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Earthwatch 1: Counting crowberry

This summer we finally got to take a trip that had originally been scheduled for 2020. It was an Earthwatch expedition to Acadia National Park in Maine. It was also the first time I'd traveled outside the Pacific time zone, flown, and taken public transit since the COVID-19 pandemic began. All of those were stressful. I get that people are "over" the pandemic and tired of taking precautions, but seriously? During our travels before and after the expedition we saw very few other people wearing masks, despite being packed into subway cars, stations, and restaurants. We avoided indoor attractions and spent our time walking around outside.

Cloudy sky over shoreline with water and a cobble beach. Coniferous trees in the background.
Shoreline of Schoodic Peninsula in Acadia National Park, ME
© Allison J. Gong

This particular Earthwatch expedition is all about climate change. During the week we participated in three different, but related, research projects in the park, mostly on the Schoodic Peninsula. The first was called Refugia. At first I couldn't tell if that was a place name, a project title, or something else. Turns out that it refers to the actual project. The target of this project is a plant called black crowberry, Empetrum nigrum. Black crowberry is a low-growing tundra plant, living near its southern limit at Acadia. This is possible because the Schoodic Peninsula juts down into the Gulf of Maine, a region where cold water from the Arctic—specifically, the Labrador Current—meets warm water from the Gulf Stream. Thus, the Schoodic Peninsula may be indeed be a climate refuge for E. nigrum.

Map showing New England coast and the Gulf of Maine. The Schoodic Peninsula is labelled.

The Gulf of Maine, however, seems to be warming more quickly than other ocean regions, possibly due to northward extensions of the Gulf Stream1. As a result, plants such as E. nigrum may be a bellwether for how the ecology of Acadia will be affected by climate change.

The Refugia study examines abundance of E. nigrum along the coast of Acadia, as well as phenology of flowering and fruiting. Our Earthwatch group sampled at Schoodic Point and Little Moose Island, which is an actual island only at high tide. We were in Acadia during the mid-June spring tide series, which is always one of the most extreme of the year, so Little Moose Island was easily accessible for several hours.

The study itself involved setting up two perpendicular transects and collecting several sets of data:

  • Geographic data—GPS location and direction
  • Photos for iNaturalist
  • Presence/absence of E. nigrum at 10 cm intervals
  • Presence/absence of flowers and fruits
  • Visual estimation of the percent of E. nigrum that is alive vs. dead

We worked in teams of four, with each pair setting up and evaluating one of the transects.

Here's how E. nigrum appears in its natural habitat:

Sloping rocks in foreground and conifers in background. In the midground, a carpet of red-and-green low-lying plants.
Coastline of Schoodic Peninsula in Acadia National Park
© Allison J. Gong

The crowberry is the red-and-green plant growing low among the rocks. Like all tundra plants, E. nigrum grows low to the ground and doesn't get more than about 15 cm tall. We were told that the red bits were the parts that died back over the winter, and the green was the new spring growth.

Here's a close-up look at the carpet of crowberry:

Carpet of red-and-green low-lying plant on a rocky slope
Black crowberry (Empetrum nigrum) on the Schoodic Peninsula in Acadia National Park
© Allison J. Gong

We found E. nigrum mostly in open areas, but also occasionally in the spruce forest where there is much less light at ground level. It seemed not to require much soil, and was often found tucked between rocks on the coast above the high tide line.

Black crowberry fruits are small berries, green when unripe and ripening to a blackish purple. The fruits we saw, ripe and unripe, ranged in size from 2 to 8 mm. We were told that they were unpalatable even when ripe.

Plant with short stubby leaves and cluster of small green and larger purplish berries
Cluster of black crowberry (Empetrum nigrum) ripe and unripe fruits
© Allison J. Gong

The protocol had us setting up a 5-meter transect parallel to the coast, where we saw a patch of E. nigrum, and then a second 5-meter transect perpendicular to the first at its midpoint. The result is a big plus sign draped over or through whatever terrain happened to be there. We had to do quite a bit of climbing up and down rocks and pushing through bushes. If this were in California we'd have to worry about poison oak. Fortunately, they don't have poison oak in Maine, and there was no poison ivy at any of our study sites.

Four people wearing yellow high-visibility vests, standing on a rocky landscape with conifer foliage. Two long yellow measuring tapes lie on the ground and cross at their midpoints.
Transects for black crowberry (Empetrum nigrum) at Schoodic Point, by team members (left to right): Alex, Karin, Sally, and Mara
© Allison J. Gong

To give you an idea of crowberry habitat, here's some wider context:

Transect pair at Schoodic Point
© Allison J. Gong

The last part of the protocol was to estimate the percent of E. nigrum that was alive, in a 1-meter belt that straddles each of the transect lines. This is one of those qualitative evaluations that at first would seem to be all over the place, depending on the observer. However, the study takes into account any variation resulting from data collectors' individual estimates by pooling the percentages into bins. So instead of having to agree that 22% of the crowberry in a certain belt transect is alive, we only had to agree on a bin of, say, 20-30%. To give you an example, here's a photo of a patch of crowberry:

Black crowberry (Empetrum nigrum) at Acadia National Park
© Allison J. Gong

What percentage of this crowberry is alive, in your estimation?

I should mention that we had this glorious sunny weather on only one day that we worked on the Refugia project. The first day it was raining, which was fine because we all had brought rain gear with us. But the rain made it difficult to work with the tablets on which we were recording data. The wet screens didn't want to register our finger taps, but would instead register rain drops as touches. That was incredibly frustrating. We persisted and managed.

Over the summer several other groups of Earthwatch volunteers will collect additional data for the project. I think we set a pretty high standard for the sheer number of transect pairs we completed. I liked working on this project because I got to learn about the ecology of a plant that had been entirely unknown to me. That's always fun!

1Seidov, Dan, et al. 2021. "Recent warming and decadal variability of Gulf of Maine and Slope Water." Limnology and Oceanography Vol. 66: 3472-3488.

2 thoughts on “Earthwatch 1: Counting crowberry

  1. SarahWang

    Glad you had fun, Allison, thanks for sharing the Earthwatch experience. Hope it felt like a vacation despite the work involved, and that you didn't catch Covid. Excited/anxious to learn the results of the survey.

  2. Mara

    WOW! Love this piece, and all the embedded photos Allison! It was so great to meet you and work together this summer.


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