Ecological network analysis of traits reveals variable response capacity to stress.

Response diversity increases the potential 'options' for ecological communities to respond to stress (i.e. response capacity). An indicator of community response diversity is the diversity of different traits associated with their capacity to be resistant to stress, to recover and to regulate ecosystem functions. We conducted a network analysis of traits using benthic macroinvertebrate community data from a large-scale field experiment to explore the loss of response diversity along environmental gradients. We elevated sediment nutrient concentrations (a process that occurs with eutrophication) at 24 sites (in 15 estuaries) with varying environmental conditions (water column turbidity and sediment properties). Macroinvertebrate community response capacity to nutrient stress was dependent on the baseline trait network complexity in the ambient community (i.e. non-enriched sediments). The greater the complexity of the baseline network, the less variable the network response to nutrient stress was; in contrast, more variable responses to nutrient stress occurred with simpler networks. Thus, stressors or environmental variables that shift baseline network complexity also shift the capacity for these ecosystems to respond to additional stressors. Empirical studies that explore the mechanisms responsible for loss of resilience are essential to inform our ability to predict changes in ecological states.

A pioneer morphological and genetic study of the intertidal fauna of the Gerlache Strait (Antarctic Peninsula).

The underexplored intertidal ecosystems of Antarctica are facing rapid changes in important environmental factors. Associated with temperature increase, reduction in coastal ice will soon expose new ice-free areas that will be colonized by local or distant biota. To enable detection of future changes in faunal composition, a biodiversity baseline is urgently required. Here, we evaluated intertidal faunal diversity at 13 locations around the Gerlache Strait (western Antarctic Peninsula), using a combination of a quadrat approach, morphological identification and genetic characterization. Our data highlight a community structure comprising four generally distributed and highly abundant species (the flatworm Obrimoposthia wandeli, the bivalve Kidderia subquadrata, and the gastropods Laevilitorina umbilicata and Laevilitorina caliginosa) as well as 79 rarer and less widely encountered species. The most abundant species thrive in the intertidal zone due to their ability to either survive overwinter in situ or to rapidly colonize this zone when conditions allow. In addition, we confirmed the presence of multiple trophic levels at nearly all locations, suggesting that complex inter-specific interactions occur within these communities. Diversity indices contrasted between sampling locations (from 3 to 32 species) and multivariate approaches identified three main groups. This confirms the importance of environmental heterogeneity in shaping diversity patterns within the investigated area. Finally, we provide the first genetic and photographic baseline of the Antarctic intertidal fauna (106 sequences, 137 macrophotographs), as well as preliminary insights on the biogeography of several species. Taken together, these results provide a timely catalyst to assess the diversity and to inform studies of the potential resilience of these intertidal communities.

Benthic studies adjacent to Sakhalin Island, Russia, 2015 I: benthic biomass and community structure in the nearshore gray whale feeding area.

Okhotsk or western gray whales feed in summer along the northeastern coast of Sakhalin Island, Russia, a region with oil and gas extraction facilities. Seismic surveys increased sound levels in the nearshore feeding area in 2015 for part of the summer, potentially displacing whales from preferred foraging habitat or reducing foraging efficiency. Since lost foraging opportunities might lead to vital rate effects on this endangered species, detailed benthic surveys were conducted to characterize benthic community biomass patterns and spatial and temporal differences. Benthic biomass demonstrated strong spatial-temporal interactions indicating that prey biomass differences among locations were dependent on sampling period. Of greatest interest, Amphipoda biomass declined from June to October in the northern and southern portions of the nearshore study area but increased in the middle and Actinopterygii biomass increased in the northern area in mid-summer. Water depth and sediment type were significant covariates with community structure, and water depth strongly covaried with bivalve biomass. Total average prey biomass was ~ 100 g/m2 within the nearshore feeding area with no evidence of reduced biomass among sampling periods or locations, although there were fewer amphipods in the south. Multi-prey investigations provide a stronger basis for inferences than single-prey studies of amphipods when gray whales feed on diverse prey. Benthic community-level variability was moderate to high as would be expected for a shallow-water nearshore area. Overall, spatial and temporal changes in dominant macrofauna biomass reflected small to medium-sized effects that were well within the natural boundaries expected for benthic communities.

Benthic studies adjacent to Sakhalin Island, Russia 2015 III: benthic energy density spatial models in the nearshore gray whale feeding area.

Energy densities of six dominant benthic groups (Actinopterygii, Amphipoda, Bivalvia, Cumacea, Isopoda, and Polychaeta) and total prey energy were modeled for the nearshore western gray whale feeding area, Sakhalin Island, Russia, as part of a multi-disciplinary research program in the summer of 2015. Energy was modeled using generalized additive mixed models (GAMM) with accommodations for zero-inflation (logistic regression and hurdle models) and regression predictions combined with kriging to interpolate energy densities across the nearshore feeding area. Amphipoda energy density was the highest nearshore and in the south whereas Bivalvia energy density was the highest offshore and in the northern portion of the study area. Total energy was the highest in mid-range distances from shore and in the north. Amphipoda energy density was higher than minimum energy estimates defining gray whale feeding habitats (312-442 kJ/m2) in 13% of the nearshore feeding area whereas total prey energy density was higher than the minimum energy requirement in 49% of the habitat. Inverse distance-weighted interpolations of Amphipoda energy provided a broader scale representation of the data whereas kriging estimates were spatially limited but more representative of higher density in the southern portion of the study area. Both methods represented the general trend of higher Amphipoda energy density nearshore but with significant differences that highlight the value of using multiple methods to model patterns in highly complex environments.

Can intensive fish farming for 20 years induce changes in benthic ecosystems on a scale of waterbody? An assessment from Cephalonia bay (Ionian Sea).

The environmental impacts of fish farming on benthic ecosystems beneath the fish cages have been widely addressed the past decades. However, the chronic release of nutrients can cause a shift in local primary productivity and a chronic increase in the sedimentation of organic material at a large spatial scale which could be reflected in benthic ecosystems. In this context, the indirect effects of aquaculture on the benthic ecosystem were studied in a semi-closed bay (Cephalonia, Ionian Sea) where a relatively large fish farm has been operating since 1982. Results from the present sampling were compared to historical data obtained in 1996 and 2001, in order to detect if nutrient release that could impact phytoplankton dynamics in the bay could indirectly alter benthic communities, as well. Macrofaunal communities have not shown deterioration but rather a small, yet statistically significant, improvement in diversity indices and ecological status indicators, and no significant change regarding bioturbation potential. This indicated that processes involved in nutrient consumption and transfer are highly effective in such an oligotrophic environment.

Territoriality in the tompot blenny Parablennius gattorugine from photographic records.

The behaviour of the tompot blenny Parablennius gattorugine was studied from a long-term underwater photographic record from two sites on the south-west coast of the U.K. Repeated observations of individually identifiable P. gattorugine during 112 dives revealed that male P. gattorugine may guard eggs in a particular crevice over subsequent breeding seasons, reside in the same location for up to 4 years and recover from injuries received in disputes over territory. Further observations included resident males wiping eggs with greatly expanded anal glands, adult-type fighting between juveniles and unusual behaviour where a large male manipulated an empty mollusc shell for the attention of two smaller conspecifics.

Salinity and sedimentation rate influences on the community structure of polychaetes associated with two sympatric congeneric oyster species.

This study focused on spatial-temporal variations in the composition and structure of polychaete communities associated with two coexisting oyster species in a southern Gulf of Mexico coastal lagoon, showed that Crassostrea rhizophorae hosted 23 polychaete species and C. virginica only four. The observed variability was mainly explained by differences in salinity and sedimentation rate, two factors that also influenced the host species distribution. The highest values of richness and diversity occurred at C. rhizophorae sites during the rainy season, coinciding with increased salinity and a decrease in sedimentation rate. The shell-borer species Nereis garwoodi and Polydora websteri occurred in both oysters, but showing higher frequencies in C. virginica during the Nortes season (i.e., the cold fronts season). Our results underscore the contrasting diversity of associated polychaetes with two coexisting oyster species and emphasize the need for considering additional environmental parameters to allow better understanding of the factors that are driving the structure of these communities.

Body traits variation of a reef building polychaete across a latitudinal gradient.

Body size is considered the most important trait in ecology, and as such, helps to understand the species-environment interactions. We explored the relationship between body traits and environmental variables along a gradient range using the polychaete Phragmatopoma caudata, with well-defined and diversified morphological structures. Measurements of five traits (body length, opercular crown, branchiae, tentacles and building organ sizes) were taken at nine sites along the Southwestern Atlantic coast and their relationships to temperature, salinity, tidal range, waves height, and dissolved oxygen were assessed. Our results demonstrate that traits were influenced by the environmental gradient and temperature was the main factor that drives this variation in body traits, while the other variables showed a minor influence on this. The approach showed patterns of variation of body traits in a macroscale context, increasing the understanding of its relationships with environmental variables and eventual shifts in the distribution in the future climate scenarios.

A dynamic subtropical coastal hotspot of benthic foraminifera in the Southeastern Mediterranean indicates early-stage tropicalization.

Due to ongoing ocean warming, subtropical environments are becoming accessible to tropical species. Among these environments are the vermetid reefs of the Southeastern Mediterranean (SEM). In the last decades, these valuable coastal habitats witnessed the proliferation of numerous alien species of tropical origin. Among the meiofauna thriving on these reefs are benthic foraminifera, single cell marine organisms that make a significant contribution to global carbonate production. It has been widely recognized that benthic foraminifera, among other invasive species, thrive in the macroalgal cover, and it has been suggested that their populations are becoming a significant new source of sediment substrate. Here, we report on the first systematic assessment of the population size of the benthic foraminifera, allowing a comparison with data from the native tropical habitat of these species. Our study is based on a seasonal sampling of benthic foraminifera from confined sampling areas at four sites along the vermetid reef platforms of the Israeli SEM coast. Our survey reveals a patchy distribution of each species with peak population densities exceeding 100,000 specimens per m2, making the SEM a hotspot of benthic foraminifera, with population densities comparable to tropical coral reef environments. The assemblages of the SEM hotspot are dominated by cosmopolitan foraminiferal taxa and tropical invaders from the Indo-Pacific (e.g., Amphistegina lobifera, Pararotalia calcariformata, soritids, and Hauerina diversa). In contrast to foraminiferal hotspots in the tropics, which are completely dominated by larger symbiont-bearing taxa, the SEM hotspot stands out due to high abundances of non-symbiont-bearing species Textularia agglutinans and small miliolids. An intriguing observation is the significant heterogeneity in composition and density of foraminiferal assemblages between the vermetid reefs' southern and northern areas (Israel), indicating that the productivity of the dominant species are also modulated by local yet unknown environmental factors.

Ecology of Bathymodiolus puteoserpentis mussels from the Snake Pit vent field (Mid-Atlantic Ridge).

Along the northern Mid-Atlantic Ridge (nMAR), in habitats under moderate (<10 °C) hydrothermal influence on the Snake Pit vent field (SP), large assemblages dominated by Bathymodiolin mussels remain poorly characterised, contrary to those in warmer habitats dominated by gastropods and alvinocaridid shrimps that were recently described. In this study, we assessed and compared the population structure, biomass, diversity and trophic interactions of two Bathymodiolus puteoserpentis assemblages and their associated fauna at SP. Three sampling units distanced by 30 cm were sampled in 2014 during the BICOSE cruise at the top of the Moose site (''Elan'' site), while few meters further down three others, distanced by ∼1 m were obtained in 2018 during the BICOSE 2 cruise at the edifice's base. We observed a micro-scale heterogeneity between these six sampling units partially explained by temperature variations, proximity to hydrothermal fluids and position on the edifice. Meiofauna dominate or co-dominate most of the sampling units, with higher densities at the base of the edifice. In terms of macrofauna, high abundance of Pseudorimula midatlantica gastropods was observed at the top of the vent edifice, while numerous Ophioctenella acies ophiuroids were found at the base. Contrary to what was expected, the apparent health and abundance of mussels seems to indicate a current climax stage of the community. However, the modification of B. puteoserpentis isotopic signatures, low number of juveniles decreasing over the two years and observations made during several French cruises in the study area raise questions about the fate of the B. puteoserpentis population over time, which remains to be verified in a future sampling campaign.

New interactive machine learning tool for marine image analysis.

Advancing imaging technologies are drastically increasing the rate of marine video and image data collection. Often these datasets are not analysed to their full potential as extracting information for multiple species is incredibly time-consuming. This study demonstrates the capability of the open-source interactive machine learning tool, RootPainter, to analyse large marine image datasets quickly and accurately. The ability of RootPainter to extract the presence and surface area of the cold-water coral reef associate sponge species, Mycale lingua, was tested in two datasets: 18 346 time-lapse images and 1420 remotely operated vehicle video frames. New corrective annotation metrics integrated with RootPainter allow objective assessment of when to stop model training and reduce the need for manual model validation. Three highly accurate M. lingua models were created using RootPainter, with an average dice score of 0.94 ± 0.06. Transfer learning aided the production of two of the models, increasing analysis efficiency from 6 to 16 times faster than manual annotation for time-lapse images. Surface area measurements were extracted from both datasets allowing future investigation of sponge behaviours and distributions. Moving forward, interactive machine learning tools and model sharing could dramatically increase image analysis speeds, collaborative research and our understanding of spatiotemporal patterns in biodiversity.

Benthic functionality under climate-induced environment changes offshore on the Antarctic Peninsula continental shelf.

Marine ecosystems in Antarctica are thought to be highly vulnerable to aspects of dynamic global climate change, such as warming. In deep-water ecosystems, there has been little physico-chemical change in seawater there for millions of years. Thus, some benthic organisms are likely to include strong potential indicators of environmental changes and give early warnings of ecosystem vulnerability. In 2017 we sampled deep-water benthic assemblages across a continental shelf trough in outer Marguerite Bay, West Antarctic Peninsula (WAP). This region is one of the hotspots of climate-related physical change on Earth in terms of seasonal sea ice loss. Video and images of the seabed were captured at 5 stations, each with 20 replicates. From these, we identified substratum types and biota to functional groups to assess variability in benthic composition and diversity. We also collected coincident environmental information on depth, temperature, salinity, oxygen and chlorophyll-a (using a CTD). Climax sessile suspension feeders were the most spatially dominant group, comprising 539 individuals (39% of total abundance) that included Porifera, Brachiopoda and erect Bryozoa. ST5, the shallowest station was functionally contrasting with other stations. This functional difference was also influenced by hard substrata of ST5, which is typically preferred by climax sessile suspension feeders. Depth (or an associated driver) and hard substrates were the most apparent key factor which functionally characterised the communities, shown by the abundance of climax sessile suspension feeders. Our study showed that non-invasive, low taxonomic skill requirement, functional group approach is not only valuable in providing functional perspective on environment status, but such groupings also proved to be sensitive to environmental variability.

Biodiversity patterns of the benthic macrofaunal communities across the intertidal sedimentary shores of two Antarctic islands.

Antarctic benthic ecosystems support a unique fauna characterized by high levels of diversity and endemism. However, our knowledge of the macrofauna communities across the Antarctic intertidal sedimentary shore is limited, and their fundamental ecological features, including spatial variability, remain poorly understood. This study aimed to investigate the abundance, community structure (i.e. taxa-specific abundance), and biodiversity patterns (α-, ß-, and λ-diversity) of benthic macrofauna communities on intertidal sedimentary shores of two Antarctic islands (South Shetland archipelago, N of Antarctic Peninsula): Livingston and Deception. We conducted a quantitative sampling during two Austral summer campaigns (2004 and 2005), studying eleven intertidal sites, with five sites located on Livingston and six on Deception. Our results demonstrated a significantly higher abundance of intertidal benthic macrofauna communities on Livingston than on Deception. Furthermore, significant differences in community structure were observed between the two islands. In terms of biodiversity patterns, there were no significant differences in the number of taxa within communities (α-diversity) between the two islands. However, significant differences in the variation of community composition (determined by the number and identity of taxa) between intertidal sites (ß-diversity) were observed, shedding light on the higher total taxa count (λ-diversity) on Livingston compared to Deception. We suggest that the island-specific characteristics (e.g., granulometric characteristics, ice disturbance, sedimentation rates, and geothermal activity) determine the differences observed in macrofauna communities. However, other ecological processes and factors are operating on different spatial and temporal scales (e.g., population dynamics, biotic interactions, oceanographic conditions, and climate change) that influence the occurrence and abundance of macrofaunal taxa. Our findings contribute to the fundamental understanding of the spatial variability of these communities and provide essential information for better management decisions and conservation practices in Antarctic coastal ecosystems.

Microscale dispersion of intertidal seagrass macrofauna.

Previous studies of dispersion of intertidal seagrass-associated macrobenthos in subtropical Moreton Bay, Queensland, showed that patchiness characterised its assemblage abundance with scale-invariant magnitude across areas ranging from >8000 to 0.1 m2. Those studies were here continued across the smaller scales (down to 0.014 m2) arguably more relevant to the dominant 2-10 mm long animals, using 16 replicate blocks of 5x5 contiguous 0.0024 m2 cores nested within the previously studied site. At microscales ≥0.09 m2, the earlier congruence of conclusions derived from patchiness indices and spatial autocorrelation broke down. At >0.014 m2, adjacent points (cores) no longer together formed larger spatial units of related abundance (i.e. showed no autocorrelation), but point abundances were still highly disparate (as reflected in patchiness indices). Congruent indications of patchiness only manifested at 0.014 m2 spatial scales. Assemblage dispersion pattern was partly consequent on one microgastropod (Pseudoliotia) occurring superabundantly in scattered 0.0024 m2 hotspots.

Effects of macroalgae and sea urchin grazing pressure on zoantharians growth under laboratory conditions.

In the context of ocean warming, thermophilic organisms such as zoantharians are expanding and altering shallow benthic habitats. Here, a four-month laboratory experiment was performed to examine the influence of three types of macroalgae morphotypes common in the Canary Islands (turf algae, Lobophora spp., and crustose coralline algae) on the growth of two zoantharian species, Palythoa caribaeorum and Zoanthus pulchellus. Additionally, the grazing effects of echinoids Diadema africanum and Paracentrotus lividus were assessed as facilitators of substrate colonization by means of controlling macroalgae cover. Colony and algal coverages were measured at the beginning, middle and end of the experiment, and increments were calculated. Results indicated a general decrease in zoantharian colony sizes in contact with different algal types in the absence of sea urchins. However, P. caribaeorum colonies showed significant growth in the presence of D. africanum, highlighting the ecological importance of sea urchins in zoantharian population proliferation and subsequent community modification. This study represents the first investigation into zoantharian-macroalgae interactions under controlled conditions.

Spatial distribution of meiofaunal and macrofaunal assemblages in the tidal flats of the southern Korean coast in relation to natural and anthropogenic impacts.

We investigated the spatial variability of macrofaunal and meiofaunal assemblages in intertidal flats on the southern coast of Korea. Abiotic and biotic samples were collected at five stations. The species richness, density, and composition of the assemblages differed significantly among stations. Nematoda and Annelida were the most dominant meiofaunal and macrofaunal taxa, respectively, although taxon dominance differed among stations. Distance-based linear models showed that sediment-related variables and heavy metals were the main environmental factors determining the spatial variability of the assemblages. Macrofauna had only sediment-related variables and heavy metals as major environmental factors, but meiofauna were also influenced by other environmental factors such as sea surface temperature, dissolved oxygen-related variables, and salinity. This study can provide basic ecological data for understanding the spatial distribution of macro-meiofaunal assemblages and aid in the development of marine environmental management strategies on the western south coast of Korea.

The role of the Sunda shelf biogeographic barrier in the cryptic differentiation of Conus litteratus (Gastropoda: Conidae) across the Indo-Pacific region.

Geographical and oceanographic processes have influenced the speciation of marine organisms. Cone snails are marine mollusks that show high levels of endemism and a wide distributional range across the Indian and Pacific Oceans. Discontinuities in distributions caused by biogeographic barriers can affect genetic connectivity. Here we analysed the connectivity within Conus litteratus using samples from the Lakshadweep archipelago (Arabian Sea, Indian Ocean) and from the Pacific Ocean. Maximum likelihood analyses based on the mitochondrial cytochrome C oxidase subunit I (COI) and on the non-coding 16S ribosomal RNA (16S rRNA) genes revealed cryptic diversity within C. literatus occupying distinct oceanographic regions. The intraspecific genetic distances between the two distinct clades of C. literatus from the Arabian Sea and the Pacific Ocean ranged from 7.4% to 7.6% for COI and from 2.4% to 2.8% for 16S rRNA genes, which is larger than the threshold limit for interspecific differentiation. The haplotype network analysis also corroborated the existence of two different lineages within C. litteratus. The detected genetic discontinuities reflect the effect of the Sunda shelf biogeographic barrier on the allopatric divergence of C. litteratus.

Intraspecific variation in reproductive traits and embryo elemental composition of the crab Hemigrapsus crenulatus (Milne Edwards, 1837) across fluctuating coastal environments along Chilean coasts.

The estuarine crab Hemigrapsus crenulatus has a wide distribution range along the coast of the South Pacific Ocean (from 20 °S to 53 S°). This decapod is abundant in these coastal and estuarine habitats and plays a key ecological role as prey of the snook fish (Eleginops maclovinus) and kelp gull (Larus dominicanus). Its diet consists of detritus, dead fish, and crustaceans, and the macroalgae Ulva sp. In response to contrasting environmental conditions and anthropogenic impacts along the Chilean coast, H. crenulatus may present intraspecific variations in its reproductive traits and changes in the elemental composition of its embryos, directly affecting its biological fitness. Along the Chilean coast, female individuals were collected during late spring 2019 and early summer 2020 (from November 2019 to February 2020) in six areas of Chile (north: Tongoy (30°S); south-central: Lenga (36°S), Tubul (37°S); south austral: Calbuco (41°S), Castro (42°S), Quellón (43°S). The environmental conditions (i.e. sea surface temperature, precipitation and chlorophyll α) present during each sampling event were also recorded. We evaluated the reproductive parameters of females (fecundity, reproductive output (RO)) as well as their body size (carapace width and dry weight), volume, water content, dry weight, elemental composition (carbon, hydrogen, nitrogen: CHN), and finally the energy content of their embryos. Our results indicated that the environmental conditions of the sea water temperature, precipitation (proxy of water salinity) and chlorophyll α (proxy of food availability) have direct effects on the reproductive parameters of females and the characteristics of their embryos. We observed a low fecundity and high RO in Calbuco and Quellón, where precipitation was high (i.e. diluted salinity) and temperatures and productivity was low. For embryo traits, the highest values of volume and water content were observed in female crabs from the estuarine areas (i.e. Tongoy, Lenga, Tubul), values much higher than those found in the internal sea of Chile (i.e. Calbuco, Castro, Quellón). For the elemental composition, we observed high nitrogen levels and a low C:N proportion in embryos from female crabs from Lenga (a nitrogen enriched area). Fluctuating environmental variables among localities proved to modulate intraspecific variations in females and embryos of H. crenulatus, revealing different reproductive strategies, particularly in the quality and energy investment per embryo, which subsequently influenced successful embryogenesis and larval survival.

Integrated Assessment of Chemical and Biological Recovery After Diversion and Treatment of Acid Mine Drainage in a Rocky Mountain Stream.

Responses of stream ecosystems to gradual reductions in metal loading following remediation or restoration activities have been well documented in the literature. However, much less is known about how these systems respond to the immediate or more rapid elimination of metal inputs. Construction of a water treatment plant on the North Fork of Clear Creek (NFCC; CO, USA), a US Environmental Protection Agency Superfund site, captured, diverted, and treated the two major point-source inputs of acid mine drainage (AMD) and provided an opportunity to investigate immediate improvements in water quality. We conducted a 9-year study that included intensive within- and among-year monitoring of receiving-stream chemistry and benthic communities before and after construction of the treatment plant. Results showed a 64%-86% decrease in metal concentrations within months at the most contaminated sites. Benthic communities responded with increased abundance and diversity, but downstream stations remained impaired relative to reference conditions, with significantly lower taxonomic richness represented by a few dominant taxa (i.e., Baetis sp., Hydropsyche sp., Simulium sp., Orthocladiinae). Elevated metal concentrations from apparent residual sources, and relatively high conductivity from contributing major ions not removed during the treatment process, are likely limiting downstream recovery. Our study demonstrates that direct AMD treatment can rapidly improve water quality and benefit aquatic life, but effectiveness is limited, in part, to the extent that inputs of metals are captured and treated. Consideration should also be given to the effects of elevated major ion concentrations from the treated effluent not removed during the lime treatment process. Continued chemical and biological monitoring will be needed to quantify the NFCC recovery trajectory and to inform future remediation strategies. Environ Toxicol Chem 2023;42:512-524. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Variations in epilithic microbial biofilm composition and recruitment of a canopy-forming alga between pristine and urban rocky shores.

Brown algae of the genus Ericaria are habitat formers on Mediterranean rocky shores supporting marine biodiversity and ecosystem functioning. Their population decline has prompted attempts for restoration of threatened populations. Although epilithic microbial biofilms (EMBs) are determinant for macroalgal settlement, their role in regulating the recovery of populations through the recruitment of new thalli is yet to be explored. In this study, we assessed variations in microbial biofilms composition on the settlement of Ericaria amentacea at sites exposed to different human pressures. Artificial fouling surfaces were deployed in two areas at each of three study sites in the Ligurian Sea (Capraia Island, Secche della Meloria and the mainland coast of Livorno), to allow bacterial biofilm colonization. In the laboratory, zygotes of E. amentacea were released on these surfaces to evaluate the survival of germlings. The EMB's composition was assessed through DNA metabarcoding analysis, which revealed a difference between the EMB of Capraia Island and that of Livorno. Fouling surfaces from Capraia Island had higher rates of zygote settlement than the other two sites. This suggests that different environmental conditions can influence the EMB composition on substrata, possibly influencing algal settlement rate. Assessing the suitability of rocky substrata for E. amentacea settlement is crucial for successful restoration.