Why no barnacles at Sekiu?

[gcbryan]

For anyone who knows...why are there no barnacles on the rocks at Sekiu? It would seem to be the type of environment where you would see them. Perhaps there's something in the rock that is not compatible with barnacles?

[Greg Jensen]

This is one of those classic ecology questions, and without studying the area in question, one can't say as there are a lot of different possibilities. There ARE gooseneck barnacles on the rock pinnacles just west of the jetty.
I did a lot of work on porcelain crabs out in that area many years ago. Those are very high energy beaches, getting swells from the mouth of the strait, and things get moved around a lot. I initially wondered why some boulder/cobble beaches there seemed perfect for my crabs but had none, while a seemingly identical beach a mile away was crawling with them. It turned out that the rocks on the 'no crab' beaches would get completely buried by sand during parts of the year, eliminating all the under-rock habitat (and would smother any barnacles as well). On beaches that don't get the sand treatment, small rocks can grind around in the surf and crush any attached organisms. Often in these areas you can still find barncles, but they're a lot smaller than you're used to seeing, tucked in crevices and on the lee side of big rocks.
Some areas may have lots of predators (snails, seastars etc.) that can feed on other things as well but make short work of any barnacles that settle out.
Some areas may just not be 'downstream' of a source population for larval barnacles.
In some places the 'rocks' are more like hard clay or other soft material and sessile organisms like barnacles slough off, though this is not the case for a lot of the rocks in that area.

[gcbryan]

Thanks for the info Greg.

I guess I've never noticed the Gooseneck Barnacles at Sekiu. I've seen tons of them at Shi-Shi on the outer coast.

[nwscubamom]

I've never noticed them either, and would LOVE to see them - it would be a first for me.

Interesting stuff, Greg - thanks for the explanation.

All I know is I hate walking UP that beach after a dive One step forward, sink down two backwards...but it's one of my favorite dives. Just get it on high tide so there's a little bit of depth!

- Janna

[Greg Jensen]

The goosenecks I've seen there were on the rocks/pinnacles that are highest on the shore, mostly on the shoreward side and down low. You'd never see them diving unless it was an exceptionally high tide and calm enough that you weren't getting bashed around. They are passive filter feeders, extending their cirri into the water as it runs back off the rocks (rather than actively sweeping, like acorn barnacles) so in general are not in areas where divers would encounter them- more for the tidepooling crowd.
They do occur deeper, in a few places where currents are particularly strong.

[gcbryan]

I've never noticed them either, and would LOVE to see them - it would be a first for me.

Interesting stuff, Greg - thanks for the explanation.

All I know is I hate walking UP that beach after a dive One step forward, sink down two backwards...but it's one of my favorite dives. Just get it on high tide so there's a little bit of depth!

- Janna

It's funny you should mention the sinking step problem there. I stumpled down to my knee's twice on my two dives there this time coming out of the water. There was a particularly large step that had to be made in only 2 feet of water and every time I tried the surge came in and "uncompacted" the sand resulting in the sinking that you're referring to.

Next time you're in the Neah Bay area and beyound go to the rocky structures on the beaches of the outer coast and they are covered with Gooseneck Barnacles. As Greg mentions you don't see them diving but rather while strolling along the beach.

[nwscubamom]

Yeah, I've found myself down on my knees more than once at that site trying to exit the water. Not fun!!

I will hopefully be going out there in August for the OCNMS survey - and I will make a point of looking for the Gooseneck barnacles when I'm there!

- Janna