Rocky Intertidal Communities Research Articles

Regional processes are stronger determinants of rocky intertidal community dynamics than local biotic interactions.

Understanding the relative roles of species interactions and environmental factors in structuring communities has historically focused on local scales where manipulative experiments are possible. However, recent interest in predicting the effects of climate change and species invasions has spurred increasing attention to processes occurring at larger spatial and temporal scales. The "meta-ecosystem" approach is an ideal framework for integrating processes operating at multiple scales as it explicitly considers the influence of local biotic interactions and regional flows of energy, materials, and organisms on community structure. Using a comparative-experimental design, we asked (1) what is the relative importance of local biotic interactions and oceanic processes in determining rocky intertidal community structure in the low zone within the Northern California Current System, and (2) what factors are most important in regulating this structure and why? We focused on functional group interactions between macrophytes and sessile invertebrates and their consumers (grazers, predators), how these varied across spatial scales, and with ocean-driven conditions (upwelling, temperature) and ecological subsidies (nutrients, phytoplankton, sessile invertebrate recruits). Experiments were conducted at 13 sites divided across four capes in Oregon and northern California. Results showed that biotic interactions were variable in space and time but overall, sessile invertebrates had no effect on macrophytes while macrophytes had weakly negative effects on sessile invertebrates. Consumers, particularly predators, also had weakly negative effects on both functional groups. Overall, we found that 40-49% of the variance in community structure at the local scale was explained by external factors (e.g., spatial scale, time, upwelling, temperature, ecological subsidies) vs. 19-39% explained by functional group interactions. When individual functional group interaction strengths were used, only 2-3% of the variation was explained by any one functional group while 28-54% of the variation was explained by external factors. We conclude that community structure in the low intertidal zone is driven primarily by external factors at the regional scale with local biotic interactions playing a secondary role.

Microbiome acquisition during larval settlement of the barnacle Semibalanus balanoides.

Barnacles are conspicuous members of rocky intertidal communities and settlement of the final larval stage, the cyprid, is influenced by the presence of biofilms. While modulation of cyprid settlement by biofilms has been studied extensively, the acquisition of a specific microbiome by the settling larva has not. This study investigated settlement in the field of Semibalanus balanoides in two consecutive years when the composition of the benthic bacterial community differed. In both years, settling cyprids adopted a specific sub-set of benthic bacteria that was distinct from the planktonic cyprid and the benthos. This microbiome was consistent, regardless of annual variability in the benthic community structure, and established within hours of settlement. The results imply that a natural process of selection occurs during the critical final transition of S. balanoides to the sessile form. The apparent consistency of this process between years suggests that optimal growth and survival of barnacles could depend upon a complex inter-kingdom relationship, as has been demonstrated in other animal systems.

Non-parametric estimation of the structural stability of non-equilibrium community dynamics.

Environmental factors are important drivers of community dynamics. Yet, despite extensive research, it is still extremely challenging to predict the effect of environmental changes on the dynamics of ecological communities. Equilibrium- and model-based approaches have provided a theoretical framework with which to investigate this problem systematically. However, the applicability of this framework to empirical data has been limited because equilibrium dynamics of populations within communities are seldom observed in nature and exact equations for community dynamics are rarely known. To overcome these limitations, here we develop a data-driven non-parametric framework to estimate the tolerance of non-equilibrium community dynamics to environmental perturbations (that is, their structural stability). Following our approach, we show that in non-equilibrium systems, structural stability can vary significantly across time. As a case study, we investigate the structural stability of a rocky intertidal community with dynamics at the edge of chaos. The structural stability of the community as a whole exhibited a clear seasonal pattern, despite the persistent chaotic dynamics of individual populations. Importantly, we show that this seasonal pattern of structural stability is causally driven by sea temperature. Overall, our approach provides novel opportunities for estimating the tolerance of ecological communities to environmental changes within a non-parametric framework.

Biogeographical zonation of rocky intertidal communities along the coast of Peru (3.5-13.5° S Southeast Pacific).

The biogeography of the Peruvian Eastern Pacific coast has been described based on oceanographic parameters and qualitative species occurrence data. This has generated disagreement about the limits and existence of different biogeographic units. In this study, the distribution of rocky-shore macrobenthic communities were recorded over 41 sites along the Peruvian coastline (3.5°S-13.5°S) and analyzed together with historic abiotic data in order to quantitatively evaluate the biogeographic zonation of rocky intertidal communities throughout the region and its relationship with environmental variables to propose an update bioregionalization. Clusters and non-metric multidimensional scaling were performed using Bray-Curtis dissimilarity matrices from abundance data to evaluate biogeographic patterns of dissimilarities of rocky-shore communities. Significant turnover of taxa among defined biogeographical units was tested using permutational multivariate dispersion. Relationships between of the biogeographical community’s structure and environmental factors were examined using Random Forest analysis on datasets available at Bio-Oracle and Jet Propulsion Laboratory—California Institute of Technology. Variation of community structure of 239 taxa depicted three biogeographical units along the region matching Panamic, transitional and Humboldt provinces. Beta diversity analysis indicated a significant turnover of taxa within the transitional unit. Random forest analysis showed a strong correlation between biogeographic units with phosphate, sea surface temperature, nitrate, dissolved oxygen, cloud fraction, and silicates. Our results set the putative limits of three biogeographic units for rocky-shore communities along the coast of Peru, providing base-line information for understanding further biogeographic changes on communities associated with the ongoing regional coastal cooling and impacts of El Niño events.

Assessment of spatial patterns in benthic macrofauna of the U.S. west coast continental shelf.

We assessed whether currently described marine biogeographic boundaries apply to shelf macrofauna and which environmental drivers were most associated with species differences among regions. Pacific coast of North America from the Strait of Juan de Fuca in Washington to the California-Mexico border. Van Veen grab samples were collected from soft sediment 28-138 m deep and sieved using 1 mm mesh. Spatial patterns of species richness, diversity, and abundance were examined in relation to latitude and environmental parameters (temperature, salinity, dissolved oxygen, sediment % fines, and total organic carbon). Analyses of latitudinal distribution patterns of individual species were combined with multivariate analyses of community composition to determine biogeographic and habitat boundaries for mid-depth continental shelf macrofauna. Species richness, diversity, and abundance significantly decreased with increasing latitude, primarily between 32 and 40° N. There were positive associations of richness, diversity (H'), and abundance with upwelling index, sediment % fines, and TOC (<2%). Temperature and DO also were significant for richness and H' but not abundance. Assessment of individual species ranges found major faunal transitions at latitudes 33-34°, 37°, 44°, and 46-47°. Major assemblage differences were found at 34.5°, and 42°. Within each latitudinal region, significantly different macrofauna communities were found in sediment with <5% fines. The biogeographic boundaries proposed under the Marine Ecoregions of the World schema are more closely aligned with shelf fauna distributions than those developed using west coast rocky intertidal communities. However, the proposed province boundary at Cape Mendocino is not apparent in the shelf macrofauna, and a transition appears to occur closer to the Oregon-California border. Further, the shelf macrofauna indicate the Channel Islands should be a separate subregion from mainland southern California Bight. Multivariate community analyses minimizing the impact of rare species appeared more useful in determining macrofaunal community biogeographic boundaries than analysis of individual species range endpoints, which are strongly influenced by uncommon species.

Impact of multiple disturbances and stress on the temporal trajectories and resilience of benthic intertidal communities

AbstractCoastal ecosystems face severe environmental change and anthropogenic pressures that affect both the structure and functioning of communities. Understanding the response and resilience of communities that face multiple simultaneous disturbances and stresses becomes essential. We observed the recovery of a rocky intertidal subarctic macrobenthic community dominated by a macroalgal canopy (Fucus spp.), a habitat‐forming species, over a period of 14 months. Using 0.25‐m2 plots, we ran an in situ one‐pulse experiment (removal of all materials to bare rock and then burning of the surface) followed by a full orthogonal factorial design of three press‐type disturbances or stresses: grazer reduction, canopy removal, and nutrient enrichment. We evaluated the single and interactive effects of the three disturbances and stresses on species diversity and abundance structure. Of all the main effects, canopy removal has the most severe impact, resulting in decreased biomass, richness, and diversity, as well as an altered community structure. Canopy‐removed plots had fewer invertebrates and more ephemeral algae; beyond this, however, there was minimal effect from grazer reduction and nutrient enrichment acting individually. We categorized the interaction types of all significant interaction effects: Canopy removal had a dominant effect over grazer reduction on richness, and it also dominated over nutrient enrichment on diversity and evenness. Nutrient enrichment and canopy removal had a negative synergistic interaction effect on richness at the end of the experiment. Without stressors, 11 months were required to achieve full recovery. The three stressors affected recovery time differently, depending on the identity and the number of stressors. Three stressors generally increased the time of recovery or even prevented recovery from being fully attained. Moreover, community structure and composition of plots subjected to the triple‐stressor treatment had not fully recovered by the end of the study. Our results suggest that multiple stressors may interact on community indices and structure and that their interaction cannot be predicted from the outcome of single stressor studies. The inclusion of multiple disturbances and stresses in field experiments provides a better understanding of the mechanisms that shape community structure and their functioning following various forms of disturbance.

Reduced tenacity during “high-speed” territorial encounters in the intertidal owl limpet, Lottia gigantea: Agonistic escalation increases risk of wash-off

The dislodging effect of breaking waves is among the critically important factors structuring rocky intertidal communities. Because behavior is so difficult to study in the field, the interaction of wave force with behavior of intertidal organisms is poorly understood. Here, we present a field study of the interaction of breaking waves with the natural behavior of individuals of Lottia gigantea, an intertidal limpet with a complex territorial behavioral ecology. We hypothesized that limpets engaging in fast-moving territorial chase in response to intraspecific contact are more vulnerable to wash-off by a passing wave than are slowly foraging limpets that do not take part in such chase. We measured the lift force required to dislodge limpets while they were engaged in three natural behavioral responses to intraspecific contact in the field: 1.) continued foraging, 2.) retreat, and 3.) territorial pursuit. We divided the measured force-to-remove by aperture area to estimate resistance to wave-induced lift force, or tenacity. Tenacity (Newtons·cm−2) in slowly foraging limpets was 2–4 times stronger than previously reported for moving limpets (retreating at high speed from sea stars). Small foraging limpets showed stronger tenacity than did large limpets. Tenacity was significantly reduced by high-speed territorial and retreat responses, especially in small limpets. We compounded the wash-off probabilities of tenacity during the expected number of high-speed chases in the face of an entire year of reported waves at a nearby ocean buoy, and estimated that limpets should suffer substantially greater mortality (11.5%) than do limpets that refrain from all territorial chase (2.9%). Overall, these data support our hypothesis that dislodgement by breaking waves comprises a significant risk attendant to territorial chase. The fact that limpets nevertheless engage in these chases suggests that the resources gained by this behavior are substantial.

Gastropod diversity at Pulau Punyit and the nearby shoreline – a reflection of Brunei’s vulnerable rocky intertidal communities

Pulau Punyit (PPUN), a small islet on the South China Sea coastline of Brunei Darussalam, represents a significant portion of the country’s natural rocky-shore ecosystem. We carried out a rapid survey of the intertidal gastropod species richness at PPUN, and compared this with species richness at other nearby natural and artificial rocky shores [Tungku Punyit (TPUN), Pantai Jerudong (PJER), Jerudong Park Medical Centre (JPMC) and Pantai Tungku (TUNK)]. A total of thirty two (32) species were collected from all of the shores. Species richness was greatest at the two natural shores studied (numbering 21 and 22 species at PPUN and TPUN, respectively), while the artificial shores were relatively depauperate. The natural shores however differed in species composition, abundance and body size of gastropods. These attributes varied with shore height, and appeared to relate to height-specific differences in abiotic stresses at the shores - at PPUN the high-shore is more exposed to the wind and sun, whereas at TPUN the mid-shore experiences greater sedimentation and mainland acidic seepage. Faunistic differences between the artificial and natural shores (Bray-Curtis similarity analysis) seemingly associate more closely with degree of habitat availability and abiotic stress than with shore proximity. We conclude that the country’s rocky intertidal biodiversity, as reflected by the gastropod diversity, is mainly constituted by the natural rocky shore system. Because this is spatially constrained and vulnerable to locality-specific environmental stresses, this diversity is threatened and deserving of greater protection status.

Benthic–pelagic coupling and bottom‐up forcing in rocky intertidal communities along the Atlantic Canadian coast

AbstractBenthic species from rocky intertidal systems are irregularly distributed along marine coastlines. Nearshore pelagic conditions often help to explain such variation, but most such studies have been done on eastern ocean boundary coasts. We investigated possible benthic–pelagic coupling along the Atlantic coast of Nova Scotia, a western ocean boundary coast. In 2014, we surveyed high‐intertidal habitats from nine wave‐exposed bedrock locations spanning 415 km of coastline. At each location in the spring, we measured the recruitment of barnacles and mussels, the two main filter‐feeders. Recruitment varied irregularly along the coast. Satellite data on coastal phytoplankton and particulate organic carbon (food for intertidal filter‐feeders and their pelagic larvae) and in‐situ data on sea surface temperature explained, to varying degrees, the geographic structure of recruitment. In turn, the summer abundance of barnacles and mussels was positively related to their spring recruitment. Ultimately, intertidal predator (dogwhelk) abundance was positively related to the recruitment and/or abundance of barnacles and mussels (the main prey of dogwhelks). Sea ice may also have influenced this predator–prey interaction. Drift ice leaving the Gulf of St. Lawrence in late winter strongly disturbed the northern surveyed locations, making barnacles (through high spring recruitment) the only food source for dogwhelks (which survived ice scour in crevices) in such places. Overall, this study supports the occurrence of benthic–pelagic coupling and bottom‐up forcing on this coast. Investigating the oceanographic drivers of pelagic food supply and seawater temperature should help to further understand how this large metacommunity is organized.

Biogeographic patterns of communities across diverse marine ecosystems in southern California

AbstractIntegrating results from monitoring efforts conducted across diverse marine ecosystems provides opportunities to reveal novel biogeographic patterns at larger spatial scales and among multiple taxonomic groups. We investigated large‐scale patterns of community similarity across major taxonomic groups (invertebrates, fishes or algae) from a range of marine ecosystems (rocky intertidal, sandy intertidal, kelp forest, shallow and deep soft‐bottom subtidal) in southern California. Because monitoring sites and methods varied among programs, site data were averaged over larger geographic regions to facilitate comparisons. For the majority of individual community types, locations that were geographically near or environmentally similar to one another tended to have more similar communities. However, our analysis found that this pattern of within community type similarity did not result in all pairs of these community types exhibiting high levels of cross‐community congruence. Rocky intertidal algae communities had high levels of congruence with the spatial patterns observed for almost all of the other (fish or invertebrate) community types. This was not surprising given algal distributions are known to be highly influenced by bottom‐up factors and they are important as food and habitat for marine fishes and invertebrates. However, relatively few pairwise comparisons of the spatial patterns between a fish community and an invertebrate community yielded significant correlations. These community types are generally comprised of assemblages of higher trophic level species, and additional ecological and anthropogenic factors may have altered their spatial patterns of community similarity. In most cases pairs of invertebrate community types and pairs of fish community types exhibited similar spatial patterns, although there were some notable exceptions. These findings have important implications for the design and interpretation of results of long‐term monitoring programs.

Are submarine groundwater discharges affecting the structure and physiological status of rocky intertidal communities?

This study evaluated the impacts of submarine groundwater discharges (SGD) on a rocky intertidal community of South Portugal, during April–November 2011. Chlorophyll-a concentration was higher at the SGD site in respect to the Reference site. Epibenthic community structure differed between sites, with an increase in Chthamalus spp. and a decrease in macroalgae coverage at the SGD site. The abundance and body size of Mytilus galloprovincialis were consistently higher at the SGD site. During mid-spring, under potentially higher SGD and less favorable conditions for coastal phytoplankton, the ecophysiological condition of M. galloprovincialis and G. umbilicalis was also higher at the SGD site. These beneficial effects on filter-feeders and herbivores probably resulted from local increases in prey availability, supported by SGD-driven nutrient inputs. Conversely, P. depressa was not favoured by SGD, probably due to a lower dependency on algae as food. The analysis of epibenthic community structure and ecophysiological condition represents a promising approach to disentangle the ecological impacts of SGD on intertidal ecosystems.

Fundamental contradictions among observational and experimental estimates of non-trophic species interactions.

The difficulty of experimentally quantifying non-trophic species interactions has long troubled ecologists. Increasingly, a new application of the classic "checkerboard distribution" approach is used to infer interactions by examining the pairwise frequency at which species are found to spatially co-occur. However, the link between spatial associations, as estimated from observational co-occurrence, and species interactions has not been tested. Here we used nine common statistical methods to estimate associations from surveys of rocky intertidal communities in the Northeast Pacific Ocean. We compared those inferred associations with a new data set of experimentally determined net and direct species interactions. Although association methods generated networks with aggregate structure similar to previously published interaction networks, each method detected a different set of species associations from the same data set. Moreover, although association methods generally performed better than a random model, associations rarely matched empirical net or direct species interactions, with high rates of false positives and true positives, and many false negatives. Our findings cast doubt on studies that equate species co-occurrences to species interactions and highlight a persistent, unanswered question: how do we interpret spatial patterns in communities? We suggest future research directions to unify the observational and experimental study of species interactions, and discuss the need for community standards and best practices in association analysis.

Characterizing the vulnerability of intertidal organisms in Olympic National Park to ocean acidification

Ocean acidification (OA) will have a predominately negative impact on marine animals sensitive to changes in carbonate chemistry. Coastal upwelling regions, such as the Northwest coast of North America, are likely among the first ecosystems to experience the effects of OA as these areas already experience high pH variability and naturally low pH extremes. Over the past decade, pH off the Olympic coast of Washington has declined an order of magnitude faster than predicted by accepted conservative climate change models. Resource managers are concerned about the potential loss of intertidal biodiversity likely to accompany OA, but as of yet, there are little pH sensitivity data available for the vast majority of taxa found on the Olympic coast. The intertidal zone of Olympic National Park is particularly understudied due to its remote wilderness setting, habitat complexity, and exceptional biodiversity. Recently developed methodological approaches address these challenges in determining organism vulnerability by utilizing experimental evidence and expert opinion. Here, we use such an approach to determine intertidal organism sensitivity to pH for over 700 marine invertebrate and algal species found on the Olympic coast. Our results reinforce OA vulnerability paradigms for intertidal taxa that build structures from calcium carbonate, but also introduce knowledge gaps for many understudied species. We furthermore use our assessment to identify how rocky intertidal communities at four long-term monitoring sites on the Olympic coast could be affected by OA given their community composition.

Herbivory enables marine communities to resist warming.

Climate change can influence ecosystems via both direct effects on individual organisms and indirect effects mediated by species interactions. However, we understand little about how these changes will ripple through ecosystems or whether there are particular ecological characteristics that might make ecosystems more susceptible-or more resistant-to warming. By combining in situ experimental warming with herbivore manipulations in a natural rocky intertidal community for over 16 months, we show that herbivory regulates the capacity of marine communities to resist warming. We found that limpet herbivores helped to preserve trophic and competitive interactions under experimental warming, dampening the impact of warming on overall community composition. The presence of limpets facilitated the survival of the main habitat modifier (barnacles) under warmer conditions, which, in turn, facilitated the presence of a consumer guild. When limpets were removed, environmental warming altered trophic, competitive, and facilitative interactions, with cascading impacts on community succession and stability. We conclude that conserving trophic structure and the integrity of interaction networks is vitally important as Earth continues to warm.

TAXONOMIC LEVEL NEEDED TO DETECT SIGNIFICANT CHANGES IN POLYCHAETE COMMUNITIES OVER DIFFERENT MACROPHYTE ASSEMBLAGES ON ROCKY INTERTIDAL SHORES

Environmental degradation has more significant impacts on rocky intertidal communities after global changes increase progressively. Thus, ecological monitoring should be conducted properly to analyse potential drivers and their impacts. However, most of the ecological monitoring in rocky intertidal shores is more interested in macroalgae. Polychaetes associated with macrophyte assemblages should be also involved in the monitoring because they are important in determining coastal health and productivity. A successful ecological monitoring should consider three factors: taxonomic level, statistical power, and sample size. In this study, those factors were analysed in the relationships between polychaetes and macrophytes. Four taxonomic levels of polychaetes (i.e. order, family, genus, species) were tested based on 25 samples collected from rocky intertidal shores of Gunung Kidul, Yogyakarta, Indonesia. Relationships between each of taxonomic richness of polychaetes and each of macrophytes variables (i.e. species richness, biomass, species composition) were analysed using a Generalised Linear Models fitted by Poisson Distribution and log link. The statistical power of those relationships and the sample size needed to obtain a strong statistical power (&gt;0.8) were also recorded. Relationships between each of taxonomic composition of polychaetes and each of macrophyte variables were analysed using a distance-based Redundancy Analysis based on Bray-Curtis dissimilarity on log(x+1) transformed abundance data with 999 permutations. Results showed that family-based data analysis was sufficient to detect significant relationships between polychaetes and macrophytes. However, the statistical power of most relationships was relatively weak (&lt;0.8). Hence, the family-based data analysis should select a 44-sample size to gain significant relationships with a strong statistical power.

Planktonic Subsidies to Surf-Zone and Intertidal Communities.

Plankton are transported onshore, providing subsidies of food and new recruits to surf-zone and intertidal communities. The transport of plankton to the surf zone is influenced by wind, wave, and tidal forcing, and whether they enter the surf zone depends on alongshore variation in surf-zone hydrodynamics caused by the interaction of breaking waves with coastal morphology. Areas with gently sloping shores and wide surf zones typically have orders-of-magnitude-higher concentrations of plankton in the surf zone and dense larval settlement in intertidal communities because of the presence of bathymetric rip currents, which are absent in areas with steep shores and narrow surf zones. These striking differences in subsidies have profound consequences; areas with greater subsidies support more productive surf-zone communities and possibly more productive rocky intertidal communities. Recognition of the importance of spatial subsidies for rocky community dynamics has recently advanced ecological theory, and incorporating surf-zone hydrodynamics would be an especially fruitful line of investigation.

Altering species interactions outweighs the effects of experimental warming in structuring a rocky shore community

The strength and direction of interspecific interactions governing communities is expected to change with increasing global temperatures. However, in many ecosystems it remains unclear which species interactions are most likely to be altered under increasing thermal stress and what impacts, if any, such altered interactions will have on community structure. We investigated the interactive effects of increased temperature and altered species interactions on the structure of a rocky intertidal community by deploying black and white plates in areas with or without the dominant grazer, the limpet Cellana tramoserica. Plates effectively manipulated substratum temperature, whilst anti-fouling paint effectively manipulated the strength of algal-herbivore interactions. Plates without C. tramoserica quickly developed and maintained abundant macroalgal assemblages irrespective of thermal stress. By contrast, the abundance of barnacles remained relatively low and did not differ across thermal treatments, although they were slightly more abundant in plots where C. tramoserica had been excluded. These results support recent findings that altered species interactions are anticipated to have greater effects on community structure than the direct impacts of warming, challenging the view community structure under warming climatic conditions can be predicted from individual responses of populations to increasing thermal stress. Based on these and other recent findings we therefore advocate for greater inclusion of biotic interactions into climate change models that aim to predict the state of future ecological communities.

Stoichiometric Mismatch between Consumers and Resources Mediates the Growth of Rocky Intertidal Suspension Feeders.

The concept of ecological stoichiometry—the balancing of elemental ratios in ecological interactions—has transformed our thinking about processes in natural systems. Here, this perspective is applied to rocky shore ecosystems to explore the consequences of variation in internal nutrient ratios across two trophic levels. Specifically, I measured the internal concentrations of carbon (C) and nitrogen (N) in mussels (Mytilus spp.) and particulate organic matter (POM) to evaluate the effects of stoichiometric mismatch—the difference in the carbon-to-nitrogen ratio (C:N) between a consumer and its resources—on mussel growth at sites on the coasts of Oregon, USA, and the South Island of New Zealand. As POM quality (i.e., Chl a, a proxy for phytoplankton availability in the POM) increased, C:N of the POM declined, but C:N of mussels increased. This resulted in a greater mismatch in C:N between mussels and their food source at low Chl a. Mussel growth across sites was positively associated with Chl a, particulate organic carbon (POC), and particulate organic nitrogen (PON) but negatively associated with stoichiometric mismatch. Overall, as the elemental ratios of consumers became more different from those of their resources, growth declined, likely due to the energetic cost associated with processing lower quality food. Furthermore, the effect of food quantity on growth depended on stoichiometric mismatch. In New Zealand, where mismatch was high—i.e., consumer C:N differed substantially from resource C:N—consumer growth was strongly affected by resource quantity (Chl a or POC). However, in Oregon, where mismatch was low, the relationship between resource quantity and growth was considerably weaker. This interaction between resource quantity and mismatch was not apparent for PON, which is consistent with variation in PON underlying variation in POM C:N and highlights the role of N in limiting growth. Previous research has neglected the importance of ecological stoichiometry as a mediator of consumer-resource interactions in rocky intertidal communities. I show that resource quality and quantity interact to determine consumer growth, highlighting the utility of ecological stoichiometry in understanding spatial subsidies in benthic marine systems.

General spatial spectral variation in rocky intertidal communities from three biogeographical regions

Aim Understanding general spatial patterns of multiple species is a central aim of biogeography. Spatial analyses of coastal marine assemblages have shown an emergent pattern in that the variability in population abundances increases with increasing spatial scale of observation; i.e. a “red” spectrum of variation in population abundances. However, the generalization of these patterns to other ecological levels and across biogeographical regions remains unexplored. Here, we evaluate the consistency of a reddened relationship between the scale of observation and the variance in ecosystem properties in sessile intertidal rocky-shore assemblages across three biogeographical regions. Location Replicate sites located in temperate (southern-central Chile), sub-Antarctic (Chilean South Patagonia) and Antarctic (West Antarctic Peninsula) regions. Methods A total of 16,225 photo-quadrants were used to analyse local patterns of total community cover, bare substratum, total algal cover and total invertebrate cover. We used spectral analyses in which the spatial variance of each property was decomposed along a gradient of increasing distances between observations. Cross-semivariograms were used to analyse the spatial covariation of dominant taxa. Results The analysed ecosystem properties showed a general reddened spectrum of variation that resembled patchy configurations of local communities. Additionally, cross-semivariance analyses indicated mainly negative relationships of covariation between the abundances dominant sessile species at each site, suggesting a general trend of spatial asynchrony between competing species. Main conclusions To the best of our knowledge, this is the first study showing a general reddened pattern of spatial variation in relevant ecosystem-level properties across the Pacific shore of South America, southern Patagonia and West Antarctic Peninsula. These patterns reflect the result of multiple biotic and abiotic processes that interact across spatial scales. In particular, we suggest that processes that generate spatial asynchrony between competing species, such as compensatory dynamics, are relevant to maintain the spatial structure of rocky-shore communities.

Anthopleura and the phylogeny of Actinioidea (Cnidaria: Anthozoa: Actiniaria)

Members of the sea anemone genus Anthopleura are familiar constituents of rocky intertidal communities. Despite its familiarity and the number of studies that use its members to understand ecological or biological phenomena, the diversity and phylogeny of this group are poorly understood. Many of the taxonomic and phylogenetic problems stem from problems with the documentation and interpretation of acrorhagi and verrucae, the two features that are used to recognize members of Anthopleura. These anatomical features have a broad distribution within the superfamily Actinioidea, and their occurrence and exclusivity are not clear. We use DNA sequences from the nucleus and mitochondrion and cladistic analysis of verrucae and acrorhagi to test the monophyly of Anthopleura and to evaluate the pattern of distribution of acrorhagi and verrucae. We find that Anthopleura is paraphyletic: although species of the genus cluster together, some groups also include members of genera like Bunodosoma, Aulactinia, Oulactis, and Actinia. This paraphyly is explained in part by the discovery that acrorhagi and verrucae are pleisiomorphic for the subset of Actinioidea studied.