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)

Acanthophora spicifera

A. spicifera has solid cylindrical branches from I to 3 mm in diameter that are covered with many distinctive small, spine-like branches. It can vary in height from 3 to 20 cm and is abundant on calm, shallow reef flats, in tide pools, and on intertidal rocky benches swept by small waves. This seaweed can be red, brown, or dark green in color, but often turns yellow when exposed to bright sunlight.

Actinotrichia fragilis

A. fragilis is red or yellow with cylindrical branches about I mm in diameter that are covered with closely spaced rings of short, dark, stiff hairs. This lightly calcified seaweed is from 2 to 6 cm high and grows in tide pools, on reef flats, and in deeper subtidal habitats.

Ahnfeltia concinna ('aki'aki)

Ahnfeltia concinna ('aki'aki)

A. concinna is often the highest-growing intertidal seaweed on basalt rock coastlines, where it can form an extensive dense band or be present only in small cracks and crevices. It has tough rubbery cylindrical branches 0.5 to 3 mm in diameter and 2 to 60 cm long. The color is variable; those growing highest are bright yellow, while those growing lowest are dark red.

Amansia glomerata

A. glomerata, which grows to 15 cm tall, is bush-like in appearance with a round central stipe and flattened blades from 3 to 7 mm wide. It is dark red, but is often covered with epiphytic crustose coralline seaweeds which give it a pink appearance. This seaweed is widespread, being found in shaded areas of almost any habitat.

Amphiroa fragilissima

A. fragilissima is a heavily calcified seaweed that is very brittle and breaks easily into small pieces. It is pink, has branches less than 1 mm in diameter, and often forms extensive mats 2 to 6 cm thick in shallow tide pools.

Asparagopsis taxiformis (kohu)

A. taxiformis is red to bluish violet in color, has a fluffy appearance, and is shaped like a Christmas tree. This seaweed is 3 to 15 cm high, and commonly grows in shallow subtidal habitats with heavy water motion, such as reef crests, where there are continually breaking waves.

Botryocladia skottsbergii

B. skottsbergii has a unique appearance, resembling rounded balls on short stalks. This seaweed is dark red to dark green, I to 3 cm tall, and grows in clusters in shaded places such as overhanging ledges, holes, and crevices on reef flats and in lower intertidal habitats along rocky coastlines.

Centroceras clavulatum

C. clarulatum has Y-shaped branches less than I mm in diameter with the final two branches often curving inward, creating a claw-like appearance. It is usually dark red, from 0.5 to 5 cm long, and grows in turfs and mats in lower intertidal habitats, in tide pools, and on reef flats.

Champia sp.

Champia has segmented branches from 1 to 3 mm in diameter that resemble earthworms. It can be red to light pink, but often has a blue or green iridescence. It forms clumps from 2 to 6 cm high and is found on reef flats and in other shallow subtidal habitats, where it grows on rocks or as an epiphyte on larger seaweeds.

Cladymenia pacifica

C pacifica has flat branches from 2 to 6 mm wide that are iridescent light blue or light green. It varies from 2 to 10 cm in length and is usually found growing on rocky substrata in subtidal habitats below 3 m.

Coelothrix irregularis

C. irregularis has round rubbery elastic branches from 1 to 2 mm in diameter that are very dark red, often with a shiny surface. This seaweed grows on rocks in lower intertidal habitats and on reef flats, where it forms loosely woven mats 5 to 15 cm across.

Coralina sp.

Corallina is a heavily calcified seaweed with main branches consisting of short segments, each of which has a small segment on each side. It is pink, I to 5 cm tall, and grows in rocky intertidal habitats, in tide pools, and on reef flats.

Dasyopsis sp.

Dasyopsis sp.

Dasyopsis, a beautiful iridescent blue, green, or violet, is rarely overlooked. This seaweed is from 2 to 8 cm high and is found in tide pools, on reef flats, and in other shallow subtidal habitats. Its branches are covered with many fine branchlets, which produce its characteristic fluffy appearance.

Desmia hornemannii

D. hornemannii produces a distinctive strong odor. It is bright red. fron1 2 to 6 cm high' and has branches that are rolled back at the tips. This seaweed grows in almost any habitat. from rocky intertidal to in between the branches of corals at subtidal depths. It resembles Plocamium sandvicense, but its rolled-back branch tips and strong odor are distinctive.

Dotyella havvaiiensis

This beautiful bluish-purple seaweed is usually found growing on the branches of corals in subtidal habitats below 5 m. It has many fine, soft branches and can reach a length of 10 cm.


Galaxaura acuminata

G. acuminata can be found in shaded areas of deep tide pools or at deeper depths, where it often grows between the branches of corals. It has hollow branches, but this is not immediately apparent because they are flattened, frryn1 I to 4 mm wide. This calcified seaweed is pink to red and grows to 15 cm in length.

Galaxaura fastigiata

G. fastigiata has hollow cylindrical branches I to 2 mm in diameter with deep pits in the ends. It is found in tide pools and on reef flats, where it reaches a height of 15 cm. This calcified seaweed is white to pink in color.

Galaxaura filamentosa

G. filamentosa is usually found in tide pools, but is sometimes present l on reef flats. It has cylindrical branches I to 3 nlZI1 in diameter that are I covered with fine, soft hairs. The main part of the branch is white or pink, while the hairs are dark red. This calcified seaweed can reach a height of 8 cm.

Galaxaura rugosa

G. rugosa is commonly found growing in tide pools. It has hollow cylindrical branches I to 3 mm in diameter with obvious pits in the ends. The color is usually yellow at the tips, turning to red at the base. This lightly calcified seaweed can be from 3 to 8 cm tall.

Gelidiella acerosa

G. acerosa has cylindrical branches about I mm in diameter and grows in lower intertidal habitats, in tide pools, and on reef flats, where it intertwines with other seaweeds to form dense turfs. The exposed parts of this seaweed are yellow, while the parts tangled down in the turf are dark red.

Gelidiella machrisian

G. machrisiana is found in shallow tide pools, where it usually grows in a dense turf with many other different seaweeds. Its small, round branches are less than I mm in diameter and reach a length of 3 cm. When present, this seaweed rarely escapes notice, because it is brilliant green, yellow, or bluish iridescent.

Gelidiopsis scoparia

G. scoparia is a tough, wiry seaweed with rounded or flattened branches less than I mm across that sometimes become wider and more flattened where branching occurs. The height varies from 2 to 8 cm. This seaweed is dark brownish red in color and grows in intertidal habitats along rocky coastlines. The swellings at the tips of the branches in the picture are reproductive structures and are not present in all specimens.

Gibsmithsia hawaiiensis

The unusual appearance of G. hawaiiensis is unmistakable; it has many thick, loose branches from a tough central stalk. The color varies from red to white, and the size from 3 to 12 cm. This seaweed is most often found growing between the branches of coral in water deeper than 5 m, but can occasionally be found on reef flats.

Gracilaria bursapastoris

G. bursapastoris is one of the larger red seaweeds in Hawaii, sometimes growing to 60 cm in length. Its branches are cylindrical, from 1 to 4 mm in diameter, and have pointed tips that are long and narrow. This seaweed grows on reef flats and is red, but can be light brown, light green, or almost white in areas with bright sunlight.

Gracilaria coronopifolia (manauea)

G. coronopifolia has solid cylindrical stiff branches from 1 to 4 mm in diameter that have short pointed tips. It is red in color, but often bleaches to pink or white in bright sunlight. This seaweed commonly grows on reef flats, where it is 6 to 20 cm tall, but may occasionally be found in tide pools.

Gracilaria salicornia

G. salicornia has cylindrical branches from 2 to 5 mm in diameter that often but not always have distinctive constrictions. This seaweed grows in tide pools and on reef flats, where it forms mats from I to 5 cm thick, by itself or tangled with other seaweeds. The color is bright yellow in sunny areas, turning to greenish brown in shady habitats.

Grateloupia filicina (huluhuluwoena)

G. filicina is a soft, limp seaweed with somewhat flattened branches that can be red, green, brown, or almost black. The size and shape very greatly; from 0.5 to 5 mm wide, from 2 to 30 cm long, with only a few branches or with many branches. This seaweed grows at about the zero tide level on rocky coastlines and on shallow reef flats.

Grateloupia hawaiiana

G. hawaiiana has a flat, branched blade that usually grows from a short cylindrical stipe. It is red to dark red, 3 to 20 cm high, and is found in intertidal habitats along open rocky coastlines or on reef flats.

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Last update: 1/25/2005