Distribution of E. turbinata
can be patchy and abundance may vary with season. In the IRL, large
clusters can carpet the undersides of floating docks, and the submerged
lengths of red mangrove prop roots. In the Mediterranean, densities
can reach 175 zooids per square meter (Carballo 2000).
Adult E. turbinata
are simultaneous hermaphrodites, but can reproduce sexually or asexually.
Sexual reproduction occurs most frequently in the spring and summer
when water temperatures are warm. The mangrove tunicate is ovoviviparous,
and larvae are brooded in the peribranchial cavity for approximately
7 to 9 days after fertilization before being released into the water
column (Carballo et al. 2000).
Ascidians produce tadpole
larvae with a visible notochord. Hence, they are placed in the phylum
Chordata, along with mammals, birds and fishes. Tadpole larvae of
E. turbinata are conspicuous, bright orange to yellow and
approximately 4.5 mm in length (Young & Bingham 1987). They
are lecithitrophic (Carballo 2000), obtaining nutrients from yolk
reserves instead of feeding on plankton (planktotrophic). Because
of this life-history trait, the planktonic stage of E. turbinata
is short, and larvae must find a suitable habitat to settle before
food reserves are exhausted. Locomotion throughout the water column
facilitates this search. Larvae swim in a similar fashion to fishes,
bending at the junction between the trunk and the tail to undulate
through the water (McHenry 2005). After finding a suitable habitat,
larvae attach themselves to the substratum via a series of adhesive-producing
structures at the front of the trunk called papillae. When attachment
is complete, larvae metamorphose into juvenile tunicates.
IV. PHYSICAL TOLERANCES
The mangrove tunicate
is generally found in warm tropical and sub-tropical waters, where
it commonly encounters average temperatures of 25 to 32 °C (Vázquez
& Young 1996). It occurs in the Mediterranean in the summer
months, but dies back at temperatures below 17 °C, when only
the stolons remain. From these remnants, colonies usually recover
when waters begin to warm (Carballo 2000).
As a common inhabitant
of estuarine ecosystems, E. turbinata can withstand relatively
large salinity fluctuations. However, the presence of haloclines
causing stratification in the water column has been shown to reduce
the ability of larvae to migrate vertically (Vázquez &
Young 1996). Vertical migrations are a critical dispersal mechanism
for many zooplankton. When prevented, genetic mixing between populations
and/or expansion of newly recruited tunicates to other habitats
may be inhibited.
V. COMMUNITY ECOLOGY
is a sessile, benthic filter-feeder. The incurrent siphon takes
water into a sieve-like pharyngeal basket that filters out food
of the appropriate size range before water is pumped from the animal
via the excurrent siphon.
are present in both larval and adult mangrove tunicates. In the
case of adults, high concentrations of vanadium are likely to reduce
palatability of the tissues (Stoecker 1980). This defense, coupled
with yellow or orange warning coloration at nearly all life stages,
eases predatory pressure on the species (Young & Bingham 1987)
with the exception of the tiger flatworm, Maritigrella
crozieri. By extruding its pharynx into individual zooids,
the flatworm feeds exclusively on E. turbinata (Ruppert
& Barnes 1994), with one individual consuming an average of
19 zooids in 24 hours (Newman et al. 2000).
As a component of coastal
and estuarine fouling communities, E. turbinata is found
alongside several species of invertebrates, namely sponges and other
ascidians. In addition, at least three species of amphipods, dwelling
inside the tunic, are found in association with E. turbinata.
The amphipod, Anamixis hanseni appears to be host-specific,
occurring only in this species (Theil 1999), and Leucothoides
pottsi and Leucothoe spinicarpa have been found in
individual tunics as well (Thomas 1979). Although details of such
symbiotic relationships are unclear, it appears that the amphipods
gain protection from predators and feed on particulates entering
the tunic through the incurrent siphon (Thomas 1979).
VI. SPECIAL STATUS
The mangrove tunicate
produces a compound called ecteinascidin-743 (ET-743, also known
as trabectedin), which has gained attention for its anti-cancer
properties (eg. Carballo et al. 2000). Although clinical trials
support its effectiveness in reducing various solid-type tumors,
the size and abundance of this ascidian make large-scale production
of ET-743 difficult and costly. Approximately one metric ton of
E. turbinata must be collected and extracted to produce
one gram of the cancer-fighting agent (Proksch et al. 2003).
In recent years, the medical industry has been producing trabectedin
through semisynthesis (Cuevas & Francesch 2009), currently eliminating
the need for the original natural product. Trabectedin, marketed
under the brand name Yondelis, is the first marine anticancer agent
approved in the European Union for use in patients with soft tissue
sarcoma (STS) (Cuevas & Francesch 2009). In the United States,
the drug is undergoing clinical trials where it has been shown to
reduce or stabilize the growth of STSs, including leiomyosarcomas
and liposarcomas (Amant et al. 2009, Schöffski et
Amant, F, Coosemans, A, Renard, V,
Everaert, E & I Vergote. 2009. Clinical outcome of ET-743 (Trabectedin;
Yondelis) in high-grade uterine sarcomas: report on five patients
and a review of the literature. Int. J. Gynecol. Cancer.
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Report by: LH Sweat,
Smithsonian Marine Station at Fort Pierce
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