Planktonic Predators Research Articles

Annual boom–bust cycles of polar phytoplankton biomass revealed by space-based lidar

Polar plankton communities are among the most productive, seasonally dynamic and rapidly changing ecosystems in the global ocean. However, persistent cloud cover, periods of constant night and prevailing low solar elevations in polar regions severely limit traditional passive satellite ocean colour measurements and leave vast areas unobserved for many consecutive months each year. Consequently, our understanding of the annual cycles of polar plankton and their interannual variations is incomplete. Here we use space-borne lidar observations to overcome the limitations of historical passive sensors and report a decade of uninterrupted polar phytoplankton biomass cycles. We find that polar phytoplankton dynamics are categorized by ‘boom–bust’ cycles resulting from slight imbalances in plankton predator–prey equilibria. The observed seasonal-to-interannual variations in biomass are predicted by mathematically modelled rates of change in phytoplankton division. Furthermore, we find that changes in ice cover dominated variability in Antarctic phytoplankton stocks over the past decade, whereas ecological processes were the predominant drivers of change in the Arctic. We conclude that subtle and environmentally driven imbalances in polar food webs underlie annual phytoplankton boom–bust cycles, which vary interannually at each pole. Phytoplankton productivity is high in the polar oceans. Lidar observations from 2006–2015 reveal that phytoplankton biomass was characterized by annual cycles influenced by sea-ice extent in the Antarctic and ecological processes in the Arctic.

Acoustic surveys of euphausiids and models of baleen whale distribution in the Barents Sea

As in many high-latitude ecosystems, euphausiids (order Euphausiacea, 'krill') play a key role in the Barents Sea by channeling energy from primary producers to fish and other zoo- plankton predators. We used multifrequency acoustic data from several recent multidisciplinary surveys to describe the spatial distribution of backscatter likely to be from euphausiids. Spatial patterns in euphausiid backscatter observed in 2010, 2011, and 2012 were correlated with verti- cally integrated euphausiid biomass collected with plankton nets, and were also broadly consis- tent with the distribution of euphausiids expected from the literature. We used the high-resolution and broad-spatial coverage of our euphausiid backscatter data to update multiple regression models of baleen (fin, humpback, and minke) whale distribution to test the hypothesis that these animals aggregated where euphausiids were abundant. After controlling for physical environ- mental factors and the densities of capelin and several other potential prey taxa, we found that fin whale densities were positively and linearly associated with euphausiid backscatter, and higher than average densities of humpback whales were found in areas with high euphausiid back - scatter. No association was found between minke whales and euphausiids. Densities of all 3 whale species were also positively associated with capelin. For fin and humpback whales, the effects of capelin and euphausiids on whale densities appeared to be principally separate and additive, although there was some evidence for a stronger effect of euphausiids at low capelin densities. In terms of their preference for euphausiids and capelin, these whale species appeared to be flexible, opportunistic predators.

Planktonic predation risk: effects of diel state, season and prey life history stage

Fil: Kerr, Kecia A.. Mc Gill University; Canada. Instituto Smithsonian de Investigaciones Tropicales; Panama

The effect of habitat structure on prey mortality depends on predator and prey microhabitat use.

Structurally complex habitats provide cover and may hinder the movement of animals. In predator-prey relationships, habitat structure can decrease predation risk when it provides refuges for prey or hinders foraging activity of predators. However, it may also provide shelter, supporting structures and perches for sit-and-wait predators and hence increase their predation rates. We tested the effect of habitat structure on prey mortality in aquatic invertebrates in short-term laboratory predation trials that differed in the presence or absence of artificial vegetation. The effect of habitat structure on prey mortality was context dependent as it changed with predator and prey microhabitat use. Specifically, we observed an 'anti-refuge' effect of added vegetation: phytophilous predators that perched on the plants imposed higher predation pressure on planktonic prey, while mortality of benthic prey decreased. Predation by benthic and planktonic predators on either type of prey remained unaffected by the presence of vegetation. Our results show that the effects of habitat structure on predator-prey interactions are more complex than simply providing prey refuges or cover for predators. Such context-specific effects of habitat complexity may alter the coupling of different parts of the ecosystem, such as pelagic and benthic habitats, and ultimately affect food web stability through cascading effects on individual life histories and trophic link strengths.

Flow disturbances generated by feeding and swimming zooplankton.

Interactions between planktonic organisms, such as detection of prey, predators, and mates, are often mediated by fluid signals. Consequently, many plankton predators perceive their prey from the fluid disturbances that it generates when it feeds and swims. Zooplankton should therefore seek to minimize the fluid disturbance that they produce. By means of particle image velocimetry, we describe the fluid disturbances produced by feeding and swimming in zooplankton with diverse propulsion mechanisms and ranging from 10-µm flagellates to greater than millimeter-sized copepods. We show that zooplankton, in which feeding and swimming are separate processes, produce flow disturbances during swimming with a much faster spatial attenuation (velocity u varies with distance r as u ∝ r(-3) to r(-4)) than that produced by zooplankton for which feeding and propulsion are the same process (u ∝ r(-1) to r(-2)). As a result, the spatial extension of the fluid disturbance produced by swimmers is an order of magnitude smaller than that produced by feeders at similar Reynolds numbers. The "quiet" propulsion of swimmers is achieved either through swimming erratically by short-lasting power strokes, generating viscous vortex rings, or by "breast-stroke swimming." Both produce rapidly attenuating flows. The more "noisy" swimming of those that are constrained by a need to simultaneously feed is due to constantly beating flagella or appendages that are positioned either anteriorly or posteriorly on the (cell) body. These patterns transcend differences in size and taxonomy and have thus evolved multiple times, suggesting a strong selective pressure to minimize predation risk.

The role of internal waves in larval fish interactions with potential predators and prey

Tidally driven internal wave packets in coastal environments have the potential to influence patchiness of larval fishes, prey, and gelatinous predators. We used the In Situ Ichthyoplankton Imaging System (ISIIS) to synoptically sample larval fishes, copepods, and planktonic predators (ctenophores, hydromedusae, chaetognaths, and polychaetes) across these predictable features in the summer near Stellwagen Bank, Massachusetts, USA. Full water column profiles and fixed depth transects (∼10m depth) were used to quantify vertical and horizontal components of the fish and invertebrate distributions during stable and vertically mixed conditions associated with tidally generated internal waves. Larval fishes, consisting mostly of Urophycis spp., Merluccius bilinearis, and Labridae, were concentrated near the surface, with larger sizes generally occupying greater depths. During stable water column conditions, copepods formed a near surface thin layer several meters above the chlorophyll-a maximum that was absent when internal waves were propagating. In contrast, ctenophores and other predators were much more abundant at depth, but concentrations near 10m increased immediately after the internal hydraulic jump mixed the water column. During the propagation of internal waves, the fine-scale abundance of larval fishes was more correlated with the abundance of gelatinous predators and less correlated with copepods compared to the stable conditions. Vertical oscillations caused by the internal hydraulic jump can disperse patches of zooplankton and force surface dwelling larval fishes into deeper water where probability of predator contact is increased, creating conditions potentially less favorable for larval fish growth and survival on short time scales.

Planktonic predation risk varies with prey life history stage and diurnal phase

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 503:99-109 (2014) - DOI: https://doi.org/10.3354/meps10735 Planktonic predation risk varies with prey life history stage and diurnal phase K. A. Kerr1,2,3,*, A. Cornejo2,4, F. Guichard1,3, R. Collin2,3 1Department of Biology, McGill University, 1205 Docteur Penfield, Montréal, Québec H3A 1B1, Canada 2Smithsonian Tropical Research Institute, Apartado Postal 0843-03092, Panamá, Republic of Panama 3McGill-STRI Neotropical Environment Option (NEO), Faculty of Science, McGill University, Montréal, Québec H3A 2T6, Canada 4Department of Biology and Chemistry, University of Bremen, Bibliothekstraße 1, Bremen 28359, Germany *Corresponding author: kecia.kerr@mail.mcgill.ca ABSTRACT: Predation risk is believed to shape many aspects of the behavior, morphology and life history of marine organisms. The timing of synchronous larval release, postlarval migrations to adult habitat and diurnal vertical migrations are all considered adaptations to predictable variations in predation risk. However, despite the fact that predation risk is expected to vary predictably over time, this variation remains poorly understood for planktonic animals in the field. In this study, we conducted dock-based predation risk assays using tethered brine shrimp Artemia franciscana. We tested for the combined effects of prey life history stage and diurnal phase by measuring loss of adult and larval tethered individuals. We sampled during day and night, and during large and small amplitude tides on the Pacific coast of Panama. On the Caribbean coast of Panama and the Atlantic coast of Florida (where tidal amplitude is smaller), we sampled during day and night but did not test for an effect of tidal amplitude. Although predation risk differed between sites, the trends were the same at all 3 docks. Predation risk was significantly higher during the day than at night for larvae, whereas adults experienced the opposite trend in risk across the diurnal cycle, although the difference was not significant. Our results demonstrate a temporal gradient in planktonic predation risk across the diurnal cycle that depends on prey life history stage. KEY WORDS: Predation risk · Plankton · Diurnal cycle · Size-dependent predation · Plankton tethering unit · Predator-prey interaction · Size refugia Full text in pdf format PreviousNextCite this article as: Kerr KA, Cornejo A, Guichard F, Collin R (2014) Planktonic predation risk varies with prey life history stage and diurnal phase. Mar Ecol Prog Ser 503:99-109. https://doi.org/10.3354/meps10735 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 503. Online publication date: April 29, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Jellyfish as prey: frequency of predation and selective foraging of Boops boops (Vertebrata, Actinopterygii) on the mauve stinger Pelagia noctiluca (Cnidaria, Scyphozoa).

In recent years, jellyfish blooms have attracted considerable scientific interest for their potential impacts on human activities and ecosystem functioning, with much attention paid to jellyfish as predators and to gelatinous biomass as a carbon sink. Other than qualitative data and observations, few studies have quantified direct predation of fish on jellyfish to clarify whether they may represent a seasonally abundant food source. Here we estimate predation frequency by the commercially valuable Mediterranean bogue, Boops boops on the mauve stinger jellyfish, Pelagia noctiluca, in the Strait of Messina (NE Sicily). A total of 1054 jellyfish were sampled throughout one year to quantify predation by B. boops from bite marks on partially eaten jellyfish and energy density of the jellyfish. Predation by B. boops in summer was almost twice that in winter, and they selectively fed according to medusa gender and body part. Calorimetric analysis and biochemical composition showed that female jellyfish gonads had significantly higher energy content than male gonads due to more lipids and that gonads had six-fold higher energy content than the somatic tissues due to higher lipid and protein concentrations. Energetically, jellyfish gonads represent a highly rewarding food source, largely available to B. boops throughout spring and summer. During the remainder of the year, when gonads were not very evident, fish predation switched towards less-selective foraging on the somatic gelatinous biomass. P. noctiluca, the most abundant jellyfish species in the Mediterranean Sea and a key planktonic predator, may represent not only a nuisance for human leisure activities and a source of mortality for fish eggs and larvae, but also an important resource for fish species of commercial value, such as B. boops.

Predator–prey encounter and capture rates in turbulent environments

Lay AbstractIn this article, we review the ways in which turbulent water flow affects predator–prey encounter and capture rates. In quiet environments, zooplankton rely on self‐induced motions to encounter their prey. However, flows in nature, the oceans in particular, are usually turbulent. Fluid turbulence is very effective at mixing the water and can also greatly enhance the encounter rate between predators and prey—especially when both are carried passively by the flow. In this sense, there is an advantage for planktonic predators to be in a turbulent environment, but turbulence can also reduce the probability of prey capture. Our estimates suggest that there is an optimum turbulence level where the gain by enhanced encounter rates is balanced by reduced capture rates. These optimum conditions can be expressed mathematically in terms of the basic variables describing the problem, where the water flow is characterized by its kinematic viscosity, the turbulence by the specific energy dissipation rate, and plankton by their capture range and opening angle of its field of reception and a minimum time needed for capturing prey. The velocities of the self‐induced motions with respect to the local flow are also important. Turbulence not only affects the relative motion between predator and prey but also disturbs signals from the sensory organs on their antennae. Enhanced turbulence levels can be interpreted as noise by plankton by giving rise to random velocity variations along their antennae. This noise can be misinterpreted as a signal of the presence of prey. Similarly, prey can interpret such disturbances as false evidence of a predator. In the first case, a predator can attack even in absence of prey, while in the latter case prey can be seen to perform escape responses in the absence of a predator. Simple mathematical models can explain the basic features of this problem and help to increase our understanding of plankton ecology.

A full life cycle and spatially explicit individual-based model for the giant mud crab (Scylla serrata): a case study from a marine protected area

AbstractThe giant mud crab (Scylla serrata) is an important fisheries species throughout southeast Asia and the South Pacific. In Australia, marine protected areas (MPAs) and fish habitats have been declared specifically to protect the local populations of S. serrata. The cannibalistic behaviour of S. serrata coupled with the potential attraction of increased predators may counteract the effect of excluding fishing from these areas as a means of increasing the local crab population. The population dynamics of S. serrata could also be confounded by the spatio-temporal variability in environmental conditions (e.g. run-off and temperature). Here, we used a spatially explicit individual-based model (IBM) to explore the population dynamics of S. serrata in an MPA located in southern Moreton Bay, Queensland, Australia. This IBM simulated the life cycle dynamics of individual S. serrata and integrated the key processes affecting its population dynamics. These processes include physical transport of the planktonic life stages, movement, growth, metamorphosis, setting, reproduction, spawning, harvesting, and predation. Individual variability was built into the model to account for demographic variation. The modelled scenarios indicated that the effect of the different harvest strategies trialled on the population dynamics after 30 months and the MPA influenced the number of individuals in the creek system resulting in a partial 35% population increase. Further development and application of this model has implications for MPAs and catch limits under multiple stressors including climate change.

Behavioural responses of freshwater zooplankton vary according to the different alarm signals of their invertebrate predators

Single behavioural interactions between two freshwater planktonic crustaceans and invertebrate predators from different zones of the common environment were studied. The planktonic prey organisms were the cladoceran Ceriodaphnia dubia and the copepod Notodiaptomus conifer. The three invertebrate predators were the shrimp Macrobrachium borellii, the crab Trichodactylus borellianus and the larva of the dipteran midge Chaoborus. Feeding experiments were first performed to document the effects of exposure time and prey density on predation. All the selected predators fed on C. dubia and N. conifer, and predation rates were dependent on prey density and exposure time. The ability of microcrustaceans to modify their swimming and avoidance behaviour when faced with cues from each predator was then analysed. The cladoceran was more vulnerable to decapod predation, whereas the prey microcrustaceans were taken equally by the dipteran larvae. The analysis showed that the microcrustaceans detected the presence of at least one invertebrate predator through the predator alarm signals. The cladoceran responded to chemical signals from the three predators but copepods modified their behaviour only in the presence of infochemicals of M. borellii. The different outcomes suggest that macrocrustaceans have different vulnerabilities when faced with the same predator and so have evolved specific and different strategies to reduce invertebrate predation.

Priming the larval pump: resurgence of bay scallop recruitment following initiation of intensive restoration efforts

Bay scallop Argopecten irradians irradians populations and fisheries in the Peconic Bays of eastern Long Island, New York, USA, were decimated by brown tide algal blooms between 1985 and 1995. Despite the absence of brown tide since 1995, populations did not recover on their own over the next 11 yr. We hypothesized that this was due to recruitment limitation and initiated an intensive restoration program to jump-start populations by planting several million hatchery-reared scallops at high densities to ensure high fertilization success and boost larval sup- ply. We observed 11- to 32-fold increases in larval recruitment in different embayments by 2010, compared to the period 2005 to 2006 (before intensive restoration); the most dramatic increase (3239%) occurred in Orient Harbor, the focus of restoration efforts. Recruitment was highly corre- lated with our index of total fertilized egg production in Orient Harbor and Hallock Bay, but not in 2 other embayments—where larval export or population overestimation probably compromised the correlation. Resurgent recruitment following restoration was not correlated to coincidental changes in adult fecundity, water temperature, salinity, rainfall, chlorophyll a, total particulate nitrogen, or local winds; decreased planktonic predation and allochthonous larval infusion were deemed unlikely drivers. We conclude that Peconic bay scallops were recruitment-limited follow- ing the 1995 brown tide and that resurgent recruitment was driven, initially, by our intensive res- toration efforts and later by the rebuilding natural populations. Sustained restoration, conducted with high scallop numbers/densities, may help boost natural populations above threshold levels at which they become self-sustaining.

The effect of habitat complexity on the contribution of some littoral–benthic Cladocera to the pelagic food web

Littoral zones of lakes are settled by typical littoral animals, but they are also explored by mobile vertebrate and invertebrate predators. The relative importance of habitat complexity on the availability of littoral–benthic species of Cladocera, including Alonella exigua, A. excisa and A. nana (Chydoridae), to planktonic predators (Leptodora and cyclopoid copepods) was investigated in a series of laboratory experiments and under natural conditions (Lake Piaseczno, eastern Poland). The laboratory experiments showed that invertebrate predators influenced the density of cladocerans, but that predatory success was related to spatial complexity. A treatment imitating a habitat of water milfoil provided the highest survival rate, whereas a treatment imitating a habitat of macroalgae provided the lowest survival rate of the Alonella species, independently of the type of predators. Leptodora showed a higher predation pressure than did the cyclopoid copepods in a treatment imitating a habitat of common reed. In the field research, inverse correlations between the density of Alonella and potential invertebrate predators in distinct habitats were found. The species most strongly preyed on under the experimental conditions showed the highest fecundity, thus suggesting that the predation pressure by planktonic invertebrates influences the demography and life-history trade-offs of juvenile Alonella individuals in the lake. The obtained results extend our knowledge on the type and magnitude of interactions between the littoral–benthic and pelagic food webs.

Who is eating whom? Morphology and feeding type determine the size relation between planktonic predators and their ideal prey

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 445:1-12 (2012) - DOI: https://doi.org/10.3354/meps09502 FEATURE ARTICLE Who is eating whom? Morphology and feeding type determine the size relation between planktonic predators and their ideal prey Kai W. Wirtz* Institute of Coastal Research, Helmholtz-Zentrum Geesthacht, Germany *Email: kai.wirtz@hzg.de ABSTRACT: Body size determines the position of organisms in plankton food webs. The mass or diameter ratio between predators and their optimal prey is therefore a central element of size-based models, which attempt to link consumer groups across trophic levels. Despite a renaissance of size-based approaches in plankton ecology, however, this relation still lacks a generic and also mechanistically sound formulation. An empirically derived constant value of this ratio cannot describe the wide scatter in optimal prey diameter for specific predator size classes, especially in the mesozooplankton range. In this study, I propose that a given morphometric ratio between feeding-related apparatus and total body volume decreases when predator size increases. This ratio decrease is due to the additional need for structural components in larger organisms for maintaining intra-body transport. Non-isometric scaling results in a non-linear dependency of optimal prey size on predator diameter. This dependency defines an average relation which enables the quantitative definition of feeding mode. This new trait variable explains a component of the variability in optimal prey diameter that is independent of predator diameter. Feeding mode as a trait can be interpreted as activity during grazing, mostly in terms of speed regulation in swimming or in feeding-current generation. Feeding mode, in concert with the classical trait predator size, accurately determines optimal prey size. This was extensively tested using literature data for the entire plankton domain. The theory predicts increasing feeding activity in larger consumer species. It elucidates how successional shifts in the composition of zooplankton communities are linked to weakly coupled changes in mean body size and feeding mode. KEY WORDS: Zooplankton grazing · Optimal prey size · Biomechanics · Size-based model Full text in pdf format Information about this Feature Article Supplementary material NextCite this article as: Wirtz KW (2012) Who is eating whom? Morphology and feeding type determine the size relation between planktonic predators and their ideal prey. Mar Ecol Prog Ser 445:1-12. https://doi.org/10.3354/meps09502 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 445. Online publication date: January 20, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Larval biomass and chemical composition at hatching in two geographically isolated clades of the shrimp Macrobrachium amazonicum: intra- or interspecific variation?

The shrimp Macrobrachium amazonicum (Heller 1862) has an extremely large geographic range (>4000 km across) in northern and central South America, comprising estuarine and fully limnic inland populations, which are hydrologically isolated from each other. Significant variations in ecology, physiology, reproduction, and larval development suggest an at least incipient allopatric speciation due to limited genetic exchange. In a comparative experimental investigation with shrimps from the Pantanal (upper Paraguay River basin) and the Amazon delta, respectively, we measured larval body size, dry weight (W), biochemical (total protein; lipid; fatty acids, FA), and elemental composition (carbon, hydrogen, nitrogen; collectively CHN) at hatching. All these early larval traits are relevant for the degree of developmental dependence on planktonic food sources. Various consistent differences were observed between the two populations: Newly hatched larvae produced by shrimps from the Amazon delta were significantly smaller and showed lower values of W, CHN, protein, and unsaturated FA compared to those from the Pantanal. On the other hand, they contained significantly higher quantities of total lipid and saturated FA and, in consequence, higher ratios of lipid:protein, C:N, and saturated:unsaturated FA. All these differences in biomass and chemical composition suggest that the larvae of the Amazon population are energetically better adapted to planktonic food limitation, which likely occurs during riverine downstream transport toward coastal marine waters, also explaining previous observations of much stronger initial starvation tolerance in larvae from the Amazon versus those from the Pantanal. The latter develop in highly productive lentic inland waters, where large body size, an early onset of feeding, and a strong musculature (indicated by a high protein content) should facilitate their role as planktonic predators and allow for fast growth. An initial independence from food (lecithotrophy in the zoea I stage) as well as a preference for oligohaline rather than fully limnic conditions observed in the Pantanal larvae are interpreted as traits that have persisted from an ancestral coastal marine clade. Altogether, consistent ontogenetic differences between shrimps from the Pantanal and the Amazon estuary support the hypothesis that the taxon M. amazonicum comprises a complex of closely related but separate species.

Experimental Taphonomy of Benthic Chaetognaths: Implications for the Decay Process of Paleozoic Chaetognath Fossils

Abstract. Despite their small sizes (ca. 2–120 mm), chaetognaths, or arrow worms, are the most important planktonic carnivorous predators both in terms of biomass and abundance, and they represent the second most important component of modern marine ecosystems. The fossil record of chaetognaths is patchy and only consists of five Paleozoic species, which are still the object of a vigorous debate due to their unclear state of preservation. The two main diagnostic characters for the assignment of a fossil to chaetognaths are the presence of caudal and lateral fins as well as the existence of grasping spines on both sides of the head. However, among the five putative chaetognaths from the Paleozoic, none shows simultaneously these two characters. Our new experiments on the decay process of benthic chaetognaths Paraspadella gotoi demonstrate the differential alteration of various diagnostic characters through time. Six individuals were dissected and their decay was checked regularly in separate dishes contain...

Species-specific effects of fluid shear on grazing by sea urchin larvae: comparison of experimental results with encounter-model predictions

Small-scale turbulence can alter the rate of plankton predator–prey encounters. Encounter models predict that prey ingestion by slow-swimming zooplankton is enhanced at low levels of turbulence. We investigated whether small-scale turbulence increases ingestion for the slow-swimming, suspension-feeding pluteus larvae of the white urchin Lytechinus pictus and the purple urchin Strongylocentrotus purpuratus. Model predictions of the critical level of turbulence, ecr, above which encounters due to turbulence are greater than those due to behavior (swimming or suspension feeding) alone, were experimentally tested using shortand long-term grazing treatments. Because urchin larvae are smaller than the smallest eddy scales of turbulence and thus experience turbulence as laminar shear, larvae were exposed to flow conditions using a simple laminar shear flow with dissipation rates, e, of 0, 0.1, 0.4, and 1 cm2 s–3. Short-term ingestion of beads by L. pictus larvae was unaffected by e < 1 cm2 s–3 but was 30% greater at this level, which was greater than ecr based on flow speeds produced in suspension feeding. Long-term flow treatments with algal prey had no significant effect on grazing or growth. Short-term ingestion of beads by S. purpuratus larvae was unaffected by e < ecr based on suspension feeding; the effect of long-term flow exposure on ingestion and growth could not be investigated because of high mortality, suggesting greater sensitivity to flow exposure compared to L. pictus. Experimental results are consistent with model predictions that ecr is high, and thus levels of turbulence in the ocean are not expected to significantly increase ingestion and reduce food limitation in suspension-feeding urchin larvae.

Pleistocene‐driven diversification in freshwater zooplankton: Genetic patterns of refugial isolation and postglacial recolonization in Leptodora kindtii (Crustacea, Cladocera)

In this study we investigate the extent to which successive range fragmentations, postglacial expansions, and recolonizations influenced intraspecific genetic diversity and patterns of diversification in freshwater zooplankton. Specifically, we explore the global phylogeography of the Holarctic predatory cladoceran Leptodora kindtii Focke, 1844. Phylogenetic analyses based on the mitochondrial cytochrome c oxidase subunit I recover seven deeply divergent lineages (11.8–20.0%) comprising two sister clades within the Nearctic and east Palearctic and three related clades within the west Palearctic. Strong continental endemism was also supported by the nuclear 18S ribosomal gene. Intra‐continental divergence levels (&lt; 6%) suggest that many speciation events in Leptodora were initiated by glacial isolation. Demographic and network analyses indicate that in the Nearctic and west Palearctic, regions heavily affected by the Pleistocene glaciations, Leptodora persisted in both classic (e.g., Cascadia, Mississippi, southern Europe) and cryptic refugia (e.g., northeastern Europe, Carpathian basin). Strong signatures of late Pleistocene range expansions and secondary contact were observed in most clades. Deeper intraspecific phylogeographic structure occurs across much finer geographic scales in unglaciated regions of the east Palearctic than across glaciated Nearctic and west Palearctic regions. Leptodora's ecological and biological characteristics, such as a reliance on temperate, permanent lakes, weak dispersal ability, and specific geological settings likely shaped the complex pattern of diversification in this important planktonic predator. Our data suggest the Pleistocene glaciations were important in the diversification of Holarctic freshwater zooplankton.

The transition from nauplii to copepodites: susceptibility of developing copepods to fish predators

Escape success of copepod nauplii (N5–6) of the copepod Acartia tonsa was signifi-cantly lower than that of copepodites (C1–2) when exposed to a coral reef fishAcanthemblemaria paula, but no difference was observed when exposed to the sea-horse Hippocampus zosterae. The addition of low level turbulence inhibited feedingby the seahorse but did not affect overall capture success in A. paula, although ashift in predator behavior occurred. This study highlights the importance of con-sidering predatory mode and behavior in the context of planktonic predator–preydynamics.KEYWORDS: copepod; Acartia tonsa; development; escape; fish predationCopepods are subject to high predation rates and theserates are often greatest for the younger, developingstages (Sell et al., 2001).Earlier developmental stages arepresumably less capable of detecting a potential preda-tor, and when a predator is detected, the escaperesponse of a young copepod is less effective comparedwith that of later stages (Sell et al., 2001; Titelman2001). However, the ability to produce an escape jumpis present in even the earliest naupliar stage (N1)(Buskey, 1994). However, the escape is produced by adifferent set of appendages than in the adult and manyof the mechanoreceptors for the hydrodynamic sensingof an approaching predator are missing in the youngeststages (Mauchline, 1998). During an escape, copepodsare propelled forward by metachronal strokes of thethoracic pereiopods (Strickler, 1985) and can achievespeeds over 500 body lengths per second (Buskey et al.,2002; Lenz et al., 2004). However, the mechanism forescape differs for naupliar stages. Nauplii lack pereio-pods, so instead they must use the first and secondantennae to generate escapes (Gauld, 1958). The devel-opment of pereiopods in copepodites results in anescape that is faster (Bradley, 2009). With each sub-sequent molt from C1 to C5, a new pair of pereiopodsemerge and older ones become larger (Dahms, 1990)and presumably more powerful.The molt from the N6 naupliar stage to the C1 cope-podite stage is arguably the most significant. Duringthis molt, the copepod’s change in mass proportional toother molts is small (Leandro et. al., 2006), yet there is a

Direct and indirect effects of an invasive planktonic predator on pelagic food webs

The relative importance of top‐down invader effects relative to environmental drivers was determined by sampling crustacean zooplankton, rotifer, and phytoplankton communities in a set of invaded and noninvaded reference lakes. The non‐native invertebrate predator Bythotrephes had significant effects on zooplankton community size structure, rotifers, and phytoplankton taxonomic composition, but no significant effects on crustacean zooplankton taxonomic and functional group composition. Part of the variation in phytoplankton communities was explained by the presence of the invader. Because Bythotrephes is generally known to be a carnivore and to not consume phytoplankton, this effect is likely mediated by the zooplankton community's response to environmental gradients. Although Bythotrephes appears to indirectly alter phytoplankton composition in invaded lakes, there was no evidence of a trophic cascade, and edible phytoplankton biovolume did not increase in invaded lakes. These complex direct and indirect interactions suggest that effects of invaders may be highly context‐dependent, and therefore pose a significant challenge for predicting wider community and ecosystem responses.