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Nonindigenous Ascidians in Tropical Waters

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Title: Nonindigenous Ascidians in Tropical Waters
Authors: Lambert, Gretchen
Issue Date: Jul 2002
Publisher: University of Hawai'i Press
Citation: Lambert G. 2002. Nonindigenous ascidians in tropical waters. Pac Sci 56(3): 291-298.
Abstract: Ascidians (invertebrate chordates) are abundant in many ports around
the world. Most of them are nonindigenous species that tolerate wide fluctuations
in temperature, salinity, and even pollution. These sessile suspension
feeders have a rapid growth rate, usually a short life span of a few months, reach
sexual maturity when only a few weeks old, and produce large numbers of shortlived
nonfeeding planktonic larvae. They thrive on marina floats, pilings, buoys,
and boat bottoms in protected harbors where there is reduced wave action and
enhanced nutrients from anthropogenic activities. Nonindigenous ascidians
frequently overgrow oysters and mussels, which are often cultivated in or near
busy harbors. Adult ascidians on ship or barge hulls may survive transport over
thousands of kilometers to harbors with conditions similar to those they left;
occasionally live larvae have also been recovered from ships' ballast water. U.S.
Navy dry dock movements between major Pacific ports have transported large
masses of fouling nonindigenous taxa, including ascidians. Transfer between
culture sites of oysters, mussels, and associated lines and nets may provide an
additional mode of transport. Once nonindigenous ascidians become established,
they provide large local sources of larvae for further possible invasions
into additional harbors and nearby natural marine communities. Invasive species
include both solitary and colonial forms, with a preponderance of large solitary
species that thrive in highly disturbed habitats. In Guam, for example, most
nonindigenous ascidians are confined to harbor structures and have not as yet
significantly colonized natural reefs. In contrast, healthy natural benthic regions
both inside and outside the harbors of Guam are usually stable coral reef communities
containing a high diversity, but very low biomass, of native colonial
ascidian species. However, in several areas of the Caribbean a native colonial
didemnid has recently begun overgrowing coral reefs. In the Gulf of Mexico a
nonindigenous didemnid now covers many offshore oil rigs and may become a
threat to neighboring natural reefs. Additional data on nonindigenous ascidians
in Australia, Palau, Hawai'i, and the Mediterranean are included. Although serious
invasion of coral reefs has not yet been reported, more studies and regular
monitoring are needed.
ISSN: 0030-8870
Appears in Collections:Pacific Science Volume 56, Number 3, 2002

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