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1. MICROPLASTIC POLLUTION IN THE TIJUANA ESTUARY BEACHESOF SOUTHERN CALIFORNIA

   Sheppard, Q.; Gray, S.C. (February 2022, Ocean Sciences Meeting)

   no editor. (Ed.)

   The Tijuana River Watershed encompasses 1750 square miles of territory in both Mexico and the United States, culminating at the National EstuarineResearch Reserve. While this area comprises one of the largest undisturbed wetlands in the state, it is one of the most polluted rivers in SouthernCalifornia, draining raw sewage and nonpoint source pollution. Despite extensive research, microplastic pollution along the beaches has not been explored. The objective of this study is to determine how the abundance and morphology of microplastic pollution in beach sediments vary with distance along the littoral cell from the Tijuana River outfall. Twenty samples were collected at 10 sites that span from the Tijuana River outfall to Mission Beach, San Diego. They are characterized as outfall sites, low-visitation beaches near the outfall, and high-visitation beaches further from the outfall. Solutions of 100ml sediment and 400ml hyper-saline solution were mixed and settled for 16 hours before being processed using a vacuum filtration system in a laminar fl ow hood. The microplastics (MP)were counted and classified using light microscopy. Laboratory practices to reduce laboratory contamination were employed and analytical blanks were run for every 3 samples. MPs ranged from 1 to 199/100ml sediment, of which approximately 91% were fibers. The greatest MP abundance occurred at the river outfall sites, but recovery rates were highly variable, and the analytical blanks ranged from 3-63/100ml sediment. The results oft his study suggest that microplastic distribution in sandy beach sediments is patchy but higher near the Tijuana River Outfall, and that future studies should report analytical blanks and employ methods to reduce contamination. Understanding the relationship between watersheds and microplastic distributions may inspire policy change on water quality protections in watersheds. 

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2. Coastal influences on sedimentary organic matter in deep basins offshore of Southern California

   Nelson, C.; Sarner, R.; Saavedra-Alvarado, J.; Gray, S.C. (February 2020, Ocean Sciences Meeting)

   none. (Ed.)

   The concentration and isotopic composition (δC; C/N) of sedimentary organic matter (SOM) in near-shore bays and offshore shelves and basins is impacted by organic matter source (e.g., marine algae, terrestrial plants, and agricultural and sewage runoff) and natural and anthropogenic processes such as pollution, terrestrial runoff, and climate change, which can expand oxygen minimum zones, leading to decreased bottom-water dissolved oxygen (DO) and enhanced organic matter preservation. The factors that affect the sources and concentrations of SOM have not been extensively investigatedin the California margin. The objective of this study was to determine how the SOM concentrations andstable isotopes (δC; C/N) vary between shallow urban bays, offshore shelves, and deep basins and with other factors (water depth, DO and grain size). On cruises in 2018, surface sediments were collected using multicores and van-veen grabs. Samples were collected from shelves (10-14km offshore; 100-300m) and basins (90-130km offshore; 618-997m)and for comparison, urban bays in San Diego. The dissolved oxygen (DO) concentrations of seafloor-water preserved in the multicores were measured with a hand-held DO meter. In the lab, SOM concentrations were determined by Loss on Ignition (5 hours, 550°C) and grain-size distributions were determined by scanning on a CILAS 1190 particle size analyzer. Select sediments were dissolved in HCl and filtered to remove inorganic carbonates and the δC and C/N measured at UC Davis. All sediments were organic rich (2-21%) with mean grain sizes of fi ne sand or silt with variable clay (3-12%). In general, the sands were lower in organic matter (< 5%) compared to silty samples withvariable concentrations (2-22%). The greatest organic matter was found in the deeper hypoxic basins where DO was less than 1.5 mg/L. The δC & C/N were consistent with mixed terrestrial and marine organic sources and there was not a difference in mean values between the bays, shelves and basins.However, the values were highly variable for the urban bay and shelf sediments suggesting heterogenous input. Organic matter in coastal sediments are an important component of the global carbon cycle and abetter understanding of controlling factors is important in the face of climate change and increased anthropogenic impacts. 

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3. Spatiotemporal variability of benthic and planktonic foraminifera off the coast of San Diego

   Renssen, B.; Gray, S.C. (November 2021, CERF 26th Biennial Conference)

   no editor (Ed.)

   Foraminifera (single celled protists with tests primarily of Calcium Carbonate) are directly influenced by ocean warming and hydrographic changes such as expansion of the low oxygen areas associated with anthropogenic climate change. Benthic and planktonic foraminifera communities are good indicators of hydrographic conditions at the sea-floor and sea surface, respectively. Though previous studies have demonstrated that there has been overall ocean surface warming in Southern California and that the oxygen minimum zone has expanded, the relationship between water temperature, dissolved oxygen and foraminifera abundance in the area offshore San Diego has not been extensively examined. Cored sediment samples along with hydrographic data collected during annual research cruises (2001-2012, 2018) on the RV Sproul at three stations (water depth 100 m, 200m 300 m) due west from San Diego, CA provide an opportunity to evaluate how benthic and planktonic foraminiferal communities have changed over the past 19 years. The objective of this research was to identify the foraminifera in these sediments and compare patterns between years to temperature and dissolved oxygen (DO). Sediment samples from the upper 1 cm of the seafloor using a multicore were sieved and the foraminifera were picked and examined under a Leica S9i microscope for identification to genus. Sea surface and bottom water temperature and DO concentrations were measured using a CTD. Analyses of the variation between sites and over time will indicate whether benthic and planktonic community changes track environmental changes in temperature and dissolved oxygen, providing valuable data to assess whether climate change is impacting marine communities. 

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4. Relative exposure to microplastics and prey for a pelagic forage fish

   https://doi.org/10.1088/1748-9326/ac7060  

   Chavarry, J M; Law, K L; Barton, A D; Bowlin, N M; Ohman, M D; Choy, C A (June 2022, Environmental Research Letters)

   Abstract In the global ocean, more than 380 species are known to ingest microplastics (plastic particles less than 5 mm in size), including mid-trophic forage fishes central to pelagic food webs. Trophic pathways that bioaccumulate microplastics in marine food webs remain unclear. We assess the potential for the trophic transfer of microplastics through forage fishes, which are prey for diverse predators including commercial and protected species. Here, we quantify Northern Anchovy ( Engraulis mordax ) exposure to microplastics relative to their natural zooplankton prey, across their vertical habitat. Microplastic and zooplankton samples were collected from the California Current Ecosystem in 2006 and 2007. We estimated the abundance of microplastics beyond the sampled size range but within anchovy feeding size ranges using global microplastic size distributions. Depth-integrated microplastics (0–30 m depth) were estimated using a depth decay model, accounting for the effects of wind-driven vertical mixing on buoyant microplastics. In this coastal upwelling biome, the median relative exposure for an anchovy that consumed prey 0.287–5 mm in size was 1 microplastic particle for every 3399 zooplankton individuals. Microplastic exposure varied, peaking within offshore habitats, during the winter, and during the day. Maximum exposure to microplastic particles relative to zooplankton prey was higher for juvenile (1:23) than adult (1:33) anchovy due to growth-associated differences in anchovy feeding. Overall, microplastic particles constituted fewer than 5% of prey-sized items available to anchovy. Microplastic exposure is likely to increase for forage fishes in the global ocean alongside declines in primary productivity, and with increased water column stratification and microplastic pollution. 

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5. Microplastics in Atlantic Ribbed Mussels (Geukensia demissa) from the Delaware Inland Bays, USA

   https://doi.org/10.3390/microplastics3010009  

   Ashley, Jeffrey; Pilat, Amanda; Ohlweiler, Ariana; Ogden, Connor; Bradley, Owen; Modi, Priya; Talbot, Spencer; Smith, Caya; O’Pella, Justin; Ozbay, Gulnihal (March 2024, Microplastics)

   Due to the prevalence of plastic pollution in coastal ecosystems, aquatic organisms are at high risk for accumulating microplastics (MPs). Filter-feeding bivalves, such as mussels and oysters, may be exposed to, and subsequently accumulate, MPs due to the high volume of water they pass through their bodies. This study assessed the levels of MPs within Atlantic ribbed mussels (Geukensia demissa), a common filter feeder found along the United States Atlantic Coast, from 12 sites within Rehoboth Bay, Indian River Bay, and Little Assawoman Bay, collectively known as the Delaware Inland Bays. Composited mussels from each site were digested using potassium hydroxide and filtered. Microplastics were physically identified, sorted based on color, and counted using a digital microscope. Microplastics, almost entirely dominated by synthetic microfibers, were found in all mussels well above laboratory blanks. Across all sites, 40% of microfibers were black, and 27% of fibers were clear. The composite concentrations of MPs ranged from 0.25 to 2.06 particles/g wet tissue, with a mean of 0.08 ± 0.06. In general, higher concentrations were found in mussels collected at sites that were adjacent to more urbanized land use versus those from rural sites. At two sites, individual mussels, in addition to composites, were analyzed and had MP concentrations ranging from 11 to 69 particles/mussel. This study represents the first evaluation of MPs in this ecologically important coastal species and suggests its viability as a biomonitoring species for microplastic pollution. 

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