Plastics Grazers
Manatees
Manatee Gut Content
Manatees play a crucial role in the trophic transfer of microplastics because they graze in seagrass beds where many microplastics accumulate. Manatees from the Marine Mammal Pathobiology Lab were necropsied using their standard protocols, including manual palpation of the digestive tract and visual examinations. The digestive tracts were sub-sampled into five categories (stomach, duodenum, cecum, distal and proximal colon) in search of smaller plastic particles. The sub-sample were then concentrated on a 212 µm sieve and a visual inspection method was used to look for microplastics. Manatees have a high cellulose diet, which is why the entire gut contents were not fully digestible. Nile Red staining was used to identify the plastic particles.
The data collected from 18 manatee carcasses between 2017-2019 showed that there was a high frequency of microplastic contamination and showed that plastic was present in all of segments of the GI tract that were examined. Student researchers examine the gut content of manatees recovered from Tampa Bay provided by the FWC marine mammal pathobiology lab. The purpose of examining manatee gut content is to understand plastics presence in seagrass beds, the primary food source of these animals.
Plastics found inside
Micro and Macroplastics have been found in dead manatees.
A Peaceful Species
Manatees are well known for being docile and nonaggressive organisms. Understanding how they're being affected by plastics can assist in the process of protecting them.
Image Archived from FWC manatee tracking and behavior
Plastics in their food
Most of the plastics that enter a manatee's gut comes from the seagrass they eat. Plastics can get trapped on seagrasses and a manatee can't see the plastics during herbivory.
Copepods
Copepod Sampling
Microplastics are threatening the consumers at the base of the marine food web. Through biomagnification, interactions between lower trophic level organisms and microplastics have implications on the larger ecosystems. Our project studies microplastic load in environmental samples of copepods found in the Tampa Bay Estuary.
At each of the 7 stations, copepod samples were collected using a 200 µm mesh ring net tow (0.5 meter diameter) for 3 minutes. 1,000 copepods (when available) where picked from each of the samples and digested to release the contents of their guts. The samples were stained for 20 minutes in a 1mL:5mL Nile Red incubator and the stained plastic particles were visualized using epifluorescent microscopy, quantified, photographed, and sized using image analysis.
The number of microplastics that were consumed per 1,000 copepods ranged from 4 - 55, and diameter ranged from 1.8 µm to 351 µm. The data showed that there was no spatial or temporal trends, however, the encounter rates from this study where higher than the only other two field studies done on copepod ingestion of microplastic.
The results show that estuaries may be a site of increased microplastic ingestion because of the closer proximity to anthropogenic activities and semi-enclosed geography.
Copepods are analyzed under fluorescent light to determine microplastic concentration inside their guts. In every cruise during the summer of 2018, microplastics were found in copepod guts.
A Vital Part of the Food Web
Copepods make up a large portion of the base of a marine food web. If copepods were removed from the marine system, drastic effects could occur.
Copepods and Plastics
Microplastics can impede food intake, affect behavioral patterns, and slow digestion. As copepods are a food-source for many marine organisms, when these organisms eat copepods, the microplastics are passed on.