Escape performance of temperate king scallop,Pecten maximus under ocean warming and acidification

Among bivalves, scallops are exceptional due to their capacity to escape from predators by swimming which is provided by rapid and strong claps that are produced by the phasic muscle interspersed with tonic muscle contractions. Based on the concept of oxygen and capacity-limited thermal tolerance, the following hypothesis was tested: ocean warming and acidification (OWA) would induce disturbances in aerobic metabolic scope and extracellular acid-case status and impair swimming performance in temperate scallops. Following long-term incubation under near-future OWA scenarios [20 vs. 10 °C (control) and 0.112 kPa CO₂ (hypercapnia) vs. 0.040 kPa CO₂ (normocapnic control)], the clapping performance and metabolic rates (MR) were measured in resting (RMR) and fatigued (maximum MR) king scallops, Pecten maximus, from Roscoff, France. Exposure to OA, either alone or combined with warming, left MR and swimming parameters such as the total number of claps and clapping forces virtually unchanged. Only the duration of the escape response was affected by OA which caused earlier exhaustion in hyper- than in normocapnic scallops at 10 °C. While maximum MR was unaffected, warm exposure increased RMR in both normocapnic and hypercapnic P. maximus resulting in similar Q ₁₀ values of ~2.2. The increased costs of maintenance and the observation of strongly reduced haemolymph PO₂ levels indicate that at 20 °C scallops have reached the upper thermal pejus range with unbalanced capacities for aerobic energy metabolism. As a consequence, warming to 20 °C decreased mean phasic force during escape performance until fatigue. The observed prolonged recovery time in warm incubated scallops might be a consequence of elevated metabolic costs at reduced oxygen availability in the warmth.     

Impact of ocean acidification on escape performance of the king scallop, Pecten maximus, from Norway

The ongoing process of ocean acidification already affects marine life, and according to the concept of oxygen and capacity limitation of thermal tolerance, these effects may be intensified at the borders of the thermal tolerance window. We studied the effects of elevated CO₂ concentrations on clapping performance and energy metabolism of the commercially important scallop Pecten maximus. Individuals were exposed for at least 30 days to 4 °C (winter) or to 10 °C (spring/summer) at either ambient (0.04 kPa, normocapnia) or predicted future PCO₂ levels (0.11 kPa, hypercapnia). Cold-exposed (4 °C) groups revealed thermal stress exacerbated by PCO₂ indicated by a high mortality overall and its increase from 55 % under normocapnia to 90 % under hypercapnia. We therefore excluded the 4 °C groups from further experimentation. Scallops at 10 °C showed impaired clapping performance following hypercapnic exposure. Force production was significantly reduced although the number of claps was unchanged between normocapnia- and hypercapnia-exposed scallops. The difference between maximal and resting metabolic rate (aerobic scope) of the hypercapnic scallops was significantly reduced compared with normocapnic animals, indicating a reduction in net aerobic scope. Our data confirm that ocean acidification narrows the thermal tolerance range of scallops resulting in elevated vulnerability to temperature extremes and impairs the animal’s performance capacity with potentially detrimental consequences for its fitness and survival in the ocean of tomorrow.     

Delayed growth of mussel (Mytilus edulis) and scallop (Pecten maximus) veligers at low temperatures

Veliger larvae of Mytilus edulis (L.) from Menai Straits, North Wales, were maintained for up to 2 mo during 1981 at 5°C and then grown on to metamorphosis at 17°C. Larvae so treated showed similar low mortality and equivalent spat production to control larvae. Growth rate at 17°C was less in treated larvae than in controls, but treated larvae grew a little during the period at low temperature. Larvae of Pecten maximus (L.) from the Irish Sea suffered high mortality at low temperature but larvae surviving 2 wk at 8°C could be grown on to spat at 17°C. The longevity of M. edulis larvae is discussed in relation to the genetic homogeneity of adult populations around the UK.     

Early development of the gill and implications for feeding in Pecten maximus (Bivalvia: Pectinidae)

Despite the importance of understanding feeding in the early stages of bivalve development, little information is available concerning the organogenesis of the bivalve gill. The present study used histological and scanning electron microscopical techniques to present a detailed account of gill development in the early stages of the scallop Pecten maximus L. (Bivalvia: Pectinidae). Live specimens from larval cultures were observed daily using light microscopy, while five scallops were sampled for electron and light microscopy every 2 to 3 d from Day 18 to 35, then weekly to Day 56, with a final sampling on Day 58. Although development was continuous, four distinct stages were identified (1-primordia, 2-homorhabdic unreflected, 3-homorhabdic reflected, 4-heterorhabdic), partially recapitulating the presumed phylogenetic evolution of this character in the Pectinidae. The absence of a ventral grcove in all stages suggests that the particle transport mechanism of pectinids evolved independently of such a structure, which is found in other bivalve families. Similarly, the absence of latero-frontal cilia in all specimens up to the largest observed (4 mm) indicates that the single row found in adults is a later development, rather than a vestige of a more abundant ciliation in ancestral forms. The anatomical data, together with in vivo observations of feeding in postlarvae, suggest that the developmental stages of the P. maximus gill correspond to critical changes in gill function. The early life of P. maximus may thus be characterized by distinct functional changes in feeding.     

A method for rearing Pecten maximus larvae in the laboratory

Development of the scallop Pecten maximus (L.) from egg to metamorphosis takes 33 to 38 days at 16°C. The shelled veliger first appears 2 days after fertilisation, and crawling pediveligers at around 2 days before metamorphosis. The pediveliger can attach temporarily to filamentous objects by means of a byssus thread and, even after metamorphosis, periods of attachment alternate with periods of crawling. The larvae are reared in polythene bins containing 30 l of full salinity sea water (pre-filtered through 0.2 filters), which is changed every 2 days. Mixtures of algal foods (Isochrysis galbana, Chaetoceros calcitrans, Pyramimonas obovata and Tetraselmis suecica), concentrated by centrifugation, are added at each change from the third day onwards to give a concentration of 50 cells/l. Larval density is maintained below 10/ml. Antibiotics are added at each change, but very careful sterilisation of all equipment is necessary to guard against the introduction of diseases.     

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, suggesting that low spawner densities may reduce gamete production 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 nearest neighbour distance (NND), (2) the temporal pattern of spawning synchronization, and (3) the effect of site density and conspecific proximity on the probability of spawning. 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 comparable to those observed in a gonochoristic species. Spawning synchronization was highly variable, ranging between 3.5 and 59.8 % of individuals spawning. P. fumatus was more likely to engage in spawning activity when at greater densities and at closer proximity to conspecifics. This strongly suggests that lower densities in this scallop reduce not only the number of individuals contributing to the production of gametes, but also reduces the synchronization of spawning.     

Utrastructural study of oogenesis and oocytic degeneration in Pecten maximus from the Bay of St. Brieuc

An ultrastructural study of oocytic development enabled the identification of changes occurring during oogenesis in Pecten maximus collected from the Bay of St. Brieuc, France, in 1987. Auxiliary cells, closely associated with developing oocytes were observed. Each oocyte seems to be associated with only one secretory cell, which is characterised by an abundant rough endoplasmic reticulum at the onset of vitellogenesis. Contact between this cell and a developing oocyte is maintained by a desmosome-like junction which can be observed when the vitelline coat is formed. These auxiliary cells seem to play a trophic role in vitellogenesis, and may be involved in the formation of the vitelline coat of the oocytes. Oocytic degeneration is discussed in detail; in this species, it is a continuous phenomenon of varying intensity throughout the year. The ultrastructural changes resulting in lysis of the oocyte are described, and the evolution of atretic oocytes is examined.     

Seasonal variation in the properties of muscle mitochondria from the tropical scallop Euvola (Pecten) ziczac

In scallops, gametogenesis leads to considerable transfer of energetic reserves from the adductor muscle to the gonads. During an annual cycle, the scallops are exposed to changes in temperature and food availability. As these changes may affect muscle metabolic capacities, we examined whether the properties of the mitochondria in the phasic adductor muscle were modified during the annual cycle of the scallop Euvola (Pecten) ziczac (L. 1758). During our study, temperature and chlorophyll a levels generally showed an inverse relationship: high temperatures and low chlorophyll a levels occurred from mid-April to early June. Lower temperatures and higher chlorophyll a levels were found from January to late March and from mid-June to mid-September. Throughout the annual cycle, the substrate preferences and the pH sensitivity of the isolated muscle mitochondria changed little, whereas the maximal oxidative capacities and respiratory control ratios (RCR) varied considerably. Consistently, the maximal capacities for substrate oxidation were 30 to 80% lower in mitochondria isolated in May than at other times in the year. The RCR values of mitochondrial oxidation of glutamate, glutamine and succinate varied throughout the year with lower values characterizing the mitochondria from scallops harvested in May and in certain cases in August. In May, adductor muscles had lower protein levels than at other times. These data suggest that the requirements of gametogenesis, coupled with␣the high temperatures and low food availability occurring during April and May, led to a mobilization of muscle proteins which concomitantly decreased the oxidative capacity of isolated mitochondria. Received: 29 November 1996 / Accepted: 5 December 1996     

Relation of RNA/DNA ratios to growth for the scallop Euvola (Pecten) ziczac in suspended culture

We examined the relation of RNA/DNA ratios to growth for three size groups of the tropical scallop Euvola ziczac maintained in suspended culture at 8, 21 and 34 m in depth in the Golfo de Cariaco, Venezuel. Various growth parameters indicated that production decreased with depth. This was more likely due to a decrease in seston quality with depth than to temperatures or seston abundance (which were similar at the various depths studied). The RNA/DNA ratio was correlated with the G-index of muscle growth for juveniles (r ²=0.55). A much weaker correlation was observed for the maturing scallops (r ²=0.18), probably because of the interaction between reproductive and somatic growth. In fully mature scallops, somatic growth was negligible and the RNA/DNA ratios appeared to be inversely related to the level of physiological stress of the scallops. Whereas RNA/DNA ratios are difficult to interpret for maturing E. ziczac, because an increased ratio can be due to either increased gonadal or somatic growth, they are useful in predicting growth in juveniles and physiological stress in fully mature scallops.     

Temperature and development in larvae of the turbot Scophthalmus maximus

Turbot (Scophthalmus maximus L.) were reared at 12 and 16°C until 26 d after hatching. At both temperatures, starting at the neural plate stage, somites were initially formed every 75 min. Expressed as a percentage of development time (DT, fertilisation to 90% larvae hatching) somite formation occurred relatively earlier during embryogenesis at 12°C (45% DT) than at 16°C (55% DT). At 12°C, after the 32-somite stage the rate of somite formation decreased to one every 300 min. The larvae hatched after 6 d at 12°C and 3 d at 16°C at a relatively primitive stage of development, prior to the opening of the mouth and anus, with unpigmented eyes, and a straight gut. Temperature altered the relative timing of organogenesis in the larval stages. At 12°C, the following characters appeared (in this order): swimbladder>loop in the gut (at the time of yolk exhaustion)>caudal fin. In contrast, at 16°C, the caudal fin appeared at the same time as the loop in the gut. At 16°C, spines formed on the head in the region of the otic capsule at the time the swimbladder formed and the yolk was exhausted, but were absent in 12°C larvae. At both temperatures, in 1 d-old larvae the myotomes just behind the yolk-sac contained 200 inner muscle fibres (presumptive white muscle). The initial growth of inner muscle was largely due to hypertrophy, but by 26 d at 12°C and 11 d at 16°C hyperplastic growth became important, as evidenced by a significant increase in the number of small fibres (<10 m²). By 26 d the average number of inner muscle fibres had increased to 341 at 12°C and 988 at 16°C. New muscle fibres were added in distinct germinal zones at the dorsal and ventral apices of the myotomes. Metamorphosis was associated with a thickening of the superficial (presumptive red) muscle layer and the appearance of tonic muscle fibres.     

Electrophoretic survey of genetic variation in Pecten maximus,Chlamys opercularis,C. varia and C. distorta from the Irish Sea

Food selection by young larvae of the gulf menhaden (Brevoortia patronus) was studied in the laboratory at Beaufort, North Carolina (USA) in 1982 and 1983; this species is especially interesting, since the larvae began feeding on phytoplankton as well as microzooplankton. When dinoflagellates (Prorocentrum micans), tintinnids (Favella sp.), and N1 nauplii of a copepod (Acartia tonsa) were presented to laboratory-reared, larval menhaden (3.9 to 4.2 mm notochord length), the fish larvae ate dinoflagellates and tintinnids, but not copepod nauplii. Larvae showed significant (P<0.001) selection for the tintinnids. Given the same mixture of food items, larger larvae (6.4 mm notochord length) ate copepod nauplii as well as the other food organisms. These feeding responses are consistent with larval feeding in the northern Gulf of Mexico, where gulf menhaden larvae between 3 and 5 mm in notochord length frequently ate large numbers of dinoflagellates (mostly P. micans and P. compressum) and tintinnids (mostly Favella sp.), but did not eat copepod nauplii. As larvae grew, copepod nauplii and other food organisms became important, while dinoflagellates and tintinnids became relatively less important in the diet. Since the tintinnids and nauplii used in the laboratory feeding experiments were similar in size as well as carbon and nitrogen contents, the feeding selectivity and dietary ontogeny that we observed were likely due to a combination of prey capturability and larval fish maturation and learning.Contribution No. 5575 of the Woods Hole Oceanographic Institution     

Effects of UV-B radiation on the gills of Catla catla during early development

Scanning electron microscopic (SEM) study of gills of Catla catla catla (17-day-old) exposed to UV-B radiation (145?µW?cm^?2 at the water surface) for three different exposure times: 5, 10 and 15?min was conducted. Fish without UV-B exposure served as control. UV-B radiation damaged both gill filaments and lamellae. The intensity of damage was minimal in 5?min exposed fish, followed by 10?min exposed fish and maximal in 15?min. The gill epithelium was severely damaged in 15?min irradiated fish compared to control. Pavement cells (PVCs) were damaged and the numbers of microridges within PVCs decreased. The deep boundary of PVC was not clear. In some area of gill epithelium, PVCs were destroyed and mitochondrion-rich cells (MRCs) were exposed. The 5?min exposure reduced the number of microridges in the PVCs, but the boundary of PVCs was still visible. MRCs in the gill epithelium were not exposed in 5?min exposed fish. The damage to PVCs and subsequent exposure of MRCs in UV-B irradiated fish may hamper respiratory functions and disturb osmoregulation in catla.     

The osphradium in Placopecten magellanicus and Pecten maximus (Bivalvia,Pectinidae): histology,ultrastructure, and implications for spawning synchronisation

The bivalve osphradium is a band of putatively sensory tissue located in the gill axis, whose function is uncertain. In the present study, extending from 1987 to 1994, anatomical, histological, and electron microscopical techniques were used to elucidate the structure and ultrastructure of the osphradium in hatchery Pecten maximus L. and Placopecten magellanicus (Gmelin) (collected from Passamaquoddy Bay, New Brunswick, Canada). The osphradium consists of two distinct regions which run longitudinally on both sides of each gill axis: the osphradial ridge, and the dorsal tuft cilia region. The osphradial ridge was largely devoid of cilia other than those of the few free nerve fibres. The dorsal tuft cilia region contained free nerve fibres and ciliary tufts, separated by undifferentiated epithelial cells. No paddle cilia were observed under isosmotic fixation conditions, although under hypotonic conditions such cilia were quite common, suggesting an artefactual nature. Most of the cells of the osphradial ridge were highly secretory, the principal products being large pigment granules (in Pecten maximus) directly secreted by the Golgi bodies, and numerous small, electron-dense vesicles. These vesicles were arranged along extensive microtubule arrays in the basal region, indicative of axonal transport. These data support and extend Haszprunar's hypothesis of the role of the osphradium in the reception of chemical spawning cues and in the synchronization of gamete emission. Together with independent data on nerve pathways, osphradial sensory modalities, and monoamine localisation, an anatomical pathway and neurophysiological mediator are postulated.     

Effects of clotrimazole and amiodarone on early development of amphibian (Xenopus tropicalis)

Pharmaceuticals have been recognized as a continuing threat to environmental stability. Few experimental data are available for the effects of clotrimazole and amiodarone on the ecological environment. An acute test with embryos and a chronic test with larvae of amphibian (Xenopus tropicalis) were thus conducted to determine the influence of clotrimazole or amiodarone on early amphibian development. In acute test, % survival and the body length were numerically decreased by both pharmaceuticals treatments compared to control. In chronic test, the cumulative mortality was 22.2% with 0.1?µg?L^?1 clotrimazole treatment and 21.7% with 1?µg?L^?1 amiodarone. The whole body length and the biomass were significantly decreased and developmental stages significantly delayed by both pharmaceuticals. The results of our study suggest that clotrimazole exerted adverse effects on larvae of X. tropicalis at environmentally relevant concentrations.     

Effects of seawater temperature and pH on the boring rates of the sponge Cliona celata in scallop shells

Warmer, more acidic water resulting from greenhouse gas emissions could influence ecosystem processes like bioerosion of calcifying organisms. Based on summer-maxima values (temperature = 26 °C; pH = 8.1) at a collection site in New York (40°56″ N, 72°30″ W), explants of the boring sponge Cliona celata Grant, 1826 were grown for 133 days on scallop shells in seawater ranging from current values to one scenario predicted for the year 2100 (T = 31 °C; pH = 7.8). High water temperature had little effect on sponge growth, survival, or boring rates. Lower pH slightly reduced sponge survival, while greatly influencing shell boring. At pH = 7.8, sponges bored twice the number of papillar holes and removed two times more shell weight than at pH = 8.1. Greater erosion resulted in weaker scallop shells. This study suggests that lower seawater pH may increase boring rates of C. celata in shellfish, with potentially severe implications for wild and farmed shellfish populations.     

Effects of induced paralysis on hemocytes and tissues of the giant lions-paw scallop by paralyzing shellfish poison

In general, bivalves are not affected by exposure to toxic dinoflagellates that produce paralyzing shellfish poisons (PSP). After injection with PSP extracted from the Gymnodinium catenatum, Nodipecten subnodosus is paralyzed, indicating that PSP provokes effects similar to what is observed in vertebrates, including paralysis and metabolic stress. To investigate the processes involved in poisoning by PSP, lions-paw scallops were injected with gonyautoxin (GTX) 2/3 epimers in the adductor muscle. Mild doses provoked adductor muscle contractions and paralysis, mantle retraction, and incapacity of shell closure, but scallops gradually recovered in a clear, dose-time recovery pattern. With high doses of GTX 2/3, scallops were permanently paralyzed, and hemocytes in hemolymph were reduced. Surprisingly, under these conditions, scallops continued normal feeding and did not show any microscopic defect in intestine or gills, but hemocytes infiltrated the adductor muscle and abnormal vitellogenesis and mantle melanization occurred. Paralysis stress was accompanied by negative scallop responses, based on visible effects, generation of nitric oxide, lipid peroxidation, and changes in antioxidant and hydrolytic enzymes in hemocytes and tissues. These data can be used to understand potential side effects of PSP in bivalves.     

Effects of early auditory experience on the development of local song preference in female swamp sparrows

A growing number of studies show that learning about male mating signals can shape the way females discriminate among males and may influence the evolution of both female preferences and the male traits under selection. Female songbirds commonly prefer local songs over foreign songs from a different population. In some species, however, the extent of variation among songs sung by different males within a population is as great as the variation observed between populations, raising the question of how females are able to discriminate local from foreign songs. Here, we report that laboratory-reared female swamp sparrows (Melospiza georgiana) not only show a preference for the particular song types with which they were tutored as compared with both foreign songs and unfamiliar local songs but also show preference for unfamiliar local songs over unfamiliar foreign songs. An acoustic analysis comparing tutor songs and those presented as unfamiliar local and foreign songs suggests that female swamp sparrows might be attuned to the specifics of local note phonology when assessing the attractiveness of unfamiliar songs. Our results demonstrate that early auditory experience influences response to geographic song variation in female swamp sparrows, and suggest the possibility that female songbirds may generalize what they learn from songs early in life to novel songs heard in adulthood. Additional work is needed to evaluate the contribution of unlearned predispositions for local song.     

The development of functional digestive and metabolic organs in turbot,Scophthalmus maximus

The functional status of organ systems involved into the processing of exogenous food is critical for the survival and growth of fish early life stages. The present study on laboratory-reared larval turbot, Scophthalmus maximus, provides an overview on the ontogeny of structure and functions involved in digestion, absorption and metabolism of nutrients. At start of exogenous feeding the intestine of larval turbot is anatomically differentiated, with enterocytes displaying an adult-type ultrastructure and being able to process lipids. At the microvillous border of the enterocytes, enzymes of contact digestion such as aminopeptidase are found. The ultrastructure of the exocrine pancreatic cells is fully differentiated from hatching onwards. Likewise, substantial activities of trypsin-type proteases are present. A stomach anlage exists in first-feeding larvae; however, the stomach becomes functional (appearance of gastric glands and pepsin secretion) only during metamorphosis. Liver parenchymal cells already display a functional ultrastructure during the endotrophic phase; with onset of exogenous feeding they develop pronounced diet-related changes of their energy stores. Larval respiration is not executed by the gills since respiratory surface of these structures develops only towards metamorphosis. The energy generation of larval muscle tissue depends on aerobic metabolism, whereas glycolytic activities start to increase at metamorphosis. In conclusion, two important patterns can be recognized in the development of turbot larvae: (1) The structure/function is differentiated at hatching or at the onset of exogenous feeding (afterwards it experiences mainly quantitative but not qualitative growth, i.e., intestine, exocrine pancreas, liver); or (2) the structure/function is absent in larvae and develops only during metamorphosis (i.e., gills, glycolytic muscle metabolism, stomach).     

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. Received: 29 January 2000 / Accepted: 31 May 2000