Seaweeds of Hawaii
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.
C. implexa forms densely branched cushions as large as 40 cm in diameter, but they are usually smaller. It has branches from 2 to 5 mm in diameter that are solid in the middle, and the color is grayish to light brown. This seaweed resembles Rosenvingea intricata, but is usually found growing in tide pools on basalt rock, while R. intricata is found on reef flats and in tide pools in limestone rock.
C minima grows in high intertidal habitats along rocky coastlines where large waves break. It often appears in seasons when high waves strike the islands and then dies back when calmer seas prevail. The color is dark brown and the height varies from 3 to 15 cm. This seaweed often has a fuzzy growth of diatoms near the tips of the branches.
Colpomenia sinuosa (paha)
C sinuosa is a hollow saclike seaweed that is golden brown in color and can have a smooth or convoluted surface. It can be found in several habitats.
When it grows intertidally or on other seaweeds it is usually small, from 1 to 5 cm in diameter, but when it grows in tide pools and on reef flats it is considerably larger, up to 20 cm in diameter.
Dictyopteris australis (lipoa)
D. australis is an abundant deep water seaweed in Hawaii. It is often found in extensive dense beds outside reef crests at depths of 3 to 20 m, and is also occasionally present on reef flats. The color is brown with dark spots, the size varies from 10 to 40 cm, and the blades are flat, from 1 to 2 cm wide, with a midrib and ruffled margins. This seaweed produces a strong odor, as does D. plagiogramma.
Dictyopteris plagiogramma (lipoa)
This seaweed is similar to D. australis but smaller, from 5 to 20 cm high, and has narrower blades, from 0.5 to 1`cm wide. D. plagiogramma is brown and the blades have ruffled margins and a midrib. It is found on rocky shores at about the zero tide level, on reef flats, and outside reef crests in deeper water.
Dictyota acutiloba (alani)
D. acutiloba has flat, spirally twisted blades from I to 2 mm wide that branch in a Y pattern and lack a midrib. The size varies from 3 to 20 cm, and the color is light brown. This seaweed is commonly found in tide pools, on reef flats, and in deeper subtidal habitats.
Dictyota bartayresii (alani)
D. bartayresii is light iridescent bluish-green and has branches from 2 to 5 mm wide that have rounded tips and no midrib. This seaweed is erect, from 2 to 10 cm in height, and grows in rocky lower intertidal habitats and on reef flats. This seaweed never has small side branches as does D. sandvicensis.
D. divaricata produces a bright bluish or greenish iridescence. It has pointed untwisted flat branches without midribs that are 0.5 to 3 mm wide. This seaweed reaches a height of 5 cm and is often found growing intertwined with other algae in tide pools, on reef flats, and at deeper depths in between the branches of corals.
D. friabilis is light bluish-green iridescent with wide flat branches from 3 to 10 mm across that have rounded tips and lack a midrib. This seaweed grows on other algae or rocky bottoms, and is found in tide pools, on reef flats, and in other shallow subtidal habitats.
Dictyota sandvicensis (alani)
D. sandvicensis exhibits a noticeable yellowish-green iridescence. The blades are 2 to 5 mm wide, lack midribs, branch in a Y pattern, are sometimes twisted, and often but not always have many small side branches. This seaweed reaches a height of 12 cm and is common in tide pools and on reef flats.
The flat, limp blades of E. binghamiae are usually found during winter months high on intertidal rocky shores. This seaweed is light brown, unbranched, and forms small tufts of several blades 2 to 5 mm wide and 5 to 15 cm long growing from a single holdfast.
Giffordia breviarticulata (hulu'ilio)
G. breviarticulata is a very common seaweed of rocky coastlines colonizing the very high intertidal habitat. It consists of many tangled fine filaments that form a spongy, ropelike tuft from I to 5 cm long. Usually golden brown in color, it may sometimes appear greenish because of microscopic blue-green algae that grow epiphytically on its surfaces.
Hydroclathrus clathratus (poha)
H. clathratus typically forms light-to-olive brown masses that have very distinctive perforations. This seaweed can be up to 30 cm in diameter but is more often smaller. It is commonly found in warm tide pools and on shallow reef flats.
L. variegata is a flat seaweed from 1 to 8 cm across that grows prostrately over rocky substrates but is attached in only a few places. Orange to dark brown with radial markings, it is found in lower intertidal habitats, in tide pools, and on reef flats.
P. australis is a flat seaweed with an in-rolled margin that splits into narrow fan-shaped sections. It is light brown in color and slightly calcified. Attached by a single holdfast, it can be from 5 to 20 cm tall and is found in deep tide pools and on reef flats.
P. japonica is characterized by a flat blade rolled into a circle and an in-rolled margin. The upper surface of the blade is whitish due to the presence of calcium carbonate, while the lower surface, with less calcification, is brownish. This seaweed is very common in shallow tide pools, where it reaches a height of 10 cm, and on reef flats, where it can be 20 cm high.
P. thivyi has a leathery texture, in-rolled margins, and a whitish gray color due to the presence of calcium carbonate. It usually forms thick mats from 2 to 10 cm thick on reef flats and occasionally in tide pools.
There are several species of Ralisia found in Hawaii. They are dark brown crustose seaweeds that grow radially over rocky bottoms. They adhere firmly to the bottom with only the outer margins free. From 1 to 6 cm in diameter, these seaweeds can be found in almost any tide pool or reef habitat.
R. intricata forms golden-brown cushions from 3 to 10 cm high and from 5 to 15 cm in diameter. It has round hollow branches from 2 to 5 mm in diameter. This seaweed resembles Chnoospora implexa, but is found on reef flats and in tide pools in limestone rocks while C. implexa is usually found in basalt tide pools.
S. echinocarpum is commonly found in wave-swept rocky intertidal habitats, in tide pools, and on reef flats. It has golden to dark brown leaf-like blades with a mid-rib and flattened stems. The blades are usually spiny but are sometimes smooth. There are often small inflated gas bladders which have flattened stalks. This seaweed can be from 5 to 70 cm long with blades from 0.5 to 3 cm wide.
S. obtusifolium is commonly found in tide pools and on reef flats. It has light brown leaf-like blades with a midrib, round, smooth main stems, and gas bladders on round smooth stalks, although these are not always present. This seaweed can be from 5 to 50 cm tall and has blades from 0.3 to 2 cm wide.
Sargassum polyphyllum (kala)
S. polyphyllum is found on wave-swept benches, in tide pools, on reef flats, and occasionally at deeper depths. It has many light brown leaf-like blades with a midrib, and when present, gas bladders that have leaf-like stalks. The main stems have many short spiny projections. This seaweed can be from 5 to 40 cm tall and has blades from 0.5 to I cm wide.
S. solierii has flat, thin, strap-like blades without midribs that are from 5 to 40 cm long and from I to 5 cm wide. It is found on deep reef flats at depths of 1 to 5 m and is brown.
S. furcigera is a black fuzzy tuft of filaments that are all approximately the same length. Up to 2 cm tall, it commonly grows on rocky surfaces or larger seaweeds in tide pools and on reef flats.
S. hawaiiensis, from 1 to 5 cm high, exhibits a beautiful iridescent blue or green color. It consists of many flat blades that do not have an in-rolled margin as in the similar-appearing species of Padina. This seaweed is found on wave-swept benches and reef flats, where its bright coloration makes it easily noticed.
T. ornata is a stiff, erect seaweed with distinctive angular turban-like blades and a central stem. Light brown to brown, from 2 to 20 cm tall, it grows on rocky intertidal coastlines, in tidep ools, and on reef flats and crests.
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