Hawai'i Coral Reef Network

Seaweeds of Hawaii
by William H. Magruder and Jeffrey W. Hunt

This is a MOP - Maui CC project by Kim Roseman and Carl Stepath in 1999. This website is by permission of William Magruder for educational purposes and no reproductions are permitted. This permission is fully revocable at any time.


RHODOPHYTA (Red Seaweeds) -continued

Grateloupia phuquoensis

G. phuquoensis has flat blades about 1 mm thick and 2 to 4 mm wide that grow from a long stipe that is flattened at the top, but rounded near the holdfast. The color is dark red. This seaweed grows in clumps from 2 to 12 cm high in intertidal habitats along rocky coastlines that are exposed to large breaking waves.

Gymnogongrus sp

Gymnogongrus has tough stiff branches from 2 to 3 mm in diameter. The color is usually dull red or dark green with lightly colored tips, but the entire seaweed can be bleached by bright sunlight. This seaweed is from 2 to 12 cm long and grows in shaded intertidal and shallow subtidal habitats along rocky coastlines.

Halymenia f ormosa

H. farmosa is an expanded flat blade from 5 to 30 cm long, with a rough surface and a ruffled fringe that resembles a cock's comb. The color is usually bright red with white areas' but it can be yellowish. This seaweed is found on reef flats and in other subtidal habitats to a depth of 10 m.

Hydrolithon breviclavium

H. breviclaviurm can occur as a calcareous crust but more commonly occurs as a pinkish to dull reddish nodule usually smaller than a fist in size. The nodules are smooth surfaced and exhibit an extensive development of small, blunt branches. H. breviclavium occurs on reef flats and in deeper water.

Hydrolithon reinboldii

H. reinboldii, characterized by a pale grayish-blue-violet to pale bluish-violet rough-textured large knobbed surface, occurs either as a calcareous crust on dead limestone reef or ranges from small fragments up to fist-sized nodules. Nodules of H. reinboldii are formed (as are the nodules of other crustose coralline seaweeds) when the spores of the seaweed settle on and grow over loose reef rubble fragments that are rolled about by waves or surge as the seaweed grows. H. reinboldii occurs over the entire reef flat, extending into waters 20 m deep.

Hypnea cervicornis (huna)

H. cervicornis has rounded main branches from I to 3 mm in diameter with short, pointed side branches. The length varies from 3 to 30 cm. This seaweed grows in tide pools and on shallow reef flats, where it varies in color from bright yellow in areas with bright sunlight to dark red in shaded areas. It may sometimes be epiphytic on larger seaweeds.

Hypnea chordacea

H. chordacea has cylindrical main branches that are often completely covered by short spine-like branches, which produce a Christmas-tree-like form. It is from 2 to 8 cm tall and can be dark red, green, or brown. This seaweed grows tangled with other seaweeds in intertidal habitats along rocky coastlines.

Jania sp.

Jania has calcified brittle branches less than 0.5 mm in diameter. It is pink to white in color and varies from 0.3 to 2 cm in length. Close examination of almost any habitat will reveal the presence of this seaweed.

Laurencia nidifica (mane'one'o)

L. nidifica is commonly found on reef flats and in lower intertidal habitats along rocky coastlines, although it can sometimes be found at greater depths. It has round main branches from 1 to 2 mm in diameter that have many side branches growing out in all directions. The tips of the branches have pits in them from which many colorless hairs grow. This seaweed can be from 2 to 20 cm long with highly variable coloration, from bright green in sunny intertidal habitats to dark red in shaded subtidal habitats.

Laurencia obtusa

L. obtusa has cylindrical branches less than 1 mm in diameter that have very few side branches. It is reddish-green in overall appearance, but close examination will reveal distinctive colored banding and the presence of small, fine hairs at the branch tips. This seaweed grows in rocky tide pools, where It forms dense mats from 0.5 to 3 cm thick.

Laurencia succisa

L. succisa is usually found on reef flats, often in cracks or under larger seaweeds, where it reaches a height of 5 cm. Its main branches are slightly flattened with two opposite rows of short side branches with pits at their ends. This seaweed is dark red or dark green and may be slightly iridescent.

Liagora maxima

The branches of L. maxima are red and gooey at the tips but become white and calcified further back, often with a chalky cracked surface. This seaweed grows from 3 to 20 cm high with branches from 1 to 3 mm in diameter. It is usually found on large boulders in water from 0.5 to 5 m deep, but sometimes grows intertidally.

Liagora papenfussii

L. papenfussii has branches from I to 3 mm in diameter that are gooey at the tips, but are calcified and firm further back. The color is pink and the size varies from 5 to 30 cm. This seaweed grows on wave-swept benches and on shallow reef flats.

Liagora tetrasporifera

L. tetrasporifera has white lightly calcified branches about 1 mm diameter that are gooey at the tips. It varies in height from 2 to 8 cm. This seaweed is usually found on reef flats but also occurs in deeper subtidal habitats to 10 m and in tide pools.

Lithophyllum kotschyanum

L. kotschyanum appears as a stoutly branched pinkish to purplish dense head-like growth up to 10 cm high and 15 cm wide. Branches of this seaweed tend to be broadened and flattened, never pointed, often fusing near the tips. L. kotschyanum is most commonly found on the Porolithon-ridge, on reef flats, and in deeper water.

Chnoospora implexa

M. fragilis is a flat seaweed that may be completely solid and smooth or divided into a fine lacelike network on the outer portion. It is from I to 8 cm high and is common in tide pools and on reef flats, but may also be found in lower intertidal habitats and in deeper water. The color is highly variable; it is usually a shade of blue or green with light spots, but it may also be pale or part reddish orange or yellow.

Mesophyllum mesomorphum

M. mesomorphum forms dark-to-purplish-red, thin, overlapping brittle crusts that are often rose-like in appearance. This crustose coralline seaweed is most frequently found in shaded rocky intertidal habitats such as caves and holes.

Neogoniolithon frutescens

N. frutescens, pinkish in color, commonly forms 2 to 3 cm long small diameter (1 to 2 mm) highly branched nodules, but may occur less commonly as a crust. This crustose coralline seaweed usually occurs just shoreward of the reef crest or in deeper waters.

Peyssonellia rubra

P. rubra is a red to maroon crustose seaweed that is calcified on its lower surface. Its edges are free, but elsewhere it is firmly attached to the bottom. This seaweed, common in most subtidal habitats, grows on dead coral, rubble, and other hard surfaces.

Plocamium sandvicense

P. sandvicense is bright red and has branches with inwardly curving tips. It is from 2 to 8 cm long and grows on reef flats and on rocky coastlines just below the zero tide level. This seaweed resembles Desmia hornemannii but does not produce a strong odor and has branch tips that are curved inward, not rolled back.

Porolithon gardineri

P. gardineri forms pinkish calcareous crusts or much branched hemispherical-shaped heads from 10 to 30 cm across (or larger). The branch tips of P. gardinen may be rounded or fused and somewhat flattened, but some pointed branch tips are usually present. P. gardineri occurs on the Porolithon ridge, in other areas of turbulent surf, or in crevices with strong currents.

Porolithon onkodes

P. onkodes forms extensive pinkish to somewhat purplish chalky crusts in intertidal areas exposed to surf action. Due to its tolerance of strong sunlight and dessication and its crustose nature it is extremely successful in occupying high-wave-energy intertidal habitats such as the basalt coastlines of open coasts or intertidal reef crests. P onkodes performs a critical role in the formation and maintenance of the biotic reefs of Hawaii, as well as atoll land forms, by providing an actively growing reef rim, allowing consolidation and cementation of reef material to occur in the protected areas shoreward of the Porolithon ridge.

Porphyra sp.

Porphyra is a very thin, flat seaweed that grows in slippery clumps very high in wave-splashed intertidal habitats along rocky coastlines. The color is red to yellowish brown and the size is from 2 to 15 cm long and 1 to 3cm wide. This seaweed is very seasonal, appearing during winter months and disappearing by late spring.

Predaea weldii

P. weldii is found in subtidal habitats, where it grows between the branches of corals, reaching a length of 5 cm. It is extremely soft and gooey, turning into a shapeless blob when out of the water. Although not usually abundant, this seaweed is quickly noticed because the tips of its branches are fluorescent red.

Pterocladia capillacea

P. capillacea often forms an extensive band around the zero tide level in areas exposed to breaking waves. It can be found on basalt coastlines or on the outer edges of reef crests. The color is dark red, but it can appear pink because of crustose coralline seaweeds that grow epiphytically on its surface. The size varies from 2 to 25 cm but is usually around 10.

Pterocladia caerulescens

P. caerulescens is commonly found in tide pools and on reef flats, but can easily be overlooked because of its dark green to blackish color and its habit of growing intertwined with other seaweeds in dense turfs. This seaweed is usually around 2 cm high but can vary from 1 to 8 cm.

Scinaia hormoides

S. hormoides has branches from 3 to 7 mm in diameter with very distinctive regular constrictions which give it the appearance of chains of elongated spheres. The height varies from 5 to 15 cm, the color is pink to red, and it grows in subtidal habitats below 3 m.

Sporolithon erythraeum

S. erythraeum is characterized by a smooth and glazed maroon to greenish surface with large knoblike structures. S. erythraeum may occur as a thick crust or as various-sized nodules. In low-light habitats or on the undersides of nodules it appears maroonish but in stronger light, as on the upper surfaces of nodules, it is greenish. S. erythraeum, distributed over the reef flat, is one of the most important crustose coralline seaweeds, contributing through its cementing action to the consolidation of various loose reef materials into reef limestone. S. erythraeum may also be found in tide pools.

Spyridia filamentosa

S. filamentosa has branches from 0.5 to 2 mm in diameter that are covered with many soft, fine, short branches that create a fuzzy appearance. It is red to almost white, but often traps fine sediment that can make it appear many different colors. This seaweed is usually found in calm inner areas of reef flats where it forms soft, thick mats up to 20 cm thick that can cover large areas of the bottom, but it can also be found at deeper depths.

Tenarea tessellatum

T. tessellatum forms elaborate, spirally sculptured, slightly glazed calcareous crusts or nodules that are pink to pale purple in color. Interestingly, the sculptured spirals may turn either clockwise or counter clockwise. T. tessellatum, easily recognized by its distinctive spirals, is most commonly found at depths of about 10 m, but may occasionally be found on reef flats.

Tolypiocladia glomoulata

T. glomerulata forms loose mats from 0.3 to I cm thick on rubble and coral heads in subtidal habitats. Its main branches are small, less than 0.5 mm in diameter, and have many short branches growing out from all sides. In deeper water this seaweed is dark red, but in shallow water it can be pale red to almost white.

Trichogloca requienii

T. requienii has slippery round branches that are extremely gooey throughout their entire length. The branches are mostly from 3 to 6 mm in diameter and the height varies from 5 to 40 cm. This light pink, slightly calcified seaweed grows on reef flats and in deeper subtidal habitats to 10 m, where it can be observed flowing back and forth


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Last update: 1/25/2005