Subtidal Communities Research Articles

Long-Term Ecological Impacts from Oil Spills: Comparison of Exxon Valdez, Hebei Spirit, and Deepwater Horizon.

The long-term ecological impacts of the Exxon Valdez oil spill (EVOS) are compared to two extensively studied and more recent large spills: Deepwater Horizon (DWH) and the Hebei Spirit oil spill (HSOS). Each of the three spills differed in magnitude and duration of oil released, environmental conditions, ecological communities, response and clean up measures, and ecological recovery. The EVOS began on March 24, 1989, and released 40.8 million liters of Alaska North Slope crude oil into the cold, nearly pristine environment of Prince William Sound, Alaska. EVOS oiled wildlife and rocky intertidal shorelines and exposed early life stages of fish to embryotoxic levels of polycyclic aromatic hydrocarbons (PAH). Long-term impacts following EVOS were observed on seabirds, sea otters, killer whales, and subtidal communities. The DWH spill began on April 20, 2010, and released 507 million liters of light Louisiana crude oil from 1600 m on the ocean floor into the Gulf of Mexico over an 87-day period. The DWH spill exposed a diversity of complex aquatic communities in the deep ocean, offshore pelagic areas, and coastal environments to petroleum hydrocarbons. Large-scale persistent ecological effects included impacts to deep ocean corals, failed recruitment of oysters over multiple years, damage to coastal wetlands, and reduced dolphin, sea turtle, and seabird populations. The HSOS began on December 7, 2007, and released approximately 13 million liters of Middle East crude oils into ecologically sensitive areas of the Taean area of western Korea. Environmental conditions and the extensive initial cleanup of HSOS oil stranded on shorelines limited the long-term impacts to changes in composition and abundance of intertidal benthic communities. Comparisons of EVOS, DWH, and HSOS show the importance and complexity of the interactions among the environment, oil spill dynamics, affected ecological systems, and response actions.

Role of predators in the recruitment of invertebrates in a rocky subtidal community in the southwest Bay of Fundy, NB

ABSTRACTPredation is potentially an influential source of early post-settlement mortality of benthic marine invertebrates, but previous studies demonstrate conflicting results. We investigated the effect of large predators on developing subtidal invertebrate communities in cobble-filled collectors in the southwest Bay of Fundy, Canada. Two predation treatments (exclusion of predators ≥ 7 mm body width or full access for predators < 50 mm) were used to test the effect of large predators, and a partial-cage control tested for caging artefacts. Despite a reduction in the abundance and biomass of large predators, multivariate analyses indicated no effect of predator exclusion on the composition of the prey and micropredator communities. Results indicated that the largest differences were between the predator-access treatment and the other two treatments, which was potentially influenced by the caging material. There were significant but weak positive correlations between the micropredator and the other two communities. Previous studies indicate that at low predation intensity, as seemed to be the case here, other factors may play a stronger role in controlling recruit abundance. Predation control probably varies spatially and temporally, and the influence of large predators was not likely the driving force for early post-settlement mortality in the invertebrate communities measured in this study.

Glacial and depth influence on sublittoral macroalgal standing stock in a high-Arctic fjord

The motivation behind this study is the progression of global warming, which severely affects the entire Arctic and could have effects on macroalgal assemblages. Three sampling sites were located at different distances to glacier fronts to study the effect of glacial exposure on macroalgal community composition and standing stock. In addition, the variability between two depths (5 and 10 m) was investigated. The subtidal communities at each site and depth were dominated by brown macroalgae of the order Laminariales, which made up over 95% of the macroalgal biomass and at least 65% of the macroalgal abundance at each site. The mean macroalgal species richness and abundance were reduced at glacially impacted sites, but the differences were not statistically significant. The community structure based on abundance data varied between the clear and glacially exposed sites due to the higher abundances of Laminaria digitata, Phycodrys rubens and Alaria esculenta at the clear site and Saccharina latissima at the glacial sites. The biomass structure did not vary between sites. The kelp biomass distribution between depths was patchy and dependent on water properties. The maximum biomass was observed at the depth of 10 m at the clear site, while it was observed at shallower depths at the glacial sites. As deglaciation proceeds, new seabed areas are uncovered, and the number of ice-free days grows, creating favourable conditions for macroalgal expansion. However, due to increased turbidity close to the glacier fronts, decreases in species richness, abundance and biomass of macroalgae are likely to occur, as well as the reorganization of the community structure. Such changes may intensify with continued Arctic warming. The hypothesis about reduction of macrophyte abundance and biomass due to the glacial impact was not supported by our data.

Limited effects of marine protected areas on the distribution of invasive species, despite positive effects on diversity in shallow-water marine communities

Marine protected areas (MPAs) can be an effective tool for the conservation and management of marine coastal habitats. MPAs have been shown to halt habitat degradation, enhance the biomass of exploited species and diversity in general. Yet, we still know little about its role in halting the spread of non-native species. In this study, we assessed the role of MPAs in the structure of shallow subtidal communities around Sao Miguel Island, in general, and particularly on distribution of the two species of genus Asparagopsis: A. armata and A. taxiformis. In the Azores, the former is a well-established invasive species, whereas the status of A. taxiformis is still questionable. Overall, there was a significant greater diversity in terms of both species richness and number of macroalgal functional groups within MPAs. However, when considering the relative abundance of the various macroalgal functional groups, or the assemblage as a whole (multivariate analysis), there was no significant difference between areas within and outside MPAs. The cover of A. taxiformis was significantly greater within MPAs but not its biomass, whereas no significant variation was observed for A. armata. Overall, results suggest that surveyed MPAs had a positive effect on the diversity of shallow-water macroalgal communities. However, they have a limited role on the distribution of both Asparagopsis spp. and negligible effects when considering the relative abundances of macroalgal functional groups.

Epibenthic predators control mobile macrofauna associated with a foundation species in a subarctic subtidal community.

Foundation species (FS) are strong facilitators providing habitat for numerous dependent organisms. The communities shaped by FS are commonly structured by interplay of facilitation and consumer control. Predators or grazers often indirectly determine community structure eliminating either FS or their principal competitors. Alternatively, they can prey on the dependent taxa directly, which is generally buffered by FS via forming complex habitats with numerous refuges. The latter case has been never investigated at high latitudes, where consumer control is widely considered weak. We manipulated the presence of common epibenthic crustacean predators to assess their effect on mobile macrofauna of the clusters developed by a FS (barnacle Balanus crenatus and its empty tests) in the White Sea shallow subtidal (65° N). While predation pressure on the FS itself here is low, the direct effects of a spider crab Hyas araneus and a shrimp Spirontocaris phippsii on the associated assemblages were unexpectedly strong. Removing the predators did not change species diversity, but tripled total abundance and altered multivariate community structure specifically increasing the numbers of amphipods, isopods (only affected by shrimp), and bivalves. Consumer control in the communities shaped by FS may not strictly follow the latitudinal predation gradient rule.

Rarity and beta diversity assessment as tools for guiding conservation strategies in marine tropical subtidal communities

AbstractAimOur aim was to uncover patterns of distribution of marine subtidal rocky reef communities across six taxonomic groups and decompose the relative roles of species loss and turnover in total community variation. Additionally, we propose an easily calculated index that can be used to highlight areas with unique species composition for conservation planning. We estimated the strengths of associations between environmental factors and species richness and rarity.LocationIlha Grande Bay, Brazil, covering about 150,000 ha harbouring different marine habitats.MethodsWe used the Marine Rapid Assessment Protocol at 42 sites to gather information on environmental variables and species in six subtidal marine groups. We determined “singular” sites as the regions harbouring higher numbers of rare species. Then, we estimated the roles of species loss and turnover on the observed total variation among sites. We used Generalized Linear Model to partition the relative importance of the selected environmental factors in driving variation in species richness and singularity.ResultsThe singularity index and richness showed that the bay could be divided into three subregions for subtidal communities. Richness and rarity were structured at different spatial scales and associated with environmental variables related to water productivity and nutrients but varied among taxonomic groups. Community variation over space was largely associated with turnover of species.Main conclusionsHigher singularity and richness on the western side of the bay and around the main island suggested that these regions should be conservation priorities, but high species turnover across the whole bay indicated that portions of the central channel should be included in conservation strategies. This draws attention to the importance of community variation rather than just species numbers in conservation and management planning. The high species turnover indicated that these rocky reefs have high beta diversity when compared to other studied biological systems.

First quantification of subtidal community structure at Tristan da Cunha Islands in the remote South Atlantic: from kelp forests to the deep sea.

Tristan da Cunha Islands, an archipelago of four rocky volcanic islands situated in the South Atlantic Ocean and part of the United Kingdom Overseas Territories (UKOTs), present a rare example of a relatively unimpacted temperate marine ecosystem. We conducted the first quantitative surveys of nearshore kelp forests, offshore pelagic waters and deep sea habitats. Kelp forests had very low biodiversity and species richness, but high biomass and abundance of those species present. Spatial variation in assemblage structure for both nearshore fish and invertebrates/algae was greatest between the three northern islands and the southern island of Gough, where sea temperatures were on average 3-4o colder. Despite a lobster fishery that provides the bulk of the income to the Tristan islands, lobster abundance and biomass are comparable to or greater than many Marine Protected Areas in other parts of the world. Pelagic camera surveys documented a rich biodiversity offshore, including large numbers of juvenile blue sharks, Prionace glauca. Species richness and abundance in the deep sea is positively related to hard rocky substrate and biogenic habitats such as sea pens, crinoids, whip corals, and gorgonians were present at 40% of the deep camera deployments. We observed distinct differences in the deep fish community above and below ~750 m depth. Concurrent oceanographic sampling showed a discontinuity in temperature and salinity at this depth. While currently healthy, Tristan’s marine ecosystem is not without potential threats: shipping traffic leading to wrecks and species introductions, pressure to increase fishing effort beyond sustainable levels and the impacts of climate change all could potentially increase in the coming years. The United Kingdom has committed to protection of marine environments across the UKOTs, including Tristan da Cunha and these results can be used to inform future management decisions as well as provide a baseline against which future monitoring can be based.

Stability and Change in Kelp Forest Habitats at San Nicolas Island

Kelp forest communities are highly variable over space and time. Despite this complexity it has been suggested that kelp forest communities can be classified into one of 2 states: kelp dominated or sea urchin dominated. It has been further hypothesized that these represent “alternate stable states” because a site can remain in either of these states for decades before some perturbation causes a rapid shift to the other state. Our research group has maintained a subtidal community monitoring program for 38 years at San Nicolas Island consisting of twice-annual scuba-based surveys at 6 sites distributed within 4 regions around the island. Three types of perturbations are thought to be relevant to subtidal community dynamics at San Nicolas: (1) physical disturbances in the form of major storm and El Nino/ Southern Oscillation (ENSO) events; (2) invertebrate diseases, which periodically decimate urchin populations; and (3) the reintroduction and subsequent increase of sea otters (Enhydra lutris nereis). These 3 perturbations differ in spatial and temporal specificity; physical disturbances and disease outbreaks occur periodically and could affect all 4 regions, while sea otter predation has been concentrated primarily at the West End sites over the last 15 years. The different types of perturbations and the duration of the time series at the kelp forests at San Nicolas make the data set ideal for testing the “alternate stable state” hypothesis. We use nonmetric multidimensional scaling (NMDS) to examine spatial and temporal patterns of community similarity at the 4 regions. In particular, we evaluate support for the existence of stable states, which are represented on NMDS plots as distinct spatial clusters. Community dynamics at each site approximated a biased random walk in NMDS space, with one or more basins of attraction and occasional jumps between basins. We found evidence for alternative stable states at some sites, and we show that transitions from one stable state to another may be influenced by interactions between multiple perturbations.

Macrobenthic diversity and sediment-water exchanges of oxygen and ammonium: Example of two subtidal communities of the eastern English Channel

In organic-rich shallow habitats, benthic macrofauna is known to play a major role in the geochemical functioning of surficial sediments through its metabolism, as well as its bioirrigation and/or bioturbation activity. In this paper, the effects of benthic macrofauna on metabolic fluxes at the sediment-water interface were studied at four dates, from winter to late summer, on two major macrobenthic communities of the eastern English Channel (macrotidal system): the fine sand Abra alba community (2 stations) and the sandy gravel Ophiothrix fragilis community (1 station). Oxygen and ammonium fluxes showed temporal changes that could be attributed to the variation of sea water temperature. Once the effect of temperature removed (using Q10 = 2.5), the average fauna mediated fluxes (FFauna) represented respectively 77% and 76% of average total fluxes. Considering the whole dataset, species number and biomass showed a significant correlation with fauna mediated fluxes of O2 and NH4+, while the relationships with abundance were not significant. The species composition of the community might influence ecosystem functioning, but in the present study, functional groups have a very poor relationship with FFauna (O2) and FFauna (NH4+). Despite the presence of engineer species, establishing general and simple rules to link macrofaunal parameters to functional attributes remains very difficult, suggesting that communities rather followed the idiosyncrasy and rivet hypothesis.

Alien turf: Overfishing, overgrazing and invader domination in south‐eastern Levant reef ecosystems

Abstract Coastal reefs are highly diverse marine ecosystems that in many regions suffer today from growing pressures by human activities. Among the most highly‐stressed are those found in the Levantine basin (south‐eastern Mediterranean Sea). The Levant represents the trailing‐edge of distribution of native species where they are exposed to the most extreme temperature and salinity conditions, and the region is also fast‐warming and exposed to a great many alien species and strong fishing pressure. In this study, the ecological state of reefs in the south‐eastern Levant was assessed quantitatively (including inside a small marine reserve) using current, extensive, survey data with reference to anecdotal historical information on their more pristine past. The results of very extensive subtidal community surveys that were conducted in north Israel indicate that reefs in this area are currently dominated by turf‐forming algae and aliens, and sustain low numbers of top predators. Specifically, it was found that on these Levant reefs: (1) commercial species represent a very small part of the fish assemblage (except inside the reserve); (2) alien species constitute a considerable portion (23–44%) of the fish assemblage (including in the reserve) and 95–99% of epi‐benthic molluscs, including inside the marine reserve; and (3) turf barrens are the dominant substrate cover, while cover of native brown algae canopy is limited to small patches occurring only during winter and spring. These findings suggest that the Levant reefs have been highly transformed by overfishing and alien invasions, and probably also climate change, and that even well managed marine reserves had little effect on alien species presence. From a biogeographic‐conservation perspective, as both warming and bioinvasions continue in the Mediterranean, it is expected that this degraded reef state will gradually advance westward. Alleviating fishing pressure with marine reserves might make the reefs more resilient to these regional pressures, but alien invaders will remain a dominant feature in the system. Therefore, a more realistic conservation target might be the preservation or restoration of ecosystem functions rather than the original native biodiversity.

Increased sediment load during a large-scale dam removal changes nearshore subtidal communities.

The coastal marine ecosystem near the Elwha River was altered by a massive sediment influx—over 10 million tonnes—during the staged three-year removal of two hydropower dams. We used time series of bathymetry, substrate grain size, remotely sensed turbidity, scuba dive surveys, and towed video observations collected before and during dam removal to assess responses of the nearshore subtidal community (3 m to 17 m depth). Biological changes were primarily driven by sediment deposition and elevated suspended sediment concentrations. Macroalgae, predominantly kelp and foliose red algae, were abundant before dam removal with combined cover levels greater than 50%. Where persistent sediment deposits formed, macroalgae decreased greatly or were eliminated. In areas lacking deposition, macroalgae cover decreased inversely to suspended sediment concentration, suggesting impacts from light reduction or scour. Densities of most invertebrate and fish taxa decreased in areas with persistent sediment deposition; however, bivalve densities increased where mud deposited over sand, and flatfish and Pacific sand lance densities increased where sand deposited over gravel. In areas without sediment deposition, most invertebrate and fish taxa were unaffected by increased suspended sediment or the loss of algae cover associated with it; however, densities of tubeworms and flatfish, and primary cover of sessile invertebrates increased suggesting benefits of increased particulate matter or relaxed competition with macroalgae for space. As dam removal neared completion, we saw evidence of macroalgal recovery that likely owed to water column clearing, indicating that long-term recovery from dam removal effects may be starting. Our results are relevant to future dam removal projects in coastal areas and more generally to understanding effects of increased sedimentation on nearshore subtidal benthic communities.

Human Influence at the Coast: Upland and Shoreline Stressors Affect Coastal Macrofauna and Are Mediated by Salinity

Anthropogenic stressors can affect subtidal communities within the land-water interface. Increasing anthropogenic activities, including upland and shoreline development, threaten ecologically important species in these habitats. In this study, we examined the consequences of anthropogenic stressors on benthic macrofaunal communities in 14 subestuaries of Chesapeake Bay. We investigated how subestuary upland use (forested, agricultural, developed land) and shoreline development (riprap and bulkhead compared to marsh and beach) affected density, biomass, and diversity of benthic infauna. Upland and shoreline development were parameters included in the most plausible models among a candidate set compared using corrected Akaike’s Information Criterion. For benthic macrofauna, density tended to be lower in subestuaries with developed or mixed compared to forested or agricultural upland use. Benthic biomass was significantly lower in subestuaries with developed compared to forested upland use, and biomass declined exponentially with proportion of near-shore developed land. Benthic density did not differ significantly among natural marsh, beach, and riprap habitats, but tended to be lower adjacent to bulkhead shorelines. Including all subestuaries, there were no differences in diversity by shoreline type. In low salinities, benthic Shannon (H′) diversity tended to be higher adjacent to natural marshes compared to the other habitats, and lower adjacent to bulkheads, but the pattern was reversed in high salinities. Sediment characteristics varied by shoreline type and contributed to differences in benthic community structure. Given the changes in the infaunal community with anthropogenic stressors, subestuary upland and shoreline development should be minimized to increase benthic production and subsequent trophic transfer within the food web.

Distributional changes of the kelp community at a subtidal reef after the subsidence caused by the 2011 Tohoku Earthquake

The subsidence caused by an earthquake can be regarded as a large-scale depth manipulation experiment that can provide valuable information about the formation of marine subtidal communities. To assess the causes of subtidal zonation patterns in macroalgae, we established a permanent survey area (4 m wide × 30 m long offshore) and conducted a long-term monitoring survey of the kelp Eisenia bicyclis and its associated assemblages on a rocky shore of the Oshika Peninsula in northeastern Japan where a 0.9 m subsidence occurred due to the 2011 Tohoku Earthquake. After the subsidence, the distribution of E. bicyclis expanded toward the shallower area, but the density of adults remained unchanged while recruitment declined at the offshore margin. In contrast, the perennial species Sargassum confusum and Sargassum siliquastrum tended to occupy the intermediate depth area and their vertical ranges of distribution did not change over time. No clear change was observed in the distribution of grazers. The most dominant herbivorous snail Omphalius rusticus was evenly distributed over the survey area while the distribution of the sea urchin Hemicentrotus pulcherrimus was limited to the shallower area. We hypothesized that the distributional expansion of the perennial Sargassum species toward the shallower area was prevented by active snail grazing during the microscopic stages of the plants as well as spatial competition with the kelp E. bicyclis. Survival of the subsided E. bicyclis at the lower limit was longer than predicted, indicating that a subsidence event could produce time-lagged effects.

Multi‐scale drivers of community diversity and composition across tidal heights: an example on temperate seaweed communities

Summary Despite recent advances in understanding community assembly processes, appreciating how these processes vary across multiple spatial scales and environmental gradients remains a crucial issue in ecology. This study aimed to disentangle the drivers of diversity and composition of seaweed communities through a gradient of spatial scales based on a hierarchical sampling design consisting of 19 sites distributed in four sectors along the Brittany coastline. Using randomised community matrices and Moran's eigenvector maps (MEMs), we compared (i) the relative importance of deterministic and stochastic processes, (ii) the environmental correlates of community composition, and (iii) the scale of variation in community composition for seaweed communities located at two different tidal heights. Processes shaping community patterns are expected to vary along a gradient of tidal heights. Therefore, we specifically examined the following hypotheses: the contribution of deterministic over stochastic processes as well as the relative importance of environmental filtering over biotic interactions should be enhanced for seaweed communities of the infralittoral fringe compared to subtidal ones, whereas dispersal of propagules in the water column should be more restricted resulting in finer scale variation in community composition for seaweed communities of the infralittoral fringe compared to subtidal communities. Seaweed communities were largely shaped by deterministic processes, although the relative importance of deterministic processes was greater for communities of the infralittoral fringe than for subtidal communities. Sea surface temperature and geophysical variables were correlates of community composition at the two tidal heights; additionally, waves and current were correlated with the composition of the communities of the infralittoral fringe while kelp density was correlated with the composition of subtidal communities. Variation in community composition was observed at a finer scale for infralittoral fringe than for subtidal communities. Synthesis. Our results suggest that the relative importance of deterministic and stochastic processes in structuring seaweed communities varies across tidal heights. Furthermore, the Moran's eigenvector maps framework highlights that the nature of environmental correlates and the spatial scale at which they were good correlates of community composition also vary across tidal heights and may therefore be useful to broaden our understanding of community assembly across vertical gradients.

Exploring the effects of fishing pressure and upwelling intensity over subtidal kelp forest communities in Central Chile

AbstractUnderstanding the processes that drive kelp forest communities is critical for management and conservation of these productive ecosystems. As a way to advance in this direction, we explored the effects of fishing pressure and upwelling intensity over kelp forest communities along the central coast of Chile. We sampled kelp communities in different upwelling conditions associated with contrasting management regimes, namely Territorial User Rights for Fisheries (TURFs) and open‐access (OA) areas. In TURF areas, we found a 2.6‐fold increase in reef fish biomass, higher diversity of all fish trophic groups, mainly dominated by benthic carnivore feeders, and a 1.8‐fold reduction in the number of kelp grazers. On the other hand, upwelling regimes evidence a 1.6‐fold increase in abundance and recruitment of the dominant kelp (Lessonia trabeculata), and also an increase in biomass of planktivorous reef fishes. We found that grazers were capable of reducing kelp condition (measured as canopy foliage index) in OA areas outside the influence of upwelling. Enclosure experiments in the field revealed the effect of grazers on kelps, reducing kelp growth (i.e., blade elongation) and increasing blade tissue loss. Results provide evidence that TURF areas could be important ancillary conservation instruments in kelp forest ecosystems, if key processes of the subtidal community assemblages (e.g., interactions between grazers and reef fish) are maintained. We conclude that human impact interplays with the influence of upwelling in structuring kelp communities.

Isotopic determination of the trophic ecology of a ubiquitous key species – The crab Liocarcinus depurator (Brachyura: Portunidae)

Knowledge of the trophic ecology of predators is key to understanding how they affect food web structure and ecosystem functioning. The harbour crab Liocarcinus depurator (L.) (Brachyura: Portunidae) is one of the most abundant decapod species in soft-bottom areas of the Mediterranean Sea and northeast Atlantic Ocean. It is both a common prey and predator of commercial and non-commercial marine species and its predation pressure appears to have little effect on the subtidal community assemblage. However, there are few studies of its diet and little is known about its role in mediating energy flows in marine ecosystems. In this study, carbon (δ13C) and nitrogen (δ15N) stable isotope analysis (SIA) and Bayesian analytical tools were used to characterise the trophic niche of L. depurator and to quantify the most important prey supporting this species under various environmental conditions. Specimens of L. depurator, their potential prey and basal resources were collected from two different subtidal areas of the Gulf of Gaeta, one affected by human activities (north side) and the other seasonally influenced by freshwater inputs originating from the River Garigliano (south side). While there were differences between the two sampling areas in terms of the abundance and δ15N and δ13C values of the macrobenthic prey community, no differences in the δ15N values and trophic position of L. depurator were observed. Specifically, Bayesian mixing models showed Polychaeta Errantia as the main source of crab diets in both areas. The observed differences in the δ13C values and the analysis of trophic pathways also indicate that the terrestrial organic matter originating from the discharge of the River Garigliano was integrated along the food web up to L. depurator. Although this species is usually considered an opportunistic feeder, it appears to be highly selective and its trophic habits did not influence food web topology, which in contrast was found to be strongly influenced by River Garigliano discharge.

Cockles, barnacles and ascidians compose a subtidal facilitation cascade with multiple hierarchical levels of foundation species

Facilitation cascades occur when multiple foundation species in a community are involved in a hierarchy of positive interactions, and consist of a primary facilitator which positively affects secondary facilitators, each supporting a suit of dependent species. There is no theoretical limit to the number of levels in a facilitation cascade, yet the existence of more than two has rarely been examined. We manipulated biogenic substrate produced by a primary facilitator (cockle shells) and a secondary facilitator (barnacles and their empty tests) in a space-limited subtidal community to test the hypothesis that solitary ascidians would be the third-level facilitator. In the field, most ascidians were found on barnacles, and most barnacles occupied cockle shells. To produce this pattern, barnacles could nurse ascidians (a longer ‘facilitation chain’) or outcompete them from cockle shells (a shorter chain). Experimental results clearly supported the nursing hypothesis providing evidence for a facilitation cascade with three hierarchical levels of foundation species. Our findings confirm that like predation and competition, positive interspecific interactions nest into multi-tier hierarchies with numerous levels. While the number of foundation species should increase community stability and resilience as it increases diversity and reduces environmental stress, facilitation chain length may have the opposite effect.

Abiotic/Biological Interactions in Coastal Marine Communities: Insights from an Alaskan Fjord

Interactions among multi-scale coastal marine ecosystem processes can be expected to play large roles in and interact with biological processes as stresses increase, potentially allowing interfering processes (including biological interactions) to become more prevalent. Retrospective analyses of intertidal (1988–1992) and subtidal (1971–2012) species compositions from a long-term ecological research program in Port Valdez, Alaska evaluated associations between benthic community structure and physical conditions to better understand interactions between regional to local processes on flora and fauna. Low salinity, habitat structure (varying from mudflats to rocky shores over a distance of <18 km), and suspended sediments contributed to intertidal community structure via elimination of predators from low-salinity prey refugia. Subtidal communities demonstrate adjustments by macrofauna to sedimentation with smaller, disturbance-tolerant fauna towards the head of the fjord as well as effects from depth-related covariates. Shared ecological processes result in comparable community trends in subtidal and intertidal habitats among subarctic and arctic fjords and similarly among coastal environments of the North Pacific. Control exerted by interactions among climatic, oceanographic, and local processes interacting with biota contributes to the direction and length of recovery from disturbance events and environmental changes. Feedbacks, mediation of recovery by additional processes, and strengths of interactions also play important roles in determining interaction outcomes. Interactions among local, regional, and global-scale processes may become critical sources of change as global ecosystem transitions through new climate states.

Sand-mediated divergence between shallow reef communities on horizontal and vertical substrata in the western Indian Ocean

Distinctions are rarely made between vertical and horizontal surfaces when assessing reef community composition, yet physical differences are expected because of hydrodynamic differences and sediment accumulation on flat surfaces. As sand often diminishes biotic cover, we hypothesised that vertical surfaces will support a greater biomass but have lower diversity due to domination by a few species. To test this, we quantified sessile communities on vertical and horizontal surfaces at three sites in the Delagoa Bioregion on the east coast of South Africa. Community composition consistently differed: vertical communities were dominated by various filter feeders, especially the ascidian Pyura stolonifera, whereas those on horizontal reef comprised a mixture of filter feeders and various algae. The total number of species and all diversity metrics were significantly greater for horizontal reef surfaces. Contrastingly, Simpson’s dominance and biomass were significantly greater for vertical reef surfaces. Percentage cover of sand explained much of the variation in community composition whereas depth did not. Small-scale topographic differences in substratum orientation associated with differences in sand inundation will therefore influence both α and β diversity. Coastal developments and activities that alter sand movements and delivery to the coastal zone are therefore likely to have a profound influence on the maintenance and diversity of shallow subtidal communities.

Spatial pattern of distribution of marine invertebrates within a subtidal community: do communities vary more among patches or plots?

Making links between ecological processes and the scales at which they operate is an enduring challenge of community ecology. Our understanding of ecological communities cannot advance if we do not distinguish larger scale processes from smaller ones. Variability at small spatial scales can be important because it carries information about biological interactions, which cannot be explained by environmental heterogeneity alone. Marine fouling communities are shaped by both the supply of larvae and competition for resources among colonizers—these two processes operate on distinctly different scales. Here, we demonstrate how fouling community structure varies with spatial scale in a temperate Australian environment, and we identify the spatial scale that captures the most variability. Community structure was quantified with both univariate (species richness and diversity) and multivariate (similarity in species composition) indices. Variation in community structure was unevenly distributed between the spatial scales that we examined. While variation in community structure within patch was usually greater than among patch, variation among patch was always significant. Opportunistic taxa that rely heavily on rapid colonization of free space spread more evenly among patches during early succession. In contrast, taxa that are strong adult competitors but slow colonizers spread more evenly among patches only during late succession. Our findings show significant patchiness can develop in a habitat showing no systematic environmental spatial variation, and this patchiness can be mediated through different biological factors at different spatial scales.