Benthic Clam Survey - Salem Sound Coastwatch

Upper Mill River, Gloucester
Clam Survey

Thanks to all the 2009 volunteers who helped with the clam survey. We did it in two days!

PowerPoint PDF (2.6MB) for the
Upper Mill River Clam Study 2008 & 2009

To see photos from the 2008 sampling

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Salem Sound Coastwatch is conducting a benthic survey to monitor change in the Mill River inter-tidal zone (formerly an impoundment) after the installation of the new tidegate. The mudflat was sampled in October 2008, September 2009 and will be monitored again in the fall of 2010. The restoration and associated monitoring of the Gloucester Upper Mill River (once Mill Pond) is supported by technical and financial assistance from the Massachusetts Wetlands Restoration Program, the NOAA Restoration Center/ Restore America's Estuaries partnership, and The Massachusetts Corporate Wetlands Restoration Partnership (CWR) (from Bruce J. Anderson Foundation and Metcalf Eddy, Inc).

As part of the Bruce J. Anderson grant, SSCW conducted educational activities with the O'Maley sixth graders in May 2009.

Maps of the Study Site

2008 & 2009 Summary of Findings:

1. Two years of benthic shellfish and worm sampling in the upper Mill River since tidal flow restoration found a return of benthic marine species.

2. Soft-shell clams immediately recolonized the newly exposed mudflats in 2004.

By aging the Mya arenaria (soft-shell clams), it is apparent that colonization occurred as soon as the tide gate was opened in 2004. From her study of M. arenaria in Gloucester, Brousseau (1978) established a life table (see report, Appendix 6).

In 2008, 15 soft-shell clams were found. Seven were 3 to 4 years in age; five clams were in the two-year class range and one within the under one-year class.

In 2009, 29 soft-shell clams were counted. We found more young of the year (YOY) and older clams as well, one even 7 years old!

3. Macoma balthica (duck clam) are currently the dominant species.

A species of small saltwater clam in the family Tellinidae, M. balthica lives in muddy bays and is quite tolerant of low levels of salinity. its shell color normally varies between pink, purple, yellow, and white, but the Mill River specimens had blackened shells from sulphide-rich sediments (Budd 2001). Also, important to note is the fact that M. balthica are not filter feeders. They live a few centimeters below the surface and are deposit feeders. Their long inhalent siphons sweep over the mud, like vacuum cleaners. The tidal restriction and muddy conditions of upper Mill River provide the ideal habitat for Macoma balthica.

4. Initial findings are encouraging. However, community recovery in restored estuarine ecosystems is largely dependent on the level of tidal exchange. Estuarine structure and function return relatively quickly when tidal flow is unrestricted. Sites with only partial tidal exchange may never fully recover without additional modification of the hydrologic regime (Thelen 2007; Burdick et al. 1997). It appears that the levels of salinity at the mudflat are affecting the density and location of saline sensitive marine species, such as Mya arenaria.

To read more,
2009 Benthic Survey Report

Wicked Local.com article 2009:
Volunteers find signs of ecological recovery at Gloucester's Mill Pond

2008 Benthic Survey Report

To see photos from 2008 sampling

Gloucester Times article 2008:
New life in the old Mill Pond

Cape Ann Beacon article 2008:
Restoration brings clams back to Mill Pond in Riverdale

Mya arenaria and Macoma balthica

Clam worm