Half Moon Bay, California

June 9, 2023

Tidepools at Pillar Point Marsh Wetland: 10:00 am to 12:30 pm

Fouling Communities at the public docks of Pillar Point Harbor: 2:00 pm to 3:30 pm

That Friday was an overcast day with a high of 66° F.

The basis of the energy required for an ecosystem comes from the primary producers. The primary producers at the Pillar Point Tide-pools are algae and surfgrass. In the photos above we see the Coralline algae has a beautiful shape like coral, but is actually photosynthesizing and capturing energy for the food web.

The major ecological challenge for animals in the foreshore is that the environmental conditions change throughout the day. At Pillar Point, there are two low tides each day. When the tide is low, the organisms have varying degrees of access to water. A behavioral strategy to address this challenge is for organisms to place themselves in lower areas of the rock, such as in crevices and under algae and surfgrass, which helped to temper the drying out effects of being exposed to air and higher temperatures. Surfgrass is specialized for high impact zones and withstanding dessication. When anemones are exposed to air, they retract their tentacles and shrink in size. Barnacles close the opening created by their top plates.

Adaptations to the splash zone include sticking to rocks. Many intertidal organisms address the challenge of turbulence within the wave zone by anchoring to the rocks, such as chitons, anemones, mussels, barnacles, and surfgrass. Sea anemones anchor with their basal disc, mussels with byssus threads, and barnacles with a cement-like secretion. Surfgrass has high root hair development and thickened rhizomes that secrete a cement-like substance.

When the tide is low and the foreshore is no longer fully submerged, all tide-pool organisms face exposure to predators such as mammals and shore birds. Birds such as gulls, blue herons, and egrets will hunt and feed at tide pools. Camouflage strategies can be seen in all directions. Urchins place themselves in crevices and hold shells or algae over their spines to hide. Among the green algae and surfgrass, we spotted a light green shrimp, a light green baby eel, and light green crabs. Dark grey snail shells and mussel shells matched the dark grey of the rocks. The variety of hermit crab dwellings proved to be quite delightful. There was every type of shape, size, and color that could reasonably fit within one of the tide pools. I found hermit crabs with shells as small as two millimeters and with shells as large as five centimeters. The color of the shells included rose pink, maroon, dark grey, cream, orange, and marbled grey. The hermit crab that won, “Most Creative Camouflage,” had two types of algae connected to the top of its shell, including an air bladder.

I stood nearby as the baby monkeyface eel, or monkeyface prickleback, was captured. The eel’s quick instincts went into gear and it swam with fierce velocity, jumping from the water and almost managing to escape the bucket. The bright green color surprised me. A juvenile’s early diet includes zooplankton and by the time it is around five centimeters, it switches over to algae. The bright green must be from feeding on the algae. After looking up the adult with its large and fleshy lips and rock-themed stripes, I am in love!

The coloring of this fish allows them to blend in with the rocks and algae of the tidepools.

Another highlight of the day was observing the octopus. Once a fellow classmate spotted the octopus, around five of us gathered in the area to block exit routes and capture it. We noticed that it had one shorter arm. A male octopus generally has a hectocotylus, one arm that is shorter than the others and deposits sperm. It is possible that the shorter arm is its hectocotylus or it could be shorter from being eaten by a predator. An octopus is interesting in any regard, with its multiple arms with suckers, squishy body aiding its hiding ability, ink squirts, and changing color. However, the movie, “My Octopus Teacher,” taught me that an octopus’s intelligence and self-awareness is actually quite profound. While the octopus was in the bucket, it was humbling to watch it lift its eyes above the water to get a better look at us and strategize its escape. It is even more interesting considering that octopus eyes are an example of convergent evolution, taking form along a parallel evolutionary path from human eyes. Watching it walk along the rocks to decide which pool in the tidal zone was most appropriate cover was fascinating.

So many crabs of all shapes and sizes. The above striped shore crabs are an example of the range of size we observed. The left crab was about as big as a fingernail while the right crab was bigger than a hand.

Nudibranchs! I would be remiss to exclude the excitement of observing the two species of nudibranchs, the Opalescent nudibranch and the Hopkins Rose nudibranch. The vibrant colors that warned of toxicity and the unique form of each sea slug’s protruding cerata and rhinophores exposed me once again to the diversity of lifeforms on this planet.

When observing fouling communities at the docks, we observed predation in the form of suspension feeding by a colony of barnacles. Barnacles adhere to rocks, boats, and the bottom of docks. They are enclosed by hard outer plates made from a process of secreting calcium. An adaptation that prevents drying when exposed includes a set of plates at the top of the barnacle that can open and close. The barnacles we observed were fully emerged in the water at the bottom of the public boating docks. They were filter feeding by extending and retracting their appendages called cirri. As plankton and detritus floated by, the feather-like cirri reached out in a fan-like structure and the fine filaments attached to the cirri captured the food and pulled it into the opening in their top plates. With the variety of barnacle sizes, we could see the popping up and down of many tiny fans of cirri, as well as a few of the larger cirri fans.