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To: Bluedot Living
From: Town of Nantucket: Natural Resources Department
Subject: How Long-Term Benthic Dive Surveys Keep Us Informed
The sun has just risen; the tide has finally gone slack; anticipation builds among the crew. Divers check their air and ensure their dive weights, compass, transect tapes, rebar, quadrats, underwater clipboards, measuring tapes, bonus pencils, and collection bags are securely fastened to their wetsuit-cladded bodies. The pair of divers do a final runthrough of the survey methods before they roll off the gunnel with their slew of gear into the frigid fall waters of Nantucket Harbor.
It is dive survey season for the hatchery team at the Town of Nantucket’s Natural Resources Department (NRD) and they are about to begin one of the most important surveys for Nantucket’s marine ecosystem.
Nantucket Island has changed rapidly over the last few decades. When the bay scallop industry began to collapse in the late 1980’s, there was no monitoring occurring underwater; the only information came from what was coming out of the water in the form of harvests. And from 1930 to 1990, most people assumed that a majority of Nantucket’s eelgrass was lost from “wasting disease.” However, since the first attempt at eelgrass mapping was not even done until 1995 (and it was just an aerial survey), there was no true quantitative evidence about how much eelgrass the Island used to have, and how much could have been lost.
If a long-term benthic dive survey had existed, degradation could have been observed, and intervention could have been put in place sooner for both bay scallops and eelgrass.
So, What Is a Benthic Dive?
Divers go down to gather data on benthic habitat structure (benthic refers to the seabed) such as eelgrass and macroalgae coverage, as well as bay scallop, knobbed whelk, and channeled whelk size and distribution.
Long-term monitoring and documentation of environmental shifts, and subsequent understanding of what is causing these shifts, provide crucial information to stakeholders (scientists, fishermen, concerned citizens) that can be used to make meaningful decisions regarding temporary site closures, fishery extensions, harvest increases, stock enhancement, future habitat restoration initiatives, and Town management plans, such as the Eelgrass Management Plan (2025). The Town, through years of monitoring data, can now evaluate the effectiveness of past plan action items, like those in the Shellfish Management Plan (2012). Ultimately, the long-term annual survey that takes place on Nantucket has allowed stakeholders to be aware of the volatility of key marine resources in an ecosystem that experiences increasing pressure from a variety of factors. They can make informed decisions as they observe real-time changes in local marine resources and implement action items capable of protecting, restoring, and improving resiliency for future generations to be able to enjoy.
So, Whose Idea Was This?
Between 2006 and 2014, Dr. Peter Boyce and Dr. Robert Kennedy of the Maria Mitchell Association did benthic dive surveys (with the help of Dr. Valerie Hall and Forest Kennedy) that form a foundation for the Town of Nantucket’s current dive surveys.
In 2019, Dr. Stephen Heck (a former NRD intern and diver for the original surveys) came back to the island to help revamp the surveys in a pilot program funded by the Great Harbor Yacht Club Foundation, with guidance and assistance from NRD divers and resource managers. Dr. Bradley Peterson and Dr. Stephen Tettlebach provided advisory and diving help. After 39 dives and massive success, the Town took over funding for the surveys in 2020. Dr. Heck continues to dive at every site with an NRD diver and processes all the data, generating a detailed report that compiles highlights of major ecosystem shifts and trends over the years; his participation has helped standardize surveys and furnish reliable long-term data.
As of 2024, the Town survey series expanded to encompass Madaket Harbor and Tuckernuck Island. This will provide information in two regions that have not been surveyed before, which will help us understand habitat and resource differences throughout municipal waters. Also in the last two years, the town has done a spring dive series with a subset of Nantucket Harbor site locations. This series focuses purely on bay scallop size, class, and distribution. This will provide important fishery and resource management data and insights into over-winter mortality as well as how the scallop population moves between survey intervals.
To learn more about the detailed results and methodology of the benthic dive surveys, see the 2024 ecological monitoring report here.
