Natural Rocky Shores Research Articles

Can Rock-Rubble Groynes Support Similar Intertidal Ecological Communities to Natural Rocky Shores?

Despite the global implementation of rock-rubble groyne structures, there is limited research investigating their ecology, much less than for other artificial coastal structures. Here we compare the intertidal ecology of urban (or semi-urban) rock-rubble groynes and more rural natural rocky shores for three areas of the UK coastline. We collected richness and abundance data for 771 quadrats across three counties, finding a total of 81 species, with 48 species on the groynes and 71 species on the natural rocky shores. We performed three-way analysis of variance (ANOVA) on both richness and abundance data, running parallel analysis for rock and rock-pool habitats. We also performed detrended correspondence analysis on all species to identify patterns in community structure. On rock surfaces, we found similar richness and abundance across structures for algae, higher diversity and abundance for lichen and mobile animals on natural shores, and higher numbers of sessile animals on groynes. Rock-pool habitats were depauperate on groynes for all species groups except for sessile animals, relative to natural shores. Only a slight differentiation between groyne and natural shore communities was observed, while groynes supported higher abundances of some ‘at risk’ species than natural shores. Furthermore, groynes did not differ substantially from natural shores in terms of their presence and abundance of species not native to the area. We conclude that groynes host similar ecological communities to those found on natural shores, but differences do exist, particularly with respect to rock-pool habitats.

Occurrence and assemblage composition of intertidal non-native species may be influenced by shipping patterns and artificial structures

Habitat modification coupled with the spread of non-native species (NNS) are among the top threats to marine biodiversity globally. Species are known to be transported to new locations via international shipping and secondarily spread via regional vessels and artificial structures. Rapid Assessment Surveys (RAS) combining quantitative and semi-quantitative methods compared NNS richness and assemblage composition on intertidal natural rocky shores and artificial structures in harbours in different regions along the south coast of England. Quantitative data showed that artificial habitats supported higher richness than natural habitats, while semi-quantitative data found no difference in richness among habitat types. This result was attributed to additional species found in rock pools during searches of complex microhabitats in natural habitats. Assemblages on artificial structures differed among regions, with regions and harbours with greater numbers of vessels supporting greater richness. Results highlight the importance of shipping and artificial structures for NNS introduction and spread.

Do artificial structures affect the diet of the limpet Patella caerulea Linnaeus, 1758?

The current scenario of global change and the increase of human population in coastal areas is leading to the introduction of numerous man-made structures into the coastal environment. Those artificial structures provide different services at the expenses of habitat loss and a range of widely documented ecological impacts. Limpets are keystone species that are worldwide established in these artificial habitats. However, little is known about the impact of artificial coastal defence structures on the diet of limpets. Therefore, the aim of this study was to evaluate if different kinds of artificial structures (cubes, rip-raps, seawalls and tetrapods) across a geographical gradient (western to eastern Alboran Sea), could affect the food consumption of the limpet Patella caerulea by using carbon and nitrogen isotopes analysis. Our results suggested that for certain localities, there was a shift in the trophic niche of P. caerulea inhabiting artificial substrates in comparison with the nearest natural rocky shore. However, patterns were not consistent for all localities and different types of artificial structures, which reinforces the importance of considering local scales for conservation and management purposes. Finally, δ15N ratio in P. caerulea is a good indicator of eutrophication at regional scales, by showing a gradient of enrichment in the limpet tissues from oligotrophic to eutrophic waters within the Alboran Sea.

Distribution patterns of two co-existing oyster species in the northern Adriatic Sea: The native European flat oyster Ostrea edulis and the non-native Pacific oyster Magallana gigas

Abstract The Pacific oyster Magallana gigas, globally one of the most translocated marine species, has never been commercially farmed in any part of the Croatian eastern Adriatic Sea, where the native flat oyster Ostrea edulis is the only cultured oyster species. The Pacific oyster has, however, established populations on the west coast of the Istria peninsula, in the northeast Adriatic Sea. Current distribution, abundance and size structure of the flat and Pacific oysters were studied there along spatial and depth gradients in natural and artificial habitats to assess their potential for coexistence. This is the first quantitative assessment of native and non-native oyster populations on a Mediterranean-wide scale providing a baseline for determining future changes in their distribution. Both species were omnipresent, with the Pacific oyster displaying a more pronounced variability in abundance and size in relation to survey regions and depths. The population density of flat oysters was low, generally less than 1 individual/m2, with no difference among regions. The density of the Pacific oyster was significantly higher, being on average 5 individuals/m2. Dense, reef-forming aggregations of Pacific oysters were contained in Lim Bay, a nationally-important shellfish aquaculture area, where its mean density was 107 individuals/m2. Along the open coastline its densities were considerably lower and followed a latitudinal gradient. The observed abundance and size distribution patterns of the Pacific oyster suggest that Lim Bay was the introduction point, with feral settlement likely originating from short-lived experimental aquaculture trials and subsequently dispersing by prevailing local currents. The flat oysters were larger in size and settled at different depths compared to the Pacific oysters. The vertical range of Pacific oysters was mostly contained in the tidal zone, while flat oysters were present in the subtidal exclusively. Such spatial partitioning likely resulted from introduced oysters occupying a vacant ecological niche and not due to interspecific competitive exclusion. Habitat type had a strong effect on proliferation of Pacific oysters. Artificial hard substrata harboured more abundant and larger Pacific oysters than the natural rocky shore habitat. The possibility of multiple local introduction pathways in ports and marinas is also discussed. Currently, there seems to be no spatial competition between the two oyster species, but as it is hard to predict future possible impacts of non-native species, we strongly suggest regular monitoring of the Pacific oyster, prioritising sensitive and protected areas as well as areas at the edge of its distribution.

Shelving the Coast With Vertipools: Retrofitting Artificial Rock Pools on Coastal Structures as Mitigation for Coastal Squeeze

Coastal squeeze caused by sea level rise threatens the size, type and quality of intertidal habitats. Along coastlines protected by hard defences, there is a risk that natural rocky shore habitat will be lost, with remaining assemblages characteristic of hard substrata confined to sea walls and breakwaters. These assemblages are likely to be less diverse and different to those found on natural shores as these structures lack features that provide moist refugia required by many organisms at low tide, such as pools and crevices. Engineering solutions can help mitigate the impacts of sea level rise by creating habitats that retain water on existing structures. However, as experimental trials are strongly affected by local conditions and motivations, the development of new techniques and solutions are important to meet the needs of local communities and developers. Following a small scale community project, a feasibility study retrofitted five concrete-cast artificial rock pools (‘Vertipools’) on to a vertical seawall on the south coast of England. After 5 years, the artificial pools increased the species richness of the sea wall and attracted mobile fauna previously absent, including fish and crabs. The Vertipools had assemblages which supported several functional groups including predators and grazers. Although disturbance of algal assemblages on the seawall from the retrofitting process was still evident after 3 years, succession to full canopy cover was underway. Collaboration between policy makers, ecologists, children and artists produced an ecologically sensitive design that delivered substantial benefits for biodiversity and that could be adapted and scaled-up to both mitigate habitat loss and enhance coastal recreational amenity.

The microbiome and biodiversity hypothesis of health

Artificial structures are agents of change in marine ecosystems. They add novel habitat for hard-substrate organisms and modify the surrounding environment. Most research to date has focused on the communities living directly on artificial structures, and more research is needed on the potential impacts these structures have on nearby communities and the surrounding environment. We compared the sedimentary habitat surrounding two types of artificial structures (pilings and seawalls) to sediments adjacent to rocky reefs using a combination of traditional sediment analyses, stable isotope analysis, and environmental DNA. Artificial and natural shore sediments were best differentiated by sediment variables strongly associated with flow speed. Pilings sediments had significantly finer grain size, higher organic content, and generally lower C:N ratios than sediments adjacent to the other habitat types, suggesting flow is reduced by pilings. Sedimentary assemblages near pilings were also consistent with those predicted under low-flow conditions, with elevated bacterial colonization and increased relative abundances of small deposit feeders compared with other habitat types. Additionally, lumbrinerid polychaetes in pilings sediments had reduced δ15N values, suggesting different detrital resources and fewer trophic linkages compared with lumbrinerids in other habitats. Woody detritus was greater adjacent to seawalls than to natural rocky shores or pilings. Our findings suggest that artificial structures have the potential to influence adjacent soft sediments through changes to sediment properties that affect infaunal and microbial communities, as well as trophic linkages for some consumers. We hypothesize that this is due to a combination of altered flow, differing detrital subsidies, and differing adjacent land-use among habitat types. Managers should consider the potential for changed sediment properties and ecology when deciding where to build different types of artificial structures. Further manipulative experiments are needed to understand mechanisms of change and help manage the impacts of artificial structures on the seafloor.

Scan Line Intensity-Elevation Ratio (SLIER): An Airborne LiDAR Ratio Index for Automatic Water Surface Mapping

Owing to the characteristics of how a laser interacts with the water surface and water column, the measured Light Detection and Ranging (LiDAR) intensity values are different with respect to the laser wavelength, the scanning geometry and the reflection mechanism. Depending on the instantaneous water condition and the laser incidence angle, laser dropouts can appear, causing null returns or empty holes found in the collected LiDAR data. This variable intensity response offers a valuable opportunity for using airborne LiDAR sensors for automatic identification of water regions, and thus, we previously proposed an airborne LiDAR-based ratio index named the scan line intensity-elevation ratio (SLIER). Over the water surface, airborne LiDAR data are always found to have a high fluctuation of the intensity value and low variation of the elevation along each scan line, and thus, the water region has a higher SLIER value compared to the land. We examined the SLIER on a multispectral airborne LiDAR dataset collected by Optech Titan and a monochromatic airborne LiDAR dataset collected by Optech Galaxy on a natural rocky shore and a man-made shore. Our experiments showed that SLIER was able to provide a high separability between land and water regions and was able to outperform the traditional normalized difference water index (NDWI) for estimation of the water surface. With the use of SLIER as a mechanism for training data selection, our case studies demonstrated an overall accuracy of 98% in the use of either monochromatic or multispectral LiDAR data, regardless of the laser channel being used.

Distance from rocky shores affects infaunal recolonization in a subtropical tidal flat

Hard bottoms can negatively affect the surrounding infauna by hosting predatory fauna and modifying local hydrodynamics and sedimentation rates. Considering that these effects depend on the distance to the hard bottoms, we expected that the infaunal structure and recolonization would change accordingly. We assessed whether the distance from a rocky shore alters infaunal recolonization in a subtropical tidal flat. Sediment was defaunated on sites near and far from a rocky shore and the subsequent faunal recolonization was followed for 40 days. The sites near and far from the rocky shore displayed different assemblage structures, which we attributed to local variation in hydrodynamic conditions. Both the total infaunal abundance and the abundance of the dominant species recovered faster at the near site. We indicate that changes in infaunal recolonization at varying distances from natural rocky shores are primarily driven by the availability of adults. Infaunal recovery took less than 2 weeks, but recolonization rates increased near the rocky shore, as a function of its naturally variable assemblage structure and relatively lower species richness and abundances. We suggest that models of infaunal distribution and recolonization should incorporate landscape features such as the presence and distance from rocky bottoms.

Do artificial structures affect the feed of Patella caerulea limpets?

Do artificial structures affect the feed of Patella caerulea limpets?

Patchiness in habitat distribution can enhance biological diversity of coastal engineering structures

Abstract Urbanization of coastal habitats is increasing worldwide. However, most man‐made structures are poor surrogates for the habitats they replace and can strongly impact the diversity and functioning of coastal habitats. The value of coastal engineering can be enhanced by the provision of microhabitats that facilitate colonization by marine life. One step forward is moved in this research by combining species coexistence theory, resource patchiness and applied ecology in order to find ways that maximize the biological diversity of coastal defence structures. Featureless areas of a seawall were modified by the addition of microhabitats (resource) that were distributed in different configurations of patchiness. Gastropod diversity peaked at intermediate levels of microhabitat patchiness. This appeared to be driven by different patterns of resource use among species. Gastropods dispersed longer distances on unmodified seawalls than on natural rocky shores, but when microhabitats were added the dispersal decreased. The ability to find microhabitats differed among species. Our results confirm that patchiness in microhabitat distribution affects biodiversity. The extent of microhabitat patchiness could potentially be tailored by coastal engineers to meet specific conservation priorities: increasing diversity versus increasing number of individuals.

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.

CARACTERIZAÇÃO DA MACROFAUNA DE SUBSTRATOS CONSOLIDADOS DO LITORAL NORTE DO RIO GRANDE DO SUL, BRASIL

Este trabalho teve como objetivo realizar um levantamento qualitativo e descrever a zonação dos organismos incrustantes, sedentários e vágeis em diferentes substratos consolidados na costa norte do Rio Grande do Sul (RS), Brasil, contribuindo para o conhecimento da biodiversidade subtropical marinha. Os registros das espécies foram feitos através de consulta à literatura específica e também através de observações e coletas mensais em substratos consolidados naturais (costão rochoso) e artificiais (molhes, plataformas, monoboias) de março de 2010 a junho de 2011, totalizando 16 meses. Obteve-se o registo de 160 espécies de invertebrados associados a substratos consolidados para o RS através da literatura e 83 espécies a partir do levantamento de campo, sendo que 42,2 % das espécies foram registradas no costão rochoso da Praia do Meio, Torres; 24,1 % nos molhes de Imbé-Tramandaí e Torres; 45,8 % nos pilares das plataformas de pesca de Cidreira, Tramandaí e Atlântida e 72,3 % na estrutura das monoboias de oleoduto, MN601 e MN-602 de Tramandaí. Sobre a ocorrência exclusiva de espécies, verificaram-se maiores valores para as monoboias, seguida das plataformas de pesca, costão rochoso e molhes. Quanto a novos registros, 34 táxons ainda não haviam sido citados para RS.

Not all artificial structures are created equal: Pilings linked to greater ecological and environmental change in sediment communities than seawalls

Artificial structures are agents of change in marine ecosystems. They add novel habitat for hard-substrate organisms and modify the surrounding environment. Most research to date has focused on the communities living directly on artificial structures, and more research is needed on the potential impacts these structures have on nearby communities and the surrounding environment. We compared the sedimentary habitat surrounding two types of artificial structures (pilings and seawalls) to sediments adjacent to rocky reefs using a combination of traditional sediment analyses, stable isotope analysis, and environmental DNA. Artificial and natural shore sediments were best differentiated by sediment variables strongly associated with flow speed. Pilings sediments had significantly finer grain size, higher organic content, and generally lower C:N ratios than sediments adjacent to the other habitat types, suggesting flow is reduced by pilings. Sedimentary assemblages near pilings were also consistent with those predicted under low-flow conditions, with elevated bacterial colonization and increased relative abundances of small deposit feeders compared with other habitat types. Additionally, lumbrinerid polychaetes in pilings sediments had reduced δ15N values, suggesting different detrital resources and fewer trophic linkages compared with lumbrinerids in other habitats. Woody detritus was greater adjacent to seawalls than to natural rocky shores or pilings. Our findings suggest that artificial structures have the potential to influence adjacent soft sediments through changes to sediment properties that affect infaunal and microbial communities, as well as trophic linkages for some consumers. We hypothesize that this is due to a combination of altered flow, differing detrital subsidies, and differing adjacent land-use among habitat types. Managers should consider the potential for changed sediment properties and ecology when deciding where to build different types of artificial structures. Further manipulative experiments are needed to understand mechanisms of change and help manage the impacts of artificial structures on the seafloor.

Learning from nature to enhance Blue engineering of marine infrastructure

The global sprawl of urban centres is replacing complex natural habitats with relatively flat and featureless infrastructure that supports low biodiversity. In a growing countermovement, artificial microhabitats are increasingly incorporated into designs for “Green” and “Blue” infrastructure. In order to maximise the ecological value of such interventions, we need to inform the designs with observations from natural systems and existing Green and Blue infrastructure. Here, we focussed on water retaining features mimicking intertidal rock pools, as this is a widely used intervention in coastal ecosystems. Using a meta-analysis and a qualitative literature review, we compiled information on diversity and function of rock pools on natural rocky shores and built structures to assess the potential ecological benefits of water retaining microhabitats and the design metrics of rock pools that affect diversity and function. Our meta-analysis showed higher species richness in rock pools compared to emergent surfaces on built structures, but this was variable among locations. The qualitative review revealed that rock pools on both natural and artificial shores generally hosted species that were not present on emergent rock and can also host non-indigenous species, suggesting that the addition of these features can sometimes have unwanted consequences and local ecological knowledge is essential to implement successful interventions. Relationships between species richness and design metrics, such as height on shore, volume, surface area and depth of pool were taxa-specific. For example, results from the meta-analysis suggest that building larger, deeper pools could increase diversity of fish, but not benthic organisms. Finally, this study highlights major gaps in our understanding of how the addition of rock pools and design metrics influence diversity and the variables affecting the ecological functioning of rock pools. Based on the knowledge gathered so far, recommendations for managers are made and the need for future studies to add knowledge to expand these recommendations is discussed.

Functional and structural responses to marine urbanisation

Urban areas have broad ecological footprints with complex impacts on natural systems. In coastal areas, growing populations are advancing their urban footprint into the ocean through the construction of seawalls and other built infrastructure. While we have some understanding of how urbanisation might drive functional change in terrestrial ecosystems, coastal systems have been largely overlooked. This study is one of the first to directly assess how changes in diversity relate to changes in ecosystem properties and functions (e.g. productivity, filtration rates) of artificial and natural habitats in one of the largest urbanised estuaries in the world, Sydney Harbour. We complemented our surveys with an extensive literature search. We found large and important differences in the community structure and function between artificial and natural coastal habitats. However, differences in diversity and abundance of organisms do not necessarily match observed functional changes. The abundance and composition of important functional groups differed among habitats with rocky shores having 40% and 70% more grazers than seawalls or pilings, respectively. In contrast, scavengers were approximately 8 times more abundant on seawalls than on pilings or rocky shores and algae were more diverse on natural rocky shores and seawalls than on pilings. Our results confirm previous findings in the literature. Oysters were more abundant on pilings than on rocky shores, but were also smaller. Interestingly, these differences in oyster populations did not affect in situ filtration rates between habitats. Seawalls were the most invaded habitats while pilings supported greater secondary productivity than other habitats. This study highlights the complexity of the diversity-function relationship and responses to ocean sprawl in coastal systems. Importantly, we showed that functional properties should be considered independently from structural change if we are to design and manage artificial habitats in ways to maximise the services provided by urban coastal systems and minimise their ecological impacts.

Can coir increase native biodiversity and reduce colonisation of non-indigenous species in eco-engineered rock pools?

The expansion of built infrastructure in the marine environment threatens natural ecological communities at local and regional scales. An increasing interest in incorporating heterogeneity that is reflective of natural rocky shores into artificial structures through ecological engineering seeks to mitigate negative impacts. The addition of complex surfaces and novel habitats, such as water-retaining features, has been particularly successful at increasing biodiversity of marine infrastructures to date. Importantly, key habitat-forming groups, such as the complex turfing algae Corallina officinalis found on natural shores and their associated assemblages are still lacking from these eco-engineered features. Furthermore, whether observed biodiversity increases from eco-engineering are due to native or non-indigenous species remains largely unknown. Here, we investigated whether adding small-scale complexity (artificial turf) to artificial rock-pools (‘flowerpots’) on urban seawalls enhanced their effectiveness to increase native biodiversity. Responses of benthic invertebrates, algae, epifauna and fish in flowerpots with and without artificial turf (coir) were quantified. Contrary to existing literature, which reports an increase in biodiversity with an increase in complexity, no consistent effect of coir was seen on benthic, epifaunal or fish assemblages. Native species consistently occupied more than 95% of space in flowerpots while the proportion of non-indigenous species in flowerpots was small (<75% of the assemblage) regardless of treatment, and decreased over time. This result is promising, but warrants further investigation to determine if these trends reflect seasonal patterns or if non-indigenous species colonise early, but are replaced over time by native species. These are important considerations when planning large-scale deployments of eco-engineering features on seawalls to ensure that native species are targeted without increasing opportunities for non-indigenous species.

The consequences of small-scale variations in habitat conditions driven by a floating marina on reef fish assemblages of SE Brazil

Marine constructions modify physical conditions by interfering with water circulation and increasing sedimentation and pollution, leading to biological homogenization. However, they also increase the availability of hard substrata for larval recruitment, resulting in the development of a diverse sessile community and associated fish fauna. To describe how the modifications caused by a floating marina affect reef fish assemblages at São Sebastião Channel, SW Atlantic, a multiparameter probe and a visual census methodology were used to compare the abiotic conditions and the diversity and abundance of fishes between two areas: the area inside the marina where boats are moored and the breakwater, an area more similar to nearby natural rocky shores. The area inside the marina presented more turbid and productive waters, while the breakwater was more turbulent. The abundance of fishes inside the marina was greater than at the breakwater throughout the study, but species richness was higher inside the marina only during the hot and wet period (Austral Summer and Spring). Fish assemblages were strictly different between areas. Species dominance for each area and at nearby natural rocky reefs was also different. This study shows that artificial habitat causes micro-spatial modifications to local fish assemblages. As spatial variations were related to the behavioural and ecological aspects of fishes, marine facilities should be carefully planned, and engineering principles should be combined with ecological processes to better resemble natural habitats, thereby reducing environmental impacts.

Seasonal variation of peracarid assemblages in natural and artificial marine environments of the Southwestern Atlantic Ocean

The diversity and seasonal variations of two assemblages of marine benthic peracarids were studied between a natural rocky shore and an artificial harbour area over a 12-month period. Samples were obtained monthly in La Estafeta, a rocky intertidal zone with low human impact, and Mar del Plata Harbour, a polluted environment, between March 2011 and March 2012. The two sites differed markedly in the composition and abundance of species across all seasons: the tanaid Tanais dulongii was most abundant in La Estafeta rocky shore, followed by the amphipods Monocorophium acherusicum, Hyale grandicornis, Ampithoe valida, the isopod Idotea balthica, the tanaid Leptochelia sp. and the isopod Sphaeroma serratum. In contrast, M. acherusicum was most abundant in the harbour area, followed by T. dulongii, S. serratum, Ericthonius punctatus, I. balthica, Caprella equilibra and C. dilatata. Total density of peracarids varied between months in La Estafeta rocky shore and Mar del Plata Harbour. In La Estafeta rocky shore mean density increased from March to May 2011 (autumn in the southern hemisphere; ca. 45,000 ind/m2), decreased sharply until August and then increased in January 2012. In Mar del Plata Harbour the mean density was lower from March to October (ca. 500,000 ind/m3), then increased and reached a maximum in January 2012 (more than 1,500,000 ind/m3), and decreased until the following March. This study suggests that the differences in peracarid assemblages, diversity and seasonality could be related to an effect of temperature, but we should not rule out a synergistic effect of other factors, such as pollution, food availability and hydrodynamic factors.

Of Rocks and Hard Places: Comparing Biotic Assemblages on Concrete Jetties versus Natural Rock along a Microtidal Mediterranean Shore

ABSTRACT Bonnici, L.; Borg, J.A.; Evans, J.; Lanfranco, S., and Schembri, P.J., 2018. Of rocks and hard places: Comparing biotic assemblages on concrete jetties versus natural rock along a microtidal Mediterranean shore. The species composition and structure of littoral assemblages on concrete jetties were compared with those on natural rocky shores at two localities on the microtidal NE coast of Malta. Algal species richness and total algal biomass were significantly lower on jetties. Faunal species richness and faunal abundance were also lower on jetties, albeit not significantly so. Jetties and natural rocky shores differed in relative species composition. The algae Palisada perforata/Laurencia obtusa and several mobile animals, mostly crustaceans, molluscs, and polychaetes, were more abundant on rocky shores. In particular, the supralittoral gastropod Melarhaphe neritoides had a density ranging between 8 ind./m2 to 98 ind./m2 on rocky shores but was never recorded on jetties. Conversely, the algae Cla...

Room for one more? Coexistence of native and non-indigenous barnacle species

Space can be a limiting factor in intertidal communities and competition for this resource plays a role in determining community composition. Invasive species are known to be opportunistic, and are capable of rapidly colonising free space. Since its introduction to Europe, over 70 years ago, the invasive barnacle species, Austrominius (=Elminius) modestus has become widespread on European coasts and is now the dominant barnacle species at numerous locations. However, little is known about its competitive interactions with native barnacle species. During this study, 18 removal plots (25 cm2) were created at each of six sites in south-west Ireland, encompassing a range of exposure levels and including both artificial structures and natural rocky shores. Monthly monitoring of these plots over 19 months revealed that, despite high recruitment of native species seasonally, A. modestus ultimately outnumbered natives in removal plots at four sites. With the provision of free space, the invasive species increased its relative abundance at three sites, but did not entirely displace natives at any site. Continued recruitment of the native species at high abundances on a seasonal basis in addition to the invasive species not entirely colonising all available space, ensure native species can persist and co-exist with A. modestus at the majority of sites at this location.