High Pools: the most exposed intertidal areas of Cattle Point

The high intertidal is the harshest of Cattle Point tidepool environments. Though desiccation, wave action, and surge doesn't pose a threat in the upper tide pools, these pools do experience the most extreme environmental changes. The most limiting factor for life in these pools is the fluctuating temperature and salinity throughout a tidal cycle. Our characterized pool (approximately ten by fifteen feet in size) has within it surf grass, crevices, and exposed areas -- all of which are found in other environments, but the flora and fauna is almost completely different. Why? Temperature, that's why. The pools heat up seven to ten degrees during the average day, and though for air breathers like us seven degrees doesn't feel like much, in a marine environment water acts as a heat sink, draining the heat from an animal twenty five times faster than in air.

The dominant animals here are not barnacles or leather chitons, which are noticeably absent, but instead a vast number of small gastropods, including both periwinkle snails (Littorina scutulata and L. sitkana) and limpets (Lottia digitalis). On average, the mean body size of the animals in the high tide pool is smaller than those found elsewhere, and the diversity is very low. The dominant chiton in the area is the hairy chiton, Mopalia spp.. The dominant crab is the shore crab, Hemigrapsis nudus--in our target pool we found eight individuals. There were also numerous, small hermit crabs, all using very small periwinkle shells as homes.
The sea anemone Anthopleura elegentisma is found exclusively in the high intertidial at Cattle Point. This often abundant animal as been pushed to the periphery of the environment, because it is unable to compete for space elsewhere with the barnacles and rock weed.  In the high intertidal, we found clones (large colonies of anemones derived by asexual reproduction from a single founder) ranging from 20 to 30 individuals, often limited to crevices and cracks that remain moist all day.  Anthopleura feed on a diversity of species and take advantage of the occasional unlucky barnacle knocked off rocks by logs or wave action. Like most anemones, Anthopleura remove particles from suspension using their tentacles. The tentacles have numerous nematocysts, a cellular organelle that fires a sticky threat used to puncture or entangle prey. Once Anthopleura captures prey, each tentacle curls and forces the food item through the mouth into the gastrovascular cavity.  Anthopleura also derives nutrition from symbiotic algae housed within the tentacles. These algae, either zooxanthelle or zoochlorellae, provide the anemone with its characteristic green color.  Anthopleura take advantage of a large portion of the sugars generated by symbiont photosynthesis.  Anthopleura elegantissima reproduces sexually and asexually. Sexual reproduction occurs when male and female anemones broadcast spawn gametes during late summer to early fall. The larvae have a brief planktonic existence, until they settle to form adults. Asexual reproduction occurs when a large specimen undergoes longitudinal fission, dividing in half and regenerating the lost parts.  These offspring will repeatedly divide in half until a colony is formed. An individual can reproduce sexually and asexually within a year, but fission typically takes place only once a year.
Like many species in the rocky intertidal, spiral tube worms found in this habitat build tubes made of calcium carbonate to protect them from predation and desiccation. If you look along the bottom of rocks in the upper intertidal, you will see small white spirals, secreted by the worm as it grows. When the tide is in, spiral tube worms use their tentacles to pluck food from the water column. But when then tide goes out, these small marine worms retract their tentacles into their shells, which blend into the rocks like a spattering of bird droppings.

We used data recorders to monitor temperature fluctuations over two days.  The recorders were left in two different tide pools (one high; one mid-level, aka Joe's crab den).  The peaks represent the temperature reached while the tide pool was exposed and separated from the ocean. The valleys represent the temperature of the pool while sumerged as part of the ocean. The peaks correspond exactly with the daily low tides.


 Species found in the High Pools:



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