|
Invasive Algae Home Red Algae Green Algae Brown Algae Seagrasses Glossary |
|
|
||||||||||
|
||||||||||
|
|
|||||||||
|
In the sandy, shallow habitats of Mamala Bay in O‘ahu, Avrainvillea amadelpha has formed thick communities that cover the substrate, invading the reef environment and out competing other algae and our native seagrass, Halophila hawaiana.
Distribution of
Avrainvillea amadelpha in Hawai‛i
Avrainvillea amadelpha in the field. |
|
|||||||||
|
Description Plant consists of one to four wedge shaped blades that are thin, diaphanous, 1 - 4 cm wide, and 1 - 3 cm tall. Each blade is attached by a stipe, 0.4 - 1.5 cm long, to compact basal holdfast. Blades are asymmetrical, surfaces felt-like, and margins smooth to lacerated. The stipe is flattened in cross section. Color is green to green-gray, and clumps are often covered with silty sand, appearing muddy brown.
Plants may be found singly or in clumps of many blades. In larger, more mature communities, other macroalgae will be found attached to blades.
Structural Features Siphonous; cylindrical siphons 10-12 mm in diameter throughout the thallus. Non-tapering to slightly tapering, haphazardly oriented at blade margin. Range in color from transparent to green, with rare brown plug-like inclusions. If constricted, siphons’ dichotomies deeply constricted just above branch, less than 1/2 siphon’s diam. and length equal to siphon diam. Apices rounded to slightly clavate (club shaped).
Habitat Avrainvillea amadelpha is abundant in habitats of shallow, sandy substrate with low water motion. Forms dense clumps often covered with silt and sand. Overgrows coral rubble. Found from 1 to at least 10 meters deep.
Distribution Hawai‘i: O‘ahu: Kahe Point, Koko Head, Waikiki area, Diamond Head. Mechanism of Introduction: First identified in shallow water locales at Kahe Point and Koko Head. Thought to have arrived sometime after 1981. Deep water populations collected by Hodgson at 40 ft in Waikiki. Actual mechanism of introduction not known. Worldwide Distribution: Mauritius, Tuamotus, Fiji, Philippines.
Ecology/Impact Avrainvillea amadelpha is apparently a fairly recent introduction to Hawai‘i. In established communities, this green alga has invaded and now covers a large part of the substrate, becoming a secondary substrate for other reef algae. Growth proceeds from the basal region rather than from the blades, so plants are usually in tight clusters of single blade height.
First found in 1981 on the leeward shore of O‘ahu, it is now found in large communities with Acanthophora spicifera along the southern shore of O‘ahu. Sandy bays once known for large native seagrass beds, (Halophila hawaiiana) are now overgrown with these invasive species. This alga’s closely packed blades trap sediments and provide habitat for filter feeders such as worms and molluscs. With enough time, these trapped sediments added fine silt to the sandy bottom and create a mud layer upon the sand, thus changing the nature of the substrate. |
||||||||||
|
|
|
|
References Brostoff, W.N., 1989. Avrainvillea amadelpha (Codiales, Chlorophyta) from O‘ahu, Hawai‘i. Pacific Science 43(2):166-169. Littler, Mark M. and Diane S. Littler, 1999. Blade abandonment/proliferation: A novel mechanism for rapid epiphyte control in marine macrophytes. Ecology 80:1736-1746. |
Web Pages
Ecological Success of Alien/Invasive Algae in Hawai‘i:
http://www.botany.hawaii.edu/GradStud/smith/websites/
Marine Invasives in Hawai‘i: Virtual Herbarium. http://www.botany.hawaii.edu/reefalgae/greenskey.htm
|