What do sea otters eat?
Sea otters are known for being playful and frisky. They are serious eaters, however! A major part of a sea otter's diet are echinoderms, such as sea urchins. They manage to eat the soft part of the sea urchins while avoiding the huge sea urchin spines.
Importance of Echinoderms
Echinoderms are important for the ecosystem. They are also a source of food and medicine for humans.
Echinoderms play numerous ecological roles. Sand dollars and sea cucumbers burrow into the sand, providing more oxygen at greater depths of the sea floor. This allows more organisms to live there. In addition, starfish prevent the growth of algae on coral reefs. This allows the coral to filter-feed more easily. And many sea cucumbers provide a habitat for parasites such as crabs, worms, and snails.
Echinoderms are also an important step in the ocean food chain. Echinoderms are the staple diet of many animals, including the sea otter. On the other hand, echinoderms eat seaweed and keep its growth in check. Recall that the sea urchin is a grazer, mainly feeding on algae on the coral and rocks. Recently, some marine ecosystems have been overrun by seaweed. Excess seaweed can destroy entire reefs. Scientists believe that the extinction of large quantities of echinoderms has caused this destruction (Figure below).
A large die-off of the sea urchin, Diadema antillarum, in the Caribbean Sea coincided with increases in algal growth in some areas but not others.
Echinoderms as Food
In some countries, echinoderms are considered delicacies. Around 50,000 tons of sea urchins are captured each year for food. They are consumed mostly in Japan, Peru, Spain and France. Both male and female gonads of sea urchins are also consumed. The taste is described as soft and melting, like a mixture of seafood and fruit. Sea cucumbers are considered a delicacy in some southeastern Asian countries. In China they are used as a basis for gelatinous soups and stews.
Echinoderms as Medicine
Echinoderms are also used as medicine and in scientific research. For example, some sea cucumber toxins slow down the growth rate of tumor cells, so there is an interest in using these in cancer research.
Sea urchins are also model organisms used in developmental biology research. Sea urchins have been used to study the mechanisms of fertilization and egg activation, physiological processes that occur during early development, and the regulation of differentiation in the early embryo. In addition, the molecular basis of early development was studied in sea urchins. Gametes can be obtained easily, sterility is not required, and the eggs and early embryos of many commonly used species are beautifully transparent. In addition, the early development of sea urchin embryos is a highly conserved process. When a batch of eggs is fertilized, all of the resulting embryos typically develop at the same time. This makes biochemical and molecular studies of early embryos possible in the sea urchin, and has led to a number of major discoveries.
Echinoderms in Farming
The hard skeleton of echinoderms is used as a source of lime by farmers in some areas where limestone is unavailable. Lime is added to the soil to allow plants to take up more nutrients. About 4,000 tons of the animals are used each year for this purpose.
- Echinoderms are an important part of the ocean food chain, keeping seaweed in check as grazers and serving as food sources for animals like otters.
- Echinoderms are used as food, medicine, and a source of lime for farmers.
Use the resource below to answer the questions that follow.
- Smart Polymer Inspired by Sea Cucumbers at http://www.youtube.com/watch?v=tZ2HZVxsZ5U (0:59)
- What characteristics of the sea cucumbers inspired scientists to use them to develop new polymers?
- Why do scientists feel these new polymers may be useful for medical implants?
- How are sand dollars important to the ecosystem?
- What role do echinoderms play in the food chain?
- How has the sea urchin been used in research?