Question

7)Can you think of why the acceptable levels for fecal coliforms for shellfishing are so much lower than that for recreational use? (Hint: how do shellfish get their food?)

Answer 1

7. Shellfish fishing/harvesting water and recreational waters are monitored for safety using fecal coliforms. Fecal coliforms are bacteria that are present in intestine of humans and animals. Presence of fecal coliforms in water is an indicator of pollution of water bodies by feces.

Shellfish such as clams have siphons instead of head or biting mouth like other organism. Hence they will imbibe water through their incurrent siphons which then enters their gills. Their gills have cilia on their surfaces. The water will contain food for the shellfish which is then trapped by the cilia present in the gills. The food is then transferred to their mouth, for ingestion and digestion. Waste is then removed from excurrent siphon present. Mussels, on the other hand will take in large amounts of water by opening their shells. This water is then drawn over their gills leading to filtration. Thus, shellfish take in large amounts of water and filter the food from water. This leads to concentration of food in the shellfish. Along with their food, other substances will also be filtered. Hence, they are known as filter feeders.

If the waters for shellfish fishing are contaminated with fecal coliforms, then the fecal coliforms will get concentrated in the shellfish due to filter feeding of water. These fecal coliforms include bacteria like E.coli and Salmonella which can infect the gastrointestinal tract in humans and cause diarrhea. Hence, the level of fecal coliform should be very less to be acceptable for waters for shellfish fishing due to much larger possibility of causing infections in humans. Recreational waters are used for sports such as swimming, surfing, white water rafting. Hence, there is much less chances of water being ingested by the humans, thereby reducing chances of fecal coliform infection. Thus, they levels of fecal coliforms accepted for recreational water are much higher than what is acceptable for shellfish harvesting waters.