Monterey Bay is shaped like a backwards letter ‘C’, with Santa Cruz on the north end and the Monterey Peninsula on the south end. The top of the ‘C’ is comparatively smooth, while the bottom is punctuated by the Monterey Peninsula, which juts north from the city of Monterey. The most striking geologic feature is the Monterey Submarine Canyon, but of course you can’t see that from land. It is crazy to realize that the canyon starts right off the jetty at Moss Landing. It is this proximity to deep water that makes the Monterey Bay Aquarium Research Institute (MBARI) so ideally situated.
Separated by 40.2 km (= approximately 25 statute miles) as measured harbor to harbor, Santa Cruz and Monterey represent both the same and slightly different marine habitats. On a large scale they are both part of the California Current system, strongly affected and biologically defined by seasonal upwelling in the spring and summer months. On a finer scale they differ in a few ways, primarily geologic. The rock on the Santa Cruz end of the bay is a soft sand- or mudstone, and at sites like Natural Bridges can be easily eroded; you can scratch it with your thumbnail, and falling on it might give you a bruise but probably won’t beat you up more than that. The rock of the Monterey Peninsula is much less forgiving: granite with large quartz crystals. Falling on that stuff can leave you with bruises and a bad case of rock rash; I usually end up bleeding from at least one laceration when I’m in the intertidal there.
The difference in rock type between the north and south ends of Monterey Bay also manifests in the tidepools themselves. The soft mud stone of the Santa Cruz erodes into small particles, which form nice soft sandy beaches. Small particles also remain suspended in water more so than larger ones, which affects water clarity. Larger and heavier particles, on the other hand, sink out of the water, so that the water column itself tends to be less murky. Clear water has some marked advantages over murky water. For example, light transmission is directly proportional to water clarity. Thus, all other factors being equal, photosynthetic organisms such as algae have access to more light, in waters above large-grained sand than those above finer sediments.
That being said, it is not always the case that clearer water is better. Remember Phragmatopoma californica, one of the worms I wrote about recently? They build tubes out of sand grains. However, it turns out that they are particular about the sand grains they use. If you were to examine a Phragmatopoma tube under a dissecting scope you’d see that all of the sand grains are the same size. Just how they select and sort the sand grains isn’t understood, but somehow they manage to choose the particles they want and cement them together underwater. Phragmatopoma is one of the most conspicuous animals at Natural Bridges on the north side of Monterey Bay, forming large mounds of hundreds of individuals, yet very few live on the Monterey Peninsula. There are likely several reasons for this, but part of the explanation is that the sand grains are too big to be used in the worms’ tubes.
I live in Santa Cruz, on the north end of the bay, and most of my intertidal excursions these days are to locations in Santa Cruz and north along the coast. I haven’t spent nearly as much time as I’d like to in the tidepools on the Monterey Peninsula and locations further south. It’s tough getting to a site an hour away, when the low tide is at dawn. And with my post-concussion syndrome I don’t yet feel comfortable driving myself that far away and back. Fortunately for me, I am currently mentoring a student working on an independent study project, and she was willing to drive down to Asilomar last weekend. So I tagged along with her.
Asilomar State Reserve is one of California’s no-take marine protected areas (MPAs), where people can look and take pictures but are not allowed to remove anything, dead or alive. It is a glorious site. The water is clear and blue, and the biota is both similar to and different from that on the north side of the bay. I want to highlight some of the organisms that I see there, that are less common here on the north side.
Abalone (Haliotis sp.) are not unheard of here. In fact, there is a black ab (H. cracherodii) at Natural Bridges that I’ve been keeping an eye on since 2015, tucked into a crevice and generally not visible except on a minus tide. And further north at Pigeon Point I have seen red abalone (H. rufescens), both living and empty shells. But I’ve never seen as many black abs as I saw at Asilomar. Standing in a depression about as big as my kitchen table, well above the water level, I easily counted at least 20 black abs. Some of them were as big as my hand. How many can you see in the photo above?
Abalone are large herbivorous snails. They feed on macroalgae, both reds and browns. If they venture from the safety of their nooks and crannies they can chase (at a snail’s pace) down algae, but then they are vulnerable to predators such as cabezons and sea otters. Abs that live in crevices, like these, have to rely on drift algae to come to them; they don’t have the luxury of choosing what to eat. It’s the age-old compromise between safety and food, one of the driving forces in foraging behavior.
While we have four species of anemones in the genus Anthopleura at the Santa Cruz end of the bay, as well as other anemones such as Epiactis, we don’t have any in the genus Urticina–not intertidally, at least. I have seen Urticina anemones at Carmel, and last weekend saw what I think was U. coriacea. It was in a pool, and partially obscured by sand and its own pharynx.
It’s own pharynx, you ask? Yes! Anemones are cnidarians, and as such have a two-way gut. This means that food is ingested and wastes are expelled via a single opening, which for politeness’ sake we call a mouth even though it also functions as an anus. Sometimes, when an anemone is expelling wastes, it also turns out the top part of its pharynx. This is a temporary condition, and the pharynx will be returned to normal soon. The anemone in the picture above appears to be in the process of spitting out something fairly large and undigestible.
Here’s another example of an anemone eating a big meal, this time of mussels.
What do you think this thing (below) is?
I had at first misidentified these as something else, but have since been told that they are the tubes of another of those strange terebellid polychaete worms. This one is Pista elongata. As with many terebellids, P. elongata lives in a tube, the opening end of which is elaborated into a sort of basket. They reportedly range from British Columbia to San Diego. I think I’ve seen them at Carmel Point, but not at Point Piños, which I’ve visited more often. And I’m positive I’ve never seen it at Natural Bridges.
At Asilomar I saw some large clusters of P. elongata in the low intertidal. They are not clonal, to my knowledge, so these aggregations would form by gregarious settlement of competent larvae when they return to shore.
One solitary ascidian that I saw at Asilomar is Clavelina huntsmani, the appropriately called lightbulb tunicate:
For people too young to remember what an incandescent light bulb looks like, they were made of clear or frosted glass. Inside the glass bulb were tungsten filaments, through which electricity flowed; the filaments heated up enough to emit light. In Clavelina, the two pink structures running down the length of each zooid resemble the filaments of an incandescent light bulb, but are in fact parts of the pharyngeal basket, the structure used for filter feeding.
We have neither Pista nor Clavelina in Santa Cruz–at least, I’ve never seen them. They remind me that although Santa Cruz and Monterey are part of the same ecosystem, they do not represent the same microhabitat. I’m pretty familiar with the intertidal floral and fauna in Santa Cruz, but I absolutely love exploring the intertidal along the Monterey Peninsula. There’s something exciting about spending time a place I don’t know as well as the back of my hand. I hope that as my brain continues to heal I’ll eventually regain the stamina to travel so far for a low tide.