The ocean covers 140 million square miles—that's more than 70% of the Earth's surface. An additional 2% of the planet is covered with lakes, rivers, and ponds. From the deepest depths of the Pacific's Mariana Trench to the shallow tide pools (see page 24 of the 2004/2005 Coastlines pdf format of    Coastlines 2004-2005  file size 37MB for an article on tide pools) of Salem Sound, these water bodies are home to more than 1.5 million aquatic species.

Of these many life forms cohabitating in the world's water bodies, some are causing increasing concern to scientists and environmentalists… invasive species (also called alien, exotic, nonindigenous, and biological invaders). In general, a couple of criteria need to be met for a species to be considered invasive: 1) the species must have become established in an area away from where it originated; and 2) it must cause harm to the ecosystem or economy of the invaded area. Determining harm is at times difficult, so those working to manage invasives often operate under the precautionary approach that any non-native species will have harmful impacts on some scale.

In Massachusetts, invasive species are alive and, well, doing quite well (see page 33 of the 2002 Coastlines pdf format of    Coastlines 2002 - Hurricanes  file size 4MB ). The European green crab and the common periwinkle snail, along with freshwater zebra mussels and water chestnuts, are a few examples of well established invasive species that are living and reproducing in Massachusetts—typically to the detriment of native species. Not only do they crowd out existing natives, but infestations of water chestnuts and Eurasian watermilfoil pdf format of    Eurasion Milfoil  have clogged local lakes and ponds, making it difficult to boat, fish, or swim, while invasive tunicates have negatively affected eelgrass beds and threaten local scallop populations. Thousands of dollars have been spent to combat the effects of invasives in Massachusetts, making their presence a fiscal as well as environmental issue. (For more on aquatic invasives, see the Gulf of Maine Council on the Marine Environment's Marine Invasive Species report.)

SO WHAT CAN THE AVERAGE CITIZEN DO?

Familiarize yourself with invasive species so you know what to look out for. See the Massachusetts Office of Coastal Zone Management's (CZM) Aquatic Invasive Species (AIS) Program's Identifying Aquatic Invasive Species web page or download the Massachusetts Department of Conservation and Recreation's (DCR) A Guide to Selected Invasive Non-Native Aquatic Species in Massachusetts pdf format of    Aquatic Species  and MIT Sea Grant's Hitchhikers guide to know how to spot these aliens. If you should find any in your travels, report them.

If you are a boater, it's very important to thoroughly clean your boat's surfaces and dispose of any plant or animal material, which could include invasive species, in a trash can. (If there is no trash can handy, you can bag the material, freeze it, and throw it away at home.) The Indiana Clean Marina Guidebook gives additional information.

If you use worms or crustaceans for fishing bait, do not release any leftover bait into the water. Worms and crustaceans are not regulated in Massachusetts (unlike fish used for bait), and imported, potentially invasive worms have been found in vending machines in New England. Dispose of any live bait by freezing it and throwing it away. Also, do not discard the bait packing material into the water—it can contain hidden invasives. See the AIS Program's Bait Industry/Recreational Fishing page for more.

When wearing waders or boots while fishing, make sure that you thoroughly clean them—particularly felt soles—after leaving any water body. Plant matter and organisms responsible for Whirling Disease can easily attach to shoes and other fishing gear and be introduced to new areas if proper steps aren't taken. For more facts and tips, see the Northeast Aquatic Nuisance Species Panel's decontamination fact sheet and DCR's Prevent the Spread of Invasive Species pamphlet pdf format of    Boating Brochure  .

After dining on crabs, lobsters, mussels, or clams, bag up your remnants and dispose of them in the trash. Even seafood that has been locally harvested can have invasive species attached to the shells. As detailed by Woods Hole Oceanographic Institution, the clam industry in Massachusetts has been hit by QPX (Quahog Parasite Unknown), and there is no telling what other parasites, known or unknown, may be lurking on your leftovers.

If you have an aquarium or water garden, never dispose of any plants or aquatic life by releasing them into the ocean, a lake, or a pond. Unfortunately, many invasive species have been sold in pet and garden supply stores. They are often hardy, which makes them desirable for these artificial systems—but when released into their non-native territory, they can take over. If you have unwanted plants or fish and can't give them away to an institution or another person who could take care of them, contact the store you originally purchased them from to see if they will take them back. Otherwise, as harsh as this may sound, the best thing to do is bag them, freeze them, and throw them in the trash. See the Massachusetts Bays Program's Protect Your Pets/Preserve the Environment flyer pdf format of    Protect Your Pets  file size 1MB or the Habitattitude website, a national initiative developed by the Aquatic Nuisance Species Task Force and its partner organizations, for more information.

When setting up an aquarium or water garden, make sure you don't select species on the Massachusetts Department of Agriculture's prohibited plant list and DCR's aquatic invasive species list. Before making your purchase, ask for the scientific name and country of origin, and if you are unsure, do some research before committing to buy.

When landscaping along the coast, choose native plants. By doing so, you will be rewarded with a low-maintenance yard (which means less watering and no-to-minimal fertilizers), and you will eliminate any risk of spreading invaders. CZM's Coastal Landscaping website has additional information, including sample landscaping plans for coastal banks and dunes. If you are ever unsure of a species, you can look it up on the Massachusetts Prohibited Plant List, or the Invasive Plant Atlas of New England.

If you go hiking or camping, make sure you clean off your clothing and equipment before you leave the site—if an invasive species has attached itself to any surfaces, it can be spread to another area through your movement. Also, as per the information on the Reserve America's campground finder site, be aware that you cannot bring your own firewood to state parks in Massachusetts. Instead, you can purchase it on site.

Volunteer! Learn to identify and monitor marine invasive species through CZM's Marine Invader Monitoring and Information Collaborative or hunt down freshwater invasive plants through DCR's Weed Watchers Program.