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1.
Gelatinous plankton is an important food resource for several species of fishes in the Southwestern Atlantic Ocean. Some fish depend heavily on these organisms and are specialized to feed on ctenophores, salps and medusae, while others only consume gelatinous plankton occasionally. We hypothesize that consumption of gelatinous plankton by fishes represents an alternative food resource when primary prey are not available during cold periods in the study area. To determine seasonal variations of gelatinous plankton consumption by fishes, data samples were grouped into cold and warm periods. A total of 64,567 stomachs belonging to 106 species of fish were analysed, of which 32,943 (51%) contained food items. Of those containing food items, 2719 (8.2%), from 38 fish species, contained gelatinous items. Fourteen species ingested gelatinous in warm period, nine in cold period, and 15 in both periods. The proportion of stomachs with gelatinous was significantly greater during the cold period. Ctenophores were the most predominant prey in both periods, followed by salps and medusae. Consumption of ctenophores, salps and medusae was unevenly distributed within the area during the different periods. Classification methods (group average sorting utilizing Bray–Curtis similarity measures based on log (X + 1) identified eight areas of consumption. SIMPER (similarity percentages) analyses revealed that nine fish species contributed most to gelatinous plankton consumption. The seasonal and spatial variation of gelatinous consumption by fish would be related to the availability of food in each period. Strategies of gelatinous consumption, including survival, feeding opportunities and prey specialization, are discussed.  相似文献   

2.
Cyanobacteria blooms are an increasing problem in temperate freshwater lakes, leading to reduced water quality and in some cases harmful effects from toxic cyanobacteria species. To better understand the role of zooplankton in modulating cyanobacteria blooms, from 2008 to 2010 we measured water quality and plankton abundance, and measured feeding rates and prey selectivity of the copepod Diacyclops thomasi before, during and following summertime cyanobacteria blooms in a shallow, eutrophic lake (Vancouver Lake, Washington, USA). We used a combined field and experimental approach to specifically test the hypothesis that copepod grazing was a significant factor in establishing the timing of cyanobacteria bloom initiation and eventual decline in Vancouver Lake. There was a consistent annual succession of zooplankton taxa, with cyclopoid copepods (D. thomasi) dominant in spring, followed by small cladocerans (Eubosmina sp.). Before each cyanobacteria bloom, large cladocerans (Daphnia retrocurva, Daphnia laevis) peaked in abundance but quickly disappeared, followed by brief increases in rotifers. During the cyanobacteria blooms, D. thomasi was again dominant, with small cladocerans abundant in autumn. Before the cyanobacteria blooms, D. thomasi substantially consumed ciliates and dinoflagellates (up to 100% of prey biomass per day), which likely allowed diatoms to flourish. A shift in copepod grazing toward diatoms before the blooms may have then helped to facilitate the rapid increase in cyanobacteria. Copepod grazing impact was the highest during the cyanobacteria blooms both years, but focused on non-cyanobacteria prey; copepod grazing was minimal as the cyanobacteria blooms waned. We conclude that cyclopoid copepods may have an indirect role (via trophic cascades) in modulating cyanobacteria bloom initiation, but do not directly contribute to cyanobacteria bloom decline.  相似文献   

3.
This study quantifies the occurrence of gelatinous zooplankton in the stomach contents of fishes from the southwest Atlantic Ocean (33°–55°S). More than 69,000 fish stomachs belonging to 107 species were examined. A total of 39 fishes were documented as consumers of gelatinous zooplankton, 23 of which were newly discovered. Three gelatinous organism consumption categories are recognized: (1) very frequent consumers (10 species, six of which were exclusive); frequent consumers (five species); and occasional consumers (26 species). Three types of gelatinous prey (ctenophores, salps and medusae) were found in the stomach contents of fishes. Ctenophores were consumed at high levels across almost the entire continental shelves of Argentina and Uruguay. Salps were frequent prey on the slope and southern shelf. In contrast, medusae were consumed in coastal areas, slopes and the southern shelf. Classification methods (group average sorting of the Bray–Curtis similarity measures based on log (X?+?1)-transformed percentage data) determined six areas where fishes predated on gelatinous organisms. SIMPER (similarity percentages) analysis determined which fishes contributed more to the consumption of gelatinous organisms. Results revealed that two fish species (Stromateus brasiliensis and Squalus acanthias) had high gelatinous zooplankton predation rates throughout the entire study area, while another six species (Patagonotothen ramsayi, Helicolenus dactylopterus lahillei, Macrourus holotrachys, Merluccius hubbsi, Schroederichthys bivius, and Macruronus magellanicus), while widely distributed, seemed to have specific areas where consumption occurred. This study not only provides new knowledge about the importance of gelatinous zooplankton in the diet of numerous fishes, but might also be valuable for planning and managing local fisheries.  相似文献   

4.
Abstract. Medusae were the earliest animals to evolve muscle‐powered swimming in the seas. Although medusae have achieved diverse and prominent ecological roles throughout the world's oceans, we argue that the primitive organization of cnidarian muscle tissue limits force production and, hence, the mechanical alternatives for swimming bell function. We use a recently developed model comparing the potential force production with the hydrodynamic requirements of jet propulsion, and conclude that jet production is possible only at relatively small bell diameters. In contrast, production of a more complex wake via what we term rowing propulsion permits much larger sizes but requires a different suite of morphological features. Analysis of morphometric data from all medusan taxa independently confirms size‐dependent patterns of bell forms that correspond with model predictions. Further, morphospace analysis indicates that various lineages within the Medusozoa have proceeded along either of two evolutionary trajectories. The first alternative involved restriction of jet‐propelled medusan bell diameters to small dimensions. These medusae may be either solitary individuals (characteristic of Anthomedusae and Trachymedusae) or aggregates of small individual medusan units into larger colonial forms (characteristic of the nectophores of many members of the Siphonophorae). The second trajectory involved use of rowing propulsion (characteristic of Scyphozoa and some hydromedusan lineages such as the Leptomedusae and Narcomedusae) that allows much larger bell sizes. Convergence on either of the differing propulsive alternatives within the Medusozoa has emerged via parallel evolution among different medusan lineages. The distinctions between propulsive modes have important ecological ramifications because swimming and foraging are interdependent activities for medusae. Rowing swimmers are characteristically cruising predators that select different prey types from those selected by jet‐propelled medusae, which are predominantly ambush predators. These relationships indicate that the different biomechanical solutions to constraints on bell function have entailed ecological consequences that are evident in the prey selection patterns and trophic impacts of contemporary medusan lineages.  相似文献   

5.
Calanoid copepods possess remarkable abilities to detect andescape from hydrodynamic disturbances, such as those createdby approaching predators. At the same time, a number of studiesin coastal ecosystems have suggested that gelatinous predators,including medusae in the Class Scyphozoa, exert top-down controlon copepod populations. Although prey escape behavior playsa critical role in predation models, we have relatively littleempirical data on how copepods respond to encounters with scyphomedusae.In this study, I used video to quantify encounter rates andescape behaviors of the copepod Acartia hudsonica during interactionswith two scyphomedusae, Aurelia aurita and Cyanea sp., in twoflow regimes. Escapes were complex, variable and effective.Fewer than 1% of encounters resulted in ingestion. Typically,A.hudsonica avoided contact by responding when predators remainedseveral body lengths (4 to 10 mm) distant and stringing togethermany escape jumps at submaximum velocities (33 to 59 mm s–1).In addition, copepodite stages behaved passively—or failedto respond—following encounters with medusae more oftenthan did adults. Because escape behavior exhibited by A.hudsonicawas so variable, it is unlikely that medusae capture copepodsusing a single, quantifiable mechanism. A range of responseswithin populations and individuals may be the best strategyfor zooplankton faced with strong predation pressure from avariety of predators.  相似文献   

6.
Since the canids and felids diverged in the mid‐Eocene or earlier, each family has developed a suite of morphological and behavioural adaptations for obtaining and consuming prey. We here distinguish between prey taxa captured and eaten as a result of these phylogenetic adaptations, and those because they are fortuitously encountered, and argue that such supplementary prey, often opportunistically caught, create a buffer between sympatric, and potentially competitive, canids and felids and thus enhance coexistence. We base our analysis on dietary data derived from the stomach contents of four sympatric canid and felid species in the Free State Province, South Africa (canids: Cape fox Vulpes chama and black‐backed jackal Canis mesomelas; felids: African wild cat Felis silvestris lybica and caracal Caracal caracal), and from results of studies on these species elsewhere in southern Africa. The two canid species preyed heavily on invertebrates, and thus opportunistically, while the felids (especially the caracal) concentrated on mammals, prey they are phylogenetically adapted to capture. Only three species of mammalian prey are shared by the four species. The ratio of opportunistically‐to‐phylogenetically mediated prey taxa used (the O/P ratio) differ between the species, with the black‐backed jackal having the most opportunistically caught taxa in its diet, and the caracal the least. As predicted, a comparison of this data with those from dietary studies of the same species carried out elsewhere indicates that the number of opportunistically obtained prey taxa varies more than those resulting from phylogenetic adaptations. The largest canid had the widest food spectrum (35 prey taxa) while the smallest felid had the most restricted one (11 prey taxa). We argue that using the O/P distinction allows a better understanding of changes in food niche breadth of particular species, especially in xeric areas, and gives a better indication of possible exploitative competition for food by sympatric carnivores than when regarding all prey taxa as actively pursued. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83 , 527–538.  相似文献   

7.
Algal blooms commonly occur along the South African west coast. In March 1994 a dense bloom developed within St Helena Bay. Its subsequent decay caused near-shore hypoxia and elevated hydrogen sulphide levels, leading to it being termed a ‘black tide’. The bloom caused immediate massive intertidal mortalities (95% reduction of biomass), significant changes in community structure, and declines in richness and diversity. Only four taxa were not diminished: ephemeral algae, the gastropod Afrolittorina knysnaensis, the anemone Bunodactis reynaudi and the false limpet Siphonaria capensis. This limpet species subsequently increased at impacted sites relative to controls, probably reflecting reduced competition from other grazers. Ephemeral algae flourished during early recolonisation while grazers were depleted, but declined as grazers re-established. Manipulative experiments demonstrated that grazers do have this capability. Perennial algae also flourished, but lagged behind ephemerals, possibly contributing to their decline. Predators took longest to recover. Differences in the responses of species reflect differing tolerances, zonation patterns and biological interactions. Communities at control sites remained unchanged over the four-year study, and those exposed to a low intensity of the bloom were little affected, but communities exposed to its full intensity failed to recover fully within four years. Increasing frequency of harmful algal blooms along the west coast of South Africa could, therefore, significantly alter rocky-shore communities if intervals between bloom events become shorter than recovery times.  相似文献   

8.
Larson  R. J.  Mills  C. E.  Harbison  G. R. 《Hydrobiologia》1991,216(1):311-317
Little is known about the biology and ecology of mesopelagic medusae. In part, this is because midwater trawls are used to collect fragile medusae and other gelatinous macroplankton. Additionally, nets cannot provide data on behavior and on biotic associations. Herein, in situ observations on northwestern Atlantic midwater medusae made using the Johnson-Sea-Link submersibles are reported. Included are depth and temperature ranges; notes on pigments; locomotory behavior; and notes on prey and predators.  相似文献   

9.
Gut content analyses on field-caught Aurelia aurita showed bothquantitative and qualitative change in diet as a function ofmedusa size. Larger medusae tended towards greater numbersand diversity of prey (up to 1550 individual prey representingas many as 13 different prey groups). We also found that medusasize was a good predictor of prey diversity recovered from themedusa gut. While a shift toward greater prey diversity inlarger medusae might be explained by increased contact rateswith 'rare' prey taxa, we also found size-based prey selectivitychanges in A. aurita. We used in situ gut content data to describeselectivity by A. aurita for three prey types representing varyingdegrees of swimming or escape velocity. Fish eggs were usedas a non-swiming prey, and small (  相似文献   

10.
A cladistic analysis of Capitata groups the families in four suborders based on medusa characters (such as manubrium morphology, position of gonads, and position and number of marginal tentacles) and hydroid characters (such as presence or absence of an oral tentacle whorl, and the different development of the tentacles of the oral and aboral whorls). On the family and generic levels, the revision results in changes which unite the separate hydroid and medusa taxonomic systems, defining genera which are not based on characters solely relating to the reduction of medusae to fixed gonophores. In those families where the reduction of the medusa can be analysed, it is shown that the reduction occurred after all synapomorphies defining the genera had evolved and usually affected individual species within a genus rather than the original species from which the other species in the genus evolved. This supports the view that medusa reduction is not in itself a valid generic character. A discussion of the theories of 'inconsistent' or 'mosaic' evolution concludes that no difference in evolutionary rate or degree of specialization can be demonstrated among taxa with free medusae and taxa with gonophores.  相似文献   

11.
Range expansions of species comprise a pervasive environmental problem worldwide and can cause substantial ecological and economic impact. However, the magnitude of impact may vary across habitats, highlighting the need to account for spatial heterogeneity in assessment studies. Here we compare invertebrate community structure in three habitats (littoral, sublittoral, and profundal) of boreal lakes that suffer recurring blooms of a regionally expanding, nuisance flagellate, Gonyostomum semen (Raphidophyta), with the assemblage structure in lakes were no blooms occur. We contrast community structure over a 6-year period using univariate metrics (total abundance, community evenness, species richness, and Simpson diversity) and multivariate community similarity to infer habitat-specific associations of local (alpha) diversity. We also calculated indices of multivariate dispersion to infer associations with beta diversity; i.e., whether or not habitats in bloom lakes show faunal homogenisation. Results show that the magnitude of assemblage alteration in bloom relative to bloom-free lakes varied with habitat and increased from the littoral to the profundal habitats. Littoral assemblages in bloom and bloom-free lakes shared similar alpha (taxon richness, evenness and Simpson diversity) and beta diversity characteristics, despite differing in multivariate community similarity. By contrast, alteration of assemblage structure was most severe in the profundal and manifested in reduced diversity and faunal homogenisation (i.e. decreased beta diversity) in bloom relative to bloom-free lakes. This was due to numerical dominance of the predatory phantom midge, Chaoborus flavicans, in the profundal of bloom lakes. Not only do the results highlight that spatial heterogeneity should be accounted for to assess the potential broader impact of nuisance species on biodiversity within lakes; more generally, the dominance of a single species suggests a reduced overall resilience of bloom lakes, making them more susceptible to environmental perturbation.  相似文献   

12.
Blooms of freshwater cyanobacteria are a worldwide spread environmental issue. Despite toxin producing planktonic species are generally expected to be poor competitors for resources, dense blooms of toxic cyanobacteria, such as Microcystis, do often occur in nature. Experimental results suggest that the formation of such blooms is promoted by the predatory activity of zooplankton. In fact, such predator grazes on both the nontoxic and toxic species despite the toxicity of the latter actually inhibits its growth. We model this phenomenon through a Lotka–Volterra reaction–diffusion system. Our goal is to investigate the coupled role of toxicity and zooplankton's predation in the persistence of the toxic prey and to study the mechanisms behind the formation of spatially local toxic blooms. It is known that the classical Lotka-Volterra system consisting of one prey and one predator never exhibits pattern formation. In this paper, we show that the introduction of a toxic prey may destabilize the spatially homogeneous coexistence and trigger spatial pattern formation. We also show that local blooms more likely occur when predators avoid the toxic prey and when the strength of the toxicity is of an intermediate level.  相似文献   

13.
Population dynamics and evolutionary dynamics can occur on similar time scales, and a coupling of these two processes can lead to novel population dynamics. Recent theoretical studies of coevolving predator-prey systems have concentrated more on the stability of such systems than on the characteristics of cycles when they are unstable. Here I explore the characteristics of the cycles that arise due to coevolution in a system in which prey can increase their ability to escape from predators by becoming either significantly larger or significantly smaller in trait value (i.e., a bidirectional trait axis). This is a reasonable model of body size evolution in some systems. The results show that antiphase population cycles and cryptic cycles (large population fluctuation in one species but almost no change in another species) can occur in the coevolutionary system but not systems where only a single species evolves. Previously, those dynamical patterns have only been theoretically shown to occur in single species evolutionary models and the coevolutionary model which do not involve a bi-directional axis of adaptation. These unusual dynamics may be observed in predator-prey interactions when the density dependence in the prey species is strong.  相似文献   

14.
Phytoplankton (including plant-like, animal-like algae and Cyanobacteria) blooms have recently become a serious global threat to the sustenance of ecosystems, to human and animal health and to economy. This study focused on the composition and stability of blooms as well as their taxa-specific ecological sensitivity to the main causal factors (especially phosphorus and nitrogen) in degraded urban lakes. The analyzed lakes were assessed with respect to the trophic state as well as ecological status. Total phytoplankton biomass (ranging from 1.5 to 181.3 mg dm−3) was typical of blooms of different intensity, which can appear during a whole growing season but are the most severe in early or late summer. Our results suggested that steady-state and non-steady-state bloom assemblages including mono-, bi- and multi-species or heterogeneous blooms may occur in urban lakes. The most intense blooms were formed by the genera of Cyanobacteria: Microcystis, Limnothrix, Pseudanabaena, Planktothrix, Bacillariophyta: Cyclotella and Dinophyta mainly Ceratium and Peridinium. Considering the sensitivity of phytoplankton assemblages, a new eco-sensitivity factor was proposed (E-SF), based on the concept of Phytoplankton Trophic Index composed of trophic scores of phytoplankton taxa along the eutrophication gradient. The E-SF values of 0.5, 1.3, 6.7 and 15.1 were recognized in lakes having a high, good, moderate or poor ecological status, respectively. For lake restoration, each type of bloom should be considered separately because of different sensitivities of taxa and relationships with environmental variables. Proper recognition of the taxa-specific response to abiotic (especially to N and P enrichment) and biotic factors could have significant implications for further water protection and management.  相似文献   

15.
Male–male fighting (MMF) in snakes is a sexually dimorphic trait in adults that is expressed during breeding periods and confers reproductive advantages to winners. This trait, however, is not ubiquitous among the approximately 2,700 species of extant snakes, and past research shows evidence of taxonomic trends. We evaluated the phylogenetic distribution of MMF in extant snakes using two previously published estimates of snake evolutionary history. We clearly identified multiple independent gains and losses of MMF in snakes and phylogenetically important taxa for which information on MMF is lacking. We followed this with two tests of the association of MMF with mode of prey capture using the concentrated-changes test (CCT) of Maddison (1990), and a third test using the subtree decomposition method of Read and Nee (1995). In the CCT analyses, first we tested whether MMF was randomly distributed with respect to mode of prey subjugation in snake lineages. This hypothesis was rejected, with MMF being significantly more concentrated in taxa that subjugate prey by constriction and/or envenomation. Second, we tested a more temporally exact hypothesis: whether changes in state of MMF were randomly distributed with respect to occurrences of state changes in mode of prey subjugation. Results of this test depended on the exact test parameters used. In general, however, this hypothesis also was rejected, suggesting that loss of constriction and/or envenomation typically results in loss of MMF, or vice versa. Last, the subtree decomposition test indicated a significant correlation between evolution of MMF and evolution of constriction and/or envenomation as the primary mode of prey subjugation. We propose that the relationship between these states is not causal but results from both characters being independent adaptations to energy resource scarcity. Received in revised form: 20 March 2001 Electronic Publication  相似文献   

16.
A growing number of studies correlate changes in zooplanktonpopulations with abundance of medusae, but we cannot yet explainor predict the specific factors driving these interactions.This study demonstrates that the size of copepods has a significantinfluence on their vulnerability to predation by scyphomedusae.This finding is important because prey size, independent ofbehavior, has been neglected in theoretical models of predationby medusae. In experiments in a planktonkreisel, we used liveand heat-killed prey (Acartia hudsonica adults and copepodites)to separate the effects of copepod size and behavior on feedingrates by two medusae (Aurelia aurita and Cyanea sp.). Resultsrevealed that: differences in copepod size had a significantimpact on feeding rates, and thus small size can provide a refugefrom predation; behavior of adults diminished the liabilityassociated with larger size; and medusae with different morphologiesingested A.hudsonica at similar rates. Other experiments demonstratedthat medusae digested copepods at different rates based on preysize and predator species, findings that have implications forall future laboratory and field studies that assess feedingby scyphomedusae. Finally, this study illustrates how laboratorystudies serve as critical supplements to field observations.The effect of prey size on feeding rates can be confounded bydifferences in prey behavior, yet explains why small copepodswere typically ingested at relatively low rates by medusae.Size was clearly a dominant factor influencing copepod vulnerabilityacross scyphomedusan species, even those with very differentmorphologies. Future work should focus on the mechanisms ofsize selection, or the factors influencing contact and retentionrates.  相似文献   

17.
Watermass stratification has been considered the essential physical condition that dinoflagellates require to bloom because of their relative inability, unlike diatoms, to tolerate the elevated shear-stress associated with water-column mixing, turbulence and high velocity, coastal currents. The swimming speeds of 71 flagellate taxa, with a focus on dinoflagellates, are compared to the turbulence fields and vertical velocities that develop during representative wind conditions, upwelling and at frontal zones. The results suggest that the classical stratification–dinoflagellate bloom paradigm needs revision. Tolerance of turbulence, growth within well-mixed watermasses and survival and dispersal while entrained within current systems are well developed capacities among dinoflagellates. Their secretion of mucous, often copious during blooms, is suggested to be an environmental engineering strategy to dampen turbulence. Biophysical tolerance of turbulence by dinoflagellates is often accompanied by high swimming speeds. Motility speeds of many species exceed in situ vertical current velocities; this also allows diel migrational patterns and other motility-based behavior to persist. Species belonging to “mixing-drift” life-form assemblages can increase their swimming speeds through chain formation, which helps to compensate for the increased turbulence and vertical water-column velocities of their habitats. The ability of dinoflagellate species to tolerate the vertical velocities of offshore, frontal zones, where abundant populations often develop, suggests that fronts may serve as “pelagic seed banks”, occurring as pelagic analogues of nearshore seed beds, from which seed stock is dispersed. The different ecologies associated with the hypothesized, “pelagic seed banks” of vegetative cells and the “seed beds” of resting stage cells deposited onto sediments are discussed. There is a contradiction in the stratification–HAB paradigm: the quiescent conditions of a stratified watermass, with its characteristic nutrient-poor conditions are expected to promote stasis of the population, rather than growth and blooms. The analyses suggest that dinoflagellate blooms do not preponderate in stratified watermasses because the bloom species are biophysically intolerant of the higher velocities and turbulence of more mixed watermasses. The watermass stratification that often accompanies flagellate blooms is probably a secondary, parallel event and less essential than some other factor(s) in triggering the observed bloom.  相似文献   

18.
Dinophysis acuminata and Dinophysis acuta are recurrent species off NW Iberia but their outbreaks occur under different conditions. A decade (2004–2013) of weekly data for each species at two sentinel stations located at the entrance of Rias de Aveiro-AV (NW Portugal, 40°38.6′ N) and Pontevedra-PO (Galicia, Spain, 42°21.5′ N), were used to investigate the regional synchronism and mesoscale differences related to species detection, bloom (>200 cells L−1) initiation and development. Results highlight the high interannual variability of bloom events and summarize the associated meteorological/oceanographic conditions. D. acuta blooms were observed in 2004–2008 and 2013, and the species highest maxima at AV occurred after the highest maxima of its prey Mesodinium, with a time-lag of 2–3 weeks. D. acuminata blooms were observed every year at both stations. The cell concentration time series shows that the blooms generally present a sequence starting in March with D. acuminata in PO and three weeks later in AV, followed by D. acuta that starts at AV and three months later in PO. Exceptionally, D. acuminata blooms occurred earlier at AV than PO, namely in high spring upwelling (2007) or river runoff (2010) years. A four-year gap (2009–2012) of D. acuta blooms occurred after an anomalous 2008 autumn with intense upwelling which is interpreted as the result of an equatorward displacement of the population core. Numerical model solutions are used to analyze monthly alongshore current anomalies and test transport hypotheses for selected events. The results show a strong interannual variability in the poleward/equatorward currents associated with changes in upwelling forcing winds, the advection of D. acuta blooms from AV to PO and the possibility that D. acuminata blooms at AV might result from inocula advected southward from PO. However, the sensitivity of the results to vertical position of the lagrangian tracers call for more studies on species distribution at the various bloom stages.  相似文献   

19.
Reflections on the ballast water dispersal—harmful algal bloom paradigm   总被引:1,自引:0,他引:1  
The ballast water dispersal—HAB paradigm, increasingly invoked circumstantially to explain puzzling and unaccountable HAB species outbreaks when lacking the multiple tests of confirmation recommended by Bolch and de Salas (2007), is evaluated. The types and examples of natural dispersions and taxon cycles are compared to exotic species bloom behavior linked to ballast water vectoring. The regional spreading, bloom behavior and disjunct distributions of the brown tide pelagophyte Aureococcus anophagefferens and the toxic dinoflagellate Gymnodinium catenatum, attributed to ballast water vectoring, are used as representative examples to evaluate the general application of the ballast water—HAB paradigm and associated interpretative problems. Human-aided emigration has a seeding and colonization ecology that differs from bloom ecology. For self-sustaining blooms to occur, these two ecologies must be accommodated by habitat growth conditions. The three stages that a non-native species must pass through (pioneering, persistence, community entry) to achieve colonization, community maintenance, and to bloom, and the niche-related factors and role of habitat disturbance are discussed. The relevance of cryptic occurrences, cyst deposits, dormancy periods and bloom rhythms of HAB species to their blooms attributed to ballast water-assisted introductions is also sketched. The different forms of HAB species rarity, their impact on the ballast water dispersal—HAB paradigm, and the dispersion and blooms of specialist and generalist HAB species are discussed. The remarkable novel and, often, monospecific blooms of dinoflagellate HAB species are being paralleled by similar eruptive bloom behavior cutting across phylogenetic lines, and being found also in raphidophytes, haptophytes, diatoms, silicoflagellates, etc. These blooms cannot be explained only as seeding events. An ecological release of ‘old barriers’ appears to be occurring generally at coastal bloom sites, i.e. something significant is happening ecologically and embedded within the ballast water—HAB paradigm. There may be a relationship between Life Form type [Smayda, T.J., Reynolds, C.S., 2001. Community assembly in marine phytoplankton: application of recent models to harmful dinoflagellate blooms. J. Plankton Res. 23, 447–461] and mode of expatriation; HAB dinoflagellate species commonly reported to produce ballast water-assisted toxic blooms invariably are members of cyst-producing Life Forms IV, V, VI. Ballast water vectoring of Life Forms I, II, III is rarely reported, even though many produce cysts, and where their novel introductions do occur they are more likely to be ichthyotoxic and vectored in shellfish stock consignments. The relevance of, and need to distinguish between morphospecies and their geographic/ribotype clades are discussed based on the Alexandrium tamarense/catenella/fundyense complex. Morphospecies-level ballast water dispersions are probably minor compared to the dispersal of the different ribotypes (toxic/non-toxic clades) making up HAB morphospecies; the redistribution and admixture of genotypes should be the focus. Ballast water-assisted expatriations impact the global occurrence of HABs through the direct transfer of previously absent species or introduction of genetic strains from the donor habitat that are ecologically favored over resident strains. The hybridization of species may be of potentially greater impact, resulting from the (1) mating of individuals from the donor and recipient habitats, or (2) through the interbreeding of strains introduced from two different donor sites into the recipient site, and whose progeny have greater ecological fitness than indigenous strains. Exceptional ecological changes of some sort appear to be occurring globally which, in combination with the genetically altered ecophysiological behavior of HAB species linked to ballast water dispersion and admixture, underpins the global HAB phenomenon. The impact of ballast water and shellfish transplantation on HABs and phytoplankton community ecology, generally, is considerably greater than the current focus on HAB species distributions, vectoring, and blooms. The methodological, investigative and conceptual potential of the ballast water—HAB paradigm should be exploited by developing a GEOHAB type intiative to advance quantification of global HAB ecology.  相似文献   

20.
The in situ behavior of three scyphomedusan species was videorecorded by scuba divers in natural daytime lighting with minimalinterference to the medusae. The mean percentage of time thatindividual medusae spent swimming ranged from 93 to 100%. Therewere no significant differences in the percent time spent swimmingbetween life stages of a species (ephyra, adult) or betweenspecies. The predominance of swimming activity by medusae indicatesthat swimming, and hence the creation of fluid motions responsiblefor prey entrainment and capture, plays a widespread functionalrole in feeding by scyphomedusae.  相似文献   

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