Northwest Fisheries Science Center

Newportal Blog

A gateway to oceanographic adventures from the Newport Line and beyond

Blog on ocean conditions along the Newport Line and the northern CA Current.

Beam Trawl Invertebrates

By Marilyn Leary
February 24, 2017


A little bit of everything seems to live on the ocean floor. The beam trawls give us an opportunity to see and touch some of the life that thrives in the sand and mud and gravel of the ocean floor. Identifying and describing every animal that we have pulled up would be a near-impossible task, so I have selected only a few interesting animals to meet and look at more closely.

The Parasitic Isopod

If you bottomfish, you may have seen this isopod. It almost looks like it should come from a horror movie, a mysterious creature born of the subconscious. They are usually pale and whitish, with dull eyes and sharp hooks at the ends of their legs. They are often found latched inside the gill covers of rockfish and ling cod; this individual was found outside, crawling on the eyed side of a flatfish. If you pick it up, be careful—if you hold it long enough for it to get comfortable with you, it will sink its claws into your skin.

Parsitic isopod captured in the beam trawl.

 

Mole Crab (Emerita analoga) Zoea

Occasionally on sandy beaches, one can find what looks like thousands of mole crabs washed up on the beach, drawing a high-water mark in the sand. These are the molts of the mole crab, the exoskeleton periodically shed to allow the animal to grow. The adults live burrowed in sandy beaches, using their antennae to collect food when water flows over them. But, they do not start life in the sand. As larvae, they drift in the ocean with the other zooplankton, eventually recruiting to the sandy shore when they metamorphose into adults. This larva is a zoea, a transparent, three-pronged creature that found its way into our net.

A mole crab (Emerita analoga) Zoea stage 5 from a net tow.

Nudibranchs

Nudibranchs (“naked gill”) are shell-less gastropods. The Pink Tritonia and Striped nudibranchs were collected along with their favorite food—sea whips and sea pens. While these individuals tended to be small, one Pink Tritonia was large and weighty—it fit snugly in the palm of my hand. I think Nudibranchs are some of the most colorful and alien-looking animals in the ocean, and many species can be found easily in the intertidal of the Oregon coast.

A Pink Tritonia nudibranch from the beam trawl.
A Striped nudibranch from the beam trawl.

 

 

 

 

 

 

 

 

A burrowing anemone from the beam trawl.

Burrowing anemone

For myself, the greatest joy of marine science is finding the thing that you have never seen before—that is so alien to you, you cannot even confidently decide how it is sorted into the tree of life. Two of these animals showed up in the trawls. The first was represented by many individuals; the color can best be described as “pink lemonade with freckles”. When first isolated from the conglomerate mass of organisms , these animals would curl into themselves; their shape was fairly non-distinct, and they looked like an odd-colored fat worm. When left alone and observed, a tiny rosette would flesh out of one end, and the animal would move it around like a head. Later, I learned it was a burrowing anemone.

I only saw one individual of the second animal. It was found at the bottom of a bucket used for sorting; when I tried to pull it out, I found that it had suctioned one end of its worm-like body to the bottom of the bucket. I had to carefully pry it loose, and even then I cannot confidently say that I did not damage it. It was bumpy and charcoal gray, one end of its body thick and the other tapered. It looks most like a peanut worm, an unsegmented marine worm that lives in burrows and uses its frilly mouth parts to collect food.

An unknown organism from the beam trawl. Perhaps it is a sea cucumber?

Tagged: NCC

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