Using an integral projection model to assess the effect of temperature on the growth of gilthead seabream Sparus aurata

Accurate information on the growth rates of fish is crucial for fisheries stock assessment and management. Empirical life history parameters (von Bertalanffy growth) are widely fitted to cross-sectional size-at-age data sampled from fish populations. This method often assumes that environmental factors affecting growth remain constant over time. The current study utilized longitudinal life history information contained in otoliths from 412 juveniles and adults of gilthead seabream, Sparus aurata, a commercially important species fished and farmed throughout the Mediterranean. Historical annual growth rates over 11 consecutive years (2002-2012) in the Gulf of Lions (NW Mediterranean) were reconstructed to investigate the effect of temperature variations on the annual growth of this fish. S. aurata growth was modelled linearly as the relationship between otolith size at year t against otolith size at the previous year t-1. The effect of temperature on growth was modelled with linear mixed effects models and a simplified linear model to be implemented in a cohort Integral Projection Model (cIPM). The cIPM was used to project S. aurata growth, year to year, under different temperature scenarios. Our results determined current increasing summer temperatures to have a negative effect on S. aurata annual growth in the Gulf of Lions. They suggest that global warming already has and will further have a significant impact on S. aurata size-at-age, with important implications for age-structured stock assessments and reference points used in fisheries

Otolith fingerprints as natural tags to identify juvenile fish life in ports

International audienceThe construction of ports has caused substantial habitat destruction in coastal areas previously used as nursery grounds by many fish species, with consequences to fish stocks. These artificial coastal areas might provide alternative nursery habitats for several species for juvenile fish abundances and growth in ports, although their contribution to adult stocks had never been estimated. The variability of otolith composition in the juveniles of two Diplodus species was investigated in three contrasting port areas and two adjacent coastal juvenile habitats of the Bay of Toulon (northwestern Mediterranean) in order to determine the possible use of otolith fingerprints as natural tags for the identification of juvenile fishes in ports. The global accuracy of discrimination between ports and coastal areas was very high (94%) irrespective of species, suggesting that otolith fingerprints can be used with confidence to retrospectively identify past residency in the ports of this bay. However, Ba was systematically the most discriminating element, since its concentrations in otoliths were generally higher outside ports than in inside them, probably due to river runoff. Moreover, otolith signatures varied greatly by species and between sampling sites. Furthermore, although Cu and Pb concentrations in water were at least 2.3–34-fold higher inside ports than outside, this was not consistently reflected in fish otoliths, confirming that spatial differences in otolith concentrations depend on the species and do not directly reflect differences in environmental contamination levels. Therefore, it seems unlikely that otolith microchemistry could provide a universal fingerprint capable of discriminating ports from other coastal areas. Nevertheless, the contribution of ports to adult fish populations can be determined well by establishing a library of otolith fingerprints for all juvenile habitats

Jellyfish degradation in a shallow coastal Mediterranean lagoon

Recurrent jellyfish blooms in the coastal zone call for understanding the impacts of jelly-falls on the functioning of benthic communities, especially in shallow enclosed ecosystems where their biomass can affect local carbon cycling and productivity. Each year, blooms of the jellyfish Aurelia coerulea appear and collapse in a semienclosed coastal Mediterranean lagoon (the Thau lagoon, south of France). Although the lagoon is shallow, large accumulations of dead jellyfish are never observed on its bottom, so it was hypothesized that decaying jellyfish were rapidly consumed by local macrobenthic organisms. The current work aimed to test this hypothesis, by estimating the impact of the presence of dead A. aurelia medusae on local macrobenthic community composition and assessing their biomass loss rates under different scenarios of accessibility by the macrobenthos. Unexpectedly, our results revealed a limited role of macrobenthic scavengers in the disappearance of dead medusae, although this later was particularly fast (19-78h). Only one taxon (Tritia sp., Nassariidae family) showed a significant response to the presence of dead A. coerulea medusae on the seabed. Thus, our results suggest that the fast disappearance of dead jellyfish biomass in Thau results from its rapid degradation and consumption by local microorganisms, likely due to the combined effects of high local temperatures and the small size of A. coerulea medusae. Thus, the important biomass produced during A. aurelia blooms in Thau might essentially boost its microbial food web. The potential role of jellyfish blooms in controlling biogeochemical cycles and food web functioning in shallow lagoons is discussed, underlying the need to include this process in ecosystem-based models.info:eu-repo/semantics/publishedVersio

Getting a good start in life ? : a comparative analysis of the quality of lagoons as juvenile habitats for the gilthead seabream Sparus aurata in the Gulf of Lions

Temperate coastal lagoons are considered key habitats for several highly prized marine fishes, which colonise them as nurseries. Lagoons can, however, exhibit diverse abiotic and biotic conditions, with potential consequences for their quality as habitats. To investigate this, we compared size, body condition (Fulton's condition factor K and lipid classes), past growth rate (from otoliths) and sources of food web organic matter (OM), among group 0 juveniles of the gilthead sea bream Sparus aurata L. 1758, captured at the end of their first summer of residence in four lagoons of the Gulf of Lions in the NW Mediterranean (Mauguio, Thau, Bages and Salses-Leucate). These lagoons have different environmental conditions and freshwater inputs. Although age was similar for all lagoons, juveniles from Mauguio and Bages were significantly larger and heavier than those from Thau and Salses-Leucate. They were also in better condition, with higher white muscle triacylglycerol/sterol ratio (mean±SD 35.7±20.1 in Mauguio and 23.2±9.8 in Bages versus 15.1±15.2 in Thau and 7.4±7.9 in Salses-Leucate). All exhibited similar otolith growth rates for their larval marine phase (2.8 +/- 0.4 mu m day(-1)), but significant differences were found for the lagoon phase, with higher values in Mauguio and Bages (10.1±0.9 and 9.7± 1.0 &#956;m day-1, respectively) than those in Thau and Salses-Leucate (8.4 +/- 1.2 and 8.9 +/- 0.8 mu m day(-1), respectively). White muscle stable isotope analysis revealed that terrestrial carbon use by the juveniles was >33 % in Mauguio and <5 % in Salses-Leucate, with intermediate values (~15 %) in Thau and Bages. Although these effects on fish condition and growth rate may relate in part to differences in water salinity and dissolved oxygen in the four lagoons, it is probable that they are mostly related to differences in food web enrichment with terrestrial OM

Offshore-onshore linkages in the larval life history of sole in the gulf of lions (NW-Mediterranean)

International audienceUnderstanding individual dispersion from offshore natal areas to coastal nurseries during pelagic larval life is especially important for the sustainable management of exploited marine fish species. For several years, the hatching period, the larval life duration, the average growth rate and the otolith chemical composition (d13C, d18O, Sr:Ca and Ba:Ca) during the larval life were studied for young of the year (YOY) of sole collected in three main nurseries of the Gulf of Lions (GoL) (Thau, Mauguio and Berre). We investigated the spatial variation in the origin of the sole larvae which colonised the nurseries around the GoL, and whether temporal differences in environmental conditions during this life stage affected growth and larval life duration. The hatching period ranges from October to March, depending on year and site. Average ages at metamorphosis varied between 43 and 50 days, with the lowest and highest values consistently found for Mauguio and Berre, respectively. Otolith growth rates ranged between 2.7 and 3.2 mm d-1, with the lowest values in Thau and Mauguio and the highest in Berre. Otolith chemical composition during the larval life also varied, suggesting contrasted larval environmental histories in YOY among nurseries. In fishes from Berre and Mauguio, larval life was more influenced by the Rhone River, showing consistently higher larval Ba:Ca ratios (10/23 mmol mol-1) and lower d13C (-6.5/-6.1 pour mille) and d18O values (-1.6/0.1 pour mille) than for Thau (with Ba:Ca ratios < 8 mmol mol_1, d13C ~_2.3 pour mille and d18O ~1.5 pour mille). Differences in larval otolith composition were observed for 2004, with higher Ba:Ca and lower d13C and d18O values than in the two other years. These differences were explained by changes in composition and chemical signatures of water masses after an exceptional flooding event of the Rhone River in late 2003

Extensive larval dispersal and restricted movement of juveniles on the nursery grounds of sole in the Southern North Sea

Connectivity between spawning and nursery grounds influences the colonization, replenishment and resilience of populations of marine organisms. Connectivity rate, measured as the exchange of individuals between spawning and nursery grounds, is therefore a crucial determinant of stock size. However, connectivity of early-life stages is hard to explore due to sampling limitations and insufficient knowledge on potential larval sources. Here we present new insights into pre- and post-settlement dispersal of the common sole (Solea solea L.) at a spatial scale of 5–500 km in the Southern North Sea. Patterns at a scale of <100 km were considered local, whereas patterns further than 100 km were considered regional. Multi-elemental signatures of the otolith edge of 213 juvenile sole were used to discriminate at 79% of overall accuracy three main nursery grounds in the Southern North Sea, namely UK coast, Belgian coast and Dutch Wadden Sea. Interregional differences in otolith composition (especially for Mg, Mn and Ba) suggest that sole migration following settlement is limited in the Southern North Sea. Elemental signatures of the same fish indicated mixing during larval dispersal. Each nursery ground recruited an important mix of juveniles from three of the four chemically distinct natal sources identified from the larval otolith signatures. However the percentage of correct regional re-assignment varied from 67 to 80% with a maximum in the Wadden Sea. The results contributed to the validation of biophysical models of larval drift. Our findings support decision making for both fisheries management and marine spatial planning at the national and European level

Field investigations for management and conservation of shallow water lagoons : practices and perspectives

International audienc