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Divers Can Learn by Observing Animal Behavior and Feeding Habits

Understanding the Ocean's Food Chain

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Covering seventy-one percent of the Earth’s surface, the ocean provides us with a magnificent variety of creatures. Each of these creatures occupies a unique position on the food web, or trophic web, which is composed of producers, consumers, and decomposers. For an environment to remain healthy, the food chain must remain unbroken. If one link in the chain is broken, all creatures on the chain may be endangered.

The Trophic Web, Coral Reef Style

Scuba diver with sea turtle
Georgette Douwma/Stone/Getty Images
Coral reefs provide an excellent example of the trophic web since they are a biodiversity hotspot. Every link of the food web is represented in a healthy coral reef. Let’s look at some of the inhabitants of the coral reef food web.

Level 1: Producers

trophic web
© NOAA
Photosynthetic organisms, like seaweed, zooxanthellae (algae living in coral tissue), and turf algae, make up this group. Turf algae is opportunistic, meaning it will claim any available reef real estate. A reef covered in turf is probably in poor health.

Level 2: Primary Consumers

trophic web
© NOAA
Herbivores snacking on level 1 organisms form this group. Sea urchins, some crab species, sponges, and even the large green sea turtle are primary consumers. The surgeonfish, a member of this group, mows down the turf algae to a healthy level. If surgeonfish are absent from a reef, divers can count on an algae invasion!

Ever wonder where sand comes from? Parrotfish are algae eaters that use powerful fused beaks to remove algae from dead coral. The Stoplight and Queen parrotfishes even take a nips of coral. The parrotfish gut then processes the coral calcium carbonate skeleton. The final product, sand, is then sprinkled over the reef. This is where most reef and beach sand comes from.

Level 3: Secondary Consumers

trophic web
© NOAA
Dining on primary consumers, these animals are carnivorous. Goatfish and wrasses eat everything from snails and worms to crustaceans. This group also includes many species of coral eaters such as butterflyfish, filefish, triggerfish, and damselfish. Their specialized, elongated mouths enable them to chow down on the tiny individual polyps of the coral. Their absence paints a picture of a reef with few corals.
Conservation for scuba divers:
• Guide to Coral Diseases
• The Atlantic Lionfish Invasion
• Sea Turtle Conservation
• Is Shark Baiting Ever Okay?

Level 4: Tertiary Consumers

trophic web
© NOAA
These are the large fish that excite divers! Barracuda, groupers, snappers, and, of course, sharks, moray eels and dolphins are at the top of the food chain. Their feast includes other fish, crustaceans, and even octopi. At-risk reefs have low numbers of these top-level (apex) predators. They help to keep other fish populations at bay. Considering that tertiary consumers are commercially fished, their absence is a possibility and even a reality in many regions.

Level 5: Decomposers

trophic web
© istockphoto.com
The little-glorified job of decomposing dead sea animals and plants is left to bacteria. Animal and plant wastes are converted to a food form subsequently used by animals throughout the food chain.

The Ocean Is in Trouble

trophic web
As in any chain, when a link is missing or weakened, the chain as a whole is also weakened and no longer functions correctly.

Fish stocks are being depleted to worrying levels. Many species are listed as endangered or threatened. This is primarily due to pressure from human consumption. Whether due to feeding the population or offering shark fin soup at a Chinese wedding, fish populations are not given the necessary time to replenish. These problems have solutions. Humans must understand that we are part of the complex and dynamic food chain- not at the top of it. We must take better care of our marine food resources. We must adapt fishing methods to be less damaging to ocean habitats and the animals they support. Programs which promote long-term sustainability must become more than political talking points. They must be programs that are put into action.

As a Diver, How Can I Help?

trophic web
© istockphoto.com

Join a Monitoring Program
Conservation programs such as Global Vision International (GVI) offer divers the opportunity to participate in fish monitoring research. For example, dives can contribute to scientific research by collecting census statistics on fish.

Eat Responsibly
Get your hands on a pocket guide to choosing sustainable fish and chow down on only those that are ocean-friendly. The Monterrey Bay Aquarium has a great Seafood Watch pocket guide. They even offer an app for your smartphone!

Let Your Money Talk For You
Don't Patronize restaurants and seafood retailers that offer products that threaten the ocean and ocean life. Effect change by spending your money at businesses and restaurants that support ocean conservation.

The Take-Home Message About the Ocean's Trophic Web

A healthy reef is filled with member of each level of the trophic web. When creatures from one level are threatened, the health of the entire reef is in jeopardy. To ensure that coral reefs are present for the next generations to enjoy, humans must take steps to protect plants and animals at every level of the food chain.

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