Mechanisms behind the metabolic flexibility of an invasive comb jelly

Mnemiopsis leidyi is an invasive comb jelly which has successfully established itself in European seas. The species is known to produce spectacular blooms yet it is holoplanktonic and not much is known about its population dynamics in between. One way to gain insight on how M. leidyi might survive between blooms and how it can bloom so fast is to study how the metabolism of this species actually responds to environmental changes in food and temperature over its different life-stages. To this end we combined modelling and data analysis to study the energy budget of M. leidyi over its full life-cycle using Dynamic Energy Budget (DEB) theory and literature data.An analysis of data obtained at temperatures ranging from 8 to 30 °C suggests that the optimum thermal tolerance range of M. leidyi is higher than 12 °C. Furthermore M. leidyi seems to undergo a so-called metabolic acceleration after hatching. Intriguingly, the onset of the acceleration appears to be delayed and the data do not yet exist which allows determining what actually triggers it. It is hypothesised that this delay confers a lot of metabolic flexibility by controlling generation time.We compared the DEB model parameters for this species with those of another holoplanktonic gelatinous zooplankton species (Pelagia noctiluca). After accounting for differences in water content, the comparison shows just how fundamentally different the two energy allocation strategies are. P. noctiluca has an extremely high reserve capacity, low turnover times of reserve compounds and high resistance to shrinking. M. leidyi adopts the opposite strategy: it has a low reserve capacity, high turnover rates of reserve compounds and fast shrinking.     

Intra- and interspecies comparison of energy flow in North Atlantic flatfish species by means of dynamic energy budgets

The quantitative aspects of growth and reproduction in four flatfish species (plaice, flounder, dab, sole) in terms of energy flow are described on the basis of a dynamic energy budget (DEB theory). This theory consists of general assumptions about energy uptake, storage and utilisation and describes an individual by two state variables: structure and reserve, whereby body size exerts its influence through the ratio between surface area and volume. Comparison between model estimates and field data shows that the DEB model successfully describes the energetics of growth and reproduction in a number of flatfish species. Differences between species could be captured in the same model using different parameter values. Intraspecific differences in growth between males and females are mainly caused by differences in maximum surface area-specific ingestion rates. Differences between species are reflected in the surface area-specific maximum ingestion rate, the energy partitioning over growth and reproduction, and in egg volume. According to these parameters at 283 K (10°C), the species could be ranked as follows: surface area-specific maximum ingestion rate (W m⁻²) plaice: 56.6; flounder: 54.5; sole: 45.1 and dab: 36.1 W m⁻². Fraction of energy allocated to reproduction (–): flounder: 0.35; plaice: 0.15; dab: 0.15 and sole 0.10. As a consequence of these differences in surface area-specific maximum ingestion rate and in the fraction of utilised energy allocated to reproduction, the gonad masses (g) of females of 0.5 kg wet mass differ considerably: flounder: 149 g; plaice: 86 g; sole: 70 g; and dab: 69 g. However, due to differences in egg size between species, the potential annual egg production shows a completely different pattern: dab: 2200 10³; flounder: 1560 10³; sole: 343 10³ and plaice: 130 10³ eggs.     

Different sperm allocation strategies in two populations of the semiterrestrial crab Neohelice granulata (Brachyura,Grapsoidea, Varunidae)

Sperm reserves are costly to produce and so the development of different sperm allocation strategies may be advantageous. Knowledge of sperm allocation strategies is important from an evolutionary perspective because they contribute to characterize mating systems. However, population differences in sperm allocation strategies of the same species have rarely been assessed. Here, we studied the male sperm allocation strategies in two different populations of Neohelice granulata in Mar Chiquita Lagoon (MCL) and San Antonio Oeste (SAO), Argentina. We found that the quantity of ejaculate transferred by N. granulata males depended on different factors such as male size and female receptivity duration, while it was independent of female size, at both study areas. Regarding the operational sex ratio factor, the amount of ejaculate transferred depended on it in MCL but not in SAO. Thus, N. granulata males may have the capacity to regulate the quantity of ejaculate transferred based on individual factors such as their own size and female receptivity duration, and population factors such as operational sex ratio, which varies in the two populations studied.     

The AquaDEB project (phase I): Analysing the physiological flexibility of aquatic species and connecting physiological diversity to ecological and evolutionary processes by using Dynamic Energy Budgets

The European Research Project AquaDEB (2007–2011, http://www.ifremer.fr/aquadeb/) is joining skills and expertise of some French and Dutch research institutes and universities to analyse the physiological flexibility of aquatic organisms and to link it to ecological and evolutionary processes within a common theoretical framework for quantitative bioenergetics [Kooijman, S.A.L.M., 2000. Dynamic energy and mass budgets in biological systems. Cambridge University Press, Cambridge]. The main scientific objectives in AquaDEB are i) to study and compare the sensitivity of aquatic species (mainly molluscs and fish) to environmental variability of natural or human origin, and ii) to evaluate the related consequences at different biological levels (individual, population, ecosystem) and temporal scales (life cycle, population dynamics, evolution). At mid-term life, the AquaDEB collaboration has already yielded interesting results by quantifying bio-energetic processes of various aquatic species (e.g. molluscs, fish, crustaceans, algae) with a single mathematical framework. It has also allowed to federate scientists with different backgrounds, e.g. mathematics, microbiology, ecology, chemistry, and working in different fields, e.g. aquaculture, fisheries, ecology, agronomy, ecotoxicology, climate change. For the two coming years, the focus of the AquaDEB collaboration will be in priority: (i) to compare energetic and physiological strategies among species through the DEB parameter values and to identify the factors responsible for any differences in bioenergetics and physiology; and to compare dynamic (DEB) versus static (SEB) energy models to study the physiological performance of aquatic species; (ii) to consider different scenarios of environmental disruption (excess of nutrients, diffuse or massive pollution, exploitation by man, climate change) to forecast effects on growth, reproduction and survival of key species; (iii) to scale up the models for a few species from the individual level up to the level of evolutionary processes.     

Contribution of different generations of the brown shrimp Crangon crangon (L.) in the Dutch Wadden Sea to commercial fisheries: A dynamic energy budget approach

In this paper a contribution is made to the ongoing debate on which brown shrimp generation mostly sustains the autumn peak in coastal North Sea commercial fisheries: the generation born in summer, or the winter one. Since the two perspectives are based on different considerations on the growth timeframe from settlement till commercial size, the Dynamic Energy Budget (DEB) theory was applied to predict maximum possible growth under natural conditions. First, the parameters of the standard DEB model for Crangon crangon L. were estimated using available data sets. These were insufficient to allow a direct estimation, requiring a special protocol to achieve consistency between parameters. Next, the DEB model was validated by comparing simulations with published experimental data on shrimp growth in relation to water temperatures. Finally, the DEB model was applied to simulate growth under optimal food conditions using the prevailing water temperature conditions in the Wadden Sea. Results show clear differences between males and females whereby the fastest growth rates were observed in females. DEB model simulations of maximum growth in the Wadden Sea suggest that it is not the summer brood from the current year as Boddeke claimed, nor the previous winter generation as Kuipers and Dapper suggested, but more likely the summer generation from the previous year which contributes to the bulk of the fisheries recruits in autumn.     

Life strategies of Halobatrachus didactylus (Bloch and Schneider, 1801) in the Tagus estuary: Comparison among different morphotypes

The Lusitanian toadfish, Halobatrachus didactylus (Bloch and Schneider, 1801), is a subtropical sound-producing marine teleost that inhabits estuaries and other brackish water ecosystems in its northern distribution area. The relative isolation of populations within estuaries may cause important modifications in the bio-ecology of this species. The males of this species present two morphotypes which are more accurately distinguishable during the reproductive season. In the Tagus estuary population, the two types of reproductive males were present: type I, the “characteristic” morphotype, and type II, the alternative morphotype. The opportunistic males had more developed testis while type I males had more developed accessory glands. Type I males presented more developed swimbladders and larger body size and live longer than type II males. On the contrary, type II males grew faster and matured earlier. The feeding habits of the two male morphotypes were similar during the reproductive season but differences were found between reproductive specimens and non-reproductive specimens. The diet of reproductive specimens was mainly composed of benthic prey in contrast to predominance of nectobenthic prey in the diet of non-reproductive specimens. The females of H. didactylus generally had an intermediate pattern between the two male morphotypes. The percentage of type II males tended to be higher in denser areas of the estuary. In comparison with populations from different size ecosystems, smaller ecosystems revealed important modifications on the bio-ecology of the species due to the increased competition for nesting sites and mating partners, favouring alternative male tactics.     

Population ecology of fiddler crab, Uca lactea annulipes (Decapoda: Ocypodidae) in Sirik mangrove estuary,Iran

Fiddler crabs are known as the most conspicuous bioturbating animals in mangrove forest, which by their burrowing activities promote nutrient cycling in ecosystems. Mangroves, crabs and bacteria are connected in the form of positive feedback loop, whereby an increase in the activity of any participant will tend to increase the activity of all others as well. Population structure, growth, mortality, recruitment, biomass and production of fiddler crabs as dominant species of deposit-feeder crabs have been investigated from May 2005 to March 2006 in the Sirik mangrove estuary in the eastern part of Strait of Hormuz. Ten 1 m² squares of the substrate were randomly sampled during low tide. There was a significant change in organic content in the sampling area during study period. The sex ratio was significantly deviated from 1:1 ratio in large sizes, where males were dominated year around. Fiddler crabs showed seasonal growth pattern during a year, which the maximum growth was observed during autumn and early summer and ceased during winter by low temperature. Growth parameters were estimated by Appeldoorn's method and fitted with seasonalized von Bertalanffy growth models. The Kimura likelihood ratio test revealed significant differences in the overall growth curves between males and females, originated from the differences in k$k$ and L_∞$L_{\mathrm{\infty }}$ between sexes. Males were found to exhibit higher growth rate and larger size than females, this could be attributed to the higher investment of energy for reproduction in females. Reproduction was restricted to spring and early summer, while recruitment occurs at the end of summer. Total annual production of males and females was 37.90 and 10.05 g dry weight/10 m² respectively and major production took place during early summer. Because of impact of temperature on the activity of fiddler crabs in subtropical regions, density of crabs has significant positive correlation with temperature (P < 0.01), while growth rate shows significant negative correlation with organic matter of sediment (P < 0.05). In conclusion these crabs showed lower mortality and production rate with the seasonal growth and recruitment in comparison with tropical species.     

Population Dynamics of Sergio mirim RODRIGUES 1971 Decapoda: Thalassinidea: Callianassidae in Cassino Beach, Southern Brazil

Abstract. Thalassinid shrimps have been extensively exploited for bait in many countries around the world. In order to prepare future management strategies for a little-exploited population of Sergio mirim in southern Brazil, growth, mortality and reproduction of this species were studied between June 1988 and November 1992. Size-frequency distributions were dominated by mature individuals, and recruitment occurred in austral spring, with widely variable abundances between years. Females attained larger mean and maximum sizes than males. The sex ratio was balanced for young individuals and female-biased for the mature segment of the population, as previously reported for other species of burrowing shrimps. Ovigerous females were found mostly between September and January, and egg numbers were a function of carapace length. From parameters of the VON BERTALANFFY growth curves, a maximum life span of approximately 4 years was estimated for both sexes. Among callianassids for which reproductive measures are known. S. mirim represents one of the highest reproductive potentials. The advantages of the thalassinidean female-biased sex ratio pattern is discussed.     

Sex‐related differences in size,function and regeneration of the major cheliped in the hermit crab Pagurus filholi

Pagurus hermit crabs have a well‐developed right cheliped (major cheliped) and in some species the major cheliped of males is longer than that of females. This paper describes sex‐related differences in major cheliped length and regeneration pattern of the major cheliped in the hermit crab Pagurus filholi. We also examined the function of the major cheliped in male–male competition. Major cheliped length of males was longer than that of females in P. filholi. Males regenerated larger chelipeds than females at the first molt after experimentally induced autotomy. Body size growth in males of the regeneration group was less than that in intact males of the control group while there was no significant difference in body size growth of females between regeneration and control groups. Major cheliped length was included in the best model to explain the outcome of male–male competition and thus sexual selection appears to be a causative factor in the sex‐related difference of the major cheliped length. Sex‐related differences in the regeneration pattern may reflect differences in evolutionary pressures on males for large major chelipeds and females for large body size.     

Validation of age and growth of the Picasso triggerfish (Balistidae: Rhinecanthus aculeatus) from Okinawa Island, Japan, using sectioned vertebrae and dorsal spines

To understand age and growth of the Picasso triggerfish, Rhinecanthus aculeatus, monthly sampling was conducted from February 2010 to October 2011 on the subtropical Okinawa Island, Japan, using trammel net and speargun. Fish were measured by weight (W) and standard length (SL) and age was determined by examining thin-sections of the first dorsal spine and the second abdominal vertebra. A total of 352 fish were caught ranging from 20.9?mm to 209.5?mm (SL). Marginal increment analysis indicated that translucent rings were deposited annually during the colder season from October to January. The relationship of observed SL and age was described by the original form of the von Bertalanffy growth equation. Male and female growth models were significantly different. Overall growth was rapid during the first 2.5?years for both sexes, thereafter growth curves diverged. Males consequently reached larger sizes and greater ages. Maximum age for males and females was 13.5 and 9.5?years, respectively. Regression models of somatic growth (SL) as a function of vertebral and spine radii were significantly correlated (r?=?0.98 and r?=?0.96, respectively). According to the weight?Clength relationship, growth in R. aculeatus was negative allometric. Small recruits (SL?<?40?mm) appeared in high numbers in shallow coastal areas starting from August. This is the first record of age and growth for R. aculeatus. Our data suggest that the Picasso triggerfish is a moderately long-lived balistid and that the observed sex-specific growth pattern is driven by the fish??s polygynous mating system and different reproduction strategies of males and females.     

Reproductive patterns of the abyssal asteroid Styracaster elongatus from the N.E. Atlantic Ocean

We analysed the reproductive biology of the asteroid species Styracaster elongatus based on time-series samples from a 5000-m-deep site on the Porcupine Abyssal Plain (N.E. Atlantic). The ratio of males to females, the gonadosomatic index (GI), and pyloric caecum index (PCI) were determined and the results were corroborated by histological examination of the gonads. Fecundity and oocyte-size distribution were determined by histological and image analyses. Styracaster elongatus is a gonochoric asteroid and the ratio of males to females was not significantly different throughout the year. Oogenesis was asynchronous. The previtellogenic oocytes grew to a size of ～230 μm before undergoing vitellogenesis. Maximum oocyte size was ～620 μm. The ovary volume was mainly occupied by small previtellogenic oocytes (100–150 μm) at any one time. Mean GI was 6.38±3.30 for females and 9.04±4.1 for males. Mean PCI was 7.44±1.66 for females and 7.66±1.46 for males. Mean fecundity was 16,373±5988 oocites per female. There were no seasonal variations in GI and fecundity. There was evidence of a pyiloric caecum seasonal development for females and males. For S. elongatus there is no direct relationship among seasonal primary production at the surface and production of vitellogenic oocytes. Nevertheless, this species takes advantage of the pulse of phytodetritus to the seabed by increasing the storage of nutrients in the pyloric caecum in order to maintain a constant production of eggs and sperm.     

Modelling the growth of white seabream (Diplodus sargus) and gilthead seabream (Sparus aurata) in semi-intensive earth production ponds using the Dynamic Energy Budget approach

Fish growth models may help understanding the influence of environmental, physiological and husbandry factors on fish production, providing crucial information to maximize the growth rates of cultivated species. The main objectives of this work were to: i) develop and implement an Individual Based Model using a Dynamic Energy Budget (IBM-DEB) approach to simulate the growth of two commercially important Sparidae species in semi-intensive earth ponds, the white seabream which is considered as a potential candidate for Mediterranean aquaculture and the gilthead seabream that has been cultivated since the early 80s; ii) evaluate which model parameters are more likely to affect fish performance, and iii) investigate which parameters might account for growth differences between the cultivated species. The model may be run in two modes: the “state variable” mode, in which an average fish is simulated with a particular parameter set and the “Individual Based Model” (IBM) mode that simulates a population of n fishes, each with its specific parameter set assigned randomly. The IBM mode has the advantage of allowing a quick model calibration and an evaluation of the parameter sets that produce the best fit between predicted and observed fish growth. Results revealed that the model reproduces reasonably well the growth of the two seabreams. Fish performance was mainly affected by parameters related to feed ingestion/assimilation and reserves utilization, suggesting that special attention should be taken in the estimation of these parameters when applying the model to other species. Comparing the DEB parameters set of the two sparids it seems that the white seabream's low growth rates are a result of higher maintenance costs and a lower feed assimilation efficiency. Hence, the development of new feed formulations may be crucial for the success of white seabream production in semi-intensive earth ponds.     

Biochemical composition of deep-sea decapod crustaceans with two different benthic life strategies off the Portuguese south coast

The objectives of the present study were to characterize the benthic life strategies of Aristeus antennatus (Crustacea: Penaeidea), Parapenaeus longirostris (Crustacea: Penaeidea) and Nephrops norvegicus (Crustacea: Astacidea) on the basis of biochemical composition (proximate chemical composition, total lipids, glycogen and cholesterol contents), and its response to biological and environmental factors (sex, maturation, reproduction, food availability and depth) into account. The specimens were collected at depths between 200 and 600 m off the Portuguese south coast (Algarve). The nektobenthic species (A. antennatus and P. longirostris) showed higher protein, lipid, cholesterol and glycogen contents, and lower moisture content in the muscle than the benthic–endobenthic species (N. norvegicus). Consequently, the energy content of the nektobenthic species was also higher. Principal component analyses were used to assess the relationship between the different biochemical contents and to relate them to the biotic and abiotic factors. Depth seems to have the most important role in the observed trends of the biochemical composition. The increase of the ovarian lipid levels occurs as a result of the maturation process. The highest values were obtained in mature N. norvegicus females. The differences can be due to maternal investment (lipid metabolism of the female is geared to the provision of egg lipid), since N. norvegicus produce large lecithotrophic eggs. The biochemical differences observed in the three species did not seem to be due to distinct trophic strategies, but instead were a consequence of depth, which may have a significant interspecific effect on food intake. It was also evident that reproductive cycle has profound effects upon the biochemistry of the three species. Gonadal maturation has large associated energy costs due to the increase in biosynthetic work. Moreover, the biochemical composition would be influenced by or synchronized with seasonal feeding activity or food availability.     

Population Genetic Structure of Rock Bream (<Emphasis Type="Italic">Oplegnathus fasciatus</Emphasis> Temminck &amp; Schlegel, 1884) Revealed by mtDNA COI Sequence in Korea and China

The rock bream, Oplegnathus fasciatus, is a common rocky reef game fish in East Asia and recently has become an aquaculture species. Despite its commercial importance, the population genetic structure of this fish species remains poorly understood. In this study, 163 specimens were collected from 6 localities along the coastal waters of Korea and China and their genetic variation was analyzed with mtDNA COI sequences. A total of 34 polymorphic sites were detected which determined 30 haplotypes. The genetic pattern reveals a low level of nucleotide diversity (0.04 ± 0.003) but a high level of haplotype diversity (0.83 ± 0.02). The 30 haplotypes are divided into two major genealogical clades: one that consists of only Zhoushan (ZS, East China Sea) specific haplotypes from the southern East China Sea and the other that consists of the remaining haplotypes from the northern East China Sea, Yellow Sea, Korea Strait, and East Sea/Sea of Japan. The two clades are separated by approximately 330~435 kyBP. Analyses of AMOVA and F_st show a significant population differentiation between the ZS sample and the other ones, corroborating separation of the two genealogical clades. Larval dispersal and the fresh Yangtze River plume are invoked as the main determining factors for this population genetic structure of O. fasciatus. Neutrality tests and mismatch distribution analyses indicate late Pleistocene population expansion along the coastal waters of Korea and China approximately 133–183 kyBP during which there were periodic cycles of glaciations and deglaciations. Such population information needs to be taken into account when stock enhancement and conservation measures are implemented for this fisheries species.     

Numerical modelling of spatio-temporal variability of growth of Mytilus edulis (L.) and influence of its cultivation on ecosystem functioning

One of the key needs of the aquaculture industry is the implementation of effective management methods to ensure the sustainability, economic viability and minimization of negative impacts on both human and ecosystem well-being. The authors developed a Fortran 90 implementation of the dynamic energy budget (DEB) model for Mytilus edulis. The model has been further developed to include physiological interactions with the ecosystem and coupled to a biogeochemical nutrient–phytoplankton–zooplankton–detritus (NPZD) model. Phytoplankton and detritus uptakes, oxygen utilisation, CO₂ production, NH₄ excretion, egestion of faeces, and assimilation of food are modelled. A novel approach was derived that accounts for the allocation of C and N in mussel flesh and shell organic fraction. The DEB–NPZD model has been subsequently coupled to a high resolution three dimensional numerical coastal ocean model of the south–west coast of Ireland, where approximately 80% of national rope mussel is produced annually. Simulations have been carried out for the time period July 2010–June 2011, for which the field data on mussel biometrics and ambient seawater properties were collated. The model accurately reproduced the spatio-temporal variability in blue mussel growth. It is also shown that the ecosystem dynamics is affected by the presence of aquaculture farms. The modelling system presented allows for the assessment of the impacts of aquaculture activities on water quality, quantification of the production and ecological carrying capacities and improvement of our understanding of the ecosystem functioning with particular emphasis on interactions between various trophic levels.     

大治河河口无齿螳臂相手蟹生长和成熟的研究

无齿螳臂相手蟹是长江口潮间带和潮上带的优势种之一,具有重要的生态功能。为探求无齿螳臂相手蟹不同阶段的异速生长和成熟状况,于2009年10月至2010年9月期间采集样本,通过聚类和分段线性回归等分析方法对雌雄蟹头胸甲、螯、腹部等形态数据进行分析,建立区别不同生长阶段的判别函数并用逻辑斯蒂回归估计其50%形态成熟点。结果如下:雌雄蟹50%形态成熟点分别为头胸甲宽18.22mm和16.36mm。雄蟹的螯宽和雌蟹的腹宽均表现出明显的异速生长;根据相对生长率的不同,雄蟹异速生长可分为三个阶段,雌蟹分为2个阶段;不成熟的雄蟹异速生长拐点发生在壳宽11.78mm,不成熟和成熟雌蟹腹部在壳宽13.04～18.64mm范围内重叠。同时研究了50%的生理成熟大小,雌雄成熟大小分别为17.50mm,17.20mm。雄性形态成熟大小小于生理成熟大小,而雌性则相反。     

Sex identification of Carcinus maenas by analysis of carapace geometrical morphometry

The European green crab Carcinus maenas is a widely spread invasive species. Studying the most recently introduced population of the species in the Atlantic coast off Patagonia, it became apparent to us that carapaces (the dorsal cover of the visceral-cavity detaching from the rest of the exoskeleton after ecdysis) accumulated on the intertidal may be used as a valuable complementary material to analyze the size structure of crabs. However, since growth rate (and consequently size at instar) of crabs differs between males and females, finding a method to distinguish crab sex by observation of carapace morphology was necessary to allow the construction of independent size frequency distributions for each sex. In this work, we examined the shape of the carapaces from both sexes of C. maenas, and using Elliptical Fourier Analysis successfully identified sexual dimorphism. Thus, a reliable method to identify sexes by visual observation of the carapace was developed. Based on our results, we discuss the evolutionary significance of carapace form differentiation of both sexes.     

Intraspecific diet shift in Talitrus saltator inhabiting exposed sandy beaches

Talitrid amphipods are the most abundant herbivores on exposed sandy beaches. Despite their important role as trophic intermediates between macrophytes and higher levels (i.e. insect and bird) of beach food webs, very little information is available on their feeding patterns. The main aim of this study was to investigate intraspecific differences in the feeding behaviour of Talitrus saltator. We tested the hypotheses that: (1) adult females and males showed different isotope signatures and therefore relied on different sources of food; and (2) patterns of variation of isotope signatures of juveniles differed from those of adult specimens, evidencing a diet shift during the development. We used stable isotope signatures and tested for differences upon the level on the shore, times of the year and beaches experiencing similar morpho-dynamic and environmental conditions. Finally, we investigated the trophic significance of macrophyte detritus in the diet of males, females and juveniles. Results showed that adult males had a more variable diet than females and juveniles (inferred from δ¹³C and δ¹⁵N values). Dual-isotope graphs suggested that Sargassum muticum and Cystoseira baccata wrack could be among the main food sources for both juvenile and adult stage.