The rocky intertidal zone of sheltered shores in Breiðafjörður, north-west Iceland is dominated by monospecific stands of canopy-forming brown algae Ascophyllum nodosum, which provide habitat for mobile organisms and has been subjected to long-standing rotational harvesting. We investigated the assemblage composition of little-studied mobile brachyuran crabs in this area, to track distributional shifts in a native species responding to climate change and extent of occupancy of the intertidal by a primarily subtidal invasive non-native species. Potential interactive effects of seaweed harvesting were explored. Breiðafjörður was compared with two reference sites in Faxaflói, south-west Iceland. The study revealed clear poleward expansion of the native European green crab Carcinus maenas in the region, displacing the native spider crab Hyas araneus particularly at mid-shore levels. The invasive non-native Atlantic rock crab Cancer irroratus had negligible occupancy in the intertidal zone, indicating limited effects on the intertidal crab assemblage, composition, and abundance. The current harvesting regime of A. nodosum in Breiðafjörður did not affect the composition and abundance of the brachyuran crab assemblage in the rocky intertidal zone. H. araneus is likely being squeezed by displacement subtidally by C. irroratus, and intertidally by C. maenas. Overall, we provide insights into the potential interactions between climate change, invasive species, and human activities in the rocky intertidal zone.

Rocky shore ecology has been studied for a long time, starting with qualitative descriptions and becoming more quantitative and experimental over time. Some of the earliest manipulative experimental ecological studies were undertaken on rocky shores. Many, over time, have made considerable contributions to ecological theory, especially highlighting the importance of biological interactions at the community level. The suitability of rocky shores as convenient test systems for ecological experimentation is outlined. Here we consider contributions from rocky shores to the emerging concepts of supply-side ecology, the roles of competition, predation and grazing, disturbance and succession and positive interactions in structuring communities along environmental gradients. We then address alternative stable states, relationships between biodiversity and ecosystem functioning, and bottom-up and top-down control of ecosystems. We briefly consider the feedback and synergies between ecological concepts and experimental work on rocky shores, whilst still emphasizing the traditional values of marine natural history upheld in JMBA since its first publication. The importance of rigorous experimental designs championed by Underwood and co-workers is emphasized. Recent progress taking advantage of new technologies and emerging approaches is considered. We illustrate how experimental studies have shown the importance of biological interactions in modulating species and assemblage-level responses to climate change and informed conservation and management of coastal ecosystems.

Examining how variability in population abundance and distribution is allotted among different spatial scales can inform of processes that are likely to generate that variability. Results of studies dealing with scale issues in marine benthic communities suggest that variability is concentrated at small spatial scales (from tens of centimetres to few metres) and that spatial patterns of variation are consistent across ecosystems characterized by contrasting physical and biotic conditions, but this has not been formally tested. Here we quantified the variability in the distribution of intertidal rocky shore communities at a range of spatial scales, from tens of centimetres to thousands of kilometres, both in the NE Atlantic and the Mediterranean, and tested whether the observed patterns differed between the two basins. We focused on canopy-forming macroalgae and associated understorey assemblages in the low intertidal, and on the distribution of Patella limpets at mid intertidal levels. Our results highlight that patterns of spatial variation, at each scale investigated, were consistent between the Atlantic and the Mediterranean, suggesting that similar ecological processes operate in these regions. In contrast with former studies, variability in canopy cover, species richness and limpet abundance was equally distributed among spatial scales, possibly reflecting the fingerprint of multiple processes. Variability in community structure of low intertidal assemblages, instead, peaked at the largest scale, suggesting that oceanographic processes and climatic gradients may be important. We conclude that formal comparisons of variability across scales nested in contrasting systems are needed, before any generalization on patterns and processes can be made.

Life history accounts for the chance of survival and reproductive success of a species, considering, for example, when, how often and how much a species reproduces. Consequently, it is directly related to the success or failure of bioinvasions. Here, we investigated some aspects of the life history of the cryptogenic calcareous sponge Sycettusa hastifera. A population from Arraial do Cabo, Brazil (south-western Atlantic) was investigated from September 2008 to December 2009 by monthly collections and histological analyses. We observed that S. hastifera reproduced continuously throughout the year without seasonality and presented high fecundity. The fecundity was not different depending on the sponge body part (top or base), but it was related to the wet weight of the sponge (although a minimum size was not required for reproduction). Reproduction could not be predicted by the seawater temperature. The reproductive characteristics of S. hastifera were similar to those of other previously studied calcareous sponges. Sycettusa hastifera shows traits of an invasive species, such as high fecundity, short life cycle, early sexual maturity and the ability to use pioneer habitats. Consequently, it possesses several characteristics that would allow it to invade new areas.

Peracarid crustaceans are an important component of the vagile fauna associated with coralline algal beds, which often characterize the infralittoral fringe of tropical rocky shores. Among other variables affecting faunal assemblages, sedimentation, food supply and oxygen concentration within mats or turfs of coralline algae may greatly depend on the exposure to waves. In this study, peracarid assemblages were compared at replicated rocky shores within different levels of wave exposure, along a coastline in south-eastern Brazil. Overall amphipod diversity (11 species) was much higher than tanaidacean diversity (two species). Correlation analyses did not support any biological interactions between amphipods and tanaidaceans. Habitat complexity, while apparently limiting amphipod populations, did not affect tanaidaceans at a local scale. Amphipod abundance, not assemblage structure, was positively affected by wave exposure, probably improving oxygen concentration levels and renewal of food resources. Rather than abundance, which remains fairly stable, exposure to waves determined species identity in tanaidaceans, with Zeuxo coralensis found at exposed shores and Leptochelia aff. dubia found at sheltered shores, except for two L. aff. dubia individuals found at one of the exposed sites. Differences in the supply of sediment and the ability of these species in manipulating grains for tube building may explain such a striking pattern.

The rocky shore of Punta Este, Golfo Nuevo (Patagonia, Argentina), was sampled by means of the standardized NaGISA (CoML) protocol, that was aimed to generate biodiversity baseline data in six levels, from high intertidal to 10 m depth. Based on the generated data, we analysed the benthic assemblage structure, species richness, mean abundance and the distribution pattern of invertebrate functional groups, typifying species in each intertidal and subtidal level. The intertidal sampled is exposed to extreme physical conditions higher than any other rocky shore system studied, with air temperature variation of 40°C during the year, maximum winds of 90 km/h and semidiurnal tides of 5 m amplitude; on the other hand subtidal presents less thermal variation (ΔT 10°C throughout the year) and more homogeneous physical conditions. We identified 64 taxa represented by six animal phyla: Mollusca, Arthropoda, Annelida (Polychaeta), Echinodermata, Cnidaria and Nemertea; and three algal phyla: Chlorophyta, Rhodophyta and Heterokontophyta (class: Phaeophyceae). Ordination non-metric multidimensional scaling plots showed three different assemblages in terms of species composition (intertidal, subtidal 1 m level and subtidal 5–10 m levels). The intertidal was represented by suspension feeders, mainly Mollusca. The tiny mussels Brachidontes rodriguezii and Brachidontes purpuratus, and the algae Corallina officinalis dominated the intertidal and promote positive interaction (amelioration), preventing other species from the extreme physical stress. The subtidal was mainly represented by grazers. Our results showed a tendency of suspension feeders to decrease and grazers and predators to increase from high intertidal to subtidal, probably driven by decreasing physical stress. The gastropod Tegula patagonica, the sea urchins Arbacia dufresnii and Pseudechinus magellanicus and the invasive algae Undaria pinnatifida were the most abundant species in 1 m–10 m levels. Based on previous work performed in the region, we hypothesize that the differences registered between intertidal and subtidal levels could be explained in part by an increase in physical stress at the intertidal, with low predation pressure that promotes positive interactions, while in the subtidal the increase in consumers and decrease of physical stress could lead to associational defences. Our results could be useful as baseline data to develop a sustainable network for long-term monitoring of benthic community changes due to anthropogenic activities.

The few records of introduced barnacles in Brazil are most commonly reported on artificial (anthropic) substrates. Here we examine the barnacle assemblage in the intertidal regions of rocky shores and natural reefs and build a data base for future monitoring and study for Brazil. We sampled 24 locations between 3 and 29°S latitude. While we found three introduced (Amphibalanus reticulatus, Megabalanus coccopoma and A. amphitrite) and three cryptogenic species (M. tintinnabulum, A. improvisus and Newmanella radiata), they were uncommon at all locations and only M. coccopoma was widespread south of 20°. Native species still predominated in all samples. Management strategies should focus on preventing future invasions on locations where species have not reached yet.

Sedentary consumers play an important role on populations of prey and, hence, their patterns of abundance, distribution and coexistence on shores are important to evaluate their potential influence on ecosystem dynamics. Here, we aimed to describe their spatio-temporal distribution and abundance in relation to wave exposure in the intertidal rocky shores of the south-west Atlantic to provide a basis for further understanding of ecological processes in this system. The abundance and composition of the functional groups of sessile organisms and sedentary consumers were taken by sampling the intertidal of sheltered and moderately exposed shores during a period of one year. The sublittoral fringe of sheltered areas was dominated by macroalgae, while the low midlittoral was dominated by bare rock and barnacles. In contrast, filter-feeding animals prevailed at exposed shores, probably explaining the higher abundance of the predator Stramonita haemastoma at these locations. Limpets were more abundant at the midlittoral zone of all shores while sea urchins were exclusively found at the sublittoral fringe of moderately exposed shores, therefore, adding grazing pressure on these areas. The results showed patterns of coexistence, distribution and abundance of those organisms in this subtropical area, presumably as a result of wave action, competition and prey availability. It also brought insights on the influence of top-down and bottom-up processes in this area.

The present study aimed at estimating the characteristics of the Ascophyllum nodosum stands along the coast of Brittany, France. Although both an ecologically and economically important macroalga on sheltered rocky shores of the North Atlantic, no study has simultaneously dealt with the variability of the densities, lengths and biomasses of A. nodosum together with a description of its associated algal and animal diversity. There were significant differences in mean lengths and variations in the length–population structures between sites. However, the biomasses and densities showed no significant differences. The biomasses are amongst the highest ones estimated over the entire species distribution. The algal and animal assemblages were typical of A. nodosum zones, but only the identity composition of the algal communities seemed to reflect site differences in environmental forces. The biomasses measured in the present study should help improve future macroalgae biomass and metabolism estimates on regional or global scales. Finally, the data will provide a reference state for future studies on the responses of fucoid canopies to environmental changes.

There is mounting evidence that parasites can influence the composition and structure of natural animal communities. In spite of this, it is difficult to assess just how important parasitism is for community structure because very few studies have been designed specifically to address the role of parasites at the community level, no doubt because it is difficult to manipulate the abundance of parasites in field experiments. Here, we bring together a large amount of published information on parasitism in intertidal communities to highlight the potential influence of parasites on the structure and biodiversity of these communities. We first review the impact of metazoan parasites on the survival, reproduction, growth and behaviour of intertidal invertebrates, from both rocky shores and soft-sediment flats. Published evidence suggests that the impact of parasites on individuals is often severe, though their effects at the population level are dependent on prevalence and intensity of infection. We then put this information together in a discussion of the impact of parasitism at the community level. We emphasize two ways in which parasites can modify the structure of intertidal communities. First, the direct impact of parasites on the abundance of key host species can decrease the importance of these hosts in competition or predator-prey interactions with other species. Second, the indirect effects of parasites on the behaviour of their hosts, e.g. burrowing ability or spatial distribution within the intertidal zone, can cause changes to various features of the habitat for other intertidal species, leading to their greater settlement success or to their local disappearance. Our synthesis allows specific predictions to be made regarding the potential impact of parasites in certain intertidal systems, and suggests that parasites must be included in future community studies and food web models of intertidal ecosystems.