Environmental drivers of small scale spatial variation in the reproductive schedule of a commercially important bivalve mollusc (original) (raw)
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Marine and Freshwater Research, 2004
Reproduction and spawning of the scallop Pecten novaezelandiae were monitored at four sites in the Hauraki Gulf, New Zealand, from July 2000 to July 2001. A visual grading system based on the macroscopic appearance of the gonad was developed and tested, and changes in visual grade, quantitative histology, and standardised gonad mass were used to describe seasonal and spatial patterns in gametogenesis and spawning. Visual grade was significantly correlated with histological and gonad mass data (r 2 = 0.74-0.87) and validated as an accurate method for measuring reproduction in P. novaezelandiae. Visual grading facilitates rapid assessment of reproductive condition and can be conducted non-destructively, thus providing a tool allowing long-term studies of individual spawning behavior in relation to environmental signals. Scallops exhibited episodic spawning, with spawning events detected in spring, summer, autumn, and even early winter. Gonad recovery and subsequent gamete development and maturation were apparent between spawnings. Within-season variability in gonad size and condition could be the result of multiple (serial) spawnings during a season. The timing of spawning varied among populations, probably reflecting differences in environmental conditions that influenced reproduction. However, the largest spawning events occurred at all sites in early summer (December/January), coincident with wind-driven upwelling conditions.
Aquaculture, 2008
In Norway sea ranching depends on deployment of animals of local origin, and growers demand large spat outside the natural production season. To develop stock-specific production of juveniles, knowledge on local scallop reproductive cycle and performance in hatchery was needed. Broodstock sized scallops (Pecten maximus) were collected from 5 locations along the coast of Norway from 59°N to 65°N during 2004 and 2005, and translocated to natural sea location at 61°N. The reproductive cycles were characterised and the possibility of performing successful hatchery conditioning and spawning outside the natural reproduction cycle was investigated. Results showed that scallops from southwestern Norway (3 locations) all had distinct season summer peaks in the reproductive cycles. Scallops from the northern part (2 locations) quickly rebuilt the gonad after spawning and seemed to have full gonads through most of the year. Gonad indices in the southern group varied between 5 and 15%, while in the northern group it was 10 to 25% of total tissue weight. Both in December and March most individuals (N 75%) in the southern group had empty gonads, while most individuals in the northern group were characterised as being in gonad maturation stages 3-6. There was no complete synchronous gonad development through the year, and most developmental stages were present at all times. Scallops from the southern locations showed small changes in gonad maturation after translocation to the new environment. Scallops from northern locations kept the original cycle, but seemed to spawn later in summer. Scallops from the 3 southern locations responded to conditioning methods in the hatchery from late autumn to spring, as did one of the northern populations, while the other northern population could not be conditioned in winter. Based on reproductive cycle and hatchery performance we suggest that scallops from the 5 locations belonged to 3 distinct different populations. The differences in timing of gametogenesis and response to conditioning environment have implications for spat production in the hatchery and must be accounted for in order to fulfil the requirements of site-specific spat for scallop sea ranching in Norway.
Journal of Shellfish Research, 2008
The reproductive cycle of Pecten sulcicostatus is described as part of an investigation into the potential commercial culture of this species in South Africa. Scallops were collected monthly from False Bay, from August 2004 to October 2005, to determine seasonal variation in the gonadosomatic index (GSI) and to assess associated histological changes within the gonads. The reproductive cycle of P. sulcicostatus demonstrated clear seasonality. The mean GSI was highest from June to September (winter to early spring), and lowest from November to January (late spring to summer). The GSI findings were corroborated by histological analysis of the gonads with the mean oocyte diameter reaching a maximum in August and a minimum in November. Seasonal stratification and corresponding changes in phytoplankton biomass are considered to control the reproductive cycle of P. sulcicostatus in False Bay as winter spawning and the subsequent decline in the GSI coincide with the transition to spring upwelling conditions and a decline in bottom water temperature and food availability.
Strengthening recruitment of exploited scallops, Pecten maximus, with ocean warming
Marine Biology, 2010
There is evidence that ocean warming has effects on the ecology, including recruitment dynamics, of marine organisms. In association with rising mean spring temperatures in the Irish Sea, a time-series of juvenile scallop Pecten maximus density around the Isle of Man showed a significant increasing trend since 1991. Favorable conditions (warmer water and correspondingly greater food availability) during gonad development can increase scallop gamete production. We examined the possibility that ocean warming has directly increased recruitment of exploited P. maximus around the Isle of Man by enhancing gonad development. From 1991–2007, there was a significant positive correlation between scallop recruitment and mean spring (the main period of gonad development) temperature in the year of larval settlement. Detrended (i.e., accounting for a time effect) recruitment data showed a marginally non-significant correlation to temperature. Gonadal somatic index of adult scallops and temperature were positively correlated. These relationships support the hypothesis that greater gamete production associated with ocean warming may be primarily responsible for observed increases in recruitment success and CPUE in a commercially important shellfish stock.
Journal of Sea Research
The present study aimed to improve understanding of the environmental conditions influencing the reproductive cycle of the great scallop Pecten maximus in two locations in Brittany (France). We also evaluated potential consequences of future climate change for reproductive success in each site. We simulated reproductive traits (spawning occurrences and synchronicity among individuals) of P. maximus, using an existing Dynamic Energy Budget (DEB) model. To validate and test the model, we used biological and environmental datasets available for the Bay of Brest (West Brittany, France) between 1998 and 2003. We also applied the scallop DEB model in the Bay of Saint-Brieuc (North Brittany, France) for the same period (1998-2003) to compare the reproductive cycle in different environmental conditions. In order to accurately model the P. maximus reproductive cycle we improved the scallop DEB model in two ways: through (1) energy acquisition, by incorporating microphytobenthos as a new food source; and (2) the reproductive process, by adding a new state variable dedicated to the gamete production. Finally, we explored the effects of two contrasting IPCC climate scenarios (RCP2.6 and RCP8.5) on the reproductive cycle of P. maximus in these two areas at the 2100 horizon. Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. phenology through an earlier onset of spawning by 20 to 44 days depending on the year. Highlights ► We aimed at better understanding and quantifying the effect of environmental variables (temperature and food sources) on the reproduction variability of the Great Scallop Pecten maximus in Brittany. ► We improved an existing scallop-DEB model at two different levels, by adding a new food source and a more detailed reproduction module. ► We compared reproductive traits of the Great Scallop in two Brittany locations for the period 1998-2003 and we made forecasts at the 2100 horizon within a context of ocean warming. ► We evidenced two different effects of the increase of seawater temperature depending on the location: a most efficient autumnal last spawning in the Bay of Brest and an earlier onset of spawning in the Bay of Saint-Brieuc.
Reproductive phenology of coastal marine bivalves in a seasonal environment
Journal of Plankton Research, 2014
Environmental conditions during the larval phase (food concentration and temperature) impact recruitment success of marine bivalves by affecting growth and survival. We analysed the seasonal match between environmental conditions and larval presence of six coastal bivalve species over eight consecutive years (2006 -2013) in the western Wadden Sea, taking species-specific physiological responses to these conditions into account. The larval occurrence of four species overlapped with their optimum in environmental conditions as calculated following the Dynamic Energy Budget theory: the occurrence of larvae of Cerastoderma edule, Mya arenaria and Mytilus edulis matched with their optimum food conditions, while larvae of Crassostrea gigas were mainly found during the temperature optimum of this species. Larvae of Ensis directus and Macoma balthica, however, only occurred months after their most favourable food conditions. The first group probably uses the energy immediately after uptake for the production and release of gametes ('income breeders'), whereas the second group accumulates and stores energy reserves for later reproduction ('capital breeders'). Larvae of C. gigas and M. balthica were observed much earlier in the year than expected from previous occurrences and from formerly know threshold temperatures for spawning. These apparent changes in timing of spawning suggest that Pacific oysters and Baltic tellins have recently acclimated to new environmental conditions.
Marine Ecology Progress Series, 2001
The number of eggs produced in the annual spawning season by an adult female Macoma balthica (L.) of Wadden Sea origin increases in a non-linear manner with increasing shell length and body weight. It depends primarily on the weight-at-length immediately before spawning. Lean individuals with a low body-mass index (BMI) of 5.6 mg cm-3 or less spawn no eggs. Gamete output increases to about one-third of soft-body weight (in the order of 100 000 eggs) at the maximal BMIs observed (~15 mg cm-3). Long-term monitoring (> 20 yr) of densities of a Wadden Sea M. balthica population revealed that survival to the spawning season of the next year declined from about 65% at higher-than-average values of BMI (> 8 mg cm-3) to about 30% at the lowest values of BMI observed (5 to 6 mg cm-3). Annual growth was also significantly lower in years starting with a low BMI value. Because spawning lowers body weight and thus the BMI, spawning is bound to reduce subsequent survival rates and bodyweight increments. Thus, a trade-off situation exists between immediate and future spawning outputs. The consequences for total lifetime egg production of various levels of gamete output at first spawning (at an age of 2 yr) were estimated by model calculations, starting from a wide range of body weights at a standard length. The model results realistically predict that maximal lifetime egg production can be achieved only if M. balthica refrain from spawning at BMIs below a certain threshold value (viz. ~6 mg cm-3 , which is close to their actual threshold of 5.6 mg cm-3) and if their spawning output increases with weight-at-length (again in a manner close to what actually happens). It is concluded that M. balthica populations in the Wadden Sea apply a spawning strategy adapted to the local conditions.