Kelp & Seaweed Ecosystems  Seaweed refers to a diverse group of red, green, & brown algae. All provide the bases for ecosystems among their stipes, holdfasts, & blades.  Among these, kelp ecosystems are probably the most diverse. You find kelp forests globally in cool water. This is because they require the nutrients found in a cool ocean.  Kelp forests & other seaweed-based ecosystems are among the most biologically productive ecosystems.  Their primary production exceeds the primary productivity of terrestrial forests & is almost equal to the productivity of coral reefs.

Kelp & Seaweed Ecosystems  Because of its dependence on sunlight, cool water, & nutrients, kelp responds noticeably to environmental changes.  During ENSO events, for example, the coastal water temperatures in Southern California rise. This often causes massive die offs of kelp, disrupting the local ecosystems for a year or more.  Kelp provides a clear example of why it’s important to study ecology, not simply individual organisms.  Until protected, in some areas the sea otter was hunted nearly to extinction. Amazingly, in these areas the kelp began to die off rapidly.

Kelp & Seaweed Ecosystems  It turns out that while very few organisms eat kelp, one that does is the sea urchin.  Sea urchins are one of the sea otter’s primary foods, once the sea otter population declined, the sea urchin population increased & decimated the kelp population.  The energy required by marine mammals living in cool seawater is considerable, so the average sea otter eats a substantial number of sea urchins.

Kelp & Seaweed Ecosystems  Killing the sea otters disrupted the kelp forest’s ecological balance by removing the sea urchin’s chief predator.  This allowed the sea urchin population to rise relatively unchecked. More sea urchins meant more grazing on kelp holdfasts. In the end, the sea urchins ate the kelp faster than it could grow.  This is an excellent example of the interdependence that exists within an ecosystem. It shows that each organism contributes to a balance that allows life to thrive there.