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For example, it might surprise many that fisheries scientists have never been able to consistently locate juvenile lobsters in the wild (despite considerable efforts to do so!). Such information gaps are detrimental because they hinder the establishment of appropriate fisheries legislation, the protection of key habitats, and even the conservation benefits of our release strategies. As a result, we have been actively increasing understanding in basic parts of the lobster’s reproductive and population ecology.
We have genetically profiled the clutches of egg-bearing female, finding that only one male typically fathers the offspring, and have counted the number of eggs produced by female lobsters, showing that regional variation in clutch size may be driven by environmental temperature. Using genetic and genomic techniques, we are also working to characterise the relatedness and spatial bounds of lobster populations at a local, regional and continental scale. So far we have found that lobster stocks throughout our release areas appear relatively well mixed, but that distant populations may be distinct.
2012-2015: Charlie Ellis – PhD studentship, University of Exeter. ‘Genotype reconstruction of paternity in European lobster egg clutches.’
Funded by ESF and the Fishmongers Company.
Ellis CD, Hodgson DJ, André C, Knutsen H, Sørdalen TK, Griffiths AGF. (2015) Genotype reconstruction of paternity in European lobsters (Homarus gammarus). PLoS ONE. 10(11): e0139585. doi:10.1371/journal.pone.0139585
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Decapod crustaceans exhibit considerable variation in fertilisation strategies, ranging from pervasive single paternity to the near-ubiquitous presence of multiple paternity, and such knowledge of mating systems and behaviour are required for the informed management of commercially-exploited marine fisheries. We used genetic markers to assess the paternity of individual broods in the European lobster, Homarus gammarus, a species for which paternity structure is unknown. Using 13 multiplexed microsatellite loci, three of which are newly described in this study, we genotyped 10 eggs from each of 34 females collected from an Atlantic peninsula in the south-western United Kingdom. Single reconstructed paternal genotypes explained all observed progeny genotypes in each of the 34 egg clutches, and each clutch was fertilised by a different male. Simulations indicated that the probability of detecting multiple paternity was in excess of 95% if secondary sires account for at least a quarter of the brood, and in excess of 99% where additional sire success was approximately equal. Our results show that multiple paternal fertilisations are either absent, unusual, or highly skewed in favour of a single male among H. gammarus in this area. Potential mechanisms upholding single paternal fertilisation are discussed, along with the prospective utility of parentage assignments in evaluations of hatchery stocking and other fishery conservation approaches in light of this finding.
2012-2015: Charlie Ellis – PhD studentship, University of Exeter. ‘Meta-analysis of population variation in size-specific fecundity.’
Funded by European Social Fund and Fishmongers Company.
Ellis CD, Knott H, Daniels CL, Witt MJ, Hodgson DJ. (2015) Geographic and environmental drivers of fecundity in the European lobster (Homarus gammarus). ICES Journal of Marine Science. 2015; 72 (S1): i91-i100, doi: 10.1093/icesjms/fsv044.
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Fecundity in the European lobster (Homarus gammarus) has been shown to exhibit extensive spatial variation across northern Europe. Previously, this has been attributed to a lack of methodological standardization among samples. Instead, we show significant correlations between fecundity and both geographical and environmental drivers. We use linear mixed-effect models to assess the contribution of latitude, longitude, and measures of sea surface temperatures on the size-fecundity relationships of 1058 ovigerous females from 11 locations in the UK, Ireland, and Norway. We include new data for 52 lobsters from Falmouth, UK, the southwest limit of existing samples. Fecundity at mean female size correlated positively with eastings and greater annual ranges in sea surface temperature, but not with mean temperature or latitude. This contradicts the established latitudinal and mean temperature dependency reported for the closely related H. americanus. We postulate that proximity to stable Atlantic currents is the most likely driver of the relationship between fecundity and longitude. Mechanisms are discussed by which egg production or retention may be influenced by temperature range rather than by mean temperature. With further validation, we propose that temperature-correlated fecundity predictions will provide a valuable tool in ensuring that management thresholds are appropriate for the reproductive characteristics of lobster populations.
2013: Hannah Knott – Plymouth University, BSc industrial placement. ‘Towards understanding fecundity rates in the Cornish lobster fishery.’
Research conducted during this placement contributed to the publication of Geographic and environmental drivers of fecundity in the European lobster (Homarus gammarus).
Fecundity in the European lobster (Homarus gammarus) has been shown to exhibit extensive spatial variation across northern Europe. Previously, this has been attributed to a lack of methodological standardization among samples. Instead, we show significant correlations between fecundity and both geographical and environmental drivers. We use linear mixed-effect models to assess the contribution of latitude, longitude, and measures of sea surface temperatures on the size-fecundity relationships of 1058 ovigerous females from 11 locations in the UK, Ireland, and Norway. We include new data for 52 lobsters from Falmouth, UK, the southwest limit of existing samples. Fecundity at mean female size correlated positively with eastings and greater annual ranges in sea surface temperature, but not with mean temperature or latitude. This contradicts the established latitudinal and mean temperature dependency reported for the closely related H. americanus. We postulate that proximity to stable Atlantic currents is the most likely driver of the relationship between fecundity and longitude. Mechanisms are discussed by which egg production or retention may be influenced by temperature range rather than by mean temperature. With further validation, we propose that temperature-correlated fecundity predictions will provide a valuable tool in ensuring that management thresholds are appropriate for the reproductive characteristics of lobster populations.
Sørdalen TK, Halvorsen KT, Harrison HB, Ellis CD, Vøllestad LA, Knutsen H, Moland E, Olsen EM. (2018) Harvesting changes mating behaviour in European lobster. Evolutionary Applications, 11 (6), 963-977. Full text
2015-Present: Tom Jenkins – PhD studentship, University of Exeter. ‘Connectivity and gene flow in pink sea fans and European lobsters: implications for temperate Marine Protected Area (MPA) designation.’ Funded by NERC
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2012-2015: Charlie Ellis – PhD studentship, University of Exeter. ‘European lobster population genetic structure.’
Funded by European Social Fund and Fishmongers Company.
Ellis CD, Hodgson DJ, Daniels CL, Collins M, Griffiths AGF. (2017) Population genetic structure in European lobsters: implications for connectivity, diversity and hatchery stocking. Marine Ecology Progress Series. 563: 123–137.
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The European lobster, Homarus gammarus, is a marine crustacean prized for seafood, but populations across its range are threatened by fishery over-exploitation. The species’ larval stages are planktonic, suggesting considerable dispersal among populations. The potential threats of over-exploitation and erosion of population structure due to hatchery releases or inadvertent introductions make it important to understand the genetic structuring of populations across multiple geographic scales. Here we assess lobster population structure at a fine scale in Cornwall, south-western UK, where a hatchery stocking operation introduces cultured individuals into the wild stock, and a broader European level, in order to compare the spatial scale of hatchery releases with that of population connectivity. Microsatellite genotypes of 24 individuals from each of 13 locations in Cornwall showed no fine-scale population structure across distances of up to ~230 km. Significant differentiation and isolation by distance were detected at a broader scale, using 300 additional individuals comprising a further 15 European samples. Signals of genetic heterogeneity were evident between an Atlantic cluster and samples from Sweden. Connectivity within the Atlantic and Swedish clusters is high, although evidence for isolation by distance and a transitional zone within the eastern North Sea suggest that direct gene exchange between these stocks is limited and fits a stepping-stone model. We conclude that hatchery-reared lobsters should not be released where broodstock are distantly sourced but, using Cornwall as a case study, microsatellites reveal no evidence that the normal release of hatchery stock exceeds the geographic scale of natural connectivity.
Jenkins TL, Ellis CD, Stevens JR. (2018) SNP discovery in European lobster (Homarus gammarus) using RAD sequencing. Conservation Genetics Resources. 1-5, doi:10.1007/s12686-018-1001-8. Abstract
Holt C , Foster R, Daniels CL, Van Der Giezen M, Feist SW, Stentiford GD, & Bass D. (2018) Halioticida noduliformans infection in eggs of lobster (Homarus gammarus) reveals its generalistic parasitic strategy in marine invertebrates. Journal of Invertebrate Pathology. 154: 109–116.
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A parasite exhibiting Oomycete-like morphology and pathogenesis was isolated from discoloured eggs of the European lobster (Homarus gammarus) and later found in gill tissues of adults. Group-specific Oomycete primers were designed to amplify the 18S ribosomal small subunit (SSU), which initially identified the organism as the same as the ‘Haliphthoros’ sp. NJM 0034 strain (AB178865.1) previously isolated from abalone (imported from South Australia to Japan). However, in accordance with other published SSU-based phylogenies, the NJM 0034 isolate did not group with other known Haliphthoros species in our Maximum Likelihood and Bayesian phylogenies. Instead, the strain formed an orphan lineage, diverging before the separation of the Saprolegniales and Pythiales. Based upon 28S large subunit (LSU) phylogeny, our own isolate and the previously unidentified 0034 strain are both identical to the abalone pathogen Halioticida noduliformans. The genus shares morphological similarities with Haliphthoros and Halocrusticida and forms a clade with these in LSU phylogenies. Here, we confirm the first recorded occurrence of H. noduliformans in European lobsters and associate its presence with pathology of the egg mass, likely leading to reduced fecundity.
