Juvenile Sea Scallops Placopecten Magellanicus Research Articles

Behavioural mechanisms underlying functional response of sea stars Asterias vulgaris preying on juvenile sea scallops Placopecten magellanicus

The functional response characterises the relationship between prey density and the consumption rate of individual predators. Typically, it is studied by fitting a model to observations of predation rate at different prey densities. The behavioural mechanisms underlying a functional response are not well understood, and estimates of model parameters seldom conform to observations of behaviour. We have developed a mechanistic approach that directly incorporates behavioural observations into characterisation of the functional response. Laboratory experiments were used to record predation rates and observe foraging behaviour of sea stars Asterias vulgaris preying on juve- nile sea scallops Placopecten magellanicus at different densities. Experiments were conducted in tanks with no sediment and tanks with sediment. Behavioural data from the experiments were used to calculate parameters of functional response models Th (handling time per prey) and a (rate of suc- cessful search). On both substrates, Th remained constant across prey density, while a was density- dependent. An inverse quadratic was used to describe a and was incorporated into a functional response model. Estimates of a were also obtained by fitting the functional response model to the pre- dation rate data using regression analysis. These estimates of a were highly consistent with the esti- mates calculated from behavioural data. On both substrates, sea stars preying on scallops had a Type III sigmoid-shaped functional response; on sediment, predation rate decreased at high prey densities. Sea star ability to capture attacked prey was probably the mechanism underlying the observed responses. In general, behavioural information can lead to better understanding of observed func- tional responses.

Behavioural mechanisms underlying functional response of sea stars Asterias vulgaris preying on juvenile sea scallops Placopecten magellanicus

Behavioural mechanisms underlying functional response of sea stars Asterias vulgaris preying on juvenile sea scallops Placopecten magellanicus

Shell and tissue growth of juvenile sea scallops ( Placopecten magellanicus) in suspended and bottom culture in Lunenburg Bay, Nova Scotia

Hatchery-reared juvenile sea scallops Placopecten magellanicus (mean shell height = 22.2 ± 0.1 mm) were grown uncontained on the seabed (5–9 m depth) and suspended in pearl nets (3 m above the seabed) at three sites (Site 1, 2 and 3) in Lunenburg Bay, N. S., Canada, between March 1992 and March 1993. Shell and tissue growth rates reached their peak in mid-summer and decreased to the lowest values in winter, although growth never stopped. Monthly measurements of shell heights of individually tagged scallops in pearl nets (100 per net) and on the seabed, yielded mean (± s.e.) annual growth rates of 93 ± 5.5 and 117 ± 4.5 μm/day, respectively, at Site 1, 72 ± 3.0 and 93 ± 3.8 μm/day at Site 2, and 79 ± 2.8 and 73 ± 5.6 μm/day at Site 3. There were significant differences in shell growth rates among the three sites and between the two culture methods in most of the months. The highest shell growth rates generally occurred at Site 2, regardless of culture method. Shell growth rates were significantly higher in bottom than in suspended culture during most measurement periods. Mean final soft tissue condition index of scallops in suspended culture was significantly higher than in bottom culture at Site 2. Mean final adductor muscle condition index and mean final whole dry weights of scallops were significantly lower in suspended culture than in bottom culture at Site 2. Water temperature at all three sites ranged from ~ −2 to 16 °C during the year. There were significant differences in annual mean particulate organic matter concentration between depths, but not among sites. Annual mean chlorophyll concentration differed among sites, but not between depths within sites. Stepwise multiple regression analyses, with water temperature, total particulate matter concentration, and chlorophyll concentration as independent variables, were highly significant for all sites and culture methods. They explained between 46% and 66% of the total variance of shell growth rates in suspended culture and between 36% and 78% in bottom culture, respectively and 55% and 80% for soft tissue growth rates of scallops in suspended and bottom culture, respectively. Growth of scallops in bottom culture at these shallow sites is comparable to animals of the same seed populations grown in the more expensive and labour-intensive suspended culture at the same sites.

Effects of site and season on movement frequencies and displacement patterns of juvenile sea scallops Placopecten magellanicus under natural hydrodynamic conditions in Nova Scotia, Canada

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 128:225-238 (1995) - doi:10.3354/meps128225 Effects of site and season on movement frequencies and displacement patterns of juvenile sea scallops Placopectenmagellanicus under natural hydrodynamic conditions in Nova Scotia, Canada Carsen AE, Hatcher BG, Scheibling RE, Hennigar AW, Taylor LH In this study, we examine the effect of site and season (spring vs fall) on the movement frequency and net displacement of juvenile sea scallops Placopectenmagellanicus, and the relationship between the net movement direction of scallops and the near-bed current direction at 2 sites in Lunenburg Bay, Nova Scotia, Canada. At each site, a total of 150 and 100 individually marked juvenile sea scallops were released on the sea bed at 2 points (Stns 1 and 2) placed 50 m apart for the spring (March) and fall (September) studies. The movement frequency and net displacement of the scallops were monitored within a 10 m radius from the release point approximately once a week during the spring study, and once a day during the fall study. Current meters placed 60 cm off the sea bed recorded near-bed current velocity. There was a significant interaction between site and season on the movement frequency of scallops. Scallop activity was low during the spring study at both sites when ~30% of scallops were found at their release point on the sea bed after 30 d. Scallops were much more mobile during the fall study when &LT5% of scallops were found at their release point after 2 d. However, the net daily displacement was &LT3 m for more than 60% of scallops recorded. In ~50% of the surveys, the net movement direction of scallops was significantly related to the direction of the main current vectors over daily to monthly periods, whereas in the other cases the net movement direction was independent of the direction of the main current vectors. The results of this study indicate that local hydrodynamics is not a good predictor of the swimming dispersion of juvenile P. magellanicus in natural habitats. Currents . Displacement patterns . Juveniles . Movement frequencies . Placopectenmagellanicus . Sea scallops Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 128. Publication date: November 23, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

Temperature effects on predation of juvenile sea scallops [ Placopecten magellanicus (Gmelin)] by sea stars ( Asterias vulgaris Verrill) and crabs ( Cancer irroratus Say)

Predation of juvenile sea scallops Placopecten magellanicus by sea stars Asterias vulgaris (80–100 mm diameter) and crabs Cancer irroratus (80–98 mm carapace width) was examined in the laboratory at different seawater temperatures. Prey sizes used were those demonstrated previously to be preferentially consumed by the respective predators. Consumption rate of small (5–9 mm shell height, SH) scallops by sea stars was not significantly different at 4° and 8 °C, but was significantly higher at 15 ° C ( Q 10 = 6.9). Similarly, consumption rate of large (19–23 mm SH) scallops by crabs was not significantly different at 3 ° and 8 ° C, but was significantly higher at 15 ° C ( Q 10 = 2.1). Increased predator activity, as indicated by increased time spent searching for prey, increased predator searching movement velocities (which, for sea stars, resulted in increased encounter rates with scallops), and shorter prey handling times, explained part of the increased predation rate by sea stars and most of that by crabs. Predation rate by sea stars also increased with temperature because of decreased effectiveness of the scallops' escape response, as evidenced by a significantly higher probability of capture upon encounter at 15 °C than at 4° and 8 ° C, although the probability of sea stars capturing scallops was very low (< 0.1) at all experimental temperatures. The probability of crabs capturing encountered scallops was higher (> 0.3) and independent of temperature. The probability of sea stars and crabs consuming captured scallops was ~ 1 and temperature independent.

Behavioral mechanisms of prey size selection by sea stars ( Asterias Vulgaris verrill) and crabs ( cancer irroratus say) preying on juvenile sea scallops ( placopecten magellanicus (Gmelin))

Predation upon different size classes of juvenile sea scallops Placopecten magellanicus (Gmelin) (5–25 mm shell height) by different size classes of predatory sea stars Asterias vulgaris Verill (30–150 mm diameter) and crabs Cancer irroratus Say (45–120 mm carapace width) was studied in laboratory experiments using single prey size (no choice) and multiple prey size (choice) designs. Components of predation rate were quantified to assess the relative importance of prey vulnerability and active predator choice in determining observed prey selection. All sizes of sea stars consumed more small scallops than medium or large ones. Encounter rates between predator and prey were similar, irrespective of sea star and scallop size, and did not differ from encounter rates calculated on the basis of body sizes and movement velocities. Scallops assumed a ready-to-swim position when contacted by sea stars, and often actively escaped. The probability of capture by sea stars upon encounter was generally low (< 0.2), but significantly higher for small scallops than for medium or large ones. Active selection was unimportant, since sea stars did not select a given scallop size more often in a choice situation than in a non-choice situation. Apparent preference for small scallops by sea stars was primarily due to size-related differences in prey vulnerability. In single prey size experiments with crabs, more medium scallops were consumed than small or large ones. However, in the multiple prey size experiment, large scallops were preferred over small and medium ones. The preference for large scallops over medium ones resulted from active selection, since crabs selected large scallops more often in a choice situation than in a non-choice situation. Conversely, low consumption rates of small scallops were due to low encounter rates with crabs, since encounter rates reflected body sizes and movement velocities. Scallops often closed their valves upon encounter with crabs, resulting in a higher probability of capture upon encounter (generally > 0.2) than that observed with sea stars. Therefore, prey size selection by crabs appears to be determined by both size-related differences in prey vulnerability, due to differential encounter rates, and active selection of larger prey.

Procedural effects of prey tethering experiments: predation of juvenile scallops by crabs and sea stars

This study examines the effects of an experimental tethering procedure often used in field predation experiments. In laboratory experiments, juvenile sea scallops Placopecten magellanicus, either free or tethered, were offered to predatory crabs Cancer irroratus and sea stars Asterias vulgaris. The effect of the tethering procedure on predation rates was specific to a predator-prey interaction and could be predcted based on an understanding of the underlying behavioural mechanisms. In crab-scallop interactions, encounter rate was a major determinant of predation rate. Since tethering did not affect encounter rates, it did not significantly affect predation rates by crabs. In contrast, in sea star-scallop interactions, the probability of sea stars capturing encountered scallops was a major determinant of predation rate. Tethering limited the scallops' escape response, which increased the probability of capture and, hence, predation rate. Therefore, assessment of the relative importance of these 2 predators in determining would be biased by the procedure. scallop survival in field experiments differential effects of the tethering

Survival analysis of tethered juvenile sea scallops Placopecten magellanicus in field experiments: effects of predators, scallop size and density, site and season

Survival analysis of tethered juvenile sea scallops Placopecten magellanicus in field experiments: effects of predators, scallop size and density, site and season