Enteromorpha flexuosa is a filamentous light green alga with
worldwide distribution in shallow brackish or marine habitats (Mairh, Pandey and
Tewari 1986, Littler and Littler 1989). The term 'enteromorpha' literally means
'intestine shaped' and is used to describe the hollow, tube-like filaments of
E. flexuosa grows to 20 cm but generally tends to be
smaller. It typically grows in clusters on mangrove roots, rocks, wood or as an
epiphyte on other plants. It is found at depths ranging from the high intertidal
zone to approximately 5 m. below the surface. Species of this weedy genus are often
the first to colonize open substrata (Beach et al. 1995).
The ecological success of E. flexuosa
and other pioneering species is in part attributed to the readily available pool
of motile unicells that are able to rapidly colonize new areas. The chance for
successful settlement of these cells is greatly enhanced because gametes and
zoospores of this species remain viable for 10 or more days due to their ability
to photosynthesize, often achieving photosynthetic rates approaching those of
the adult thalli (Beach et al. 1989).
HABITAT AND DISTRIBUTION
E. flexuosa is an excellent pioneer species and is highly cosmopolitan in shallow marine or brackish habitats.
E. flexuosa is found lagoon-wide. It is common in inlet areas
and around spoil islands and grows in tufts on substrata such as mangrove roots,
wood, rocks, etc., primarily at low tide level. It is often epiphytic on other
algae and seagrasses. E. flexuosa is highly abundant during the summer
months in Florida.
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
Mairh, Pandey and Tewari (1986) observed maximum growth and increase in the
biomass of E. flexuosa when it was growing at or near the surface of the
water. Significantly lower biomass was observed when E. flexuosa was
grown at a depth of 40 cm. If left undisturbed and ungrazed by fish and
invertebrates, E. flexuosa can grow to approximately 20 cm.
Highly abundant, especially throughout the summer months in
Optimum reproduction temperature is under 30°C (Mairh, Pandey and Tewari 1986) in waters with a pH of approximately 8.2.
E. flexuosa is highly fecund (Beach et al. 1989), with
propagule release via both mitotic
spores and meiotic gametes occurring on a daily basis in the lower latitudes.
Release of reproductive cells (spores and gametes) into the intertidal zone is
driven by tidal and lunar rhythms (Smith 1947, Christie and Evans 1962, Beach et
al. 1995). Spores and gametes of this species are photosynthetically competent
upon release into the water column, with unicells remaining motile for up to 11
days. Both gametes and zoospores have higher cellular respiration rates when
compared to parental tissues, presumably due to their motility. Additionally,
the photosynthetic rate for gametes and zoospores of E. flexuosa and
several other pioneering species is substantially higher than photosynthetic
rates observed in the reproductive cells of later successional genera such as
the kelps (Phaeophyta). Thus, motility coupled with photosynthetic ability
increase the ecological success in settlement and recruitment of this species.
Growth of this species in outdoor ponds in India
(Mairh, Pandey and Tewari
1986) showed that E. flexuosa was able to sustain growth in water
temperatures as high as 30°C. Favorable growth was maintained at temperatures
ranging from 15.5 - 30°C.
At 33°C, bleaching of a few branches begins
to occur, and above this temperature, adverse effects on growth increase as
more and more branches become bleached.
is an excellent pioneer species, able to colonize newly available substrata
year-round (Emerson and Zedler 1978). Yet, it is not a good competitor with
other successional species. Emerson and Zedler (1978), in an experimental study
of recolonization of intertidal algae following disturbance, showed that E.
flexuosa tends to be present in low density (as measured in % cover)
throughout the year in undisturbed zones. Following disturbance to an area, the
density of this species increases dramatically within 2-3 weeks. However, as
other algae become established, the percent cover for this species declines. This
observation suggests that E. flexuosa may be unable to maintain dominance
in the presence of later successional species such as Ulva rigida, Lithrothrix
aspergillum, and other perennial algae (Emerson and Zedler 1978).
E. flexuosa is found to depths of 5 meters in shallow brackish
areas, or marine habitats in close proximity to freshwater seeps (Littler and
Litter 1989). It is also likely to be found in areas influenced by municipal or
industrial discharge. Rosas and Ruiz (1989) showed that Enteromorpha
species, as well as some Ulva species, develop abundantly in zones
directly affected by pollution, even as the abundance of other genera decreases.
In areas affected by pollutive discharge, E. flexuosa becomes a highly
successful fouling organism.
E. flexuosa is often found in association with pioneering
species such as Ulva sp. and other fouling organisms. These are often the
first plants to colonize freshly disturbed areas, or open substrata.
E. flexuosa has some commercial importance due to its antibacterial
activity against Mycobacterium tuberculosis (Mairh, Pandey and Tewari
1986). This algal species has also been investigated for its potential value as
a bioindicator of trace metal pollution in coastal waters (Sivalingam 1978).
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