The Pacific Northwest probably conjures images of waves smashing against rocky and inhospitable shorelines — places no living organisms could possibly call home. But some of those seemingly hostile intertidal zones support a variety of marine life, whether the tide is high or low or coming in or going out.
The intertidal zone is rich with life and essential to the ecosystem’s health. (Illustration: Soren Henrich)
The Puget Sound fjord estuary is home to a veritable plethora of such intertidal zones — the stretch of shore between land and water that is exposed between high and low tides. And with the help of Earth’s tug and pull with the sun and the moon, tides vary and range from high to very high and low to very low.
The moon’s orbit gets a lot of credit for affecting Earth’s tides, but Earth’s orbit around the sun plays a role, too. (Source: splashmaritime.com.au)
On a recent summer day I joined my esteemed colleagues from a University of Washington marine biology class to examine the rocky intertidal zone of Constellation Park in West Seattle, a densely populated peninsula across the bay from downtown Seattle.
At a time during the month when the tide was at its lowest, we sampled small, rectangular swaths of a beach that was covered with small, smooth rocks, and discovered a variety of life thrived even far from the water line.
Marine life can thrive even where high tide infrequently refreshes the variety of species. (Photo: George Thomas Jr.)
In one small quadrant in the high tide zone we observed the usual suspects, seaweed and algae, but also barnacles — 230 feet from the low-tide water line.
And closer to the water, underneath an abundance of Sea Lettuce (Ulva lactuca), hid tube worms, crabs, clams, and mussels — a total of nearly three dozen unique marine organisms, most hidden from view.
Nearly three dozen marine species were observed in the tidal zone exposed during low tide. (Source: Thomas et al, 2018)
Marine life, jobs, and economics
Even in a densely populated area — as most estuaries are — marine life can thrive, given the proper restraints of protecting shorelines and responsible urban development. And maintaining the health of massive estuaries like Puget Sound and Chesapeake Bay isn’t just good for marine life, it’s good for local economies as well. In the United States, coastal communities generate millions of jobs and contribute $111 billion to the economy.
How carbon dioxide threatens estuaries
As global warming persists, record-setting high summer temperatures and weather extremes dominate the headlines, but the threat to oceans and estuaries is equally alarming. A portion of the leading greenhouse gas, carbon dioxide, gets absorbed by the ocean, where chemistry takes over, resulting in ocean acidification.
When the acidity of seawater increases, even by a fraction, marine life like oysters have difficulty surviving. And even smaller organisms like pteropods, which serve as a critical food source for salmon, are at risk. Every day we are increasingly reminded of how delicately balanced our ecosystems are.
If you have the good fortune of being at the shore during an extreme low tide, be mindful of the delicate hidden habitat beneath the rocks.
Data for the marine biology lab in Constellation Park gathered in collaboration with my esteemed colleagues Sydney Beaumont, Mason Guiste, and Anthea Guthrie-Honea.
