Home to thousands of marine organisms, this rock is at North Point in Morro Bay. It is often hard to get close to the rock as it is in the very low intertidal and a tide of -1.3 or more is needed to get close. But take a look at some of the organisms.
Bare on the top, this is about the area of the splash zone or over 6 feet. Then there is a dense stand of mixed blue mussels, goose neck barnacles and all kinds of little things tucked into the shelter of the crevices. These indicate the spray and high tide zone, approximately 4-6 ft.
There is an abrupt cut-off of these organisms below and it usually coincides with the height that the sea stars can reach and still survive being out of the water for a long period. Since the sea star wasting disease has finished off many of the stars, this edge is moving downward in many places as there is no competition anymore. Notice there is no, or minimal, algae at this level. It’s too much out of the water for the algae to survive.
Next note the area below the mussel ledge in the picture below. This is a mix of aggregating anemones, giant green anemones, and hanging red and brown algae. These organisms indicate the bottom of the high tide zone and into the mid tide, where water covers and uncovers daily so they can survive.
Another picture of this level shows some of the other organisms that can be found here: giant green anemones, sand castle worms in the upper right mass, beautiful iridescent red algae, some small amounts of feather boa kelp and, in the lower left, a hanging brown that is very special.
This special brown alga, seen in the picture below, is Desmarestia, a brown alga or kelp that produces sulfuric acid in its tissues when it is chewed on or released from the rock. This is a deterrent to herbivory by other organisms and is also a deterrent to people picking up handfuls of it to take and eat. It has a distinctive aroma and can cause a chemical burn if held too long in your hand. It will also bleach out other algae if in the same collecting bag and it can etch rocks!
Notice it is mainly in the water, or at the low tide level. It tolerates minimal drying and needs to be in water most of the time. The pink in the picture is a mix of erect and crustose coralline algae and there is also some of the iridescent algae in the upper center. The bottom of the picture is the sand which moves in and out with the tides, waves and seasons.
Another alga or kelp attached to the bottom of the rock is the feather boa kelp, as seen below. It has large floats to keep it on the surface for photosynthesis and can get up to 20 feet long. It is usually in the mid to low tide range.
Around to the side of the big rock are some more interesting organisms including 3 beautiful ochre sea stars, more iridescent red algae and lots of funny looking green rectangular things. These are closed-up anemones that have lost some of their water and are just hanging like little green sacs. This side of the rock gets more wave action and the organisms stay wetter than on the other side. Notice that the orange star is right at the base of the mussels. That’s about as far as it can go and survive for any period of time. It’s doing a good job of keeping the mussels up where they belong.
The last organism seen on this day was the cancer crab, crawling along the base of the rock, in and out of the seaweed, looking for things to pick at and eat. Note the black tips on its claws. This is the red rock crab and it can be very tasty for otters, gulls and humans alike when it is much bigger.
So, looking at this rock from the opposite side, you can see that it is covered almost all the way around and is imposing in its environment. Lots of things live and thrive on it, but it can also change throughout the year. It’s always exciting to visit the rock to see what’s there. Take a trip to North Point (off Yerba Buena Drive in Morro Bay) on a really low tide and see for yourself!