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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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Intertidal rocky shores in south-eastern Australia are dominated by a diverse assemblage of grazing invertebrates that feed on micro-algal biofilms. This resource is spatially variable and frequently over-grazed, causing strong inter-and intra-specific competition among grazers. Most studies on intertidal grazing are about gastropod molluscs. We observed, however, damaged patches in intertidal biofilms that appeared to be associated with the herbivorous asterinid starfish Patiriella exigua (Lamarck). In contrast with predatory starfish, there have been few ecological studies about herbivorous starfish, even though they are often abundant. We demonstrated that these patches were caused by grazing by this starfish. We then used field-based remote-sensing methods to demonstrate that amounts of chlorophyll were reduced inside grazing marks, quantified these changes and measured their longevity. In experiments, starfish could graze up to 60% of the epilithic micro-algae beneath their everted stomach during a single feeding event lasting on average 22 min. Over 5 d, 2 caged starfish could remove nearly half of the available micro-algae from areas of 144 cm 2 . Changes to the amounts of chlorophyll in grazing marks were persistent, remaining visible on sandstone substrata for several weeks. Amounts of chlorophyll on grazed areas of substratum were significantly different from ungrazed areas up to 28 d after being grazed. Recovering areas were demonstrated to be bio-equivalent to ungrazed areas after a similar period. Thus, P. exigua can have a large effect on the temporal and spatial distribution of micro-algal food, with numerous possible consequences for intertidal assemblages. The ecological importance of herbivorous starfish may be greater than previously perceived.KEY WORDS: Herbivore · Intertidal · Echinoderm · Micro-algae · Spatial heterogeneity · Chlorophyll · Food 376: 153-163, 2009 species, persistence of poorer competitors may be dependent on physical heterogeneity in the distribution of resources (Fletcher & Underwood 1987, Fransen et al. 2001. Heterogeneous dispersion of resources can also support greater densities of organisms (Doncaster 2001). Resale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESSMar Ecol Prog SerSettlement of the dispersive larvae of many sessile invertebrates (e.g. barnacles, oysters) is also influenced strongly by amounts and types of biofilm (Keough & Raimondi 1995, 1996, Wieczorek & Todd 1998. Thus, grazers altering the amounts, types and distributions of biofilms also affect patterns of settlement and subsequent assemblage structure.Grazing on micro-algae also removes the early stages of development of macro-algae, preventing the growth of foliose macro-algae, which has numerous effects on the diverse assemblages in these habitats (reviewed in Hawkins & Hartnoll 1983). Where the early microscopic phases of life history are not removed by grazing, fleshy, branched algae grow, smothering sessile animals, such as barnacles (B...

Epilithic microphytobenthos (EMPB) is of core importance in intertidal assemblages and responds to a variety of environmental variables, including season, light, temperature and exposure to waves. To help understand responses by EMPB to these variables and their interactions, EMPB was compared at 2 different latitudes in eastern Australia. In subtropical Brisbane and temperate Sydney, EMPB was sampled at 4 different heights on shores exposed to, or sheltered from, waves during the austral winters and summers of 2006 to 2008. Trends of increasing biomass with decreasing height on shore supported previous studies. In particular, the interaction between season and height was similar to results of previous studies in Australia. There were no differences in biomass of standing stock between Sydney and Brisbane. Differences in timing of sampling occasions confounded some comparisons, and some observed patterns may be due to differences in rates of recolonisation among treatments. Spectrometric assessment of the composition of pigments in EMPB differed with latitude. Spectral samples were more similar to those from assemblages of cyanobacteria than to assemblages of green algae, and this was more marked in Sydney than in Brisbane. Amounts of chlorophyll a were greater on sheltered shores than on those exposed to waves. These patterns are not easily explained, but serve to illustrate the difficulties of extrapolating patterns and processes from one area to another. Variations in pattern at different heights on the shore and in different years emphasise the need for spatially and temporally extensive data in order to make reliable predictions about EMPB. Improved capacity to make reliable predictions will help us understand how EMPB may respond to our changing climate, which is forecast to be hotter with more frequent storms.