Fouling ascidians (Chordata: Ascidiacea) of the Galápagos: Santa Cruz and Baltra Islands.
The Galápagos Marine Bioinvasions Expedition (April 24-May 4, 2016) carried out a survey of the biofouling communities on a number of floating docks and pilings, as well as numerous previously deployed settlement panels both uncaged and caged, on two of the Galápagos Islands: Santa Cruz and neighboring Baltra. The suspended panels had been submerged for either 3 months or 14 months. Studies were concentrated at two sites on Santa Cruz Island, which is the location of the main town Puerto Ayora and has the most vessel traffic. The small adjacent Baltra Island contains the airport and there is frequent boat traffic there, as well as a Navy base with a floating dock. Ascidians were the dominant foulers on most panels, especially the caged ones, with a dramatic difference in coverage between caged and uncaged which is presumed to result from differential fish predation pressure since the panels were all suspended with none touching the benthos. There were schools of small fish around all the docks observed to be constantly nipping at the dock surfaces. Eighteen species of ascidians were collected, comprising 12 new records. Of the 14 identified to species level, 11 are considered introduced and 3 cryptogenic. The most common species included Didemnum perlucidum Monniot, 1983, Diplosoma listerianum (Milne Edwards, 1841), Polyclinum constellatum Savigny, 1816, Ascidia sydneiensis Stimpson, 1855, Ascidia ceratodes (Huntsman, 1912), an Ascidia sp. with long tunic spines, Polyandrocarpa zorritensis (Van Name, 1931), Styela canopus (Savigny, 1816), and Pyura haustor (Stimpson, 1864). Other foulers included small colonies of Botrylloides niger Herdman, 1886, a few small colonies of Symplegma brakenhielmi (Michaelsen, 1904), a dark Didemnum sp. and another unidentified didemnid, a pink Symplegma rubra Monniot, 1972, three very tiny Molgula sp. and a single specimen of Microcosmus exasperatus Heller, 1878. Several colonies of Botrylloides giganteus (Pérès, 1949) were retrieved from plates on the Baltra Navy dock. Two large specimens (∼ 6 cm) of Halocynthia dumosa (Stimpson, 1855) (usually incorrectly referred to as H. hispida (Herdman, 1881)) were collected from the Baltra dock and one by SCUBA at 12.2 m off of Bartolome Island. A complete species list is presented, with a comparison with previous published and unpublished records.