In 2013, the total eelgrass cover in the Great Bay Estuary was 1683.4 acres, 58% below the PREP Management Goal of 2900 acres. It is important to note that eelgrass can increase or decrease year to year and therefore annual data should be looked at in the context of a longer term data set. This data will be included in the long-term data set used for PREP’s State of Our Estuaries Reports. In general, the largest concentration of eelgrass was found in Great Bay, very little eelgrass was observed in Little Bay or the Piscataqua River above Seavey Island. In Great Bay, many of the beds were a mix of macroalgae and eelgrass particularly on the eastern side of the Bay.
Methods for this year’s monitoring efforts included high-resolution aerial imagery collected by airplane in August 2013 at the height of the eelgrass growing season, an extensive on-the-ground effort of divers and kayakers and underwater camera imagery, and photo interpretation and coverage mapping. The final report, maps and all related imagery and data is publicly available online through NH GRANIT at UNH and PREP’s website. Additionally, groundtruth videos and field sheets are available by contacting PREP.
|Phil Trowbridge clears seaweeds off the underwater camera that drags behind the groundtruthing boat|
“Understanding and monitoring eelgrass is vital to understanding the overall health of the Great Bay Estuary. Eelgrass health and populations gives great insight into the vitality of the estuary as a whole and the interactions of the ecosystem, its population relies on a variety of factors, including water quality, nutrients, sediment control, oxygen, sunlight and currents,” said Rachel Rouillard, PREP’s Director.
“Eelgrass is often called ‘the canary in the coal mine’ in terms of its ability to determine the health of an estuary, so it is critically important that we monitor and collect good data on this keystone habitat that can be used to inform good and effective decision-making regarding the Bay,” she said.
There are additional characteristics to investigate in determining the health and vigor of eelgrass habitats – the biomass (how dense and healthy the beds are), the extent of epiphytes (plants that can grow on eelgrass blades, causing it to be shaded and die off) and nuisance macroalgae that can get caught and tangled up in the beds, smothering eelgrass at the base of the plants. The partners will continue to work on gathering data to better understand these factors related to overall eelgrass health.
The high-quality aerial imagery is not only useful for determining eelgrass habitat but it will also be used to understand the extent of nuisance macroalgae, and salt marsh habitat throughout the estuary, as well as a range of other uses.
“The communities recognize and appreciate the value of the estuary and are committed to protecting and enhancing this beautiful natural resource we share. Working together on the eelgrass mapping survey is just one example of how when communities share the cost of work that is important to everyone, the task becomes feasible and affordable,” says Dean Peschel, Environmental Consultant with the City of Dover.
The partners – NHDES, EPA, PREP and the communities have committed to continued coordination and investment in ongoing monitoring of the Great Bay Estuary, all to better inform the understanding of the health of the estuary and to enable greater protections for its vitality.
“This project is an important step forward in a number of ways,” explains Ted Diers, NH Dept. of Environmental Services’ Watershed Management Bureau Administrator. “First, it demonstrates the old adage that ‘many hands make light work’ in that a variety of players made an expensive project more manageable. Second, it contributes to better scientific data on eelgrass and other keystone habitats. Finally, the results show that the eelgrass in the estuary continues on its worrisome downward trajectory,” Diers said.