Intertidal Habitats Research Articles

Outwelling of reduced porewater drives the biogeochemistry of dissolved organic matter and trace metals in a major mangrove‐fringed estuary in Amazonia

AbstractMangrove‐fringed estuaries are intertidal ecosystems discharging significant amounts of dissolved organic matter (DOM) into coastal oceans. DOM in these ecosystems is derived from autochthonous production, fluvial input, and mangrove porewater outwelling; however, differentiating between these sources remains challenging. Our incomplete understanding of the biogeochemical factors controlling DOM dynamics and its relationship with nutrient and trace metal cycling still hinders the formulation of elemental budgets in coastal environments. Here, we relate the DOM composition in a mangrove‐fringed estuary in North Brazil (Amazonia) to the redox conditions at the formation sites. We combined molecular DOM analyses via ultrahigh‐resolution mass spectrometry (FT‐ICR‐MS) with parallel factor analysis of excitation–emission fluorescence matrices (EEM‐PARAFAC), nutrient and redox‐sensitive trace metal analyses. During low tide, the influx of oxygen‐depleted porewater carried terrigenous DOM, inorganic nutrients, and trace metals into the mangrove‐fringed creeks. Precipitation of metal(hydr)oxides and microbial turnover controlled nutrient and trace metal dynamics in the estuary. The highest inorganic nitrogen concentrations within the upper mangrove‐fringed estuary indicated outwelling from mangrove sediments as an essential source. Phosphate concentrations were highest within the lower mangrove‐fringed estuary, where available phosphate likely exceeded precipitation with iron(hydr)oxides. We tracked the DOM transport to the coastal ocean using a novel molecular index derived from sulfidic porewater (ISuP). Outwelling of recalcitrant DOM from mangrove habitats is relevant in the context of blue carbon storage. Therefore, applying our molecular proxy (ISuP), together with trace‐metal and optical DOM analyses, is a powerful approach for differentiating contributions of diverse DOM sources in highly complex coastal ecosystems.

Evaluating the biocompatibility of ceramic materials for constructing artificial reefs

IntroductionCoastal ecosystems, including reefs, are becoming increasingly threatened as anthropogenic development continues to encroach on intertidal habitats with little initiative to establish ecologically considerate infrastructure. Submerging human-made, shelter-providing structures known as artificial reefs (AR) can contribute to the preservation of these ecosystems. ARs are historically used for promoting the abundance and biodiversity of marine species for aquaculture, conservation, and ecotourism; and are typically made of concretes or metal structures. An AR’s success correlates to its ability to establish a surface layer of microorganisms, such as microalgae and bacteria, known as a biofilm. The productivity of the biofilm can be influenced by material surface properties. It is hypothesized that material pH and porosity affect the rate of biofilm formation.MethodsHere - a range of concrete mixtures were cast and submerged in circulating seawater and mass per surface area of biofilm accumulation was measured to evaluate this theory. These mixtures included standard Portland Cement (PC), PC with admixtures of diatomaceous earth (PDC) and limestone (PLC), fine-aggregate high-performance concrete (DUC), and terra cotta (TER). ARs were manufactured as 38mm tall cylinders, 76mm in diameter, and submerged in circulating seawater to evaluate mass per surface area of biofilm accumulation.ResultsOur results indicate that biofilm formation is directly affected by surface porosity and less-so by pH, as determined by measuring material properties after submersion. We found that the PDC samples were most successful in forming a biofilm despite being more fragile than other concrete samples.DiscussionThis preliminary study provides insight into how different material properties influence the accumulation of biofilm as a starting point for designing ARs. Future work will investigate the long-term performance of such samples in relevant conditions.

Cassidinidea andamanensis sp. nov., a new species of intertidal Sphaeromatidae (Crustacea: Isopoda) from the Andaman Islands, northern Indian Ocean.

Cassidinidea andamanensis sp. nov. was collected from intertidal habitats on the coast of South Andaman, Andaman Islands, India and is described and illustrated in detail. Cassidinidea andamanensis sp. nov. the second definitive record of the genus from India, is characterized by: smooth body surface, prominently convex epistome anterior margin, pleotelson dorsal smooth surface and the posterior margin is subtruncate and weakly convex with small setae, the appendix masculina posterior margin is narrowly rounded.

Evaluating bottom-up forcing of a rocky intertidal resource harvest on a high trophic-level consumer group

The importance of ecosystem-based management (EBM) frameworks for resource harvest has increased over the past several decades as ecosystems face numerous anthropogenic stressors. In these frameworks, resource managers must consider the suite of interactions that comprise food webs and how resource harvest drives responses in non-target organisms. In rocky intertidal zones along North Atlantic coastlines, rockweed (Ascophyllum nodosum)—a canopy-forming brown seaweed—has been commercially harvested for centuries, yet most research on the effects of harvest have focused on the responses of the target resource and the macroinvertebrate assemblage. In this study, we used a Before-After Control-Impact experiment to assess the bottom-up effects of commercial rockweed harvest on a high trophic-level consumer group (birds) in Maine (USA). Overall, there was no evidence for strong bottom-up forcing of rockweed harvest on birds' site visitation. There was a small (fewer than two birds) positive effect size of harvest during the one-year post-harvest recovery interval. Several of the trends observed for the full bird assemblage appear to be driven more strongly by the low tide than the high tide bird assemblage. Independent of treatment, site visitation by birds was low in our study (60% of surveys recorded no birds) and highlights questions about the use of rocky intertidal habitats relative to other habitat types in coastal birds' home ranges. To our knowledge, there are no comparable assemblage-level bird studies in this system that can provide context to our results. Further research on coastal birds’ habitat use within home ranges and food-web connections with rockweed-associated macroinvertebrates is needed to more confidently incorporate this high trophic-level consumer group into an EBM framework for a rocky intertidal resource harvest.

Tidal range electricity generation into the twenty-second century

Tidal range electricity generation schemes are designed to have a minimum operational life of at least 120 years, making it important to plan for changes such as sea-level rise (SLR). Earlier studies have shown that schemes can maintain the existing tidal range within the impoundment and protect areas from flooding. Here it is demonstrated that tidal range technology can maintain the current tidal extent despite SLR and suggests the operational strategies to achieve it. The approach is the only way to safeguard existing intertidal habitats. Mechanical and electrical plant requires a major overall, upgrade or replacement every 40 years; the levelised cost of energy is structured in 40-year periods reducing after the first period. Increasing the capacity or efficiency of the plant during the refits allows the protection of low-lying areas to be maintained and more electricity to be generated. The strategy requires energy to be used in pumping to achieve the current low tidal limits and the incoming tide to be curtailed to maintain the high tide extent, but there is very little effect on annual electricity production. Flexible operation can offer some protection from riverine flooding and existing inundation cycles can be maintained.

Complete mitochondrial genome of Striatobalanus tenuis Hoek, 1883 (Balanomorpha: Balanidae) and a novel molecular phylogeny within Cirripedia

Barnacles are crustaceans that are critical model organisms in intertidal ecology and biofouling research. In this study, we present the first mitochondrial genome of Striatobalanus tenuis which is a circular molecule of 15,067 bp in length. Consistent with most barnacles, the mitochondrial genome of S. tenuis encodes 37 genes, including 13 PCGs, 22 tRNAs and 2 rRNAs. A novel insight into the phylogenetic analysis based on the nucleotide data of 13 PCGs showed that the S. tenuis clusters with Striatobalanus amaryllis (bootstrap value = 100) of the same genus, then groups with other Balanoidea species, the Chelonibiidae, Austrobalanidae and Tetraclitidae cluster together forming superfamily Coronuloidea. The result can help us to understand the novel classification within Balanomorpha.

Global taxonomic and functional patterns in invertebrate assemblages from rocky-intertidal mussel beds

Mussels form extensive beds in rocky intertidal habitats on temperate seashores worldwide. They are foundation species because their beds host many invertebrates. Mussels and their associated species differ taxonomically among biogeographic regions, but all mussel beds exhibit similar structural and functional properties. Therefore, we investigated if rocky-intertidal mussel beds from around the globe host associated communities that are functionally similar despite their underlying taxonomic differences. We gathered datasets on the abundance of invertebrates found in rocky-intertidal mussel beds from the eastern and western boundaries of the Pacific and Atlantic Oceans from both hemispheres and, then, we compared their taxonomic and functional properties. Taxonomic composition differed markedly among coasts when analyzed at the taxonomic resolution reported by the surveys (often species). However, taxonomic groups with similar ecologies (28 groups including barnacles, decapods, gastropods, polychaetes, etc.) were more universally present in mussel beds. Concomitantly, functional categories of trophic level, body type, and mobility were almost always present on all studied coasts. These taxonomic groups and trait categories, however, showed regional patterns based on their relative abundances. Overall, the ability of mussel beds to host a core community type based on taxonomic groups and functional traits emphasizes their importance for biodiversity and community functioning, making them critical organisms to preserve.

Massive barnacle recruitment on the Gulf of St. Lawrence coast of Nova Scotia (Canada) in 2024 linked to increased sea surface temperature.

With the ongoing climate and oceanographic change, an increasing number of studies are reporting dramatic population losses caused by thermal extremes in intertidal habitats. Under moderate warming, however, populations can fare better in places where species normally experienced suboptimal temperatures. This article reports the massive recruitment of the barnacle Semibalanus balanoides on the Gulf of St. Lawrence coast of Nova Scotia (Canada) in 2024. As recruits appear mostly during May in this region, coastal sea surface temperature (SST) in April is critical for the ecological performance of larvae, as they are pelagic and live in the water column for weeks before intertidal settlement. Thus, a study that spanned 12 years (2005 to 2016) on this coast found that annual barnacle recruitment was positively correlated to April SST. In April 2024, coastal SST was 116% higher than for the same month averaged over those 12 years (4.1 vs. 1.9 °C). This SST spike was followed by an elevated recruitment that was 111% higher than the average for those 12 years (1,278 vs. 607 recruits dm-2). Overall for the studied years, the amount of variation in annual barnacle recruitment statistically explained by April SST was 51%. While the southern distribution limit of S. balanoides has moved northwards in recent decades due to lethal warming, our results support the notion of improving reproductive success with seawater warming on colder northern shores.

Juvenile mangrove growth is restricted by belowground competition with mature tree roots

Mangroves provide important ecosystem services and are uniquely structured forests due to strong biotic and abiotic influences in their intertidal habitat. These challenging conditions often create above- and belowground resource limitations which can interact to suppress juvenile growth resulting in an understory dominated by supressed juveniles. Though the response of juvenile mangrove growth to experimental release from aboveground resource limitations has been tested, less is known about the effect of belowground competition with mature tree root systems on juvenile growth. We experimentally released juvenile mangroves from mature tree belowground competition by repeated soil cutting treatments over 52 weeks. When belowground competition was reduced and thus belowground resource limitations relaxed, juvenile mangroves grew taller. Undisturbed control juveniles did not grow, though they had similar survival probabilities as treated juveniles across our sampling year. We demonstrated that release from belowground resource limitations was sufficient to restart growth of understorey juvenile mangroves, even when mature tree aboveground competition remained. This result enhances our understanding of species distribution and forest maintenance in this unique and important coastal ecosystem.

Mantid expansion into North American salt marshes

Abstract Mantids are influential generalist predators in terrestrial systems. Therefore, large mantid species like the European mantid, Mantis religiosa (Linnaeus, 1758), are often used by humans and purposefully introduced as a form of biocontrol, greatly expanding their geographic ranges. However, mantids are rarely recorded in marine systems. In this study, we present an observation of European mantids living in a salt marsh and actively moulting in the vegetation in Elkhorn Slough, in Monterey Bay, California, United States of America. Not only are these European mantids a nonnative species, but every observed individual was a flightless juvenile, meaning they hatched nearby. Although mantids are not usually associated with intertidal ecosystems, there are multiple potential reasons that mantids would be drawn to salt marshes, including food, potential for camouflage, and lower predation pressure. The addition of a generalist predator could produce a complex mix of positive and negative impacts on the marsh itself and, given the importance of marsh systems, these possible effects warrant further study.

Functional ecological traits in young and adult thalli of canopy-forming brown macroalga Gongolaria barbata (Phaeophyta) from a transitional water system.

Gongolaria barbata is a canopy-forming brown macroalga that thrives in the intertidal and subtidal habitats of the warm-temperate Mediterranean Sea, which is particularly exposed to environmental changes due to its peculiar geographical location and exposure to both global and local stressors. Testing whether this species is featured by specific functional, eco-physiological and biochemical traits allowing an efficient use of habitat resources and adaptation to environmental stress, and whether this potential might change with population growth, is essential for predicting the performance of the algae under different environmental abiotic variables (e.g., temperature, nutrient availability, light) and biotic interactions (such as grazing). Young (juveniles) and adult thalli of G. barbata were sampled in the winter season from the Venice Lagoon, Italy, featured by high environmental changes (temperature, salinity) and analyzed for thallus dry matter content (TDMC), photosynthetic activity, photosynthetic pigment and protein content, and antioxidant capacity to assess if thallus age may be considered a significant driver in determining the ecological responses of this species to environmental changes. Our results showed that TDMC was higher in adults than juveniles. At the functional level, rapid light curves indicated an elevated photosynthetic efficiency in juveniles compared to adults highlighted by the higher quantum yield of PSII electron transport, electron transport rate, and Rubisco content observed in juveniles. On the contrary, adults exhibited a higher non-photochemical quenching and total pigment concentration. No difference in maximum PSII photochemical efficiency and D1 protein content between the two thalli groups was found. Along with better photosynthesis, juveniles also displayed a higher amount of total polyphenols, flavonoids, and tannins, and a stronger antioxidant capacity compared to adults. Our findings revealed significant differences in the eco-physiological characteristics of G. barbata at different growth stages. It was observed that young thalli, allocate more energy to photosynthesis and chemical defenses by increasing the production of antioxidant compounds, such as polyphenols, flavonoids, and tannins. With growth, thalli likely adopt a more conservative strategy, reducing photosynthesis and promoting structural biomass accumulation to mitigate the potential risks associated with prolonged exposure to environmental stressors, such as the wavy way. Although our study focused on a single phase of G. barbata life cycle under winter settings, it offers preliminary insights into this species eco-physiological traits and auto-ecology. Future research could explore the potential implications of these findings, evaluating the species' resilience to environmental changes at the population level.

An assessment of the utility of green gravel as a kelp restoration tool in wave-exposed intertidal habitats

Abstract Kelp forests are being degraded and/or lost in many regions, and as such, interest in active kelp restoration approaches to reinstate forests is growing. ‘Green gravel’ is a promising new kelp restoration technique that involves seeding small rocks with kelp zoospores, rearing the gametophyte and juvenile sporophyte stages in aquaria before outplanting them at restoration sites. However, to be considered a viable approach to kelp forest restoration, the efficacy of this technique needs to be assessed across a range of environmental contexts and kelp species. Here, we aimed to understand the utility of green gravel as a kelp restoration technique for wave-exposed intertidal shores. Two substrate types – gravel and cobbles – were seeded with Saccharina latissima, reared in the aquarium and outplanted at two sites along the northeast coast of England. Outplanted rocks were monitored for retention, and the density and length of S. latissima. Juvenile sporophytes persisted on both rock types, although declines in density and variations in length were observed over time. Substrate retention was low, with gravel more likely to be removed from restoration sites compared to cobbles, and all outplanted rocks were lost after eight months. While our initial testing of the green gravel restoration technique on wave-exposed shores was not successful, our results provide important insights for developing/refining the technique and a baseline for comparison for future efforts. However, prior to commencing large-scale kelp restoration in wave-exposed areas using green gravel, further testing of the technique and comparisons with other restoration approaches are needed.

Genetic differentiation of Hippa adactyla based on CO1 gene sequence in Sundaland

The Hippidae is a family of sand crabs that inhabit intertidal ecosystems, specifically in sandy areas scattered throughout the coast. Differences in habitat conditions cause variations in Hippidae members. Hippa adactyla is a member of the genus Hippa. This study aimed to map the genetic differentiation between Hippa adactyla populations in the Greater Sunda Islands. The sand crab (Hippa adactyla) samples were taken from Sumatra (Pariaman, Bengkulu, Lampung) and Java (Pangandaran, Pelabuhan Ratu, Banyuwangi) by handcatching then stored in alcohol 96%. Total genomic DNA was extracted from the muscle tissue of the samples using a commercial DNA Extraction KIT. The upper part of the COI gene (5' end) (±750 bp) was amplified using specific primers. Based on the K2P substitution model, the genetic distance of the Pangandaran population to the Bali Strait population is the same as that of the Sumatran population (0.062). Genetic diversity ranges from 0.000 to 0.123. Haplotype diversity was 0.928, consisting of 18 haplotypes.

Citizen science monitoring uncovers resilience of intertidal assemblages in a tropical urban environment

Coastal intertidal sand and mudflats are home to a rich and uniquely evolved ecological community. With increasing knowledge of the importance of these ecosystems and the threats they are facing, efforts to conserve them have become a priority to many coastal managers. However, these can be constrained by knowledge gaps and resource limitations, and citizen science is an emerging strategy to complement traditional methods of data collection. Intertidal Watch is a citizen science program that was set up in Singapore in 2016, to better understand and monitor the biodiversity of Singapore’s urban tropical intertidal ecosystems. It also aims to increase public awareness of marine habitats by involving members of the community in citizen science. Through analyzing eight years of data collected by Intertidal Watch, this study documented rich ecological diversities in four intertidal sand and mudflats located in areas that had been reclaimed between the 1970s and 1980s, with evident community distinctions between a macroalgae-dominant site and the remaining seagrass-dominant sites. While there were fluctuations in biological populations over time, study sites were observed to largely remain resilient to changes in direct anthropogenic pressures. Our study highlights the power of citizen science in facilitating systematic conservation while bringing about positive community benefits.

Distribution Pattern of Black Sea Cucumber (Holothuria atra Jaeger, 1833) at the Intertidal Ecosystem of Bilik Coastal, Baluran National Park

Baluran National Park (BNP) is a natural resource conservation area known for its diverse land and water ecosystems. The intertidal ecosystem of Bilik Coast is home to sea cucumbers (Holothuria atra), which have both ecological and economic value. It is important to note that H. atra is a protected species in the BNP conservation area. Therefore, studying the distribution pattern of H. atra in the intertidal ecosystem of Pesisir Bilik is crucial. This study aims to determine the type of distribution pattern of H. atra and describe its spatial distribution. Purposive sampling was conducted at maximum low tide, and biotic data were collected using the Global Positioning System (GPS) to obtain coordinates. Biotic data were measured at 9 points as a representative area. The type of distribution pattern of H. atra was analyzed using the Nearest Neighbor Index using ArcGIS 10.7 which shows the type of distribution pattern and describes its spatial distribution. The research results showed that the distribution pattern of H. atra was categorized as clustered based on the result of R (ratio) < 1 (0.458). H. atra species were distributed in seagrass communities, macroalgae communities, open areas, and coral reef communities.

Investigating the bacterial community of gray mangroves (Avicennia marina) in coastal areas of Tabuk region.

Mangrove vegetation, a threatened and unique inter-tidal ecosystem, harbours a complex and largely unexplored bacterial community crucial for nutrient cycling and the degradation of toxic pollutants in coastal areas. Despite its importance, the bacterial community composition of the gray mangrove (Avicennia marina) in the Red Sea coastal regions remains under-studied. This study aims to elucidate the structural and functional diversity of the microbiome in the bulk and rhizospheric soils associated with A. marina in the coastal areas of Ras Alshabaan-Umluj (Umluj) and Almunibrah-Al-Wajh (Al-Wajh) within the Tabuk region of Saudi Arabia. Amplicon sequencing targeting the 16S rRNA was performed using the metagenomic DNAs from the bulk and rhizospheric soil samples from Umluj and Al-Wajh. A total of 6,876 OTUs were recovered from all samples, of which 1,857 OTUs were common to all locations while the total number of OTUs unique to Al-wajh was higher (3,011 OTUs) than the total number of OTUs observed (1,324 OTUs) at Umluj site. Based on diversity indices, overall bacterial diversity was comparatively higher in rhizospheric soil samples of both sites. Comparing the diversity indices for the rhizosphere samples from the two sites revealed that the diversity was much higher in the rhizosphere samples from Al-Wajh as compared to those from Umluj. The most dominant genera in rhizosphere sample of Al-Wajh were Geminicoccus and Thermodesulfovibrio while the same habitat of the Umluj site was dominated by Propionibacterium, Corynebacterium and Staphylococcus. Bacterial functional potential prediction analyses showed that bacteria from two locations have almost similar patterns of functional genes including amino acids and carbohydrates metabolisms, sulfate reduction and C-1 compound metabolism and xenobiotics biodegradation. However, the rhizosphere samples of both sites harbour more genes involved in the utilization and assimilation of C-1 compounds. Our results reveal that bacterial communities inhabiting the rhizosphere of A. marina differed significantly from those in the bulk soil, suggesting a possible role of A. marina roots in shaping these bacterial communities. Additionally, not only vegetation but also geographical location appears to influence the overall bacterial composition at the two sites.

Assessing the conservation status of mangroves in Rakhine, Myanmar

Abstract Ecosystem degradation is a key challenge that human society faces, as ecosystems provide services that are tied to human well‐being. Particularly, mangrove ecosystems provide important services to communities but are suffering heavy degradation, loss and potential collapse due to anthropogenic activities. The IUCN Red List of Ecosystems is a transparent and consistent framework for assessing ecosystems' risk of collapse and is increasingly used to inform legislation and ecosystem management globally. Satellite data have become increasingly common in environmental monitoring due to their extensive spatial and temporal coverage. Here, recent advances in analyses using satellite‐derived data were implemented to reassess the conservation status of the ‘Rakhine mangrove forest on mud’, an important intertidal ecosystem in Myanmar, extending a previous national Red List assessment that assessed the ecosystem as Critically Endangered. By incorporating additional data sources and analyses, the extended assessment produced more robust results and reduced the uncertainty in the previous assessment. Overall, the ecosystem was assessed as Critically Endangered (range: Vulnerable to Critically Endangered) as a result of historical mangrove extent loss. Recent losses and biotic disruptions were also observed, which would have led to the ecosystem being assessed as Vulnerable. While the final outcome of the Red List assessment remained at Critically Endangered due to the historical state of the mangroves pre‐dating the temporal coverage from satellite data, the uncertainty of the ecosystem's status was reduced, and the reassessment highlighted the recent areal changes and mangrove degradation that has occurred. The importance of conducting reassessments when new data become available is discussed, and a template for future mangrove Red List assessments that use satellite data as their primary source of information to improve the robustness of their results is presented.

Site fidelity of migratory shorebirds facing habitat deterioration: insights from satellite tracking and mark-resighting

BackgroundSite fidelity, the tendency to return to a previously visited site, is commonly observed in migratory birds. This behaviour would be advantageous if birds returning to the same site, benefit from their previous knowledge about local resources. However, when habitat quality declines at a site over time, birds with lower site fidelity might benefit from a tendency to move to sites with better habitats. As a first step towards understanding the influence of site fidelity on how animals cope with habitat deterioration, here we describe site fidelity variation in two species of sympatric migratory shorebirds (Bar-tailed Godwits Limosa lapponica and Great Knots Calidris tenuirostris). Both species are being impacted by the rapid loss and deterioration of intertidal habitats in the Yellow Sea where they fuel up during their annual long-distance migrations.MethodsUsing satellite tracking and mark-resighting data, we measured site fidelity in the non-breeding (austral summer) and migration periods, during which both species live and co-occur in Northwest Australia and the Yellow Sea, respectively.ResultsSite fidelity was generally high in both species, with the majority of individuals using only one site during the non-breeding season and revisiting the same sites during migration. Nevertheless, Great Knots did exhibit lower site fidelity than Bar-tailed Godwits in both Northwest Australia and the Yellow Sea across data types.ConclusionsGreat Knots encountered substantial habitat deterioration just before and during our study period but show the same rate of decline in population size and individual survival as the less habitat-impacted Bar-tailed Godwits. This suggests that the lower site fidelity of Great Knots might have helped them to cope with the habitat changes. Future studies on movement patterns and their consequences under different environmental conditions by individuals with different degrees of site fidelity could help broaden our understanding of how species might react to, and recover from, local habitat deterioration.

Algal cover as a driver of diversity in communities associated with mussel assemblages across eastern Pacific ecoregions

AbstractResearch on intertidal mussel assemblages and associated communities has revealed that complexity and structure are influenced by environmental heterogeneity and local‐scale factors affecting recruitment. Research in situ in eastern and western Pacific intertidal ecosystems has suggested drivers of species diversity and community structure encompassing large geographic scales, however, there are major gaps in geographic coverage. Our aim is to fill some of these gaps by analyzing macrofaunal functional group diversity and effects of environmental factors on intertidal mussel communities from three distinct marine ecoregions in the southern and northern hemispheres. We identified the effects of algal cover and environmental heterogeneity on species richness and evenness, and we modeled factors effecting mussel layer complexity from assemblages in three marine ecoregions. We analyzed macrofaunal species diversity within one of the austral ecoregions based on the width of the coastal shelf. Species richness was highest in samples from the northern hemisphere while evenness was highest in samples from the southern hemisphere. Similarity in functional group structure for all communities sampled was ≤55% (Bray–Curtis dissimilarity) and ≤35% (Chao–Jaccard dissimilarity). Wave exposure had a significant effect on shell length and complexity of mussel matrices on rocky bench platforms. The presence of algal cover had a strong effect on species richness in mussel matrices regardless of complexity, while algal canopies had no effect on species evenness. Overall, this study provides significant new insight on the community complexity of mussel beds in parts of the world which have been poorly studied in this regard.

The birth of backbarrier marshes in Culatra Island (Ria Formosa, South Portugal)

The rapid elongation of Culatra Island, a sandy barrier in the Ria Formosa chain (S. Portugal), since the mid-1940s led to the formation of three new embayments in its backbarrier that were gradually colonised by halophytic vegetation. This provided a rare opportunity to collect information and data on the very early stages of backbarrier marsh plant establishment and evolution. Sediment (surface and subsurface) sampling in two of the recently formed bays, combined with information extracted from vertical aerial photographs, allowed us to assess modern sedimentation characteristics and vertical accretion rates since the shift from a bare sandflat to a vegetated marsh platform. Present-day topography appears largely inherited by overwash or/and inlet-related tidal deposits that provided the necessary sediment pulse for the formation of an intertidal sandy substrate, suitable for colonisation. The variability in accretion rates, noted even within the same embayment, as well as the differences in accretion balance with similarly young backbarrier marshes, highlight the importance of local conditions (sediment import, distance to creeks and marsh edge, storm frequency and intensity) to marsh build-up, even during the very early stages. Variable accretion rates were also identified over intertidal seagrass patches, indicating similar influences. Organic deposition rates were very low in all vegetated intertidal habitats, indicating the dominance of mineral deposition to the vertical growth. A lag, ranging from roughly 10–30 years, was observed between the formation of the intertidal sandy platform and plant establishment in all embayments. The different timescales in the observed lag are likely linked to differences in hydrodynamic conditions, promoted by the embayment morphology (opening width). The lowest lag was observed in protected embayments, which could reflect a ‘typical’ delay for plant establishment in the system, while the highest lag was associated with higher energy backbarrier environments.