story and photos by carlotta gessler.

the edge of the sea is not a clear edge: with each tide the ocean encroaches onto the land and then six hours later retreats, exposing the wet land back to the air. there is never stillness in this place of transition and constant motion. and yet within the change from rise to fall, from dry to wet, this water’s edge finds itself in rhythmic balance.

before rachel carson became famous for her writing about pesticides, she focused on marine ecology, particularly the seashore. in her book “the edge of the sea” she wrote, “all of the life of the shore — past and present — by the very fact of its existence, gives evidence that it has successfully dealt with the realities of this world.”

looking at the mysterious world of tidepools makes me believe she is right. intertidal creatures have endured changing chemical conditions and the constant erosive force of the waves. they have dealt with wide shifts in temperature. they alternate between floating and being stranded. to live at the shore, these creatures have mastered the art of adaptation. how did they become both water and land?

the periwinkle can draw itself into its shell to keep moisture inside during low tide. when submerged in water it moves around and feeds algae from its rocky home, as it is described by the national park service.

striped shore crabs create bubbles to wet their gills to breathe air during low tide, according to the haystack rock awareness program. when the tide rises, the crabs hunt other small animals or feed on seaweed. their activity can be correlated to the precise time of local high tide, as reported in the journal of interdisciplinary cycle research.

rockweed holds tight on the rocks. i learned from reading “between pacific tides” that, when the tide is low, this alga can fully dehydrate and then restore its abilities once it is submerged again.

aggregating anemones live in tidepools, crevices that hold sea water even during low tide. the monterey bay aquarium in monterey, california, shares that aggregating anemones can pull their tentacles in to retain moisture. their sticky skin becomes covered in tiny particles, sprinkles of shell debris and sand that give them even better protection from the sun. 

by studying monterey’s tidepools i learned how these creatures live with water, not against it. the tides shape their daily interactions. where they move. when they feed. how they breathe. they think with the tides.

like the tidepools in monterey, providence, rhode island, is also exposed to the tides. the city lies at the northern reach of narragansett bay, where three rivers come together and salt and fresh water mingle. although providence is surrounded by water, its shoreline is defined by sidewalks, roads, bridges, and buildings. the city responds to water with hard infrastructure rather than acknowledging its fluid, ever-changing nature.

the tidal changes are barely noticeable in the city, only a faint dark line along the river’s wall marks the height of the last high tide. right now the tidal rhythm does not impact the rhythm of life in providence. on most days, people can move through the city without paying attention to the tides. however, looking at sea level projections, tides could be impactful in the near future.

particularly high tides, so called king tides, can give a preview of what daily tides might look like in the future. by looking at king tides today, planners can estimate which places are going to be most impacted by rising sea levels. that’s why the mycoast organization encourages people living in cities along the u.s. east coast to capture photos of king tide impacts. on the mycoast website people have uploaded photos of flooded parking lots, walkways and parks.

as i walk along providence’s shorelines during a king tide i am reminded of the periwinkle. it would love these high water levels and become active right now. however, for me and other people, water on sidewalks and roads presents more of a threat. in recent years, it has become increasingly clear that water is one of the most powerful threats posed by climate change, for both cities and people alike.

after decades of being paved over, providence’s rivers and shorelines have only recently been uncovered again. for a long time the city has adapted water for its uses, removed wetlands and fueled its industry with the river’s energy. but with rising sea levels, keeping water in channeled places will become increasingly difficult. as the water overcomes our rigid barricades, providence like many other cities will find itself in the intertidal zone, presented with the decision of how to respond to the influx of water.

adaptations of cities can look similar to tidal ecosystems. to think like a tidal shore, we have to accept that certain portions of the city will be to some extent flooded. that does not have to mean that houses should be flooded or that water should be everywhere. some areas of the tidal shore are wetter and others are drier, and tidal communities are structured according to the tides.

places like people’s homes where water can become a threat, should be placed higher up where they are protected from water. houses can stand on stilts, or small walls can shield people from waves, just as rocks protect animals at the tidal shore. floodproof doors and windows, like the periwinkle, keep water out when tides rise. some buildings can be designed where the lowest floor is wet floodproof, meaning that the first floor can fill up with water without any damage. parks and green spaces can act like rockweed. creating shelter, by providing a buffer between people and elements. these green spaces can fill with water and dry without getting damaged.

thinking of coastal cities in connection to tidepools can make sea-level rise less scary, allowing us to embrace the watery conditions many coastal cities are facing. by learning from the adaptations that many tidal dwellers have developed to thrive in harsh tidal conditions, maybe we can, in our own way, become intertidal too.