B.Y.O. Shopping Bag

Landlubbers take heed: "There's an international ban on dumping plastic [in the ocean], so most of the plastic in the ocean comes from land," Helvarg says. Plastic bags are often mistaken for jellyfish by endangered sea turtles and other wildlife, which die from ingesting them. Other plastics "stay in the ocean and form a fine dust which then becomes a toxic sponge" that absorbs synthetic chemical toxins like polychlorinated biphenyls and DDT. The dust concentrates these poisons tens of thousands of times more than seawater can, and it winds up in the fish we eat. To recycle plastic bags, check earth911.org for nearby drop-off spots.

Green Your Aquarium

Tropical fish for saltwater aquariums are often irresponsibly harvested in the wild—90 percent of them die and coral reefs are harmed. "Fish collectors use a dilution of either bleach or cyanide [to paralyze fish]," Helvarg says. "It's better to choose a tropical freshwater aquarium, for which the fish are domestically raised in tanks, not taken out of the wild." For help, use the consumer guide to fish at reefprotect.org.

When cleaning or dismantling an aquarium, dispose of contents properly, or you could risk introducing "tropical, non-native species or microbes to surrounding bodies of water," Helvarg says. If you're giving up on your aquarium, "give the fish and flora away," Helvarg advises. Place unwanted materials in the land trash.

Don't Flush Pharmaceuticals

When we discard pills and medicines down the toilet, they wind up in waterways, where they can disrupt the reproductive systems of aquatic organisms. Sewage treatment plants aren't designed to remove chemicals from consumer products. Seal securely and put in the land trash.

Get Involved

Join the "seaweed rebels" by participating in a beach clean-up or buying a license plate that supports conservation efforts. The important thing, Helvarg says, is to do something.