Monday, June 24, 2013

Reaching the boundary

As the planet experience's this year's supermoon, the tides swing in the greatest direction.

Saturday's tide was a low 0.4 metres.  For the tidal flats at Boundary Bay, this meant we could walk a kilometre before hitting the water's edge, or a mile out to reach the cairn marking the Canada / US International Boundary Survey Monument.



On the way out, we saw beds dense with live sand dollars.
 
The tube feet and spines can clearly be seen here
 In the eel grass beds, I saw this fish with bulging eyes.  I have no idea what it could be.

I used to think of anemones as a rarity in lower mainland beaches.  Today, I saw more species of anemone in a single day than ever before on a beach.
Anemone species 1, budding.  diameter about 1cm

Anemone species 2 - a burrowing anemone. Diameter 4 cm
Crabs were abundant.  Crabbers were out in force with their hip waders and tongs.

On the way out to the cairn, I saw several metal posts positioned horizontally.  It is an oasis of sorts for the creatures that need solid footing.

Anemone species 3 and 4 on some metal structures at the cairn. Diameter about 15 cm
Crabs have amnesty when it comes to international boundaries. This one was found on the cairn, which marks the US/Canada boundary
 I used to think that a cockle's natural place was buried deep within the sand, like other clams.  I saw enough filter feeding right off the surface of the sand at Boundary Bay to make me re-evaluate this perception.
 
Species #5, in the fast flow of the outgoing tide. Diameter about 3 cm
I also saw a midshipman for the first time.  They don't have the wide head of sculpins, and the rays on their fins are not as pronounced.
A plainfin midshipman, a first for me.
Here it is, burrowing itself in the sand.

Boundary Bay hosts quite a few different habitats - the mud flats, the sandy bottoms, eel grass beds, and a solid hunk of concrete.  There are still a number of low tides left this summer...many discoveries await to be found.

Sunday, June 9, 2013

Crabbing at Boundary Bay

The last time we visited Boundary Bay, I did see a few small dungenous crabs in the water, but we spent too much time in the shallower tide pools to look for the catchable ones.  Yesterday, we tried to get to water's edge by low tide (noon) to catch something for dinner.

It was just over a kilometre of walking to get to the water's edge.
https://maps.google.ca/maps/ms?msid=210247271623531636657.0004deac4ee208b13d515&msa=0&ll=49.010923,-123.0287&spn=0.012034,0.033023

We arrived just as the tide was ascending, but still saw many crab in the knee-deep tide pools.  Many that I found were embraced in  courtship:
 
A male finds a female who is suitable for mating, and grabs her tightly.  He locates a suitable female through chemicals in her urine, which signals that she is about to moult, or discard her old shell.  The female is only receptive to mating when her shell is soft, so the male will carry her around for a few days, fighting off potential suitors, and waiting until she moults.  He will further protect soft shell from predators.


Even after pulling him out of the water, he remains firmly grasping his much smaller partner.

I didn't see many nudibranch this time, but found other soft-bodied invertibrates, like this dead lion's mane jellyfish.

Most of you have never seen a clam move, but they're terrific diggers, considering they only have one appendage.

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Sunday, June 2, 2013

Bounding about a bay

A few weeks ago, a friend convinced me that we should go to the beach.  As I hadn't done that in a while, and low tide was conveniently in the afternoon, we decided to head to Boundary Bay.

The low tide measured about 1 metre, which in the tidal flats of Boundary Bay means about a kilometre to walk out from the beach out to the water's edge.  That meant plenty of tidal pools to explore.

Eel grass provided habitat for many animals, including nudibranchs (the first time I've seen them in tide pools)





Anemone (1cm wide)

A mass of eggs of something
As we made our way out to the water's edge, we saw more and more sand dollars.  Most of you have probably seen them either at the beach or a souvenir shop - a white, chalky disk.

A sand dollar test on the North Coast Trail
This is merely the "test", or skeleton, of a sand dollar.  Sand dollars are relatives of sea urchins, and like urchins, are equipped with spines when alive.  By the time most of them wash up on the shores of beaches, the abrasive sand scrubs off most of the spines.

Live sand dollars will live where the water is fresher, in the lower portion of the intertidal zone.  It was here that we found living sand dollars.



With the spines, one can easily see the resemblance to sea urchins.  However, the spines are tiny and much more densely packed than that of an urchin, and they are used more for digging than protection.  With a coordination similar to that of a sea star (sea stars, sea urchins, and sand dollars  are all in the echinoderms phylum), the sand dollar coordinates its spines and tube feet to position itself nearly vertically in the sand, half buried. It catches small particles of food as it floats by, and moves them towards its central mouth.

Other critters were much more difficult to observe without actually catching them.

Shrimp
As we walked through the tide pools in our bare feet, we could easily see the fish darting away from us.  With their camouflage, they became invisible as soon as they stopped moving.  However, we took advantage of their escape behaviour to capture them.  Some would squirm into the shade of our feet each time we took a step.  After we got over our delight of them tickling our feet, we could trap them against our feet and our cupped hands.

Only a flounder as small my fingernail could stick onto a vertical surface

The sculpins were likely tide-pool sculpins, a common species that grows to a maximum size of a couple of inches.  As for the flounders, I knew that they start off life free-swimming in the plankton, whose eyes migrate to the same side of their head as they settle on a life on the sea floor.  I didn't know how large they are when this eye migration happens.  Internet research says that in one species, it migrates at around 1/2 of an inch in size, which matches the size of this flounder, so it's possible this is really a baby flounder and not an adult (I don't know of flounders whose adult sizes are this small).


The largest sculpin we caught was maybe an inch long

My friends and I quite thoroughly enjoyed our day exploring at the beach.  The abundance of life in what one might think is a barren mud flat will definitely bring us back.