Understanding the effects of coastal defence structures on marine biota: The role of substrate composition and roughness in structuring sessile, macro- and meiofaunal communities

The proximity to marine infrastructure affects fish diversity, the occurrence of non-indigenous species, and the dynamic of the sessile communities

Marine urbanization is changing coastal ecosystems. In this study, we examined how the proximity to recreational marinas influences the structure and recruitment of the sessile community, the diversity of fish, and predation pressure. Sessile communities on marinas supported 68 % more non-indigenous species than those farther from marine infrastructure. Conversely, native species occupied more space in natural habitats, where the diversity of fish was greater. Predation did not influence the diversity or structure of the sessile community, regardless of the habitat type. Nevertheless, predation pressure may be underestimated in artificial habitats due to the lack of connection between platforms and the seafloor. Sessile recruitment tended to be more abundant in artificial habitats. Our findings indicate that even when substrate composition, orientation, and connectivity to the seabed are standardized, proximity to marine infrastructure increases the prevalence of non-indigenous sessile species and diminishes the diversity of potential predatory fish, thereby altering the dynamics of sessile communities.

Avoiding Cognitive Trap in Habitat Restoration: A Case Study of the World's Rarest Primate

The lack of knowledge regarding the basic ecological traits of an endangered species may lead to traps in habitat restoration efforts. Understanding the ranging ecology of endangered species is essential in avoiding these traps. The Hainan gibbon (Nomascus hainanus), the world's rarest primate, reportedly takes refuge in suboptimal montane habitats and occupies an abnormally large home range, resulting in suggestions for enhancing montane habitat quality with high priority. However, these conservation suggestions and actions are not based on solid science. For the first time, we habituated two groups of Hainan gibbon, and studied their ranging ecology over a year from January to December 2022. We found that the average home range size of these groups was 164.5 ± 70.6 ha (95% KDE-href) and 155.2 ± 71.1 ha (95% MCP), which is comparable to other Nomascus gibbons and represents an adaptive trait in response to their heterogeneous habitat. Furthermore, gibbons have shown a preference for higher-altitude habitats between 800 and 1100 m, where food is more abundant than in low-altitude habitats. Our findings, combined with the evidence of favorable food conditions and short interbirth intervals of the Hainan gibbon, indicate that montane habitats meet gibbons' life-history requirements and are suitable for them. The idea that "montane habitat is suboptimal" is a cognitive trap. Given the Hainan gibbons' isolated habitat is approaching saturation, we suggest prioritizing ecological corridor construction to enable gibbons to rapidly gain access to other suitable montane forests.

Diversity and structure of epibenthic communities across subtidal artificial hard habitats in the Bay of Cherbourg (English Channel)

To inform the performance of ecological engineering designs for artificial structures at sea, it is essential to characterise their impacts on the epibenthic communities colonising them. In this context, the present study aims to compare the community structure among natural and four different artificial hard habitats with different ages and features installed in the Bay of Cherbourg (English Channel): i) cinder blocks and ii) boulders, both installed six years prior to the study, and iii) smooth and iv) rugous concrete dykes, both installed one year prior to this study. Results showed that artificial habitats installed six years ago harboured communities with functional and taxonomic diversity characteristic of mature communities but were still different from those of natural habitat. Conversely, the two dyke habitats installed one year prior to this study presented a poorly diversified community dominated by opportunistic taxa. Furthermore, while the concrete used for the two dyke habitats presented different rugosity properties, both habitats supported similar communities, suggesting that such eco-engineering measures did not affect the settlement of early colonisers. Overall, this study highlights the need for long-term monitoring to comprehensively evaluate epibenthic colonisation of artificial structures.

Topographic heterogeneity triggers complementary cascades that enhance ecosystem multifunctionality

Topographic heterogeneity sets the stage for community assembly, but its effects on ecosystem functioning remain poorly understood. Here, we test the hypothesis that topographic heterogeneity underpins multiple cascading species interactions and functional pathways that indirectly control multifunctionality. To do so, we combined experimental manipulation of a form of topographic heterogeneity on rocky shores (holes of various sizes) with a comprehensive assessment of naturally assembled communities and multifunctionality. Structural equation modeling indicated that heterogeneity: (1) enhanced biodiversity by supporting filter feeder richness; (2) triggered a facilitation cascade via reef-forming (polychaete) and biomass-dominant (macroalga) foundation species, which in turn broadly supported functionally diverse epibiotic and understory assemblages; and (3) inhibited a key consumer (limpet). The model supported that these mechanisms exerted complementary positive effects on individual functions (e.g., water filtration, ecosystem metabolism, nutrient uptake) and, in turn, collectively enhanced multifunctionality. Topographic heterogeneity may therefore serve as a cornerstone physical attribute by initiating multiple cascades that propagate through ecological communities via foundation species, ultimately manifesting disproportionate effects on ecosystem multifunctionality.

Intertidal assemblages on groynes along sandy shores in Portugal: Exploring the effects of orientation and distance to rocky shore

Coastal erosion is becoming increasingly problematic as sea level rise and coastal areas become more urbanised. In response, more defence structures such as groynes are being built, which are crucial for counteracting sediment loss and coastline retreat. Despite worldwide use, comparatively little is known about the factors that determine the species composition on such structures. In this study, the composition and abundance of intertidal benthic species on groynes was investigated as a function of groyne orientation (North vs. South) and distance to natural rocky shores (5 km vs. 42 km). While orientation showed no effect on benthic assemblages, distance to rocky shores was identified as a key factor influencing the assemblage composition. Macroalgae were found in greater abundance further away from rocky shores, while snail and barnacle species were found in greater numbers closer to rocky shores.

Unveiling the role of taxonomic sufficiency for enhanced ecosystem monitoring

The use of Artificial substrates (AS) as sampling devices addresses challenges in macrofaunal quantitative sampling. While effectively capturing biodiversity patterns, the time-intensitive identification process at the species level remains a substantial challenge. The Taxonomic Sufficiency approach (TS), where only taxa above species level are identified, arises as a potential solution to be tested across different environmental monitoring scenarios. In this paper, we analyzed three AS macrobenthic datasets to evaluate the odds of TS in improving the cost-effective ratio in AS monitoring studies and establish the highest resolution level to detect assemblage changes under different environmental factors. Results indicated that the family level emerged as a pragmatic compromise, balancing precision and taxonomic effort. Cost/benefit analysis supported TS efficiency, maintaining correlation stability until the family level. Results also showed that reducing resolution to family does not entail a significant Loss of Information. This study contributes to the discourse on TS applicability, highlighting its practicality in monitoring scenarios, including spatial-temporal studies, and rapid biodiversity assessments. Additionally, it highlights the "second best approach" of family-level practicality depending on the specific monitoring scenario and recognizes the importance of the species-level "best approach" before applying TS in monitoring studies.

Surface integrity could limit the potential of concrete as a bio-enhanced material in the marine environment

Coastal sprawl is among the main drivers of global degradation of shallow marine ecosystems. Among artificial substrates, quarry rock can have faster recruitment of benthic organisms compared to traditional concrete, which is more versatile for construction. However, the factors driving these differences are poorly understood. In this context, this study was designed to compare the intertidal and subtidal benthic and epibenthic assemblages on concrete and artificial basalt boulders in six locations of Madeira Island (northeastern Atlantic, Portugal). To assess the size of the habitat, the shorelines in the study area were quantified using satellite images, resulting in >34 % of the south coast of Madeira being artificial. Benthic assemblages differed primarily between locations and secondarily substrates. Generally, assemblages differed between substrates in the subtidal, with lower biomass and abundance in concrete than basalt. We conclude that these differences are not related to chemical effects (e.g., heavy metals) but instead to a higher detachment rate of calcareous biocrusts from concrete, as surface abrasion is faster in concrete than basalt. Consequently, surface integrity emerges as a factor of ecological significance in coastal constructions. This study advances knowledge on the impact and ecology of artificial shorelines, providing a baseline for future research towards ecological criteria for coastal protection and management.

Buoys are non-indigenous fouling hotspots in marinas regardless of their environmental status and pressure

Marinas contribute to the degradation of coastal ecosystems, constitute non-indigenous species (NIS) hotspots and function as steppingstones in invasion processes. These often enclose highly modified water bodies that promote the concentration of pollutants and propagules, favoring NIS abundance. In these habitats, floating structures are often the most invaded by fouling NIS. This study aims to address the effect of floating substrate (buoys vs pontoons) on fouling assemblages, with special focus on NIS, in 6 marinas of Cadiz Bay during summer and winter seasons. Since the effect substrate type can depend on the water physicochemical conditions and environmental state and pressures of marinas, an environmental assessment was carried out for each marina using literature, physicochemical water measurements and environmental risk assessments. Despite the registered seasonal variation in fouling assemblages and the environmental variability among the studied marinas, the type of substrate played a key role in fouling assemblages' structure and abundance. The higher abundance of fouling assemblages in buoys than pontoons favor NIS prevalence in marinas and increase the risk of NIS dispersal, particularly considering that buoys are more likely to detach and drift at sea than pontoons. The results indicate that high-risk consideration should be given to this substrate type and that the potential environmental effects of biological pollution must be considered in risk assessments.

Cut the rope: Short-term colonization of mooring lines by fouling community within the port of Livorno (Northern Tyrrhenian Sea, Western Mediterranean), focusing on alien species recruitment

The early stages of fouling development on artificial substrates were examined for spatial-temporal variation in the commercial and touristic harbours (use destinations) of the port of Livorno (Tuscany, Italy). The experiment was carried out by submerging two types of experimental ropes with different surface textures, considering three times of submersion. Particular attention was paid to the colonization dynamics of non-indigenous species (NIS). The type of rope did not significantly affect fouling development. However, when the NIS assemblage and the whole community were taken into account, the colonization of ropes varied depending on the use destination. The touristic harbour exhibited a degree of fouling colonization higher than the commercial one. NIS were observed in both harbours since the beginning of colonization, eventually achieving higher population densities in the touristic harbour. The use of experimental ropes represents a promising quick cost-effective tool for monitoring of NIS presence in port environments.

The elephant in the room: Introduced species also profit from refuge creation by artificial fish habitats

Increasingly, ecological rehabilitation is envisioned to mitigate and revert impacts of ocean sprawl on coastal marine biodiversity. While in the past studies have demonstrated the positive effects of artificial fish habitats in port areas on fish abundance and diversity, benthic colonization of these structures has not yet been taken into consideration. This could be problematic as they may provide suitable habitat for Non-Indigenous Species (NIS) and hence facilitate their spreading. The present study aimed to examine communities developing on artificial fish habitats and to observe if the number of NIS was higher than in surrounding equivalent habitats. The structures were colonized by communities that were significantly different compared to those surrounding the control habitat, and they were home to a greater number of NIS. As NIS can cause severe ecological and economical damages, our results imply that in conjunction with the ecosystem services provided by artificial fish habitats, an ecosystem disservice in the form of facilitated NIS colonization may be present. These effects have not been shown before and need to be considered to effectively decide in which situations artificial structures may be used for fish rehabilitation.

Location and building material determine fouling assemblages within marinas: A case study in Madeira Island (NE Atlantic, Portugal)

Marinas are hubs for non-indigenous species (NIS) and constitute the nodes of a network of highly modified water bodies (HMWB) connected by recreational maritime traffic. Floating structures, such as pontoons, are often the surfaces with higher NIS abundance inside marinas and lead the risk for NIS introduction, establishment and spread. However, there is still little information on how the location within the marina and the substratum type can influence the recruitment of fouling assemblages depending on water parameters and substratum chemical composition. In this study, fouling recruitment was studied using an experimental approach with three materials (basalt, concrete and HDPE plastic) in two sites (close and far to the entrance) in two marinas of Madeira Island (NE Atlantic, Portugal). The structure of benthic assemblages after 6- and 12-months colonization, as well as biotic abundance, NIS abundance, richness, diversity, assemblages' volume, biomass and assemblages' morphology were explored. Differences between marinas were the main source of variation for both 6- and 12-month assemblages, with both marinas having different species composition and biomass. The inner and outer sites of both marinas varied in terms of structure and heterogeneity of assemblages and heterogeneity of morphological traits, but assemblages did not differ among substrata. However, basalt had a higher species richness and diversity while concrete showed a higher bioreceptivity in terms of total biotic coverage than the rest of materials. Overall, differences between and within marinas could be related to their structural morphology. This study can be valuable for management of urban ecosystems, towards an increase in the environmental and ecological status of existing marinas and their HMWB and mitigation coastal ecosystems degradation.

Short-term colonization of fouling communities within the port of Livorno (Northern Tyrrhenian Sea, Western Mediterranean): Influence of substrate three-dimensional complexity on non-indigenous species establishment

The influence of substrate morphology on early stages of fouling development was assessed through submerged experimental substrates with different morphological complexity. The experiment was carried out within commercial and touristic harbours of the port of Livorno (Italy), analysing the communities at three steps of colonization (14, 28, 42 days). We assessed the effect of substrate complexity on recruitment of non-indigenous species (NIS), combined with the influence of port use destinations. NIS were recorded in both use destination areas since the first step of colonization. Substrate morphological complexity significantly affected fouling colonization and particularly NIS assemblages. We found that high-complexity substrates are particularly suitable for NIS establishment in comparison with less complex ones. The touristic harbour exhibited a potential for fouling colonization higher than the commercial harbour. These results contributed to the understanding of factors involved in NIS establishment and spread, as well as in their spatial-temporal dynamics within port environments.

Epibiont assemblages on limpet shells: Biodiversity drivers in intertidal rocky shores

Limpet shells can harbour a high diversity of species. Individuals of four limpet species (Patella depressa, Patella ulyssiponensis, Patella vulgata and Siphonaria pectinata) were collected monthly during one year in southern Portugal. Epibiont organisms were identified, counted and the percentage cover of facilitator taxa was also recorded. A total of 86 taxa were identified with abundance reaching 674 epibionts on a single basibiont shell. P. ulyssiponensis showed the highest epibiont species diversity and richness while P. depressa and P. vulgata showed similar diversity and richness. P. depressa had a more even epibiotic community mainly due to higher densities of Chthamalus sp. Overall, basibiont species was the key factor determining the epibiotic community, followed by month/season and erect algae. The presence of erect algae potentiated the epibionts diversity on limpet shells, whereas the occurrence of barnacles tended to decrease it and the presence of crustose algae had no significant effect on epibionts diversity. These findings shed further light on the biological and ecological complex relationships among keystone species inhabiting intertidal rocky shores.

Molluscs community as a keystone group for assessing the impact of urban sprawl at intertidal ecosystems

Mollusc communities are getting endangered in the aftermath of urban sprawl because artificial structures do not surrogate natural substrates. In this study, we compared the diversity, community and trophic arrangements of molluscs among different models of artificial substrate and their adjacent natural rock, to detect relationships between some abiotic variables and the mollusc communities. Complexity, chemical composition and age were tested as potential drivers of the community. Diversity, community and trophic structure differed between natural and artificial substrates. Complexity at the scale of cm was detected as the most important factor driving the community structure. In addition, a chemical composition based on silica and/or scarce calcium carbonates seems to be relevant for molluscs, as well as for the secondary substrate where they inhabit. However, age did not seem to be a driving factor. Among the different artificial structures, macroscale complexity was detected as the main factor diverging a drastically poor community at seawall from other artificial structures. In this context, macro and microscale complexity, chemical composition and mineral type are variables to consider in future designs of artificial substrates.

Coastal armouring affects intertidal biodiversity across the Alboran Sea (Western Mediterranean Sea)

Intertidal ecosystems are key habitats that are being replaced by artificial hard substrates due to the increment of human activities in coastal areas. These new substrates host generally less biodiversity mainly due to differences in complexity and composition. This is a global phenomenon and has led to the development of strategies in the framework of eco-engineering. However, mitigating measures, such as new eco-designs, must cope with the high spatial variability of the region where they are applied. Therefore, in order to assess if differences in biodiversity detected at local scales in previous studies could be scaled up to predict patterns at a wider scale, we studied taxa richness and taxonomic structure of intertidal communities across the Alboran Sea (western Mediterranean Sea). We compared four different types of artificial substrates (cubes, rip-raps, seawalls and tetrapods) to assess which produces less impact. Overall, artificial substrates host low benthic biodiversity, specially on seawalls, whereas boulder-like artificial structures such as rip-raps were more similar to natural ones. Nevertheless, the effect of a particular type of artificial structure at a regional scale seems unpredictable, highlighting the challenge that eco-engineering measures face in order to establish global protocols for biodiversity enhancement and the importance of local scale in management programmes.

Ecological quality assessement of marinas: An integrative approach combining biological and environmental data

The importance of marinas as infrastructures for recreational boating is increasing substantially. However, information on their soft-bottom benthic communities, a key tool for managing programmes, is still scarce. We combined environment features with macro- and meiofaunal soft-bottom community information for assessing the ecological status of marinas with an integrative approach. To address this issue, we focused on eight marinas of the Southern Iberian Peninsula. Macro- and meiofauna data revealed high benthic heterogeneity at a spatial scale. The environmental variables which correlated best with macrofauna were mainly phosphorus, granulometry, and total organic carbon, and secondarily important variables were faecal coliforms, the biocide Irgarol, and heavy metals; total hydrocarbon concentration was also significant for meiofauna. Annelida was the dominant phylum in terms of number of species (37%) and abundance (66%) and were better descriptors of the environmental conditions than Arthropoda and Mollusca. Although identification to the species level is desirable and mandatory for assessing biological pollution, significant differences among marinas and correlations between fauna and abiotic variables were already detected at the level of family and order. This implies that biota assessment at higher levels may still be useful in monitoring programmes limited by time and budget constraints. The major novelty of this study lies in the development of an integrative assessment method based on the following selected ecological indicators: Marinas Environmental Pollution Index (MEPI), Biocontamination Index (BCI), macrofaunal biotic indices (AMBI, M-AMBI, BENTIX, MEDOCC and BENFES), macrofaunal taxa richness and Shannon-Wiener's diversity, and nematode:copepod index. This approach was able to discriminate marinas of the Southern Iberian Peninsula based on their ecological status, which ranged from poor to good. The method can be useful to design standards for assigning "sustainable quality seals" to those marinas with better values of ecological indicators.

Do artificial structures cause shifts in epifaunal communities and trophic guilds across different spatial scales?

In the current frame of proliferation of artificial structures in the sea, the ecological effects of artificial substrates on marine environments and their associate biota become a topic of great scientific and conservationist interest. This study was focused on the amphipod communities from western Mediterranean Sea and tested, using the same secondary substrate, Ellisolandia elongata, if the community and trophic structure differ between artificial (two concrete-based: cubes and tetrapods, and one natural rock-based: rip-raps) and natural substrates. Results usually showed lower taxa number and diversity in artificial substrates, as well as differences in composition and trophic structure of the amphipod community. However, patterns were not consistent for all localities, evidencing the importance of local scale. Other potential factors, besides the substrate type, should be considered to understand particularities of each locality in management and conservation strategies.