Ascidian Biology

Despite limited natural dispersal, some species of ascidians can be transported vast distances via oceanic petroleum platforms, ship hulls and ballast water and therefore may be good indicators of bioinvasion. Usually non indigenous species (NIS) are abundant in harbors. This is caused in part because of the higher propagule delivery rate in these areas. An alternative explanation of why invasion enhanced in harbor and marinas is that environmental degradation commonly found in these habitats favors the establishment if NIS. Most surveys fir introduced species were not comprehensive and targeted mainly ports and marinas. Angra dos Reis in an excellent system that provides an opportunity to compare the potential distribution of introduced and native species of Ascidiacea between port and natural environments. Here, we compared the colonization of experimental subtidal plates placed in harbors and marinas with greater in port environments (25 versus 8). Six taxa were common to both environments while 19 taxa were exclusively native. Only three species were found exclusively in the natural in the natural sites and all were cryptogenic. The presence of introduced species only in the port areas of Angra dos Reis reinforces the need for continued, periodic monitoring in the region for early detection of new, potentially invasive, species as well as for better understanding of abnormal population growth of the already know species. Management to reduce the transfer of exotics to natural habitats must be implemented.

Ascidian spicules are reported for the first time from the upper Eocene (Paleogene) biosiliceous marls and mudstones of the Blanche Point Formation in the St. Vincent Basin, southeastern Australia. The spicules that belong to the family Polycitoridae are identified as a Recent species Cystodytes cf. dellechiajei, and Cystodytes sp. and spicules of the family Didemnidae are indentified as representing genera Lissoclinum, Didemnum, and Polysyncraton. Five other different morphological spicule types which can be classified only at the family level also
belong to the Didemnidae. This study demonstrates that ascidians had a very wide distribution by the late Eocene
and that ascidian fauna was already of a modern character.

Ascidian tadpole larvae settle on hard surfaces and undergo metamorphosis into sessile adults. To test whether tadpoles evaluate the texture of surfaces they settle upon, we presented tadpoles with surfaces that were divided into halves; each half had one of four different textures: smooth, fine sandpaper, coarse sandpaper, and sandblasted. In all cases, twice as many individuals settled on one side over the other, but this was not consistently the smooth side or the rough side. More tadpoles settled on a smooth surface than one ...

Ascidian spicules are reported for the first time from the upper Eocene (Paleogene) biosiliceous marls and mudstones of the Blanche Point Formation in the St. Vincent Basin, southeastern Australia. The spicules that belong to the family Polycitoridae are identified as a Recent speciesCystodytescf.dellechiajei, andCystodytessp. and spicules of the family Didemnidae are indentified as representing generaLissoclinum, Didemnum, andPolysyncraton.Five other different morphological spicule types which can be classified only at the family level also belong to the Didemnidae. This study demonstrates that ascidians had a very wide distribution by the late Eocene and that ascidian fauna was already of a modern character.