Background. The round goby, Neogobius melanostomus (Pallas, 1814), is a recent invader in the Curonian Lagoon, SE Baltic Sea. As invasive species are among the most severe threats for biodiversity loss and can induce food web alterations, the development of round goby population in the Curonian Lagoon and its possible impacts on fish community and the entire ecosystem are of great scientific interest. This research reports on the expansion and trophic role of round goby in the Curonian Lagoon. Materials and methods. Occurrence and abundance of round goby was investigated using a beach seine and gill nets at the northern and central parts of the Curonian Lagoon during a six-year period from 2007 to 2012. The trophic niche of the newcomer was revealed by applying gut content and stable isotope analyses (SIA). A total of 61 samples of other fish species were taken for SIA in order to reveal with which resident fish species the exploitative competition could be expected. Stable isotope mixing models were used to evaluate the contribution of round goby to the nutrition of top predators of the Curonian Lagoon: European perch, Perca fluviatilis Linnaeus, 1758; pike-perch, Sander lucioperca (Linnaeus, 1758); great cormorant, Phalacrocorax carbo; and grey heron, Ardea cinerea. Results. The survey showed that round goby expanded its distribution area and recently occurs in the entire Lithuanian part of the Curonian Lagoon. Variation in the density of round goby suggests that the invader's abundance may be stabilised in the northern part of the lagoon. Gut content and stable isotope analyses showed round goby being mainly benthivorous. The largest trophic overlap with respect to SIA was detected between the invader and ruffe, Gymnocephalus cernua (Linnaeus, 1758), the fish which presumably exploits the same habitat type. According to stable isotope mixing models round goby was included with considerable shares into the diet of top predators. Conclusion. The further expansion of round goby inside the Curonian Lagoon is ongoing. However, there is evidence on population density stabilisation in the northern part of the lagoon. Native benthivorous fish, especially ruffe, may be affected through competition for food resources in habitats where the newcomer is numerous. Round goby significantly contributes to the diet of piscivorous fish and birds. That may promote the regulation of invader population abundance in the lagoon.
Conflict arises in fisheries worldwide when piscivorous birds target fish species of commercial value. This paper presents a method for estimating size selectivity functions for piscivores and uses it to compare predation selectivities of Great Cormorants (Phalacrocorax carbo sinensis L. 1758) with that of gill-net fishing on a European perch (Perca fluviatilis L. 1758) population in the Curonian Lagoon, Lithuania. Fishers often regard cormorants as an unwanted “satellite species”, but the degree of direct competition and overlap in size-specific selectivity between fishers and cormorants is unknown. This study showed negligible overlap in selectivity between Great Cormorants and legal-sized commercial nets. The selectivity estimation method has general application potential for use in conjunction with population dynamics models to assess fish population responses to size-selective fishing from a wide range of piscivorous predators.
We undertook a comparative study of the James River Estuary, a sub-estuary of Chesapeake Bay, and the Curonian Lagoon, a sub-estuary of the Baltic Sea, to better understand the factors that determine the presence and persistence of algal toxins in food webs. Over a 2-year period, we measured microcystin concentrations in water, sediment and biota (fish and shellfish) at both sites. Across both food webs we found highest levels of microcystin among consumers of suspended particulate matter, including planktivorous fishes and filter-feeding shellfish, and lower levels of toxin among piscivores, scavengers and benthic omnivores. Despite similar levels of microcystin in the water column at the two sites, we observed higher toxin levels in fish and sediments of the Curonian Lagoon. We attribute this difference to the legacy of prior toxic cyanobacteria blooms in the Curonian Lagoon and hydrologic factors that result in a predominance of autochthonously-derived organic matter in the sediments at this site. Our results suggest that a consideration of species-specific differences in feeding habits, and organic matter sources supporting food webs are important to understanding the accumulation and persistence of algal toxins in food webs and should therefore be considered in assessment of risks to aquatic biota and human health.
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