Emergence of a neopelagic community through the establishment of coastal species on the high seas

The role of marine debris as a vector, dispersal agent, and substrate for non-indigenous species on Oceanic Islands (Northeast Atlantic)

Marine debris (MD) can be a transport vector for diverse marine communities, including non-indigenous species (NIS). This study assessed MD potential role as a substrate for colonization and dispersal vector for NIS in the Madeira Archipelago (NE Atlantic) by examining three MD categories: floating (FMD), seafloor (SMD), and beached (BMD). Opportunistic sampling, conducted in collaboration with local maritime stakeholders, documented MD sightings with photographs and GPS coordinates. A total of 92 MD items were inspected, revealing 108 fouling species across 11 phyla, with 13 % identified as NIS. SMD exhibited the highest proportion of NIS (9.6 %), followed by BMD (4.4 %) and FMD (3.9 %). Notably, the study provides evidence that FMD functions as both a substrate and a dispersal vector for NIS in Madeira waters. Combining biogeographic analyses, oceanographic modelling, and MD identification marks, this study highlighted the North Atlantic Subtropical Gyre's currents as key pathways, transporting MD items from the Wider Caribbean, the North American east coast, and the Iberian Peninsula to Madeira within 2-3 years. These findings emphasize Madeira's dual role as both a recipient and exporter of MD, with implications for NIS introductions and secondary spread. This study underscores the urgent need for standardized monitoring, stakeholder engagement, and proactive MD management strategies to mitigate NIS introductions and protect sensitive marine ecosystems like Macaronesia from the ecological risks of biological invasions.

An index to differentiate megafauna entangled in operational fishing gears from abandoned, lost, or otherwise discarded fishing gears

Classifying entanglements of marine megafauna in certain anthropogenic items is challenging because many are found in fishing-related items, with the cause being either operational fishing gear (OFG) or abandoned, lost, or otherwise discarded fishing gear (ALDFG). The distinction between OFG and ALDFG is essential as each source requires different mitigation and remediation strategies. To reduce the uncertainty in sorting between these two distinct threats, we developed the Entanglement Source Assessment (ENSA) index. This index integrates a series of criteria related to the entangling item and the affected organism. It assess the likelihood that an entanglement was caused by an OFG or by an ALDFG using a Multi-Criteria Decision Analysis approach. The index was tested on 35 entanglement events involving various taxa, using video footage and photographs recorded in the Azores Archipelago (NE Atlantic). Overall, 57 % of the entanglements were classified as likely caused by ALDFG (ENSA scoring >60), indicating they resulted from marine debris. In comparison, 23 % were classified as likely from interactions with OFG (ENSA scoring ≤40). The remaining events were ambiguous and could not be confidently assigned to either source. ENSA is a valuable tool that integrates expert knowledge, transparently providing a clear view of the steps and reasoning behind the classification process. It will promote standardization when reporting the source (OFG vs. ALDFG), which is essential for implementing adequate policy measures to address the entanglement of marine megafauna in fishing-related items at national and global scales.

Hunting for pigments in bacterial settlers of the Great Pacific Garbage Patch

The Great Pacific Garbage Patch, a significant collection of plastic introduced by human activities, provides an ideal environment to study bacterial lifestyles on plastic substrates. We proposed that bacteria colonizing the floating plastic debris would develop strategies to deal with the ultraviolet-exposed substrate, such as the production of antioxidant pigments. We observed a variety of pigmentation in 67 strains that were directly cultivated from plastic pieces sampled from the Garbage Patch. The genomic analysis of four representative strains, each distinct in taxonomy, revealed multiple pathways for carotenoid production. These pathways include those that produce less common carotenoids and a cluster of photosynthetic genes. This cluster appears to originate from a potentially new species of the Rhodobacteraceae family. This represents the first report of an aerobic anoxygenic photoheterotrophic bacterium from plastic biofilms. Spectral analysis showed that the bacteria actively produce carotenoids, such as beta-carotene and beta-cryptoxanthin, and bacteriochlorophyll a. Furthermore, we discovered that the genetic ability to synthesize carotenoids is more common in plastic biofilms than in the surrounding water communities. Our findings suggest that plastic biofilms could be an overlooked source of bacteria-produced carotenoids, including rare forms. It also suggests that photoreactive molecules might play a crucial role in bacterial biofilm communities in surface water.

Freshwater plastisphere: a review on biodiversity, risks, and biodegradation potential with implications for the aquatic ecosystem health

The plastisphere, a unique microbial biofilm community colonizing plastic debris and microplastics (MPs) in aquatic environments, has attracted increasing attention owing to its ecological and public health implications. This review consolidates current state of knowledge on freshwater plastisphere, focussing on its biodiversity, community assembly, and interactions with environmental factors. Current biomolecular approaches revealed a variety of prokaryotic and eukaryotic taxa associated with plastic surfaces. Despite their ecological importance, the presence of potentially pathogenic bacteria and mobile genetic elements (i.e., antibiotic resistance genes) raises concerns for ecosystem and human health. However, the extent of these risks and their implications remain unclear. Advanced sequencing technologies are promising for elucidating the functions of plastisphere, particularly in plastic biodegradation processes. Overall, this review emphasizes the need for comprehensive studies to understand plastisphere dynamics in freshwater and to support effective management strategies to mitigate the impact of plastic pollution on freshwater resources.

Microbial colonization patterns and biodegradation of petrochemical and biodegradable plastics in lake waters: insights from a field experiment

Introduction

Once dispersed in water, plastic materials become promptly colonized by biofilm-forming microorganisms, commonly known as plastisphere.

Methods

By combining DNA sequencing and Confocal Laser Scanning Microscopy (CLSM), we investigated the plastisphere colonization patterns following exposure to natural lake waters (up to 77 days) of either petrochemical or biodegradable plastic materials (low density polyethylene - LDPE, polyethylene terephthalate - PET, polylactic acid - PLA, and the starch-based MaterBi® - Mb) in comparison to planktonic community composition. Chemical composition, water wettability, and morphology of plastic surfaces were evaluated, through Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM), and static contact angle analysis, to assess the possible effects of microbial colonization and biodegradation activity.

Results and Discussion

The phylogenetic composition of plastisphere and planktonic communities was notably different. Pioneering microbial colonisers, likely selected from lake waters, were found associated with all plastic materials, along with a core of more than 30 abundant bacterial families associated with all polymers. The different plastic materials, either derived from petrochemical hydrocarbons (i.e., LDPE and PET) or biodegradable (PLA and Mb), were used by opportunistic aquatic microorganisms as adhesion surfaces rather than carbon sources. The Mb-associated microorganisms (i.e. mostly members of the family Burkholderiaceae) were likely able to degrade the starch residues on the polymer surfaces, although the Mb matrix maintained its original chemical structure and morphology. Overall, our findings provide insights into the complex interactions between aquatic microorganisms and plastic materials found in lake waters, highlighting the importance of understanding the plastisphere dynamics to better manage the fate of plastic debris in the environment.

Marine debris provide long-distance pathways for spreading invasive corals

Anthropogenic marine debris and invasive species are pervasive in the ocean. However, research on the mechanisms and dynamics controlling their distribution in marine systems (e.g.; by floating debris acting as vectors for invasive species) is limited. Applying a numerical modeling approach, we demonstrate that rafting invasive corals (Tubastraea spp.) can be transported over long distances and reach important tropical receptor regions. In <180 days, buoyant debris can cover distances between 264 and 7170 km moving from the Brazilian semiarid coast to the Amazon coast and reaching eight regions in the Wider Caribbean (mainly the Eastern Caribbean and Greater Antilles). Analyzing 48 simulated scenarios (4 years × 3 depths × 4 months), we demonstrate that in ~86 % of the scenarios the particles are stranded in the Caribbean and in ~71 % they end up in the Amazon coast. Our results showed litter floating trajectories at 0-10 m water depth, transported every year to the Caribbean province. However, in August this transport is frequently blocked by the retroflection of the North Brazil Current adjacent to the Amazon River estuarine plume. Our results indicate routes for fast and long-distance transport of litter-rafting invasive species. We hypothesized a high risk of bioinvasion on important marine ecosystems (e.g., coral reefs) likely becoming increasingly threatened by these invasive species and debris. This highlights the imperative need for an ocean governance shift in prevention, control, and eradication, not only focused on local actions to prevent the spread of invasive species but also a broad international action to decrease and mitigate marine debris pollution globally.

Polymer identification of floating derelict fishing gear from O'ahu, Hawai'i

Discarded fishing gear (DFG) comprises most of the plastic in the North Pacific Ocean and causes environmental and economic losses. Building evidence on the material construction of fishing gear types is critical to develop solutions to reduce DFG amounts and impacts. We forensically assessed the construction and chemical composition of eight different gear types removed as DFG around O'ahu, Hawai'i. A thorough dissection and novel analysis was conducted including the documentation of gear constructions, polymer identification using attenuated total reflection-Fourier transform infrared spectroscopy and differential scanning calorimetry, and elemental additive detection using X-ray fluorescence. Twenty-six different polymers were identified, and most gear consisted of polyethylene variants or blends. This inventory of physical and chemical characterization of DFG can help future polymer identification of particular gear types through visual techniques. Additionally, it can aid in identifying sources of these gear types and promote recycling options.

Large floating abandoned, lost or discarded fishing gear (ALDFG) is frequent marine pollution in the Hawaiian Islands and Palmyra Atoll

Abandoned, lost, or discarded fishing gear (ALDFG) is a major source of marine debris with significant ecological and economic consequences. We documented the frequency, types, sizes, and impacts of ALDFG recovered from Hawai'i and Palmyra Atoll in the Central North Pacific Ocean (CNPO) from 2009 to 2021. A total of 253 events weighing 15 metric tons were recovered, including 120 drifting fish aggregating device (dFAD) components, 61 conglomerates, fewer distinct nets, lines, buoys, and unique gear. The Hawaiian Islands were dominated by conglomerates and Palmyra Atoll by dFADs. DFADs were connected to the Eastern Pacific tropical tuna purse seine fishery. Windward O'ahu experienced up to seven events or 1800 kg of ALDFG per month. Across Hawai', ALDFG was present on 55 % of survey days, including hotspots with 100 % occurrence. Coral reef damage, entangled wildlife, navigational and removal costs are reported. The data highlight the large magnitude of ALDFG and associated impacts in the CNPO.

Daily accumulation rates of floating debris and attached biota on continental and oceanic island shores in the SE Pacific: testing predictions based on global models

Background

Long-distance rafting on anthropogenic marine debris (AMD) is thought to have a significant impact on global marine biogeography and the dispersal of non-indigenous species. Therefore, early identification of arrival sites of AMD and its epibionts is crucial for the prioritization of preventive measures. As accumulation patterns along global coastlines are largely unstudied, we tested if existing oceanographic models and knowledge about upstream sources of litter and epibionts can be used as a simple and cost-efficient approach for predicting probable arrival sites of AMD-rafting biota in coastal zones.

Methods

Using the Southeast Pacific as a model system, we studied daily accumulation rates, composition, and minimum floating times of AMD with and without epibionts on seven sandy beaches, covering the oceanic environment (Rapa Nui/Easter Island) and three regions (south, centre, north) along the Chilean continental coast, over a minimum of 10 consecutive days, and we contrast our results with predictions from published models.

Results

Total AMD accumulation rates varied from 56 ± 36 (mean ± standard deviation) to 388 ± 433 items km^-1 d^-1 and differed strongly between regions, in accordance with local geomorphology and socioeconomic conditions (presence of larger cities and rivers upstream, main economic activities, etc.). Daily accumulation of items with pelagic epibionts (indicators of a pelagic trajectory) ranged from 46 ± 29 (Rapa Nui) to 0.0 items km^-1 d^-1 (northern continental region). Minimum floating times of rafts, as estimated from the size of pelagic epibionts, were longest in the South Pacific Subtropical Gyre's (SPSG) centre region, followed by the high-latitude continental region under the influence of the onshore West Wind Drift, and decreased along the continental alongshore upwelling current, towards lower latitudes. Apart from pelagic rafters, a wide range of benthic epibionts, including invasive and cryptogenic species, was found on rafts at the continental beaches. Similarly, we present another record of local benthic corals Pocillopora sp., on Rapa Nui rafts.

Discussion

Our results agree with the predictions made by recent models based on the prevailing wind and surface current regimes, with high frequencies of long-distance rafting in the oceanic SPSG centre and very low frequencies along the continental coast. These findings confirm the suitability of such models in predicting arrival hotspots of AMD and rafting species. Moreover, storm surges as well as site-related factors seem to influence AMD arrival patterns along the Chilean continental coast and might cause the observed high variability between sampling sites and days. Our results highlight the possible importance of rafting as a vector of along-shore dispersal and range expansions along the SE Pacific continental coast and add to the discussion about its role in benthic species dispersal between South Pacific oceanic islands.

Extent and reproduction of coastal species on plastic debris in the North Pacific Subtropical Gyre

We show that the high seas are colonized by a diverse array of coastal species, which survive and reproduce in the open ocean, contributing strongly to its floating community composition. Analysis of rafting plastic debris in the eastern North Pacific Subtropical Gyre revealed 37 coastal invertebrate taxa, largely of Western Pacific origin, exceeding pelagic taxa richness by threefold. Coastal taxa, including diverse taxonomic groups and life history traits, occurred on 70.5% of debris items. Most coastal taxa possessed either direct development or asexual reproduction, possibly facilitating long-term persistence on rafts. Our results suggest that the historical lack of available substrate limited the colonization of the open ocean by coastal species, rather than physiological or ecological constraints as previously assumed. It appears that coastal species persist now in the open ocean as a substantial component of a neopelagic community sustained by the vast and expanding sea of plastic debris.

Modelling of marine debris pathways into UK waters: Example of non-native crustaceans transported across the Atlantic Ocean on floating marine debris

The long-distance transfer of non-native, potentially invasive species via floating marine debris is an increasing threat to biodiversity and conservation efforts. To address the lack of understanding around mechanisms and pathways of species transfer via marine debris, a novel modelling approach was applied to recreate the likely trajectory and source of a large piece of debris fouled by non-native species collected from UK marine waters. This approach applied the Oil Spill Contingency and Response (OSCAR) simulation tool, an adapted oil spill modelling programme, which was informed by a combination of biological trait information for the foulant species, marine debris characteristics and hydrodynamic data. The modelling output suggested an origin in the Western Atlantic, a scenario concurrent with the known distribution of the foulant species. This modelling approach represents a valuable tool with which to determine the origin and trajectory of invasive species transferred via marine debris.

Does plastic type matter? Insights into non-indigenous marine larvae recruitment under controlled conditions

Marine plastic debris (MPD) are a global threat to marine ecosystems. Among countless ecosystem impacts, MPD can serve as a vector for marine 'hitchhikers' by facilitating transport and subsequent spread of unwanted pests and pathogens. The transport and spread of these non-indigenous species (NIS) can have substantial impacts on native biodiversity, ecosystem services/functions and hence, important economic consequences. Over the past decade, increasing research interest has been directed towards the characterization of biological communities colonizing plastic debris, the so called Plastisphere. Despite remarkable advances in this field, little is known regarding the recruitment patterns of NIS larvae and propagules on MPD, and the factors influencing these patterns. To address this knowledge gap, we used custom-made bioassay chambers and ran four consecutive bioassays to compare the settlement patterns of four distinct model biofouling organisms' larvae, including the three notorious invaders Crassostrea gigas, Ciona savignyi and Mytilus galloprovincialis, along with one sessile macro-invertebrate Spirobranchus cariniferus, on three different types of polymers, namely Low-Linear Density Polyethylene (LLDPE), Polylactic Acid (PLA), Nylon-6, and a glass control. Control bioassay chambers were included to investigate the microbial community composition colonizing the different substrates using 16S rRNA metabarcoding. We observed species-specific settlement patterns, with larvae aggregating on different locations on the substrates. Furthermore, our results revealed that C. savignyi and S. cariniferus generally favoured Nylon and PLA, whereas no specific preferences were observed for C. gigas and M. galloprovincialis. We did not detect significant differences in bacterial community composition between the tested substrates. Taken together, our results highlight the complexity of interactions between NIS larvae and plastic polymers. We conclude that several factors and their potential interactions influenced the results of this investigation, including: (i) species-specific larval biological traits and ecology; (ii) physical and chemical composition of the substrates; and (iii) biological cues emitted by bacterial biofilm and the level of chemosensitivity of the different NIS larvae. To mitigate the biosecurity risks associated with drifting plastic debris, additional research effort is critical to effectively decipher the mechanisms involved in the recruitment of NIS on MPD.

The key role of surface tension in the transport and quantification of plastic pollution in rivers

Current riverine plastic monitoring best practices mainly consider surface observations, thus neglecting the underlying distribution of plastics in the water column. Bias on plastic budgets estimations hinders advances on modelling and prediction of plastics fate. Here, we experimentally disclose the structure of plastics transport in surface water flows by investigating how thousands of samples of plastics commonly found in fluvial environments travel in turbulent river flows. We show for the first time that surface tension plays a key role in the transport of plastics since its effects can be of the same magnitude as buoyancy and turbulence, therefore holding a part of the dispersed buoyant plastics captive by the water surface. We investigate two types of transport; surfaced plastics (surface tension-turbulence-buoyancy dominated), in contact with the free surface, and suspended plastics (turbulence-buoyancy dominated). We prove that this duality in transport modes is a major source of error in the estimation of plastic budgets, which can be underestimated by 90 % following current, well-established monitoring protocols if sampling is conducted solely in the water surface. Based on our empirical findings, we optimize physics-driven monitoring strategies for plastic fluxes in rivers, thereby achieving over a ten-fold reduction of the bias and uncertainty of riverine plastic pollution estimates.

Toward a long-term monitoring program for seawater plastic pollution in the north Pacific Ocean: Review and global comparison

Through a literature survey and meta-data analysis, monitoring methods and contamination levels of marine micro- and macroplastics in seawater were compared between the North Pacific and the world's other ocean basins. The minimum cut-off size in sampling and/or analysis of microplastics was crucial to the comparison of monitoring data. The North Pacific was most actively monitored for microplastics and showed comparatively high levels in the global context, while the Mediterranean Sea was most frequently monitored for macroplastics. Of the 65 extracted mean abundances of microplastics in seawater from the North Pacific, two (3.1%) exceeded the lowest predicted no-effect concentration (PNEC) proposed thus far. However, in the context of business-as-usual conditions, the PNEC exceedance probability may be expected to reach 27.7% in the North Pacific in 2100. The abundance of marine plastics in seawater, which reflects the current pollution status and marine organisms' waterborne exposure levels, is a useful indicator for marine plastic pollution. For regional and global assessments of pollution status across space and time, as well as assessment of ecological risk, two microplastic monitoring approaches are recommended along with their key aspects. Although microplastic pollution is closely linked with macroplastics, the monitoring data available for floating macroplastics and more extent to mesoplastics in most ocean basins are limited. A more specific framework for visual macroplastic survey (e.g. fixed minimum cut-off size, along with survey transect width and length according to survey vessel class) is required to facilitate data comparison. With the implementation of standardised methods, increased efforts are required to gather monitoring data for microplastics and-more importantly-floating macroplastics in seawater worldwide.

Plastisphere in lake waters: Microbial diversity, biofilm structure, and potential implications for freshwater ecosystems

Once dispersed in water, microplastic (MP) particles are rapidly colonised by aquatic microbes, which can adhere and grow onto solid surfaces in the form of biofilms. This study provides new insights on microbial diversity and biofilm structure of plastisphere in lake waters. By combining Fourier Confocal Laser Scanning Microscopy (CLSM), Transform Infrared Spectroscopy (FT-IR) and high-throughput DNA sequencing, we investigated the microbial colonization patterns on floating MPs and, for the first time, the occurrence of eukaryotic core members and their possible relations with biofilm-forming bacterial taxa within the plastisphere of four different lakes. Through PCR-based methods (qPCR, LAMP-PCR), we also evaluated the role of lake plastisphere as long-term dispersal vectors of potentially harmful organisms (including pathogens) and antibiotic resistance genes (ARGs) in freshwater ecosystems. Consistent variation patterns of the microbial community composition occurred between water and among the plastisphere samples of the different lakes. The eukaryotic core microbiome was mainly composed by typical freshwater biofilm colonizers, such as diatoms (Pennales, Bacillariophyceaea) and green algae (Chlorophyceae), which interact with eukaryotic and prokaryotic microbes of different trophic levels. Results also showed that MPs are suitable vectors of biofilm-forming opportunistic pathogens and a hotspot for horizontal gene transfer, likely facilitating antibiotic resistance spread in the environments.

A new look at the potential role of marine plastic debris as a global vector of toxic benthic algae

Marine plastic debris provides a significant surface area for potential colonization by planktonic and benthic harmful microalgae and for the adsorption of their toxins. Furthermore, floating plastics may substantially expand the substrate area available for benthic algae in the ocean, intensifying the transfer of potent toxins through pelagic food webs. In this study, we quantify the available surface area of micro- and macroplastics in different oceanic regions and assess the potential role of floating plastics as vectors for the transfer of toxins from three widespread benthic dinoflagellates, Gambierdiscus spp., Ostreopsis cf. ovata and Prorocentrum lima. To avoid bias associated to the occurrence of benthic algae in deep waters, we selected only records from 0 to 100 m depths. We estimate that 26.8 × 10¹⁰ cm² of plastic surface area is potentially available in surface waters of the global ocean, mostly in the size range of large microplastics (1.01-4.75 mm). Based on the distribution of floating plastics and the habitat suitability of the selected microalgal species, the plastic relative colonization risks will be greater in the Mediterranean Sea and in the subtropical and temperate western margins of the oceans, such as the North American and Asian eastern coasts and, to a lesser extent, southern Brazil and Australia. In places where the colonization of O. cf. ovata cells on floating plastic debris has been properly quantified, such as the Mediterranean and southern Brazil, we estimate a colonization potential of up to 2 × 10⁶ cells km^-2 of ocean surface during the regular occurrence period and up to 1.7 × 10⁸ cells km^-2 during massive blooms of this species. As plastic pollution and harmful benthic algal blooms have both increased substantially over the past decades, we suggest that their interactive effects can become a major and novel threat to marine ecosystems and human health.

Industrialised fishing nations largely contribute to floating plastic pollution in the North Pacific subtropical gyre

The subtropical oceanic gyre in the North Pacific Ocean is currently covered with tens of thousands of tonnes of floating plastic debris, dispersed over millions of square kilometres. A large fraction is composed of fishing nets and ropes while the rest is mostly composed of hard plastic objects and fragments, sometimes carrying evidence on their origin. In 2019, an oceanographic mission conducted in the area, retrieved over 6000 hard plastic debris items > 5 cm. The debris was later sorted, counted, weighed, and analysed for evidence of origin and age. Our results, complemented with numerical model simulations and findings from a previous oceanographic mission, revealed that a majority of the floating material stems from fishing activities. While recent assessments for plastic inputs into the ocean point to coastal developing economies and rivers as major contributors into oceanic plastic pollution, here we show that most floating plastics in the North Pacific subtropical gyre can be traced back to five industrialised fishing nations, highlighting the important role the fishing industry plays in the solution to this global issue.

Accumulation of marine litter in cold-water coral habitats: A comparative study of two Irish Special Areas of Conservation, NE Atlantic

Cold-water corals (CWCs) have come under threat from anthropogenic activities such as fishing despite their ecological significance as biodiversity hotspots and as such are being protected in Europe under the EU Habitats Directive with some designated as Special Areas of Conservation (SACs). This study maps the distribution and sources of marine litter in CWC habitats in two SACs on the Irish margin. Data were collected with remotely operated vehicle in the SACs. The density, abundance and composition of litter were assessed, with differences observed between the two sites. The regional morphology influences the distribution of litter in the SACs, with CWC reefs and rock exposures trapping more marine litter. Fishing gear (80.7%) and plastics (55.1%) were commonly found. The observed fisheries-derived litter in the SACs exceed global averages of 10-20% fishing gear, suggesting the SACs appear to offer limited protection to the coral habitats with respect to marine litter.