Do Filter
Feeders Filter
Plastic?

Mikaela Walsh, 4ocean Research Analyst

The ocean has biodiversity and unique animals that have adapted over the years.

Among these, manta rays and whale sharks are admired for their large size, beauty, and grace. Whale sharks and manta rays are renowned not just for their distinctive adaptations but also for their striking appearances. Despite the confusing name, whale sharks are made of cartilage and lack bones, which classifies them as a shark species rather than a whale species. They are navy blue in color with white spots, creating a symmetrical pattern. Whale sharks can reach nearly 40 feet long, while manta rays, resembling supersized sting rays, boast a wingspan of around 26 feet! Many people seek to go diving with manta rays and whale sharks across the globe due to their immense beauty and their majestic behavior. If you've never seen a manta ray or a whale shark, definitely put it on your bucket list!

These animals are slow-swimming giants that obtain food and nutrients through a mechanism known as filter feeding. The process of filter feeding requires the animal to open their mouth and then funnel or suction large amounts of water past their gills, which reaches their stomach. Following this, they expel water and guide prey into their stomach using distinct mechanisms, utilizing gill plates in manta rays and gill pads in whale sharks. These animals inhabit various regions across the globe yet tend to favor warmer water, which is influenced by their prey and body temperature preferences.

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While various aspects of whale sharks and manta rays are intriguing, diving into their filter-feeding behavior is crucial. Manta rays and whale sharks are animals that snatch their food through their gills by filter feeding. These animals have special adaptations on their gills to allow them to eat while they are swimming. Whale shark’s main food source is plankton, which are organisms that are extremely small yet vital to our ecosystem. Due to its miniscule size, whale sharks need to consume an immense quality of plankton to survive. As a result of the techniques used to filter feed, they ingest all available materials contained in the water to obtain nutrients, such as squid or small fish, to maintain dietary needs. Dreadfully, this means consuming anything that is present in the water, including plastic debris. Today, their true predator is plastic that floats in the ocean currents.

Unfortunately, manta rays and whale sharks lack the ability to filter plastic from their food, leading to the ingestion of plastic debris. Indonesia is a specific region that is a popular habitat for these animals. Here, researchers investigated whether whale sharks and manta rays could digest plastic or filter it out of their gills. The researchers examined the different types of plastic found in the waste of manta rays to determine the type of plastic pollution these animals are subject to eating. Most of the plastic debris recovered from the waste materials originates from the water's surface, primarily consisting of particles under 5mm. This aligns with their feeding habits, as their food source is very small and often found near the ocean’s surface. This is crucial information because this study concluded that filter feeders cannot filter plastic out of their food. As a result, they are eating the plastic, which has the potential to carry harmful chemicals and fill the stomach with particles that can not be digested.

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Plastic pollution has detrimental effects on all forms of life, but it is disastrous for a filter feeder.

Moreover, varying types of plastic have different densities based on manufacturing methods and material composition. Consequently, certain plastics float on the water’s surface, while others sink to the ocean floor. Plastic pollution is driving our oceans and marine life into endangerment. The population of whale sharks has decreased by 50% over the past 75 years, placing them on the endangered species list. Additionally, manta rays are currently a threatened species on the list. Both these organisms serve essential roles in our marine environment, contributing significantly to regulating plankton populations and nutrient cycling. The manta rays and whale sharks are two enormous organisms that bring life and beauty to our oceans and fulfill a necessary niche. There is still an opportunity to address the challenges faced by these beautiful animals, but swift action is necessary for meaningful change.