The genetic diversity and differentiation of mussels with complex life cycles and relations to host fish migratory traits and densities

Many landscape and biotic processes shape the genetic structure of populations. The genetic structure of species with parasitic stages may also depend on the life history and ecology of their host. We investigated population genetic structure of the mussel Margaritifera margaritifera in Southern Sweden, and in relation to the population size and life history of its hosts, Salmo trutta and S. salar. Mussel populations were genetically differentiated into two clusters, further subdivided into four clusters and distinct conservation units. Regardless of host species, the genetic differentiation was lower among mussel populations sustained by sea-migrating than by resident hosts, while the genetic diversity was higher in mussel populations sustained by sea-migrating than by resident hosts. Genetic diversity of mussel populations was positively related to host abundance. Mussel population size was positively related to high genetic diversity of mussels sustained by resident hosts, while low mussel population size sustained by sea-migrating hosts had a high genetic diversity. The results of our study suggest a combined influence of mussels and host fish on genetic structure of unionoid mussels. We suggest to conserve not only mussel population sizes and host fish species, but also consider host migratory/resident behaviour and abundance when designing conservation programs.

Spatial distribution, abundance and habitat use of the endemic Mediterranean fan mussel Pinna nobilis in Gera Gulf, Lesvos (Greece): comparison of design-based and model-based approaches

An important population of the endemic Mediterranean fan mussel Pinna nobilis thrives in the marine protected area of Gera Gulf (Lesvos island, north-eastern Aegean Sea, Greece), and was assessed for the first time. To estimate the abundance, spatial distribution and habitat use of fan mussels in Gera Gulf, a distance sampling underwater survey was conducted. Detectability was modelled to secure unbiased estimates of population density. Two approaches were applied to analyze survey data, a design-based and a model-based approach using generalized additive models. The first approach was based on stratified random sampling on two strata, an assumed ‘preferable’ zone close to the coastline and an assumed unsuitable habitat, with predominantly muddy sediments, in which low sampling effort was applied. For the needs of the model-based approach, a dedicated cruise was conducted to collect bathymetric data with a single-beam echo-sounder and map the bathymetry of the study area. A very high-resolution image from the Worldview-3 satellite was processed, based on an object-based image analysis, for mapping all main habitat types in the study area. The estimated abundance using the design-based approach was low-biased as the stratum of pre-assumed unsuitable habitat proved to include patches of suitable habitats with high population densities that were missed by sampling. The model-based approach provided an abundance estimate of 213300 individuals (95% confidence interval between 97600-466000 individuals), which renders the fan mussel population of Gera Gulf the largest recorded population in Greece. Population density peaked between 1.5-8 m depth and became practically zero at depths >15 m. A bathymetric segregation of fan mussel size classes was noted, with the density of small individuals peaking in shallow waters, while that of large individuals peaked deeper. The highest population densities were observed in Posidonia oceanica meadows, followed by mixed bottoms (with reefs, rocks and sandy patches), while densities were very low on sandy and zero on muddy sediments. The current assessment provides a baseline for future monitoring of the fan mussel population in Gera Gulf. In view of the current (2017-2018) ongoing mass mortality of the species in the western Mediterranean, continuous monitoring of the main fan mussel populations, such as the one in Gera Gulf, is of utmost importance.

Distribusi Kerang Geloina sp. (Bivalvia: Corbiculidae) di Kawasan Mangrove Segara Anakan, Cilacap

Segaraanakan merupakan salah satu estuaria terbesar di Pulau Jawa yang terkenal dengan keanekaragaman hayatinya. Diantara biota yang terdapat adalah kerang totok (Geloina sp) yang berasosiasi dengan hutan mangrove. Karena memiliki nilai ekonomis maka selalu di tangkap. Maka dari itu sangat tepat jika kerang tersebut dipelajari ekologis maupun biologisnya. Tujuan dari penelitian ini adalah untuk mengetahui distribusi dan stuktur populasi kerang Geloina sp tersebut. Penelitian dilakukan di Segaraakan Cilacap pada empat stasiun yang berbeda salinitasnya (13, 15, 30 dan 32 ppt). Sifat penelitian adalah studi kasus, metoda pengambilan sampel yang digunakan adalah metoda sampling area. Data yang diambil meliputi kerang dan kondisi perairan. Data yang didapatkan dikelompokan berdasarkan kelas ukuran panjang cangkang selanjutnya dilakukan uji chi kwadrat untuk menentukan pola sebaran.Hasil penelitian menunjukan kerang yang didapat adalah G. erosa dengan pola sebaran merata pada keempat stasiun penelitian yang berbeda salinitasnya. Adapun kepas ukuran kerang yang didapat dalam keempat stasiun dapat dikelompokan menjadi kelas ukuran <3, 3 – 3,9, 4 – 4,9, 5 – 5,9, 6 – 6,9, 7 – 7,9, .>8 cm. Populasi kerang terbanyak pada semua stasiun adalah kelas ukuran 6 – 6,9 cmKata Kunci : Segara anakan, Geloina sp, salinitasSegera anakan is the widest estuaries in Java Island and the famous high diversity. One of fauna found which associate with the mangroves was totok mussel Geloina sp. That mussel had economic value so that faced high exploited along season. Considering that condition a study of distribution and their population structure was very importance. The research was carried out on Segaraanakan Cilacap on different station which had different salinity (13, 15, 30 and 32 ppt). The case study type research and sampling area method was used to collect the data of information of the Geloina sp. The data collected in the field was mussel population and water quality condition where the mussel life. The data of mussel was grouping in several length of class and following chi quadrant test to define the distribution of Geloina sp. The result of the study showed, Thad the Geloina sp was uniform distribute along the fourth station which had different salinity and the length of class mussel was found <3, 3 – 3,9, 4 – 4,9, 5 – 5,9, 6 – 6,9, 7 – 7,9, .>8 cm. The class length of 6 – 6,9 cm was the highs number of mussel class on forth station in SegaraanakanKeywords : Segara anakan, Geloina sp, salinity