Monday, November 15, 2010

USFS Invasive Tunicate Survey: The Triangle-Winchester Bay, OR 9-28-2010 & 9-29-2010

Underwater surveys for invasive tunicates of the Triangle at Winchester Bay were undertaken by a USFS team of scientific divers on Sept. 28 and 29, 2010. They searched specifically for the non-native colonial tunicate Didemnum vexillum. D. vex has the potential to establish large colonies on firm natural or artificial surfaces. It can overgrow invertebrate life and make feeding difficult for species that depend on prey that has been smothered.

Relatively dark channels are evident on its surface and the common atrial holes used by the tunicates’ excurrent siphons form a random pattern. The organism can reproduce sexually as well as from displaced fragments.

The Triangle is enclosed by rock jetties and covers approximately 90 acres adjacent to Winchester Bay. It is connected to the mouth of the Umpqua River by four large culverts through the jetty on the north side of the Triangle. A prominent feature is an aquaculture operation growing oysters on stringers suspended from 50 horizontal lines that are held in place by floats attached to 100 mooring lines.

Led by USFS Aquatic Ecologist Bruce Hansen of the Land & Watershed Management Program at the Pacific Northwest Research Station in Corvallis, Bio Science Technicians John Estabrook and Jim and Chris Pendergrass were assisted by scientific diver Ian Chun who provided and operated the boat and acted as tender.

Samples of likely D. vex specimens were taken from 16 randomly selected sites encompassing 750’ of the 900’ length of the rocks of the jetty on the Triangle’s north side. Samples were also taken from 16 randomly selected mooring lines and 4 additional mooring lines.

All but 1 of the rock sites yielded samples that appeared to be D. vex. That lone site was the shallowest (at 16’) and furthest away from the shore. All but 2 of the mooring line sites yielded samples that appeared to be D. vex and those 2 sites were in the furthest southeast corner of the oyster operation and had the shallowest maximum depths at 7’ deep.

D. vex is known to form low mats in areas of high current and it hangs in long, ropy lobes where current velocity is low. Both manifestations seemed to occur on the jetty rocks. The largest colony noted covered many square yards and extended deep into crevices of the jetty. Only the undulating, beard-like form appeared to be evident on the mooring lines.

The organism seemed to be present at depths from 10’-23’ and most plentiful between 15’-20’. Coloration of D. vex is variable and the samples collected were yellowish to beige. Further analysis of the samples will be required for positive identification.

Maximum depths of the survey sites ranged from 16’ to 24’ along the rocks and 7 to 30’ on the mooring lines. Water temperature was 55-57 degrees and visibility was 10’ near the surface and 1’-2’ at the silty bottom.

Colonies of the non-native invasive colonial tunicates Botrylloides violaceus and Botryllus schlosseri were also present on the rocks and mooring lines. The non-native invasive colonial tunicate Molgula manhattensis was noted on one mooring line.
Special thanks to Jerry Smith and his crew at the Umpqua Lighthouse State Park for help with boat launch and gear transfer.

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