Aequipecten Opercularis Research Articles

Maerl grounds provide both refuge and high growth potential for juvenile queen scallops ( Aequipecten opercularis L.)

Human damage to biogenic substrata such as maerl has been receiving increasing attention recently. Maerl forms highly biodiverse and heterogeneous habitats composed of loose-lying coralline red algae, which fulfil nursery area prerequisites for queen scallops ( Aequipecten opercularis) and other invertebrates. The benefits obtained by queen scallops utilising maerl were poorly understood, so we used both laboratory predation and field tethering experiments to investigate the refuge and growth potential provided by pristine live maerl (PLM) grounds over other common substrata. In aquaria, more juvenile queen scallops (<35 mm shell height) survived on PLM than on gravel substrata in the presence of the crab Carcinus maenas or the starfish Asterias rubens. Field tethering experiments indicated similar survivorship of juvenile queen scallops on PLM than gravel; additionally, their growth rates were similar on both substrata. PLM allows scallops to seek refuge from predators and position themselves to optimise their food supply. Other bivalve refugia have been shown to provide poor food supply as a consequence of their high heterogeneity, yet maerl grounds provide a ‘win–win’ scallop nursery area coupling refuge availability with high food supply.

Population dynamics and metabolism of Aequipecten opercularis (L.) from the western English Channel (Roscoff, France)

Population dynamics of the queen scallop, Aequipecten opercularis, was investigated in the western English Channel off Roscoff. Annual formation of natural growth rings on the shell surface was validated by stable isotope (δ 18O and δ 13C) analysis. A von Bertalanffy growth function ( H t = 58.9 mm • (1-e −0.604• (t +0.235))) was fitted to size-at-age data of 249 individuals. Annual somatic and gonad production amounted to 19.74 kJ m −2 and 0.98 kJ m −2 y −1, respectively. Total mortality rate Z was estimated to be 1.716 y −1. Net growth efficiencies (ranging from 45% in 1-y-old to 11% in 6-y-old individuals) were in the same range as in other short-lived scallops. Individual growth, however, was distinctly slower in this population than in other A. opercularis populations from similar latitudes, most likely due to a more stressful environment.

Nursery-area function of maerl grounds for juvenile queen scallops Aequipecten opercularis and other invertebrates

The services provided by coastal ecosystems such as mangrove forests and sea-grass beds are becoming increasingly recognised, yet the functional role of maerl beds has not been ad- dressed. Maerl forms highly biodiverse habitats composed of loose-lying coralline red algae which build up over thousands of years. These carbonate-rich deposits occur in photic areas with strong water movement; they have a widespread global distribution yet remain one of the most overlooked shallow-water marine habitats, with little known about the ecosystem services maerl may provide. Our diving research in Scotland has shown that pristine live maerl (PLM) grounds fulfil nursery area prerequisites for commercial populations of queen scallops Aequipecten opercularis and other inver- tebrates, such as the soft clam Mya arenaria, the sea urchins Psammechinus miliaris and Echinus escu- lentus, and the starfish Asterias rubens, more effectively than impacted dead maerl and other common substrata. The complex architecture of maerl beds attracts high densities of these juvenile inverte- brates, which use PLM grounds as nursery areas in preference to adjacent substrata. Considering its global distribution, it is highly likely that ecosystem services provided by maerl are considerable. Maerl is easily damaged and killed by a variety of human activities, yet its protection would maintain vital nursery area function, benefiting commercial fishery yields and, pivotally, regional biodiversity.

Attachment of the juvenile queen scallop ( Aequipecten opercularis (L.)) to maerl in mesocosm conditions; juvenile habitat selection

Substratum un-acclimated juvenile queen scallops ( Aequipecten opercularis) (<18 mm and 18–30 mm shell height) were released in equal numbers onto pristine live maerl (PLM), impacted dead maerl (IDM), gravel and sand in choice chambers. Their habitat selection was monitored over a 4-day period in control and predator treatments (utilising Asterias rubens L. and Carcinus maenas (L.)). Microhabitat use of PLM by juvenile queen scallops and the presence of cues in live maerl were also investigated. In control and predator treatments juvenile queen scallops were observed to attach preferentially to PLM than IDM, gravel or sand. Juvenile queen scallops were observed to maintain a more exposed attachment site in the absence of predators but sought refuge within and between maerl nodules in the presence of both predators. Smaller queen scallops (<18 mm shell height) were more efficient at utilising maerl thalli as a refuge. Juvenile A. opercularis showed hierarchical cue responses mediated by predator presence, i.e. responding favourably to a factor associated with live maerl presence irrespective of heterogeneity in the absence of predators but favourably to higher maerl heterogeneity in their presence. If they also preferentially attach to PLM in the field, at some sites where PLM grounds cover large areas, they may thus be considered to constitute ‘nursery areas’. Habitat attachment preference appears to be predetermined and not a result of localised predator avoidance; however, habitat usage changes in the presence of predators. Maerl beds have been shown to be easily damaged by scallop dredging in Scotland and if such nursery areas are being destroyed extensively in the field, this could damage recruitment to localised adult populations.

Sequence analysis of the ribosomal DNA internal transcribed spacer region in some scallop species (Mollusca: Bivalvia: Pectinidae).

The internal transcribed spacer (ITS) region of the ribosomal DNA from the European scallops Aequipecten opercularis, Mimachlamys varia, Hinnites distortus, and Pecten maximus was PCR amplified and sequenced. For each species, three or five clones were examined. The size ranged between 636 and 713 bp (ITS1, 209-276 bp; 5.8S rRNA gene, 157 bp; ITS2, 270-294 bp) and GC content ranged between 47 and 50% (ITS1, 43-49%; 5.8S rRNA gene, 56-57%; ITS2, 44-49%). Variation within repeats was minimal; only clones from M. varia and P. maximus displayed a few variable sites in ITS2. Among scallops, including Chlamys farreri whose ITS sequence appears in databases, significant variation was observed in both ITS1 and ITS2. Phylogenetic analysis using ITS1, ITS2, or both spacer sequences always yielded trees with similar topology. Aequipecten opercularis and P. maximus grouped in one clade and the other three scallops (C. farreri, M. varia, and H. distortus) in another, where M. varia and H. distortus are the more closely related species. These results provide new insights into the evolutionary relationships of scallop species and corroborate the close evolutionary relationship between the tribes Aequipectinini and Pectinini previously deduced from 18S rDNA sequences.

Demonstration of nutrient pathway from the digestive system to oocytes in the gonad intestinal loop of the scallop Pecten maximus L.

The mechanism of nutrient transfer from the digestive system to the gonad acini and developing oocytes was investigated in the gonad-intestinal loop system of the queen scallop Pecten maximus L. Ferritin was injected directly into the purged intestine of specimens from the wild. Subsequently, a histochemical reaction and transmission electron microscopy were used to localize ferritin in various cell types. Ferritin was rapidly absorbed by the intestinal epithelium, and then appeared in hemocytes in the surrounding connective tissue. In the hemocytes, ferritin was stored in variously sized inclusions, as well as in the general cytoplasm. In all sections examined for the 12 experimental individuals, hemocytes were always found in association with connective tissue fibers extending from the base of the intestinal epithelium to gonad acini. After 30-min incubation, ferritin appeared inside the acini of all individuals. Ferritin-bearing cells were rarely found in association with male acini or gametes, nor with mature female gametes, but often with developing female gametes. Not all individuals showed the same temporal dynamics of ferritin transport, suggesting that nutrient transfer to oocytes is either not a continuous process, or that among individuals, transfer is not synchronized on short time scales. This is the first demonstration of a pathway of nutrient transfer from the intestine, and more generally the digestive system, to developing oocytes in the Bivalvia.

To what extent does upright sessile epifauna affect benthic biodiversity and community composition?

Small-scale habitat complexity, including that caused by biological structures, is an important factor in structuring benthic communities and also sometimes in increasing biodiversity. The aim of this study was to determine if hydroid colonies have an effect on the composition of benthic communities in the Irish Sea, and if so, which components of the fauna are affected. Forty-six seabed core samples were taken by divers from two sites off Port Erin, Isle of Man, Irish Sea. Half of these were centred on hydroid colonies, half were not. All taxa retained by a 63-μm sieve from the cores were identified and counted. Community composition and diversity were compared between hydroid and non-hydroid cores using multivariate and univariate methods. Benthic communities were significantly different between the two sample groups. This was almost entirely due to the presence of sessile and mobile epifaunal taxa in the hydroid cores. The tube-building amphipod, Ericthonius punctatus, was particularly abundant attached to the hydroid stems. Infauna was not significantly different between the two groups. Upright sessile epifauna may play a particularly important role in the Irish Sea as a settlement substrate for juvenile scallops (Pecten maximus and Aequipecten opercularis), which are an important fishery resource in this area. The 11-year closure of an area to dredging has not only enhanced scallop stocks but has had the added benefit of enhancing habitat complexity and biodiversity.

Substratum heterogeneity of dredged vs un-dredged maerl grounds

Maerl grounds are comparable to sea grass beds in terms of their high biodiversity, and are characterized by abundant juveniles of species such as the queen scallop, Aequipecten opercularis. Maerl grounds impacted by towed demersal fishing gears are structurally less heterogeneous than pristine, un-impacted maerl grounds, diminishing the biodiversity potential of these habitats.

Seasonal swimming behaviour in the queen scallop ( Aequipecten opercularis) and its effect on dredge fisheries

Modified dredges were used on Aequipecten opercularis (queen scallop) fishing grounds off the Isle of Man in the north Irish Sea to determine seasonal variability in swimming behaviour in queen scallops and its effect on dredge fisheries. Scallops, which evaded dredge capture by swimming up into the water column, were captured by a specially designed net deployed above the dredge gear. The gear was used over a 20-month period and the number and size distribution of queen scallops captured in both the net and dredges were recorded. A subsample of captured scallops was maintained in running seawater tanks and used to assess two components of swimming behaviour, the time taken to respond to stimuli and the number of valve adductions carried out until exhaustion. There was considerable seasonal variability in the proportion of queen scallops that avoided dredge capture by swimming. Very low numbers of queen scallops were found in the net during the winter and spring. Net capture increased in June, and was high throughout the summer and autumn when up to 42% of scallops greater than 55 mm in height, captured in dredges, swam over the dredge mouths. There was a strong positive correlation between seawater temperature and proportion of captured scallops found in the net. Swimming experiments in the laboratory indicated that the observed seasonal variability in net capture was probably a result of changes in the time taken to respond to stimuli, rather than changes in the ability to perform a large number of valve adductions. There was no relationship between reproductive state and the proportion of actively swimming scallops. Analyses of size distributions indicated limited swimming activity in the largest scallops but no effect of epifaunal load was found on the ability of scallops to avoid dredge capture.

Identification of Mytilus galloprovincialis larvae from the Galician rı́as by mouse monoclonal antibodies

The larvae of different species of bivalves are very similar in appearance during the early stages of development (D-shaped larvae). The method available today for an accurate identification of these larvae, based on the study of several ultrastructural morphological traits of the larval hinge, is impractical when the rapid identification and sorting of the larvae of bivalves are required for the numerous and complex plankton samples that field investigations generate. Therefore, in recent years, new methods such as molecular biology, biochemical, or immunological techniques are being used for efficient and accurate identification of those larvae. Here, we follow this trend and have attempted to produce specific monoclonal antibodies (mAbs) that could be used in immunological techniques for the identification of the larvae of the mussel Mytilus galloprovincialis in plankton samples from the Galician rı́as (NW of Spain). Mice were immunized with different amounts of D-shaped larvae of mussels and with larvae treated in different ways, then mouse spleen cells were fused with myeloma tumoral cells to obtain specific hybrids. We have obtained 12 mAbs against the immunizing larvae, and two of them, M2 and M3, showed a high specific recognition to M. galloprovincialis. These two antibodies do not show any cross-reaction when tested with the larvae of some other abundant species of bivalves coexisting in the area, such as Cerastoderma edule, Ostrea edulis, Aequipecten opercularis, Tapes decussatus, and Tapes philippinarum. Furthermore, each antibody displays a different pattern of staining in the larvae of mussels visualized by confocal microscope, indicating that they are directed against different antigen epitopes. The mAbs obtained, either used alone or in combination, could be very useful for the specific identification of the larvae of M. galloprovincialis, which is the only mussel species present in the area.

Identification of four scallop species using PCR and restriction analysis of the ribosomal DNA internal transcribed spacer region.

Polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis of the ribosomal DNA region spanning the 5.8S RNA gene and the 2 flanking internal transcribed spacers (ITSs) was performed to establish DNA-based molecular markers for the identification of the scallops Aequipecten opercularis, Chlamys distorta, Mimachlamys varia, and Pecten maximus. Chlamys distorta was distinguished simply by ITS size. Species-specific restriction patterns were found with the restriction enzyme AluI, and also with SmaI for A. opercularis and M. varia. When ITS sizes and the RFLPs obtained with SmaI were combined, the 4 scallops were also differentiated. Additional species-specific RFLPs were revealed after ITS-2 PCR amplification and subsequent digestion with Hsp92II. Using this marker, canned scallops were identified. Thus this work provides a simple, reliable, and rapid method for the identification of scallops that can be used when species-specific morphologic characteristics are removed or when specimens are small in size.

Ingestion of mesozooplankton by three species of bivalve; Mytilus edulis, Cerastoderma edule and Aequipecten opercularis

Mytilus edulis, Cerastoderma edule and Aequipecten opercularis were found to ingest zooplankton when suspended in mesh cages in the water column in the Firth of Clyde. Zooplankters were also found in the stomachs of bivalves that had been taken directly from their natural habitat. The bivalves consumed a wide range of zooplankton species, but selectively consumed smaller categories of zooplankton present. Condition of zooplankton in the stomachs of the bivalves varied with zooplankton species. A degree of larviphagy was evident, particularly in Mytilus edulis.

Discard analysis and damage to non-target species in the "rapido" trawl fishery

This paper describes the catch composition in the rapido trawl fishery and the direct effects on non-target species. All data were collected on commercial fishing vessels so as to reflect commercial rapido-trawling practice. The effects on non-target species were measured using two different damage scales (three- and seven-level scales) depending on the morphology of the taxa. Damage assessment was performed taking into account the whole fishing process by collecting individuals that passed through the cod-end, individuals that were retained in the cod-end and dropped onto the deck and individuals that were collected at the end of the sorting operation just before their return to the sea. Due to differences in the habitat and spatial distribution of target species, discard/commercial ratio was very different among the three different target species fisheries: 1:6 in the queen scallop (Aequipecten opercularis) fishery, 2:1 in the flatfish (Solea spp., Platichthys flesus, Psetta maximus and Scophthalmus rhombus) fishery and 9:1 in the scallop (Pecten jacobaeus) fishery. Damage sustained by non-target species was species-specific and related to the morphology of different organisms. The sorting operation produced similar levels of injury to those of the gear itself: all discarded animals showed higher levels of damage after the sorting than before. Damage to animals that had passed through the cod-end followed the same pattern, and these data could give an estimate of the "unobserved mortality". Our observations indicated a higher impact on non-target species caused by the queen scallop fishery than that caused by the flatfish fishery. This could be due to the total amount of hard-shelled species (in the queen scallop fishery, A. opercularis accounted for 87% of the total catch biomass) in any given haul, since shells macerated the catch during towing. Discarded animals from the queen scallop fishery showed higher levels of damage than those collected in the flatfish fishery. The rapido trawl fishery seemed to exert a strong selective pressure on the macrobenthic community, being able to modify the epibenthic fauna structure which, in heavily exploited fishing grounds, was dominated by bivalves, gastropods, crabs, starfish and brittlestars.

Determination and Confirmation of the Amnesic Shellfish Poisoning Toxin, Domoic Acid, in Shellfish from Scotland by Liquid Chromatography and Mass Spectrometry

During 1998 and early 1999, shellfish samples from sites in Scotland were found to contain the amnesic shellfish poisoning toxin, domoic acid (DA). Two different techniques, liquid chromatography (LC) with UV diode-array detection and LC with mass spectrometric (MS) detection, were used to detect and confirm DA in shellfish extracts. The LC/UV method was validated for routine monitoring by recovery experiments on spiked mussel and scallop tissues with a certified mussel tissue used as reference material. Crude extracts of selected samples as well as extracts cleaned with strong anion exchange (SAX) were analyzed by both LC/UV and LC/MS. Good correlation (linear regression r2 = 0.996, slope = 0.93) between the 2 methods was found for cleaned extracts. Analyses of crude extracts by LC/UV produced false-positive results in 2 crab samples, whereas LC/MS analyses gave accurate results. It was concluded that LC/UV is a valid approach for routine monitoring of DA in shellfish when cleanup is performed with a SAX cartridge to prevent false positives. A variety of shellfish species were surveyed for DA content, including Pecten maximus (king scallops), Chlamys opercularis (queen scallop), Mytilus edulis (blue mussels), Cancer pugaris (crab), and Ensis ensis (razor fish). The highest concentration of DA was 105 microg/g in Pecten maximus.

Damage sustained by epibenthic invertebrates discarded in the Nephrops fishery of the Clyde Sea area, Scotland

The Clyde Sea Nephrops fishery produces ca. 25 000 t y −1 discards with invertebrates accounting for up to 90% of the number of animals discarded. Trawling and handling of the (by-)catch often results in physical injury, the extent of which was previously unknown. Damage sustained by invertebrate discards was assessed following commercial trawling (of 62–270 min duration) and sorting on deck. Brittlestars Ophiura ophiura were most vulnerable with 100% incurring damage, followed by squat lobsters Munida rugosa (57%) and starfish Astropecten irregularis (56%). Harder-shelled species such as hermit crabs Pagurus bernhardus and queen scallops Aequipecten opercularis sustained fewer injuries (14 and 2%, respectively). Shell chipping, loss and damage of limbs were the most frequent types of injury incurred. The severity and frequency of damage was mainly correlated with species-specific morphological and behavioural characteristics. Vessel type, tow duration and animal size had a major influence on damage to the epibenthic invertebrates caught. While damage may potentially be repaired, survival is adversely affected and sublethal effects might significantly impair fitness of frequently trawled individuals and populations.

Distribution and damage to the by-catch assemblages of the northern Irish Sea scallop dredge fisheries

The major by-catch species retained during twice yearly dredge surveys of great scallop, Pecten maximus, and queen scallop, Aequipecten opercularis, (both Mollusca: Pectinidae) populations on 13 fishing grounds in the northern Irish Sea, over a period of five years, were identified and enumerated. Additionally, the damage sustained by the by-catch was assessed and related to a range of physical parameters recorded during the survey. A number of species captured in the spring-toothed dredges exhibited differences in abundance and damage sustained between years, and also between the start and end of the closed season for great scallop fishing (1 June–31 October). The by-catch assemblage varied geographically, dependent upon the underlying community structure, as well as putative factors including gear efficiency and substratum type. Two clear assemblage types were identified by multivariate analysis, one to the south-west of the Isle of Man, the other covering fishing grounds to the north, east and south of the island. There is a hierarchy of species sensitivity to damage in great and queen scallop dredges, probably related to morphological and behavioural characteristics. This selective mortality of a fraction of the community may have long-term implications at the ecosystem level. The degree of damage sustained by many species is related to both the volume of stones retained in the dredge, and the total volume of the catch (dredge fullness). If these were reduced, the overall magnitude of incidental by-catch mortality would be lower.

An in situ study of predator aggregations on scallop (Pecten maximus (L.)) dredge discards using a static time-lapse camera system

The impact of demersal fishing gears on benthic habitats and species has been the subject of much attention recently, and suggestions have been made that scavenging epifaunal species may benefit at the population level from the additional food source provided by discards. This paper investigates some aspects of this process, including the relative attractiveness to predators of different discard species, and the role of damage in scavenger attraction. A time-lapse video system with a 1000 m long cable was positioned in an area closed to fishing, adjacent to the most heavily fished scallop (Pecten maximus) ground in the Irish Sea. A variety of undamaged and damaged by-catch animals were positioned in front of the camera, and the subsequent predator aggregations investigated. Densities of scavenger species up to 200 times that of the background population were observed, and aggregations of some species persisted for up to 3 days. The most frequently recorded scavengers, and therefore presumably those species most likely to benefit from discards as a food source, were: Asterias rubens L., Astropecten irregularis (Pennant), Liocarcinus spp Stimpson, Pagurus spp Fabricius and Callionymus lyra L. Predator attraction to apparently undamaged queen scallops, Aequipecten opercularis (L.), was almost as high as to damaged A. opercularis. Of all the prey species studied, queen scallops were the most attractive to scavengers. A directional relationship was found between the ambient water current and the arrival of the starfish, Asterias rubens.

Scallop dredging has profound, long-term impacts on maerl habitats

Maerl beds are mixed sediments built by a surface layer of slow-growing, unattached coralline algae that are of international conservation significance because they create areas of high biodiversity. They are patchily distributed throughout Europe (to ∼30 m depth around the British Isles and to ∼120 m depth in the Mediterranean) and many are affected by towed demersal fishing. We report the effects of Newhaven scallop dredges on a previously unfished maerl bed compared with the effects on similar grounds that have been fished commercially in the Clyde Sea area, Scotland. Sediment cores were taken to assess the population density of live maerl thalli prior to scallop dredging on marked test and control plots. These plots were then monitored biannually over a four-year period. Live maerl thalli were sparsely distributed at the impacted site, and experimental dredging had no discernible effect on their numbers. The previously unfished ground had dense populations of live maerl and scallops (both Aequipecten opercularis and Pecten maximus). While counts of live maerl remained high on the control plot, scallop dredging led to a >70% reduction with no sign of recovery over the subsequent four years. The vulnerability of maerl and associated benthos (e.g., the delicate bivalve, Limaria hians) is discussed in relation to towed demersal fishing practices.

Effects of long-term physical disturbance by commercial scallop fishing on subtidal epifaunal assemblages and habitats

This paper examines spatial differences in the distribution of by-catch assemblages from the scallop [Pecten maximus (L.) and Aequipecten opercularis (L.)] fishing grounds in the North Irish Sea, during 1995. The sites examined have been exposed to differing known levels of fishing disturbance by scallop dredging, based on unusually high-resolution data extracted from fishermens' logbooks. Uni- and multi-variate techniques have been used on a production dataset (a value which incorporates both abundance and biomass figures), as well as abundance and biomass data individually. The original species list was reduced to higher taxonomic groupings in line with the theory that the latter is more appropriate for detecting anthropogenic change. Species diversity and richness, total number of species, and total number of individuals all decrease significantly with increasing fishing effort. Species dominance increases with effort. Total abundance, biomass and production, and the production of most of the major individual taxa investigated decrease significantly with increasing effort. Multivariate analysis reveals a significant relationship between fishing effort and by-catch assemblage structure. The taxa most responsible for the differences are the echinoids and cnidarians, but prosobranch molluscs and crustaceans also contribute to the differences. By-catch assemblage structure is more closely related to fishing effort than any other environmental parameter investigated, including depth and sediment type. We observed an approximately linear decrease in diversity with increasing fishing disturbance, and suggest this is primarily due to selective removal of sensitive species and, more importantly, habitat homogenisation. These results were interpreted in the light of ecological theories relating disturbance to community structure. The argument that invertebrate scavenger populations benefit from prolonged exposure to fishing disturbance was also examined, but no supporting evidence was found.

Molecular data from the 16S rRNA gene for the phylogeny of Pectinidae (Mollusca: Bivalvia).

The phylogenetic relationships among the species belonging to the family Pectinidae are still an issue of debate. The mitochondrial DNA sequences from the large ribosomal RNA gene may be of great value for systematic and phylogenetic studies within families. Partial sequences of the 16S rRNA gene were obtained for the scallop species Adamussium colbecki, Aequipecten opercularis, Chlamys glabra, C. islandica, C. varia, and Pecten jacobeus and compared with the published sequence of Pecten maximus. The present molecular data show that Chlamys are polyphyletic and do not support the assignment of these species to the two subfamilies Chlamydinae and Pectininae. Moreover, the minimal genetic distance between P. maximus and P. jacobeus suggests that they could belong to the same species.