Swimming and feeding by the scyphomedusa Chrysaora quinquecirrha

The semaeostome scyphomedusa, Chrysaora quinquecirrha (Desor, 1848), is an abundant and important planktonic predator in estuaries and coastal waters of the eastern USA during the summer. We videotaped free-swimming medusae in the laboratory and in the field in order to determine the relationship between swimming motions and prey encounter with capture surfaces. Medusae were collected from the Choptank River (Chesapeake Bay) in September 1992 and in the Niantic River, Connecticut, USA in July 1994. We used newly hatched Artemia sp. nauplii and fluorescein dye to trace water motions around swimming medusae. Swimming results in a pulsed series of toroids which travel along the medusan oral arms and tentacles. Prey are entrained in this flow and the location of naupliar encounter was influenced by the phase of the pulsation cycle during which entrainment occurred. Flow-field velocities, measured by tracking particles adjacent to the bell margin during contraction, increased with bell diameter. Received: 29 March 1997 / Accepted: 11 April 1997     

Morphology,fluid motion and predation by the scyphomedusa Aurelia aurita

Although medusan predators play demonstrably important roles in a variety of marine ecosystems, the mechanics of prey capture and, hence, prey selection, have remained poorly defined. A review of the literature describing the commonly studied medusa Aurelia aurita (Linnaeus 1758) reveals no distinct patterns of prey selectivity and suggests that A. aurita is a generalist and feeds unselectively upon available zooplankton. We examined the mechanics of prey capture by A. aurita using video methods to record body and fluid motions. Medusae were collected between February and June in 1990 and 1991 from Woods Hole, Massachusetts and Narragansett Bay, Rhode Island, USA. Tentaculate A. aurita create fluid motions during swimming which entrain prey and bring them into contact with tentacles. We suggest that this mechanism dominates prey selection by A. aurita. In this case, we predict that medusae of a specific diameter will positively select prey with escape speeds slower than the flow velocities at their bell margins. Negatively selected prey escape faster than the medusan flow velocity draws them to capture surfaces. Faster prey will be captured by larger medusac because flow field velocity is a function of bell diameter. On the basis of prey escape velocities and flow field velocities of A. aurita with diameters of 0.8 to 7.1 cm, we predict that A. aurita will select zooplankton such as barnacle nauplii and some slow swimming hydromedusae, while faster copepods will be negatively selected.     

Water flow and prey capture by three scleractinian corals, Madracis mirabilis, Montastrea cavernosa and Porites porites, in a field enclosure

Scleractinian corals experience a wide range of flow regimes which, coupled with colony morphology, can affect the ability of corals to capture zooplankton and other particulate materials. We used a field enclosure oriented parallel to prevailing oscillatory flow on the forereef at Discovery Bay, Jamaica, to investigate rates of zooplankton capture by corals of varying morphology and polyp size under realistic flow speeds. Experiments were carried out from 1989 to 1992. Particles (Artemia salina cysts) and naturally occurring zooplankton attracted into the enclosures were used as prey for the corals Madracis mirabilis (Duchassaing and Michelotti) (narrow branches, small polyps), Montastrea cavernosa (Linnaeus) (mounding, large polyps), and Porites porites (Pallas) (wide branches, small polyps). This design allowed corals to be used without removing them or their prey from the reef environment, and avoided contact of zooplankton with net surfaces. Flow speed had significant effects on capture rate for cysts (M. mirabilis), total zooplankton (M. mirabilis, M. cavernosa), and non-copepod zooplankton (M. mirabilis). Zooplankton prey capture increased with prey concentration for M. mirabilis and M. cavernosa, over a broad range of concentrations, indicating that saturation of the feeding response had not occurred until prey density was over 10⁴ items m⁻³, a concentration at least an order of magnitude greater than the normal range of reef zooplankton concentrations. Location of cyst capture on coral surfaces was not uniform; for M. cavernosa, sides and tops of mounds captured most particles, and for P. porites, capture was greatest near branch tops, but was close to uniform for M. mirabilis branches in all flow conditions. The present study confirms laboratory flume results, and field results for other species, suggesting that many coral species experience particle flux and encounter rate limitations at low flow speeds, decreasing potential zooplankton capture rates. Received: 17 September 1996 / Accepted: 22 November 1997     

Morphology and kinematics of prey capture in the syngnathid fishes Hippocampus erectus and Syngnathus floridae

The mechanism of prey capture in two syngnathid fishes, the lined seahorse Hippocampus erectus (Perry) and the dusky pipefish Syngnathus floridae (Jordan and Gilbert), is described based on anatomical observations and high-speed video recordings (200 and 400 images s⁻¹) of feeding events by four seahorses and three pipefish. The fish were collected near Turkey Point, Florida, U.S.A., in January 1994 to March 1995. The dominant features of the morphology of these and many other syngnathiform fishes include extreme elongation of the suspensorium and neurocranium with a small mouth located at the anterior tip of the head. In the seahorse, a preparatory phase of prey capture consisted of slow ventral head flexion. This was followed by rapid elevation of the head and snout as the prey was drawn into the mouth by suction. Both H. erectus and S. floridae capture prey rapidly, with peak head excursions and mouth opening occurring within 5 to 7 ms of the onset of the strike. There was no upper jaw protrusion. In both species the time to recovery of the cranium and hyoid apparatus to resting positions was highly variable but took at least 500 ms. Manipulations of freshly dead specimens indicated a biomechanical linkage between head elevation and hyoid depression. However, the predictions of a previously proposed four-bar linkage model that couples hyoid depression to head elevation were not fully supported by kinematic data from one seahorse, suggesting that additional linkages act during the expansive phase of prey capture. These species exhibit the generalized kinematic pattern of prey capture in bony fishes, with head elevation, hyoid depression and mouth opening occurring almost simultaneously. The derived morphology results in a unique feeding behav‐ior, in which prey are captured during a sudden up-swing of the head, which brings the mouth to the prey. Suction is used to draw the prey into the buccal cavity. Received: 4 August 1996 / Accepted: 27 August 1996     

Zooplankton capture by two scleractinian corals,Madracis mirabilis andMontastrea cavernosa,in a field enclosure

Capture of zooplankton by scleractinian corals has been noted for several species, yet quantitative information on rates of capture and differential capture by prey taxon has been lacking. We used field enclosures to examine prey capture for two coral species,Madracis mirabilis (Duchassaing and Michelotti) andMontastrea cavernosa (Linnaeus), on the north coast of Jamaica (Discovery Bay) in November 1989, February and March 1990, and January 1992.M. mirabilis has small polyps and a branching colony morphology (high surface/volume ratio), whereasM. cavernosa has large polyps and mounding colonies (low surface/volume ratio). Corals were isolated front potential prey, then were introduced into enclosures with enhanced zooplankton concentrations for 15- to 20-min feeding periods. Corals were fixed immediately after the experiment to prevent digestion, and coelenteron contents were examined for captured zooplankton. Plankton pumps were used to sample ambient zooplankton in the enclosures near the end of each run. Selectivity and capture rates were calculated for each prey taxon in each experiment; both indices were high for relatively uncommon large prey, and low for copepods, which were often the most common items in the plankton. Sizes of zooplankton captured by both species were generally larger than those available considering all prey taxa combined, but were almost the same for both coral species, even though the corals' polyp sizes are very different. This occurred primarily because small copepods, with low capture rates, dominated most plankton samples. For specific prey species, or group of species, there were few significant differences in size between the prey available and the prey captured.M. mirabilis, with small polyps, also captured far more prey per unit coral biomass than didM. cavernosa, with much larger polyps. We hypothesize that the large differences in capture rate of prey taxa are related to escape or avoidance behavior by those potential prey, and to the mechanics of capture, rather than to any selectivity by the corals.     

A comparison of strike and prey capture kinematics of three species of piscivorous fishes: Florida gar ( Lepisosteus platyrhincus), redfin needlefish ( Strongylura notata), and great barracuda ( Sphyraena barracuda)

Ram feeding is the process by which a predatory fish uses a high-velocity lunge or chase to overtake its prey. This study compares the strike and prey capture behaviors and kinematics of three species of ram-feeding fishes: Florida gar Lepisosteus platyrhincus, redfin needlefish Strongylura notata, and great barracuda Sphyraena barracuda. These ram-feeding piscivores are morphologically similar with fusiform bodies, posteriorly placed dorsal and anal fins, and large, conical teeth. Strike and prey capture kinematics for five individuals of each species were recorded with high-speed video. Pre-strike behavior in L. platyrhincus consists of a slow stalk, resulting in the close, lateral positioning of the predators head relative to the prey. Lepisosteus employ a sideways lunge of the head during the strike, which lasts only 25–40 ms and is the most rapid strike among these three species. Strongylura notata and Sphyraena barracuda exhibit longitudinal orientation to the prey before the strike, followed by a high velocity, head-on lunge, initiated by an s-start in Sphyraena barracuda. Prey capture in adult L. platyrhincus and Strongylura notata is characterized by the jaws closing on the prey, with the prey held orthogonal to the jaws. This is followed by manipulation using the inertia of the prey to reposition the prey head first, and then suction transport into the buccal cavity. Prey capture in juvenile Sphyraena is accomplished by closing the jaws after the prey has entered the buccal cavity, resulting in possible ram transport of the prey with no oral manipulation under these experimental conditions. Although these three species all employ ram feeding for prey capture of elusive prey, each species has a unique repertoire that appears to minimize hydrodynamic constraints and prey response, utilize locomotory capabilities, and may be suited to each species specific habitat.Communicated by P.W. Sammarco, Chauvin     

Mechanisms of benthic prey capture in wrasses (Labridae)

Teleost fishes capture prey using ram, suction, and biting behaviors. The relative use of these behaviors in feeding on midwater prey is well studied, but few attempts have been made to determine how benthic prey are captured. This issue was addressed in the wrasses (Labridae), a trophically diverse lineage of marine reef fishes that feed extensively on prey that take refuge in the benthos. Most species possess strong jaws with stout conical teeth that appear well-suited to gripping prey. Mechanisms of prey capture were evaluated in five species encompassing a diversity of feeding ecologies: Choerodon anchorago (Bloch, 1791), Coris gaimard (Quoy and Gaimard, 1824), Hologymnosus doliatus (Lacepède, 1801), Novaculichthys taeniourus (Lacepède, 1801) and Oxycheilinus digrammus (Lacepède, 1801). Prey capture sequences were filmed with high-speed video at the Lizard Island Field Station (14°40′S, 145°28′E) during April and May 1998. Recordings were made of feeding on pieces of prawn suspended in the midwater and similar pieces of prawn held in a clip that was fixed to the substratum. Variation was quantified among species and between prey types for kinematic variables describing the magnitude and timing of jaw, hyoid, and head motion. Species differed in prey capture kinematics with mean values of most variables ranging between two and four-fold among species and angular velocity of the opening jaw differing seven-fold. The kinematics of attached prey feeding could be differentiated from that of midwater captures on the basis of faster angular velocities of the jaws and smaller movements of cranial structures which were of shorter duration. All five species used ram and suction in combination during the capture of midwater prey. Surprisingly, ram and suction also dominated feedings on attached prey, with only one species making greater use of biting than suction to remove attached prey. These data suggest an important role for suction in the capture of benthic prey by wrasses. Trade-offs in skull design associated with suction and biting may be particularly relevant to understanding the evolution of feeding mechanisms in this group. Published online: 11 July 2002     

Feeding mechanism of the brisingid starfish Novodinia antillensis

This paper describes the food and feeding mechanisms of the bathyal brisingid sea-star Novodinia antillensis (A. H. Clark, 1934). N. antillensis is shown to be an opportunistic suspension feeder capable of capturing living planktonic crustaceans of a wide range of sizes. The sea-star extends its 10 to 14 arms into water currents to form a feeding fan with a large surface area, and uses highly retentive pedicellaria on the lateral arm spines to grasp and retain prey. The flexible arms form arm loops to complete the capture. The pedicellaria have a structure very similar to that used by other species known to capture macroscopic prey and, although they are an order of magnitude smaller, they probably function in a similar manner.     

Prey selection by the scyphomedusan predator Aurelia aurita

We describe feeding behavior of Aurelia aurita (Linnaeus) using gut content analyses of field-collected specimens and a mesocosm experiment. The field studies were conducted in Narragansett Bay, Rhode Island, USA from March to April 1988, and the mesocosm studies were done at the Marine Ecosystems Research Laboratory at the University of Rhode Island. Patterns of prey selection changed with medusa diameter. Smaller medusae (12 mm diameter) consumed mostly hydromedusan prey whereas larger medusae (up to 30 mm diameter) ingested greater numbers of copepod prey. While larger medusae did feed on copepods, their diet also contained more barnacle nauplii and hydromedusae than expected from the relative abundances of these prey types in plankton samples. A marginal flow mechanism of feeding by A. aurita provided an explanation for the patterns of prey selection we observed in medusae of different sizes and among widely divergent prey types. Our data indicated that large prey, with escape speeds slower than the marginal flow velocities around the bell margins of A. aurita, made up a substantial fraction of the daily ration when they were available. Such prey species may be more important to nutrition than the more abundant copepods and microzooplankton. Successful development of young medusae may depend upon an adequate supply of slowly escaping prey.     

Vulnerability of the copepod Acartia tonsa to predation by the scyphomedusa Chrysaora quinquecirrha : effect of prey size and behavior

Although scyphomedusae have received increased attention in recent years as important predators in coastal and estuarine environments, the factors affecting zooplankton prey vulnerability to these jellyfish remain poorly understood. Current models predicting feeding patterns of cruising entangling predators, such as Chrysaora quinquecirrha (Desor, 1948), fail to account for the selection of fast-escaping prey such as copepods. Nevertheless, our analysis of gastric contents of field-collected medusae showed that this scyphomedusa fed selectively on the calanoid copepod Acartia tonsa (Dana, 1846) and preferentially ingested adult over copepodite stages. We measured feeding rates in a planktonkreisel while simultaneously videotaping predator–prey interactions. C. quinquecirrha consumed adult A. tonsa ten times faster than copepodites. Differences in prey behavior, in the form of predator–prey encounter rates or post-encounter escape responses, could not account for the elevated feeding rates on adults. Prey size, however, had a dramatic impact on the vulnerability of copepods. In experiments using heat-killed prey, feeding rates on adults (1.5 times longer than copepodites) were 11 times higher than on copepodites. In comparison, medusae ingested heat-killed prey at only two to three times the rate of live prey. These results suggest that during scyphomedusan–copepod interactions, prey escape ability is important, but ultimately small size is a more effective refuge from predation. Received: 26 September 1997 / Accepted: 20 May 1998     

An individual-based numerical model of medusa swimming behavior

Scyphomedusae are ubiquitous in marine and estuarine systems, where they frequently play an important role in trophodynamics. Many scyphomedusae are cruising predators, and feeding rates depend, in part, on swimming behavior. Yet, no model of medusa swimming exists. An individual-based correlated random walk (CRW) model of medusa swimming behavior in three dimensions was developed. The model was validated using a previously published dataset of the swimming of 19 Chrysaora quinquecirrha (Desor, 1848) medusae that were observed in the presence or absence of zooplankton prey in laboratory mesocosms in August–October 1998 (Matanoski et al. in Mar Biol 139:191–200, 2001). In the presence of prey, medusae swam at a constant moderate rate in looping trajectories. In the absence of prey, medusae alternated periods of slow and fast swimming in more linear trajectories. In the model, looping trajectories were reproduced only when changes in movement by a medusa were oriented to its current position and orientation; more linear trajectories were reproduced by movement oriented to a fixed framework. This suggests that medusae change from swimming behavior oriented to local stimuli (e.g., contact with prey) to long-range stimuli (e.g., gravity) depending on the availability of prey. The model reproduced cyclical changes in swimming speeds by medusae in the absence of prey by simulating switching in the behavior controlling the strength of swimming bell pulsations using a probabilistic function. Model results also demonstrated that medusae tend to swim toward the surface, avoid contact with the bottom, increase time spent in prey patches if they alter swimming patterns in the presence of prey, and exhibit significant periodicities in swimming patterns that are the result of deterministic behavior. The model will permit the simulation of the complex behavior of medusae.     

Prey size selection,feeding rates and growth dynamics of heterotrophic dinoflagellates with special emphasis on Gyrodinium spirale

The relationship between size and growth rate in heterotrophic dinoflagellates (collected from the Kattegat, Denmark during 1989 and 1990) was studied. In addition, prey size selection, feeding rates and growth dynamics were studied for the naked heterotrophic dinoflagellate Gyrodinium spirale Bergh. Heterotrophic dinoflagellates have growth rates which are approximately three times lower than that of their potential competitors, the ciliates. G. spirale requires a relatively high prey concentration in order to grow. Ingestion rate at the maintenance level is about half of that of maximum ingestion rate. Consequently, yield is lower than typically found for planktonic protozoa. When exposed to low prey concentrations, the dinoflagellate is able to reduce its metabolism and thus prolong survival. The optimum prey particle size for G. spirale, which feeds by direct engulfment, corresponds to its own size. The ability to ingest relatively large prey may explain why these organisms are competitive in nature.     

Spatial overlap and trophic interactions between pelagic fish and large jellyfish in the northern California Current

Recent studies have indicated that populations of gelatinous zooplankton may be increasing and expanding in geographic coverage, and these increases may in turn affect coastal fish populations. We conducted trawl surveys in the northern California Current and documented a substantial biomass of scyphomedusae consisting primarily of two species (Chrysaora fuscescens and Aurelia labiata). Spatial overlap of these jellyfish with most pelagic fishes, including salmon, was generally low, but there were regions of relatively high overlap where trophic interactions may have been occurring. We compared feeding ecology of jellyfish and pelagic fishes based on diet composition and found that trophic overlap was high with planktivorous species that consume copepods and euphausiid eggs such as Pacific sardines (Sardinops sagax), northern anchovy (Engraulis mordax), Pacific saury (Cololabis saira), and Pacific herring (Clupea pallasi). Moreover, isotope and diet analyses suggest that jellyfish occupy a trophic level similar to that of small pelagic fishes such as herring, sardines and northern anchovy. Thus jellyfish have the potential, given their substantial biomass, of competing with these species, especially in years with low ecosystem productivity where prey resources will be limited.     

Fine-scale observations of the predatory behaviour of the carnivorous copepod <Emphasis Type="Italic">Paraeuchaeta norvegica</Emphasis> and the escape responses of their ichthyoplankton prey,Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>)

Paraeuchaeta norvegica (8.5 mm total length) and yolk-sac stage Atlantic cod larvae (4 mm total length) (Gadus morhua) larvae were observed in aquaria (3 l of water) using silhouette video photography. This allowed direct observations (and quantitative measurement) of predator–prey interactions between these two species in 3-dimensions. Tail beats, used by cod larvae to propel themselves through the viscous fluid environment, also generate signals detectable by mechanoreceptive copepod predators. When the prey is close enough for detection and successful capture (approximately half a body-length), the copepod launches an extremely rapid high Reynolds number attack, grabbing the larva around its midsection. While capture itself takes place in milliseconds, minutes are required to subdue and completely ingest a cod larva. The behavioural observations are used to estimate the hydrodynamic signal strength of the cod larva’s tail beats and the copepod’s perceptive field for larval fish prey. Cod larvae are more sensitive to fluid velocity than P. norvegica and also appear capable of distinguishing between the signal generated by a swimming and an attacking copepod. However, the copepod can lunge at much faster velocities than a yolk-sac cod larva can escape, leading to the larva’s capture. These observations can serve as input to the predator–prey component of ecosystem models intended to assess the impact of P. norvegica on cod larvae.     

Effects on larval crabs of exposure to algal toxin via ingestion of heterotrophic prey

We tested whether ingesting toxic algae by heterotrophic prey affected their nutritional value to crab larval predators, using toxic algal strains that are either ingested directly by larval crabs or rejected by them. Ingestion of toxic strains of the dinoflagellates Alexandrium andersoni and A. fundyense by the rotifer Brachionus plicatilis was confirmed. Rotifers having ingested either algal type for five days were fed to freshly hatched larvae of three crab species, with larval survival and stage durations determined. For both algal/rotifer treatments in all three crab species, larvae fed algae directly died during the first zoeal stage, while those fed rotifers that had been fed either algal strain survived to the experiment’s end (zoeal stage 3). Survival was lower, and stage duration longer, for larvae fed rotifers cultured on toxic algae when compared to those fed non-toxic algae. The role of toxic algae in the planktonic food web may be influenced by its direct or indirect ingestion by larval crabs.     

Do social spiders cooperate in predator defense and foraging without a web?

Nearly all social spiders spin prey-capture webs, and many of the benefits proposed for sociality in spiders, such as cooperative prey capture and reduced silk costs, appear to depend on a mutually shared web. The social huntsman spider, Delena cancerides (Sparassidae), forms colonies under bark with no capture web, yet these spiders remain in tightly associated, long-lasting groups. To investigate how the absence of the web may or may not constrain social evolution in spiders, we observed D. cancerides colonies in the field and laboratory for possible cooperative defense and foraging benefits. We observed spiders’ responses to three types of potential predators and to prey that were introduced into retreats. We recorded all natural prey capture over 447 h both inside and outside the retreats of field colonies. The colony’s sole adult female was the primary defender of the colony and captured most prey introduced into the retreat. She shared prey with younger juveniles about half the time but never with older subadults. Spiders of all ages individually captured and consumed the vast majority of prey outside the retreat. Young spiders benefited directly from maternal defense and prey sharing in the retreat. However, active cooperation was rare, and older spiders gained no foraging benefit by remaining in their natal colony. D. cancerides does not share many of the benefits of group living described in other web-building social spiders. We discuss other reasons why this species has evolved group living.     

Implications of life history for genetic structure and migration rates of southern African coastal invertebrates: planktonic,abbreviated and direct development

The amount of genetic structure in marine invertebrates is often thought to be negatively correlated with larval duration. However, larval retention may increase genetic structure in species with long-lived planktonic larvae, and rafting provides a means of dispersal for species that lack a larval dispersal phase. We compared genetic structure, demographic histories and levels of gene flow of regional lineages (in most cases defined by biogeographic region) of five southern African coastal invertebrates with three main types of larval development: (1) dispersal by long-lived planktonic larvae (mudprawn Upogebia africana and brown mussel Perna perna), (2) abbreviated larval development (crown crab Hymenosoma orbiculare) and (3) direct development (estuarine isopod Exosphaeroma hylecoetes and estuarine cumacean Iphinoe truncata). We hypothesized that H. orbiculare, having abbreviated larval development, would employ a strategy of larval retention, resulting in genetic structure comparable to that of the direct developers rather than the planktonic dispersers. However, regional population structure was significantly lower in all species with planktonic larvae, including H. orbiculare, than in the direct developers. Moreover, nested clade analysis identified demographic histories resulting from low levels of gene flow (isolation by distance and allopatric fragmentation) in the direct developers only, and migration rates were significantly higher in all three species having planktonic larvae than in the direct developers. We conclude that the amount of genetic structure within marine biogeographic regions strongly depends on the presence or absence of free-swimming larvae. Whether such larvae are primarily exported or retained, whether they have long or short larval duration, and whether or not they are capable of active dispersal seems to have little effect on connectivity among populations.     

Hypoxia-induced structural changes in the diet of bottom-feeding fish and Crustacea

Interactive effects of three alternating normoxia-hypoxia cycles on benthic prey exploitation by mobile fish (spot, Leiostomus xanthurus; and hogchoker, Trinectes maculatus) and a burrowing crustacean (Squilla empusa) were investigated in the York River, Chesapeake Bay, Virginia, USA, in 1989. Predators collected in four depth strata (A: 5 to 10 m; B: 10 to 14 m; C: 14 to 20 m; D:>20 m) variously affected by hypoxia were separated into size classes (three for spot and two each for hogchoker and mantis shrimp) to examine potential ontogenetic influences in prey selection. The most severe effects of hypoxia on the benthos occurred in the two deepest strata (C and D) and decreased in shallower strata (B>A), with Stratum A never affected by low oxygen. Predators investigated exhibited dietary evidence of optimal prey exploitation during or immediately after hypoxic events. In most instances gut contents contained significantly larger, deeper-burrowing prey during periods of low oxygen than during alternating peroids of normal oxygen levels. Spot consumed a greater biomass (45 to 73%) of polychaetes than other prey, with crustaceans initially also constituting a main dietary component but decreasing in importance later in the study period. The deep-burrowing anemone, Edwardsia elegans, was an important prey species for spot, particularly in the lower depth strata affected by hypoxia. Prey consumed by 10-to 15-cm-long spot increased significantly in size during some hypoxic events, suggesting a sublethal effect of hypoxia on large benthic species. Polychaetes (primarily Glycera americana, Notomastis latericeus and Loimia medusa) were dominant dietary components in hogchoker, making up between 85 and 98% of the diet. Bivalve siphons became important prey for hogchoker in the three deepest strata and were only consumed after the August hypoxia. Stomach contents of mantis shrimp were difficult to identify in most instances due to the near complete mastication of consumed prey. Crustaceans were important prey initially but became less conspicuous in the diet subsequent to the July hypoxia event, when hydroids became more dominant. Overall, predator species exhibited optimal exploitation of moribund or slowly recovering benthos affected by hypoxia. The sublethal effects of hypoxia through increased availability of benthos to resident predators can have important consequences for energy flow in areas such as the York River which experience periodic low-oxygen cycles.     

Predation by the epipelagic heteropod mollusk Carinaria cristata forma japonica

In surface waters off Southern California (USA), Carinaria cristata forma japonica van der Spoel, 1972 feeds on a variety of zooplankton, although thaliaceans, chaetognaths, and copepods predominate numerically in the diet. Feeding intensity is greatest on the most abundant of two species of thaliaceans, depending on which one dominates in the plankton at the time. Some cannibalism occurs, with the prey being about one half the size of the predator. Feeding intensity is greatest during the day, possibly because heteropods depend on vision to locate prey and because prey species are more available by day. Comparisons of the proportion of each prey species in the diet and in the plankton indicate preferential feeding on thaliaceans, chaetognaths, and mollusks; in contrast, crustaceans and especially the copepods are non-preferred prey. These preference patterns may reflect differences among prey species in the ability to escape capture. Predator and prey size are positively correlated for Doliolum denticulatum gonozoids and oozoids, Thalia democratica aggregates, and Sagitta spp. Smaller individuals of D. denticulatum gonozoids and Sagitta spp. are selectively preyed on, resulting in size refuges for larger individuals.     

Effects of water motion and prey behavior on zooplankton capture by two coral reef fishes

Water motion is an important factor affecting planktivory on coral reefs. The feeding behavior of two species of tube-dwelling coral reef fish (Chaenopsidae) was studied in still and turbulent water. One species of blenny, Acanthemblemaria spinosa , lives in holes higher above the reef surface and feeds mainly on calanoid copepods, while a second, A. aspera , lives closer to the reef surface, feeds mainly on harpacticoid copepods, and is exposed to less water motion than the first. In the laboratory, these two blenny species were video recorded attacking a calanoid copepod ( Acartia tonsa, evasive prey) and an anostracan branchiopod (nauplii of Artemia sp., passive prey). Whereas A. spinosa attacked with the same vigor in still and turbulent water, A. aspera modulated its attack with a more deliberate strike under still conditions than turbulent conditions. For both fish species combined, mean capture success when feeding on Artemia sp. was 100% in still water and dropped to 78% in turbulent water. In contrast, when feeding on Acartia tonsa, mean capture success was 21% in still water and rose to 56% in turbulent water. We hypothesize that, although turbulence reduces capture success by adding erratic movement to Artemia sp. (passive prey), it increases capture success of Acartia tonsa (evasive prey) by interfering with the hydrodynamic sensing of the approaching predator. These opposite effects of water motion increase the complexity of the predator-prey relationship as water motion varies spatially and temporally on structurally complex coral reefs. Some observations were consistent with A. aspera living in a lower energy benthic boundary layer as compared with A. spinosa: slower initial approach to prey, attack speeds modulated according to water velocity, and lower proportion of approaches that result in strikes in turbulent water.Communicated by P.W. Sammarco, Chauvin