Agroregeneration: Sea Grass and Otters

In yet another example of trophic cascade, sea otters are helping to demonstrate why intact ecosystems are more important than trying to save any one particular species.

It is well documented that sea otters have been pivotal in saving kelp forests on the Pacific coast. Without sea otters, spiny sea urchins increase in number. The urchins feed on the roots of the kelp, causing them to break free of their anchor and float away. They can often be seen washing ashore afterwards.

Because sea otters are so intelligent, they have developed cultural adaptations to make the sea urchins, and other hard shelled prey edible. As everyone knows, sea urchins are covered by a hard outer shell bristling with sharp spines. The otters dive down, grabbing a sea urchin along with a rock from the sea floor. After surfacing, they flip over on their back, place the stone on their stomach, and crack open their food item. This helps them to make use of foods that may not be accessible otherwise!

Seagrass Beds

It now appears that sea otters are an apex species in more than one ecosystem! Studies show that The increased nutrient density in coastal waters causes algae to grow on the surface of the sea grass, stealing its light and out competing it. Normally, sea slugs and small crustaceans such as Idotea would control the algae.

Unfortunately the absence of otters has allowed the crab population to explode in sea grass beds. The crabs eat the sea slugs and other herbivores which would normally keep the algae in check. This one-two punch makes the remaining portions of the ecosystem unable to take up the slack. The result is disappearing sea grass beds.

In 1984 sea otters started moving into Elkhorn Slough, one of the largest estuaries in California. Up until that point the sea grass beds in the slough had been in decline. The return of the otter showed a dramatic comeback. The predation of the crabs by otters reduced their numbers to the point that the sea grass was able to make a recovery. With the system back in balance, sea grass beds are showing even more vigor than in unpolluted areas that do not have sea otters!

It should also be noted that seagrass systems are a keystone ecosystem which acts as a nursery and breeding ground for many important commercial fisheries such as the Tiger Prawn. Many species rely on different ecosystems during different stages of their life. It is important to save these natural systems and ensure that they remain pristine and interconnected. Our overall lack of understanding necessitates this. If you don’t understand a natural system, it is difficult to know how to protect the species within it.

The more we learn about these types of issues, the better we can understand what happens in the ecosystems of our own back yards. When the otter population was originally decimated back in the 1700’s and 1800’s, our understanding of ecology was little to none. Even if we did know it would be this disruptive, it may not have made a difference. Hindsight is 20/20 and without an advocate, nature stands little chance of lobbying in its own (and our) interests.

When we exterminated wolves and brown bears from large parts of our country, we could not have known that it would put grassland and forest ecosystems in peril. We did not know what a massive impact the loss of beavers would cause for riparian ecosystems. These are just some examples of how ecosystem disruption can have unintended and unexpected consequences.

It is our desire to show people, step by step, that all things are connected and that we cannot separate ourselves from nature. We must find a way to return to it. Are you having an aphid problem or a squash bug problem? What can you do to encourage nature to solve this problem for you? Just as an aquarium must cycle to get the proper bacterial species in order, a garden, orchard, or pasture must take time to mature and ‘season’ it self. The species composition will change over time, in succession, until it reaches equilibrium. These types of systems provide the most food for the least amount of work, while creating and improving soil in the process.

Sea Otters Facilitate Recovery of Important Seagrass Beds in California

Seagrass Beds are Important to Fisheries

Both sea slugs and Idotea (the crustacean between the two sea slugs in this photo) feed on algae and increase in numbers when the crab population is controlled by sea otters. Credit: Brent Hughes

Read more at: http://phys.org/news/2013-08-sea-otters-recovery-seagrass-beds.html#jCp

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Tuesday, October 1, 2013

Sea Grass and Otters

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