Lene Friis Møller

Salinity Gradient of the Baltic Sea Limits the Reproduction and Population Expansion of the Newly Invaded Comb Jelly Mnemiopsis leidyi

The recent invasion of the comb jelly Mnemiopsis leidyi into northern European waters is of major public and scientific concern. One of the key features making M. leidyi a successful invader is its high fecundity combined with fast growth rates. However, little is known about physiological limitations to its reproduction and consequent possible abiotic restrictions to its dispersal. To evaluate the invasion potential of M. leidyi into the brackish Baltic Sea we studied in situ egg production rates in different regions and at different salinities in the laboratory, representing the salinity gradient of the Baltic Sea. During October 2009 M. leidyi actively reproduced over large areas of the Baltic Sea. Egg production rates scaled with animal size but decreased significantly with decreasing salinity, both in the field (7–29) and in laboratory experiments (6–33). Temperature and zooplankton, i.e. food abundance, could not explain the observed differences. Reproduction rates at conditions representing the Kattegat, south western and central Baltic Sea, respectively, were 2.8 fold higher at the highest salinities (33 and 25) than at intermediate salinities (10 and 15) and 21 times higher compared from intermediate to the lowest salinity tested (6). Higher salinity areas such as the Kattegat, and to a lower extent the south western Baltic, seem to act as source regions for the M. leidyi population in the central Baltic Sea where a self-sustaining population, due to the low salinity, cannot be maintained.

Community cascades in a marine pelagic food web controlled by the non-visual apex predator Mnemiopsis leidyi

Trophic cascades are a ubiquitous feature of many terrestrial and fresh-water food webs, but have been difficult to demonstrate in marine systems with multispecies trophic levels. Here we describe significant trophic cascades in an open coastal planktonic ecosystem exposed to an introduced top predator. The ctenophore Mnemiopsis leidyi was monitored for an 8-year period concurrent with measures of the food web structure of the plankton and strong trophic cascades were evident. In the 5 years when M. leidyi were found, their target prey (grazing copepods) were reduced 5-fold and the primary producers doubled their biomass when released from the grazing pressure. The increased phytoplankton biomass could unequivocally be assigned to grazing release since concurrent measurements of primary production did not differ between years with or without M. leidyi. Copepod biomass prior to the mass occurrence of the ctenophore was important. The years without M. leidyi had significantly higher biomass of copepods in July, the month preceding the outburst of the ctenophore. The profound changes of the pelagic ecosystem faced with a non-selective apex predator shows that marine communities are not exceptions from trophic cascade mechanisms.

Dispersal and speciation: The cross Atlantic relationship of two parasitic cnidarians

Abstract How dispersal strategies impact the distribution of species and subsequent speciation events is a fundamental question in evolutionary biology. Sedentary benthic marine organisms, such as corals or sea anemones usually rely on motile larval stages for dispersal and therefore have a relatively restricted distribution along coasts. Edwardsiella lineata and Edwardsiella carnea are virtually indistinguishable edwardsiid sea anemones native to the east American and the Northern European coast, respectively. E. lineata is a facultative parasite to the ctenophore Mnemiopsis leidyi, while the life cycle of E. carnea is unknown. Recently M. leidyi was found in the Skagerrak carrying Edwardsiella sp. parasites, which raised the intriguing possibility that the invasive comb jellies acted as cargo for the facultative E. lineata parasites to establish a new population in Northern Europe. Here, we assessed the genetic differences between these two cryptic Edwardsiella species and isolated parasites from the invasive comb jelly M. leidyi in Sweden by comparing rRNA, whole transcriptomes, SNPs, ITS2 sequences and the gene complements of key developmental regulators, the Wnt gene family. We show that E. carnea and the parasite transcriptomes are more than 99% identical, hence demonstrating that E. carnea has a previously unknown parasitic life stage. ITS2 sequence analysis of E. carnea and E. lineata suggest that they may not be reproductively isolated. The transcriptomes of E. lineata and E. carnea are ∼97% identical. We also estimate that the species diverged between 18.7 and 21.6 million years ago.

THE FATE OF MICROPLASTICS DURING UPTAKE AND DEPURATION PHASES IN A BLUE MUSSEL EXPOSURE SYSTEM: Microplastic fate in a blue mussel exposure system

We present a blue mussel exposure system where the fate of microplastics (polystyrene beads) is tracked during exposure and depuration phases. This enabled the establishment of a complete mass balance. Quantification of beads in mussels was done with a novel enzymatic digestion protocol. We found a similar relative distribution of beads for 2 environmentally realistic concentrations (5 and 100 beads L-1 ) and no substantial egestion of particles within 2 h of depuration. Environ Toxicol Chem 2019;38:99-105.