Declining density and extent of eelgrass at Salem Sound and Nahant could be due to storm damage

Hi! Back in the water again after a long winter in the office...

Nahant

So far we have been to the Nahant meadow twice this spring.  The first time in April we came to retrieve a hobo temp/light monitor and harvest for plantings in Boston Harbor outer islands. Notes from August 2012 at that site indicate that plants were tall and lush, 75% cover and approximately 80shts/m2 with many reproductive shoots.  The meadow was continuous with few open patches.  But in April, we observed a low density patchy bed with large eroded areas and other areas of deep sand waves.  Our screw anchor, installed back at the end of August 2012, was buried up to the eye. 

We were back at the Nahant eelgrass meadow last week looking for a site to establish a monitoring station.  We ran a drop camera along several transects spaced throughout the DEP mapped area.  We were surprised and disappointed to find a large portion of the area mapped by DEP in 2006 is now gone and the remaining grass is mostly patchy, similar to what we saw in April.  The southeast lobe of the bed persists, but has contracted from it's 2006 extent.  Check out the rough map below digitized from our field notes, showing the remaining meadow, and an area of patchy grass and other sections of the bed that are now only sand waves.

We plan to return with divers for a closer look to help determine what might have occurred.  From the camera view it appeared that sand waves had swept over the bed, possibly burying the grass.  This meadow has long been a lush dense meadow and one of the few remaining north of Boston of this size (in MA).  Many groups have used this bed as a reference bed and donor bed for eelgrass projects in Boston.  The green dots on the map above show the locations where we are investigating possible establishment of a new SeagrassNet, long term monitoring station.

Salem Sound

At our SeagrassNet site in Salem Sound (Misery Island, Beverly) we also found low density and evidence of erosion.  It looked like much of the sand had been washed away leaving a hard-packed clay.  There is still grass clinging to the clay, so hopefully as the season progresses it will fill back in.  I think we are seeing the effects of a late winter with several storms, including NEMO in February 2013.

Sand eroded away leaving hard-packed clay over much of the shallow side (transect A) of the meadow

SeagrassNet quadrat showing low density eelgrass and eroded areas of clay

erosion around a small eelgrass clump near transect A

Taking a biomass sample on Transect B