE(41.2% of variation) and velocity (19.2%) and positively correlated with conductivity (14.8%). The temperature andpHvariables lacked statistical significance for inclusion in a forward‐selection model, regardless of which other variables were included. Our results suggest that the influence of temperature (latitude) on Lake Sturgeon growth may previously have been overstated because habitat variation was not accounted for. Indeed, because populations exploit a diversity of river types across the species range, the discussion of growth needs to be placed in the context of habitat. Individuals from two Lake Sturgeon populations occupying similar latitudes can exhibit markedly different rates of somatic growth, with much of the variation being explained by juvenile density, water velocity, and conductivity. As Lake Sturgeon recovery proceeds, fisheries managers will need to contend with dynamic growth trajectory responses to increasing abundance, much as they would for other species.

Impact of Fetal Somatic Growth on Pulmonary Valve Annulus Z-Scores During Gestation and Through Birth in Patients with Tetralogy of Fallot.

Previous studies have suggested reduced pulmonary valve annulus (PVA) growth and progression of pulmonary outflow obstruction in fetuses with tetralogy of Fallot (TOF). The goals of this study were to (1) investigate the trajectory of PVA growth in utero, and (2) compare two methods of z-score determination for fetal and postnatal PVA size by echocardiography in order to improve prenatal counseling for patients with TOF. Fetal echocardiograms (FE) at a single institution with a diagnosis of TOF between 8/2008 and 12/2015 were retrospectively reviewed. Patients included had at least 2 FEs and 1 immediate postnatal echocardiogram (TTE). Fetal and postnatal demographic, clinical, and echocardiographic data were collected. Fetal body surface area (BSA) was calculated by estimating fetal weight and height; z-scores were determined based on fetal gestational age (GA) and BSA for both FEs and TTEs. Fetal PVA z-scores by GA or BSA were then compared to postnatal PVA z-scores by BSA. Twenty-two patients with 44 FEs and 22 TTEs were included. GA at the first FE was 23weeks ± 3.4 and 32weeks ± 3.1 at the second FE. There was no difference in PVA z-scores (by BSA) between the first and second FE (p = 0.34), but a decrease in PVA z-scores (by BSA) between the second FE and TTE (- 1.6 ± 0.5 vs. - 2.0 ± 0.7; p = 0.01). Repeat comparison with fetal PVA z-scores indexed to GA revealed no difference in z-scores between the first and second FE, but an increase in PVA z-scores between the second FE (by GA) and TTE (by BSA) (- 4.1 ± 1.0 vs. - 2.0 ± 0.7; p < 0.0001). The rate of PVA growth between the two FEs (23µm/day ± 9.8) and between the second FE and TTE (28µm/day ± 42) remained comparable (p = 0.57); however, the rate of BSA increase was greater in later gestation (9 cm2/day± 3 vs. 20 cm2/day ± 11; p = 0.001). In patients with TOF, the rate of PVA growth appears to remain consistent through gestation; however, somatic growth rate increases in late gestation. Fetal PVA z-scores indexed to GA are thus inaccurate in predicting postnatal PVA z-scores typically indexed to BSA. This observation should be considered during prenatal consultation and delivery planning.

Variability in the performance of juvenile Chinook salmon is explained primarily by when and where they resided in estuarine habitats

AbstractEstuarine habitats provide rearing opportunities for the juvenile life stage of anadromous fishes. Because survival is positively correlated with juvenile performance, these estuarine habitats play an important role in population abundance and productivity. To provide information for the recovery of several depressed stocks of Chinook salmon in the Columbia River Basin, we sought to identify the factors that explain variability in performance. Using otolith‐derived estimates of juvenile somatic growth rate as an index of recent performance, we observed a negative nonlinear relationship between growth rate and day of year, and a decreasing and increasing trend of growth rate over the 8 years of this study and distance from the river mouth respectively. Using a generalised linear modelling approach, we found that variability in juvenile somatic growth rate was best explained by where and when individuals were collected, their body size, contaminant loads, stock of origin, and whether a fish was hatchery produced or unmarked. Lastly, we argue that a considerable improvement to the growth rate of juveniles in estuarine habitats is physiologically possible. The results of this 8‐year study provide a baseline of the performance of juvenile Chinook salmon to evaluate habitat restoration programs and to compare against future anthropogenic conditions.

The sea urchin, Paracentrotus lividus, in an Integrated Multi-Trophic Aquaculture (IMTA) system with fish (Sparus aurata) and seaweed (Ulva lactuca): Nitrogen partitioning and proportional configurations

The long-term (460 days) performance of the macroalgivore sea urchin Paracentrotus lividus was evaluated in a semi-commercial land-based Integrated Multi-Trophic Aquaculture (IMTA) system. IMTA-produced Ulva lactuca considerably reduced nitrogen loads from the effluents by assimilating 74% of the DN and became itself a valuable crop for P. lividus. U. lactuca showed relatively fast growth and constant high protein and lipid levels throughout the year, presumably due to the continuous steady supply of nutrients from the fish pond and the minimal disturbance by grazers and epiphytes. P. lividus fed IMTA-produced U. lactuca exhibited high somatic growth rate (1.4 mm month−1), high gonad somatic index (SGI), and high quality, bright-orange gonads. Fish assimilated 21.9% of the nitrogen in the feed and their faeces contained 10.1% of it. P. lividus assimilated 13.86% of the nitrogen and their faeces contained 19.9% of it. It is suggested that 4.96 kg of the nitrogen was released during spawning, which occurred in January, May and December. Surface area ratio between the three compartments in the IMTA system was maintained at 1:3:4 for fish, Ulva and sea urchins, respectively. Annual yield production ratio (kg m3 y−1) was 3.5:10:1 for fish, Ulva and sea urchins, respectively. Annual yield using 1365 kg feed (45% protein) was 821, 7045 and 919 kg for fish, Ulva and sea urchins, respectively. Fish attained marketable size at the end of the first year. In addition to enhancing sea urchin performance, using the protein-rich U. lactuca biofilter considerably improved the system's sustainability and waste management.

Direct and Indirect Effects of Resource P-Limitation Differentially Impact Population Growth, Life History and Body Elemental Composition of a Zooplankton Consumer.

One of the central tenets of ecological stoichiometry is that consumer growth rate is strongly determined by food phosphorus (P) content. In planktonic organisms population growth rates of zooplankton have repeatedly been shown to be reduced when fed with P-limited algal food sources. However, P-limitation may also affect other quality-related aspects of algae, such as biochemical composition or palatability. We studied the population growth, detailed life history and body elemental composition of the herbivorous rotifer, Brachionus calyciflorus, in response to three different food quality treatments: algae cultured in high phosphorus conditions (average algal molar C:P ≈ 112, ‘HP’), algae cultured in low P conditions (molar C:P ≈ 631, ‘LP’) and low-P cultured algae spiked with P just before feeding (molar C:P ≈ 113, ‘LP+P’). LP+P algae thus combined high P content with a history of growth under P-limited conditions. Total P content and the C:P ratio of rotifers in the LP+P treatment equaled those of rotifers in the HP treatment. Rotifer population growth rates were higher in HP than in LP and intermediate in the LP+P treatment. Similarly, many life history traits observed for animals in the LP+P treatment, such as somatic growth rate, age at maturity, and egg production rate were also intermediate to those observed in the LP and HP treatments. However, there were important deviations from this pattern: size at first reproduction and egg mortality in the LP+P treatment equaled the HP treatment, whereas size and development time of the first eggs equaled those of the LP treatment. Our results indicate that elemental limitation cannot fully explain reduced performance of consumers fed with P-limited algae and strongly suggest that indirect, non-stoichiometric effects of P-limitation, e.g., via changes in biochemical composition or morphology of the algae also play a major role. Furthermore, our study highlights that such indirect effects have a differential impact on major fitness components and may as such also determine the population dynamics and demographic structure of consumer populations.

Assessing resource use patterns of Mediterranean loggerhead sea turtles Caretta caretta (Linnaeus, 1758) through stable isotope analysis

Stable isotope analysis is a useful tool for studying the ecology of marine consumers, as carbon (δ13C) and nitrogen (δ15N) isotope ratios may reflect individuals’ patterns of diet and habitat use. Knowledge of foraging strategies has significant implications for the conservation of endangered loggerhead turtles Caretta caretta (Linnaeus, 1758). In this study, δ13C and δ15N isotope data were used to assess resource use patterns of the Mediterranean loggerhead turtles (Aeolian Archipelago, Southern Italy). δ13C and δ15N values from carapace scutes of 54 loggerheads of different curved carapace length (CCL) and health status were compared with those of eight potential prey items (benthic, pelagic and fishery discards). MixSIAR results suggested that pelagic prey (from goose barnacles to planktivorous fish) comprised most of loggerheads’ diet, with small variations (i.e. benthic prey or fishery discards) depending on size (δ13C and δ15N) and health (δ15N) of individuals. δ13C variations with turtles’ size might reflect changes in dietary habitats during life stages. However, the loggerhead turtles and their main source of prey (pelagic prey) had a higher variation in values of δ15N compared to δ13C. This suggested that smaller-sized turtles might preferentially feed on pelagic prey in oceanic habitats and then, as they reach a larger size, gradually enter neritic waters, including in their diet prey sources with higher δ13C and δ15N. Some turtles foraging on longline baits/debris also displayed a marked increase in δ15N. These δ15N variations might be explained by differences in diet (trophic differences) and somatic growth rates among individuals, or dietary dilution.

Plasticity in life history traits of the native Proterorhinus semilunaris suggests high adaptive capacity in its invasive range

Invasion risk assessments are reliant on ecological data that assist the predictions of whether an introduced species will adapt to novel conditions. Data from the native range of potential invaders can thus assist these assessments. Here, the growth and reproductive characteristics of the Western tubenose goby Proterorhinus semilunaris, a Ponto-Caspian gobiid, were assessed in three natural lakes in their native range, as there are few extant data on these traits. Across the three lakes, the gobies were found in varying abundances. Sex ratios varied, with females significantly outnumbering males in only one lake, with equal sex ratios in the other lakes. The fish always showed a positive allometric growth, but had high variability in their somatic growth rates and relative body conditions between the lakes. Scale ageing revealed all populations comprised of individuals to four years old, with one lake having individuals to 5 years old. Reproductive characteristics, including size at maturity, gonado-somatic index and fecundity, did not differ significantly between the lakes. These data suggest that plasticity in aspects of their life history traits provides P. semilunaris with considerable adaptive capacity following their introduction into novel conditions.

Life history characteristics of the potentially invasive Ponto-Caspian goby Neogobius fluviatilis in natural lakes from its native range (Black Sea region of Turkey)

The aim of this study was to provide baseline data and fill an outstanding knowledge gap in our understanding of factors affecting the invasiveness of the Ponto-Caspian gobiid Neogobius fluviatilis. To this end, the life history traits (as somatic growth and reproduction) of N. fluviatilis were studied in three natural freshwater lakes in its native range. These populations were characterised by slow somatic growth rates, being the slowest reported across all the native and non-native ranges of N. fluviatilis. Ages were recorded to 7 years. Across the three lakes, there was considerable variability in sex ratios and reproductive traits (including length at maturity and fecundity at length and age), revealing considerable interpopulation variability. These data suggest that N. fluviatilis has considerable plasticity in the expression of its life history traits, with this plasticity argued as a key factor in facilitating the ability of N. fluviatilis to establish and invade new waters following introductions.