Size and Density of Upside-Down Jellyfish, \u3ci\u3eCassiopea\u3c/i\u3e sp., and Their Impact on Benthic Fluxes in a Caribbean Lagoon

Anthropogenic disturbances may be increasing jellyfish populations globally. Epibenthic jellyfish are ideal organisms for studying this phenomenon due to their sessile lifestyle, broad geographic distribution, and prevalence in near-shore coastal environments. There are few studies, however, that have documented epibenthic jellyfish abundance and measured their impact on ecological processes in tropical ecosystems. In this study, the density and size of the upside-down jellyfish (Cassiopea spp.) were measured in Codrington Lagoon, Barbuda. A sediment core incubation study, with and without Cassiopea, also was performed to determine their impact on benthic oxygen and nutrient fluxes. Densities of Cassiopea were 24–168 m−2, among the highest reported values in the literature. Under illuminated conditions, Cassiopea increased oxygen production \u3e300% compared to sediment alone, and they changed sediments from net heterotrophy to net autotrophy. Cassiopea increased benthic ammonium uptake, but reduced nitrate uptake, suggesting they can significantly alter nitrogen cycling. Future studies should quantify the abundance of Cassiopea and measure their impacts on ecosystem processes, in order to further determine how anthropogenic-related changes may be altering the function of tropical coastal ecosystems

Microplastic in Surface Waters of Urban Rivers: Concentration, Sources, and Associated Bacterial Assemblages

The ecological dynamics of microplastic (\u3c5 mm) are well documented in marine ecosystems, but the sources, abundance, and ecological role of microplastic in rivers are unknown and likely to be substantial. Microplastic fibers (e.g., synthetic fabrics) and pellets (e.g., abrasives in personal care products) are abundant in wastewater treatment plant (WWTP) effluent, and can serve as a point source of microplastic in rivers. The buoyancy, hydrophobic surface, and long transport distance of microplastic make it a novel substrate for the selection and dispersal of unique microbial assemblages. We measured microplastic concentration and bacterial assemblage composition on microplastic and natural surfaces upstream and downstream of WWTP effluent sites at nine rivers in Illinois, United States. Microplastic concentration was higher downstream of WWTP effluent outfall sites in all but two rivers. Pellets, fibers, and fragments were the dominant microplastic types, and polymers were identified as polypropylene, polyethylene, and polystyrene. Mean microplastic flux was 1,338,757 pieces per day, although the flux was highly variable among nine sites (min = 15,520 per day, max = 4,721,709 per day). High-throughput sequencing of 16S rRNA genes showed bacterial assemblage composition was significantly different among microplastic, seston, and water column substrates. Microplastic bacterial assemblages had lower taxon richness, diversity, and evenness than those on other substrates, and microplastic selected for taxa that may degrade plastic polymers (e.g., Pseudomonas) and those representing common human intestinal pathogens (e.g., Arcobacter). Effluent from WWTPs in rivers is an important component of the global plastic “life cycle,” and microplastic serves as a novel substrate that selects and transports distinct bacterial assemblages in urban rivers. Rates of microplastic deposition, consumption by stream biota, and the metabolic capacity of microplastic biofilms in rivers are unknown and merit further research

Prevalence of microplastics and anthropogenic debris within a deep-sea food web

Microplastic particles (\u3c5 mm) are ubiquitous throughout global marine ecosystems, including the deep sea. Ingestion of microplastics and other anthropogenic microparticles is reported in diverse marine taxa across trophic levels. Trophic transfer, or the movement of microplastics across trophic levels, is reported in laboratory studies but not yet widely measured in marine food webs. The Monterey Bay submarine canyon ecosystem contains a well-studied, known deep-sea food web in which to examine the trophic fate of microplastics. We measured microplastic abundance across 17 genera spanning approximately 5 trophic levels and a diversity of feeding behaviors. Samples were collected using remotely operated vehicles and oblique midwater trawls, and gut contents of all individuals examined (n = 157) were analyzed for microplastic abundance and other anthropogenic particles greater than 100 μm using stereo microscopy. Microparticles were analyzed with Raman spectroscopy to confirm material type. Anthropogenic particles were found in all genera examined, across crustacean, fish, mollusk, and gelatinous organisms, in amounts ranging from 0 to 24 particles per individual. There was no significant relationship between microplastic amount and fish trophic level, suggesting that the trophic transfer of microparticles is not occurring. Body size was positively correlated with microplastic abundance across all taxa. The fish genus Scomber sp. drove this relationship, suggesting higher microparticle abundance in mobile individuals with broad horizontal distributions. Future work should examine physiological pathways for microplastic transport within organisms (e.g. excretion, accumulation on gills, internal translocation of particles) and between organisms within shared habitats to more fully understand the fate of microplastics within aquatic food webs

The “plastic cycle”: a watershed‐scale model of plastic pools and fluxes

Research on plastics in global ecosystems is rapidly evolving. Oceans have been the primary focus of studies to date, whereas rivers are generally considered little more than conduits of plastics to marine ecosystems. Within a watershed, however, plastics of all sizes are retained, transformed, and even extracted via freshwater use or litter cleanup. As such, plastic litter in terrestrial and freshwater ecosystems is an important but underappreciated component of global plastic pollution. To gain a holistic perspective, we developed a conceptual model that synthesizes all sources, fluxes, and fates for plastics in a watershed, including containment (ie disposed in landfill), non-containment (ie persists as environmental pollution), mineralization, export to oceans, atmospheric interactions, and freshwater extraction. We used this model of the “plastic cycle” to illustrate which components have received the most scientific attention and to reveal overlooked pathways. Our main objective is for this framework to inform future research, offer a new perspective to adapt management across diverse waste governance scenarios, and improve global models of plastic litter

Spatial variability in nutrient concentration and biofilm nutrient limitation in an urban watershed

Nutrient enrichment threatens river ecosystem health in urban watersheds, but the influence of urbanization on spatial variation in nutrient concentrations and nutrient limitation of biofilm activity are infrequently measured simultaneously. In summer 2009, we used synoptic sampling to measure spatial patterns of nitrate (NO3−), ammonium (NH4+), and soluble reactive phosphorus (SRP) concentration, flux, and instantaneous yield throughout the Bronx River watershed within New York City and adjacent suburbs. We also quantified biofilm response to addition of NO3−, phosphate (PO43−), and NO3− + PO43− on organic and inorganic surfaces in the river mainstem and tributaries. Longitudinal variation in NO3− was low and related to impervious surface cover across sub-watersheds, but spatial variation in NH4+ and SRP was higher and unrelated to sub-watershed land-use. Biofilm respiration on organic surfaces was frequently limited by PO43− or NO3− + PO43−, while primary production on organic and inorganic surfaces was nutrient-limited at just one site. Infrequent NO3− limitation and low spatial variability of NO3− throughout the watershed suggested saturation of biological N demand. For P, both higher biological demand and point-sources contributed to greater spatial variability. Finally, a comparison of our data to synoptic studies of forested, temperate watersheds showed lower spatial variation of N and P in urban watersheds. Reduced spatial variation in nutrients as a result of biological saturation may represent an overlooked effect of urbanization on watershed ecology, and may influence urban stream biota and downstream environments

Eastern oyster (Crassostrea virginica) filtration, biodeposition, and sediment nitrogen cycling at two oyster reefs with contrasting water quality in Great Bay Estuary (New Hampshire, USA)

Benthic deposition of carbon (C) and nitrogen (N)-rich oyster biodeposits may increase denitrification, or anaerobic respiration of nitrate (NO3 −) to di-nitrogen gas (N2). However, environmental drivers of C and N dynamics in oyster biodeposits and reef-adjacent sediments require clarification. In July 2012, we collected intact sediment cores adjacent to and 15–20 m away from two oyster reefs (Crassostrea virginica) in Great Bay, New Hampshire, USA: one reference site and one site with cultural eutrophication. We also measured seston, chlorophyll a, and in situ oyster feeding and biodeposition. Cores were incubated in continuous-flow chambers where inflow water received 15N-ammonium (NH4 +), 15NO3 −, or no isotopes (control). We quantified fluxes of dissolved nutrients and gasses (oxygen, 28N2, 29N2, 30N2, and argon) after 24 h. Finally, we measured size-fractionated sediment organic matter. At the eutrophic site, abundant phytoplankton in the 5–28 µm size range was correlated with enhanced oyster feeding rates and biodeposit quality (lower C:N). This site had greater denitrification rates in reef-adjacent cores relative to distal cores. Low production of 29,30N2 in 15NH4 + amended cores suggested water column or biodeposit NH4 + were unlikely to be converted to N2. At both sites, reef-adjacent cores had more shell and higher 29,30N2 production with 15NO3 − addition relative to distal cores, suggesting direct denitrification enhancement near reefs. Oysters likely increased sediment N2 production via high quality biodeposits (eutrophic site), and NO3 − diffusion via structural complexity of reef-adjacent sediment (both sites). Overall, results suggest oyster-mediated ecosystems services may be expected to vary with environmental conditions

Microplastic deposition velocity in streams follows patterns for naturally occurring allochthonous particles

Abstract Accumulation of plastic litter is accelerating worldwide. Rivers are a source of microplastic (i.e., particles <5 mm) to oceans, but few measurements of microplastic retention in rivers exist. We adapted spiraling metrics used to measure particulate organic matter transport to quantify microplastic deposition using an outdoor experimental stream. We conducted replicated pulse releases of three common microplastics: polypropylene pellets, polystyrene fragments, and acrylic fibers, repeating measurements using particles with and without biofilms. Depositional velocity (vdep; mm/s) patterns followed expectations based on density and biofilm ‘stickiness’, where vdep was highest for fragments, intermediate for fibers, and lowest for pellets, with biofilm colonization generally increasing vdep. Comparing microplastic vdep to values for natural particles (e.g., fine and coarse particulate organic matter) showed that particle diameter was positively related to vdep and negatively related to the ratio of vdep to settling velocity (i.e., sinking rate in standing water). Thus, microplastic vdep in rivers can be quantified with the same methods and follows the same patterns as natural particles. These data are the first measurements of microplastic deposition in rivers, and directly inform models of microplastic transport at the landscape scale, making a key contribution to research on the global ecology of plastic waste

Microplastic accumulation in riverbed sediment via hyporheic exchange from headwaters to mainstems

In rivers, small and lightweight microplastics are transported downstream, but they are also found frequently in riverbed sediment, demonstrating long-term retention. To better understand microplastic dynamics in global rivers from headwaters to mainstems, we developed a model that includes hyporheic exchange processes, i.e., transport between surface water and riverbed sediment, where microplastic retention is facilitated. Our simulations indicate that the longest microplastic residence times occur in headwaters, the most abundant stream classification. In headwaters, residence times averaged 5 hours/km but increased to 7 years/km during low-flow conditions. Long-term accumulation for all stream classifications averaged ~5% of microplastic inputs per river kilometer. Our estimates isolated the impact of hyporheic exchange processes, which are known to influence dynamics of naturally occurring particles in streams, but rarely applied to microplastics. The identified mechanisms and time scales for small and lightweight microplastic accumulation in riverbed sediment reveal that these often-unaccounted components are likely a pollution legacy that is crucial to include in global assessments