Drifting mats of red algae

Yesterday MarineFisheries biologists were diving in Salem Sound near Pride's Beach in Beverly when we encountered large mats of the reddish brown algae that I think is Heterosiphonia japonica.  http://www.seaweed.ie/descriptions/Heterosiphonia_japonica.html.  This is the first we have seen it here to this extent.  In April at a site nearby we noted small amounts of it driftying through the grass bed, although it was piling up on the beach.  So yesterday we were surprised to see such an accumulation  (see pictures below).  The change from April to May may be due to the progression of the season and more algae growth, or it could simply have been a different current and wind direction blowing the algae into the bed that day, or a combination of the two.  Whatever the reason, this could definitely have a significant impact on the bed by blanketing shoots and shading them.  It will be interesting to see if the algae is there when we return to the site in the next few weeks.  We also have three transects that we monitor for SeagrassNet in this area and our next monitoring event is in July.  This highlights the reason why we need long term monitoring like SeagrassNet sites.  If there is an impact on the eelgrass bed we will hopefully be able to document it early.