||Hypnea cervicornis J. Agardh
||Hooked Red Weed
Hypnea cervicornis is a Rhodophycean algae with a wiry, entangled
form. It is yellow in color under conditions of strong sunlight, but becomes a
darker brown-red color when shaded. Its branches are short and pointed, with
branchlets that appear tendril-like. H. cervicornis lives attached to
rocks or corals via a holdfast, or as an epiphyte on other plants. It grows
3-30 cm tall to depths of 10 m (Littler and Littler 1989).
HABITAT AND DISTRIBUTION
Worldwide in tropical and subtropical zones.
In the Indian River Lagoon, H. cervicornis is common in Thalassia
LIFE HISTORY AND POPULATION BIOLOGY
The pattern of spore germination in the Rhodophyta has been used as a
diagnostic trait to taxonomically group species. Hypnea, and other
species in the Order Gigartinales, have carpospores (sexual stage) and
tetraspores (asexual stage) which settle and attach to substrata. Spores of H.
cervicornis have no resting stage, as in some other algal groups. The
attached spores undergo repeated segmentation to produce a morula-like stage
from which the holdfast and shoot emerge (Mshigeni 1976).
Release of sexual carpospores, but not asexual
tetraspores, was observed to co-occur with release of a gelatinous secretion
which enveloped the spores. A gelatinous mass of aggregated spores is likely to
sink considerably faster than individual spores, thus potentially making
carpospores better adapted for attachment to substrata (Coon et al. 1972,
Mshignei 1976). The predominance in Hawaii of Hypnea tetrasporophytes
(which develop from carpospores) over gametophytes (which develop from
tetraspores) appears to lend credence to this observation.
Survives well in the tropics and
subtropics in the shallow intertidal zone, and withstands dessication when
exposed to air during low tides.
H. cervicornis is common in the intertidal zone, and was found to
occur higher above other Hypnea species, (H. chlordacea, H.
nidifica) thus, it is more often exposed to air and direct sunlight at low
tide than other species (Mshigeni 1977). Mshigeni (1976) noted that in Hawaii, Hypnea
species show some differentiation in the holdfast (attachment disc) based on habitat type. H. cervicornis
has a somewhat smaller holdfast than some other species in the genus.
Mshigeni (1976) associated this trait with H. cervicornis' typical
habitat: calm, sandy substrata. Other species, with larger holdfasts, tended to
be found in higher energy zones.
In the IRL, is often associated with Thalassia testudinum.
Hypnea cervicornis is considered an economically important seaweed
because it produces carrageenan, a binding and smoothing agent used in many
commercial products such as toothpaste, ice cream, pet foods, etc. In addition, H.
cervicornis is important to the medical and pharmaceutical industries,
because agar, an important derivative of carrageenan, is a principal component
of bacterial culture media.
Coon DA, Neushul M, Charters AC. The settling behavior of marine algal spores. Proc 7th Intern Seaweed Symp, 1971, Sapporo, Japan. pp.237 - 242. Univ Tokyo Press.
Littler DS, Littler MM, Bucher KE, Norris JN. 1989. Marine Plants of the Caribbean, a Field Guide from Florida to Brazil. Washington, DC: Smithsonian Institution Press.
Mshigeni KE. 1976. Studies on the reproduction of selected species of Hypnea (Rhodophyta, Gigartinales) from Hawaii. Bot Mar 19: 341-346.
Mshigeni KE. 1977. Seasonal changes in the standing crops of three Hypnea species (Rhodophyta: Gigartinales) in Hawaii. Bot Mar 20: 303-306.
Report by: K. Hill,
Smithsonian Marine Station
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Page last updated: Sept. 18, 2001