• My latest book available in paperback and eBook formats

  • Available from Amazon paperback or Kindle

  • Updated w/double blind study results. Ebook or paperback

  • New updated edition available NOW!

  • Recent Posts

  • Tracking Footprints

  • Archives

  • Top Posts

  • Pages

Zone 4- Low Tide zone in Northern California

An unusually low tide is occurring for these next days.  The trick is to find the perfect combination of a good minus tide with times that you can go out on the reef…in other words, not after sunset or before sunrise.  The low tide today was around, adjusting the time a little north of the bay, 4:14 pm, a wonderful -1.5.  Tomorrow’s low tide will be at 5:00 and a -1.6.  But given that sunset is around 5pm, I decided to go out with my family today.

The place to go in Marin County to tide pool is Duxbury Reef.  Its part of Point Reyes National Seashore and, at a mile long, its the largest shale intertidal reef in North America.  To get there, you have to know where Bolinas is.  That is a trick in itself, because Bolinas is the ‘town of no signs’.  Bolinas townspeople are famous for taking the road signs down that the county puts up.  Bolinas is a wonderful little blast-from-the-past village hanging on the tip of the spit at the lagoon. Agate Beach where the reef is, is on the road to Bolinas but not in the actual town.

The reason you want to get a real good minus tide, is that you want to be able to walk out to the lowest zone.  Marine biologists divide the intertidal area into four zones.  Zone 4 is the zone that is rarely exposed to the air and for only very short periods of time.  Special plants and animals inhabit this zone, which, of course, you rarely can observe unless you want to scuba dive in a wet suit in cold water.

I’ve taken a few marine biology classes and done quite a bit of tide pooling in my past.  One of the ways you know that you are at the farthest reaches of the low tide zone is the presence of sea urchins.

Sea urchin

I met a fellow at the beach entrance taking notes on the visitors today.  He was working with the California Academy of Sciences who regularly study this reef.  I haven’t been to the reef at a minus tide this low since the early 2000’s.  I asked about the reef’s health.  He told me that this reef is, in general, healthier than its been in the past except for the urchins.  I noticed there are visibly less urchins than 10 years ago and he confirmed this.  He said they are not sure why.  It is possible that, since this little guy is an Asian delicacy, people are illegally harvesting it.  Sea urchins are almost the sole food of sea otters, so much so that their bones are visibly purple when they die.  

Another sign that you are in zone 4 is the presence of the Giant Green Anemone.  They have stinging tentacles to catch and kill their prey.  Its fun to touch them as their tentacles feel ‘sticky’.  When you touch them they close up.  My son said he’s got lots of memories of going around touching these guys.  If you keep your finger there, they’ll close up on your finger.  But don’t worry, you can always get your finger out.  They’re not stronger than us.  My bio teacher used to say that its ok to touch using your protective skin, but don’t lick them because your mucous membranes and smooth muscles aren’t protected. He said you’d have to go to the hospital then.  I decided not to lick them today.

Giant California Green anemone garden

I have no idea what this anemone ate

Sea grass was everywhere, one of the few flowering plants and its at the low tide zone.  Pisaster giganteus, the giant sea star (they are not starfish because they are not rightly fish) comes in purple and blue.  It predates on mussels and is found only at this low tide.  We found large rocks covered in every inch with mussels as well as barnacles.  The orange sea star is a mid-tide zone animal as it can stand the desiccation better.  We found this one with part of its stomach hanging out.  That’s because when a sea star eats, unlike us who keep our stomachs inside, they throw their stomachs outside their bodies and surround their meal, digesting it outside of their bodies.  Interesting.

Hard to see its extruded stomach in the middle that my son is taking a photo of.

My most favorite animal to look for are nudibranchs.  Essentially they are slugs of the sea.  There are over 100 varieties in California, many of fabulous neon-type colors.   They have an interesting relationship with anemones.  They feed on them, storing their stinging cells, or nematocysts, in their bodies.  These ‘stolen’ nematocysts help protect the slugs from predators, firing when they try and take a bite.  We saw several varieties today, with a total of about 10 individuals, which is a lot of good spotting.

Nudibranch in middle of photo

When the tide was at its lowest, we began heading back, mostly because the sun would be setting in 1/2 hour.  What a great time.  The California coast has a lot to offer, and a lot of reason for all of us to protect it for generations to come.

The Reef exposed at low tide

Duxbury Reef is here