The world I was stepping into was about to vanish beneath the waves. It was low tide at Pillar Point Harbor, near San Francisco, revealing a hidden ecosystem: the rocky intertidal, or tidepools. Dawn broke, pelicans soared overhead, and sea lions barked from the harbor, but my attention was captivated by zoologist Rebecca Johnson as she navigated the seaweed-covered rocks, pointing out surfgrass, seasack, and feather boa kelp – a seaweed wonderland. The diversity was astonishing; a boring clam puffed itself up, a brittle star danced across algae, and anemones wore tiny shell hats for sun protection.
We discovered six species of nudibranchs – vibrant sea slugs in shades of pink, orange, lemon, and white, some even adorned with orange polka dots. These creatures, Johnson explained, steal stinging cells from anemones for their own defense. This vibrant biodiversity is typical of tidepools, a concentrated hub of invertebrate life. The magic of this ecosystem, Johnson noted, lies in its fleeting visibility, a brief window into a hidden world, only accessible during low tide.
Johnson, director of the Center for Biodiversity and Community Science at the California Academy of Sciences, has been studying these tidepools for nearly three decades. Her passion is infectious, echoing my own childhood fascination with tidepools, a fascination that ignited my interest in science. But her love is tinged with concern. These unique ecosystems, like many others, face a precarious future.
The trouble began around 2014 with the arrival of ‘The Blob,’ a marine heatwave that significantly warmed Pacific waters. Johnson’s citizen science program participants reported an increase in Hopkins Rose nudibranchs, usually found further south, and alarming observations about sea stars. Starting in 2013, divers and researchers witnessed a mass die-off of sea stars, a phenomenon known as sea star wasting syndrome. While sea star wasting isn’t uncommon, the scale of this event – affecting at least 20 species across the West Coast – was unprecedented. Scientists suspect a combination of factors, including a possible virus or bacteria, exacerbated by the warmer temperatures of The Blob.
The impact on the tidepools was profound; Johnson and a colleague found a stark absence of sea stars at Pillar Point, a place she knew intimately. This loss wasn’t just aesthetic; sea stars are vital predators, maintaining the ecosystem’s balance. Their decline has far-reaching consequences, particularly for California’s kelp forests.
Kelp forests, crucial carbon sinks and coastal buffers, are grazed by purple sea urchins. Normally, these urchins feed on kelp detritus. However, without enough kelp detritus and with reduced sea star predation (including the functionally extinct sunflower sea star), urchin populations explode, leading to ‘urchin barrens’ – stretches of seafloor devoid of kelp. Sea otters are natural urchin predators, but their populations haven’t fully recovered in all areas. The near-total collapse of Northern California’s kelp forests highlights the cascade effects of sea star loss.
While the tidepools haven’t suffered the same dramatic decline as the kelp forests, they are not immune. Changes are occurring; grazing species are moving into the tidepools, and the northward shift of species due to warming temperatures is reshaping the ecosystem’s dynamics. Additional stressors, such as pollution and wildfire runoff, further complicate the situation.
Paleontologist Peter Roopnarine, studying ancient ecosystems, offers a historical perspective. While ecosystems can endure for millions of years, they are not infinitely resilient. Extreme changes, like dramatic climate shifts, can lead to their demise. The current situation, he emphasizes, is cause for serious concern; inaction will lead to grim consequences.
Hope, however, remains. Citizen science initiatives, such as uploading photos of tidepool species to help track population changes, are playing a vital role. Researchers are studying the genomes of resilient sea stars to understand their survival mechanisms. A major collaborative effort is underway to breed sunflower sea stars in captivity for eventual reintroduction into the wild. This collective effort, involving diverse institutions and expertise, offers a beacon of optimism.
The initial feeling of loss gave way to a sense of community and present-day wonder as I witnessed Johnson share her passion with others, connecting people to the beauty of this vibrant ecosystem. The tidepools, while facing challenges, are still brimming with life and magic. The work to protect them continues, driven by a blend of scientific understanding, community involvement, and a deep-seated love for the natural world. The future remains uncertain, but the present is a testament to the resilience of nature and the dedication of those striving to safeguard it.
