Seaweed, a common name for countless species of macroscopic marine algae, forms a fundamental part of ocean ecosystems. These diverse organisms are primary producers, converting sunlight into energy through photosynthesis. Along with microscopic phytoplankton, seaweeds create the base of the marine food web, supporting a vast array of marine life.
Marine Herbivores
Marine herbivores are animals that primarily consume plant material found in the ocean, such as algae, seaweed, and seagrass. These organisms are found across various animal groups. They include a range of creatures from tiny invertebrates to large mammals, each adapted to grazing on aquatic plants.
Many fish species are marine herbivores, including various tangs, blennies, and angelfish. These fish often graze on algae covering rocky surfaces or coral reefs. Invertebrates also contribute significantly to marine herbivory, with examples such as sea snails, limpets, abalones, and sea hares.
Reptiles like the green sea turtle transition to an almost entirely plant-based diet as adults, feeding on seagrass and algae. Marine mammals, also include herbivores like manatees and dugongs, which graze extensively on underwater grasses. These diverse consumers help shape marine habitats through their feeding activities.
Key Seaweed Eaters and Their Ecological Role
Parrotfish are prominent seaweed eaters on coral reefs, using their fused, beak-like teeth to scrape algae off coral and rocky surfaces. Their grazing prevents macroalgae from overgrowing and suffocating corals, allowing new coral larvae to settle and grow. This feeding behavior also contributes to the production of fine sand as they grind ingested coral bits, shaping the reef environment.
Sea urchins are effective grazers, feeding on algae and kelp on rocky substrates. They play a significant role in controlling algal populations, especially in kelp forests. However, an imbalance in their populations, often due to a lack of predators, can lead to overgrazing, transforming productive kelp forests into barren areas.
Manatees, often called “sea cows,” are large marine mammals that consume vast amounts of seagrass. They graze using their flexible lips and teeth, eating about 10-15% of their body weight daily. This consistent grazing helps maintain the health of seagrass meadows by preventing overgrowth and promoting diverse plant communities.
Marine iguanas, unique to the Galápagos Islands, are the only lizards adapted to forage in the sea, feeding on marine algae and seaweed. They dive into ocean waters to access their food, and their grazing activities help control algal growth on the rocky intertidal and subtidal zones. These reptiles possess specialized salt glands to excrete excess salt ingested with their diet, allowing them to thrive.