Prey consumption by the juvenile soles, Solea solea and Solea senegalensis, in the Tagus estuary,Portugal

The soles Solea solea and Solea senegalensis are marine flatfish that use coastal and estuarine nursery grounds, which generally present high food availability, refuge from predators and favourable conditions for rapid growth. Two important nursery grounds for these species juveniles have been identified in the Tagus estuary, one in the upper part of the estuary (nursery A) and another in the south bank (nursery B). While S. solea is only present at the uppermost nursery area, S. senegalensis is present at both nurseries. Although they are among the most important predators in these nursery grounds, there are no estimates on their food consumption or on the carrying capacity of the system for soles. The Elliott and Persson [1978. The estimation of daily rates of food consumption for fish. Journal of Animal Ecology 47, 977–993] model was used to estimate food consumption of both species juveniles in both nursery areas, taking into account gastric evacuation rates (previously determined) and 24 h sampling surveys, based on beam-trawl catches carried out every 3 h, in the summer of 1995. Monthly beam trawls were performed to determine sole densities over the summer. Density estimates and daily food consumption values were used to calculate total consumption over the summer period. Sediment samples were taken for the estimation of prey densities and total biomass in the nursery areas. Daily food consumption was lower for S. solea (0.030 g wet weight d⁻¹) than for S. senegalensis (0.075 g wet weight d⁻¹). It was concluded that thermal stress may be an important factor hindering S. solea's food consumption in the warmer months. Total consumption of S. solea over the summer (90 days) was estimated to be 97 kg (wet weight). Solea senegalensis total consumption in nursery A was estimated to be 103 kg, while in nursery B it was 528 kg. Total prey biomass estimated for nursery A was 300 tonnes, while for nursery B it was 58 tonnes. This suggests that food is not a limiting factor for sole in the Tagus estuary. However it was concluded that more in-depth studies into the food consumption of other species and prey availability are needed in order to determine the carrying capacity of this system for sole juveniles.     

Aspects of the biology of the sandsmelt Atherina boyeri Risso, 1810 (Teleostei: Atherinidae) at Oldbury-upon-Severn,Gloucestershire, England

The age structure, annual growth, length-weight relationship, reproduction and other aspects of the general biology in Boyer's sandsmelt, Atherina boyeri, from the Severn estuary, have been studied for the period 1974–1977. The results are compared with those found in previous investigations of A. boyeri from more southerly waters.     

Life-history patterns of the salt-marsh killifish Fundulus heteroclitus (L.) introduced in the estuary of the guadalquivir river (South West Spain)

Two thousand four hundred and eighty-four specimens from a population of Fundulus heteroclitus introduced into the southwestern Iberian Peninsula were used to carry out a study on age, growth and reproduction. In this new habitat the species displayed the same life-history tactics as in its original areas. The life-span was shorter, with a winter age-structure of 67·4% in 0 + group, 29·1% in 1 + group, 2·5% in 2 + group and 1·1% in 3 + group. Females showed a higher growth rate and a longer growth period than males and because of this they were always longer than males in all the age-groups. In both sexes growth stopped and the somatic condition was at a minimum from April to June, when the gonadosomatic index reached its highest values. The maximum average gonadosomatic index in females was four times higher than that of males. Specimens achieved maturity during the spawning season the year following birth at a minimum average total length of 45 mm for males and 60 mm for females. Fecundity was related to fish weight, total length and gonad weight. The overall sex ratio did not differ significantly from 1:1.     

Aspects of the biology and fisheries of an economically important sparid Dentex macrophthalmus (Bloch 1791) in the Namibe province,Angola

The sparid Dentex macrophthalmus is a widespread, important fishery species along most of the West African coast from southern Namibia to the Mediterranean. In southern Angola it is an important artisanal species targeted predominantly by handline fishers. A biological and fisheries study was conducted on this species in southern Angola between June 2008 and July 2009. It was the dominant species in the artisanal fishery, accounting for 99% of the sparids captured and 67% (by mass) of the total catch. The life history of D. macrophthalmus was characterised by slow growth (females: L_t = 309[1 ? e^{?0.06(t + 5.43)}], males: L_t = 248[1 ? e^{?0.16(t ? 1.77)}]), advanced age at maturity (females: 7.4 years, males: 6.0 years) and high longevity (females: 36 years, males: 38 years). The sex ratio was 1:1 male:female. The length- and age-frequency distributions and macroscopic observations suggested that the species is a late gonochorist. Males and females reached 50% maturity at 151 and 166 mm fork length respectively. Although individuals with ripe gonads were found during most of the year, the peak spawning period appeared to be in December and January. Despite a life history that renders D. macrophthal-mus vulnerable to overexploitation, only 38% of artisanal fishers noticed a decline in the catches of this species. Potential reasons for this include: technology creep; limited pressure on the juvenile portion of the stock as a result of late recruitment (above the length of 50% maturity); the ‘basin affect’, whereby depleted areas are reseeded by areas (e.g. deeper water) inaccessible to the linefishery; and a deep-water reserve of large individuals. It is recommended that precautionary management strategies be implemented until the age estimates are revised by the countries in which this species forms significant fisheries.     

Growth and feeding habits of invasive Pseudorasbora parva in the Chabalang Wetland(Lhasa,China) and its trophic impacts on native fish

In recent years, fish invasion has become one of the main reasons for the decline of native fish stocks. Pseudorasbora parva is considered one of the major invasive species worldwide. The present study investigated the fish resources of the Chabalang Wetland (Lhasa, Tibet) during diff erent seasons in 2009 and 2013. Four hundred and twelve individuals were subsampled to estimate age, growth, and feeding habit of P . parva . Furthermore, food relationships between P . parva and the native Schizothoracinae fish were also examined. The results revealed a significant shift in species composition and community structure characterized by the disappearance of native fish and outbreak of non-native fish. The percentage of nonnative P . parva in the fish collections significantly increased from 33.64% in 2009 to 64.08% in 2013. The standard length (SL) ranged from 22.00 to 78.71 mm, and their age was 1–5 a. The von Bertalanff y function was used to model the observed length-at-age data as L t =112.19(1–e^-0.1495 ( t +0.8012)) for females and as L t =123.12 (1–e^-0.1500 ( t +0.7132)) for males. The results indicated that P . parva in Tibet has lower growth and mortality rates compared with that from the native ranges. Ninety-seven prey taxa belonging to 9 prey categories were identified in the gut of 38 P . parva . P . parva can be considered a generalized and opportunistic predator, competing with the native fish, especially Schizothorax o’connori , Schizopygopsis younghusbandi younghusbandi , and Ptychobarbus dipogon , for Bacillariophyta and Chironomid larvae. This is an important reason for the decline in native fish population.     

双棘黄姑鱼早期发育阶段的摄食习性与生长特性

2002年5~6月,在集美大学水产学院水产试验场,采用生态学方法对人工培育的双棘黄姑鱼(Nibeadiacanthus(Lacpde))仔、稚、幼鱼的摄食习性与生长特性进行分析。结果表明,在人工培育条件下,双刺黄姑鱼仔、稚、幼鱼的摄食率达93.1%,摄食量占体质量的4.09%~21.07%,日摄食量占体质量的23.67%~57.24%;摄食具明显的昼夜节律,黄昏为摄食高峰。摄食量与体质量的关系式为y=0.1267x0.7878,全长与日龄的关系式为L=1.8603e0.0723D,体质量与日龄的回归方程为M=0.0203e0.2484D。全长与体质量的回归方程为M=0.0024L3.4633。     

Nursery fidelity,food web interactions and primary sources of nutrition of the juveniles of Solea solea and S. senegalensis in the Tagus estuary (Portugal): A stable isotope approach

Stable carbon and nitrogen isotopes were used to assess site fidelity of Solea solea and Solea senegalensis juveniles, to investigate food web interactions and to determine the dominant nutrient pathways in two nursery areas in the Tagus estuary, Portugal. Samples of water from the main sources and from the nursery areas and respective saltmarsh creeks were collected for isotope analysis, as well as sediment, benthic microalgae, saltmarsh halophytes, S. solea, S. senegalensis and its main prey, Nereis diversicolor, Scrobicularia plana and Corophium spp. While site fidelity was high in 0-group juveniles, it was lower for 1-group juveniles, possibly due to an increase in mobility and energy demands with increasing size. Analysis of the food web revealed a complex net of relations. Particulate organic matter from the freshwater sources, from each nursery's waters and saltmarsh creeks presented similar isotopic composition. Sediment isotopic composition and saltmarsh halophytes also did not differentiate the two areas. All components of the food web from the benthic microalgae upwards were isotopically different between the nursery areas. These components were always more enriched in δ¹³C and δ¹⁵N at the lower nursery area than at the nursery located upstream, appearing as if there were two parallel trophic chains with little trophic interaction between each other. A mixture of carbon and nitrogen sources is probably being incorporated into the food web. The lower nursery area is more dependent upon an isotopically enriched energy pathway, composed of marine particulate organic matter, marine benthic microalgae and detritus of the C₄ saltmarsh halophyte Spartina maritima. The two nursery areas present a different level of dependence upon the freshwater and marine energy pathways, due to hydrological features, which should be taken into account for S. solea and S. senegalensis fisheries and habitat management.     

Feeding preferences of estuarine mysids Neomysis integer and Rhopalophthalmus tartessicus in a temperate estuary (Guadalquivir Estuary,SW Spain)

Mysid shrimps are an important component of estuarine food webs because they play a key role in energy transfer as intermediate prey. We investigated the seasonal, tidal and depth specific variation in the diet of the estuarine mysids Neomysis integer and Rhopalophthalmus tartessicus and explored its implications for the planktonic community structure of a temperate estuary (Guadalquivir Estuary, SW Spain). Neomysis integer is an opportunistic omnivore feeding mainly on mesozooplankton and on members of the detrital–microbial loop, shifting prey seasonally according to availability. In contrast, R. tartessicus showed a more carnivorous diet and shifted its target prey during seasons of low resource availability. Despite statistically significant differences in diet composition, both species shared prey of similar size, particularly juvenile Mesopodopsis slabberi, the most abundant mysid species in this estuary, and copepods. Although these similarities imply inter-specific resource competition, their co-existence is achieved by niche partitioning and spatial segregation: the higher osmoregulatory capacity and foraging plasticity of N. integer confers a broader niche breadth for this species allowing N. integer to inhabit the more stressful oligohaline region of the estuary where R. tartessicus cannot survive. We propose that this mechanism relaxes the potential for competition between N. integer and R. tartessicus.     

In situ growth of Soletellina alba (Bivalvia: Psammobiidae) in response to detrital supply and mouth status in a seasonally-closed estuary

The supply of detritus is an important food source for many soft-sediment invertebrates, but its importance for their growth and condition is rarely, if ever, tested directly using manipulative field experiments. Therefore, we designed such a study to: (1) test the importance of fine particulate organic matter for the growth and condition of the infaunal bivalve Soletellina alba; (2) indirectly test the feeding mode of S. alba, which has been assumed to be a deposit feeder like other members of the same superfamily (Tellinoidea); (3) compare growth rates across two summers with contrasting patterns of estuary mouth opening/closing; and (4) compare the condition of individuals used in two field studies (i.e. present versus past) and a past laboratory study. Neither growth nor condition differed when organic content of the sediments was varied, which suggests that S. alba is either a suspension feeder or capable of switching modes of feeding. There was considerable interannual variation in growth with greater growth occurring during the summer with a longer period of mouth opening. This suggests that periods of mouth closure may reduce secondary production within seasonally-closed estuaries. Potential artefacts associated with laboratory trials were also identified, with laboratory bivalves exhibiting poorer condition than those used in two field trials. The present study provides no evidence that variable quantities and qualities of organic matter within the sediments influence the growth and condition of S. alba, but future studies should focus on food supplied via the water column when the estuary is open versus closed.     

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.     

A comparative study of mercury contamination in the Tagus estuary (Portugal) and major French estuaries (Gironde,Loire, Rhône)

Concentrations of mercury were determined for the waters, suspended matter and sediments of the Tagus and of major French estuaries.The Tagus estuary is one of the most contaminated by mercury derived from the outfalls of a chloralkali plant and from other industrial sources. In deposited sediments the median level, 1·0 μg Hg g^?1, is twenty times higher than the natural background and Hg contents depend on the sediment grain-size, age and the distance from waste-outfalls. Suspended matter is more regularly and highly contaminated (median value: 4·5 μg Hg g^?1). In the French estuaries Hg levels in the suspended material decrease with salinity due to dilution and/or remobilization processes. In June 1982, in the Loire estuary, high values of Hg are observed in the middle estuary and attributed to urban and industrial sources.In the Tagus estuary, the general distribution of total dissolved Hg confirms the contamination: it increases seaward from 10 ng 1^?1 in the river to 80 ng 1^?1 in the estuary outlet. The dissolved Hg is almost totally organic in the river, inorganic in the middle estuary due to inorganic Hg effluents and again organic in the lower estuary. This variation is related to the dissolved organic carbon values. The dissolved Hg levels in the Loire Estuary (5–300 ng 1^?1) are much higher than in the Gironde estuary (3–6 ng 1^?1) and of the same order as those observed in the Tagus estuary.     

Reproductive and growth strategies of Idotea balthica basteri (Pallas, 1772) population in the Bizerte lagoon (Tunisia,Southern Mediterranean)

We analysed several life history traits of the marine isopod Idotea balthica basteri (Pallas, 1772) from the Bizerte lagoon, Southern Mediterranean Sea. Growth was continuous throughout the life of the animal with a high growth rate in the first life phase, and the growth curve was described according to von Bertalanffy's model. The lowest growth rate (0.23 mm) was recorded in winter (December, January and February) and the maximum rate (2.31 mm) between April and June. The total number of hatched eggs or embryos was positively correlated with the body length of ovigerous females. This population of I. balthica basteri was iteroparous, showing distinct strategies of reproduction. Large ovigerous females with high fecundity were collected during the whole sampling period, while breeding in smaller females with low fecundity was restricted to the period from late spring to early autumn, Manca size increased significantly with increasing female body size and there was also a significant trade‐off between manca size and the number of eggs per brood. Reproductive allocation, ranging between 17.1 ± 1.2% in winter and 23.2 ± 1.8% in summer, was positively correlated with female weight. Accordingly, parental investment in producing a juvenile varied between 1.02% per manca in winter to 3.38% in spring. Evaluated traits show that late summer and autumn cohorts have a K‐strategy, whereas cohorts born in winter and spring, and which exhibit a shorter life time, exhibit faster development, earlier reproduction and a smaller parental investment tending towards an r‐selected strategy.     

DDT对细巧华哲水蚤（Sinocalanus tenellus）摄食、呼吸、存活和生殖的影响研究

DDT(dichloro-diphenyl-trichloroethane) as a type of organochlorine pesticides, is an important component of pesticides pollution whose impact on the marine ecosystem is urgently to be evaluated. To investigate the biological effects of DDT on the marine ecosystem, copepods being the main contributor of secondary productivity in the marine ecosystem, were selected as target animals. The influence of DDT on the feeding, respiration, survival, and reproduction of Sinocalanus tenellus(S. tenellus) was analyzed and the antioxidant enzymes activities in the individuals were measured under different exposure concentrations of DDT. The 48 h median lethal concentration(LC50) and 96 h LC50 of DDT to S. tenellus were 5.44 and 2.50 μg/dm3, respectively. The filtration rates, grazing rates, and respiration of S. tenellus decreased apparently with increased DDT concentrations. Under lower concentration(625 ng/dm3) of DDT, the activities of the antioxidant enzymes, including superoxide dismutase and catalase in the animals increased significantly compared with those in the animals without any exposure to DDT, which suggested that the antioxidant enzymes can protect the animals from oxidative damage. However, the activity of the antioxidant enzyme decreased when the animals were exposed to higher concentration(1 250–2 500 ng/dm3) of DDT. The survival rate of both females and males was reduced when they were exposed to DDT less than 250 ng/dm3, but females showed higher survival rate than males when they are under the same concentration. The hatching ratio and the egg diameters of S. tenellus decreased significantly when they were exposed to DDT with a concentration of 25 and 250 ng/dm3, however, the cumulative egg production did not show any significant variation when the animals were exposed to the above DDT concentration. These data in the preset study suggested that exposure to DDT can cause the variation of the species composition of copepods, and further affect the marine ecosystem.     

Comparison of the population structure and life-history parameters of Diplodus capensis (Sparidae) in exploited and unexploited areas of southern Angola

Blacktail seabream Diplodus capensis were sampled from proximate (10 km apart) exploited and unexploited areas in southern Angola to compare their population structures and life-history parameters. Females dominated the larger size and older age classes in the unexploited area. In the exploited area the length and age frequency distributions were more equitable, but there was a lack of large and old individuals in this area due to the selective nature of fishing gear. Growth zone deposition rate was validated as being annual using mark-recapture of chemically injected (oxytetracycline) fish. In the unexploited area, females attained larger sizes and greater ages than males; however, growth and longevity were more equitable between the sexes in the exploited area. Length- and age-at-50% maturity were similar between the sexes in both areas. The sex ratio was heavily female-skewed (1:4.7) in the unexploited area but less so in the exploited area (1:2.2). Although the growth curves were significantly different for fish between areas, this was likely due to a reduction in longevity rather than a physiological change in growth. The length- and age-at-50% maturity was also similar between areas, indicating that this species either does not have the ability to respond to exploitation through physiological change in these life-history characteristics, or that the current level of exploitation is not high enough to elicit such a response. However, the female dominance in the smallest size class in the exploited area (compared to the unexploited area) indicated that a threshold may have been reached, and that this species responds to exploitation by increasing the relative number of fish that mature as females.     

Life history and population dynamics of Moerisia sp., a non-native hydrozoan, in the upper San Francisco Estuary (U.S.A.)

Some populations of gelatinous zooplankton appear to be increasing and causing ecological disruptions during large bloom events. The goal of this study was to investigate the life history and population dynamics of the small, invasive Moerisia sp. and its potential ecological impacts in the upper San Francisco Estuary, California. Medusae and polyps were collected from 8 and 2 sites, respectively, during 2007 and 2008. Polyps emerged from a resting stage during June. Asexual reproduction of medusae buds was positively correlated with temperature and negatively related to salinity. The production of polyp buds was positively correlated with dissolved oxygen and water transparency levels. Sexual reproduction, defined by the presence of eggs, was related to the size of medusae. Cessation of reproduction of both polyps and medusae occurred in October, when temperatures dropped below 17 °C. This life history is similar to other hydrozoans and allows Moerisia sp. to reach large numbers seasonally in the San Francisco Estuary, possibly contributing to the recent declines of pelagic fish and zooplankton.