Chlorophyta, Order: Caulerpales; Family: Caulerpaceae.

 Etymology

Caulerpa, means ‘crawling stalk’. Prolifera describes the unique growth form of the species, in which the thallus’ branching (proliferation) supports additional branches.

Description

The thallus is flat and has no indentations, as do other Caulerpa species in this region. The Caulerpa prolifera’s branches resemble an elongated ‘leaf’ whose sides and edge are rounded. New ‘leaves’ develop on the backs of old ones, usually from the point closest to the upper edge of the thallus. Thus, several levels of ‘leaves’ can develop one on top of the other. Lateral and vertical fibres that support the thallus can be seen through a microscope. The thallus is a single, multi-nuclear cell with many chloroplasts and no wall (coenocyte.(

Size

The length of a ‘leaf’ can extend to 10-15 cm and its width to 0.5-2.5 cm.

Colour

The Caulerpa prolifera is green, ranging from light green to greenish-yellow.

Special features

The Caulerpa prolifera has elongated, leaf-like photosynthetic organs. The species is characterized by ‘proliferation’ (the regenerative growth of ‘leaves’ upon one another).

Habitat

Thanks to its crawling holdfast, which resembles an extension, the alga can develop even upon an unstable sandy substrate, creating a sort of ‘lawn’. The Caulerpa prolifera has been harvested at depths of 50-70 m. Professor Alim from Egypt reports sightings in polluted water, such as those in the Alexandria port.

Biology and reproduction

Towards the breeding season, the thallus loses its dark colour and is covered with dark, nipple-like spots surrounded by yellow or green rings. Upon splitting, these secrete a mucousy substance that contains zoospores. Female reproductive cells are more elongated than male ones, and both have zoospores. Following the assimilation process,the zygote loses its zoospores, becomes rounded and produces a cell wall. While germinating, the zygote grows, the number of chloroplasts rises to several dozen, until the form of the regular coenocytic thallus is achieved.

Seasonality and distribution

The Caulerpa prolifera was very common along Israeli shores, but in recent years the number of sightings has decreased, and there was fear that the community had disappeared or diminished. After many years of absence, apart from a single report by Dr. Lundeberg in 1991, I found several individuals at the Habonim beach, south of Haifa in May 1997. These were not attached to a rock and may have drifted in from the depths. They were all covered by epiphytes characteristic of the deep sea. Based on this single sighting, one may assume that in the depths, colonies of the species still exist. Colonies have been reported in the deep in past studies. The individuals growing in the intertidal

zone may have disappeared or diminished due to the activities of herbivores, especially fish that migrated from the Red Sea, including two species of siganus. A colony of Caulerpa prolifera was also found near Atlit, at a depth of about 15 m by the diver Shai Kedem (there may also be colonies in the vicinity in shallower water as well.(

The alga is not common throughout the year. Zoospores can be found between October and January. Global distribution includes the Mediterranean, the Aegean Sea, the Black Sea, the Atlantic Ocean and the Indian Ocean.