Species level identifications of morphologically simple marine algae have undoubtedly caused biodiversity assessments to be an arduous task. The green algal genus Ulva L., 1753, is notorious for morphological plasticity and cryptic speciation. We used two chloroplast-encoded (rbcL and tufA) molecular markers and the nuclear internal transcribed spacer 1 (ITS1) of the ribosomal cistron to detect Ulva ohnoi M. Hiraoka and S. Shimada, 2004, a species known for forming green tides in Japan, as a new record for the Western Atlantic, including the Gulf of Mexico (GoMX) and Atlantic coast of Florida. All rbcL sequences from this investigation were identical to reports for U. ohnoi. The Western Atlantic isolates showed relatively low genetic diversity in tufA and ITS1 sequences, which suggests that this species is not native to the GoMX and Atlantic Florida. Furthermore, we have identified U. ohnoi as the species that formed an ephemeral, localized overgrowth during July of 2013 in Biscayne Bay, Florida, an area with a persistent bloom of two other green algal species, Anadyomene stellata J. V. Lamouroux, 1812, and Anadyomene sp., due to eutrophication from anthropogenic nutrient loading near canals. A tissue nutrient analysis of samples from this overgrowth of Ulva showed that this species has a high affinity for nitrogen, especially ∂15N, which suggests anthropogenic sources of N. Further investigations are needed to assess the geographical ranges of this species in this region as well as the potential invasiveness of this alga in the Western Atlantic. It is highly recommended to monitor the abundance of this species in response to nutrient discharges in Biscayne Bay.

No abstract

Studies in the Baltic Sea have identified over 30 parasite taxa infecting the invasive round goby (Neogobius melanostomus (Pallas, 1814). In this study, we aimed at comparing parasite assemblages and infection rates (prevalence and intensity) in different populations across the invasive range in the Baltic Sea (Denmark, Lithuania, Estonia and Finland). Infection rates were 56-60% across all locations except Lithuania (28%). However, the parasite assemblages in the sampled populations were dissimilar, each location having unique parasites. In addition, many of the parasites were generalists commonly infecting native fish species. Based on the results of this study and those previously conducted in the Baltic Sea, the round goby has not retained parasites from its area of origin, but instead has been successively colonized by native generalist parasites. Although variable, overall parasite richness is still quite low around the Baltic compared to the native areas (34 vs 71 taxa, respectively). Also, prevalence and mean infection intensities in the Baltic Sea are significantly lower than in the native areas. Therefore, the invasion success of the round goby in the Baltic Sea can at least partly be attributed to enemy release, in this case shedding a significant proportion of their native parasite load.

The authors assessed the importance of the round goby Neogobius melanostomus as prey for three native predatory fish species, Atlantic cod Gadus morhua, European perch Perca fluviatilis and northern pike Esox lucius, in a northern and southern area of the Baltic Proper, using a combination of visual analysis and DNA metabarcoding of predator stomach contents. To explore the influence of environmental abundances of N. melanostomus on predation, they related the occurrence of N. melanostomus in predator diets to its abundance in survey fishing. Gadus morhua and E. lucius in the southern area showed the highest tendency to feed on N. melanostomus when it was abundant, as N. melanostomus occurred in up to 100% of stomachs and constituted up to 88% of the total diet volume proportion. The diet contribution of N. melanostomus was associated with N. melanostomus abundances for G. morhua and E. lucius, and when N. melanostomus was abundant, these predators exhibited lower prey richness and a higher degree of piscivory. G. morhua and P. fluviatilis also fed less on crustacean prey when N. melanostomus was abundant. The high importance of N. melanostomus in diets of native fish predators may modify indirect interactions between N. melanostomus and native prey species in invaded coastal communities.