As the EU's commitment to renewable energy is projected to grow to 20% of energy generation by 2020, the use of marine renewable energy from wind, wave and tidal resources is increasing. This literature review (233 studies) (i) summarizes knowledge on how marine renewable energy devices affect benthic environments, (ii) explains how these effects could alter ecosystem processes that support major ecosystem services and (iii) provides an approach to determine urgent research needs. Conceptual diagrams were set up to structure hypothesized cause-effect relationships (i.e. paths). Paths were scored for (i) temporal and spatial scale of the effect, (ii) benthic sensitivity to these effects, (iii) the effect consistency and iv) scoring confidence, and consecutively ranked. This approach identified prominent knowledge gaps and research needs about (a) hydrodynamic changes possibly resulting in altered primary production with potential consequences for filter feeders, (b) the introduction and range expansion of non-native species (through stepping stone effects) and, (c) noise and vibration effects on benthic organisms. Our results further provide evidence that benthic sensitivity to offshore renewable effects is higher than previously indicated. Knowledge on changes of ecological functioning through cascading effects is limited and requires distinct hypothesis-driven research combined with integrative ecological modelling.

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A national assessment system for the classification of the ecological status of coastal waters according to the requirements of the EU Water Framework Directive was established in Estonia in the year 2007. The Estonian Phytobenthos Index was used to assess the ecological status of coastal waters based on submerged aquatic vegetation. After the testing period it appeared that the selected method did not respond to anthropogenic pressure in two national water types: the Väinameri and Pärnu Bay. During this study new indexes were developed and validated against pressure for these areas. The PCF index was combined from the proportion of perennial species, charophytes, and Fucus spp. This index is suitable for the assessment of the ecological status in the Väinameri area. In Pärnu Bay the depth distribution of higher plants and the proportion of opportunistic species showed the strongest correlation with eutrophication variables. These metrics were combined into the HPO index. The class boundaries for assessing the ecological status of water quality were determined for both indexes. The paper describes the calculation of the indexes.

Wind energy is considered to be one of the most promising sources of renewable energy in the future. Planning and construction of offshore wind parks is very active in the Northern Europe and Baltic Sea area. Currently, numbers of largescale projects are under development in the Baltic Sea area and, in most cases, the information on proper environmental impact assessment (EIA) of this activity is missing. There are a number of environmental concerns that are well documented from terrestrial environment (e.g. effects on bird migration) but the marine environment creates some additional possible impacts and threats. Some of them are already well studied, but many aspects remain unclear. The Baltic Sea, being a unique ecosystem, is considered to be vulnerable to many pressures which can be caused by large construction activities. These harmful effects can be destruction and modification of habitat characteristics during the construction phase, noise pollution during construction and low frequency vibration during operation, modification of migration routes, formation of artificial substrate and favourable conditions for alien species invasion etc. Besides harmful impacts, also some positive effects on local biodiversity are usually mentioned, such as the so-called "reef effect".In the current paper we analyse existing information on the known effects of the construction of offshore wind parks in the Baltic Sea area and illustrate the negative and positive effects of the construction activities on local biodiversity based on a study performed in the framework of EIA of offshore wind park development project in the north-eastern Baltic Sea (Neugrund bank, Gulf of Finland). Results are generalized for the whole Baltic Sea area and recommendations are drawn for EIA studies of future development projects.