A Field Day With Hannah Webber: Rockweed and the Questions of the Intertidal

The Schoodic Institute is a nonprofit science and education partner of Acadia National Park, in Maine, working with the park on environmental challenges through research and learning. Its marine ecology director, Hannah Webber, spends her field days on the park's rocky shore. This account, by the institute's Catherine Schmitt, follows her through one of them.

Questions before the water

Even on the path through the spruce woods, Webber is asking questions. Urchin, crab and mussel shells lie scattered on the moss; there is bear scat, and gulls are calling. Who left the shells, and who is eating whom? What does it mean for the forest to receive so much from the sea? What could the seasonal timing of the shells, on rocks, in the road and among the trees, reveal? And is anyone else studying it?

The rockweed study

For her doctoral research, Webber set up rockweed sampling sites the year before to measure the effects of seaweed harvesting. Of 23 sites along the Maine coast, some are controls, showing what happens naturally to rockweed over the seasons and years, and others are impact sites, watched before and after harvesting. Because Acadia is protected, the sites inside the park are all controls.

At each site, found by GPS, notes, photographs and memory, the team:

• lays out sponges and absorbent pads, later weighed to give a rough measure of how much the rockweed beds dry out, which matters to many intertidal animals;
• measures rockweed depth, and each plant's length, girth and weight, every half meter along four-meter transects running north–south and east–west, weighing with an adapted five-gallon bucket and an unreliable scale;
• photographs small squares to track barnacles, crusts of seaweed and bacteria, and grazing by limpets, periwinkles, sea stars and crabs;
• downloads loggers, small instruments at each plot's centre that record temperature, light and water movement every half hour, to a battered field laptop.

The plots teem with life: eggs of the periwinkle Littorina obtusata (Webber has seen them on both rocks and seaweed, though accounts differ, and wonders whether it varies by place), reddish bryozoan colonies at the base of the rockweed, lumpy brown algae like underwater pompoms sheltering tiny amphipods, and isopods grazing on fallen fragments. An osprey passes, a winter wren calls from the woods, gulls prowl the low-tide rocks.

Fieldwork as a way of seeing

Webber has likened fieldwork to meditation: mind and body focused on one task, data collected steadily and carefully, broken only when an interesting animal crosses the plot, a new bird calls or a seal appears. That concentration and repetition breed questions. Beyond the big one, how harvesting affects the shore, she has many small ones: How hot does a rockweed bed get at low tide? Why does some rockweed grow knobbly and frilled? What lives among the holdfasts at high tide? Does the incoming tide whip the fronds against the rocks and knock animals off, or are they too tough? What eats rockweed's reproductive cells? Why does rockweed take so many shapes?

After a few hours the work is done. Webber will sample again in the autumn and the next spring before analysing the data, and, perhaps, answering some of her many questions.

Sources

• Catherine Schmitt, Schoodic Institute, "Hannah Webber's Many Questions," National Park Service, Acadia National Park. https://www.nps.gov/articles/000/hannah-s-questions.htm
• Two photographs by the Schoodic Institute are not reproduced here.
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.