Feeding ecology of three species of midwater fishes associated with the continental slope of eastern Tasmania,Australia

The feeding ecology of Maurolicus muelleri, Lampanyctodes hectoris and Diaphus danae was examined from samples collected from continental slope waters of eastern Tasmania between April 1984 and April 1985. A total of 2 232 stomachs was analysed. M. muelleri, L. hectoris and D. danae fed primarily on euphausiids and secondarily on copepods, although larger D. danae (> 60 mm standard length) fed on other lanternfish (chiefly L. hectoris). The diets of M. muelleri and L. hectoris overlapped substantially. Diet overlaps between D. danae and the former species was low, however, due to the large biomass of fish present in D. danae. The prey taxa consumed changed with time of year and predator size. Stomach fullness (feeding intensity) varied seasonally in all three species, but only M. muelleri showed significant diel differences in fullness. The synchronization of the size structure of the predator populations and their feeding intensity, with seasonal variations in preferred prey, is proposed as a mechanism whereby each species maximizes its share of the available food resources.     

Reproductive biology of three species of midwater fishes associated with the continental slope of eastern Tasmania,Australia

The reproductive biology of Lampanyctodes hectoris (Günther, 1876), Maurolicus muelleri (Gmelin, 1789) and Diaphus danae Tåning, 1932, from continental-slope waters of eastern Tasmania, was examined between April 1984 and June 1985. L. hectoris spawned in winter and M. muelleri spawned from late winter to early summer. Apart from one ripe male, no reproductive activity was detected in D. danae; this species may be an expatriate in these waters. Fecundity was positively correlated with standard length in L. hectoris, but not in M. muelleri. The ratio of females to males increased with length in all three species. The spermatozoa of L. hectoris and D. danae are atypical of vertebrates and have no tail.     

Diets of fishes of the upper continental slope of eastern Tasmania: content,calorific values,dietary overlap and trophic relationships

Diets of 15 species of demersal and pelagic fishes on the upper continental slope (420 to 550 m) were determined, based on samples taken every two months over 13 mo (April 1984 to April 1985) off eastern Tasmania. The calorific contribution of each prey item to the diets was determined. The fish could be divided into four trophic categories: pelagic piscivores, epibenthic piscivores, epibenthic invertebrate feeders and benthopelagic omnivores. Dietary overlap between the groups was low. The pelagic piscivores Apogonops anomalus, Trachurus declivis, Brama brama, Lepidopus caudatus and Macruronus novaezelandiae primarily consume the shelf-break myctophid Lampanyctodes hectoris; their diet is narrow, with a large overlap between species. The epibenthic piscivores Deania calcea and Genypterus blacodes both take a greater variety of prey, but have little dietary overlap. The fish feeding on epibenthic invertebrates, Coelorinchus sp. 2 and Centriscops humerosus, obtain most of their energy from benthic Crustacea and Ophiuroidea, supplemented with Lampanyctodes hectoris; the diet is broad, with little overlap. Among the benthopelagic omnivores (Cyttus traversi, Coelorinchus sp. 4, Lepidorhynchus denticulatus, Neocyttus rhomboidalis, Helicolenus percoides, Epigonus denticulatus and E. lenimen), most diets are broad and show slight overlap. All but E. denticulatus consume significant quantities of Lampanyctodes hectoris as well as Crustacea, particularly Polychaeta, Euphausiacea and Pyrosoma atlanticum. Seasonal changes in diet occurred in G. blacodes, T. declivis, Lepidopus caudatus, Coelorinchus sp. 4, Lepidorhynchus denticulatus, H. percoides, E. denticulatus and E. lenimen; these were related to changes in abundance of particular prey species, not to alterations in feeding habits. Only three species, Lepidopus caudatus, Coelorinchus sp. 2 and H. percoides, showed significant diel feeding periodicity. Ontogenetic dietary changes were evident in Cyttus traversi, Coelorinchus sp. 2, Lepidorhynchus denticulatus and H. percoides. Cyttus traversi and H. percoides progressively changed from crustaceans to fish as their size increased. The diets of size classes within species showed little overlap, except for Lepidorhynchus denticulatus, which eats chiefly euphausiids and Lampanyctodes hectoris at all sizes. In addition to describing the diets and trophic relationships of 90% of the fish biomass, the results emphasize the importance to the entire fish community of mesopelagic food resources, particularly Lampanyctodes hectoris. Many benthopelagic species undertake extensive vertical migrations in search of prey, thus playing a major role in the transport of energy from midwater regions to the benthos of the continental slope.     

Demography and reproductive biology ofMelinna palmata (Ampharetidae: Polychaeta) in Inner Galway Bay on the west coast of Ireland

A high-density population of the polychaeteMelinna palmata Grube was the focus of a two-year study at a shallow-water location in Inner Galway Bay on the west coast of Ireland. Mean densities were highest in the second year of the study following successful recruitment. Size-frequency analysis of population structure (April 1983 to March 1985) revealed the presence of four cohorts, with the 1983 settlement becoming the dominant modal class. Size comparison of this cohort with the 1982 settlement showed that growth rates were lower and mortality higher in the 1983 settlement, which may be related to density dependent intra-specific competition.M. palmata at this location live for 2 to 2.5 yr with a small number surviving to 3 yr of age.M. palmata in Galway Bay is dioecious and has an even sex ratio. Reproductively mature worms were approximately 2 yr old when they first spawned. Spawning took place between May and July, when mature oocytes had a modal size of ca. 290µm. Proliferation of previtellogenic oocytes (ca. 10µm) from the gonads occurred following spawning. Growth over the winter was slow and was followed by a period of rapid growth between March and May, coincident with rising water temperatures. The presence of mature unspawned oocytes, which were resorbed after commencement of new proliferation, was taken as evidence of the species propensity for polytely. However, post-spawning mortality appeared to be high, so that only a small number of individuals survived to spawn the following year. The highest abundance of mature males was encountered between May and August, but lower levels of mature stages were present throughout the year.     

多种聚氧乙烯牛脂胺混合物MON 0818的水生环境危害评估：脉冲暴露后沉积物、温度和恢复能力的影响

我们对一种商业表面活性剂混合物(多种聚氧乙烯牛脂胺)MON 0818进行了一系列毒性测试：1. 测定底栖无脊椎动物和鱼类在沉积物存在的情况下受到的毒性；2.测定大型蚤(Daphnia magna)和4种初级生产者经过24 h的脉冲暴露之后的恢复能力；3.鉴定水体温度上升对于2种冷水鱼类所受到MON 0818毒性的潜在影响。在沉积物存在的情况下，5种生物中有3种在最高10 mg/L的浓度下短期(24 h)死亡率为零。其余2种物种的中位有效浓度则显著高于仅对水体进行测试的结果。15 ℃下北极红点鲑(Salvelinus alpinus)的半数有效浓度统计上低于10 ℃下。绿藻(Rhabdocelis subcapitata)和普通小球藻(Chlorella vulgaris)在经过24 h 1 mg/L的暴露后的恢复期中显示出生长延迟的状况，表明该暴露可能存在潜在影响。尽管如此，2个物种的最大绝对生长速率并未改变，表明其均可恢复。1.5 mg/L下的蝾螈共生藻(Oophila sp.)和100 mg/L下的浮萍(Lemna minor)经过24 h的暴露并未显示显著反应。24 h 5 mg/L暴露之后的恢复期中，大型蚤显示出潜在的死亡率。然而存活个体的生殖终端指标并未受到影响。结果表明在沉积物的存在下MON 0818的快速损耗可以减轻对于被暴露生物的效果，在不小于环境中可能出现的MON 0818浓度情况下，24 h暴露以后的生物的完全恢复是可能的。
精选自Jose L. Rodriguez-Gil, Ryan Prosser, Gregory Hanta, David Poirier, Linda Lissemore, Mark Hanson, Keith R. Solomon. Aquatic hazard assessment of MON 0818, a commercial mixture of alkylamine ethoxylates commonly used in glyphosate-containing herbicide formulations. Part 2: Roles of sediment, temperature, and capacity for recovery following a pulsed exposure. Environmental Toxicology and Chemistry: Volume 36, Issue 2, pages 512–521, July 2017. DOI: 10.1002/etc.3558
详情请见http://onlinelibrary.wiley.com/wol1/doi/10.1002/etc.3558/full
     

High intertidal community organization on a rocky headland in Maine,USA

A mosaic patchwork of the barnacle Balanus balanoides L., the mussel Mytilus edulis L., and the alga Fucus vesiculosus L. was found in the transitional region between the mid and high intertidal zones on a rocky headland on Mount Desert Island, Maine, USA. The development of the mosaic was observed by following recruitment and survival of B. balanoides in denuded patches located at the same tidal level along a 60 m stretch of shore. Barnacle recruitment was least under canopies of F. vesiculosus and greatest in open areas kept moist at low tide by surf. Barnacle survival after settlement was least under the F. vesiculosus canopy due to the whiplash effect of the algal fronds in the surf and greatest in open areas free from competition from mussels. In open areas, early mortality was correlated with settlement density. In areas of dense settlement (60 spat cm^-2) up to 90% mortality resulted within 5 months from crowding associated with growth. In older individuals crowding produced hummocks of elongated, weakly attached barnacles which were more prone to removal by surf than uncrowded barnacles. Mussels exerted competitive dominance over barnacles for space and the presence of mussel beds prevented further barnacle recruitment. Mussels suffered extensive mortality during winter storms when surf removed dense mats of weakly attached mussels. The patchy distribution of mussels and barnacles results from irregular rock substrata producing numerous environmental patches with respect to wave exposure and drainage at low tide, and from densitydependent mortality of both mussels and barnacles which creates patches of new colonizable space within each environmental patch.     

Growth,mortality and recruitment of the yellow clam Mesodesma mactroides on Uruguayan beaches

We studied some aspects of the population dynamics of the yellow clam Mesodesma mactroides (Deshayes, 1854) which inhabits the eastern sandy beaches of Uruguay. Observations were made from March 1983 through March 1985 (harvesting season), and additional data from January 1988 to December 1989 (closed season) were also included in the analyses. Parameters of growth and mortality were estimated by methods that make use of age or length information. An age/length relationship was constructed by counting growth rings. Results were consistent with those obtained with modal class progression analysis and other length/frequency methods. The growth curve obtained from the age/length relationship did not account for seasonality in growth rate, and a seasonal growth model explained growth oscillations in a better way. The instantaneous coefficient of natural mortality (M) estimated for the closed season was 1.64, whereas an increase in fishing mortality (F) was observed during 1984. Age composition did not change during the 2 yr of study, and the first 6 mm class accounted for over 50% of the population. The main contribution of recruits was observed between late summer and early fall (February to April), and the recruitment pattern suggested one main settlement period per year. Growth and recruitment success appeared to be regulated by density-dependence processes. Some implications for management are considered in this context. Methodological aspects concerning the reliability of empirical equations and programs for estimating growth and mortality are discussed.     

The relationship between bleaching and mortality of common corals

Reef corals are likely to have many subtle but four gross responses to anomalous warm water. These are (1) not bleach and live (mortality <10%), (2) not bleach and die (mortality >20%), (3) bleach and live, and (4) bleach and die. The frequency of these four possible gross responses was determined for 18 common coral taxa over an exceptionally warm 1998 El Niño where intense bleaching was observed, and mortality determined from line transects averaged 41.2±34.7 (±SD). Field studies included (1) recording the loss of color (bleaching) and observing recently dead individuals among 6,803 colonies during five sampling periods and (2) estimating mortality based on 180 m of line-intercept transects completed 4 months before and near the end of the bleaching episode. There was no clear relationship between the loss of color and either direct observation or transect-based estimates of mortality for the 18 taxa. The morphology of the taxa did not influence color loss but branching and encrusting taxa had higher mortality than massive and submassive taxa. Loss of color and mortality are the most common responses to warm water as only Pavona did not lose color or die and only two taxa, Cyphastrea and Millepora, did not significantly lose color but died. Of the 15 taxa that lost color, five taxa, Astreopora, Favia, Favites, Goniopora, and Leptoria, did not die. These taxa are those most likely to have reduced potential mortality by the loss of pigments and associated algal symbionts. Death of the branching taxa was detected reasonably by direct field observation but some taxa were underestimated when compared with mortality estimates based on line transects. Death of encrusting and massive taxa including Echinopora, Galaxea, Hydnophora, Montipora, Platygyra, and massive Porites was poorly detected from direct observations but they proved to have modest to high mortality (20–80%) based on line transects. There was no single response of these common corals to warm water but these data, collected during an extreme warm-water anomaly, indicate that the loss of color is most frequently a sign of morbidity, particularly for branching and encrusting taxa.Communicated by P.W. Sammarco, Chauvin     

Population structure,mortality and growth of <Emphasis Type="Italic">Pinna nobilis</Emphasis> Linnaeus, 1758 (Mollusca,Bivalvia) at different depths in Moraira bay (Alicante,Western Mediterranean)

An investigation to characterize the causes of Pinna nobilis population structure in Moraira bay (Western Mediterranean) was developed. Individuals of two areas of the same Posidonia meadow, located at different depths (A1, −13 and A2, −6 m), were inventoried, tagged, their positions accurately recorded and monitored from July 1997 to July 2002. On each area, different aspects of population demography were studied (i.e. spatial distribution, size structure, displacement evidences, mortality, growth and shell orientation). A comparison between both groups of individuals was carried out, finding important differences between them. In A1, the individuals were more aggregated and mean and maximum size were higher (A1, 10.3 and A2, 6 individuals/100 m²; A1, x = 47.2 ± 9.9; A2, x = 29.8 ± 7.4 cm, P < 0.001, respectively). In A2, growth rate and mortality were higher, the latter concentrated on the largest individuals, in contrast to A1, where the smallest individuals had the higher mortality rate [A1, L = 56.03(1 − e^−0.17t ); A2, L = 37.59(1 − e^−0.40t ), P < 0.001; mean annual mortality A1: 32 dead individuals out of 135, 23.7% and A2: 16 dead individuals out of 36, 44.4%, and total mortality coefficients (z), z _A1(−30) = 0.28, z _A1(31–45) = 0.05, z _A1(46−) = 0.08; z _A2(−30) = 0.15, z _A2(31–45) = 0.25]. A common shell orientation N–S, coincident with the maximum shore exposure, was observed in A2. Spatial distribution in both areas showed not enough evidence to discard a random distribution of the individuals, despite the greater aggregation on the deeper area (A1) (A1, χ ² = 0.41, df = 3, P > 0.5, A2, χ ² = 0.98, df = 2 and 0.3 < P < 0.5). The obtained results have demonstrated that the depth-related size segregation usually shown by P. nobilis is mainly caused by differences in mortality and growth among individuals located at different depths, rather than by the active displacement of individuals previously reported in the literature. Furthermore, dwarf individuals are observed in shallower levels and as a consequence, the relationship between size and age are not comparable even among groups of individuals inhabiting the same meadow at different depths. The final causes of the differences on mortality and growth are also discussed.     

Effects of dieldrin in seawater on the development of two species of crab larvae,Leptodius floridanus and Panopeus herbstii

Some of the effets of dieldrin on the development of two species of crabs, Leptodius floridanus (Rathbun) and Panopeus herbstii (Milne-Edwards), were studied. It was found that the larvae of neither species were able to complete their development at 10 ppb dieldrin or higher in seawater. Groups of L. floridanus larvae reared in 1 ppb dieldrin in seawater had a 15 to 27% higher mortality during development to the postlarval stage than controls. The highest mortality occurred during the first zoeal stage. The time of development to the megalopal stage was as much as 11.4% longer among larvae reared in 1 ppb than among controls. The survival of L. floridanus larvae was not affected by 0.5 ppb dieldrin in seawater. The survival of P. herbstii larvae to the first crab stage was not affected by 1 ppb dieldrin in seawater at 28.5 °C, 30%.S. It was concluded that a comprehensive study of the toxicity of a given pesticide to all stages in the life cycle of a species is necessary to give even an incomplete idea of how the pesticide might affect the animal in its natural environment.     

Growth and mortality rates of the fan mussel <Emphasis Type="Italic">Pinna nobilis</Emphasis> in Lake Vouliagmeni (Korinthiakos Gulf,Greece): a generalized additive modelling approach

The temporal patterns and the effect of shell size and depth on growth and mortality rates of the endangered fan mussel Pinna nobilis were investigated in the marine Lake Vouliagmeni (Korinthiakos Gulf, Greece). A total of 160 individuals were tagged and monitored monthly for a period of 17 months. At each visit, the size of the tagged individuals (shell width, w) was measured in situ and recorded. Any mortality event was also recorded and attributed to natural causes or (illegal) fishing. Growth and mortality rates were modeled with generalized additive models, which are non-parametric flexible models that free the researcher from the limiting concept of a strict parametric shape. The use of GAMs allowed the exploration of shapes of growth and mortality response curves in relation to predictor variables and allowed the fitting of statistical models that better agree with ecological theory. Growth rates had a seasonal pattern, with an extended period of very slow growth between late autumn and early spring, i.e., during the cold season, another short period of slow growth during August (when water temperatures reached their maximum values exceeding 29°C), and a peak in growth rates during late spring–early summer, probably related to an optimum combination of temperature and food availability. Growth rates varied with shell size, with a peak at w ∼4.5 cm, followed by a sharp decline to an approximately constant level, with sizes ranging from 9 to 15 cm, and a further decline with larger sizes down to almost zero for w > 20 cm. Growth rates did not vary substantially with depth. Although P. nobilis is a protected species in the EU and its fishing is strictly prohibited, fishing mortality was very high in Lake Vouliagmeni (much greater than natural mortality), especially during the hot season when the lake was crowded by summer visitors. The fan mussels were poached exclusively by free-diving and due to the high turbidity of the lake’s water, fishing mortality was higher in shallow areas (and mostly for large individuals) and was practically zero at depths >9 m. Due to fishing mortality, a size segregation of P. nobilis was observed in the lake: large individuals were restricted to deeper areas, while young and small individuals were more abundant in shallow areas where there was preferential recruitment. Natural mortality was strikingly size dependent and P. nobilis suffered high natural mortality during the first year of life; the probability of death by natural causes quickly diminished as the fan mussels grew in size. No depth-related differences in natural mortality were found.     

Benthic and pelagic fish biomass of the upper continental slope off eastern Tasmania

Benthic and pelagic fishes were sampled east of Maria Island, Tasmania, at two-monthly intervals from April 1984 to June 1985, from the surface to the bottom (500 m depth), using commercial-sized trawls. Biomass was calculated by the area swept/volume filtered method and divided by estimated catchability coefficients so that catches from the two sampling gears could be combined. Of the 54 families caught, three (Myctophidae, Squalidae, Sternoptychidae) contributed 25% of the 115 species. Most benthic and dispersed species were caught regularly, whereas most pelagic species occurred only occasionally and in low numbers, although a core group was always present. Total fish biomass was high (range=77 to 532 g m^-2; x= 390 g m^-2), due almost entirely to the myctophid Lampanyctodes hectoris (over 90% of the biomass). Benthic biomass was relatively low and stable, but derived from many species. Pelagic biomass was high, fluctuated widely and was composed of a few species. Biomass was highest in summer: Maurolicus muelleri increased by a factor of 200, Diaphus danae by 50, and L. hectoris, Macruronus novaezelandiae and Lepidorhynchus denticulatus by almost 10. Peaks in biomass may correlate with the interactions of the subtropical convergence and the East Australian Current and the resultant marked seasonal cycle in water temperature, nutrients and primary productivity.With an appendix by T.J. Kenchington, CSIRO Division of Fisheries, Hobart, Tasmania 7001, Australia     

Lethal effects of Northwest Atlantic Ocean isolates of the dinoflagellate, Scrippsiella trochoidea, on Eastern oyster (Crassostrea virginica) and Northern quahog (Mercenaria mercenaria) larvae

The thecate dinoflagellate Scrippsiella trochoidea is a cosmopolitan, bloom-forming alga that has been generally considered non-toxic. Here, we report that environmentally relevant cell densities (10⁴ cells mL⁻¹) of Scrippsiella trochoidea strains isolated from the Northwest Atlantic Ocean caused 100% mortality in Eastern oyster (Crassostrea virginica) larvae during 3-day exposures while parallel control larvae exhibited 100% survival. S. trochoidea also exhibited lethal effects on Northern quahog (Mercenaria mercenaria) larvae (70% mortality during 3-day exposure) but were non-toxic to juvenile fish (Cyprinodon variegates). The cultures of S. trochoidea were more lethal to Northern quahog larvae than ten other species of harmful algae, including the highly toxic species Cochlodinium polykrikoides. Scrippsiella trochoidea cultures within later stages of growth were more toxic than exponential growth stages to bivalve larvae, and the toxicity was dose dependent. Furthermore, toxicity was maintained in the cultures that were sonicated, boiled, and frozen as well as in resuspended residues of the culture but was significantly lower in cell-free culture media. Collectively, these results suggest that S. trochoidea causes mortality in bivalve larvae through a physicochemical rather than strictly chemical mechanism, such as clogging of larval feeding apparatuses by materials produced by S. trochoidea (e.g., lipids, extracellular polysaccharides, and/or cell debris) which accumulate as cells in culture or blooms age. This is the first report of the lethal effects of Scrippsiella trochoidea on shellfish larvae.     

The role of turbidity as a constraint on predator-prey interactions in aquatic environments

Many of the world's most productive aquatic ecosystems usually contain turbid water. Paradoxically, many fish species that live in these habitats are also those that often rely on vision to detect their predators and their prey. For these fish, turbidity will reduce the distance at which predator-prey interactions occur, and there should be a reduction in the opportunity for behavioural modification to control the risk of predation. Under these conditions, we predict that most antipredator behaviour will become ineffective and that predator-prey interactions in turbid water will be primarily characterised by the direct effects of predator consumption of prey, rather than behavioural modification reducing the growth rates of prey. This hypothesis was tested in two laboratory experiments. The first experiment investigated how water turbidity, risk of predation, and their interaction affect habitat choice decisions by fathead minnows (Pimephales promelas). These data demonstrate that fathead minnows reduce their use of dangerous habitats, but that this effect is diminished in turbid water. A second experiment examined mortality patterns when these fish were preyed upon by yellow perch (Perca flavescens) in clear and turbid water. Absolute mortality rates were unaffected by visibility, but patterns of mortality were random in turbid water and skewed towards smaller individuals in clear water. Combined, these results support our hypothesis and suggest that the impact of predation risk will be reduced in turbid aquatic ecosystems. Received: 23 May 1996 / Accepted after revision: 18 November 1996     

Evidence for a water-borne cue inducing metamorphosis in the dorid nudibranch mollusc Adalaria proxima (Gastropoda: Nudibranchia)

The dorid nudibranch Adalaria proxima (Alder & Hancock) is a specialist predator of the cheilostome bryozoan Electra pilosa (L.). Natural induction of metamorphosis of the pelagic lecithotrophic larva of A. proxima was assessed in response to solutions from sonicated prey tissue and (live) E. pilosa-conditioned seawater (Electra-CSW). We exploited the tendency of larvae to become entrapped (rafted) at the air-water interface in cultures to examine whether larvae require direct contact with the live prey for metamorphosis to proceed. Larvae metamorphosed when rafted above colonies of live E. pilosa, above plankton mesh bags isolating live E. pilosa, and in choline chloride controls; there was no metamorphosis of larvae that were rafted in filtered seawater controls. Entrapped veliger shells remained rafted throughout the experimental period in all cases. No metamorphosis occurred in treatments containing either the supernatants or pelleted particulates obtained from sonicated colonies of E. pilosa. Both one-colony and three-colony Electra-CSW induced metamorphosis of larvae. These data are at variance with previous results in showing that direct contact with the live prey is not necessary for metamorphosis to proceed. Furthermore, the fact that competent larvae metamorphosed in response to Electra-CSW in the absence of any other cue strongly suggests that the inductive cue is water-borne.     

Dynamics and biological cycle of a Melinna palmata (Ampharetidae) population during the recolonisation of a dredged area in the vicinity of the harbour of Brest (France)

The reproductive cycle and growth parameters were studied in a Melinna palmata population, for 3 yr after dredging, in the vicinity of the harbour of Brest, France. This species first settled in May 1979, 8 mo after dredging had ceased. Measurements of the diameter of coelomic oocytes indicated that spawning took place from August to October and settlement in autumn and early winter. The first settled cohort displayed a high growth rate (0.25 mm width mo^-1 in summer) and a low longevity (22 mo); the growth rate of the second settled cohort was not significantly different from the first, but its longevity was higher (28 mo); the third settled cohort had a lower growth rate (0.15 mm width per month), but lower mortality and therefore a longer life expectancy. A fourth cohort appeared in August 1981 but was not followed because of the termination of the study. M. palmata colonised the dredged area in two ways: by settlement of juveniles in autumn and by probable immigration of young and adults in May. The population increased in number and biomass from the end of dredging (August, 1978) to June 1981 and decreased after this period. The demographic strategy of this species changed from r- to K-selection during this recolonization as a result of intraspecific and interspecific competition.     

RNA:DNA ratios and growth of herring (Clupea harengus) larvae reared in mesocosms

Autumn-spawned North Sea herring larvae (Clupea harengus L.) were released in two outdoor mesocosms of 2500 m³ (A) and 4000 m³ (B). The mesocosms were monitored for temperature, salinity, oxygen, chlorophyll a, zooplankton and herring larvae abundance. The density of suitable prey for first feeding larvae (mainly copepod nauplii) was initially low in Mesocosm A (<0.11^-1) compared to in Mesocosm B (>11^-1). Half-way through the experiment the situation was reversed, with higher densities of prey in Mesocosm A (>31^-1) as compared to Mesocosm B (11^-1). The average temperature declined steadily in both mesocosms from 18°C at release to 11–12°C by the end of the experiment 60 d later. The RNA:DNA values of individual herring larvae were related to protein growth rates and temperature adjusted according to Buckley (1984). A corresponding DNA growth index (Gdi) was given as: Gdi=0.68 TEMP+3.05 RNA:DNA-9.92. The RNA:DNA based growth indices were significantly correlated with other somatic growth estimates. The average estimated protein growth rate in the two mesocosms followed the same temporal pattern as the somatic growth rate, but with a lag of 2 d or more. Residual analysis of the regression of ln RNA versus ln DNA also showed the same temporal pattern as the RNA:DNA ratios, but the shift in condition as estimated by this method occurred more in synchrony with the other somatic growth measures. Larvae in Mesocosm A had RNA:DNA values similar to the starvation control kept in the laboratory the first days after release, confirming that larvae in Mesocosm A initially were in poor nutritional condition. On the other hand, the majority of the herring from Mesocosm B were characterised as starving or in poor nutritional condition towards the end of the experiment. The assessment of growth and nutritional condition were in accordance with independent survival estimates which suggested that the majority of the total mortality occurred during the first 15 d in Mesocosm A and there-after in Mesocosm B.     

Mechanisms of habitat segregation between an invasive (Mytilus galloprovincialis) and an indigenous (Perna perna) mussel: adult growth and mortality

The invasive mussel Mytilus galloprovincialis and the indigenous mussel Perna perna coexist intertidally on the south coast of South Africa through partial vertical habitat segregation: M. galloprovincialis dominates the upper shore and P. perna the lower shore. Recruitment patterns can explain the zonation of P. perna, but not the invasive species. We examined the role of post-recruitment interactions by measuring spatial and temporal differences in adult growth and mortality rates of the two species. Specifically, we tested the hypothesis that interspecific differences in growth and mortality reflect adult distribution patterns. The two study locations, Plettenberg Bay and Tsitsikamma, are 70 km apart with two sites (separated by 300–400 m) per location, each divided into three vertical zones. Growth was measured seasonally using different marking methods in 2001 and 2003. Cumulative adult mortality was measured through summer in 2003/2004. Both species generally grew more slowly upshore, but they showed different effects of season. For P. perna, growth was significantly reduced in winter in the low zone, but unaffected by season in the high zone. For M. galloprovincialis, growth was either unaffected by season or increased in winter, even in the high zone. Thus, growth of P. perna and M. galloprovincialis was reduced under cool winter and warm summer temperatures, respectively; and while growth was more similar between species in summer, M. galloprovincialis grew much faster than P. perna in winter. Mortality of P. perna increased upshore. For M. galloprovincialis, mortality was not zone-dependent and was significantly greater than for P. perna on the low-shore and (generally) across the shore in Tsitsikamma. Both species had higher growth and mortality rates in Plettenberg Bay than in Tsitsikamma. Thus, P. perna seems able to maintain spatial dominance on the low-shore and at certain sites because of higher mortality of M. galloprovincialis. We conclude that seasonality in growth of the two species reflects their biogeographic affinities and that coexistence is possible through pre-recruitment effects that limit the vertical distribution of P. perna and post-recruitment effects that limit M. galloprovincialis.     

Clam predation by whelks (Busycon spp.): Experimental tests of the importance of prey size,prey density,and seagrass cover

In 57 l-m² samples within a meadow of Halodule wrightii in Bogue Sound, North Carolina, USA, densities of the clams Mercenaria mercenaria and Chione cancellata were positively associated with seagrass cover. Where seagrass was experimentally removed, marked individuals of both clam species exhibited high rates of mortality in fine sand sediments during two successive experiments spanning 13 months. In the unaltered (control) seagrass meadow, M. mercenaria density remained constant over 13 months and C. cancellata density declined at a slower rate than in the unvegetated plots. Seagrass provides these clams with a refuge from whelk (Busycon carica, B. contrarium, and B. canaliculatum) predation, the major cause of mortality and population decline in experimentally unvegetated plots. In 2 factorial field experiments in unvegetated substratum in which densities of M. mercenaria and C. cancellata were varied independently, first over 5 levels (0 X, 1/2X, 1 X, 2 X, 4 X) and subsequently over 4 levels (0 X, 1/4 X, 1 X, 4 X), there was no repeatable intra- or interspecific effect of density on percent survival, or on the rate of any mortality type. Whelk predation fell preferentially on larger size classes of both species, whereas factors which contribute to clam disappearance usually acted more intensely on smaller sizes. Experimental exclusion of large predators by caging demonstrated that even in unvegetated substratum survivorship of both clam species was high in the absence of whelks and other predators. Individuals of C. cancellata live closer to the sediment surface than those of M. mercenaria, which may explain why seagrass does not serve as effectively to protect them from whelk predation. The mechanism of whelk inhibition may depend upon sediment binding by the H. wrightii root mat, which produces a demonstrable decrease in the physical penetrability of surface sediments.     

马拉硫磷及其水解产物对圆瘤浮萍的生长抑制及氧化损伤作用

为了探讨马拉硫磷和主要水解产物对圆瘤浮萍的生长抑制作用及可能的氧化损伤机制,采用静态培养法,研究不同浓度的马拉硫磷及其水解产物二甲基二硫代磷酸酯(DMDTP)、二甲基硫代磷酸酯(DMTP)、二甲基磷酸酯(DMP)对圆瘤浮萍生长、叶绿素含量、叶绿体活性、超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性及丙二醛(MDA)含量的影响。结果表明,暴露7 d后,浓度为100 mg a.i.·L-1处理下的浮萍叶状体生长量与空白对照组无显著性差异;DMDTP、DMTP和DMP对圆瘤浮萍叶状体生长量的半数抑制浓度(7 d-IC50)分别为52.9、45.5和98.0 mg a.i.·L-1。随着试验液中DMDTP、DMTP和DMP浓度的升高,圆瘤浮萍叶绿素含量均明显降低,叶绿体活性则分别表现为诱导-抑制、抑制和抑制效应。在DMDTP、DMTP和DMP胁迫下,脂质过氧化产物丙二醛(MDA)含量明显增加;圆瘤浮萍体内的抗氧化酶系统均受到影响。总体表现为随着DMDTP浓度的增加,SOD活性先降低后升高;DMTP和DMP胁迫下,SOD活性呈现先降后升再降的趋势;POD和CAT活性则随3种水解产物浓度的增加呈现先升后降趋势;这表明抗氧化酶系统对外部胁迫的应答很复杂。马拉硫磷对圆瘤浮萍的毒性较小,其水解产物DMDTP、DMTP和DMP均对圆瘤浮萍的生长产生一定的毒性作用。在实际生产中,应多加关注马拉硫磷水解产物对环境生物的风险评估。