Invasive species have increasingly become a major problem in the marine environment, as well as on land. Several species that were introduced and colonized these waters many years ago are quite common today, including periwinkles and green crabs. Others are beginning to appear in large populations as they compete with native plants and animals.
Codium fragile, also called dead manís fingers and green fleece, is a green alga that originated from Asia, most likely Japan. It might have arrived on these shores by attaching to ships, or possibly oyster shells from Europe. It has now spread, and is a pest species on the southern shores of Cape Cod.
The young plant can attach to practically any hard surface, particularly shellfish. It can grow over the filter-feeding siphons of mollusks and block them. It can also weigh down the motile scallops, which also prevents them from feeding. This alga has branches that are bright green and spongy in texture. It can reproduce very quickly by fragmentation in which a small piece breaks off from the adult plant and grows into a new one.
An introduced animal that has spread into this region since the 1980ís is the Asian shore crab (Hemigrapsus sanguineus) which can be identified by three spines on its colorful carapace or shell, and reddish spots on its claws. This crab is 1.5 to 3 inches long, and can feed on the young stages of many mollusk species. Some believe it could be a major problem for aquaculture activities.
One animal that is getting a lot of attention because of its potential negative impact on fish habitats is the colonial tunicate (Didemnum vexillum). Found mainly in deeper waters, this tunicate has a white to pale yellow color, and can completely cover floats, piers, or a rocky substrate, its population has recently been spreading.
Controlling these, and other, marine invaders is not easy. There are management plans available at the state level which includes the gathering of scientific data, as well as monitoring sensitive ecosystems such as estuaries. The proper cleaning of boat hulls and trailers, particularly if they are used in different states, is an effective way of preventing the movement of harmful species. Sometimes just a few larvae or a small piece of an alga can get easily established in a new area. Everyone with an interest in the marine environment should pay close attention to this serious problem of invasive species.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.