Monitoring at MacMillan Wharf, Provincetown, MA

Monitoring at MacMillan Wharf, Provincetown, MA
Marine Invasive Species (MIS) Monitoring at MacMillan Wharf, Provincetown, MA.

Sunday, June 30, 2013

Coast Watch - 2013

Expectations for the Season

It's another monitoring season and plans are underway for assessing marine invasive species in Provincetown and Wellfleet this year. Looking back at the findings from the last two years raises somes questions about this year's marine growth.  Each Spring, the sides of docks usually have areas of clean substrate that are available for settlement.  Both invasive and native species compete for these sites.  

Ascidians are one of the most competitive groups of species that attach to the docks.  In the Gulf of Maine, the colonial species Diplosoma, Didemnum, Botryllus, and Botrylloides, and the solitary ascidians Styela, Ascidiella, Ciona, and Molgula complete with other groups such as mussels, bryozoa, and algae. Last year, Diplosoma was a major colonizing ascidian of clean substrates, co-colonizing with Botryllus and Botrylloides on the sides of docks below the water line.  Ascidiella has not yet established a foothold in Provincetown, although it is common in other parts of the Gulf of Maine (  In contrast, Molgula which occupies a similar ecological niche to Ascidiella, is common and may have a competitive edge in settlement due to the large number of individuals producing larvae.

It will be interesting to see whether two MIS crustaceans make an appearance and, if so, how abundant they will be.  Caprella mutica was not recorded in Provincetown last year although it was abundant in 2010 and early 2011, and a few Palaemon elegans were seen for the first time in Provincetown during the summer of 2012 living among schools of Palaemonetes pugio.

I find that a visit to the docks is always enhanced by searching for hanging ropes, submerged boating gear, buoys, or improvised objects such as automobile tires that may be attached to the sides of docks.  Ropes hanging from the docks usually show variation in algae and invertebrate species distribution with depth due to light and temperature factors.  Juvenile green and Asian crabs, usually around the size of a dime or nickel, are typically seen during monitoring sessions crawling over species on the docks, on ropes, or living in the protection of attached structures on the dock. The photos below show a few examples of previous years findings.
Public Docks at MacMillan Wharf 
The main docks rest on large concrete-covered styrofoam floats whereas most of the side docks rest on modular commercial floats composed of expanded polystyrene cores enclosed by a black polyethylene shell. 
Codium Green Algae and Colonial Asicidians on a Hanging Rope
Part of a light weight rope that looped from one dock to another.  Near the water line, Codium covered a short strand of rope tied to a dock.  Orange Botrylloides violaceus covered another section of the rope that was hanging deeper in the water.  A few small specimens of Ulva sea lettuce can also be seen along the rope.  

Small Mytilus edulis Mussels on a Nautical Rope 
Mussels are another species that colonizes docks and ropes near the waterline.  When larvae settle at the same time, a cohort of uniformly sized mussels is formed.
Heavy Colonization of a Hanging Rope by Colonial and Solitary Ascidians
Didemnum, Botryllus, Botrylloides, Molgula, and other invertebrates grow over each other and entangle eel grass and other debris to form large masses on a hanging rope.
Spider Crabs Visit the Main Dock of MacMillan Wharf
Two young Libinia emarginata spider crabs were found hanging out together in a protected area under the dock.  One individual had a small colony of Botrylloides violaceus growing on its back.  This was a rare treat because green and Asian crabs are usually the only crab species that are seen on the docks.