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Biogenic structures that persist post‐mortem are ubiquitous, but rarely considered as key ecological features. Post‐mortem structures in many ecological systems exert community‐level effects and thus the dynamics of their degradation (i.e. taphonomy) become important in affecting community functions and ecosystem services, and these often‐overlooked effects may rival the influence of recruitment and typical post‐recruitment processes. Moreover, in some highly researched habitat types, post‐mortem structures may be mistaken for living organisms, thus introducing significant error into our understanding of population processes. We examined widespread patterns and processes in marine assemblages with calcareous tubeworms and brackish‐water assemblages with bryozoans, in order to test the importance of taphonomy for populations and communities. In tubeworm assemblages, taphonomic variability caused differential accumulation of post‐mortem structures, exerting community‐level influence, and importantly it negated effects from recruitment on the community functions. For tubeworms and bryozoans, proportions of post‐mortem structures varied between sheltered and exposed habitats with overall distributional variability being caused by the share of post‐mortem structures, not living animals. Population‐level inferences in such systems would be extremely problematic without careful differentiation of dead/living structures. Dynamics emerging from the interaction of taphonomic processes and recruitment ecology are relevant for many other important biogenic habitats, especially coral reefs with death assemblages of bleached corals; a failure to consider variability in processes acting on the death assemblages, alongside the living, may severely distort understanding of patterns and processes in populations and communities.

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.

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.

The availability of suitable microhabitats has emerged as a key requirement for maximising species diversity gains from ecological engineering of coastal habitats. This includes intertidal boulder field habitat, which is threatened by increasing urbanisation. We examined faunal use of microhabitats offered by natural intertidal boulders on two continents, South Africa and Australia, and then used artificial boulders to test possible mechanisms driving the observed patterns. Gaps often occur between the undersides of boulders and the substratum on which they lie. Substrata underneath boulders are generally uneven, so gaps can occur anywhere along the boulder undersurface, but gaps are generally larger near the edges of naturally-occurring boulders. Boulder edges were found to provide a microhabitat that had greater densities of almost all macrofauna than closer to the centre of boulder undersides. To test the model that microhabitat use of boulder edges reflects their larger gap sizes (relative to boulder centres), artificial boulders were constructed with the underside surface either flat, or with a gap underneath mimicking the mean size of the gap normally found only under boulder edges (when their average shape is considered among numerous naturally-occurring boulders). Artificial boulders were deployed intertidally for seven weeks, and macrofaunal colonisation was compared (a) between flat boulders and those with gaps, and (b) between edges and centres. Five times more macrofauna colonised boulders with artificial gaps, while no effect of proximity to edges was found when the gap-width was controlled for. The size of gaps under boulders appears to be an important microhabitat feature that can explain a widespread distributional pattern in the diverse assemblages of boulder fields. Such gaps are clearly used by numerous species, including some that are rare or commercially important. Provision and augmentation of this microhabitat should be considered for any ecological engineering project that involves intertidal or subtidal boulders.

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.

Marine-springs containing relic intertidal species can be used to observe how assemblages usually found only on open coasts are structured when free from disturbances associated with water movement. This study tested if two previously described patterns from disturbance-prone boulder habitats occurred within a South Australian marine-spring. I aimed to determine how species are associated with the interface between boulders and the surface of the bottom sediment, a habitat feature suggested to be important for some key benthic invertebrates. Testing species associations to this feature is normally difficult because boulders and sediment are regularly disturbed, but on stable marine-spring boulders, fine-scale associations of species with this interface could be measured. Also investigated was a previously described negative correlation of peracaridan (Crustacea) densities with boulder size. This could possibly occur due to variability in disturbance related to boulder-size/stability, in which case...

Many rigorous methods have been developed to manipulate and sample rocky benthic species, but development of field methodology is less advanced for disturbance-prone rocky habitats e.g. cobbles and boulders. These habitats can have ecological and economic importance but research is complicated by their complex physical structure that necessitates causing disturbance when sampling, possibly resulting in mobile species being lost from samples. We used simulated/controlled sampling conditions to determine the proportions of mobile species successfully captured or lost during sampling. Boulders and cobbles were lifted out of shallow water (i.e. “littoral” sampling) and sampled in simulated sublittoral conditions, targeting biota attached to the undersurfaces. Variation in sample losses associated with different methods was tested – sampling in shallow vs deep water and small vs large boulders/cobbles. Different species and locations were also compared. Tests were done to determine contexts producing minimal losses and thus deserving prioritisation. Experiments were replicated in southern Australia and NE Baltic Sea. Large proportions of littoral amphipods and isopods were not successfully captured during sampling in most contexts (overall mean loss = 35%). This means lifting boulders from shallow water cannot accurately sample them. This finding is important especially for highly researched boulder or cobble associated invasive amphipods with large ecological impacts. Seventeen percent of littoral gastropods were lost from samples in both regions; in Australia greater proportions were occasionally lost when sampling larger boulders. Chitons and one gastropod (Theodoxus fluviatilis) could be sampled from shallow water with consistently high reliability. During sublittoral sampling, mean sample loss was 13% with no significant interspecific variability. Boulder/cobble size and water depth rarely caused influence. The results reveal sampling contexts where more sophisticated methods may be used for highly accurate abundance measurements in recent research programmes of ecological restoration and conservation of rare species involving marine but also freshwater habitats.

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.

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.