Eelgrass Distribution and Biomass in the Great Bay Estuary for 2015

See also: Eelgrass/Macroalgae Discussion Primer for TAC Activities 2016-2017 http://scholars.unh.edu/prep/355 Eelgrass (Zostera marina L.) is an essential habitat for the Great Bay Estuary (GBE) because it is the basis of an estuarine food web that supports many of the recreationally, commercially and ecologically important species in the estuary and beyond. Eelgrass provides food for ducks, geese and swans, as well as food, nursery habitat, and shelter for juvenile fish and shellfish. Eelgrass filters estuarine waters and improves water clarity, removing both nutrients and suspended sediments from the water column; its roots and rhizomes bind and hold sediments in place, thereby reducing turbidity. Historically, eelgrass has been the primary habitat in the Great Bay Estuary, for many decades covering the most area of any of the three major habitats: eelgrass, salt marsh, and mud flat. Eelgrass in the Great Bay Estuary is a vital resource to the State of New Hampshire’s marine environment, and eelgrass habitat is essential to the health of the estuary (Trowbridge 2006, Short 2014). The report was written for the Piscataqua Region Estuaries Partnership (PREP), and covers the entire Great Bay Estuary, from the Atlantic Coast to the Great Bay, and including the estuarine portions of the tributaries

SeagrassNet Monitoring in Great Bay, New Hampshire, 2015

SeagrassNet is a global monitoring program begun in 2001 and designed to scientifically detect and document seagrass habitat change (Short et al. 2006a, 2014). Monitoring of eelgrass (Zostera marina L.) in the Great Bay Estuary using SeagrassNet was conducted in Portsmouth Harbor between 2001 and 2009 (Short et al. 2006b, Rivers and Short 2007), and in Great Bay starting in 2007 (Short 2009). Results from SeagrassNet 2015, supported by PREP and conducted in Great Bay, are described in this report

Eelgrass Distribution in the Great Bay Estuary for 2012

Eelgrass in the Great Bay Estuary declined in both distribution and biomass between 2011 and 2012, continuing the long-term trend of eelgrass loss. In 2012, eelgrass was once again mainly present in the Great Bay itself with limited distribution in Portsmouth Harbor and Little Bay. Eelgrass distribution in Great Bay decreased 1.5% between 2011 and 2012 with no change in biomass. In Great Bay,eelgrass distribution has declined 36% since 1996 and biomass is a quarter of what it was in the early 1990s. Nuisance macroalgae in Great Bay continued to proliferate in 2012 and to impact eelgrass by smothering eelgrass shoots and reducing shoot density. In the Piscataqua River, a new, small bed of eelgrass was present in 2012. The eelgrass bed in Little Bay that first appeared in 2010 retracted by 28% between 2011 and 2012 and had very low percent cover in 2012. In 2012, no significant change in eelgrass distribution or biomass was seen in the Portsmouth Harbor and Little Harbor area of the estuary. Overall, eelgrass distribution in the Estuary from 2011 to 2012 decreased 3.9%. The long-term trend of eelgrass decline in the Great Bay Estuary continued in 2012, with a loss of eelgrass distribution of 37% estuary-wide since 1996

Eelgrass Distribution in the Great Bay Estuary for 2009 : Final Report

Eelgrass in the Great Bay Estuary in 2009 was once again present only in Great Bay itself and in Portsmouth Harbor. For the second year in a row, there was no eelgrass in Little Bay or in the Piscataqua River. In 2009, there was a continued loss of eelgrass biomass in Great Bay; there has been a 66.4% loss of biomass in Great Bay since 1996 and distribution is 30% less than in 1996. Although eelgrass distribution in Great Bay itself increased between 2008 and 2009, primarily due to continued expansion from natural seeding of bare areas, the Bay’s eelgrass biomass continued to decline as a result of decreases in plant density in existing beds. Nuisance macroalgae in Great Bay continued to proliferate and impact eelgrass by smothering eelgrass shoots and reducing shoot density. In 2009, Portsmouth Harbor experienced a 16% loss of eelgrass distribution since 2008, for a loss of 31% of the Harbor’s eelgrass distribution in the past three years, an alarming trend. Although the number of acres of eelgrass has increased, driven by gains in Great Bay, even with these areal gains, biomass is down for the Bay itself and the trends of loss in Portsmouth Harbor of both eelgrass distribution and percent cover continue. Despite the increase in eelgrass distribution in Great Bay Estuary due to the increased seed recruitment in Great Bay, the loss of percent cover and biomass in Great Bay and in Portsmouth Harbor again this year (2008 – 2009) indicate the continuing adverse water quality conditions in the Estuary

Eelgrass Distribution in the Great Bay Estuary 2002

Eelgrass (Zostera marina) is an essential habitat for the Great Bay Estuary (GBE) because it provides food for wintering waterfowl and habitat for juvenile fish. Eelgrass is the basis of an estuarine food chain that supports many of the recreational, commercial and ecologically important species in the estuary. Additionally, eelgrass filters estuarine waters, removing both nutrients and suspended sediments from the water column. Eelgrass in the Great Bay Estuary is the largest monoculture in the State of New Hampshire and is considered a vital resource to the State’s marine environment. The UNH Seagrass Ecology Group has mapped the distribution of eelgrass in Great Bay every year from 1986 to 2001 (Short, unpublished data). Eelgrass in the entire Great Bay Estuary system (Great Bay, Little Bay, tidal tributaries, Piscataqua River, and Portsmouth Harbor) was mapped in 1996, 1999, 2000, and 2001. Eelgrass cover in Great Bay has been relatively constant for the past 10 years at approximately 2,000 acres. Earlier, in 1989, there was a dramatic decline in eelgrass beds to only 300 acres (15% of normal levels). The cause of this crash was an outbreak of a slime mold Labryrinthula zosterae, commonly called “wasting disease”. Recently, the greatest extent of eelgrass in the GBE was observed in 1996. In 2002, the NH Estuaries Project provided financial support to the University of New Hampshire to digitize eelgrass distribution information in Great Bay Estuary for the years 1999-2001. That project was completed and those historic eelgrass coverages are now in the NHEP database. In 2003, the NHEP committed to support the annual monitoring program for eelgrass starting with aerial photography of eelgrass coverage for 2003 and mapping of eelgrass distribution from information gathered in 2002. The present report presents eelgrass distribution information for 2002

Eelgrass Distribution in the Great Bay Estuary for 2006

Eelgrass in Great Bay itself decreased substantially (43%) between 2005 and 2006, due to losses in both biomass and distribution. Little Bay and the Piscataqua River showed greater change(loss of 40%) between 2005 and 2006 than previously, with very low levels of eelgrass compared to historical distributions and the large beds of ruppia in the Bellamy, Oyster and upper Piscataqua Rivers also diminished. The Portsmouth Harbor – Little Harbor area experienced a decrease in eelgrass abundance (14%) between 2005 and 2006. All of the Great Bay Estuary has decreased eelgrass beds compared to historic distributions. In the decade from 1996 to 2006, the Great Bay Estuary has lost almost half its eelgrass

Eelgrass Distribution in the Great Bay Estuary for 2011

Eelgrass in the Great Bay Estuary declined in both distribution and biomass between 2010 and 2011. In 2011, eelgrass was once again mainly present in the Great Bay itself with limited distribution in Portsmouth Harbor and Little Bay. Eelgrass distribution in Great Bay itself decreased between 2010 and 2011 and experienced an alarming 26% loss of biomass in a single year. In Great Bay itself there has been a loss of 35% of eelgrass distribution since 1996. In 2011, despite recent consecutive excellent growing years in terms of weather, we saw a reverse of the trend of slight increases in 2009 and 2010. Nuisance macroalgae in Great Bay continued to proliferate in 2011 and impact eelgrass by smothering eelgrass shoots and reducing shoot density. For the fourth year in a row in the Piscataqua River, there was virtually no eelgrass. The eelgrass bed in Little Bay that first appeared in 2010 expanded greatly. Portsmouth Harbor also showed increased eelgrass distribution in the outer harbor. Overall, eelgrass distribution in Great Bay Estuary from 2010 to 2011 decreased 0.3%. There has been a 35% overall loss of eelgrass distribution in the Estuary since 1996. The 2011 gains seen in Portsmouth Harbor and Little Bay were largely a result of the plant reproductive response to stress and a good growing season, but could not compensate for overall losses, which created a downward trend. The long-term trend of eelgrass decline in the Great Bay Estuary continued in 2011

Eelgrass Mapping Great Bay Estuary for 1981

The methods for this project followed the procedures specified in the approved QA Project Plan (Short and Trowbridge, 2003). Eelgrass meadow polygons for 1981 were mapped from USDA black-and-white aerial photographs, on file at the Strafford County and Rockingham County (NH) offices. The photographs were scanned and analyzed digitally after “rubber sheeting” the images to fit the Great Bay Estuary base map. The 1981 photographs were not ortho-photographs and some distortion across each photograph was evident. To minimize this effect, multiple photographs for each area were used to geo-reference actual locations on the eelgrass distribution map. Some areas of the estuary did not have adequate 1981 images to allow mapping; these areas are marked in red on the map (Figure 1). Ground truth verification of distribution was done by comparison to eelgrass mapping done by NH Fish and Game (Nelson, 1981). Eelgrass cover classes were determined using the standard protocol (Short and Trowbridge, 2003) with the added limitations of black-and-white photograph

Eelgrass Distribution in the Great Bay Estuary 2003

In 2004, the NHEP funded annual monitoring for eelgrass in GBE. We collected aerial photography of eelgrass coverage for 2004 and mapped eelgrass distribution for 2003 from the information gathered the previous year. The present report presents the eelgrass distribution information for 2003