Petersburg Pilot -


Local fisherman finds unidentified yellow growth in North Harbor


Submitted Photo

Didemnum vexillum, a.k.a. D. vex

Local fisherman, Ed Wood, spied a bright yellow growth on one of the pilings at the minus tide of the North Harbor Thursday morning.

“I went to the Alaska Department of Fish and Game and brought Becky Knight to look at the growth,” Wood said. “While she was taking photos, I crawled down and got a sample of it with my knife.”

One of the bigger fears of fishermen in these waters is the growth called Didemnum vexillum, also called D. vex, which was found in Sitka a few years ago. D. vex, also known as rock vomit, is an invasive species that smothers the ocean bed and disallows area fish from feeding. D vex is commonly known as the Whangamata sea squirt, but also referred to as a colonial, compound ascidian and/or tunicate. It is a filter feeding animal, sponge-like in appearance, yellow or orange in color and its surface has darkish leaf-like veins with pores. Colonies often droop when living under surfaces.

The origin of this species is unknown at this time. Natural dispersal of this species is created sexually by releasing tailed larvae which can be dispersed via water currents. Alternatively, colonies can reproduce asexually by budding, hence fragments can break off and grow into new colonies.

Artificial dispersal happens by way of infected hulls of vessels, aquaculture equipment and fragments in ballast water.

This invasive species is a threat to the marine farming industry because of the species smothering capabilities and preference and great survival rate on artificial structures such as wharf pylons, mooring lines and vessel hulls.

Colonies of D. vex exhibit a wide variety of morphological variants. Where velocity is low, they form long, ropey or beard-like colonies that commonly hang from hard surfaces such as docks, lines and ship hulls. Where current velocity is high, they form low, undulating mats with short superficial appendages that encrust and drape rocky sea beds.

According to a June article written in Pacific Fisherman Magazine, the Alaska legislature passed a bill ordering the Department of Fish and Game to put together a prototype emergency response plan for quick, geographically localized action when a new aquatic invasive species is discovered anywhere in the state.

This bill, HB 365, was introduced out of frustration with the department’s plodding response to the potentially catastrophic infestation of Sitka’s Whiting Harbor.

The potential danger of this invasive species to the marine life in Petersburg’s own harbors should keep fishermen and harbor officials on their toes and cause them to be on the lookout.

The species found by Wood Thursday morning has been sent to officials with the National Marine Fisheries Service. NMFS representative has stated, “Upon first glance, this looks like a sponge and not the D. vex, but will run tests to see.”

There are procedures for collecting and preserving samples of D. vex for identification. If possible, photograph D. vex in its natural environment, do not attempt to remove D. vex if smothering other organisms. Place each D. vex sample inside separate screw top containers with enough sea water to just cover the specimens. Sprinkle menthol crystals on top of the sample and place the lid on tightly. Gently tip the sample upside down to ensure mixing. Menthol crystals help relax the D. vex to assist with the identification procedure. In place of menthol crystals, place specimens inside a plastic bag and freeze for 24 hours and label.

The growth found by Wood, may not be the invasive D. vex that could be so damaging to any fishing community, but awareness is still needed in this situation.


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