Great fields of sand

Looking south towards the Olympics from the San Juan Channel

Man, its been too long....almost three months since my last blog post.  Too much going on.  I still have a fourth edition of the sea level rise posts I started back in August in mind, but I'm going to back-burner that in favor of a shorter and easier post.  I'm back at Friday Harbor Labs, once more teaching the Marine Sedimentary Processes research apprenticeship.

Last week our class had one day of time on the R/V Centennial that we have traditionally used to make a long one-day cruise to Elwha.  But we decided instead to stay local, partner up with other classes at Friday Harbor, and make a trip out to the sand field in the San Juan channel.  We had two over-all goals.  First, many of the students had projects focused on investigating the use of this sand field by Pacific Sand Lance...and much of our time was spent pulling sand samples from the field, and sorting the PSL out of those sand grabs.  Next, we wanted to sample around the sand field to get a sense for the grain sizes immediately adjacent to it.  How distinct was the boundary of the field?

The name of the game is plucking as much sand as possible off the bottom using the biggest grab available

Sorting through a sample of sand

Pacific Sand Lance, and coarse sand

So first off, the PSL utilization of this sand field is unbelievable.  We took a total of 10 grabs of sand from the field, with the grab bringing maybe 5 gallons of sand to the surface at a go.  The average number of fish in each of those grabs was probably about 15...and the max?  An incredible 50 fish in one grab.

Pacific San Lance emerging out of a sample of sand

Interestingly enough, while the abundance of PSL in the sand field is pretty high, the sand field has pretty low diversity of invertebrates.  Just a few were pulled up.

2 of these shellfish came up, from 10 grabs.  Juvenile Clinocardium?

One sample included this beautiful worm.  Flatworm I think?

And out of 10 grabs, one amphipod.  

Our samples away from the sand field were, perhaps unsurprisingly, pretty coarse.  The currents in the channel are intense, which presumably makes this area unsuitable for the deposition of most fine sediment.  But it begs the question...how is the sand field itself maintained?  How does it persist?  These samples outside of the sand field were also notable for their relatively high invertebrate diversity.

A characteristically coarse grab sample from the San Juan Channel, outside of the sand field

We pulled up a good number of these beautiful brachiopods...its been a good long while since I've seen one of these.  I think maybe Hemithiris?  There is a lot of interest in these, not least because they are so prevalent in the fossil record.  

High chiton abundance, but we dredged up only tiny specimens like this one

A couple of these came up...juvenile Cancer oregonensis I think?

A great wealth of Podedesmus at these sites...shown here with a nice encrusting bryozoan

The only scallop we pulled up, and I'm not totally sure, but maybe a rock scallop (Hinnites) just prior to cementing itself in place (?), with maybe a boring sponge (Cliona??)