Payton, T. G., Sims, R. J., & Childress, M. J. (2024). Abundance, patterns, and taxa
associations of anthropogenic marine debris on reefs in the middle Florida Keys. Frontiers in
Marine Science, 11, 1412858. https://doi.org/10.3389/fmars.2024.1412858
Fishing trap. Image credit: Matt Kieffer via Flickr Creative Commons
The Florida reef tract, a 350 km stretch of coral reefs once teeming with life, has been hit by coral disease outbreaks, extreme temperatures, disturbances from recreational activities, and other threats that have led to its decline. In the last fifty years, the Caribbean alone has lost 45% of its coral cover. In an attempt to make up for the loss of coral reefs, scientists are working to install artificial reefs from materials like metal and ceramic to provide more habitat space for fish.
In addition to coral loss, the area has undergone two more changes. First, the composition of the coral reefs has drastically transformed to be populated by far less complex corals. Second, the amount of marine debris (including abandoned fishing gear such as wood, hooks, and rope) collected in reef areas has increased significantly, damaging corals and reducing their immunity to disease. Scientists don’t fully understand how a shift in coral composition affects the organisms that call the reef their home, but the damage caused by pollution has been well documented.
Much research on marine debris has focused on its negative impacts on marine life like entanglement and ingestion – but what about the surprising evidence that some marine debris has been utilized by marine animals for refuge and coral settlement?
In this study, researchers analyzed the influence of debris on marine ecosystem complexity in the Florida Keys over a three year period in an attempt to reveal if marine debris may help the marine environment.
Uncovering the Features of the Reef
The study was performed on 15 reef sites in the Florida Keys National Marine Sanctuary. Each reef’s features, including substrate type, roughness, and fish behavior, had been previously assessed. Seven of the sites were inshore (4 km or 2.5 miles from shore) and eight were offshore (>8 km or 5 miles from shore).
SCUBA divers assessed the reefs each summer from 2020 to 2022 using photographs to measure percent cover and observations to measure roughness. Marine debris types observed were separated into nine categories: plastic, mixed, wood, metal, concrete, glass, cloth, paper, and other. Observed uses of marine debris by animals were also separated into the following categories: catches in derelict fishing gear, use of debris as a mobile home, debris covering an organism, entanglement within debris, use of debris as refuge, and use of debris as a substrate.
Examples of positive and negative interactions between marine animals and marine debris observed in this study. A) Use of a lobster trap as a refuge by a bicolor damselfish (positive); B) use of a concrete substrate by corals and sponges (positive); C) fire coral entangled in fishing line (negative); D) cloth smothering a soft coral (negative).
The Good and The Bad
Roughness was found to be positively influenced by hard coral cover and marine debris abundance. Inshore reefs are more shallow with higher hard coral cover, meaning more roughness. Offshore reefs are deeper, with higher soft coral cover.
There was more marine debris found in inshore reefs than offshore reefs, with far more plastic debris in inshore reefs as well. Plastic debris primarily consisted of rope from fishing traps. Other material types did not appear more in one location or the other.
The types of animals that were observed interacting with debris included sponges, hard corals, and green and brown algae. Plastic debris was associated with the highest species richness (number of different species in an area) compared to other debris materials. Mobile organisms used all debris materials except cloth and paper for shelter. Sedentary organisms used concrete.
In summary, the most debris was found on shallow, inshore reefs, areas with higher roughness, coral cover, and algae. This was likely because large stony corals on these reefs trap more discarded fishing gear and create a more complex habitat for reef life.
What next?
Future research should assess whether debris removal efforts impact marine life on the reef. Additionally, while this study indicated that some interactions and materials are more beneficial to marine life than others, the extent to which marine debris can be positively used in the marine environment is unclear. Most debris materials that have the potential for positive influence also have the potential for negative influence and should therefore be implemented cautiously.
It is clear that marine debris materials can impact species composition and habitat utilization in coral reefs. However, there is a crucial difference between materials that are discarded unintentionally or ignorantly (e.g. abandoned fishing gear and litter) and intentionally installed human-made materials (e.g. artificial reefs). Sometimes, unintentional debris can be useful too, however the net benefits of such items are questionable.
Luckily, there are ongoing efforts to remove litter from the ocean, such as The Global Ghost Gear Cleanup to address this problem. While the notion that not all debris is completely detrimental to marine life is promising, cleanup efforts should continue to be pursued in order to begin to return the oceans to a more pristine state.
I received my MPS in Marine Biology & Ecology from the University of Miami’s Rosenstiel School of Marine, Atmospheric, and Earth Sciences in May 2024. I plan to use my education and experience to pursue a career in science writing or film production to help communicate the importance of the ocean to the general public.