Scallop Pecten Fumatus Research Articles

Stomach content characterisation of the marine range-shifting Octopus tetricus using DNA metabarcoding

The common Sydney octopus Octopus tetricus has undergone range extension along the east coast of Australia, associated with regional warming and the strengthening and southward extension of the East Australian Current (EAC). Its historical range of distribution is from southern Queensland to southern New South Wales, but it is now also found off north-east Tasmania, where it may affect local ecosystem dynamics due to changes in trophic interactions. This study aims to identify the prey and trophic level of O. tetricus from specimens collected off Tasmania to anticipate potential ecological, economic, and conservation effects in the range-extended area. The stomach contents of 18 O. tetricus individuals captured off north-east Tasmania in 2011 were characterised using DNA metabarcoding. Sixteen families of prey were identified; crustaceans (Alpheidae, Calcinidae, Diogenidae, and Galatheidae) were the most frequently detected prey, followed by fishes and bivalves. Prey species of commercial importance included blue-throated wrasse Notolabrus tetricus and the scallop Pecten fumatus. O. tetricus was found to have an intermediate trophic level of 3.66, participating in the transfer of energy from lower to upper trophic levels. Predation by O. tetricus could present competition to local fishers for resources and additional pressure on local fishery stocks, and may alter estimates of natural mortality used by fisheries management. The present study may be useful to scientists, fishery managers, and conservationists because it provides a preliminary assessment of the diet of O. tetricus, with potential ecological, economic, and conservation implications in the range-extended area.

Exposure to seismic air gun signals causes physiological harm and alters behavior in the scallop Pecten fumatus

Seismic surveys map the seabed using intense, low-frequency sound signals that penetrate kilometers into the Earth's crust. Little is known regarding how invertebrates, including economically and ecologically important bivalves, are affected by exposure to seismic signals. In a series of field-based experiments, we investigate the impact of exposure to seismic surveys on scallops, using measurements of physiological and behavioral parameters to determine whether exposure may cause mass mortality or result in other sublethal effects. Exposure to seismic signals was found to significantly increase mortality, particularly over a chronic (months postexposure) time scale, though not beyond naturally occurring rates of mortality. Exposure did not elicit energetically expensive behaviors, but scallops showed significant changes in behavioral patterns during exposure, through a reduction in classic behaviors and demonstration of a nonclassic "flinch" response to air gun signals. Furthermore, scallops showed persistent alterations in recessing reflex behavior following exposure, with the rate of recessing increasing with repeated exposure. Hemolymph (blood analog) physiology showed a compromised capacity for homeostasis and potential immunodeficiency, as a range of hemolymph biochemistry parameters were altered and the density of circulating hemocytes (blood cell analog) was significantly reduced, with effects observed over acute (hours to days) and chronic (months) scales. The size of the air gun had no effect, but repeated exposure intensified responses. We postulate that the observed impacts resulted from high seabed ground accelerations driven by the air gun signal. Given the scope of physiological disruption, we conclude that seismic exposure can harm scallops.

Reproductive strategies and energy sources fuelling reproductive growth in a protracted spawner

Most marine invertebrates experience variable environments and for broadcast spawners, fertilisation success increases with greater synchronisation of spawning, so a capital breeding strategy is predicted. However, this prediction should be tested for species with protracted breeding seasons, since it is not clear how reproduction is fuelled over several consecutive months of spawning. The simultaneous hermaphrodite scallop Pecten fumatus was used to test the hypothesis that protracted spawning is supported by both capital and income strategies, depending on the state of energy reserves and food availability at the time of oocyte maturation. The study was carried out in Great Bay, Tasmania, Australia (147.335W, 43.220S) in 2010/2011. The use of glycogen, protein and lipid in the muscle, gonad, and digestive gland was examined, along with the role of atretic eggs as an alternative energy source for oogenesis and maturation. The reproductive stage of an individual was determined using only the ovaries. P. fumatus uses a capital breeding strategy early in the reproductive cycle during winter and spring (August–October) with muscle glycogen and protein and digestive gland lipid providing energy for oogenesis. Given there was no evidence of energy stores being used later in the reproductive cycle in late spring and summer (November–March), when less food was available for direct fuelling of reproduction, it appears that metabolites produced from oocyte lysis may have fuelled oogenesis. Recycling of energy from oocyte resorption must be considered as part of the strategy of energy use to fuel reproduction in marine invertebrates.

Early post-settlement mortality of the scallop Pecten fumatus and the role of algal mats as a refuge from predation

Abstract Early post-settlement mortality is one of the main processes determining distribution and abundance patterns of marine benthic invertebrates. Most scallops have an attached phase as spat before they release the byssus and move onto the soft sediments. Thus, spat differ from other stages of life in their use of microhabitat, lack of mobility, and therefore in their vulnerability to mortality processes such as predation. However, the contribution of predation to explain levels of mortality experienced by spat and early juvenile scallops is unknown. Complex habitats such as seagrasses and algae provide a substrate upon which spat can attach and might confer an advantage as a refuge from predation. This study investigates the contribution of early post-settlement predation on abundance of Pecten fumatus and determines the role of the algae Hincksia sordida as a refuge from predation. Data were collected using field observations, a predator exclusion experiment, and tethering techniques. Mortality of up to 85% during the first weeks after settlement appeared to have prevented the establishment of an adult population at our study site. Mats of the macroalgae H. sordida provided a settlement substrate for P. fumatus spat. However, increased algal biomass did not provide greater protection from predation to juvenile scallops than lower algal biomass. Our study suggests that prey survival in submersed vegetation is likely to be dynamic among years, and affected by prey behaviour and density as well as the characteristics of the submerged vegetation.

Role of density in aggregation patterns and synchronization of spawning in the hermaphroditic scallop Pecten fumatus

In broadcast spawners, low densities and poor spawning synchronization can reduce fertilization success. In wild populations, individuals in close proximity tend to spawn more synchronously than those further apart, sug- gesting that low spawner densities may reduce gamete pro- duction by lessening the efficacy of pheromone signalling. This study assessed the role of adult density in aggregation patterns and spawning synchronization in a semi-sessile, hermaphroditic scallop, Pecten fumatus. The study was carried out in Great Bay, Tasmania, Australia (147.335 W, 43.220 S) in 2010-2012 by assessing (1) the relationship between density, small-scale aggregation patterns and near- est neighbour distance (NND), (2) the temporal pattern of spawning synchronization, and (3) the effect of site density and conspecific proximity on the probability of spawn- ing. Densities observed in the field ranged from 1.455 to 0.021 ind m −2 . Sites with lower densities had less small- scale aggregation and greater NNDs. Patterns of small- scale aggregation and NNDs in P. fumatus were compara- ble to those observed in a gonochoristic species. Spawning synchronization was highly variable, ranging between 3.5

Habitat Characteristics Predicting Distribution and Abundance Patterns of Scallops in D’Entrecasteaux Channel, Tasmania

Habitat characteristics greatly influence the patterns of distribution and abundance in scallops, providing structure for the settlement of spat and influencing predation risk and rates of survival. Establishing scallop-habitat relationships is relevant to understanding the ecological processes that regulate scallop populations and to managing critical habitats. This information is particularly relevant for the D’Entrecasteaux Channel, south-eastern Tasmania (147.335 W, 43.220 S), a region that has supported significant but highly variable scallop production over many years, including protracted periods of stock collapse. Three species of scallops are present in the region; the commercial scallop Pecten fumatus, the queen scallop Equichlamys bifrons, and the doughboy scallop Mimachlamys asperrima. We used dive surveys and Generalized Additive Modelling to examine the relationship between the distribution and abundance patterns of each species and associated habitat characteristics. The aggregated distribution of each species could be predicted as a function of sediment type and species-specific habitat structural components. While P. fumatus was strongly associated with finer sediments and E. bifrons with coarse grain sediments, M. asperrima had a less selective association, possibly related to its ability to attach on a wide range of substrates. Other habitat characteristics explaining P. fumatus abundance were depth, Asterias amurensis abundance, shell and macroalgae cover. Equichlamys bifrons was strongly associated with macroalgae and seagrass cover, whereas M. asperrima abundance was greatly explained by sponge cover. The models define a set of relationships from which plausible hypotheses can be developed. We propose that these relationships are mediated by predation pressure as well as the specific behavioural characteristics of each species. The findings also highlight the specific habitat characteristics that are relevant for spatial management and habitat restoration plans.

Production of microalgal concentrates by flocculation and their assessment as aquaculture feeds

A novel technique was developed for the flocculation of marine microalgae commonly used in aquaculture. The process entailed an adjustment of pH of culture to between 10 and 10.6 using NaOH, followed by addition of a non-ionic polymer Magnafloc LT-25 to a final concentration of 0.5 mg L −1. The ensuing flocculate was harvested, and neutralised giving a final concentration factor of between 200- and 800-fold. This process was successfully applied to harvest cells of Chaetoceros calcitrans, C. muelleri, Thalassiosira pseudonana, Attheya septentrionalis, Nitzschia closterium, Skeletonema sp., Tetraselmis suecica and Rhodomonas salina, with efficiencies ≥80%. The process was rapid, simple and inexpensive, and relatively cost neutral with increasing volume (cf. concentration by centrifugation). Harvested material was readily disaggregated to single cell suspensions by dilution in seawater and mild agitation. Microscopic examination of the cells showed them to be indistinguishable from corresponding non-flocculated cells. Chlorophyll analysis of concentrates prepared from cultures of ≤130 L showed minimal degradation after 2 weeks storage. Concentrates of T. pseudonana prepared using pH-induced flocculation gave better growth of juvenile Pacific oysters ( Crassostrea gigas) than concentrates prepared by ferric flocculation, or centrifuged concentrates using a cream separator or laboratory centrifuge. In follow up experiments, concentrates prepared from 1000 L Chaetoceros muelleri cultures were effective as supplementary diets to improve the growth of juvenile C. gigas and the scallop Pecten fumatus reared under commercial conditions, though not as effective as the corresponding live algae. The experiments demonstrated a proof-of-concept for a commercial application of concentrates prepared by flocculation, especially for use at a remote nursery without on-site mass-algal culture facilities.

Impact of an exotic clam, Corbula gibba, on the commercial scallop Pecten fumatus in Port Phillip Bay, south-east Australia: evidence of resource-restricted growth in a subtidal environment

Corbula gibba (Olivi, 1792) a small exotic bivalve from the eastern Atlantic and the Mediterranean has been present in Port Phillip Bay, Victoria, Australia, from as early as 1987. C. gibba is widespread, abundant, and possesses characteristics such as fast growth which may confer a competitive advantage over endemic species like the commercial scallop Pecten fumatus Reeve, 1855. Experimental manipulations in the field showed that ambient densities of C. gibba significantly affected the size and growth of juvenile P. fumatus. This effect was greater than the effect of an equivalent number of conspecific scallops. C. gibba did not, however, affect scallop condition or survival in the short term, although the power of the test to detect a 50% decrease in survival was low. The percentage of experimental scallops lost to different sources of mortality was also unaffected by the presence of C. gibba, as was the density of predators found in experimental enclosures. This study is the first to experimentally demonstrate the impact of an introduced marine mollusc on an endemic species in Australia. A possible mechanism underlying this impact is compe- tition for food, as both species are suspension feeders which live in an environment where resource limitation may occur.

Impacts and efficiency of scallop dredging on different soft substrates

Impacts of scallop dredges and their efficiency were examined experimentally in three areas with different soft substrates in Port Phillip Bay, southeastern Australia. Physical and biological changes were measured on large (600 × 600 m) experimental plots that were dredged with an intensity and duration similar to normal fishing operations. Dredges were most efficient on soft, flat, muddy sediments (51-56% of commercial-sized scallops caught) and least efficient on firm, sandy sediments with more topographic variation (38-44%). Dredging flattened all plots, but changes to topography were most apparent on plots dominated initially by callianassid mounds. Dredges caught predominantly the scallop Pecten fumatus, and damage to bycatch species was slight, except for high mortality rates (>50%) of spider crabs and the probable mortality of many discarded ascidians. Changes to benthic community structure caused by scallop dredging were small compared with differences between study areas, and even marked reductions in the size and longevity of scallops over the last two decades may not be due entirely to dredging. The recent cancellation of all scallop dredging licences offers a unique opportunity to determine the contribution of scallop dredging to ecological changes in the bay over the past 30 years.

Temperature and nutrition as factors in conditioning broodstock of the commercial scallop Pecten fumatus Reeve

Difficulty in obtaining ripe broodstock of the commercial scallop Pecten fumatus from wild populations in New South Wales prompted the development of hatchery conditioning protocols. Microalgal diets, feeding rates and holding temperatures conducive to rapid gonadal growth and development were identified. Results of microalgal clearance rate experiments indicated that the species Pavlova lutheri, Tahitian Isochrysis aff. galbana, Chroomonas salina and Chaetoceros gracilis are ingested by adult scallops at similar rates at 14, 18 and 21 °C, but more slowly at 11 °C. Maximum (satiation) ingestion rate using mixed diets containing approximately equal numbers of cells of these four species, was estimated as about 6 × 10 9 cells per day for broodstock in the range 55 to 75 mm shell height. Large numbers of cells of the microalga Tetraselmis suecica passed through the digestive tract of scallops undigested. Egg production rate, gonad size and condition factors were all highest when broodstock were held at 15 °C, lowest for scallops maintained at 21 °C and of intermediate values at temperatures of 12 and 18 °C. Gonad condition and egg production increased as feeding rates were raised from 12.5 to 100% of satiation at all test temperatures in the range 12 to 21 °C. Frequent spawning triggered by routine handling of broodstock during these experiments emphasised the need for conditioning equipment and protocols that minimise handling and other disturbance factors. No unplanned spawning occurred at feeding rates of 25% or 12.5% of satiation at 12 °C. The use of low temperature and low feeding rate might therefore enable short term stockpiling of broodstock once they attain prime breeding condition. Findings of these experiments were successfully applied to a subsequent large scale conditioning and induced spawning trial.

Detachment of commercial scallop Pecten fumatus, spat from settlement substrates

The ability of chemical irritants and several forms of physiological stress to induce Pecten fumatus spat to detach from settlement substrates was evaluated. Hypersaline baths (45‰) and exposure to air (emersion) for 2 h were both found to be effective in inducing more than 95% of spat to detach from mesh settlement screens. Hypersaline baths, created by the addition of an artificial sea salt to seawater, produced greater spat detachment after 2 h than those created by equivalent additions of sodium chloride. The rate of detachment in hypersaline baths was unaffected by increasing temperature from 20°C to 26°C, but was depressed at 11°C. Addition of magnesium chloride (27 g/kg) to seawater and reduction of seawater pH to 2 were also effective in increasing spat detachment rate, but not as effective as hypersaline baths or air exposure. With the exception of spat exposed to seawater containing 115 mg/kg available chlorine, no significant mortality and > 95% reattachment occurred within 24 h of all detachment methods tested.

Salinity tolerance and absorption of L-Methionine by some Australian bivalve molluscs

The salinity tolerance range of the scallop Pecten fumatus Reeve was 25-40 g 1-1, of the pipi (clam) Plebidonax deltoides (Lamarck) and the flat oyster Ostrea angasi Sowerby, 20-45 g I-1, and of the blue mussel Mytilus edulis planulatus Lamarck and the Sydney cockle Anadara trapezia (Deshayes), 15-45 g I-1. All of these bivalves absorbed substantial amounts of the amino acid L-methionine directly from seawater.