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Marine plastic pollution is receiving much public attention, as the civil society sees it as a tangible threat to our oceans and its services. Regrettably, this perception and its evident effects on marine habitats (entanglement, ingestion, aesthetic aspects of contamination) link people to the sea through a connection of strong negative traits. The fact that plastic is identified as a hazard can help against its misuse and mismanagement, but it does not provide a durable commitment to the ocean, which must be sought by other means and new communication styles. The ocean is facing multiple anthropic pressures, not tangible on a spatial or temporal human scale in most cases. What once drove children to become todays’ marine scientists were the wonder and curiosity that the ocean and its creatures could elicit: the spectacle of ocean life undoubtfully creates a magic “connectedness” that amazes and binds. The feelings arising from a pristine sea enable the awareness that the ocean soothes the eyes and the soul and heals, positively reconnecting humans to nature in the “one-health” perspective. In recent experiences we examined children’s “good” bond to nature through questionnaires, and their engagement in the quest for plastic trash, aimed at sparking kids’ natural curiosity and exploration desire. We humans are better able to protect what we care for: the relationship with nature fosters care and understanding, which should be encouraged from an early age to recreate the “connectedness” fundamental to rebuild respect, love and commitment for the ocean that we want and need.&nbsp

Understanding residence times of plastic in the ocean is a major knowledge gap in plastic pollution studies. Observations report a large mismatch between plastic load estimates from worldwide production and disposal and actual plastics floating at the sea surface. Surveys of the water column, from the surface to the deep sea, are rare. Most recent work, therefore, addressed the “missing plastic” question using modeling or laboratory approaches proposing biofouling and degradation as the main removal processes in the ocean. Through organic matrices, plastic can affect the biogeochemical and microbial cycling of carbon and nutrients. For the first time, we providein situmeasured vertical fluxes of microplastics deploying drifting sediment traps in the North Atlantic Gyre from 50 m down to 600 m depth, showing that through biogenic polymers plastic can be embedded into rapidly sinking particles also known as marine snow. We furthermore show that the carbon contained in plastic can represent up to 3.8% of the total downward flux of particulate organic carbon. Our results shed light on important pathways regulating the transport of microplastics in marine systems and on potential interactions with the marine carbon cycle, suggesting microplastic removal through the “biological plastic pump”.

One of the major knowledge gaps in the study of plastic pollution is the understanding of residence times of these anthropogenic particles once they reach our oceans. Observations report a mismatch between estimates of plastic loads from worldwide plastic production and mismanaged plastic waste and actual plastic concentration seen floating at the sea-surface. Surveys of the water column -from the surface to the deep sea- are rare. Most of the recent efforts have thus addressed this question with modeling approaches or laboratory experiments that individuate in biofouling an important factor for the removal efficiency of plastics at sea and a likely explanation for the “missing plastic”. For the first time, we providein-situmeasured fluxes and removal rates of microplastics using deployments of drifting sediment traps in the North Atlantic Gyre from 50 m down to 600 m depth. We identified and quantified plastic contents with two different analytical approaches, FTIR and Py-GC/MS to determine polymer mass and particle distribution over depth. From derived data, interaction with biogenic polymers and thus particles transfer from the surface to the deep ocean are reconstructed. These findings shed a light on important pathways that regulate microplastics fate in marine ecosystems, from possible harmful repercussions on marine biota to impacts on fundamentals elements cycles.

Microplastics are substrates for microbial activity and can influence biomass production. This has potentially important implications in the sea-surface microlayer, the marine boundary layer that controls gas exchange with the atmosphere and where biologically produced organic compounds can accumulate. In the present study, we used six large scale mesocosms to simulate future ocean scenarios of high plastic concentration. Each mesocosm was filled with 3 m3 of seawater from the oligotrophic Sea of Crete, in the Eastern Mediterranean Sea. A known amount of standard polystyrene microbeads of 30 μm diameter was added to three replicate mesocosms, while maintaining the remaining three as plastic-free controls. Over the course of a 12-day experiment, we explored microbial organic matter dynamics in the sea-surface microlayer in the presence and absence of microplastic contamination of the underlying water. Our study shows that microplastics increased both biomass production and enrichment of carbohydrate-like and proteinaceous marine gel compounds in the sea-surface microlayer. Importantly, this resulted in a ∼3 % reduction in the concentration of dissolved CO2 in the underlying water. This reduction was associated to both direct and indirect impacts of microplastic pollution on the uptake of CO2 within the marine carbon cycle, by modifying the biogenic composition of the sea's boundary layer with the atmosphere.

Three-dimensional hydrogels of organic polymers have been suggested to affect a variety of processes in the ocean, including element cycling, microbial ecology, food-web dynamics, and air-sea exchange. However, their abundance and distribution in the ocean are hardly known, strongly limiting an assessment of their global significance. As a consequence, marine gels are often disregarded in biogeochemical or ecosystem models. Here, we demonstrate the widespread abundance of microgels in the ocean, from the surface to the deep sea. We exhibit size spectra of two major classes of marine gels, transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP) for three different ocean regimes: (a) Polar Seas, (b) Eastern Boundary Upwelling Systems, and (c) the oligotrophic open ocean. We show the variations of TEP and CSP over the water-column, and compare them to dissolved organic carbon (DOC). We also discuss how the observed distributional patterns inform about productivity and particle dynamics of these distinct oceanic regimes. Finally, we exploit current research topics, where consideration of microgels may give new insight into the role of organic matter for marine biogeochemical processes.

The ubiquitous presence of microplastics in marine habitats has potential impacts on biogeochemical cycling as well as ecological consequences across trophic levels. Microplastics provide increased surface area for microbial growth, with consequences on carbon and nutrient dynamics at the basis of all marine food webs. Despite their high and increasing concentration in the ocean, microplastics’ influence on the transformation and composition of marine organic matter is largely unknown. In the POSEIDOMM project (www.poseidomm.eu), we are exploring the impact of microplastics on the microbial processing of both dissolved and particulate organic matter in controlled marine conditions. Studies have been completed in a series of laboratory microcosms investigations and in a large scale outdoor mesocosm experiment. The initial results indicate that the presence of standard polystyrene microbeads increased the production of dissolved (microcosms) and particulate organic matter (mesocosms) and their accumulation at the air-sea interface. This increase could result from either higher microbial production or enhanced transformation of pre-existing substrates. In the upper 100 µm of the mesocosms’ surface, we also observed a higher accumulation of marine gels which led to a modified surface film, with consequences on the air-sea exchange of oxygen and CO2. Given their low density and wide distribution, microplastics present an elevated potential to influence the dynamics of the upper ocean., File of the talk provided upon request.

Slides from a science communication workshop presented at 2020 Oceans Sciences meeting in San Diego, CA (17 Feb 2020).

The plastic invasion of marine habitats represents a global priority with impacts across ecosystems and societies. Although considered inert, plastic and microplastics can provide substrate and carbon source for the growth of microorganisms, thus interfering with marine nutrient and carbon dynamics. Despite the high and increasing abundance of microplastics in the ocean, their influence on the transformation and composition of marine organic matter is largely unknown. In the European POSEIDOMM project (www.poseidomm.eu) we explored the impact of microplastics on the microbial production and processing of organic matter in controlled surface marine conditions, both in microcosms and in a mesocosm experiment. Following the addition of standard inert microplastic particles to microcosms and mesocosms, we observed an increased production of both dissolved and particulate organic matter, potentially linked to an increased microbial production or an enhanced transformation of pre-existing organic substrates. Since much of the low-density plastic debris at sea is positively buoyant, surface plastic accumulation may have multiple effects on marine surface waters. Changes in the concentrations of organic matter in marine surface layers can modify the penetration of solar radiation, microbial activity and air-sea gas fluxes. By interacting with dissolved and particulate organic components in surface waters, microplastic accumulation can interfere with the aquatic cycling of carbon and nutrients.

Plastics waste is a globalemerging threat for aquatic ecosystems,ubiquitous in rivers, lakes and marine areas, whereabout 8 million metric tons of plastic debris end up every year. It is estimated that 80% of marine debris has land based origins, transported to the sea by rivers and sewage.By comparison, the amount of plastics released into freshwater and terrestrial environments is likely to be much higher as these provide the main transport pathways to the marine environment.As an example, in the Mediterranean Sea, terrestrial debris represent 94%, of which 95% consists of macro and micro plastic litter. However, relatively little is known about the abundance and sources of this anthropogenic litter. This information is fundamental to determine its impact and to identify successful mitigation strategies prior to its arrival in our waters. Importantly, while the scientific community (including ourselves) is dedicating much effort on the impacts of plastic on marine and in general, aquatic ecosystems, the problem of plastic pollution needs to be tackled on land. We present here a citizen-science project aimed at promoting public stewardship of local aquatic resources, quantifying the type and quantity of plastic entering our rivers with the aim of reducing the amount of plastic reaching our seas. Efforts to solve the plastic problem require a partnered approach between research institutions, municipalities, educational institutions and citizens, achievable through citizen science. Focusing on the connectivity of all aquatic ecosystems in the emerging challenge of plastic debris in the hydrosphere, we present recent research activity and the efforts of the community of citizen scientists monitoring local water bodies for anthropogenic litter presence and composition.

Marine bacteria are the main consumers of the freshly produced organic matter. In order to meet their carbon demand, bacteria release hydrolytic extracellular enzymes that break down large polymers into small usable subunits. Accordingly, rates of enzymatic hydrolysis have a high potential to affect bacterial organic matter recycling and carbon turnover in the ocean. Many of these enzymatic processes were shown to be pH sensitive in previous studies. Due to the continuous rise in atmospheric CO2 concentration, seawater pH is presently decreasing at a rate unprecedented during the last 300 million years with so-far unknown consequences for microbial physiology, organic matter cycling and marine biogeochemistry. We studied the effects of elevated seawater pCO2 on a natural plankton community during a large-scale mesocosm study in a Norwegian fjord. Nine 25m-long Kiel Off-Shore Mesocosms for Future Ocean Simulations (KOSMOS) were adjusted to different pCO2 levels ranging from ca. 280 to 3000 µatm by stepwise addition of CO2 saturated seawater. After CO2 addition, samples were taken every second day for 34 days. The first phytoplankton bloom developed around day 5. On day 14, inorganic nutrients were added to the enclosed, nutrient-poor waters to stimulate a second phytoplankton bloom, which occurred around day 20. Our results indicate that marine bacteria benefit directly and indirectly from decreasing seawater pH. During both phytoplankton blooms, more transparent exopolymer particles were formed in the high pCO2 mesocosms. The total and cell-specific activities of the protein-degrading enzyme leucine aminopeptidase were elevated under low pH conditions. The combination of enhanced enzymatic hydrolysis of organic matter and increased availability of gel particles as substrate supported higher bacterial abundance in the high pCO2 treatments. We conclude that ocean acidification has the potential to stimulate the bacterial community and facilitate the microbial recycling of freshly produced organic matter, thus strengthening the role of the microbial loop in the surface ocean.