Thursday, December 22, 2016

tsujii abounds

For the first time ever, I was able to collect all at once hundreds of Vargula tsujii, the California Sea Firefly. Here is the story.

I've collected V. tsujii at Catalina Island and in San Pedro Los Angeles in the past. But never before have I trapped more that a few 10's of them at a time.

But on Sunday December 18, we got nearly 1000 in our traps at San Pedro. Cabrillo Beach is just in front of the public aquarium by the same name. There is a boat launch there. In past years, I collected tsujii there by trapping. On the pier next to the boat launch, I would get a few animals in the traps. There used to be a jetty extending out perpindicular to the beach. I'd walk out to the end of that and was able to get more animals in each trap, perhaps up to 50 at a time. But for several years, I was not getting any at all in traps, and folks from our lab also tried, to no avail. The disappearance seemed to correspond to with beach dredging that I saw going on several years ago. This might be the project listed in 2013 here. A colleague told me she'd gotten some animals recently, so I decided to try again, when high seas foiled a trip to Catalina to get tsujii.

I set 5 PVC traps in just a couple feet of water, maybe 20 feet out on the pier next to the boat launch. I always try to drop the traps in dark places, because I think many ostracods are negatively phototactic. I set the traps at about 5:30 pm and brought them in around 10:00 pm. When I looked at the traps later in the hotel, I couldn't believe my eyes. The mesh funnels were caked with 'cods. I had never seen this many tsujii. I've seen hilgendorfii in this abundance and Photeros annecohenae, but never tsujii.

The habitat does look cleaner to me now, compared to before the dredging. The Port of LA was required by law to clean up the area, according to this link. I can't be certain, but it sure seems like this has improved the tsujii in the area. I used to see weedy algae and thousands of caprellid amphipods in that algae. Now there is sea grass and kelp, and the water looks much clearer. The salt marsh is also restored (news story link above) and it might allow more fish to survive, food for the ostracods. Of course, we also had warmer seas last year from El Nino, so that might have contributed, too.

Back at UCSB, I sorted the tsujii from the remaining bait, sand, and algae. I counted roughly 800 animals alive, plus some that died during transit. All in all, perhaps pushing 1000.

After a couple days in the flowing sea water at UCSB, in various containers (some of which may have leaked), we sorted and counted all the stages. These are the results:

Adult    males: 49
Adult females: 228
Brooding females: 3
Juveniles: 348

for a total of 628. This is less than the 800 of my rough count, some were lost out of one container, and I may have counted wrong. But as a BARE minimum, we got over 600 healthy animals to UCSB from San Pedro!

We also sorted a sample of the juveniles to get an idea of the demographics, with these results:

A-1: 121
A-2: 153
A-3: 75
A-4: 12
A-5: 1

I am keeping these is sea water at UCSB. Since they are local (small populations live here, we've trapped a few of them), we can use flowing sea water, which makes care easier. I'm keeping them in small mesh boxes made for breeding fish. Water flows through them to keep the water fresh, but the ostracods cannot swim through the mesh.

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