There are several invasive algae that have been found in southern California. A few of them are listed below. If you think you see any of these algae in the tidepools, note the location and alert a Park Ranger as soon as possible.
Although many species of Caulerpa are used in aquariums, the aquarium strain of Caulerpa taxifolia is of greatest concern. In 1984, this invasive strain was accidentally released from the Oceanographic Museum of Monaco into the Mediterranean Sea, where it formed one small patch that rapidly grew into a large bed. Spread by small fragments transported primarily by boat anchors and fishing gear, Caulerpa taxifolia now blankets over 30,000 acres of seafloor off six Mediterranean countries. Extensive dense carpets of Caulerpa have smothered diverse natural communities and dramatically reduced biodiversity by displacing native seaweeds and animals. Fisheries and tourism have suffered as a result, and in some cases boating restrictions have been instituted to slow the spread of the species. Caulerpa taxifolia infestations have also resulted from its release into Australian waters. Because Caulerpa contains toxins that make it unpalatable to many grazing animals that feed on other seaweeds, it encounters no native enemies in the waters it has invaded.
Sargassum filicinum/Sargassum horneri
The brown seaweed Sargassum filicinum or Sargassum horneri is native to Asia. First thought to be two different species, but now considered just one, was first spotted in Long Beach Harbor in October 2003. In April 2006, it was found near the Wrigley Marine Science Center, Cherry Cove and Emerald Bay on Santa Catalina Island at depths of 4-12 m (12-40’). It was most recently found in Mission Bay, but it was still absent from the Cabrillo tidepools during a 2013 survey by UCSD Biologist Jill Harris. The young plants have flat, symmetrical (fern-like) fronds with a notched tip. Older specimens are 1+ m tall and loosely branched, with small oval bladders and long, finger-like receptacles. Look for the zigzag shape of the frond – it is unique to this species.
The invasive Sargassum muticum has become so prevalent in southern California in recent years, that it has somewhat been adopted – meaning, there’s really no way to remove it in a marine environment. To really confuse things – we also have a native Sargassum. Sargassum muticum is a large yellowish-brown or olive-brown seaweed that can be distinguished from most other Pacific coast seaweeds by its small, spherical float bladders. It grows on rocks, shells or other hard objects, attached by a stout, spongy holdfast. The lowest part of the stalk just above the holdfast is sometimes divided into a few main stems, and gives off several flat, blade-like leaves up to 10 cm long. Above that, the main stems branch repeatedly to form a bushy plant that is often 1-2 m long, with a maximum length of about 10 m. The branches bear small leaves, club-shaped reproductive bodies, and the spherical float bladders. The leaves are up to 2 cm long and either smooth-edged or toothed (the latter resembling small holly leaves). The reproductive bodies are about 1 cm long and 1-2 mm in diameter. The float bladders are gas-filled spheres up to 3 mm in diameter, borne on short stalks, and occurring either singly or in clusters.
For more information about the Sargassum algae, visit the following links:
Last revised 05-Jan-16