Nightpooling

Hawaii has a relatively small tide range compared to the west coast of the US mainland. For example, the spring tide range is less than a meter at Hanalei Bay on the north shore of Kauai. That is much smaller than I am accustomed to in California or the Pacific Northwest where daily fluctuations of the tide can be several meters. However, even with a reduced range, low tide in Hawaii can help reveal interesting intertidal biota on both more wave swept and calmer shores.

Anahola Bay, Kauai with the moon over the horizon.

At the southeast corner of Anahola Bay on the northeast coastline of Kauai, there was significant shelter from the wind that blew in heavy tropical air over most of this coastal enclave during our visit last November. I was exploring the rocks in this calm near sunset and noticed that I had conveniently stumbled upon low tide. As the sun would soon set, I returned to the beach cabin for lights before heading back out to the intertidal. Thus was born my temporary rediscovery of night tidepooling, which I had done only intermittently over the years.

With low tides creeping later with each passing day, I returned to the same corner of Anahola Bay the next evening with the crew. We ambled along the edge of a relatively narrow intertidal of basalt rock inshore of a wide flat reef that was still under some water. Photography in the dark was a new challenge, but not impossible. I held the waterproof camera in one hand, and worked with a headlamp in the other to illuminate organisms from the side where the light would not reflect off the water surface right into the camera.

Our headlamps and lights had a limited reach in the night sky, so my observing eye necessarily focused on organisms immediately in sight. Night brought a sense of being enveloped, like thick coastal fog, where everything beyond the short distance of what was visible would remain a mystery.

Spiny, striped sea cucumber.

Invertebrates and algae on the dark boulders were easiest to observe. Crabs, and large spiny sea cucumbers (echinoderms of the Class Holothuroidea) were common here. I found creeping mats of the green alga Caulerpa and red seaweeds. Much easier to observe during the day, I did see some fish as well. A few brightly colored species swam in the shallows, and in somewhat deeper water offshore, where little light could reach, I observed a few elusive dark, elongated forms. These lurkers may have been large eels.

The lights illuminated tiny dots among the rocks too – the eyes of little shrimp common in the intertidal, shining electric specks.

Night pooling along much of the California or Oregon coastline would probably be rather hazardous at night, especially where large waves frequently crash into the shoreline. But the calm tropics seem particularly well suited for this adventure, and I’ll have to remember this on my next trip to Hawaii!