Click on pictures for larger
Ulva fasciata, also known as limu palahalaha and
sea lettuce, is a common green alga that is used for consumption in many
parts of the world. High nutrients and fresh water are often indicated
by its presence.
in a tidepool at O‘ahu.
Thalli thin, sheet-like, consisting of wide blades, 10 - 15
cm wide at base, tapering upward to less that 2.5 cm wide at tip. Up to 1
meter long. Basally broadened, but upper portions divided deeply into many
ribbon like segments; margins smooth, often undulate. Holdfast is small
without dark rhizoids. Bright grass green to dark green, gold at
margins when reproductive. May be colorless when stressed.
U. rigida is similar but has tough dark rhizoids,
smaller, more rectangular cells, and separates easily into two sheets.
Thalli with expanded blades two cells thick; parenchymatous:
cell division may occur anywhere on the thallus but always in a plane
perpendicular to the thallus surface. Cells usually square, 8-20 µm wide,
14-40 µm long, irregularly arranged and quadrate to slightly elongate
anticlinally. Cell walls fibrillar and made up of cellulose.
Ulva fasciata is commonly found on intertidal rocks, in
tidepools, and on reef flats. Often abundant in areas of fresh water runoff
high in nutrients such as near the mouth of streams and run-off pipes.
Hawai‘i: All Hawaiian Islands.
Mechanism of Introduction:
Indigenous to Hawai‘i.
Eastern Atlantic, Caribbean, Indian and Pacific Oceans.
Ulva fasciata, or "sea lettuce", is commonly found in
areas where nutrients are high, wave forces low and herbivory reduced. It is
tolerant of stressful conditions, and its presence often indicates
freshwater input or pollution.
Ulva species are early-successional algae, quickly
taking over new substrate on boulders that are cleared by storm disturbance.
U. fasciata and Enteromorpha flexuosa are generally the first
macroalgae to colonize newly opened substrate in intertidal areas with high
nutrients. Their opportunistic success can be attributed to their simple
morphologies and fecundity. In Ulva species, between 20 to 60 percent
of their overall biomass can be allocated monthly to reproduction. The
alga’s reproductive success is partly due to the reproductive cells’
photosynthetic ability. The zoospores’ and gametes’ ability to
photosynthesize subsidizes their motility and rapid growth once attached to
the substrate. Reproductive cells of U. fasciata have similar
photosynthetic rates to adult vegetative cells, with higher respiration
Ecologically successful green alga like U. fasciata
are potentially invasive. Coastal waters near harbors, industrial complexes
and residential areas with nutrient- rich and/or fresh water input often
have blooms of Ulva species that coat ships’ hulls, cover pilings and
shorelines, and restrict outflow pipes. U. fasciata is classified as
a marine fouling organism, and studies in control and eradication are
In Hawai‘i, U. fasciata, or Limu palahalala is
a popular seaweed for consumption. Preparation methods include chopped in
salads with other limu varieties, boiled in soups, or as a relish.
Abbott, I.A., 1996. Limu: An ethnobotanical study of some
Hawaiian seaweeds. National Tropical Botanical Garden, Lawai, Kaua‘i,
Hawai‘i. 4th edition.
Beach, K.S., C.M. Smith, T. Michael, and H.W. Shin, 1995.
Photosynthesis in reproductive unicells of Ulva fasciata and
Enteromorpha flexuosa: implications for ecological success. Mar. Ecol.
Prog. Series, 125: 229-237.
Littler, D.S. and Mark M., 2000. Caribbean Reef Plants.
OffShore Graphics, Washington, D.C.
Magruder, W.H. and J.W. 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.
Introduction to Marine Botany, Stanford University.
Hawaiian Reef Algae.