Ecological consequences of ontogenetic shifts in predator diet: Seasonal constraint of a behaviorally mediated indirect interaction

Predators play an important role in structuring assemblages through direct and cascading indirect effects. While there has been recent interest in how the strength and direction of trophic cascades vary spatially, seasonal variability in trophic links is seldom considered. In North Carolina, recruitment-failure of bay scallops typically occurs following the spring but not the fall spawning despite the presence in each of these seasons of predatory blue crabs. One explanation for this pattern is that in the fall, seasonally abundant predators of blue crabs reduce the foraging efficiency of crabs on scallops and thus the overall magnitude of top-down effects. Quantification of bay scallop consumption by blue crabs in closed mesocosms with or without pinfish supported the hypothesis that seasonally abundant adult pinfish indirectly increase survivorship of bay scallop recruits in fall by reducing predation by blue crabs. Despite voracious consumption of bay scallops during both the day and night in mesocosms to which only small blue crabs were added, blue crabs in mesocosms with visually-foraging adult pinfish consumed bay scallops only by night. Juvenile pinfish that dominate estuarine populations in spring did not impede consumption of bay scallops by blue crabs. In mesocosms from which animals could not emigrate, the addition of neither adult nor juvenile pinfish increased the mortality of blue crabs, indicating a behaviorally mediated interaction. Blue crabs restricted by adult pinfish to nocturnal feeding did not compensate for lost feeding time by increasing their night-time consumption of bay scallops. These results strongly suggest that greater survivorship of bay scallops in fall than spring is due to adult pinfish, potential predators of small blue crabs, restricting blue crab foraging to hours of dark. In spring, when pinfish are small and incapable of consuming blue crabs, blue crabs consume bay scallops by day and by night. Such seasonal variation in the number of trophic links in a system may have important evolutionary implications. By timing reproduction to occur in fall when the pinfish-crab-scallop cascade is in operation, bay scallops maximize recruitment.     

Site-specific and density-dependent extinction of prey by schooling rays: generation of a population sink in top-quality habitat for bay scallops

Bay scallops (Argopecten irradians concentricus) are patchily distributed on two dominant spatial scales: (1) geographically restricted to highly saline marine lagoons, and (2) locally abundant within such lagoons only in relatively discrete beds of seagrass habitat. In the Cape Lookout lagoonal system of North Carolina, adult bay scallop abundance in the most densely occupied seagrass bed (Oscar Shoal) exhibits repeatable declines from up to 70 m^-2 to near zero in a 2- to 4-week period during late summer. This crash is completed before fall spawning can be initiated, thereby creating a population sink in what is the singly most productive patch of habitat. Field experiments conducted in the summers of 1996 and 1998 demonstrated that the seasonal extinction of bay scallops on Oscar Shoal can be prevented by the erection of 1-m² stockades, made of 50-cm-high vertical poles, spaced every 25 cm, which inhibit access by cownose rays. Because these stockades were porous to emigration and physical transport, and open to access by all other predators of adult scallops, predation by migrating cownose rays is the only viable explanation for the crash. Consequently, the natural predation process in this system achieves the reproductive extinction of prey in the habitat patch of highest productivity. Over 7 years of observation, the mortality rate in this patch increased with summer density, reaching the asymptote of 100% at 10 m^-2. The site-specific habitat selection by schools of rays may be based on prey density, which could render this example representative of a widespread generator of population sinks in habitat patches of high quality. The virtual extinction of scallops within Oscar Shoal despite nearby patches with relatively high density may be related to the highly efficient feeding behavior of schools and the high vulnerability of bay scallops in a context of multiple alternative prey types.     

Comparative physiology of young and old cohorts of bay scallop Argopecten irradians irradians (Lamarck): mortality,growth, and oxygen consumption

The bay scallop Argopecten irradians (Lamarck) undergoes rapid population decline in its second year of life. Pre-(1st-yr) and postreproductive (2nd-yr) bay scallops were held in cages at two sites on Long Island, New York, U.S. Survival, growth, and metabolic rates of the two cohorts were compared monthly throughout the autumn and winter. Second-year scallops, the harvestable crop of the year, maintained a positive energy balance until late November–December. Both age classes experienced similar relative tissue weight losses during overwintering (9–11% at the site where milder environmental conditions prevailed, and 24–25% at the more stressful site). Ambient water temperature explained a significant proportion (93%) of the seasonal variation in the rate of oxygen consumption. Thus the northern bay scallop A.i. irradians shows a limited ability to acclimatise oxygen consumption to seasonal temperature changes over the range of 1–23°C. A significant increase in oxygen uptake was associated with increased gametogenic activity of young scallops in May. Metabolic rate at this time was 50% higher than that predicted based on temperature, providing an estimate of the metabolic cost of reproduction in this species. The weight-normalized oxygen uptake rate of senescent scallops was significantly lower than that of young scallops. Mass natural mortality of the older cohort occurred during the winter, before the onset of a second gametogenesis; only 50% of the population survived beyond late January in 1985. Mortality was delayed by 2.5 months during a similar experiment conducted in 1986. Results of this study suggest that senescent mortality of New York bay scallop populations is not directly linked to the energy drain of a second reproductive event following overwintering stress.     

Factors affecting the distribution of juvenile estuarine and inshore fish

The differential distributions of juveniles and adults of 25 species of teleost were investigated and compared from four habitat types in sub-tropical Moreton Bay, Queensland. The aim of the study was to identify factors influencing the distribution of juveniles, particularly the species which enter estuaries. The following habitats were sampled: a shallow, sheltered tidal estuary (Caboolture); a shallow, exposed bay with muddy substrates (Deception Bay); an exposed area of sandy substrates and seagrass (Toorbol Point) and a sheltered oceanic site with sandy substrates and seagrass (Kooringal). Data on diet, spawning seasons and recruitment periods of fry are presented together with measurements of salinity, temperature and turbidity. Species entering estuaries recruited mainly in summer (rainy season). The possible preference of juveniles for calm water, the roles of food and predation pressure, the effects of salinity, temperature and turbidity are discussed in relation to the biology and distribution of the fish. Salinity and temperature were probably not important to most juvenile fish. The effects of calm water, suitable food and predators vary according to species. Although all juveniles studied preferred shallow water, in the case of those entering estuaries, turbidity was the single most important factor. Juveniles of the same species occurred in both the estuary and Deception Bay where abiotic and biotic factors other than turbidity were different. During summer, turbidity gradients extended from east to west in Moreton Bay with highest turbidities in Caboolture estuary and Deception Bay. In winter, turbidities throughout Moreton Bay were low and relatively uniform. At this time many of the ‘clear water’ species occurred in Deception Bay. The influence of high turbidity on fish may be linked to reduced predation pressure and perhaps food supply in shallow water. Turbidity gradients in summer may aid fry in locating estuarine nursery grounds. It is apparent however, that juveniles of many species are probably not attracted to estuaries per se but to shallow turbid areas.     

Effects of the toxic dinoflagellate Alexandrium catenella on histopathogical and escape responses of the Northern scallop Argopecten purpuratus

Juvenile Northern scallops Argopecten purpuratus were exposed to cultures of the paralytic shellfish toxin (PST) producing dinoflagellate, Alexandrium catenella, or a non-toxic microalga as a control, T-iso. After 3 and 6 days of exposure to either A. catenella or T-iso, scallops were stimulated to elicit an escape response by exposing them to the predatory sea star Meyenaster gelatinosus. We monitored the escape response of the scallops in terms of reaction time after first contact with the sea star, number of claps (burst of rapid valve closures) until exhaustion, clapping time, clapping rate, the time scallops spent closed when exhausted, and recovery from the initial number of claps, clapping time and clapping rate. Additionally, histopathological and stress responses (through heat-shock protein [hsp70] induction), as well as accumulation of Paralytic Shellfish Poisoning (PSP) toxins, were monitored on scallops after 3 and 6 days of exposure to A. catenella. After 6 days of exposure, scallops exposed to A. catenella accumulated PSTs and reacted more rapidly with a higher clapping rate, however the duration of their escape response was shorter than controls, when exposed to M. gelatinosus. Additionally, scallops exposed to A. catenella showed histopathological features, especially after 6 days of exposure, including increased melanization of the tissues and myopathy, with high levels of degeneration of the muscle fibers. A six-day exposure to A. catenella also caused an increase in prevalence of rickettsiales-like organisms within scallop tissues. This study suggests that PST accumulation can affect the interaction between the Northern scallop and both pathogens and predators, potentially increasing their susceptibility to either of them.     

Temporal variation in habitat use by nekton in a subtropical estuarine system

Utilisation by fish of different estuarine habitats is known to vary at many different temporal scales, however no study to date has examined how utilisation varies at all the relevant times scales simultaneously. Here, we compare the utilisation by fish of sandy, intertidal foreshore habitats in a subtropical estuary at four temporal scales: between major spawning periods (spring/summer and winter), among months within spawning periods, between the full and new moon each month, and between night and day within those lunar phases. Comparisons of assemblage composition, abundance of individuals and of fish in seven different ‘ecological guilds’ were used to identify the temporal scales at which fish varied their use of unvegetated sandy habitats in the lower Noosa Estuary, Queensland, Australia. Fish assemblages were sampled with a seine net at three different regions. The most numerically dominant species caught were southern herring (Herklotsichthys castelnaui: Clupeidae), sand whiting (Sillago ciliata: Sillaginidae), weeping toadfish (Torquigener pleurogramma: Tetraodontidae), and silver biddy (Gerres subfasciatus: Gerreidae). Considerable variation at a range of temporal scales from short term (day versus night) to longer term (spawning periods) was detected for all but one of the variables examined. The clearest patterns were observed for diurnal effects, where generally abundance was greater at night than during the day. There were also strong lunar effects, although there were no consistent patterns between full moon and new moon periods. Significant differences among months within spawning periods were more common than differences between the actual spawning periods. The results clearly indicate that utilisation of sandy, unvegetated estuarine habitats is very dynamic and highly variable in space and time.     

Seasonal changes in the common dab, Limanda limanda (L.) in Isle of Man Waters

Otolith accretion was greatest in summer when opaque bands were laid down and slowest in winter when hyaline rings were formed. Food intake was minimal in winter and maximal in summer. Liver weight was high in summer and winter and low in spring after spawning. Growth in length was higher in summer than winter. Gonad weight was greatest in winter for both sexes. Spawning occurred from February to April. After spawning males recovered earlier than females and testes ripened earlier than the ovaries. From winter to summer, the sea temperature increased from 7.5–13.0°C; the day length from 7–17h; and the salinity varied from 34.07−34.36%.     

Domestication reduces the capacity to escape from predators

Phenotypic plasticity in response to variations in predatory pressure frequently occurs in wild populations, but it may be more evident and critical in species subjected to high exploitation rates and aquaculture. The Chilean scallop Argopecten purpuratus is becoming a domesticated species and the production of hatchery-reared scallops (closed environment), has implied the development of successive generations of individuals deprived of several stimuli normally present in their natural habitats (e.g. predators). We compared the escape capacities between wild and cultured A. purpuratus and also evaluated the effect of reproductive investment on the escape response capacities. Wild and cultured scallops, at different reproductive stages (maturing, mature and spawned), were stimulated to escape with the predatory sea star Meyenaster gelatinosus. We recorded: (1) the time to reaction, (2) the total number of claps, the duration of the clapping response and the clapping rate until exhaustion, (3) the time they spent closed after exhaustion, and (4) the proportion of claps recovered, the duration of the clapping response and the clapping rate after 20 min of recuperation. We found that wild A. purpuratus (1) reacted earlier when contacted by their natural predator, (2) escaped faster (greater clapping rates), (3) spent less time with their valves closed when exhausted, and (4) most of their escape capacities (i.e. claps number; clapping time; capacity of recuperation) were less affected by the energetic requirements imposed by gonad maturation and/or spawning than in cultured scallops. We considered that all these aspects of the escape response would make wild scallops less vulnerable to predation than cultured scallops, thus decreasing predation risk. Given the reduction of escape performance in cultured scallops, we suggest that this aspect should be considered for the success of culture-based restocking programs.     

Warming and hypoxia reduce the performance and survival of northern bay scallops (Argopecten irradians irradians) amid a fishery collapse

Warming temperatures and diminishing dissolved oxygen (DO) concentrations are among the most pervasive drivers of global coastal change. While regions of the Northwest Atlantic Ocean are experiencing greater than average warming, the combined effects of thermal and hypoxic stress on marine life in this region are poorly understood. Populations of the northern bay scallop, Argopecten irradians irradians across the northeast United States have experienced severe declines in recent decades. This study used a combination of high-resolution (~1 km) satellite-based temperature records, long-term temperature and DO records, field and laboratory experiments, and high-frequency measures of scallop cardiac activity in an ecosystem setting to quantify decadal summer warming and assess the vulnerability of northern bay scallops to thermal and hypoxic stress across their geographic distribution. From 2003 to 2020, significant summer warming (up to ~0.2°C year⁻¹) occurred across most of the bay scallop range. At a New York field site in 2020, all individuals perished during an 8-day estuarine heatwave that coincided with severe diel-cycling hypoxia. Yet at a Massachusetts site with comparable DO levels but lower daily mean temperatures, mortality was not observed. A 96-h laboratory experiment recreating observed daily temperatures of 25 or 29°C, and normoxia or hypoxia (22.2% air saturation), revealed a 120-fold increased likelihood of mortality in the 29°C-hypoxic treatment compared with control conditions, with scallop clearance rates also reduced by 97%. Cardiac activity measurements during a field deployment indicated that low DO and elevated daily temperatures modulate oxygen consumption rates and likely impact aerobic scope. Collectively, these findings suggest that concomitant thermal and hypoxic stress can have detrimental effects on scallop physiology and survival and potentially disrupt entire fisheries. Recovery of hypoxic systems may benefit vulnerable fisheries under continued warming.     

Heat shock protein responses in thermally stressed bay scallops, Argopecten irradians, and sea scallops, Placopecten magellanicus

The effects of thermal stress on the induction of heat shock proteins (HSPs) were examined in northern bay scallops, Argopecten irradians irradians, a relatively heat tolerant estuarine species, and sea scallops, Placopecten magellanicus, a species residing in cooler, deeper water. Polyclonal antibodies used in this work for analysis of inducible HSP70 and HSP40 only recognized proteins of 72 and 40 kDa respectively from the mantles of both scallop species. Additionally, HSP quantification using the antibody to HSP70 was equally effective by either immunoprobing of western blots or ELISA, demonstrating that either approach could be successfully employed for analysis of thermal response in scallops. Sea scallop HSP70 and HSP40 did not change when animals were heat-shocked for 3 h by raising the temperature from 10 °C to 20 °C; however, a 24 h treatment of the same magnitude elicited a significant response. Conversely, bay scallops displayed rapid and prolonged HSP70 and HSP40 responses during the recovery period following a 3 h heat shock from 20 °C to 30 °C. Temperature reduction from 20 °C to 3 °C for 3 h also caused significant HSP70 and HSP40 increases in bay scallops; this represents the first time cold shock was shown to induce HSP synthesis in bivalve mollusks. The onset of the HSP40 response was more rapid than for HSP70, occurring at the end of the cold shock itself prior to transfer to a recovery temperature. Both proteins responded maximally during recovery at control temperature. HSP responses of sea and bay scallops to thermal stress may be related to their habitat in the natural environment and they suggest a differential capacity for adaptation to temperature change. This is an important consideration in assessing the response of these scallops to different culture conditions.     

Edge effects in patchy seagrass landscapes: The role of predation in determining fish distribution

Predation is often described as an underlying mechanism to explain edge effects. We assessed the importance of predation in determining edge effects in seagrass using two approaches: a video survey to sample predators at small scales across seagrass edges, and a tethering experiment to determine if predation was an underlying mechanism causing edge effects. Underwater videos were placed at four positions: middle of seagrass patches; edge of seagrass; sand immediately adjacent to seagrass and sand distant from seagrass. Fish abundances and the time fish spent in view were measured. The main predatory fish (Australian salmon, Arripis spp.) spent more time over adjacent sand than other positions, while potential prey species (King George whiting, Sillaginodes punctata (Cuvier), recruits) were more common in the middle of seagrass patches. Other species, including the smooth toadfish, Tetractenos glaber (Freminville), and King George whiting adults, spent more time over sand adjacent to seagrass than distant sand, which may be related to feeding opportunities. King George whiting recruits and pipefish (Stigmatopora spp.) were tethered at each of the four positions. More whiting recruits were preyed upon at outer than inner seagrass patches, and survival time was greater in the middle of shallow seagrass patches than other positions. Relatively few pipefish were preyed upon, but of those that were, survival time was lower over sand adjacent to seagrass than at the seagrass edge or middle. Video footage revealed that salmon were the dominant predators of both tethered King George whiting recruits and pipefish. The distribution of predators and associated rate of predation can explain edge effects for some species (King George whiting) but other mechanisms, or combinations of mechanisms, are determining edge effects for other species (pipefish).     

On the fringe of the invasion: the ecology of cane toads in marginally-suitable habitats

Understanding how invasive species flourish under climatic conditions outside those found within their native range can inform management. In southeastern Australia, cane toads (Rhinella marina) are spreading into montane areas cooler than have been predicted to be suitable. We monitored the presence of active toads in two high-elevation sites (750–1010 m above sea level [asl]) and two adjacent low-elevation sites (150–210 m asl) in northeastern New South Wales over spring and summer. We radio-tracked 28 field-collected adult toads (n = 5–9 toads per site) and quantified their thermoregulatory opportunities and body temperatures. Toads were active at low-elevation sites in spring, but were not seen in high-elevation sites until late summer. At low elevations, toads had access to a wide range of temperatures and selected cool diurnal refugia. In montane sites, toads had less control over their temperatures, because thermal differentials between exposed and sheltered microhabitats were smaller. Overall though, body temperatures of toads at high-elevation sites in summer were not different to those of conspecifics at lower elevations in spring. As a result, toads at high elevations moved as far (mean daily displacement around 50 m) as did low-elevation conspecifics. Toads in high elevations spent the day in superficial shelter, often partly exposed. Thus, although toads only appear in high-elevation sites seasonally, their behaviour at those sites (spending the day exposed; moving extensively at night) likely exacerbates their ecological impact by bringing them to the attention of vulnerable native predators.     

Feeding ecology of King George whiting Sillaginodes punctatus (Perciformes) recruits in seagrass and unvegetated habitats. Does diet reflect habitat utilization?

This study investigated the feeding ecology of King George whiting Sillaginodes punctatus recruits to determine how diet composition varies between habitat types (seagrass and unvegetated habitats), and between sites separated by distance. Broad-scale sampling of seagrass and unvegetated habitats at nine sites in Port Phillip Bay (Australia) indicated the diet composition varied more by distance into the bay than by habitat. Near the entrance to the bay the diet was dominated by harpacticoids and gammarid amphipods, in the middle reaches of the bay the diet was completely dominated by harpacticoids, while at sites furthest into the bay, mysids and crab zoea were also important. Abundances of prey in guts was significantly higher between 1000 and 2200 hours compared with other times, indicating diurnal feeding. Laboratory determined gut evacuation rate (based on an exponential model) was estimated to be -0·54. Daily rations were highly variable among sites and habitat types. Sillaginodes punctatus recruits consumed much higher quantities of prey on unvegetated habitat than seagrass habitat at some middle reach sites; with prey consumption of harpacticoid copepods on unvegetated habitat approaching 3000 individuals per day at one site. The results of this study provide insight into why habitat associations of S. punctatus recruits within mosaics of seagrass and unvegetated habitat show high spatial variation.     

紫扇贝与海湾扇贝通用SSR的检测及其在杂交子代鉴定中的应用

以紫扇贝DNA为模板,用已开发的147个海湾扇贝微卫星标记引物扩增,结果表明100个微卫星标记能成功扩增,其中有47个表现出多态性,等位基因数目从2到9不等.观测杂合度范围为0.128 0～1.000 0(平均0.660 4),期望杂合度范围为0.503 1～0.862 1(平均0.671 9),有6个位点偏离Hardy-Weinberg平衡(P<0.05).用7对引物分别对紫扇贝、海湾扇贝及其种间正反杂交F1各30个个体进行PCR扩增,发现它们可明确区分紫扇贝与海湾扇贝,且所检测60个杂交子代均同时含海湾扇贝与紫扇贝的相应种特异性条带,证明全部为种间杂交子代.将该7对引物的扩增产物克隆测序,发现这些位点在两种扇贝中的序列同源率为40.22%～91.95%,其中3个位点在紫扇贝中的扩增产物仍然含有微卫星.     

Ecophysiological plasticity of annual populations of giant kelp (Macrocystis pyrifera) in a seasonally variable coastal environment in the Northern Patagonian Inner Seas of Southern Chile

Annual populations of Macrocystis pyrifera in Southern Chile have been the main focus of studies intending to understand how these populations can couple consecutive sporophytic generations. Research has included studying the population dynamics and gametophytic responses to environmental conditions and the role of recruitment, grazing, and the use of benthic filter feeders as secondary substrate. Adult sporophytes undergo senescence due to changes in abiotic factors during summer and autumn producing 100 % mortality. This study provides evidence about the environmental factors driving the decline in sporophyte populations occurring in summer and fall by monitoring two independent kelp populations and also by running experiments using 400 L tubular photobioreactors with semicontrolled environmental factors for testing the capacity for new recruits to recover population levels under winter conditions. The study of natural populations of giant kelp indicates that high temperatures (>15–17 °C) explain the high mortality of adult plants in summer. On the other hand, the sporophytes established in late winter/early spring are able, under high nitrogen availability, to increase their chlorophyll content significantly, allowing the individuals to reduce their light saturation point and thus allow a higher productivity under the low light conditions that exist in late winter and early spring. These results, in addition to the recruitment facilitation produced by filter feeders, help to explain how giant kelp can deal with, and couple sporophytic generations, in variable environments. These results also emphasize the highly plastic physiology of giant kelp that enables this species to colonize diverse habitats across its large distributional range.     

Movement Patterns and Residency of the Critically Endangered Horseshoe Crab Tachypleus tridentatus in a Semi-Enclosed Bay Determined Using Acoustic Telemetry

The horseshoe crab Tachypleus tridentatus is critically endangered in Japan due to rapidly decreasing numbers resulting from the loss of tidal flats and sandy beaches, and the deterioration of coastal environments. We monitored the year-round migratory patterns and residency of this species in a coastal embayment at Tsuyazaki, Japan, using acoustic telemetry. Total 20 adult crabs (15 males and 5 females) were tagged with ultrasonic transmitters and tracked during two periods (2006–2008; n = 10 and 2007–2009; n = 10). Adult crabs were more active during periods of higher water temperatures and their activity peaked in July, during the spawning period. Water temperature appeared to be one of the key factors influencing the movement patterns for the species. Moreover, the crabs tended to be more active at night than in the day. The nocturnal activity pattern was clearly evident before and during the reproductive period (May–August). Tracking data also showed that one pair-bond was maintained for a maximum of 17 days after the pair-bonded female had spawned. Overall, 11 males (73% of 15 individuals) remained in the bay area over winter, whereas three females (60% of 5 individuals) overwintered outside of the bay. Telemetry data showed that over 60% (13 of 20) of tagged crabs overwintered within the bay where there are sandy beaches, mudflats, and scattered seagrass beds. This year-round residence by adult T. tridentatus in the bay area identifies it as a critical habitat for the management of this species, regardless of life-stage. Not only is it a comprehensive management strategy that effectively reflects this species’ habitat use patterns but also its implementation, such as the establishment of a protected area, would contribute to its conservation.     

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.     

Gonad development and fatty acid composition of Patella depressa Pennant (Gastropoda: Prosobranchia) populations with different patterns of spatial distribution, in exposed and sheltered sites

The present study examines the effect of shore exposure on the feeding performance (assessed by fatty acid analyses of the whole body) and gonad condition (stage of development and gonad somatic index, GSI) of Patella depressa populations. Male and female limpets were collected at exposed and sheltered sites, during winter and summer. The population at the exposed site was at a more advanced stage of gonad development, with a higher dispersion of gonad stages, both in winter and summer. Additionally, limpets from the exposed site, particularly the males, presented a higher GSI than the corresponding stage in the sheltered site. The quantitatively most important fatty acids were the saturated fatty acids (SFA) 16:0, 14:0, and 18:0, the monounsaturated fatty acids (MUFA) 18:1(n−7), 18:1(n−9), 16:1(n−7) and 20:1(n−9) and the polyunsaturated fatty acids (PUFA) 20:5(n−3) and 20:4(n−6). Females had a significantly higher fatty acid methyl esters (FAME) content (in summer and winter) and higher amounts of SFA and MUFA (in summer), which points to a higher degree of storage of neutral lipids in this sex. Male and female limpets at the exposed site had a significantly higher FAME, SFA, MUFA, PUFA and highly unsaturated fatty acids (HUFA) content than the corresponding sex in the sheltered site in summer. In addition, an inversion in the eicosapentaenoic acid (EPA)/arachidonic acid (ARA) and (n−3)/(n−6) ratios was observed in the sheltered site, as a result of the significantly higher levels of ARA and (n−6) fatty acids and lower amounts of EPA and (n−3) fatty acids found in the sheltered limpets. A high variability among patches in the fatty acid composition in the exposed site was found in winter, possibly related to the aggregation of limpets at this time. The differences found between limpets from the exposed and sheltered sites suggest qualitative and quantitative differences in their diets. Additionally, the results show that the spatial aggregation strategy adopted by limpets in sites of great wave and wind exposure does not affect their feeding and reproductive success, at least in the site examined here. In fact, more developed gonads, a higher GSI and an elevated FAME content was found in the exposed population. Possible factors are suggested and discussed to explain these observations.