Brian Lapointe of the Harbor Branch Oceanographic Institution in Ft. Pierce, Fla., examines a piece of Caulerpa verticillata about 1 mile off the southern coast of Florida. Ordinarily, this seaweed inhabits meter-deep coastal waters and grows in small, isolated patches. Over the past 3 years, however, the inch-high alga has begun smothering coral and other sea life as it blankets the seabed at depths up to 30 m in a swath some 6 miles long and a half mile wide.
Unlike its rogue cousin, a Caulerpa overtaking the Mediterranean (SN: 7/4/98, p. 8: https://www.sciencenews.org/sn_arc98/7_4_98/bob1.htm), this alga is a native species. Lapointe has evidence that its new invasiveness traces to overfertilization with sewage rich in ammonium, potassium, and nitrates. Injected deep underground on the mainland, the pollution appears to migrate underground, he says, eventually welling up from the ocean floor around coral reefs.
