Distances of dispersal of juvenile bivalves (Mya arenaria (Linnaeus), Mercenaria mercenaria (Linnaeus), Gemma gemma (Totten))

Although it is recognized that many species of benthic invertebrates continue to disperse after settlement, particularly in soft-bottom habitats, the scale over which movements of juveniles occur is not well known. This study combined laboratory flume experiments assessing the effects of clam size, species, and water velocity on rates and distances of dispersal of three species of juvenile bivalves with field measurements of loss rates and distances of dispersal of transplanted bivalves in the Navesink River estuary in New Jersey, USA. Dispersal distances measured in the laboratory ranged from an average of 1.6 to 40 cm h^− 1 depending on clam size, species, and flow speed. Distances and likelihood of dispersal were generally greater for Mya arenaria than for Mercenaria mercenaria or Gemma gemma, although differences between species were not consistent. As predicted, smaller (1.3 mm) M. arenaria tended to disperse more than larger (3.7 mm) ones, although no significant differences were detected between two sizes (1.8 and 3.4 mm) of M. mercenaria. The similarity of the erosion thresholds of dead clams across sizes and species suggests that burrowing behaviour plays an important role in determining variation in dispersal due to clam size and species. In the field, densities of clams (M.arenaria and M.mercenaria) were reduced to half of that in controls after 3.5-5 h, indicating high levels of dispersal and/or mortality. Some individuals were recovered up to 50 cm away from their initial locations. Overall, our results suggest that dispersal distances of these three species due to bedload transport are likely to be on the order of centimeters per hour. Although these dispersal distances are small, such movements are likely to occur frequently due to tidal currents and, consequently, may have profound impacts on patterns of abundance and distribution.     

Fine-grained spatial genetic structure in the bivalve Gemma gemma from Maine and Virginia (USA), as revealed by Inter-Simple Sequence Repeat markers

Gemma gemma is a small ovoviviparous bivalve distributed in shallow sand flats along the North American Atlantic and Gulf of Mexico coasts. Genetic variation in G. gemma was analysed by means of Inter-Simple Sequence Repeats (ISSRs) at the following levels: (i) between localities (Maine and Virginia), (ii) among 10-m-diameter patches within localities, and (iii) within patches. Thirty individuals/patch and three patches/locality were analysed. Individuals were genotyped for 67 ISSR polymorphic loci from five primers. The portion of the genetic variation found between localities (2%) was small compared to that found either among patches within localities (37%) or within patches (61%). ISSRs in G. gemma allowed the detection of significant differentiation at individual and patch levels. By contrast, a low degree of genetic variability was found between localities. The small-scale genetic heterogeneity does not follow a simple, consistent pattern. Our results contrast with the generally accepted rule that aplanic species are locally homogeneous and globally heterogeneous and teleplanic species are the inverse.     

Predation by bluegill sunfish (Lepomis macrochirus rafinesque) upon mealworm larvae (Tenebrio molitor)

Eleven responses comprise behaviour of bluegill sunfish (Lepomis macrochirus Rafinesque) preying upon mealworm larvae of Tenebrio molitor. Since each response could be repeated during an attack, behaviour can become quite complex in terms of total number of components comprising a predatory chain. When sunfish attacked the first prey of feeding sessions, predatory sequences contained an average of 8·0 components. Sequences dealing with the second and with all subsequent prey averaged 9·5 and 12·4 components respectively. Increased sequence complexity with increasing satiety depended upon increases in the frequencies of orienting and approaching prey as well as stopping and turning away from prey. Accordingly, satiety is hypothesized to produce more selective responsiveness to prey rather than simple diminution of feeding behaviour.     

Mucus trail following by the snail Biomphalaria glabrata (Say)

An experimental procedure involving time-lapse cinematography was used to investigate the responses of the freshwater pulmonate, Biomphalaria glabrata (Say), to their mucus trails. It has been shown that individuals of this species are capable of following their own trails and also those laid by other individuals of the same species. The capacity of mucus trails to influence snail behaviour is lost after a brief period of between 10 and 30 min. The snails tend to move in the direction the trail was laid with expectation greater than by chance. They do not follow mucus trails laid by another species, Limnaea stagnalis. The possible adaptive significance of trail following is discussed.     

Stereotypic and size-selective predation in Polinices pulchellus (Gastropoda: Naticidae) Risso 1826

Polinices pulchellus were size-selective in their choice of Cerastoderma edule. Large predators (12-15.9 mm shell length) selected both larger and a wider size range of cockles than smaller individuals (4-11.9 mm shell length). Considerable overlap occurred in the sizes of cockles frequently drilled by different size classes of snails, indicating that certain sizes of cockles may be most profitable to a wide range of predator sizes. Consumption rates were highest during July and August and were closely related to seawater temperature. Inner and outer drill hole diameters were both correlated with predator size, and the morphology of the drill hole was geometrically similar across a range of predator sizes. Polinices pulchellus showed no preference for either the left or right valve and drilled most cockles in the centre of the shell valve. The relationship between the distance of the drill hole from the umbo and prey size was unaffected by predator size, such that predators of different sizes were not found to drill cockles in different positions. When disturbed during drilling, incomplete drill holes were abandoned and, when drilling resumed, it occurred in new locations on the surface of the shell valve. The findings of this study highlight the stereotyped nature of drilling behaviour seen in the family Naticidae.     

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.     

Predation by Pterostichus melanarius (Illiger) (Coleoptera: Carabidae) on immature Rhagoletis mendax Curran (Diptera: Tephritidae) in semi-field and field conditions

Practices that enhance abundance and diversity of generalist predators are often employed with the objective of improving biological control of insect pests. Ground beetles and other predators can prey on blueberry maggot, an important pest of blueberries, when mature larvae pupate in the ground. We conducted mesocosm and field experiments to determine if Pterostichus melanarius, a common predatory ground beetle, lowers maggot numbers in compost mulch or when predator and alternative prey abundances are manipulated. At background (field) densities of alternative prey, increasing densities of P. melanarius did not significantly reduce pest numbers in mesocosms containing compost or soil. When alternative prey were removed from compost, beetles reduced pest numbers by up to 35%. In field experiments, maggot numbers were higher when beetles and other predators were excluded from soil plots, but beetle exclusion had no effect in compost plots where both predator and alternative prey numbers were high. Our results indicate that there can be some reduction of blueberry maggot by P. melanarius and other potential predators when there are few alternative prey. However, despite attracting large numbers of predators compost mulch did not lead to a significant reduction in blueberry maggot; in fact, the high abundance of alternative food associated with compost appeared to interfere with beetle predation on blueberry maggot.     

Predation of the sea urchin Heliocidaris erythrogramma by rock lobsters (Jasus edwardsii) in no-take marine reserves

The formation of sea urchin ‘barrens’ on shallow temperate rocky reefs is well documented. However there has been much conjecture about the underlying mechanisms leading to sea urchin barrens, and relatively little experimentation to test these ideas critically. We conducted a series of manipulative experiments to determine whether predation mortality is an important mechanism structuring populations of the sea urchin Heliocidaris erythrogramma in Tasmania. Tethered juvenile and adult sea urchins experienced much higher rates of mortality inside no-take marine reserves where sea urchin predators were abundant compared to adjacent fished areas where predators were fewer. Mortality of tagged (but not tethered) sea urchins was also notably higher in marine reserves than in adjacent areas open to fishing. When a range of sizes of sea urchins was exposed to three sizes of rock lobsters in a caging experiment, juvenile sea urchins were eaten more frequently than larger sea urchins by all sizes of rock lobster, but only the largest rock lobsters (> 120 mm CL) were able to consume large adult sea urchins. Tagging (but not tethering) juvenile and adult sea urchins in two separate marine reserves indicated that adult sea urchins experience higher predation mortality than juveniles, probably because juveniles can shelter in cryptic microhabitat more effectively. In a field experiment in which exposure of sea urchins to rock lobster (Jasus edwardsii) and demersal reef fish predators was manipulated, rock lobsters were shown to be more important than fish as predators of adult sea urchins in a marine reserve. We conclude that predators, and particularly rock lobsters, exert significant predation mortality on H. erythrogramma in Tasmanian marine reserves, and that adult sea urchins are more vulnerable than smaller cryptic individuals. Fishing of rock lobsters is likely to reduce an important component of mortality in H. erythrogramma populations.     

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.     

Size-related and seasonal patterns of egg collar production in Polinices pulchellus (Gastropoda: Naticidae) Risso 1826

Polinices pulchellus held in the laboratory produced egg collars all year round. Egg collar production was greatest during July and August and only occurred in females >8-10 mm shell length. The largest individuals (14-16 mm shell length) had the highest fecundity and ceased egg-laying in late September, whilst 8-14 mm individuals laid egg collars until November. Small females (4-6 mm) grew rapidly during the warmer, summer months (April to August), became sexually mature and began laying egg collars in mid-September. Both the range of egg collar wet weights and the maximum wet weight of an individual egg collar increased with female size class. Temperature strongly affected the length of time between the laying of egg collars and the hatching of larvae (9-10 days at 19-20 °C and 14-15 days at 13-14 °C). A close relationship was also found between egg collar wet weight and the number of veliger larvae released.     

Effect of the snail Ilyanassa obsoleta (Say) on dynamics of the amphipod Corophium volutator (Pallas) on an intertidal mudflat

We investigated interactions between two dominant invertebrate species of intertidal soft-sediment environments of the northwest Atlantic, the mud snail Ilyanassa obsoleta and the burrowing amphipod Corophium volutator, on a mudflat of the upper Bay of Fundy, Canada. Distribution of I. obsoleta on the mudflat was highly patchy and negatively correlated with density of C. volutator. Manipulation of snail density in cages showed that I. obsoleta influences C. volutator; specifically, increasing density of snails reduced density, increased patchiness in distribution, decreased recapture rates and decreased immigration of C. volutator. Ilyanassa obsoleta seems to be affecting C. volutator through an influence on survival rate and emigration rate, although temporal variation in these effects was observed. Given that both I. obsoleta and C. volutator show a preference for tide pools, an important microhabitat on mudflats, snails might have a profound impact on C. volutator population dynamics.     

Predatory behaviour in the ant-like wasp Methocha stygia (Say) (Hymenoptera: Tiphiidae)

An examination of prey-orienting behaviour of Methocha stygia has demonstrated that adult females regularly transport prey (Cicindela larvae) when they are removed from their burrows. On a single occasion a wasp was also observed to utilize a naturally occurring depression in the soil as a nest site, instead of depending on the prey's own burrow. This flexibility in response might be a carryover of the behaviour that surely existed in the ancestors of the methochine wasps, insects which were close to if not identical with the ancestors of the ants. When Methocha females were crowded together with prey in the laboratory, frequent avoidance and aggressive behaviours were noted, but no sign of any form of co-operation.     

Size-dependence of growth inhibition among juvenile lobsters (Homarus)

Growth inhibition of post-larval lobsters (Homarus) in compartments immediately downstream from older individuals was found to depend upon size relative to the upstream animals, but not upon species or age combination per se at least within the species, age, and size combinations used in this experiment. The growth of juveniles downstream from smaller individuals was greater than that downstream from juveniles their own size, confirming previous indications of disinhibition of growth by smaller upstream individuals.     

Effects of Ilyanassa obsoleta (Say) on the abundance and vertical distribution of Corophium volutator (Pallas) on mudflats of the upper Bay of Fundy

Invertebrates in soft-bottom marine communities exhibit a range of responses to predators and competitors, including both emigration and avoidance. Corophium volutator (Pallas), a burrowing amphipod abundant in the upper Bay of Fundy, Canada, frequently interacts with the eastern mudsnail, Ilyanassa obsoleta (Say), as both species utilize similar habitats and food resources. Typically these interactions result in negative effects on C. volutator. There is evidence that Corophium species exhibit avoidance behaviour when interacting with other species, but whether such a response occurs in the presence of I. obsoleta is unknown. To investigate C. volutator response to I. obsoleta, total C. volutator abundance and vertical distribution within the sediment was examined in a field experiment involving I. obsoleta enclosures and exclosures at two mudflats in the upper Bay of Fundy. I. obsoleta densities were manipulated between June and August 2008 and their effects on C. volutator abundance and vertical distribution observed. Results varied between mudflats and C. volutator size classes. At Peck's Cove, total C. volutator abundance was largely unaffected by I. obsoleta. No size class exhibited a distribution shift in response to I. obsoleta, though both mid-sized individuals and adults occupied deeper layers of sediment late in the summer. Abundance of C. volutator in all size classes at Grande Anse was reduced in July in direct proportion to exposure to I. obsoleta, and adults occupied higher sediment layers in July when I. obsoleta were excluded, suggesting that I. obsoleta curtailed use of these upper layers. Juvenile abundance rebounded in August, possibly due to the mass dispersal of a newly produced juvenile cohort. Adults were reduced in all treatments in August, probably as a result of normal seasonal mortality. Differences in C. volutator responses between mudflats highlight the site-specific nature of such interactions.     

Effect of age and body size on selected temperature by juvenile wood turtles (Glyptemys insculpta)

In an aquatic thermal gradient of 15–30 °C, 3-, 6-, and 12-month-old juvenile wood turtles (Glyptemys insculpta) acclimated to 20 °C selected the warmest temperature available (30 °C) and avoided the coldest temperatures available (15 and 18 °C). Mean selection of chambers differed between control and gradient tests across all temperatures except 27 °C. Turtles of all age classes relocated between chambers less often when the gradient was present than during control tests. Six- and 12-month-old turtles selected 30 °C more frequently, and selected colder temperatures less frequently, than 3-month-old turtles, suggesting that the ability to select preferred temperatures is better developed in older hatchlings.     

Predation on mammals by the chimpanzee (Pan troglodytes)

With respect to prey selectivity and predation frequency, chimpanzees (Pan troglodytes) show local differences as well as diachronic variability within the same population. When data on predation from three long-term studies at Mahale, Gombe, and Tai are compared, some differences and similarities emerge; Mahale is more like Gombe than Tai in regard of prey selection but features of hunting at Tai with respect to predation frequency are not conspicuous. The most responsible factor for diversity in prey selectivity is a distinct “prey image” maintained by chimpanzees of different populations, although it is necessary to clarify in future studies why and how such tradition develops. Relative body size of chimpanzees to prey species and/or the degree of cooperation among members of a hunting party may explain the variability in prey size selected at each site, the latter influencing the frequency of successful hunts at the same time. Although various degrees of habituation and different sampling methods including artificial feeding might have obscured the real differences, recent data from the three populations do not seem to be biased greatly by such factors. Nevertheless, it is still difficult to make strict comparisons due to the lack of sufficient standardized data across the three populations on the frequency of hunting and predation. It is suggested that the size or demographic trend of a chimpanzee unit-group, especially the number of adult males included, necessarily influences its hunting frequency as well as its prey profile. It is also suggested that factors which bring these males together into a party (e.g. fruit abundance, swollen females, conflict between unit-groups etc.) strongly affect theactual hunting and kill rates. Other possible factors responsible for the local differences are forest structure (e.g. tree height), skilful “hero” chimpanzees, and competition with sympatric carnivorous animals. A total of at least 32 species have been recorded as prey mammals of chimpanzees from 12 study sites and the most common prey mammals are primates (18 species), of which 13 species are forest monkeys. Forest monkeys, colobine species in particular, are often the most common victims of the predation by chimpanzees at each site. We may point out a tendency toward selective hunting for the forest monkeys in terms of the selectivity of prey fauna among all three subspecies of chimpanzees, including populations living in drier environment. The mode of chimpanzee hunting seems to correspond to the highest available biomass of gregarious, arboreal monkeys in the forest, colobine species in particular. In contrast, bonobos (P. paniscus) are less carnivorous than chimpanzees, only rarely preying on a few species of small mammals. The sharp contrast of the two allied species in their predatory tendencies appears to have something to do with the differences in the structure of primary production between their habitats.     

Predation by Callinectes sapidus (Rathbun) within Spartina alterniflora (Loisel) marshes

This study examined predation by the blue crab, Callinectes sapidus Rathbun, within intertidal Spartina alterniflora (Loisel) marshes of Dauphin Island, Alabama. Species and size preferences displayed by the predator when foraging within the marsh were investigated using nektonic, epifaunal, and infaunal prey populations including Fundulus similis Baird and Girard, Littorina irrorata Say, and Geukensia demissa Dillwyn.

Short-term field experiments involving the use of predator inclusion cages, in which the relative abundances of all prey species and the density of macrophyte vegetation were manipulated, indicated that mean mortality differed significantly among species. Blue crabs exhibited a distinct species preference for Littorina, and to a lesser extent, for Fundulus. However, the predator rarely choses infaunal individuals. Within predator inclusion cages, size selection by the crabs among three size classes of each prey was evident for Littorina and Fundulus but not for Geukensia. Blue crabs tended to select intermediate-sized snails and large fish while not exhibiting a size preference for infaunal bivalves.

In the marsh, mean percentage of the Littorina population within the 14–18 mm size class exhibited an increased mortality as compared to two other size classes, which was negatively correlated with increasing tidal height. Such a relationship may have been due to a decreasing gradient of crab predation associated with increasing tidal height. Geukensia size class distributions showed little evidence of differences along the tidal height gradient. No data are available for Fundulus, a mobile species which would not experience such differential predation along a marsh gradient.

In comparing crab predation patterns among prey species, it is apparent that Callinectes utilizes prey species differentially. Such differential utilization may be based on optimization of energy yield and minimization of energy expenditure. Thus, the preference of blue crabs for nektonic and epifaunal prey is hypothesized to be the result of a smaller energy expediture as a result of the crab's visual evaluation of these prey. Infaunal prey species (e.g., Geukensia) require a greater energy investment because of the necessity of excavating the prey item. Such prey also allow little selection by size because of being cryptic.     

The effects of history on the shell preference of the hermit crab Pagurus longicarpus (Say)

The effect of disturbance by two macroinvertebrates, the sand dollar Mellita quinquiesperforata (Leske) and the sea pansy Renilla reniformis (Cuvier) on meiofauna was studied on a sandbar in North Inlet, Georgetown, South Carolina. Abundances of nematodes and the harpacticoid copepod Apodopsyllusunguiformis Coull &; Hogue decreased significantly in the presence of sand dollars; other taxa were not affected. In two Renilla experiments, one natural and another where artificial and real Renilla were implanted, we could determine no consistent effect on any meiobenthic taxon. However, sediments disturbed by implanting living and artificial Renilla returned to ambient levels within 1 h.