Life in the Tidepools at Redwood: How Intertidal Creatures Survive and Are Monitored

Giant green anemone. NPS.

Past the redwoods, rivers and prairies of Redwood National and State Parks lies the coast — and at low tide, the rocky intertidal zone: pools between rocks, a crab slipping into the sand, an anemone, perhaps a purple sea star.

Plenty of food, a hard life

The Pacific here is highly productive: tiny plant-like phytoplankton make abundant food, and in late spring and early summer upwelling brings cold, nutrient-rich water to the surface. But the intertidal zone is pounded by winter and spring waves, and twice a day the tide transforms it. At high tide come seawater, surf and hungry fish; at low tide, sun, air, and predatory mammals and seabirds.

Ways to survive

Adaptations come in two kinds. Behavioral ones are things an organism does: the shore divides into spray, high, middle and low zones — the spray zone rarely submerged, the low zone almost always — and each species settles where it can tolerate the exposure, temperature, salinity and wave shock. Morphological ones are body features, such as hard shells, strong tube feet and flexible tissue.

California mussels (Mytilus californianus) form dense beds that shelter many other species. NPS.

Seaweeds matter too. Rockweeds, turfweed and sea palm are primary producers, anchored by a root-like holdfast and flexible enough to take the surf. They feed grazing limpets, chitons and abalone and give shelter. Sea palm can only grow where a disturbance clears a patch in a mussel bed, and anemones host single-celled algae that feed them energy.

Rockweed (Fucus distichus). NPS.

Chitons, limpets and abalone, all grazers of the rocky shore. NPS.

Watching the rocky shore

A change in one population can ripple through the whole food web. Since 2013, sea star wasting disease has killed huge numbers of ochre sea stars — a keystone species, a top predator whose effect far outweighs its numbers.

Since 2004, the Klamath Inventory and Monitoring Network and UC Santa Cruz scientists have monitored three sites in the park — Enderts Beach, Damnation Creek and False Klamath Cove — as part of the coastwide Multi-Agency Rocky Intertidal Network (MARINe).

Monitoring the intertidal community at Redwood. NPS.

On each visit, researchers log the time, weather, tide, debris, and counts of birds, marine mammals and people. Then they survey biodiversity and check target species in fixed plots, which never move — small ones for sedentary species, larger ones for mobile ones. The targets here:

• northern rockweed (Fucus gardneri) and dwarf rockweed (Pelvetiopsis limitata)
• turfweed (Endocladia muricata)
• California mussel (Mytilus californianus)
• barnacles (Chthamalus/Balanus)
• surfgrass (Phyllospadix scouleri/torreyi)
• ochre sea star (Pisaster ochraceus)

From 2004 to 2018 there were changes but no major shift in community structure. A storm may strip part of a mussel bed; the mussels come back — a sign of a stable community.

Tread lightly

Here, tides — not people — are the main disturbance. But sea-level rise, warming water, plastic and oil pollution and careless visitors threaten tidepools everywhere. Visit, but step gently and treat the intertidal zone with respect.

Sources

Based on Natalie DiNenno, "On the Edge: The Curious Lives of Intertidal Organisms and How We Monitor Them," Klamath Inventory and Monitoring Network, Klamath Kaleidoscope, Fall–Winter 2022, National Park Service; a work of the United States government in the public domain. The source spells the ochre sea star's name Pisaster ochraceous.