Benthic assemblages, biodiversity and invasiveness in marinas and commercial harbours: an investigation using a bioindicator group

Environment and shipping drive environmental DNA beta-diversity among commercial ports

The spread of nonindigenous species by shipping is a large and growing global problem that harms coastal ecosystems and economies and may blur coastal biogeographical patterns. This study coupled eukaryotic environmental DNA (eDNA) metabarcoding with dissimilarity regression to test the hypothesis that ship-borne species spread homogenizes port communities. We first collected and metabarcoded water samples from ports in Europe, Asia, Australia and the Americas. We then calculated community dissimilarities between port pairs and tested for effects of environmental dissimilarity, biogeographical region and four alternative measures of ship-borne species transport risk. We predicted that higher shipping between ports would decrease community dissimilarity, that the effect of shipping would be small compared to that of environment dissimilarity and shared biogeography, and that more complex shipping risk metrics (which account for ballast water and stepping-stone spread) would perform better. Consistent with our hypotheses, community dissimilarities increased significantly with environmental dissimilarity and, to a lesser extent, decreased with ship-borne species transport risks, particularly if the ports had similar environments and stepping-stone risks were considered. Unexpectedly, we found no clear effect of shared biogeography, and that risk metrics incorporating estimates of ballast discharge did not offer more explanatory power than simpler traffic-based risks. Overall, we found that shipping homogenizes eukaryotic communities between ports in predictable ways, which could inform improvements in invasive species policy and management. We demonstrated the usefulness of eDNA metabarcoding and dissimilarity regression for disentangling the drivers of large-scale biodiversity patterns. We conclude by outlining logistical considerations and recommendations for future studies using this approach.

Early colonization of sessile megabenthos on electrolytic carbonated structures (Alicante's harbor, Western Mediterranean)

Biofouling of different artificial substrates was studied to determine the differences in biofouling assemblages among different substrates. However, studies on biofouling on natural substrates like electrolytic carbonated ones are lacking. These substrates have a great potential for coral reef restoration in tropical areas and for biofilter construction. Thus, this study was developed to examine the colonization of sessile macrofouling in the port of Alicante (SE Spain, Western Mediterranean) on two types of substrates: electrolytic carbonated and bare steel (as control) over three months of immersion (October 2019-January 2020). The community diversity was studied through different biotic parameters and abundance of assemblages, and preference of organisms according to their status and functional group (active filter feeders). Univariate and multivariate analyses (PERMANOVA and SIMPER) were also applied to examine the differences between carbonate and control substrates. The carbonated substrate had a more structured community and higher abundance, recruitment, and diversity indexes than the bare steel. Moreover, filter feeders (Porifera, Bivalvia, and Ascidiacea) were more abundant, and most of them only appeared in the carbonated substrate. These results show the potential of carbonated structures as biofilters.

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.

A comparison of prokaryotic symbiont communities in nonnative and native ascidians from reef and harbor habitats

Harbor systems represent passive gateways for the introduction of nonnative ascidians that compete with the surrounding benthos and may spread through localized dispersal, even populating adjacent natural reefs. To investigate the potential role of microbial symbionts in the success of ascidian introductions and spread, we evaluated the host-specificity of prokaryotic communities within two ascidian species commonly found off the North Carolina coast. Replicate samples of the native ascidian Eudistoma capsulatum, the nonnative ascidian Distaplia bermudensis and seawater were collected from artificial (harbor) and natural reef substrates. Prokaryotic communities in seawater samples and ascidian tunics were characterized via next-generation sequencing of partial 16S rRNA gene sequences. Ascidian microbiomes clustered strongly in response to host species, with significant differences in community structure between the two species and seawater. Further, symbiont community structure differed significantly between E. capsulatumindividuals collected from artificial and natural habitats, though this was not the case for D. bermudensis. These findings suggested that some ascidian species possess stable microbial symbiont communities that allow them to thrive in a wide range of habitats, while other species rely on the restructuring of their microbial communities with specific symbionts (e.g. Chelativorans) to survive under particular environmental conditions such as increased pollution.

Role of commercial harbours and recreational marinas in the spread of non-indigenous fouling species

The role of commercial harbours as sink and source habitats for non-indigenous species (NIS) and the role of recreational boating for their secondary spread were investigated by analysing the fouling community of five Italian harbours and five marinas in the western Mediterranean Sea. It was first hypothesised that NIS assemblages in the recreational marinas were subsets of those occurring in commercial harbours. However, the data did not consistently support this hypothesis: the NIS pools of some marinas significantly diverged from harbours even belonging to the same coastal stretches, including NIS occurring only in marinas. This study confirms harbours as hotspots for marine NIS, but also reveals that numbers of NIS in some marinas is higher than expected, suggesting that recreational vessels effectively facilitate NIS spread. It is recommended that this vector of NIS introduction is taken into account in the future planning of sustainable development of maritime tourism in Europe.

Distinct community dynamics at two artificial habitats in a recreational marina

Man-made facilities along coastlines modify water circulation and sedimentation dynamics which can affect the structure of marine benthic and pelagic communities. To test how environmental heterogeneity associated with a recreational marina affects the structure of the fouling community and the benthic-pelagic link, we conducted an experiment in which predation effects on recruitment and community structure were assessed in two artificial habitats: inside the marina, an area of calm waters and often disturbed by boating activity, and the breakwater, a more hydrodynamic area. Using visual censuses and video footages we also described the predation pressure and the identity of predators on the two areas. Inside the marina, the recruitment of ascidians and serpulids, but not of bryozoans, was restricted in some occasions, possibly due to reduced water circulation. Predation, mainly by the silver porgy fish Diplodus argenteus, reduced the survivor of didemnid ascidians on both areas, but predation intensity was 40 times higher in the breakwater than inside the marina. While the two artificial habitats did not necessarily support distinct communities, low recruitment coupled to weak predation inside the marina, a less dynamic environment, likely imply lower resilience and more susceptibility to disturbance.