This afternoon, I went walking up Purisima Creek Trail, off Higgins Canyon Road in Half Moon Bay. Purisima Creek flows down through a canyon in which grow Coastal Redwoods. It’s a perennial stream, but at this time of year the water is only a few inches deep. I was curious to see if I could find any organisms living in the creek.
The first organism I saw was a water strider, probably Aquarius remigis, Common Water Strider; in a half an hour of walking along the creek, I saw dozens of these water striders, in sizes ranging from tiny (I was barely able to see them) up to an inch or so long. They were mostly quite aware of my presence, and if I moved too quickly, or got too close to fast, they would skate away from me over the surface of the water. The only other organism I saw in the stream was a Banana Slug, which had somehow gotten to a rock in the middle of the stream; it was mostly out of the water.
But I didn’t see anything else living in the water. Most of the plants I saw grew on the steep banks at least half a foot from the water, and my guess is that the bottom of the stream bed gets well-scoured when water comes pouring down the creek after winter storms; any plants that manage to take root there in the summer get torn away in winter. Nor did I see any other insects, crustaceans, amphibians, or other animals living in the stream; though I suspect there are other animals in the stream. I did see several hatches of small insects dancing in a cloud a few feet above the stream; did they hatch from the water? do their nymph forms live in the water? I’ve seen California Newts (Taricha torosa) in this area; I would guess some of these newts breed in this stream, the largest stream in the vicinity, and that the tadpoles must therefore live in the stream for a time.
But today, the only organisms I saw in the stream were the water striders.