Chapter 21.2, Problem 1CSR

Cauferpa taxifolia, the invasive seaweed that threatens to overrun the Mediterranean, is a chlorophyte. This species and other members of its genus have very unusual bodies. Outwardly, they appear plantlike, with rootlike structures that attach to the sea-floor and with other structures that look like stems and leaves, rising to a height of several inches. Despite its seeming similarity to a plant, however, a Cauferpa body consists of a single, extremely large cell. The entire body is surrounded by a single, continuous cell membrane. The interior consists of cytoplasm that contains many nuclei but is not subdivided. That a single cell can take such a complex shape is extraordinary.

A potential problem with Cauferpa’s single-celled organization might arise when its body is damaged, perhaps by wave action or when a predator takes a bite out of it When the cell membrane is breached, all of the organism’s cytoplasm could potentially leak out, an event that would be fatal. But Cauterpa has evolved a defense against this potential calamity. Shortly after the cell membrane breaks, it is quickly filled with a “wound plug” that closes the gap. After the plug is established, the cell begins to grow and regenerates any lost portion.

This ability to regenerate is a key component of the ability of Caulerpa taxifolia to spread rapidly in new environments. If part of a Caulerpa breaks off and drifts to a new location, the fragment can regenerate a whole new body. The regenerated individual becomes the founder of a new, quickly growing colony—and these quickly growing colonies might appear anywhere in the world. Authorities in many countries worry that the aquarium strain of Caulerpa could invade their coastal waters, unwittingly transported by ships from the Mediterranean or released by careless aquarists. In fact, invasive Cauferpa is no longer restricted to the Mediterranean. It now thrives in at least 13 locations in Australia. It also appeared at two locations in California, but authorities there were able to eradicate it after seven years of intensive, expensive effort. Australia has not been so fortunate, and Caulerpa taxifolia continues to spread there.