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Close up of Dictyosphaeria cavernosa. Note the hollow chambers inside
or "green bubble algae" is an
opportunistic green alga which is invasive in overfished, high nutrient reef
communities. The large "bubbles" efficiently trap sediments, nutrients and
infaunal inside the chambers of the plant.
Dictyosphaeria cavernosa growing over Porites compressa at
Kaneohe Bay, Oahu.
Thallus to 12 cm in diameter, saclike, hollow, spherical
when young, becoming convoluted, ruptured, and irregularly lobed when old.
Firm, tough texture, consisting of large bubble-shaped cells that are easily
seen by eye. Rhizoids are short, branched or unbranched.
Daughter segments are formed as occasional segments become
inflated, forming large monostromatic bladders attached to the parent plant.
They may remained attached to the thallus or break away and become
independent plants. Grass green, but sometimes blueish in color.
Can be easily confused with
D. versluyii. D. versluyii
is smaller, completely solid, and remains rounded.
Primary cells 0.1-3.0 mm diam., in monostromatic layer,
angular or polyhedral in surface view, appearing honey-comb like, adhering
to one another by hapteroid cells at juncture of walls isodiametric, 35 - 45
Dictyosphaeria cavernosa is found attached to rocks or
coral rubble on shallow, calm reef flats and in tidepools. Young plants may
form small clusters of "bubbles" scattered among turfs on hard substrate.
Older plants can form large convoluted mats from 1 to 10 cm thick that may
cover large areas subtidally to 59 meters.
Hawai‘i: Northwest Hawaiian
Islands, O‘ahu, Maui, Moloka‘i and Lana‘i.
Mechanism of Introduction:
Indigenous to Hawai‘i.
Eastern Atlantic, Caribbean, Red Sea, Arabian Sea, Indian and
Dictyosphaeria cavernosa is a native alga that has shown
invasive tendencies in reef communities experiencing nutrient enrichment and
overfishing. The thallus’ sheet-like morphology enables it to cover large
areas of reef and create large hollow chambers where organisms and gases are
trapped. Like other invasives, D. cavernosa efficiently captures
available nutrients, resulting in high growth rates. The morphology of this
particular green alga, however, is especially efficient: nutrients trapped
in sediments are released to the water column and trapped in the chambers of
D. cavernosa where they are held for uptake. This special "bubble"
morphology has proven successful in areas of long term nutrient loading
where the sediments have become a reservoir for additional nutrients.
The solid sheets of D. cavernosa can be devastating to
coral reefs. Since the 1960’s, and possibly earlier, D. cavernosa has
overgrown and displaced corals on reef slopes and outer reef flats in
Kane‘ohe Bay, O‘ahu, Hawai‘i. The alga uses coral and limestone outcrops as
an anchorage and proceeds to overgrow them, killing the corals by
smothering. In a study of the standing crop of frondose algae at Waikiki as
much as 300gm/m2 wet weight of
the biomass was attributed to this species.
Dictyosphaeria species grow by segregative cell
division, producing daughter segments that are initiated inside parent
segments but grow outwards in the form of a bubble. The species also
reproduces sexually by freeing flagellate reproductive cells through pores
in the walls of the vegetative cells of the thallus. In conditions of high
nutrient loading and overfishing, Dictyosphaeria species are fecund
and successful competitors.
Abbott, I.A., 2001. Unpublished manuscript.
Egerod, L.E, 1952. An analysis of the siphonous chlorophycophyta.
University of California Publications in Botany, V. 25 (5): 325-454.
Larned, S.T., and J. Stimson, 1997. Nitrogen-limited growth in the
coral reef chlorophyte Dictyosphaeria cavernosa and the effect of
exposure to sediment-derived nitrogen on growth. Mar Ecol Prog Ser 145:
Magruder, W.H, and JW. Hunt, 1979. Seaweeds of Hawai‘i. Oriental
Publishing Company, Honolulu, Hawai‘i.
Russell, D. J. and G. H. Balazs, 2000. Identification manual for
dietary vegetation of the Hawaiian green turtle, Chelonia mydas.
NOAA TM-NMFS-SWFSC-294. 49 pp.
Stimson, J., S.T. Larned and E. Conklin., 2001. Effects of herbivory,
nutrient levels, and introduced algae on the distribution and abundance of
the invasive macroalga Dictyosphaeria cavernosa in Kane‘ohe Bay,
Hawai‘i. Coral Reefs, DOI 10.1007/s003380000123.
Frondose Algae of Waikiki.
Hawaiian Reef Algae.