Genetic analysis reveals the diversity of larval Gobiidae in a temperate estuary.

Using molecular tools to examine Gobiidae, the second most abundant taxon in ichthyoplankton samples in the Gulf of Riga (Baltic Sea), the sand goby Pomatoschistus minutus was the most abundant taxon (82% of all individuals analysed), the common goby Pomatoschistus microps constituted 12% and the black goby Gobius niger 6%. The spatiotemporal distribution of P. microps and G. niger indicated a preference for habitats closer to the river inlet and their abundances increased slightly towards the end of the sampling period in summer. The species composition was interpreted in the context of the prevailing habitat conditions, characterized by extremely low water transparency, low salinity, limited spread of vegetated area and dominance of sandy-muddy substrata.

International arrivals: widespread bioinvasions in European Seas.

The European Union lacks a comprehensive framework to address the threats posed by the introduction and spread of marine non-indigenous species (NIS). Current efforts are fragmented and suffer substantial gaps in coverage. In this paper we identify and discuss issues relating to the assessment of spatial and temporal patterns of introductions in European Seas (ES), based on a scientifically validated information system of aquatic non-indigenous and cryptogenic species, AquaNIS. While recognizing the limitations of the existing data, we extract information that can be used to assess the relative risk of introductions for different taxonomic groups, geographic regions and likely vectors. The dataset comprises 879 multicellular NIS. We applied a country-based approach to assess patterns of NIS richness in ES, and identify the principal introduction routes and vectors, the most widespread NIS and their spatial and temporal spread patterns. Between 1970 and 2013, the number of recorded NIS has grown by 86, 173 and 204% in the Baltic, Western European margin and the Mediterranean, respectively; 52 of the 879 NIS were recorded in 10 or more countries, and 25 NIS first recorded in European seas since 1990 have since been reported in five or more countries. Our results highlight the ever-rising role of shipping (commercial and recreational) as a vector for the widespread and recently spread NIS. The Suez Canal, a corridor unique to the Mediterranean, is responsible for the increased introduction of new thermophilic NIS into this warming sea. The 2020 goal of the EU Biodiversity Strategy concerning marine Invasive Alien Species may not be fully attainable. The setting of a new target date should be accompanied by scientifically robust, sensible and pragmatic plans to minimize introductions of marine NIS and to study those present.

Impact of extreme climate and bioinvasion on temporal coupling of spring herring (Clupea harengus m.) larvae and their prey.

We used weekly observational data from mid-May to end of July in 1958-2012 in Gulf of Riga to investigate temporal coupling between spring herring larvae and their first prey - copepod nauplii, under the extreme hydroclimatic conditions. We focused on a small shallow estuary that is important nursery ground for larvae of the Gulf of Riga (Baltic Sea) herring population. We quantified the effect of extreme values of the winter air temperatures, time of ice retreat and spring water temperatures on the timing of peak abundance of herring larvae and copepod nauplii. We also assessed whether the invasion of the non-native cladoceran Cercopagis pengoi had notable effect on timing and abundance of copepod nauplii during the peak occurrence of herring larvae. In the years of earliest ice retreat the peak abundance of herring larvae was five weeks earlier than in the years of latest ice retreat, while the timing of nauplii remained unchanged. Abundant presence of the C. pengoi affected neither timing nor maximum abundance of copepod nauplii during the herring larvae first feeding period. Thus, we conclude that processes induced by climate variability are superior to invasion of C. pengoi in determining the timing and coupling of larval herring and copepod nauplii.

Feeding ecology of pelagic fish species in the Gulf of Riga (Baltic Sea): the importance of changes in the zooplankton community.

The feeding ecology of four pelagic fish species was studied in relation to their prey availability in the Gulf of Riga (Baltic Sea) during the summer 1999-2006. The zooplankton community was dominated by the cladoceran Bosmina longispina, rotifers Keratella cochlearis and K. quadrata and the copepod Eurytemora affinis, with the highest interannual variability in abundance recorded for B. longispina. The last influenced the diet of adult sprat Sprattus sprattus, juvenile smelt Osmerus eperlanus and three-spined stickleback Gasterosteus aculeatus as these were strongly selecting for B. longispina. The fish feeding activity did not match the abundance dynamics of their preferred prey, suggesting that fishes may switch to consume other prey in case the preferred diet was limited. A considerable dietary overlap indicated high potential competition between pelagic fish species. While herring Clupea harengus membras and G. aculeatus were relying on very different food, the diets of young O. eperlanus and G. aculeatus were very similar. Interannual variability in zooplankton composition and abundance significantly affected the diet composition of fishes, but those changes were insufficient to exert a consistent influence upon fish feeding activity and total amounts of zooplankton consumed.