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Trophic transfer of microplastics from copepods to jellyfish in the marine environment

By Meagan Ando​, SRC intern

 Our oceans face great threats in this day and age. The list is quite expansive, but one such threat is microplastics. Microplastics are tiny bits of plastic, usually around the size of a sesame seed or smaller, that originate from everyday items such as water bottles or straws that find their way into the ocean (Image 1). Because of their size proximity to plankton, many marine organisms ingest these microplastics unknowingly, which can easily accumulate and be passed through trophic levels from zooplankton to fish and to other larger marine animals (Cole et al., 2013; Farrell and Nelson, 2013). Trophic levels are sequential stages in a food chain that comprises primary producers and subsequent primary, secondary, and sometimes tertiary consumers. Each predator/prey interaction involves a fraction of the amount of energy produced/consumed on the previous trophic level, making it possible for the exchange of these microplastics from level to level. This can be quite alarming, especially if these microplastics end up in the fish you eat for dinner in your home. That’s why the study of microplastic transfer between trophic levels is necessary. Although there was some information known regarding this topic, Costa et al. (2020) set out to answer more questions and fill the gap of knowledge regarding the microplastic transfer among zooplankton. This information about zooplankton was vital due to the fact that they are an important link between the primary producing phytoplankton (Turner, 2004), that use the process of photosynthesis to create energy, and the higher trophic levels (Costa et al., 2020).  

In order to simulate a trophic level transfer system, the group created a simple two-level trophic cascade using the nauplii zooplankton species of the T. fulvus copepod as the prey and the ephyrae stage of the Aurelia species of jellyfish as predator (Costa et al., 2020). We know these species for being easy to study because of their large abundance, ease of culturing methods, and their role as excellent models in the evaluation of microplastic contamination. In short, they exposed the zooplankton nauplii to polyethylene microplastics for 6 hours and then offered to the ephyrae jellyfish for 24 hours in order to simulate the consumption of prey in the wild. The amount of consumed microplastics in the zooplankton were examined and verified using fluorescent microscopes to confirm that the nauplii were contaminated and that there was something for the jellyfish to be polluted with. In order to test the negative side effects of the microplastic contamination in the jellyfish, they evaluated both immobility and pulsation frequency in hopes of shedding some light on what ecotoxicological effects these tiny bits of plastics could have on a predator in a short time. Such results were determined using a recording system along with a video graphic analyzer. Immobility percentages, including those jellyfish that were completely motionless, were recorded, along with the pulsation frequency that was calculated using a recording of pulsations in a time frame of 1 minute (Costa et al., 2020). 

Overall, the results found that the jellyfish had in fact ingested microplastics, confirming this physical trophic transfer (Image 2). Quite interestingly, there were not any significant ecological responses because of the influx of microplastics in the jellyfish population; immobility percentages were not statistically significant, and pulsation frequencies were only slightly decreased (Figure 1). To conclude, this group of researchers found that the trophic transfer of microplastics is clear through the indirect ingestion by predators and is significant in the ocean because of the ability of these jellyfish to carry heavy metals in their gelatinous tissues. Also, they agreed that a longer exposure time frame (over 24 hours) could lead to more visible, measurable ecotoxicological effects (Costa et al., 2020). This information is vital in protecting the health and well-being of not only the oceans and the organisms that inhabit it but also our very own family and friends. We can all help take steps in the reduction of microplastics in the environment by reducing our plastic usage (by using reusable items such as water bottles and bags) and recycling those items in which we use. 

Figure 1: Graphic visual showing the pulsation frequencies between uncontaminated jellyfish and jellyfish containing the contaminated copepods (Costa et al., 2020).

Image 1: Example of everyday plastics found on a beach (Tim Hüfner).

Image 2: Set of images showing the trophic transfer after 24 hours. Image A shows the control jellyfish, completely free of contamination. Images B,C show copepod clusters within the jellyfish with white arrows pointing to the polyethylene microplastics (Costa et al., 2020).

Works cited 

Cole, M., Lindeque, P., Fileman, E., Halsband, C., Goodhead, R., Moger, J., et al. (2013). Microplastic ingestion by zooplankton. Environ. Sci. Technol. ​47, 6646–6655. 

Costa, E., et al. (2020). Trophic transfer of microplastics from copepods to jellyfish in the marine environment. Frontiers in Environmental Science​​. Vol. 8. 

Farrell, P., and Nelson, K. (2013). Trophic level transfer of microplastic: Mytilus edulis ​(L.) to Carcinus maenas ​(L.). Environ. Pollut. ​177, 1–3. 

Tim Hüfner via Unsplash. 

Turner, J. T. (2004). The importance of small planktonic copepods and their roles in pelagic marine food webs. Zool. Stud. ​43, 255–266. 

Ocean Plastics

By: Nick Martinez, SRC Intern

The world’s oceans face a variety of challenges ranging from rising sea levels and sea surface temperatures, to overfishing and excessive amounts of anthropogenic debris being tossed into the oceans. Many studies have focused on the large scale effects of each of these dire issues, yet few have ventured into the realm of marine plastics and how these objects actually aid in the dispersal and recruitment of various species throughout the oceans of the world. Since the earliest known recording of anthropogenic waste in the world’s oceans back in the 1970’s (Goldstein et al. 2014), scientists have begun paying particular attention to the way many sessile species have proven to be a key foundation species in the recruitment and dispersal of various organisms throughout the world. Due to the anatomy of these sessile species, scientists have found a variety of microecosystems thriving on the surface of these plastics. Barnacles and other sessile species turn the smooth, unprotected surfaces of the plastics into a more structured surface where rafting organisms can hide and seek shelter from the otherwise harsh pelagic conditions. Because these ocean plastics have been virtually transformed by sessile organisms, these plastics and other anthropogenic debris augment a natural floating substrate in the open ocean, allowing “islands” of substrate-associated organisms to persist in an otherwise unsuitable habitat (2014). In other words, these sessile species have been able to successfully recruit and colonize these ‘floating islands,’ granting them the unique opportunity to create an environment where other organisms can survive and travel vast distances across the Pacific and Atlantic oceans (Fig 1). While this is certainly a unique way of nature overcoming one of our many detrimental anthropogenic effects, there is in fact a small trojan horse that this feat of nature carries throughout the world’s oceans. With the ability to travel vast distances across the ocean, scientists have begun uncovering the major issue of invasive species dispersal and global disease spread between the ‘floating islands’ and foreign ecosystems. To understand exactly how this is possible, a closer look into the plastics and their superiority over biotic debris must be taken into account.

Figure 1. In boxes a, b and c we can see a collection of barnacles that have colonized the various plastic substrates. In box d, we see a small trigger fish that has made the floating debris its home. In boxes e and f we see a close up view of the lethal folliculinid ciliates that cause skeletal eroding band disease in corals (Gill and Pfaller 2016).

For hundreds of millions of years, organisms have had limited travel on floating marine algae, plant trunks, pods, or other biotic floating parts (Barnes et al. 2004). In fact, scientists were previously aware of marine organism dispersal to other parts of the world via debris transportation. However, the key difference between the biotic and anthropogenic debris is that anthropogenic debris lasts significantly longer than biotic debris. The ability for plastics to resist degradation, made it highly persistent to haline environments and environments exposed to harsh UV light for long periods of time. For this reason, ocean plastics have drastically increased the dispersal for many marine organisms throughout the world (Carlton 1987). The plastics alone, however, would be nothing without the various sessile taxa that have transformed the smooth substrate of the plastics into a more rugged surface suitable for protection from the harsh pelagic conditions. With protection from the harsh conditions, organisms are more likely to successfully recruit to that environment and survive long periods of time. Thus, with a significantly longer lifespan and the ability for organisms to successfully recruit onto the transformed surfaces of the debris, ocean plastics have been able to transport organisms from as far south as the southernmost tip of South America to the northernmost reaches of Greenland (Fig. 2). While this is certainly a unique feat of nature, it poses a lot of issues regarding species invasion and the forced eradication of native species over time.

 

Figure 2. This figure shows a collection of plastic debris sampled from the southern to the northern hemispheres of the Atlantic oceans. The dark circles represent floating debris while the open circles represent debris sampled on the shores of small islands. Each sample produced an abundance of various organisms all thriving off of the ecosystem created by barnacles (Gill and Pfaller 2016).

Figure. 3. In this figure we see a collection of histogram charts displaying the abundance various taxa found on or around floating debris (Goldstein et al. 2014).

In a study conducted on the effects of Lepas barnacles (a proven foundation species for ocean plastics) by Gil et al. 2016, shows that these organisms were able to recruit a higher abundance of mobile taxa not previously observed on any floating debris. In fact, Gil goes on to state that the structural habitat provided by the Lepas barnacles could facilitate settlement of immigrating organisms e.g., adults or larvae originating from faraway coastlines or other rafts (Fig. 3). For this reason, Gil states that the barnacles’ ability to recruit a diverse array of species can prove detrimental to coastal ecosystems around the world. With the ability to successfully recruit and disperse organisms over long periods of time, there’s no way of stopping the invasion of foreign species to coastlines around the world. In addition to the dispersal of invasive species to foreign coastlines, scientists have also found an abundance of a folliculinid ciliate native to the South Pacific and Indian oceans that has managed to make its way to the Caribbean and the Hawaiian islands via plastic debris (Goldstein et al. 2014). This disease is a lethal pathogen that triggers skeletal eroding band disease in corals and while it was predominantly a disease with a fixed environmental range, ocean plastics have allowed the pathogen to cross borders and affect foreign reef systems. With the discovery of ocean plastics as being a viable source for transportation and dispersal, scientists have come to realize the detrimental effects of plastic debris beyond just polluting the ocean’s waters. Though scientists have all called for further studies regarding this topic, there is no doubt that the active limiting of plastic debris being thrown into the ocean needs to be taken more seriously.

Work Cited:

Barnes, D. & Milner, P. Drifting plastic and its consequences for sessile organism dispersal in the Atlantic Ocean. Mar. Biol. 146, 815–825 (2005).

Carlton JT. Patterns of transoceanic marine biological invasions in the Pacific Ocean. Bull Mar Sci  41:452–465 (1987).

Gil, M.A., & Pfaller, J.B. Oceanic barnacles act as foundation species on plastic debris: implications for marine dispersal. Scientific reports (2016).

Goldstein, M., Carson, H. & Eriksen, M. Relationship of diversity and habitat area in North Pacific plastic-associated rafting communities. Mar. Biol. 1–13, doi: 10.1007/s00227-014-2432-8 (2014).

 

A Study of Microplastics in San Francisco Bay

By Lauren Kitayama, SRC intern

Introduction

Microplastics (defined as being < 5mm in size) are small enough to be ingested by filter feeders and planktonic organisms. Studies have shown that the average seafood consumer could be ingesting 11,000 pieces of microplastic annually (Cauwenberghe & Janssen, 2014). The human health impacts are not well understood, but preliminary research suggests that the particles themselves may not be able to pass through the intestinal wall. However, additives and toxins including chemicals that are known carcinogens and hormone disruptors are still a cause for concern (Galloway, 2015) Microplastics come as pre-production beads (often called nurdles), exfoliating beads in personal car products, microfibers that come from washing synthetic clothes, and the breakdown of larger plastics already in the ocean.

Plastic from facial scrub next to a dime. Photo credit: Dave Graff. Source: plasticaware.org

Plastic from facial scrub next to a dime. Photo credit: Dave Graff. Source: plasticaware.org

Average measurements of 700,000 microplastic particles/ km2 (range: 15,000-2,000,000 particles/km2) makes the waters of San Francisco Bay the most microplastic polluted body of water sampled in North America.

Microplastics in San Francisco Bay

In 2016, researchers sampled eight wastewater treatment facilities that discharged into the San Francisco Bay. These facilities represent about 60% of wastewater discharged into the Bay. They voluntarily allowed researchers to sample their final effluent (the water that would be directly released). The rate of microplastic discharge from the wastewater treatments plants was 0.086 particles per liter, which equates to about 90 million particles a day. There was no difference among discharge rates between facilities that had secondary or tertiary treatment suggesting that waste water treatment plants are ineffectual at capturing and removing microplastics from waste water. Fibers were the most common type of microplastic found.

Samples were collected once from each wastewater facility during peak flow by passing the wastewater through 0.355 mm and 0.125mm sieves for 2 hours. They were then cleaned, and organic material was dissolved. Plastic particles were visually identified, and classified as one of five categories: fragment, pellet, fiber, film or foam.

Microplastics were also sampled at 9 sites inside the bay using a Manta Trawl and standard protocols. These surveys occurred at rising tides. Samples were cleaned, all organic material removed and visually classified just like the wastewater samples. All surface samples contained plastic ranging from 15,000 to 2,000,000 particles/ km2. On average, density was higher in SF Bay, than the Great Lakes, Chesapeake Bay and Salish Sea.

Estimated abundance of microplastic particles in surface water at nine sites in San Francisco Bay. Circles are located at trawl midpoints. (Sutten et al, 2016).

Estimated abundance of microplastic particles in surface water at nine sites in San Francisco Bay. Circles are located at trawl midpoints. (Sutten et al, 2016).

High concentrations of microplastic pollution in the San Francisco Bay could be due to a high urban population surrounding a small, closed body of water. However this does not necessarily explain why densities would be higher in San Francisco Bay than in other urban surrounded bodies of water. Possible explanations include water conservation measures taken by the state during a severe drought that concentrates plastic. Other pollution pathways such as runoff and fragmentation may also play a large role. This study was an initial snapshot of microplastic pollution in SF Bay. Its findings indicate the need for more in-depth studies to look at the possible effect of tidal flux, 24-hour water use differences and impacts of storm water runoff. It also makes clear the need to better understand the implications of exposure to wildlife and humans. (Sutton et al, 2016).

The Bigger Picture on Little Plastics

Microplastics are becoming increasingly recognized as a threat to ocean and human health. Global release of primary microplastics is estimated to be 1.5 Mtons/year (Boucher & Friot, 2017). Microbeads in personal care products are often considered to be a large source of these microplastics. In fact in 2015 US passed the Microbead-Free Waters Act, banning the manufacturing and sales of products with microbeads with the intent of decreasing microplastic pollution in the countries waterways (2015). Canada, Ireland, the UK and the Netherlands have similar national legislation. But recent reports show that these exfoliating microbeads represent a small portion of microplastics pollution (2%). Whereas microfibers, released during the laundering of synthetic materials represents 35% of microplastics (Boucher & Friot, 2017).

Breakdown of primary microplastic loss into the ocean. (Boucher & Friot, 2017).

Breakdown of primary microplastic loss into the ocean. (Boucher & Friot, 2017).

Companies like Patagonia have begun recognizing this threat to the planet, and are investing in solutions like a laundry bag that captures microfibers before they get blown out of the drier vent (O’Connor, 2017).

Work Cited

Sutton et al (2016). Microplastic contamination in the San Francisco Bay, California, USA. Marine Pollution Bulletin 109: 230-235. http://dx.doi.org/10.1016/j.marpolbul.2016.05.077

Microbead-Free Waters Act. (2015). 21 U.S.C. 331. https://www.gpo.gov/fdsys/pkg/BILLS-114hr1321enr/pdf/BILLS-114hr1321enr.pdf

O’Connor, M. (2017). Microfibers are polluting our food chain. This laundry bag can stop that. The Guardian. https://www.theguardian.com/sustainable-business/2017/feb/12/seafood-microfiber-pollution-patagonia-guppy-friend

Cauwenberghe, L. and Janssen, C. (2014). Microplastics in bivalves cultured for human consumption. Environmental Pollution 193: 65-70. http://dx.doi.org/10.1016/j.envpol.2014.06.010

Boucher, J. and Friot D. (2017). Primary Microplastics in the Oceans: A Global Evaluation of Sources. Gland, Switzerland: IUCN. 43pp. https://portals.iucn.org/library/sites/library/files/documents/2017-002.pdf

Galloway, T. (2015). Micro- and Nano-plastics and Human Health. Marine Anthropogenic Litter pp 343-366. http://link.springer.com/chapter/10.1007/978-3-319-16510-3_13