Effects of the toxic dinoflagellate Alexandrium catenella on histopathogical and escape responses of the Northern scallop Argopecten purpuratus

Juvenile Northern scallops Argopecten purpuratus were exposed to cultures of the paralytic shellfish toxin (PST) producing dinoflagellate, Alexandrium catenella, or a non-toxic microalga as a control, T-iso. After 3 and 6 days of exposure to either A. catenella or T-iso, scallops were stimulated to elicit an escape response by exposing them to the predatory sea star Meyenaster gelatinosus. We monitored the escape response of the scallops in terms of reaction time after first contact with the sea star, number of claps (burst of rapid valve closures) until exhaustion, clapping time, clapping rate, the time scallops spent closed when exhausted, and recovery from the initial number of claps, clapping time and clapping rate. Additionally, histopathological and stress responses (through heat-shock protein [hsp70] induction), as well as accumulation of Paralytic Shellfish Poisoning (PSP) toxins, were monitored on scallops after 3 and 6 days of exposure to A. catenella. After 6 days of exposure, scallops exposed to A. catenella accumulated PSTs and reacted more rapidly with a higher clapping rate, however the duration of their escape response was shorter than controls, when exposed to M. gelatinosus. Additionally, scallops exposed to A. catenella showed histopathological features, especially after 6 days of exposure, including increased melanization of the tissues and myopathy, with high levels of degeneration of the muscle fibers. A six-day exposure to A. catenella also caused an increase in prevalence of rickettsiales-like organisms within scallop tissues. This study suggests that PST accumulation can affect the interaction between the Northern scallop and both pathogens and predators, potentially increasing their susceptibility to either of them.     

Effect of reproduction on escape responses and muscle metabolic capacities in the scallop Chlamys islandica Müller 1776

In scallops, gametogenesis leads to mobilization of glycogen and proteins from the adductor muscle towards the gonad. This mobilization is likely to diminish the metabolic capacities of the adductor muscle and thereby the scallops' escape response. We examined the escape response in terms of number of valve claps until exhaustion, rate of clapping and the recovery during and after valve closure in adult scallops, Chlamys islandica, sampled at different stages in the reproductive cycle (immature, mature, before and after spawning). In parallel, we measured muscle glycogen, protein and phosphoarginine contents, the oxidative capacity of mitochondria isolated from the adductor muscle and levels of muscle enzymes which are active during exercise and recovery. The number of claps (24-26), rate of clapping ( approximately 13 clapsmin(-1)) and phosphoarginine and arginine kinase levels were similar during the different reproductive stages. All immature scallops responded to restimulation immediately after opening their valves, while only 62% of mature, 82% of prespawned and 38% of spawned scallops responded. Immature animals completely recovered their initial swimming capacity within 4 h of opening their valves, but mature, prespawned and spawned scallops needed 18, 12 and 18 h, respectively. Overall phasic adductor muscle from mature, prespawned and spawned animals showed decreased glycogen phosphorylase, phosphofructokinase, pyruvate kinase (except for prespawned), octopine dehydrogenase and citrate synthase levels, a deterioration of the oxidative capacity of mitochondria and a marked decrease in glycogen content compared to immature scallops. Therefore, during gonadal maturation and spawning, C. islandica did not change its clapping capacity, but slowed its recuperation from exhausting burst exercise, both during and after valve closure, likely due to the decreased metabolic capacity of the adductor muscle.     

Prey selection and the functional response of sea stars (Asterias vulgaris Verrill) and rock crabs (Cancer irroratus Say) preying on juvenile sea scallops (Placopecten magellanicus (Gmelin)) and blue mussels (Mytilus edulis Linnaeus)

Predators in nature include an array of prey types in their diet, and often select certain types over others. We examined (i) prey selection by sea stars (Asterias vulgaris) and rock crabs (Cancer irroratus) when offered two prey types, juvenile sea scallops (Placopecten magellanicus) and blue mussels (Mytilus edulis), and (ii) the effect of prey density on predation, prey selection, and component behaviours. We quantified predation rates, behavioural components (proportion of time spent searching for prey, encounter probabilities) and various prey characteristics (shell strength, energy content per prey, handling time per prey) to identify mechanisms underlying predation patterns and to assess the contribution of active and passive prey selection to observed selection of prey. Sea stars strongly selected mussels over scallops, resulting from both active and passive selection. Active selection was associated with the probability of attack upon encounter; it was higher on mussels than on scallops. The probability of capture upon attack, associated with passive selection, was higher for mussels than for scallops, since mussels can not swim to escape predators. Sea stars consumed few scallops when mussels were present, and so did not have a functional response on scallops (the target prey). Rock crabs exhibited prey switching: they selected mussels when scallop density was very low, did not select a certain prey type when scallop density was intermediate, and selected scallops when scallop density was high relative to mussel density. The interplay between encounter rate (associated with passive selection) and probability of consumption upon capture (associated with both active and passive selection) explained observed selection by crabs. Scallops were encountered by crabs relatively more often and/or mussels less often than expected from random movements of animals at all scallop densities. However, the probability of consumption varied with scallop density: it was lower for scallops than mussels at low and intermediate scallop densities, but tended to be higher for scallops than mussels at high scallop densities. When mussels were absent, crabs did not have a functional response on scallops, but rather were at the plateau of the response. When mussels were present with scallops at relatively low density, crabs exhibited a type II functional response on scallops. Our results have implications for the provision of protective refuges for species of interest (i.e., scallops) released onto the sea bed, such as in population enhancement operations and bottom aquaculture.     

Effects of substrate on interactions between juvenile sea scallops (Placopecten magellanicus Gmelin) and predatory sea stars (Asterias vulgaris Verrill) and rock crabs (Cancer irroratus Say)

We investigated the effect of substrate (glass bottom, sand, granule, pebble) on predation of juvenile sea scallops (Placopecten magellanicus) by sea stars (Asterias vulgaris) and rock crabs (Cancer irroratus) at two prey sizes (11-15 mm and 24-28 mm shell height), and two prey densities (10 and 30 scallops per aquarium) in laboratory experiments. Specifically, we quantified predation rate and underlying behaviours (proportion of time a predator spent searching for and handling prey, encounter rate between predators and prey, and various outcomes of encounters). We detected a significant gradual effect of particle size of natural substrates on sea star predation: specifically, predation rate on and encounter rate with small scallops tended to decrease with increasing particle size (being highest for sand, intermediate for granule, and lowest for pebble). Substrate type did not significantly affect predation rates or behaviours of sea stars preying on large scallops or of rock crabs preying on either scallop size classes. Other factors, such as prey size and density, were important in the scallop-sea star and scallop-rock crab systems. For example, predation rate by sea stars and crabs and certain sea star behaviours (e.g. probability of consuming scallops upon capture) were significantly higher with small scallops than with large scallops. As well, in interactions between small scallops and sea stars, predation rate and encounter rate increased with prey density, and the proportion of time sea stars spent searching was higher at low prey density than high prey density. Thus, substrate type may be a minor factor determining predation risk of seeded scallops during enhancement operations; prey size and prey density may play a more important role. However, substrate type still needs to be considered when choosing a site for scallop enhancement, as it may affect other scallop behaviours (such as movement).     

Tonic contractions allow metabolic recuperation of the adductor muscle during escape responses of giant scallop Placopecten magellanicus

To escape from starfish predators, giant scallops, Placopecten magellanicus, swim using series of strong phasic contractions interrupted by tonic contractions. To investigate whether these tonic contractions allow metabolic recuperation of the adductor muscle, we sampled scallops at rest (Control), after an initial series of phasic contractions (Phasic) and after 1 min of tonic contraction following their initial phasic contractions (Phasic + Tonic) and compared muscle levels of phosphoarginine, adenylate nucleotides (ATP, ADP and AMP) and adenylate energy charge (AEC). Scallops in the two active groups did not differ in the numbers of phasic contractions or the mean phasic force production. Phosphoarginine concentrations in the adductor muscle decreased with phasic activity and remained low after 1 min of tonic contraction. ATP and ADP and total adenylate levels did not differ between the three groups, but AMP levels were higher in the scallops sampled after phasic contractions than in control scallops. The AEC was reduced by phasic contractions but returned to control levels after 1 min of tonic contraction. A significant negative correlation between AEC and the number of claps in the Phasic group disappeared in the Phasic + Tonic group. Thus, tonic contractions following phasic contractions allow partial metabolic recovery of the adductor muscle by returning AEC to control levels. However, phosphoarginine levels did not recover during tonic contractions, and a negative correlation between the number of claps and phosphoarginine levels remained in the Phasic + Tonic group. By interspersing tonic contractions between series of phasic contractions, scallops improved muscle energetic status, which should help maintain phasic force production during the remainder of the escape response.     

Behavioural mechanisms of sea stars (Asterias vulgaris Verrill and Leptasterias polaris Müller) and crabs (Cancer irroratus Say and Hyas araneus Linnaeus) preying on juvenile sea scallops (Placopecten magellanicus (Gmelin)), and procedural effects of scallop tethering

We compared predation rates and behaviours of sea stars (Asterias vulgaris and Leptasterias polaris) and crabs (Cancer irroratus and Hyas araneus) preying on juvenile sea scallops (Placopecten magellanicus, 25-35 mm shell height) in laboratory. These predatory species co-occur with sea scallops on the sea bed of the Gulf of St. Lawrence, Canada, and limit scallop survival in seeding operations. We also examined, under controlled conditions, the effect of tethering scallops on predator-prey interactions. Predation rates, time budgets and encounter behaviours observed for A. vulgaris and C. irroratus preying on free (untethered) scallops were comparable to previous studies. C. irroratus were more effective predators as they consumed 3.1 scallops predator^− 1 day^− 1, although they spent only 0.9% of their time searching for prey. A. vulgaris consumed 0.9 scallops predator^− 1 day^− 1 and spent 7.6% of their time searching. Sea stars L. polaris had a lower predation rate (0.02 scallop predator^− 1 day^− 1) than A. vulgaris. The frequent avoidance behaviour of L. polaris and its low ability to capture scallops support the notion that scallops are not a main component of this sea star's diet. Crabs H. araneus had similar predation rates (1.3 scallops predator^− 1 day^− 1) and behaviours to C. irroratus, although the probability of consumption upon capture was affected by relatively high numbers of rejections and post-capture escapes of scallops. As expected, the tethering procedure increased predation rate of L. polaris (about 19 times higher), but surprisingly did not significantly affect that of A. vulgaris. Examination of behaviours indicated that A. vulgaris offered tethered scallops tended to have a higher probability of capture, but spent less time searching for prey (possibly because satiation was reached) than A. vulgaris offered free scallops. Predation rates and behaviours of both crab species were not affected by tethering, since encounter rate was the primary determinant of crab-scallop interactions. Identification and quantification of behaviours underlying the predation process allowed us to mathematically model predator-related mortality for the four predator species.     

Swimming performance, metabolic rates, and their correlates in the Iceland scallop Chlamys islandica

The dramatic escape response of some scallops is modified by reproductive investment and by acclimation temperature. Despite considerable knowledge of the physiology of the escape response, functional links between escape response performance, organismal rates of oxygen uptake, and tissue metabolic capacities are little known. We measured oxygen consumption rates (standard, maximal, and aerobic scope), escape behavior (initial and repeat performance), tissue mass, condition index, protein content, and tissue metabolic capacities in the Iceland scallop Chlamys islandica to examine links between these parameters. Postexercise oxygen consumption rates were positively linked to contraction rate (repeat test) and to pyruvate kinase activity in the adductor muscle but negatively linked to digestive gland wet mass. Swimming behavior was mainly related to activity of glycolytic enzymes, and enzymatic activities were related to anatomic parameters. Scallop behavior and physiology change with size, both within our samples and on a larger scale. Small scallops showed more intense swimming activity and had higher arginine kinase activities but lower glycolytic enzyme activities in their adductor muscle than larger scallops. This corresponds to the ontogenetic change in susceptibility to predation and in habitat use observed in C. islandica.     

The motile escape response of a sessile prey: A sponge-scallop mutualism

The association of the sponges Myxilla incrustans (Esper) and Mycale adhaerens (Lambe) with the scallops Chlamys hastata hericia Gould and C. rubida (Hines) is shown to be a mutualism, which protects the sponges from predatory sponge-rasping dorid nudibranchs and the scallops from predatory starfish. The sponge is protected by scallop motility (also shown for the Suberites ficus-hermit crab association). The sponge helps to protect the scallops by altering the surface texture of the shell so increasing the efficacy of the swimming escape response by decreasing the adhesive abilities of asteroid tube-feet. The sponge also provides tactile camouflage against certain predatory starfish. There was no evidence that either component chemically deceived or repelled the predators of the other component. Predation pressure on both components of the association appears to be the major force leading to the mutualism.     

Vulnerability of newly settled plaice (Pleuronectes platessa L.) to predation: effects of habitat structure and predator functional response

Plaice (Pleuronectes platessa) nursery grounds on the Swedish west coast have been subject to increasing cover of annual green macroalgae during recent years, with growth of algae starting at the time of plaice settlement in April to May. A laboratory experiment was performed to investigate how the vulnerability to predation of metamorphosing plaice was affected by the presence of filamentous algae. Predation by shrimps (Crangon crangon) on settling plaice larvae was higher on sand than among algae, whereas predation by crabs (Carcinus maenas) was unaffected by habitat type, suggesting a lower overall mortality of plaice in the vegetated habitat. When predators and prey were presented with a combination of the two habitats, predation by shrimps was as high as that in the sand treatment alone, whereas predation by crabs was lower than that in the two treatments with one habitat. Based on these results, an additional experiment was performed, investigating the functional response of shrimps to six densities of juvenile plaice in a sand habitat with alternative prey present. The proportional mortality of juvenile plaice (12-16 mm total length (TL)) was density-dependent and was best described by a type III (sigmoid) functional response of the predatory shrimps. The results suggested that the combined predation pressure from shrimps and crabs was lower among algae than on sand, but settling plaice and predatory shrimps chose the sand habitat. Plaice densities in the sigmoid part of the obtained functional response curve represented normal to high field densities of plaice on the Swedish west coast, suggesting that shrimp predation could have a stabilising effect on plaice recruitment. The formation of macroalgae mats could therefore lead to a concentration of plaice juveniles in the remaining sand habitat and increased mortality through density-dependent predation by shrimps.     

Edge effects in patchy seagrass landscapes: The role of predation in determining fish distribution

Predation is often described as an underlying mechanism to explain edge effects. We assessed the importance of predation in determining edge effects in seagrass using two approaches: a video survey to sample predators at small scales across seagrass edges, and a tethering experiment to determine if predation was an underlying mechanism causing edge effects. Underwater videos were placed at four positions: middle of seagrass patches; edge of seagrass; sand immediately adjacent to seagrass and sand distant from seagrass. Fish abundances and the time fish spent in view were measured. The main predatory fish (Australian salmon, Arripis spp.) spent more time over adjacent sand than other positions, while potential prey species (King George whiting, Sillaginodes punctata (Cuvier), recruits) were more common in the middle of seagrass patches. Other species, including the smooth toadfish, Tetractenos glaber (Freminville), and King George whiting adults, spent more time over sand adjacent to seagrass than distant sand, which may be related to feeding opportunities. King George whiting recruits and pipefish (Stigmatopora spp.) were tethered at each of the four positions. More whiting recruits were preyed upon at outer than inner seagrass patches, and survival time was greater in the middle of shallow seagrass patches than other positions. Relatively few pipefish were preyed upon, but of those that were, survival time was lower over sand adjacent to seagrass than at the seagrass edge or middle. Video footage revealed that salmon were the dominant predators of both tethered King George whiting recruits and pipefish. The distribution of predators and associated rate of predation can explain edge effects for some species (King George whiting) but other mechanisms, or combinations of mechanisms, are determining edge effects for other species (pipefish).     

Hydrodynamic mediation of predator-prey interactions: differential patterns of prey susceptibility and predator success explained by variation in water flow

In most shallow water marine systems, fluid movements vary on scales that may influence local community dynamics both directly, through changes in the abundance of species, and indirectly, by modifying important behaviors of organisms. We examined how differences in current speed affect the outcome of predator-prey interactions for two species of marine benthic predators (knobbed whelks, Busycon carica, and blue crabs, Callinectes sapidus) foraging on two common prey species (bay scallops, Argopecten irradians, and hard clams, Mercenaria mercenaria). The predators differ in their foraging strategies and prey in their potential escape responses. Predation by blue crabs, highly mobile predators/scavengers that rely upon chemical odors transported in the water column to locate prey, could be strongly affected by changes in current speed and turbulent mixing because their foraging strategy relies on a high degree of spatial integration of prey odor plumes. Whelks, slow moving, predatory gastropods that often forage with their bodies buried in the sediment, may be less susceptible to flow-induced distortion of prey odor plumes because their sluggish movements result in a high degree of temporal integration of prey odors. Bay scallops, relatively mobile bivalves capable of rapid short-distance swimming burst, and hard clams, sedentary bivalves, have been shown to respond to varying degrees to predator odors that are dispersed in the water column. Flow regime for the predator-prey experiments was manipulated in situ using large channels. Predation by blue crabs on both juvenile hard clams and bay scallops decreased with increases in water flow (0-12 vs. 0-30 cm s⁻¹). Whelk predation on bay scallops increased with increases in water flow, whereas predation by whelks on hard clams did not differ between flow regimes. For blue crabs movement decreased at periods of high water flow. Because blue crabs locate prey through chemolocation of water-borne cues, which are diluted rapidly at higher flows, decreases in foraging may result from the inability to successfully detect prey at enhanced flows. Differences in predation by whelks could not be explained by a similar mechanism. Visual observations of foraging whelks revealed no differences in whelk behavior between the two flow regimes. The pattern of higher whelk predation on scallops at enhanced flow is likely to be related to a flow-inhibiting ability of scallops to detect predator approach. Thus, flow enhancement interferes with three of the predator-prey systems but the effect on predator success depends on whether the predator or prey is most affected.     

High-energy phosphate metabolism during exercise and recovery in temperate and Antarctic scallops: an in vivo 31P-NMR study

In vivo (31)P-nuclear magnetic resonance (NMR) spectroscopy was used to measure the levels of ATP, phospho-l-arginine (PLA), and inorganic phosphate in the adductor muscle of the Antarctic scallop Adamussium colbecki and two temperate species, Aequipecten opercularis and Pecten maximus. Graded exercise regimes from light (one to two contractions) to exhausting (failing to respond to further stimulation) were imposed on animals of each species at its habitat temperature (0 degrees vs. 12 degrees C, respectively). NMR spectroscopy allowed noninvasive measurement of metabolite levels and intracellular pH at high time resolution (30-120-s intervals) during exercise and throughout the recovery period. Significant differences were shown between the magnitude and form of the metabolic response with increasing levels of exercise in each species. After exhaustion, short-term (first 15 min) muscle alkalosis was followed by acidosis of up to 0.2 pH units during the recovery process. Aequipecten opercularis had similar resting muscle PLA levels compared with either P. maximus or A. colbecki but used a fivefold greater proportion of this store per contraction and was able to perform only half as many claps (maximum of 24) as the other species before exhaustion. All species regenerated their PLA store at a similar rate despite different environmental temperatures. These findings argue for some cold compensation of muscular performance and recovery capacities in the Antarctic scallop, albeit at levels of performance similar to scallops with low activity lifestyles from temperate latitudes.     

Parasite-induced alteration of odour responses in an amphipod–acanthocephalan system

Odour-related behaviours in aquatic invertebrates are important and effective anti-predator behaviours. Parasites often alter invertebrate host behaviours to increase transmission to hosts. This study investigated the responses of the amphipod Hyalella azteca when presented with two predator chemical cues: (i) alarm pheromones produced by conspecifics and (ii) kairomones produced by a predatory Green Sunfish (Lepomis cyanellus). We compared the responses of amphipods uninfected and infected with the acanthocepalan parasite Leptorhynchiodes thecatus. Uninfected amphipods reduced activity and increased refuge use after detecting both the alarm pheromones and predator kairomones. Infected amphipods spent significantly more time being active and less time on the refuge than uninfected amphipods, and behaved as if they had not detected the chemical stimulus. Therefore, L. thecatus infections disrupt the amphipods’ anti-predator behaviours and likely make their hosts more susceptible to predation.     

Sex differences in reproductive investment: maternal care reduces escape response capacity in the whelk Buccinum undatum

We evaluated the effect of reproductive state and biochemical status of male and female whelks Buccinum undatum on their escape responses (foot contortions) when touched by their major predator, the sea star Leptasterias polaris. Gonad growth in males was not associated with a decrease in their general energetic and metabolic capacity, nor in their capacity for escape responses, but did reduce the rate of foot contortions during recuperation from exhaustive exercise. Similarly, the energetic status of females was good when the ovary was mature, suggesting that oogenesis did not require somatic reserves. On the other hand, the energetic status and muscle metabolic capacities of females dropped with egg laying. This decrease was associated with a reduced capacity for escape responses. Thus, egg laying resulted in (1) major drops in the carbohydrate and protein contents of the foot, (2) decreased activities of several glycolytic enzymes (LDH, ADH and APK) in the foot muscle, (3) a sharp drop in the digestive gland index, (4) a decrease in the number of foot contortions and (5) a decreased ability to recover from exhaustive escape exercise. Reproductive costs are much greater for females than males (as females must produce protective egg capsules, search for egg-laying sites and lay the capsules). Females have greater escape capacities than males, except directly after egg laying when their energetic reserves are virtually depleted. The greater capacity of females for escape responses may attenuate the risks associated with their greater boldness in stealing food from their predator L. polaris, particularly prior to egg laying.     

Swimming behavior and morphometry of the file shell Limaria fragilis

Swimming has evolved in only a few orders of Bivalves. In this study, the behavior, morphometry, and mechanics of swimming in the file shell Limaria fragilis were characterized and compared to the better understood scallops. Absolute swimming speed (cm?sec^?1) increased with increasing shell height, although relative swimming speed (body lengths?sec^?1) did not covary with shell height. The increase in absolute swimming speed was due to an increase in the distance covered during each valve clap as clap distance (cm?clap^?1) also increased with shell height while clapping frequency (claps?sec^?1) did not covary with animal size. Limaria fragilis displayed a variety of morphological changes related to size. Shell length was negatively allometric with shell height indicating the shell became proportionately slimmer in larger animals. Dry shell mass was negatively allometric with shell height, while both dry adductor muscle mass and dry mantle + tentacle mass were positively allometric. Autotomy of mantle tentacles significantly decreased clap distance by 13% without affecting clapping frequency or swimming speed.     

Escape tactics by a neotropical montane lizard: a comparison of flight responses against natural and nonnatural predators

Prey must judge the level of threat related to a given predator attack to employ the most efficient escape strategy at a low cost. In this context, the capacity of prey to correctly assess the threat from predators might optimise their decision on the strategy employed to flee. We examined the escape behaviour of the montane lizard Tropidurus montanus in response to different types of predatory stimuli. Lizards stimulated by a model of a natural predator ran shorter distances straight towards shelter and spent less time in flight. On the other hand, when exposed to a model of a nonnatural predator, T. montanus performed longer flights in distance and time, running across open and exposed substrates in the view of predators. These results showed that the lizard T. montanus made different escape decisions according to the type of predatory stimulus.     

Spatio-temporal patterns in the mortality of bay scallop recruits in North Carolina: investigation of a life history anomaly

By timing reproduction to occur when predatory mortality on progeny is minimal, organisms may maximize recruitment to adult populations. Accordingly, an hypothesis to explain the greater importance of fall than spring spawning to North Carolina populations of bay scallops (Argopecten irradians) is that predatory mortality of bay scallop recruits is lower in fall and winter than spring and summer. To test this hypothesis, we measured predatory mortality of scallop recruits monthly. To infer the identities of predators that are most important in determining patterns of mortality of bay scallop recruits in spring and in fall, predatory mortality of bay scallop recruits was compared between the edge and interior of sheltered and exposed seagrass patches during the day and at night in May and November. Consideration of predatory mortality throughout the year indicated that mortality of scallop recruits over late spring and summer approaches 100% but is negligible over late fall and winter. In May, predatory mortality of scallop recruits was similar during day and night but greater at exposed than sheltered sites. In November, predatory mortality was greater during night than day and slightly greater at sheltered than exposed sites. In neither month did position within patch influence mortality, and at all times and places, missing and crushed scallops contributed a higher proportion than drilled scallops to the total dead. These spatio-temporal patterns of mortality of scallop recruits suggest that mud crabs, Dyspanopeus sayi, which are more abundant in exposed than sheltered seagrass beds during spring and can feed by day and night, are a likely major contributor to spatio-temporal pattern in mortality of scallop recruits in North Carolina. Blue crabs, Callinectes sapidus, which are many times more abundant in summer than winter, may also contribute to observed seasonal patterns in mortality. The dramatically lower rates of predation on bay scallops over the winter months appear to provide fall settlers with a temporal window of opportunity to recruit to the adult population. Although spring spawning contributes little to adult populations in most years because of high rates of predatory mortality during summer, we hypothesize that spring spawning persists because infrequent devastating perturbations, such as hurricanes and red tides, can result in complete failure of fall recruitment.     

Avoidance and escape responses of the gastropod mollusc Olivella biplicata (Sowerby) to predatory asteroids

The sand-dwelling gastropod Olivella biplicata (Sowerby) gives two chemically-mediated defensive responses to predatory asteroids — an avoidance and an escape response. An avoidance response is triggered by water-borne chemicals diffusing from distant starfish. When snails on the surface of the sand sense a distant predatory starfish, they avoid the predator by burying themselves in the sand. Strong avoidance responses are given to the predatory asteroids Pisaster brevispinus (Stimpson), P. ochraceus (Brandt), and Pycnopodia helianthoides (Brandt). Little or no response is given to the omnivorous asteroid Patiria miniata (Brandt) or to the predatory gastropod Polinices lewisii (Gould). An escape response is given when a snail on the surface is contacted by the starfish Pisaster brevispinus. Upon contact, the snail immediately retracts the propodium, sometimes throwing the metapodium forward at the same time; the snail then turns sharply away from the point of contact, and buries itself. Both avoidance and escape responses can be observed in the field and laboratory.     

Locomotor performance and muscle metabolic capacities: impact of temperature and energetic status

In aquatic ectotherms, muscle metabolic capacities are strongly influenced by exogenous factors, principally temperature and food availability. Seasonal changes in temperature lead many organisms to modify their metabolic machinery so as to maintain capacity even in "slower" cold habitats. Modifications of mitochondrial capacities are central in this response. The increases in protein-specific oxidative capacities of mitochondria during cold acclimation of temperate fishes do not occur during the evolutionary adaptation to cold in Antarctic species. Instead, Antarctic fishes tend to increase the proportion of fibre volume devoted to mitochondria, perhaps to facilitate intracellular distribution of oxygen and metabolites. Variation in energetic status can drastically modify muscle metabolic status, with glycolytic muscle changing more than oxidative muscle. This in turn impacts swimming performance. A decrease in the condition of cod leads endurance at speeds above Ucrit to drop by 70%. Sprint swimming is less affected, perhaps as it does not exhaust glycolytic muscle. We used interindividual variation in muscle metabolic capacities to identify correlates of swimming performance in stickleback and cod. Activities of cytochrome c oxidase in glycolytic muscle are a correlate of sprint swimming in stickleback (Gasterosteus aculeatus) and cod (Gadus morhua), whereas lactate dehydrogenase activities in glycolytic muscle are a correlate of cod endurance swimming. In scallops, gonadal maturation leads to virtually complete mobilisation of glycogen from muscle. This does not reduce the capacity of the scallops, Chlamys islandica and Euvola ziczac, to mount escape responses, but significantly slows their recuperation from exhaustive exercise. Muscle metabolic capacities fall in parallel with glycogen mobilisation. In the compromise between muscles' dual roles as a motor and a macromolecular reserve, a significant loss in locomotory ability occurs during gametogenesis and spawning. Reproductive fitness takes the upper hand over maintenance of performance.     

Contemporary Parallel Diversification,Antipredator Adaptations and Phenotypic Integration in an Aquatic Isopod

It is increasingly being recognized that predation can be a strong diversifying agent promoting ecological divergence. Adaptations against different predatory regimes can emerge over short periods of time and include many different traits. We studied antipredator adaptations in two ecotypes of an isopod (Asellus aquaticus) that have, diverged in parallel in two Swedish lakes over the last two decades. We quantified differences in escape speed, morphology and behavior for isopods from different ecotypes present in these lakes. Isopods from the source habitat (reed) coexist with mainly invertebrate predators. They are more stream-profiled and have higher escape speeds than isopods in the newly colonized stonewort habitat, which has higher density of fish predators. Stonewort isopods also show more cautious behaviors and had higher levels of phenotypic integration between coloration and morphological traits than the reed isopods. Colonization of a novel habitat with a different predation regime has thus strengthened the correlations between pigmentation and morphology and weakened escape performance. The strong signature of parallelism for these phenotypic traits indicates that divergence is likely to be adaptive and is likely to have been driven by differences in predatory regimes. Furthermore, our results indicate that physical performance, behavior and morphology can change rapidly and in concert as new habitats are colonized.