ASK A SCIENTIST
Question: Why is seaweed so important to fish and sea creatures?
Answer: I remember as a boy trying to complete a YMCA mile swim along the coast of Santa Catalina Island, California. Everything was fine until I noticed kelp blades reaching up from the depths as if to grab hold of me. I leaped into the boat traveling beside me in seconds. Kelp is really the largest form of algae, known as brown algae, and it really isn't dangerous despite my reaction at the time. Other marine algae include green and red varieties, and all algae living in saltwater are commonly referred to as seaweed.
Not all the plant-like organisms in the sea are seaweed, and some seaweed isn't really a plant. The sea grass common near Caribbean coral reefs and fed upon by sea turtles isn't seaweed; it's really a land plant living in water that possesses aquatic pollen. To make things even more complicated, kelp is one of the few forms of algae that isn't a plant! What all the above seaweed-like organisms have in common is that they use sunlight and carbon dioxide to make glucose (food) and oxygen in a process called photosynthesis just like plants on land.
The two products of photosynthesis make up two of the three reasons why seaweed is so important to fish and sea creatures. Fish as with all animals need to 'breath' oxygen, and of course, all animals need to find food to survive - they can't make their food like plants. Many smaller fish, sea urchins and mollusks feed on algae, and then they in turn are fed upon by larger marine predators such as sea otters and seals. All sea creatures are part of food webs that ultimately depend on the food produced by algae, which occur as floating microscopic organisms or the larger 'leafed' forms commonly attached near shore that we refer to as seaweed.
The third way in which seaweed is important to sea creatures is in providing shelter. Unlike in a rainforest or even within a coral reef, most seas of the world are open habitats, and organisms living in them are exposed to attack by predators. In the sunlit surface waters of the sea, the protective kelp forests typical of colder ocean waters are a great place to hide, as are sea grass beds and the floating algal mats of the Sargasso Sea located in the middle Atlantic Ocean. Creatures dwelling within marine algal communities can quickly hide in these structures when predators lurk nearby, and many slow-moving algal dwellers even look like the algae to disguise themselves. Now, unlike in my youth, one of my favorite places is a kelp forest, for here, thanks to seaweed, dwells an amazing diversity of marine life, second only to the protective coral reefs of warmer tropical waters.
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