Four easily accessible tidal zones await the curious explorer
Photos and blog by Barbara Swanson. For full-size images in blog, please see slide show below.
Exploring an area for wildlife with an expert is always a great way to learn, so I was fortunate to be part of a small group that included two retired marine biologists during a very low tide at Bird Rock in La Jolla. While this area may not be as well known as several other San Diego county tide pooling locations, it offered ample wildlife and limited crowds. Low tide was around 3:30 in the afternoon at minus 1.4 feet, allowing us up to 400 feet of access along the substrate from shore. It was a sunny day with good light for plentiful photography!
Public access to Bird Rock is located via stairsteps from the southwest terminus of Bird Rock Avenue three blocks west of the roundabout on La Jolla Boulevard, which passes through La Jolla South’s mercantile strip.
Many of the critters in the slide show below were initially found by the marine biologists with their local experience, allowing me to photograph many more of them than I could have done on my own. Also, by following the guide of our marine biologists, we were careful to disturb the animals as little as possible. This is very important for their survival. After all, how would I feel if my home were suddenly visited by strange aliens with giant lenses? I would be much better off if they didn’t tear me away from the little block I live on, then carelessly throw me back into some dangerous, unknown place with predators and little food.
In rocky areas, bounded by the lowest breakers of low tides and the high splashes of the high tides, there are four ecological zones which support various habitat niches. This whole region is called the intertidal zone and is located between the mean high water mark and the mean lowest low water line. The uppermost zone is the splash zone, which is above the high tide line but can become wet from waves. The next region is the high intertidal zone, which is covered during high tide but dry for the rest of the tidal cycle. The animals that inhabit this region are able to withstand crashing waves, hours of limited water and temperature extremes. The middle intertidal zone is lower and is cyclically wet and dry during the tidal cycle. The low intertidal zone is only exposed during very low tides, such as what we experienced during our outing. Because of the very low tide, we were able to explore all of the described intertidal zones and find representative species in each region.
I used a 105 mm macro lens (1:1) for all of the marine photographs and used autofocus. A polarizing filter may have helped with glare in some circumstances, but it also reduces the light getting into the camera. As this was a very low tide and a calm day, there was no chance of getting splashed by waves where we were exploring. I carried extra batteries and cleaning supplies in a backpack, and used watertight plastic bags for the batteries and my phone just in case I fell into a pool of water. I wore surf footwear with some tread on it, as the rocks and seagrass were very slippery, and rolled up my quick-dry pants. Having the right clothing and equipment made the outing safe and enjoyable — Barbara Swanson.
SLIDESHOW BELOW: SOME FAVORITES FROM THE TIDE POOLS
Click on any image or its arrow ⇒ button lower right for enhanced views of the photos. Photos by Barbara Swanson.
View taken from the bottom of the stairs at the west end of Bird Rock Avenue. In order to access the tide pools, a person must navigate over the large boulders placed at the base of the stairs to help prevent cliff erosion.
A western gull studies its next move from the rocks of low tide.
Except for a few gulls and brown pelicans flying by, the only bird I saw at the tidepools was this whimbrel (Hudsonian). It seemed to be very successful at foraging, catching several crabs in less than ten minutes. It can probe for tasty invertebrates with its long bill. Some whimbrels spend the winter in the San Diego area but should be leaving soon on their long migration to breed in the arctic tundra.
Found in the high and middle intertidal zones, aggregating anemones, Anthopleura elegantissim, are animals that attach to rocks and divide to form clonal clusters. When two clonal colonies grow close, they fight one another using stinging cells. To eat, they sting the small animals that swim or float into range. When each animal opens up its tentacles under water, sometimes you can see that parts of the animal are green due to photosynthesizing symbiotic algae growing inside of them. As shown in the photo, when anemones are closed up, the gravel and bits of shell they hold on to appear to cover the anemone.
This small school of juvenile opaleyes, Girella nigricans, were photographed in the upper or middle tidal zone. They had a relatively large tide pool to swim around in, with places to hide from hungry birds. The juveniles eat algae and small invertebrates in the tide pools until they are large enough to survive in the subtidal zone.
Striped shore crab, Pachygrapsus crassipes, lives in the mid to high intertidal zones and are common. They are skittish but if you wait quietly by a tidepool they will eventually come back out from their hiding places. They grow to about 2”. They are adaptable animals, living in water and on land and can survive up to 70 hours out of the water! These crabs have a varied diet of mussels, algea, seaweed, all sorts of small animals and will even scavenge. While they prefer to come out at night, they can easily be found in tidepools during the day. The crab’s coloration blended in well with its surroundings by matching the colors in its habitat.
Wire Weed, Sargassum agardhianum, is a native seaweed that looks similar to the invasive Sargassum muticum and is distinguished by the sharp point at the end of each float bladder. It attaches to hard objects such as rocks.
There are 7 or 8 species of abalone in California, and they are struggling compared to their plentiful historical levels; most are either endangered or a species of concern. We found abalone today measuring 3-4” across, which was encouraging, as mature green abalone Haliotis fulgens are 2.5 - 5”. The name comes from the indigenous Rumsen people around Monterey Bay, who called them aulun, which was adapted to abulon by the Spanish.
It was very exciting to see a good-sized octopus (this species is Octopus bimaculatus), but I think it was less excited to see us as it wanted to hide. Octopi live in both the intertidal and subtidal regions and eat a variety of animal prey. They have a short lifetime of less than 2 years, dying a short time after mating. This octopus was a dark green on the rock, making it very difficult to see (a few of its suckers are easily visible but you can see a number of its tentacles). It moved into the tidepool and settled down in the sand by a rock, changing to a light pattern. Octopi are able to quickly change their appearance due to chromatophores in their skin.
Conspicuous chiton, Stenoplax conspicua, is found in the middle intertidal zone and is well named due to its contrasting bright pink and green colors. The pink color is exposed when the outer shell is worn away, as shown in the close-up photo of part of the shell. The chitons we found on rocks were around 4” long and close to full-size. They usually feed at night.
This California sea hare, Aplysia californica, was one of the favorite creatures of the day. It is a sea slug that eats kelp and algae, and its coloration is a reflection of the color of the algea it has eaten. The adults are found in the middle and lower tidal zones. It is not named for its speed, but rather for the two protruding rhinophores on its head.
This sea snail of the first animals found this afternoon and was the most colorful and locally rare species of the day: Felimare californiensis is the beautiful California blue dorid, found in the low intertidal zone. It was less than 2” long but stood out from the vegetation due to its brilliant blue color. This nudibranch became locally extinct by 1984 but has reappeared in the last decade. Water pollution has been cited as possibly the main reason for its earlier decline.
Giant keyhole limpet, Megathura crenulata, is a gastropod found in the intertidal zone and subtidal zone to about 100 feet. They eat plants, small animals and algae at night and have a limited coastal range from Monterey, California to Baja California. Water and waste pass out of the animal through a top hole. They leave chemical signatures in their mucus trails to make it easier for them to find their way around, like the children's story about remembering to leave bread crumbs. This one was not yet full size.
Bat star, Patiria miniata, are found in the low intertidal and subtidal zone to 300 m; the one photographed was about 1" in size while mature bat stars can grow to 4" - 8". While this one was a reddish-orange, a common color for them, they are also found in a range of colors along the Pacific coast. They eat a wide variety of plants, including algae, and animals.
Spiny brittle star, Ophiothrix spiculata, lives in the low intertidal zone and the subtidal zone to 2,000 meters. This one was moved into a small tidepool to photograph and quickly hid among the rocks, blending in well with its cryptic coloration. We didn’t measure it but it looked close to full size. These animals eat a variety of foods, sometimes by extending a couple arms from its hiding spot to capture small food suspended in the water.
I enjoyed the wonderful images and informative narratives about these interesting animals. I especially liked the images of the whimbrel, the spiny brittle star and the striped shore crab. Thank you for sharing your adventures with us!