Phagotrophic Mechanisms and Prey Selection in Free-living Dinoflagellates1

Three types of feeding mechanisms are known in dinoflagellates: pallium feeding, tube feeding, and direct engulfment. Pallium feeding has only been described for heterotrophic thecate species (Protoperidinium, Diplopsalis group). Tube feeding is commonly found among both naked and thecate species of mixotrophic and heterotrophic dinoflagellates (e.g. Amphidinium, Dinophysis, Gyrodinium, Peridiniopsis). Direct engulfment is mainly found among naked species (e.g. Gymnodinium, Gyrodinium, Noctiluca): recently, however, some thecate species have been shown to use this feeding mechanism as well. Feeding behavior in dinoflagellates involves several steps prior to actual ingestion, including precapture, capture, and prey manipulation. As feeding mechanisms allow the ingestion of relatively large prey or parts thereof, dinoflagellates are regarded as raptorial feeders. While prey size plays an important role in the ability of dinoflagellates to ingest food, this alone cannot explain observed prey preferences. Some dinoflagellate species can be very selective in their choice of prey, while others show a remarkable versatility.     

Prey-dependent retention of dimethylsulfoniopropionate (DMSP) by mixotrophic dinoflagellates

We investigated the retention of dimethylsulfoniopropionate (DMSP) in phototrophic dinoflagellates arising from mixotrophy by estimating the cellular content of DMSP in Karlodinium veneficum (mixotrophic growth) fed for 7-10 days on either DMSP-rich Amphidinium carterae (phototrophic growth only) or DMSP-poor Teleaulax sp. (phototrophic growth only). In K. veneficum fed on DMSP-poor prey, the cellular content of DMSP remained almost unchanged regardless of the rate of feeding, whereas the cellular content of DMSP in cells of K. veneficum fed on DMSP-rich prey increased by as much as 21 times the cellular concentration derived exclusively from phototrophic growth. In both cases, significant fractions (10-32% in the former case and 55-65% in the latter) of the total DMSP ingested by K. veneficum were transformed into dimethylsulfide and other biochemical compounds. The results may indicate that the DMSP content of prey species affects temporal variations in the cellular DMSP content of mixotrophic dinoflagellates, and that mixotrophic dinoflagellates produce DMS through grazing on DMSP-rich preys. Additional studies should be performed to examine the universality of our finding in other mixotrophic dinoflagellates feeding on diverse prey species.     

Capture mechanisms used by the lobate ctenophore, Mnemiopsis leidyi, preying on the copepod Acartia tonsa

Although the lobate ctenophore Mnemiopsis leidyi is an influentialplanktonic predator, the mechanisms enabling it to capture itscharacteristically wide range of prey have not been systematicallyexamined. We recorded interactions between free-swimming M.leidyiand two stages (nauplii, adults) of the calanoid copepod Acartiatonsa in order to determine a mechanistic explanation of thisfeeding process. Prey encounter with Mnemiopsis involved twodifferent processes. The first depended on fluid motions createdby the nearly continuous beating of cilia lining the four auricles.These cilia created a low-velocity flow in which A.tonsa naupliiwere entrained (94% of naupliar encounters) and transportedpast the oral lobes onto the tentillae (oral tentacles). Thenauplii, although capable of rapid escape responses, generallyappeared to be insensitive to the current in which they werecarried. The second process relied upon the collision of swimmingprey with the inner surfaces of the oral lobes and was not obviouslyinfluenced by the auricular feeding currents. Adult A.tonsawere rarely entrained in the auricular flow, but, instead, propelledthemselves into contact with the oral lobes (97% of adult encounters).Both prey capture processes functioned simultaneously. The synergisticfunctioning of these processes probably explains the broad patternsof prey ingestion found by in situ studies of Mnemiopsis feeding.     

THECATE HETEROPHIC DINOFLAGELLATES: FEEDING BEHAVIOR AND MECHANISMS1

The feeding of 18 species of thrcale hetrophi dinoflagellates from three genera (Protoperidininm, Oblea, Zygabikodinium) can all be described within one general framework. These species engulf diatoms and other prey with a pseudopod (herein terned a “Pallium”)which originates at the flagellar pore in the sulcus. The pallium is a highly plastic, membranous organ which rasily strethes to accommodate spines and many as 58 diatom cells in a chain. The contents of the phytoplanklon prey are liquified and transporued throughthe pallioum typically within 7 to 30 minutes of capture (although feeding may last 2 h) teaving an intact but empty cell wall or frustule. Thus far, with few exceptions, Protoperidinium specises have been observed feeding inly on diatoms, whereas two diplopsaloid species feed on dinoflagellates and prasinophytes as well. In four species from the three genera studied. a capture filament has been observed that connects the food to the dinoflagellate prior to extension of the pallium, sometimes allowing the cell to pull the food while swimming. A distinctive precapture swimming behavior is also deseribed foe six species, suggesting that the dinoflagellates are selective grazers.     

Biomass and feeding activity of phagotrophic mixotrophs in the northwestern Black Sea during the summer 1995

Biomass and activities of planktonicmicroorganisms (bacteria, nanoplankton andmicroplankton) were measured in the northwestern BlackSea during summer 1995. The method based on theuptake of fluorescently labeled prey was chosen todetermine the ingestion rate of bacteria andnanoplankton by phagotrophic microorganisms. Thismethod revealed the presence of mixotrophic organismssuch as ’plastid-retaining ciliates‘ in the wholecoastal area. Mixotrophic ciliates were dominated bymicro-sized forms and maximum biomasses were recorded inthe water masses characterised by low nutrientconcentrations but high food particle concentrations. Mixotrophic nanoflagellates were absentand mixotrophic dinoflagellates were observed at onestation only. Mixotrophic ciliates were shown to ingestpreferably bacteria while mixotrophic dinoflagellateswere grazing almost exclusively on nanoflagellates.Although the biomass of mixotrophic organisms weresignificantly lower than those of aplastidic protozoa,their feeding activity contributed to 14 and 24% ofthe ingestion of bacteria and nanoplankton, respectively.This is due to the high specificingestion rate of mixotrophic micro-sized ciliates anddinoflagellates, which were two and three times higher,respectively, than the specific ingestion rate ofbacteria and nanoplankton by aplastidic protozoa. Thissuggests a significant contribution of phagotrophicmixotrophs to the microbial network of thenorthwestern Black Sea. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mixotrophy among Dinoflagellates1

Mixotrophy, used herein for the combination of phototrophy and phagotrophy, is widespread among dinoflagellates. It occurs among most, perhaps all, of the extant orders, including the Prorocentrales, Dinophysiales. Gymnodiniales, Noctilucales, Gonyaulacales, Peridiniales, Blastodiniales. Phytodiniales, and Dinamoebales. Many cases of mixotrophy among dinoflagellates are probably undocumented. Primarily photosynthetic dinoflagellates with their “own” plastids can often supplement their nutrition by preying on other cells. Some primarily phagotrophic species are photosynthetic due to the presence of kleptochloroplasts or algal endosymbionts. Some parasitic dinoflagellates have plastids and are probably mixotrophic. For most mixotrophic dinoflagellates, the relative importance of photosynthesis, uptake of dissolved inorganic nutrients, and feeding are unknown. However, it is apparent that mixotrophy has different functions in different physiological types of dinoflagellates. Data on the simultaneous regulation of photosynthesis, assimilation of dissolved inorganic and organic nutrients, and phagotophy by environmental parameters (irradiance. availablity of dissolved nutrients, availability of prey) and by life history events are needed in order to understand the diverse roles of mixotrophy in dinoflagellates.     

ESTUARINE HETEROTROPHIC CRYPTOPERIDINIOPSOIDS (DINOPHYCEAE): LIFE CYCLE AND CULTURE STUDIES1

Cryptoperidiniopsoids are an unclassified group of delicately thecate heterotrophic dinoflagellates known to be common in eastern U.S. estuarine waters. Over the past 10 years cryptoperidiniopsoids were isolated from different geographical regions and cultured with cryptophyte algal prey. In the seven clonal isolates examined, reproduction was strongly linked to the availability of prey cells. The dinoflagellates phagocytized the contents of prey cells through a tube‐like peduncle, similarly as close relatives of Pfiesteria spp. and several other heterotrophic species. Cell division occurred while encysted, most commonly yielding two biflagellated offspring. Abundant fusing gametes, phagotrophic planozygotes, and cysts with a pronounced nuclear cyclosis characterized persistent sexuality. Cysts with nuclear cyclosis produced two flagellated offspring cells. The resistance of reproductive cysts to antimicrobial treatments was examined, and a simple high‐yield technique was developed for population synchronization while ridding the dinoflagellates of most contaminating vacuolar prey DNA and external contaminants. The DNA content and population DNA profiles of synchronously excysted cryptoperidiniopsoids from different isolates were measured using flow cytometry and were related to the life history of these and other dinoflagellates. Cryptophyte‐fed cultures with versus without extracellular bacteria were compared, and bacteria apparently promoted cryptoperidiniopsoid feeding and growth. Externally bacteria‐free dinoflagellates were cultured in media enriched with dissolved organic nutrients, and nutritional benefit may have occurred in some treatments. The potential for mixotrophic nutrition from maintenance of cryptophyte chloroplasts was examined using flow cytometrically sorted cells, but evidence of kleptoplastidy was not found in these isolates under the conditions imposed.     

甲藻的异养营养型

综述了甲藻的异养类型。目前已知异养营养型在甲藻中广泛存在,只有很少几种甲藻营严格自养营养方式。有近一半的甲藻物种是没有色素体的,还有很多甲藻即使具有色素体也会有异养营养需求,称为兼养营养类型。这些兼养类群不一定主要以有机物作为其获取碳的来源,而仅仅是补充一些生长必需的有机物如维生素、生物素等。兼养类群以渗透营养和腐食营养方式进行,同时也可以寄生方式和共生方式进行兼养生活。无色素体的甲藻以有机物作为碳的唯一来源,仅仅依靠异养方式生存,属于严格异养营养方式,又称有机营养型。它们是甲藻异养营养型的主体,其主要类型有寄生、渗透营养和吞噬营养。由于吞噬营养是甲藻异养的主要类型,因此论述了3种吞噬营养型:吞噬营养方式、捕食茎营养方式和捕食笼营养方式。吞噬营养方式在无甲类和具甲类甲藻中都有存在,主要通过甲藻细胞的纵沟或底部对猎物进行吞噬,也有研究发现吞噬部位为顶孔或片间带。捕食茎营养方式是通过捕食茎刺穿猎物细胞膜并吸食其细胞质来获取营养,在异养甲藻中也较常见。捕食笼营养方式只在原多甲藻属(Protoperidinium)和翼藻属(Diplopsalis)里发现,是甲藻通过鞭毛孔分泌细胞质到胞外形成捕食笼将猎物包裹并进行消化来摄食的。甲藻摄食对象尺寸范围变化较大,小至几微米,大至几百微米。有些甲藻具有摄食选择性,通过感应猎物释放的化学物质来判断猎物的位置并进行摄食,摄食完成后由于体积的增加经常会发生细胞分裂和蜕鞘。对于甲藻异养的其他形式如拦截摄食营养方式、伪足摄食营养方式、口足摄食营养方式、触手摄食营养方式等只作简单介绍。还就甲藻异养的研究方法、其生态学意义和进化学意义进行简要论述,并对相关研究进行展望。     

Quantification of flow during suction feeding in bluegill sunfish

Nearly all aquatic-feeding vertebrates use some amount of suction to capture prey items. Suction prey capture occurs by accelerating a volume of water into the mouth and taking a prey item along with it. Yet, until recently, we lacked the necessary techniques and analytical tools to quantify the flow regime generated by feeding fish. We used a new approach; Digital Particle Image Velocimetery (DPIV) to measure several attributes of the flow generated by feeding bluegill sunfish. We found that the temporal pattern of flow was notably compressed during prey capture. Flow velocity increased rapidly to its peak within 20 ms of the onset of the strike, and this peak corresponded to the time that the prey entered the mouth during capture. The rapid acceleration and deceleration of water suggests that timing is critical for the predator in positioning itself relative to the prey so that it can be drawn into the mouth along with the water. We also found that the volume of water affected by suction was spatially limited. Only rarely did we measure significant flow beyond 1.75 cm of the mouth aperture (in 20 cm fish), further emphasizing the importance of mechanisms, like locomotion, that place the fish mouth in close proximity to the prey. We found that the highest flows towards the mouth along the fish midline were generated not immediately in front of the open mouth, but approximately 0.5 cm anterior to the mouth opening. Away from the midline the peak in flow was closer to the mouth. We propose that this pattern indicates the presence of a bow wave created by the locomotor efforts of the fish. In this scheme, the bow wave acts antagonistically to the flow of water generated by suction, the net effect being to push the region of peak flow away from the open mouth. The peak was located farther from the mouth opening in strikes accompanied by faster locomotion, suggesting faster fish created larger bow waves.     

Implications of the feeding current structure of Euchaeta rimana, a carnivorous pelagic copepod, on the spatial orientation of their prey

Many marine planktonic organisms create water currents to entrainand capture food items. Rheotactic prey entrained within thesefeeding currents often exibit escape reactions. If the directionof escape is away from the feeding current, the prey may successfullydeter predation. If the escape is towards the center of thefeeding current, the prey will be re-entrained towards its predatorand remain at risk of predation. The direction of escape isdependent on (i) the ability of the prey to escape in a directiondifferent than its pre-escape orientation and (ii) the orientationcaused by the interaction of the prey's body with the movingfluid. In this study, the change in orientation of Acartia hudsonicanauplii as a result of entrainment within the feeding currentof Euchaeta rimana, a planktonic predatory copepod, was examined,When escaping in still water, A.hudsonica nauplii were ableto vary their pre-escape direction by only 10. This allowsonly a limited ability to escape in a direction different thantheir pre-escape orientation. Analyses of the feeding currentof E.rimana show the flow speed to be most rapid in the centralregion with an exponential decrease in speed distally. In contrast,flow vorticity is minimal in the center of the feeding currentand maximal at 1.75 mm along the antennae. As a result, thedegree of rotation of the prey towards the center of the feedingcurrent shows a strong dependency on the prey's location withinthe feeding current. The feeding current of E.rimana rotatedthe prey 14 when near the center of the flow field and up to160 when located more distal in the feeding current Since theprey's escape abilities cannot compensate for the rotation dueto the flow, this mechanism will maintain the escaping preywithin the feeding current of their predator. Therefore, thefeeding current facilitates predatory copepods in capturingprey by (i) increasing the amount of water which passes overtheir sensors and through their feeding appendages and (ii)controlling the spatial orientation of their prey prior to escape.     

Prey detection in a cruising copepod

Small cruising zooplankton depend on remote prey detection and active prey capture for efficient feeding. Direct, passive interception of prey is inherently very inefficient at low Reynolds numbers because the viscous boundary layer surrounding the approaching predator will push away potential prey. Yet, direct interception has been proposed to explain how rapidly cruising, blind copepods feed on non-motile phytoplankton prey. Here, we demonstrate a novel mechanism for prey detection in a cruising copepod, and describe how motile and non-motile prey are discovered by hydromechanical and tactile or, likely, chemical cues, respectively.     

Algal toxins alter copepod feeding behavior

Using digital holographic cinematography, we quantify and compare the feeding behavior of free-swimming copepods, Acartia tonsa, on nutritional prey (Storeatula major) to that occurring during exposure to toxic and non-toxic strains of Karenia brevis and Karlodinium veneficum. These two harmful algal species produce polyketide toxins with different modes of action and potency. We distinguish between two different beating modes of the copepod's feeding appendages-a "sampling beating" that has short durations (<100 ms) and involves little fluid entrainment and a longer duration "grazing beating" that persists up to 1200 ms and generates feeding currents. The durations of both beating modes have log-normal distributions. Without prey, A. tonsa only samples the environment at low frequency. Upon introduction of non-toxic food, it increases its sampling time moderately and the grazing period substantially. On mono algal diets for either of the toxic dinoflagellates, sampling time fraction is high but the grazing is very limited. A. tonsa demonstrates aversion to both toxic algal species. In mixtures of S. major and the neurotoxin producing K. brevis, sampling and grazing diminish rapidly, presumably due to neurological effects of consuming brevetoxins while trying to feed on S. major. In contrast, on mixtures of cytotoxin producing K. veneficum, both behavioral modes persist, indicating that intake of karlotoxins does not immediately inhibit the copepod's grazing behavior. These findings add critical insight into how these algal toxins may influence the copepod's feeding behavior, and suggest how some harmful algal species may alter top-down control exerted by grazers like copepods.     

Sensory cues and mechanisms involved in the capture of euphausiids by the Australian salmon, Arripis trutta (Bloch & Schneider)

Experiments indicated that the initial detection of euphausiid prey by Arripis trutta is visual with the cues being shape and/or movement. Immediately before capture of prey in midwater, swimming speed of the fish increased from 15 to 33 cm s⁻¹. The sequence of morphological events during capture is similar to that described for suction feeding in other teleosts such as Atlantic salmon Salmo salar . Occasionally prey would be ejected from the mouth after capture by means of a reversal of the mechanism used in suction feeding.     

Plankton predation rates in turbulence: a study of the limitations imposed on a predator with a non-spherical field of sensory perception

This paper presents an extension to previously published work which studied encounter rates of planktonic predators with restricted perception fields, to examine the related problems of prey capture and predation rates. Small-scale turbulence influences planktonic predation in two ways: the extra energy of the flow enhances the number of encounter events between individual predator and prey meso/micro-zooplankton, but it lowers the capture probability (because the time spent by the predator and prey in close proximity is reduced). Typically, an 'encounter' has usually been defined as an event when a potential prey swims (or is advected) to within a distance R of the predator in any direction. However, there is a considerable body of experimental evidence showing that predators perception fields are far from spherical; often they are wedge shaped (e.g. fish larvae), or strongly aligned with the directions of sensory antennae (e.g. copepods); and this is certain to influence optimal predation strategies. This paper presents a theoretical model which for the first time examines the combined problems of both encounter and capture for a predator with a restricted perception field swimming in a turbulent flow. If such a predator adopts a cruising strategy (continuous swimming, possibly with direction changes) the model predictions suggest that predation rates actually vary little with swimming speed, in contrast to predictions made for spherical perception fields. Consequently, cruising predators are predicted to swim at relatively low speeds whilst foraging. However, application of the model to examine the net energy gain of a typical pause-travel predator (the Atlantic cod larva), does predict the existence of an optimal ratio of the length of pauses to time spent swimming (specifically one pause phase to every two travel phases), in line with experimental observations. Kinematic simulations are presented which support these findings.     

Directional Hydrodynamic Sensing by Free-Swimming Organisms

Many aquatic organisms detect the presence of moving objects in their environment, such as predators, by sensing the hydrodynamic disturbances the movements produce. The resultant water flow is readily detectable by stationary organisms, but free-swimming organisms are carried with the surrounding water and may not detect the bulk surrounding flow, which limits the available information about the source. We have developed a theory that clarifies what information is contained in disturbances generated by an attacking predator that is available to a free-swimming organism and might be extracted from local flow deformations alone. The theory shows that, depending on how well the deformations can be measured in space and time, an organism can reduce the range of possible locations, speeds, sizes, and arrival times of the predator. We apply the theory to planktonic copepods that have mechanosensory hairs along a pair of antennules. The study reveals the presence of “blind spots,” potential ambiguities in resolving from which of two sides a predator attacks, and whether it generates a bow wave or suction. Our findings lead to specific testable hypotheses concerning optimal escape strategies, which are helpful for interpreting the behavior of evasive prey and designing free-swimming robots with sensory capabilities.     

The Ecological Roles of Heterotrophic Dinoflagellates in Marine Planktonic Community1

Heterotrophic dinoflagellates are ubiquitous and often abundant protists in marine environments. Recently, several novel predator-prey relationships between heterotrophic dinoflagellates and other planktonic organisms have been discovered and shown to have diverse ecological roles. Heterotrophic dinoflagellates are predators on a wide array of prey items, including phytoplankton, copepod eggs, and early naupliar stages. They are in turn important prey for some metazoa. Some heterotrophic dinoflagellates are predators of and simultaneously prey for other dinoflagellates. These newly discovered predator-prey relationships may influence our conventional view of energy flow and carbon cycling in the marine planktonic community.     

Mixotrophy in the newly described phototrophic dinoflagellate Woloszynskia cincta from western Korean waters: feeding mechanism, prey species and effect of prey concentration

Woloszynskia species are dinoflagellates in the order Suessiales inhabiting marine or freshwater environments; their ecophysiology has not been well investigated, in particular, their trophic modes have yet to be elucidated. Previous studies have reported that all Woloszynskia species are photosynthetic, although their mixotrophic abilities have not been explored. We isolated a dinoflagellate from coastal waters in western Korea and established clonal cultures of this dinoflagellate. On the basis of morphology and analyses of the small/large subunit rRNA gene (GenBank accession number=FR690459), we identified this dinoflagellate as Woloszynskia cincta. We further established that this dinoflagellate is a mixotrophic species. We found that W. cincta fed on algal prey using a peduncle. Among the diverse prey provided, W. cincta ingested those algal species that had equivalent spherical diameters (ESDs) ≤12.6 μm, exceptions being the diatom Skeletonema costatum and the dinoflagellate Prorocentrum minimum. However, W. cincta did not feed on larger algal species that had ESDs≥15 μm. The specific growth rates for W. cincta increased continuously with increasing mean prey concentration before saturating at a concentration of ca. 134 ng C/ml (1,340 cells/ml) when Heterosigma akashiwo was used as food. The maximum specific growth rate (i.e. mixotrophic growth) of W. cincta feeding on H. akashiwo was 0.499 d(-1) at 20 °C under illumination of 20 μE/m(2) /s on a 14:10 h light-dark cycle, whereas its growth rate (i.e. phototrophic growth) under the same light conditions without added prey was 0.040 d(-1). The maximum ingestion and clearance rates of W. cincta feeding on H. akashiwo were 0.49 ng C/grazer/d (4.9 cells/grazer/d) and 1.9 μl/grazer/h, respectively. The calculated grazing coefficients for W. cincta on co-occurring H. akashiwo were up to 1.1 d(-1). The results of the present study suggest that grazing by W. cincta can have a potentially considerable impact on prey algal populations.     

The functional morphology of lingual prey capture in a scincid lizard,Tiliqua scincoides (Reptilia: Squamata)

We investigated the functional morphology of lingual prey capture in the blue‐tongued skink, Tiliqua scincoides, a lingual‐feeding lizard nested deep within the family Scincidae, which is presumed to be dominated by jaw‐feeding. We used kinematic analysis of high‐speed video to characterize jaw and tongue movements during prey capture. Phylogenetically informed principal components analysis of tongue morphology showed that, compared to jaw‐feeding scincids and lacertids, T. scincoides and another tongue‐feeding scincid, Corucia zebrata, are distinct in ways suggesting an enhanced ability for hydrostatic shape change. Lingual feeding kinematics show substantial quantitative and qualitative variation among T. scincoides individuals. High‐speed video analysis showed that T. scincoides uses significant hydrostatic elongation and deformation during protrusion, tongue‐prey contact, and retraction. A key feature of lingual prey capture in T. scincoides is extensive hydrostatic deformation to increase the area of tongue‐prey contact, presumably to maximize wet adhesion of the prey item. Adhesion is mechanically reinforced during tongue retraction through formation of a distinctive “saddle” in the foretongue that supports the prey item, reducing the risk of prey loss during retraction.     

Mixotrophy in red tide algae raphidophytes

Marine raphidophytes are common red tide organisms that are distributed worldwide. They are known to be harmful to other plankton and fish and have often caused large-scale fish mortality in many countries. Thus, the population dynamics of raphidophytes is a critical concern for scientists, the aquaculture industry, and government officers from many countries. Raphidophyte growth and mortality should be investigated to understand bloom dynamics. Raphidophytes were thought to be exclusively autotrophic organisms. However, several recent studies have revealed that raphidophytes are able to feed on heterotrophic and autotrophic bacteria, i.e. raphidophytes are mixotrophic algae. Further, high-resolution video microscopy has revealed the mechanism by which raphidophytes feed on bacteria, which involves capturing prey cells in the mucus excreted by mucocysts and engulfing the cells through mucocysts. These discoveries may influence the conventional view on both raphidophyte bloom dynamics and plankton energy flow and carbon cycling. In the present study, I review prey, feeding mechanisms, and ingestion rates of mixotrophic marine raphidophytes. In addition, I examine the ecological significance of raphidophyte mixotrophy.     

Effects of ram speed on prey capture kinematics of juvenile Indo-Pacific tarpon,Megalops cyprinoides

We examined the effects of variation in swimming speed, or ‘ram speed’, on the feeding kinematics of juvenile Indo-Pacific tarpon, Megalops cyprinoides. Tarpon were filmed feeding on non-elusive prey at 500 images s^?1. Prey items were offered at one end of the filming tank, the opposite end where tarpon grouped, to encourage them to use a ram strategy to capture their prey. We describe tarpon as ram-suction feeders. Ram speed varied among strikes from 0.19 to 1.38 m/s and each individual produced speeds that spanned at least 0.9 m/s across trials. Although suction distances were much less variable, prey movement towards the predator was present in all feeding trials. There was a strong positive relationship between initial predator – prey distance and ram speed (r²=0.72, P<0.001). When tarpon initiated their strike from further away, they achieved higher ram speeds, but also took longer to capture their prey. All other timing variables were unaffected by ram speed whereas at higher ram speeds tarpon exhibited greater expansion of the mouth and buccal cavity. Greater buccal expansion accomplished in the same period of time implies that both the total volume of water captured and the water flow rate entering the mouth was greater in strikes at higher ram speeds. Our results demonstrate how feeding kinematics may vary as a function of ram speed, and how fish predators that lack jaw protrusion and have a large gape capacity can maximize their feeding success by altering their swimming speed.