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Wild harvest of seaweed supports small-scale, high-value industries in a number of regions in the world. Information is lacking on how increasing carbon dioxide (CO2) concentrations in seawater could impact seaweeds in wild harvest situations. This study focuses on a mixed unattached loose-lying red algal community of Furcellaria lumbricalis in close association with Coccotylus truncatus that is found in the West Estonian Archipelago Sea, NE Baltic Sea. In Estonian coastal waters, the wild harvest of F. lumbricalis started in 1960s and it has since been used as raw material for furcellaran production. The aim of this study was to determine how ocean acidification may impact the balance of these two red algal species in the community. Mechanistic assessment of the carbon physiology of F. lumbricalis and C. truncatus was used to predict productivity and competitive interactions between these species in a high-CO2 world. Carbon use strategies in macroalgae were determined by analysing the natural abundances of carbon isotopes (δ13C), pH drift experiments and photosynthesis vs. dissolved inorganic carbon (DIC) curves. Photosynthesis of F. lumbricalis (operating with a CO2 concentrating mechanism or CCM) performed worse along the broader range of DIC concentrations compared to C. truncatus (non-CCM), especially those characterized under future climate conditions. Therefore, changing seawater carbon chemistry through ocean acidification has the potential to influence the balance of F. lumbricalis and C. truncatus in the community and the efficiency of the wild harvest of this community and the quality of product provided.

Anthropogenically influenced habitats are becoming increasingly impacted by multiple invasive species that can regionally control main ecological processes and functions. Management requires predictions of invasive species’ effects, but multiple invasions may cause unpredictable outcomes, for example, synergistic impacts or interactions among trophic levels causing trophic cascades. The Baltic Sea is prone to species invasions that increasingly occur at multiple trophic levels. We used a laboratory experiment to test whether multiple invasive predators may cause interactive effects in the Baltic Sea. In aquaria, we simulated a coastal community that has developed dominated by invasive species—the decapod predators Palaemon elegans and Rhithropanopeus harrisii, the amphipod grazer Gammarus tigrinus, and the filter‐feeder Dreissena polymorpha. The orthogonal experiment determined separate and interactive effects from predators on the lower trophic level invasive species and native algae including the foundation species Fucus radicans. The main result was that while both predators significantly impacted the community, in no cases were their effects interactive. Another important result was that P. elegans appeared to cause a trophic cascade, as in its presence F. radicans and its epiphytes had the greatest biomass while G. tigrinus grazers were heavily reduced. G. tigrinus were negatively correlated with F. radicans biomass, so variable amphipod grazing may be the link allowing an indirect effect of P. elegans on F. radicans. R. harrisii also reduced G. tigrinus abundance but did not affect F. radicans biomass. Both predators significantly affected the lengths of F. radicans plant stems that were comprised of new vegetative growth—P. elegans reduced the lengths of new vegetative tissue while R. harrisii increased it. Thus, the presence of P. elegans induced shorter and denser F. radicans bushes compared to taller and thinner bushes observed in other treatments. Lastly, R. harrisii caused significant declines in D. polymorpha numbers. Overall, ecological management needs to consider positive effects from predator invasion which may reduce grazing pressure on low trophic level foundation species. A trophic cascade involving two invasive species highlights the importance of multi‐species approaches to management of Baltic Sea invasive species and in other regions prone to biological invasions.

The asterinid seastars Parvulastraparvivipara and P.vivipara share atypical viviparous reproductive modes that have made them of interest for research on life-history evolution and population genetics. This article briefly reviews life-history traits of these endemic Australian species and information on distribution and rarity, as well as providing some additional new analysis. Almost exclusive self-fertilisation has led to extreme genetic poverty in both species and viviparity limits dispersal potential causing relatively small geographical ranges. There is some evidence that the number of intertidal boulder-fields harbouring P.parvivipara, and the overall geographical range, may have become reduced in recent years. In addition, approximately 25 % of boulder-fields with P.parvivipara have been colonised by invasive oysters (Magallanagigas). To understand potential effects of oysters on P.parvivipara, we tested for correlations between P.parvivipara abundances and cover of oyster encrustations that included this invader (native + non-native oyster shells were assessed together because they produced similar encrustations and largely could not be differentiated). Linear regression showed no evidence, however, for any correlation. For P.vivipara, population survey data from the mid 1970’s to present shows marked decline in areas of previous abundance. Parallel with this decline, the boulder habitat has experienced infill and siltation and cementing of the substratum by M.gigas, sponges and other encrusters as well as anoxia. Important future research outcomes on consequences of atypical life-history traits may be allowed by continued research on these seastars but only if their populations are able to persist within the small number of boulder-fields where they occur. Current trends may indicate a need for conservation intervention.

Compared to stable reef habitats, dynamic boulder-reefs (commonly called boulder-fields when intertidal) host many habitat specialist species. Most occur underneath boulders where they are largely ...

Spatiotemporal environmental variation affects fish feeding behaviour and capacity for piscivorous control of prey populations, which is important for management when prey include invasive species causing ecosystem impacts. We assessed gut-contents of an important piscivore (European perch Perca fluviatilis) over two years, and analysed variables affecting initiation and amounts of feeding, focusing on an important invasive prey species, round goby (Neogobius melanostomus). We show that predation is primarily controlled by variation of physical and habitat characteristics surrounding perch. Fish prey began being incorporated in diets of perch that were >150 mm, with temperature conditions controlling initiation of their feeding. Total amounts of fish in perch diets, and amounts of round goby individually, were strongly affected by macrophyte cover; seldom were fish present in perch stomachs when macrophyte cover was >40%. Environmental densities of round goby were related to multivariate diet composition in ways that suggest predation of some native species may be relaxed in areas of dense round goby populations. There was evidence that perch predation is unlikely to limit populations of the invader, as there was only a weak relationship between round goby densities and amounts in gut contents. The results have ecosystem management implications, because some variables found to be important could be manipulated to control round goby or other similar invaders e.g. fisheries management of native piscivore stock-density and body-size, or modification of benthic environment structure.

It is recognised that more research is needed on ecology of rare intertidal invertebrates to understand their ecological functions and aid their conservation. An example is chitons which are specia...

Refugia within successional mosaics where localized conditions inhibit successional replacement may support large abundances of early colonizing species and their coexistence with strongly competitive late colonizers. Numerous habitats have been hypothesized as refugia from succession with important landscape-scale consequences from export of propagules, but their commonness among ecological systems is unknown because tests to demonstrate their existence have not been formulated and applied. In this study on an intertidal model system, an early successional tubeworm was highly abundant in a hypothesized refuge habitat-type where late successional algae could not establish. In adjacent non-refuge habitat, a change in species dominance involving tubeworms shifting to algae occurred from early to late succession following experimentally induced disturbance. No such change occurred in refuges where early successional tubeworm populations steadily increased throughout succession. Tubeworm recruitment was reduced in the presence of late successional algae, likely from competition in the non-refuge. The presence of habitats providing refugia from succession may have important consequences, e.g. promoting low but consistent levels of local-scale coexistence of early and late successional taxa observed here even without disturbance. Experimental tests such as these to identify refugia from succession will be useful to apply to larger-scale land/seascapes if, as in this study, the scale of experimentation is optimized for the species and processes of interest. If the inferences from these results are extrapolated to larger-scale systems, they may inform our understanding of spread of early successional species such as weeds with large impacts that are potentially influenced by this landscape feature.

Highlights: • We summarized 20 ecosystem services provided by coastal Baltic ecosystems. • Information on how services translate into socio-economic benefits is lacking. • The deep knowledge gap impairs the sustainable management of the benefits. • We propose a framework with four key measures to close this knowledge gap. • Toxins and Nutrients are the most well-document pressures to these services. Abstract: Seagrass meadows, algal forests and mussel beds are widely regarded as foundation species that support communities providing valuable ecosystem services in many coastal regions; however, quantitative evidence of the relationship is scarce. Using the Baltic Sea as a case study, a region of significant socio-economic importance in the northern hemisphere, we systematically synthesized the primary literature and summarized the current knowledge on ecosystem services derived from seagrass, macroalgae, and mussels (see animated video summary of the manuscript: Video abstract). We found 1740 individual ecosystem service records (ESR), 61% of which were related to macroalgae, 26% to mussel beds and 13% to seagrass meadows. The most frequently reported ecosystem services were raw material (533 ESR), habitat provision (262 ESR) and regulation of pollutants (215 ESR). Toxins (356 ESR) and nutrients (302 ESR) were the most well-documented pressures to services provided by coastal ecosystems. Next, we assessed the current state of knowledge as well as knowledge transfer of ecosystem services to policies through natural, social, human and economic dimensions, using a systematic scoring tool, the Eco-GAME matrix. We found good quantitative information about how ecosystems generated the service but almost no knowledge of how they translate into socio-economic benefits (8 out of 657 papers, 1.2%). While we are aware that research on Baltic Sea socio-economic benefits does exist, the link with ecosystems providing the service is mostly missing. To close this knowledge gap, we need a better analytical framework that is capable of directly linking existing quantitative information about ecosystem service generation with human benefit.

Incorporating ecosystem changes from non-indigenous species (NIS) is an important task of maritime spatial planning. Maritime spatial planning requires a framework that emphasises ecological functioning in a state of dynamic change, including changes to ecosystem services from functions introduced by new NIS. Adaptable modelling toolsets should be developed that can readily incorporate knowledge of new NIS. In the Baltic Sea, recent NIS examples are the North American mud crab Rhithropanopeus harrisii and the Ponto-Caspian round goby Neogobius melanostomus. We performed environmental niche modelling that predicted N. melanostomus will spread across large areas of the Baltic Sea coast while R. harrisii will be limited to regions with high temperature and low salinity conditions. We then performed a meta-analysis on literature showing effects in the Baltic Sea from these NIS and calculated the standardised effect-sizes on relevant ecosystem services. Half the impacts identified for N. melanostomus were considered to increase ecosystem service outcomes, while all R. harrisii impacts caused apparent decreases. Effect coefficients were incorporated into an online impact assessment tool developed by the Estonian Marine Institute. Users with or without science training can use the portal to estimate areas impacted and changes to natural assets (km2) caused by these NIS and cumulative effects from other pressure-types. Impact estimates are based on best available knowledge from manipulative and correlative experiments and thus form a link between science and management. Dynamic modelling techniques informed from varied ecological and methodological perspectives will effectively advise spatial planners about rapid maritime changes and mitigation actions to reduce NIS impacts especially in the focus areas.

Studies investigating the many ecologically and economically important species in benthic boulder habitats often use artificial boulders for determining species colonization. In some cases square-edged blocks are used that are shaped much differently than the ovoid or ‘round’ boulders often occurring naturally. Here it was tested if the shape of boulders affects the distribution across the boulder surface of crustose coralline algae (CCA), a taxon that strongly influences ecological dynamics in this habitat. The distance that CCA extends from the edge of boulders toward the centre of the underside was measured, and it was found that CCA extended further underneath boulders that were round-shaped compared with those that were block-shaped, probably because of light reaching further underneath round boulders. This result shows how at least one important taxon can be affected by variation in the shape of these boulders. Hypotheses being tested that use artificial substrata to model naturally occurring boulders should be carried out only in places where the artificial and naturally occurring boulders match physically.

Most species ofIschnochitonare habitat specialists and are almost always found underneath unstable marine hard-substrata such as boulders. The difficulty of experimenting on these chitons without causing disturbance means little is known about their ecology despite their importance as a group that often contributes greatly to coastal species diversity. In the present study we measured among-boulder distributional patterns ofIschnochiton smaragdinus, and used time-lapse photography to quantify movement behaviours within different habitat types (pebble substrata and rock-platform). In intertidal rock-pools in South Australia,I. smaragdinuswere significantly overdispersed among boulders, as most boulders had few individuals but a small proportion harboured large populations.I. smaragdinusindividuals emerge from underneath boulders during nocturnal low-tides and move amongst the inter-boulder matrix (pebbles or rock-platform). Seventy-two percent of chitons in the pebble matrix did not move from one pebble to another within the periods of observation (55–130 min) but a small proportion moved across as many as five pebbles per hour, indicating a capacity for adults to migrate among disconnected habitat patches. Chitons moved faster and movement paths were less tortuous across rock-platform compared to pebble substrata, which included more discontinuities among substratum patches. Overall, we show that patterns of distribution at the boulder-scale, such as the observed overdispersion, must be set largely by active dispersal of adults across the substratum, and that differing substratum-types may affect the degree of adult dispersal for this and possibly other under-boulder chiton species.

Disturbances in ecological systems can cause new resources to become available and can free the resources held by strongly competitive species. In intertidal boulder fields, wave-action causes disturbance by overturning boulders and freeing space for re-colonisation. In this study, mensurative experiments showed that boulder disturbance may also cause new biogenic-habitat resources to become available, if pre-disturbance boulders originally had tubeworm encrustations on their undersides. On the high-shore of a South Australian rocky coast, a small proportion of boulders had extensive encrustations of serpulid and spirorbid worm-tubes on their uppersides, and were likely to have recently been overturned, as spirorbid tubeworms are almost always only underneath boulders while living. Ulva macroalgae was absent from all boulders, except those with worm-tubes, where up to 61% Ulva cover was observed. Many boulders with tubes did not, however, have much algae, and this was likely caused by grazing. While limpets were seldom observed attached to tube encrustations, snails such as Nerita atramentosa and Bembicium nanum were equally abundant on and off tubes. N. atramentosa was likely the main grazer, as its densities were negatively correlated with Ulva cover. The mechanism causing association of Ulva and worm-tubes is unknown, but may be related to retention of moisture or algal spores within the complex topography of the tubes. Alternatively, some tubes may still have been living and providing nutrients for Ulva from excretory products. This study takes the first step towards understanding a very distinct habitat requirement which allows an important alga to persist in the hostile environment of the rocky-intertidal high shore.

The importance of the substratum to benthic species can vary depending on the material of its construction. Intertidal boulder reefs with different rock types often have distinct benthic assemblages, and their ecology is structured strongly by succession. Therefore, dynamics causing assemblage variability may involve an interaction of factors involved in succession with features of the substratum. The current experiments monitored 11 month successional trajectories of benthic invertebrates on 2 rock types (siltstone and limestone) with differing physical charac- teristics. Unmanipulated boulders in siltstone and limestone reefs had different assemblages, but when bare boulders of the non-native rock type were transplanted into reefs, assemblages devel- oping on non-native boulders were in most ways similar to those on boulders of the reef's native rock type. A substratum-dependent variation in successional trajectories was observed for one taxon, the true limpet Notoacmea spp. Under specific conditions of rock type at the individual boulder scale and the wider reef scale, evidence was found of a consistent peak in abundance dur- ing early succession. Notoacmea spp. was also positively associated not only with siltstone reefs but also with individual siltstone boulders, suggesting an effect of rock type at the boulder scale. Although processes occurring at scales encompassing whole reefs mostly dictate how these assemblages are associated with rock type, some species are affected by rock type at the boulder scale, and the effect can vary during succession. For such species, successional processes and environmental factors need to be considered synergistically to understand spatial and temporal population variability.

The rock type of hard substrata marine habitats can affect numerous benthic invertebrates, but little is known of the effects on molluscan assemblages, for example, the chitons often found under intertidal boulders. We compared chiton assemblage composition, abundance, species richness, and patterns of frequency distribution in 10 boulder fields containing either hard metamorphic/igneous boulders or soft limestone boulders in two geographical areas in South Australia. Similar species richness occurred in both types of boulder fields, but hard rock boulder fields had greater overall abundances, because of particularly large abundances of some common species. Differences in abundances of common species also resulted in significantly different assemblages occurring between the boulder field types. Some species appeared aggregated among boulders, but this pattern was variable between boulders in differing areas and of differing rock type. In one area, a common species had variable aggregation that caused freq...

Patchy distributions within landscapes may be caused by migration in response to different types of habitat patches. Intertidal boulder fields are landscapes in which boulders are discrete habitat patches, often with chitons attached to their under-surfaces. Chiton densities and associations with patch edges differed between boulders overlying coarse- versus fine-sediment types, with greater densities occurring over fine sediments. We tested whether adult migration caused between-boulder distributions by measuring immigration and emigration following experimental replacement of coarse sediments with fine sediment under boulders. We also assessed whether the manipulations altered chiton positions relative to patch edges, and large-scale generality was tested by including data from two continents. The manipulations did not influence the association of chitons with edges or amounts of emigration, but chitons did display positive density-dependent immigration that mirrored their distributional patterns, indicating the importance of immigration. Strikingly, all results were consistent between continents despite involving different species and even genera of chitons. By using boulder fields as a small-scale, easily manipulated landscape, we show that, even in sedentary organisms, patchy distributions within landscapes can be caused by migration alone, without the need to invoke mortality or larval recruitment.

The sea star Parvulastra parvivipara is a small-range endemic known from only seven granitic headlands in South Australia. Evidence from previous studies suggests that its unstable boulder habitat will experience increased disturbance as sea levels rise. This study investigated distributional and ontogenetic patterns of P. parvivipara across different-sized boulders that vary in physical stability and susceptibility to disturbance. To develop a better understanding of community dynamics in P. parvivipara habitat, patterns were also assessed for a chiton with which the sea star commonly co-occurs (Ischnochiton variegatus), and assemblages of encrusting species were also measured, as these can vary amongst boulder sizes and influence mobile animals. Large boulders had many tubeworms, contributing to a significant boulder-size effect on encrusting species assemblage structure. P. parvivipara was most abundant on the smallest boulders; there was no evidence that abundances were influenced by encrusters. I. variegatus abundances were unaffected by boulder size, but a positive correlation between lengths of individuals and encruster cover occurred on the smallest boulders. Overall, physical habitat features, not encrusting biota, likely caused an association of P. parvivipara with small boulders, while I. variegatus displayed apparent ontogenetic use of encruster-related habitat features. As P. parvivipara uses mostly small boulders that are particularly susceptible to disturbances that are increasing with rising sea levels, future ecological restoration efforts to protect this rare species may be required. Such efforts can be properly informed about necessary habitat requirements from these results.