Seagrass meadows are facing structural degradation worldwide, losing both area and biodiversity.Habitat restoration could reverse this degradation, but so far, the success rate of seagrass restoration has been low.Incorporating facilitative interactions between plants and mussels into habitat restoration projects could potentially improve restoration success by increasing eelgrass survival and growth.In this study, we tested whether co-restoring two ecosystem engineers, namely eelgrass Zostera marina and blue mussels Mytilus edulis/trossulus would increase eelgrass restoration success in different sites.We also tested the rope method of eelgrass transplantation in sites where eelgrass was known to have previously existed.These small-scale field experiments were conducted in 2017-2019, in the northeastern Baltic Sea where the eelgrass reproduces only vegetatively.We found that co-restoration of eelgrass and mussels did not work at small scales because mussels were washed away within the first growing season.However, the shoot density of eelgrass increased over time, especially over the second growing season in the sheltered site, indicating that restoration is possible in these areas.Similarly, the restoration was most successful with the rope method in the sheltered site, suggesting that this method also has potential at larger spatial scales.Our results suggest that in such dynamic ecosystems abiotic factors, particularly exposure, play a larger role compared to biotic interactions, and thus the success of habitat restoration largely depends on local environmental conditions.

In this paper we describe the invasion history of benthic crustacean species that have recently invaded the Estonian coastal sea.Physical characteristics of their habitat and communities associated with the invasive species were explored.The crustaceans Gammarus tigrinus, Chelicorophium curvispinum, Pontogammarus robustoides, and Paramysis intermedia are the most recent newcomers in the Estonian coastal sea.All these species have formed permanent populations and more aggressive species have likely caused significant shifts in the community structure and functioning.Besides the true invasive species, some native amphipod species have significantly expanded their range in the Baltic Sea.This group consists of rare or previously not spotted benthic invertebrate species in the northern Baltic Sea range such as Echinogammarus stoerensis, Calliopius laeviusculus, and Melita palmata.

Increased eutrophication has caused a bloom of opportunistic macroalgae and development of drift algal mats in coastal seas worldwide including the Baltic Sea. To date the patterns of the drift algae have been described at one scale (usually at a sampling unit scale i.e. <100 m) ignoring an infinite variety of other possibilities. Therefore, these analyses do not capture a substantial fraction of overall variance and thus, have limited ecological significance and descriptive power. The objective of this study was to investigate in which of studied spatial scales (sampling unit, 100. 1000 and 10,000 m scales) abiotic environmental variability explained best the biomass patterns of drifting algae and associated invertebrates in the Gulf of Riga, northern Baltic Sea. In addition we assessed whether the species composition and biomass structure of drift algae were related to the biomass structure of three invertebrate functional groups. The biomass distribution of drift algae was better explained by large-scale environmental variability than small-scale environmental variability. The occurrence of topographic depressions at 10,000 m scale seems very important for drifting algal mats to remain in the study area. Non-migrating herbivore community was more strongly related to the biomass patterns of drift algae than mobile herbivore community. The biomass pattern of non-migrating suspension feeders was mainly explained by coastal morphology at different spatial scales indicating that the drift algae had minor or no effects on this functional group. (C) 2008 Elsevier B.V. All rights reserved.