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This fine, delicate green alga has overgrown and smothered
coral and other algae during blooms in Maui.
Cladophora sericea bloom in Maui, Hawai‛i.
Plants bushy or spreading, not tufted. Filaments slightly to
profusely branched; plants usually in soft to stiff clumps, often floating;
The main axis branches dichotomously and has lateral branches that are
shorter, narrower (20 - 40 µm diameter) and arranged alternately, opposite
or on one side. Lateral branches near the tip often have shorter branches
between longer branches. Attachment is by rhizoids from basal poles of mid
to lower cells, or by cluster of basal rhizoids. Pale green to grass green.
Main axes 50-70 µm diameter, cells 4-8x longer than wide
containing reticulated choloroplasts.
Cladophora sericea occurs in small amounts with other
algae or in abundant loose strands attached to coral, basalt substrate, and
other hard surfaces on reef flats near low tide line to 2m deep.
Hawai‘i: Northwest Hawaiian
Islands, O‘ahu, Maui, Kaua‘i, Lana‘i, Moloka‘i and Hawai‘i Island.
Mechanism of Introduction:
Indigenous to Hawai‘i.
World-wide distribution: Australia, Atlantic Ocean,
Mediterranean, Caribbean, Indian and Pacific Oceans.
Cladophora sericea is a branching green filamentous alga
found on most reefs in Hawai‘i. This small green alga is usually a small
part of the biomass of the diverse, highly competitive intertidal community.
By virtue of its dense and self-shading form, the alga rarely experiences
photo inhibition except in the branches on the very top of the tuft, and thus
tends to attach to solid substrate areas that are quite exposed. In
addition, the alga has demonstrated nitrate storage capabilities which
increase its longevity in stressful conditions. All of the Cladophora
species are opportunistic settlers that respond to environmental variation.
Nutrient loading, water temperature fluctuations, and downwelling
illumination all influence the growth rates and longevity of these alga. In
areas of eutrophication, opportunistic species like C. sericea may play an
important role in coral reel community shifts.
C. sericea has demonstrated invasive characteristics in
Hawai‘i, unlike the intertidal C.
vagabunda. Approximately 10 years ago the alga became exceedingly abundant on
leeward reefs in Maui and large blooms now occur seasonally. During the
blooms, large masses of the alga drift in the water column, snagging on
coral and rock outcroppings and smothering out the organisms beneath.
Cladophora species can be difficult to identify. The
morphology can be altered significantly by environmental conditions, to the
extent that in many cases even the cellular structure used to define the
species can be variable among individuals of the same species. Therefore,
the genus as a whole should be observed for invasive tendencies.