What a difference a day makes…yesterday we got over an inch of rain and today the weather was beautiful!
We did all 14 of the quadrats and also had time to do timed searches for black and red abalones (Haliotis rufescens and Haliotis craacherodii) and ochre stars (Pisaster ochraceous). We had help from PRBO interns, Stephen and Amanda, which made our tasks even quicker.
We found five abalones in the Queen’s Bath tidepool.. It is rare on the mainland to find a protected tidepool that is big enough to swim in….but I have seen a few on the island. Gery swam around to look under overhangs for abalone.
The water is really clear in many of the pools. The island including the intertidal is granitic, make up of granodiorite and quartz diorite the granitic diorite…unlike most of the reefs (Duxbury, Fitzgerald Marine Reserve and Pillar Point) near San Francisco, which are made up of soft sedimentary rock (mudstone), these rocks don’t cloud up the water with sedimentation. Additionally, because the granitic rock is so much harder animals that bore into mudstone on the mainland, can’t do so on the island.
You can see the difference in the purple sea urchins (Strongylocentrotus purpuratus)…the first picture is from Duxbury reef (the animals are surrounded by the mudstone that has beenworn away by the combined eroding action of their spines and their feeding structure (called an Aristolte’s lantern). The second is from Queen’s bath on the Farallones, where the rock it too hard to be worn away by their spines.
Duxbury Reef urchins-on mudstone