Elemental composition of sole otoliths as a population discrimination tool

Otolith microchemistry, the study of the minor and trace elemental composition of otoliths (earbones), has been developing rapidly with a wide range of applications in fishery science. This is because otoliths (1) grow continuously, resulting in daily and seasonal structures, (2) have an elemental composition that reflects the environmental concentrations and conditions, (3) are metabolically inert. All of these characteristics make trace element uptake useful for reconstructing environmental histories. The elemental composition is therefore a powerful tool in stock To study connectivity among North Sea sole (Solea solea) populations and to improve our understanding of the relationship between its spawning grounds and nursery areas, genetic markers and otolith microchemistry will be used as complementary discrimination tools. We performed a pilot study to test for differences in sole otolith elemental fingerprints among three sampling locations, using LA-ICPMS. This technique makes it possible to determine composition at discrete points across the otolith (corresponding with different events in the fish’s lifetime). A hierarchical design (Basin, Sea, within Sea) enables us to assess the power of this method for the simultaneous large and small scale discrimination of populations.Preliminary results of this study will be shown and discussed in the light of current European wide research objectives. size and increasing the number of sampling locations

Influence of DNA isolation from historical otoliths on nuclear-mitochondrial marker amplification and age determination in an overexploited fish, the common sole (<i>Solea solea</i> L.)

Historical otolith collections are crucial in assessing the evolutionary consequences of natural and anthropogenic changes on the demography and connectivity of commercially important fish species. Hence, it is important to define optimal protocols for purifying DNA from such valuable information sources while avoiding any damage to the physical structure of the otolith. Before being able to conclude on the harmlessness of a method, it is important to validate protocols on different kinds of otoliths by testing purification methodologies under standardized conditions. Here we compare the effect of two DNA extraction methods on the success in identifying the age in an overexploited marine fish, the common sole (Solea solea L.). To ensure optimal future population genetic and demographic analyses, we assessed DNA quantity and tested the DNA quality by investigating the amplification success of a mitochondrial and nuclear marker. Our results show that the choice of the DNA extraction method had a significant effect on the success of using these otoliths in age and growth analyses. Standard commercial and published protocols resulted in a severe damaging of the otolith structure, hampering accurate preparation and analyses of the morphological structures of the otoliths. Shortening the lysis time and lowering the EDTA (ethylene diamine tetraacetic acid) and SDS (sodium dodecylsulphate) concentration turned out to be beneficial for the stability of otolith structure, while maintaining an overall high DNA quality measured through polymerase chain reaction amplification success. We therefore recommend that care should be taken when choosing the extraction method for a molecular study on archived samples, in order to enable the maximal use of information embedded in historical material

Influence of DNA isolation from historical otoliths on nuclear–mitochondrial marker amplification and age determination in an overexploited fish, the common sole (Solea solea L.)

Historical otolith collections are crucial in assessing the evolutionary consequences of natural and anthropogenic changes on the demography and connectivity of commercially important fish species. Hence, it is important to define optimal protocols for purifying DNA from such valuable information sources while avoiding any damage to the physical structure of the otolith. Before being able to conclude on the harmlessness of a method, it is important to validate protocols on different kinds of otoliths by testing purification methodologies under standardized conditions. Here we compare the effect of two DNA extraction methods on the success in identifying the age in an overexploited marine fish, the common sole (Solea solea L.). To ensure optimal future population genetic and demographic analyses, we assessed DNA quantity and tested the DNA quality by investigating the amplification success of a mitochondrial and nuclear marker. Our results show that the choice of the DNA extraction method had a significant effect on the success of using these otoliths in age and growth analyses. Standard commercial and published protocols resulted in a severe damaging of the otolith structure, hampering accurate preparation and analyses of the morphological structures of the otoliths. Shortening the lysis time and lowering the EDTA (ethylene diamine tetraacetic acid) and SDS (sodium dodecylsulphate) concentration turned out to be beneficial for the stability of otolith structure, while maintaining an overall high DNA quality measured through polymerase chain reaction amplification success. We therefore recommend that care should be taken when choosing the extraction method for a molecular study on archived samples, in order to enable the maximal use of information embedded in historical material

Direct and indirect effects of predation on an intertidal benthic community

Intertidal estuarine habitats are extensively used as feeding grounds by birds, fishes and crustaceans. The impact of predation on the intertidal macrobenthic community has been measurable, although not consistently. A macrobenthos monitoring study at various tidal heights on a mudflat in the Scheldt estuary revealed that when fish abundance was high, the density of the main prey species (Corophium volutator) was significantly reduced on the lower and middle shore, but not on the higher shore. On the lower parts of the shore, where the inundation time is longer, fish predation may reduce the density of macrobenthic prey. The effect of predation on the intertidal macrobenthic community was examined by excluding both birds and fishes from the mudflat. A first caging experiment lasted for two months and excluded both birds and fishes, while a second experiment ran for a whole year and excluded only birds. Fish and bird predation did not have a significant direct effect on the abundance of macrobenthic species. Diet analysis showed that both predators select the larger size classes of the macrobenthic species, but only birds were shown to influence the size distribution of their prey. From the exclosure experiments, fish predation turned out to be relatively unimportant as a structuring factor for the macrobenthic prey community. However, fish abundance during the caging experiments was much lower than during the monitoring study. The effects of short-term experiments may only be noticeable at higher predator densities. In the long-term experiment, the density of C. Volutator in the cages was significantly lower than in the uncaged plots. In the absence of predation, infaunal interactions like competition may become more important and regulate the benthic community structure

The power of integrating genetic and otolith analytical approaches into the management of exploited marine fishes

Marine exploited populations exhibit various degrees of discreteness, ranging from historical evolutionary to contemporary ecological levels of differentiation. An integrated approach combining complementary population discrimination tools such as otolith microchemistry and genetics may capitalize on these different time scales to improve the discrimination and traceability power in management applications. Additionally, novel statistical and technological improvements have enabled the joint extraction of demographic, life-history and genetic information from archived otolith collections, to unveil the evolutionary consequences of anthropogenic pressure in wild fish populations. Here, I overview the most recent integrated results obtained from genetic markers (microsatellites and SNPs) and otoliths (growth-maturity, microchemistry and shape data) on adult sole (Solea solea) populations in the North-East Atlantic Ocean. While genetic markers provide a clear regional differentiation and local adaptation pattern, otoliths data often provide an improved small scale geographical resolution. At the temporal scale, combining molecular and otolith back-calculation data enables a powerfull assessment of changes in population size/demography, while tracing back the genetic basis of life-history trait evolution under heavy anthropogenic pressure. Our results highlight the power of a multi-marker approach depending on the required spatial resolution scale and emphasize the relevance of integrated phenotypic-genetic temporal analyses to unveil human induced selection factors in future management scenarios. Monitoring efficiently the resilience of marine harvested populations hence requires interdisciplinarity in research priorities, covering both the evolutionary and ecological components of population connectivity and demography

Multi-marker estimate of genetic connectivity of sole (Solea solea) in the North-East Atlantic Ocean

A thorough knowledge on the genetic connectivity of marine populations is important for fisheries management and conservation. Using a dense population sampling design and two types of neutral molecular markers (10 nuclear microsatellite loci and a mtDNA cytochrome b fragment), we inferred the genetic connectivity among the main known spawning grounds of sole (Solea solea L.) in the North-East Atlantic Ocean. The results revealed a clear genetic structure for sole in the North-East Atlantic Ocean with at least three different populations, namely the Kattegat/Skagerrak region, the North Sea and the Bay of Biscay, and with indications for a fourth population, namely the Irish/Celtic Sea. The lack of genetically meaningful differences between biological populations within the southern North Sea is likely due to a large effective population size and sufficient connection (gene flow) between populations. Nevertheless, an isolation-by-distance pattern was found based on microsatellite genotyping, while no such pattern was observed with the cytochrome b marker, indicating an historical pattern prevailing in the latter marker. Our results demonstrate the importance of a combined multi-marker approach to understand the connectivity among marine populations at region scales

The power of integrating genetic and otolith analytical approaches into the spatial management of exploited marine fishes

Marine exploited populations exhibit various degrees of discreteness, ranging from historical evolutionary to contemporary ecological levels of differentiation. An integrated approach combining complementary population discrimination tools such as otolith microchemistry and genetics may capitalize on these different time scales to improve the discrimination and traceability power in management applications. Here, I discuss the most recent integrated results obtained from genetic markers (microsatellites and SNPs) and otoliths (microchemistry and shape data) on juvenile/adult sole (Solea solea) populations in the North-East Atlantic Ocean. While genetic markers provide a clear regional differentiation and local adaptation pattern, otoliths data often provide an improved small scale geographical resolution. Our results highlight the power of a multi-marker approach depending on the required spatial resolution scale in future management scenarios. Monitoring efficiently the resilience of marine harvested populations hence requires interdisciplinarity in research priorities, covering both the evolutionary and ecological components of population connectivity. Such information is pivotal to reliably develop, validate and later apply integrated traceability tools for fisheries enforcement

Microchemical variation in juvenile Solea solea otoliths as a powerful tool for studying connectivity in the North Sea

Estimating connectivity between juvenile and adult fish habitats can provide an important contribution to effective fisheries management, through a better understanding of population resilience to harvesting pressure. Indirect methods for quantifying connectivity, such as geochemical or genetic techniques, allow us to assign adults from various sampling regions to their natal location, provided that natal origin data can be defined. The elemental composition of otoliths from juvenile sole Solea solea collected at 4 sampling locations in the Southern Bight of the North Sea was measured using laser-ablation inductively-coupled plasma mass spectrometry (LA-ICPMS), to determine elemental fingerprints indicative of distinct nursery grounds. Significant differences in elemental composition were detected among the 4 locations, with Na, Sr, Ba, Mn and Rb concentrations varying the most between groups. A discriminant model resulted in high assignment proportions of the juvenile fish to their respective nursery grounds with a total jackknife reclassification success of 88%. Even though some interannual variability in otolith chemistry was observed in juveniles from the Scheldt estuary, spatial patterns seemed to dominate. Our results constitute a firm basis for future investigations on nursery area contributions and quality, adult dispersal history and applications of population traceability