Seagrass meadows can be found all over the seafloor, from temperate to tropical climates. They are one of the most productive marine environments, with a significant contribution being carbon sequestration (Newman et al., 2007). This process involves capturing carbon from the environment and storing it. As climate change becomes more prevalent, seagrasses as a carbon sink are becoming increasingly important. Not only are seagrass meadows themselves productive environments, but they also help make other habitats more productive by providing connectivity between them. They replace what would otherwise be an empty sandbank between habitats, such as mangroves and coral reefs, and promote more biodiversity, nurseries, and feeding grounds (Goss et al., 2018).
Bimini’s seafloor is accompanied by many surrounding seagrasses. Turtle grass, Thalassia testudinum, is one of the most common types of seagrasses found in Bimini. It has long, rounded blades that are connected to roots anchored in the bottom. Species ranging from primary consumers to top predators live in the seagrass. Green sea turtles (Chelonia mydas) and Southern stingrays (Hypanus americanus) in Bimini can be seen foraging among turtle grass. Nurse sharks (Ginglymostoma cirratum), blacktip sharks (Carcharhinus limbatus), and lemon sharks (Negaprion brevirostris) are among some of the top predators that inhabit these areas for protection and food. Because many of these species are near threatened, vulnerable, or endangered, it is important to understand the role of seagrasses on their survival, growth, and reproduction (Driscoll, 2021).
[A green sea turtle grazes on sea grass. Photo: Baylie Fadool]
Seagrasses face many threats exacerbated by anthropogenic effects, making them one of the most threatened marine habitats (Driscoll, 2021). Recent coastal development in Bimini has resulted in dredging that has removed extensive mangrove and seagrass habitat and removed essential habitat for species and ecosystem functioning. According to Driscoll (2021), this dredging has resulted in as high as 18% destruction of turtle grass habitat. In addition to coastal development, plastics are entering the ocean at alarming rates that have impacted marine ecosystem functioning. As opposed to non-vegetated areas, microplastics are much more enriched in seagrass beds (Sanchez-Vidal et al., 2021). Although limited research has been done on the accumulation of plastic on the ocean floor, it can enter food webs through consumption by marine foragers and predators. Goss et al. (2018) observed microplastics trapped in turtle grass in Belize that much herbivorous fish eat. As a result, similar microplastic introduction to seagrass beds could be occurring in other marine food webs elsewhere, damaging the integrity of those ecosystems.
[Blacknose shark in the seagrass around Bimini. Photo: Baylie Fadool]
Luckily, seagrasses may be able to react and respond to microplastic accumulation. Seagrasses lose their leaves in autumn, similar to trees, which get washed ashore and form variations of seaballs. Microplastics have been found in these seaballs, indicating that seagrasses could be ejecting microplastics entangled in their blades. A study by Sanchez-Vidal et al. (2021) revealed that an endemic, Mediterranean seagrass (Posidonia oceanica) forms tightly packed seaballs called aegagropilae (EG). Only this seagrass can form EG because of its physical characteristics (Sanchez-Vidal et al., 2021). Because of its ability to tightly pack, it has a higher abundance of plastic debris found within its seaballs compared to other seagrasses (Sanchez-Vidal et al., 2021). The fate of EG is still unclear, though, so it needs to be better understood to create better management practices. With the addition of more plastics in the ocean, other seagrasses could adapt similar responses to P. oceanica to buffer and trap plastic.
[Lush seagrass beds in Bimini. Photo: Baylie Fadool]
The response of some seagrasses to plastic accumulation provides hope for the reaction of seagrasses and the ocean to increased anthropogenic change. If some seagrasses are adapting along with their rapid environmental alterations, they may be developing ways to counteract threats such as plastic accumulation, increased ocean temperatures, and dredging. Because the ability of P. oceanica to trap plastics in its seaballs is one of the first studies of its kind, more research needs to be done to understand this process and where the plastic eventually ends up. Although seagrasses may be developing alongside environmental change, if their environment is changing too rapidly, they may not respond quickly enough. This could result in detrimental effects for their ecosystems, as their disappearance would result in unbalanced ecosystems, loss of habitat, and diminished food resources. As a result, it is still essential that we take action to understand and protect these critical habitats, even though seagrasses may be combating anthropogenic influences. Working together can create a better world to live in, not only for seagrasses but also for ourselves.
References:
Driscoll, S. R. T. (2021). Using Principles of Seascape Ecology to Consider Relationships Between Spatial Patterning and Mobile Marine Vertebrates in a Seagrass-Mangrove Ecotone in Bimini, Bahamas.
Goss, H., Jaskiel, J., & Rotjan, R. (2018). Thalassia testudinum as a potential vector for incorporating microplastics into benthic marine food webs. Marine pollution bulletin, 135, 1085-1089.
Newman, S. P., Handy, R. D., & Gruber, S. H. (2007). Spatial and temporal variations in mangrove and seagrass faunal communities at Bimini, Bahamas. Bulletin of Marine Science, 80(3), 529-553.
Sanchez-Vidal, A., Canals, M., de Haan, W. P., Romero, J., & Veny, M. (2021). Seagrasses provide a novel ecosystem service by trapping marine plastics. Scientific reports, 11(1), 1-7.