A Baseline State for the Subtidal Zone of Appledore Island

This portal presents data collected during the Shoals Undergraduate Research Group (SURG) 10-Week Field Internship on Fisheries Management in the Isles of Shoals, ME. Appledore Island, 6 miles offshore from Portsmouth, NH is home to  Shoals Marine Laboratory , the oldest and largest field station of its kind with a specific emphasis on creating undergraduate research opportunities and providing access to field education. It is co-sponsored by Cornell University and the University of New Hampshire.

The Gulf of Maine is one the fastest-warming bodies of water on the planet, reportedly warming 97% faster than the rest of the Earth’s ocean ecosystems. 2022 is the second hottest year on record for the region with an annually averaged sea surface temperature of 53.66 °F. Insofar as during 2022 alone, 353 days exceeded the local threshold for marine heatwaves, we must work to better understand the impact of this climatological crisis on local habitats (GMRI, 2023). This unprecedented phenomenon is responsible for ecological turmoil that has disrupted the Gulf of Maine’s standards for biodiversity and population size for local fisheries, including the subtidal habitat along the Isles of Shoals. Appledore Island, 6 miles off the mainland coast of Portsmouth, NH, is home to Shoals Marine Laboratory (SML) which is the oldest and largest undergraduate research-oriented lab in the country. The hallmark of SML’s experiential education is the over 40-year-long database of patterns of diversity and abundance found in the Island’s intertidal zone (SML, 2018). The intertidal zone rests above the lowest low tide demarcation and below the highest high tide’s reach. The shallow subtidal zone begins where the lowest low tide recedes, all the way down to the coastal seafloor. In comparison to the rich and long-standing intertidal dataset, the shallow subtidal zone along Appledore is under-documented. Using underwater videography to repeatedly sample subtidal zones along Appledore, we can build the foundations for a long-term dataset to accompany the historical intertidal archive. The concept of a shifting baseline underscores the fact that conditions considered typical for an environment today are likely different from the typical state decades prior (Soga et al., 2018). Without a longstanding subtidal database, we lack the information needed to assess generational differences in coastal environments in the Isles of Shoals. A strong subtidal dataset can be used to establish a modern baseline as of 2023 for the state of biodiversity and abundance in the Isles of Shoals, as climate change continues to exacerbate ocean warming, acidification, and sea level rise. Over time, we will then be able to understand the full scope of the impact of climate change on this local ecosystem and project what the future holds for New England’s subtidal environments.

Key Terms: Shifting Baseline Theory, Appledore Island, Isles of Shoals, Fisheries Ecology

What is the current state of species diversity in the shallow subtidal zone of Appledore Island?

How abundant are the populations of the most common species in the shallow subtidal zone of Appledore Island?

What are the impacts of environmental factors such as depth, seafloor temperature, and exposure on species diversity and abundance? 

9 sampling sites were established in the four quadrants of Appledore Island, Maine in the Isles of Shoals. They were each revisted a total of 5 times over the course of a 5-week period from June 22- August 7, 2023. The camera drops were replicated through the use of visual geographic bearings to situate the vessel. 8 of the sampling sites are split into pairs in the same sampling site. Within each pair, there was a shallow depth treatment and a deeper water treatment. Shallow camera drops were deployed in water less than or equal to 8 meters in depth. Deep camera drops were deployed in water greater than 8 meters up to and including 16 meters in depth. Sites A and B were in the northwest quadrant, situated in between the wind turbine and a permanent red metal buoy. Sites C and D were in the northeast quadrant, settled within the cove known as “Devil's Dance Floor.” Sites E and D were in the southeast quadrant, in line with a large rubble pile and the roof of Bartels House. Sites G and H were placed within the southwest quadrant, inside of a small mooring cove just off of the leftmost private homes. Site I was assigned to Shoals Marine Lab’s mooring field and into the Great Tide Pool. Sites A, C, E, G, and I were used for shallow water deployments. Sites B, D, F, and H were used for deeper water deployments. Depth was measured using a LuckyLaker portable wireless depth finder that was trailed over the side of the inflatable boat. 

In a typical field trip, 3 PVC remote underwater videography rigs were deployed over the side of a small inflatable vessel. The AKASO EK7000 camera batteries maxed out at around 80 minutes of footage. After about 90 minutes of submerging the camera rigs, equipment was retrieved and camera memory was processed. To achieve a complete weekly sample of all 9 sites, this study had at least 3 sample days per week. This resulted in a total of 45 videos at the end of the 5-week period. Sample sites were randomly grouped into triplets by pulling 3 sites from a hat and assigning them a calendar sampling date. This was to avoid sampling the same sites in the same groups on the same dates. 

All footage was manually reviewed at 2x speed and slowed in the presence of fish or other marine life, identifying as many taxa as possible. Whenever possible, taxa were identified at a species level. Each video has metrics for the total number of species, the total number of individuals across species, and the total number of individuals in each species. Observations were also made for the type of substrate, vegetation length, percent of algal cover in camera view, and intensity of current sway. 

In order to capture a conservative and accurate estimate of population size per species, the industry standard for MAXn was utilized (Carolan 2023, Mallet 2014). This constitutes counting the maximum number of individuals in a single frame of footage. In practicality, this meant that a few frames that seemed to be relatively abundant with individuals, not necessarily the single most crowded frame, were randomly sampled. MAXn is most useful for accounting for schools of fish that are very dense by minimizing the double-counting of fish. The MAXn method works under the assumption that fish of the same species school together. Taxa that are less clearly defined in the water column were tallied into an unidentified teleost column. For example: a school of Atlantic pollock Pollachius pollachius was counted using MAXN, only including the fish that are morphologically identifiable as pollock. Teleost species were differentiated using distinct patterns and details such as lateral lines, fin shape, number of rays, and approximate size in relation to the PVC rig. Invertebrate, pinniped, and avian species were identified using skin, feather, and shell colors as well as body shape. Over the 5-week sampling period, 17 teleost, mammal, invertebrate, and avian species were identified via underwater videography in the shallow subtidal zone along Appledore Island.  

Utilizing the same underwater videography setup, three bait treatments were tested on camera. 50g Atlantic Mackerel Scomber scombrus, 50g Invasive European Green Crab Carcinus Maenas, and a 25g/25g mixture of the two baits were attached to camera rigs in bait bags. Each treatment was repeated 6 times, with random calendar assignment, at different shallow sampling sites each time (Sites A, C, E, G, I, J all ≤8 meters) around Appledore Island. Most lobster/ fish are caught within the first hour when the bait is most fresh. For context, traditional bait choices such as forage fish like the Atlantic Mackerel are overfished and expensive to source. At the same time, lobster fishermen may use up to 2 pounds of baitfish for every 1 pound of lobster landings (Donovan, 2022). To address this pressure on the bait fishery, the goal was to test how competitive alternative baits are when compared on camera to traditionally successful baits. The European Green Crab is an invasive species that is increasingly abundant and socially dominating the shallow subtidal zone, threatening endemic species like the Jonah Crab Cancer borealis. To raise awareness about invasive species threats and see if we can repurpose the Green Crab, it was included in this experiment.

The sample size yielded too few bait interactions to discern a clear pattern of competition between the different bait treatments. However, within the trial run's dataset, the mixed bait attracted the attention of fish and lobster on more occasions than the green crab bait. This suggests that the next research step could explore the minimum ratio of mackerel to filler baits, such as the Green Crab. This way we can reduce the amount of wasted baitfish and continue testing alternative bait options.

In an ideal redesign, researchers would deploy a series of lobster pots (ventless trap survey) baited with varying ratios of mackerel to alternative bait (i.e. European Green Crab). The key to this second phase experiment is to test the bait in the actual gear that fishermen use during their workday. This would create a more representative sample of how bait performs compared to the 2023 underwater camera experiment. The experiment could examine the lobster/crab landings after a traditional 4-5 night soak. Or, because the bait is most potent within the first hour of deployment, a shorter soak time could be tested to maximize data collection in a shorter experiment period. A meta-analysis could compare the two procedures of a 4-5 night soak and a 60-minute soak to see how lobster escapes impact the two haul datasets. The inclusion of underwater cameras makes the most sense for a short soak time due to limitations in battery life, as experienced in this project.

Madeleine Wenger is a senior at Cornell University majoring in archaeology and minoring in marine biology and Spanish. For more information visit  Madeleinewengerillustrations.com