Wellfleet Harbor is located on the west side of the Cape Cod Peninsula (see satellite images of Cape Cod along sidebar at right) and is home to the renown Wellfleet oysters. The town marina is located at the north end of the harbor and was built over a natural strip of land at the mouth of Duck Creek. A long permanent dock is located on the north side of the marina that I monitored during the summer of 2011 (see satellite image and photo of the marina, below). The dock rests on concrete covered polystyrene floats similar to those found in Provincetown. Virtually all the boats moor rear-first at the dock, but there is a perpendicular, seasonal dock with wood sides near or at the end of the long dock for side boat-entry. During the winter, I am told that the individual sections of the permanent dock are brought to the west end of the bay for protection against winter storms.
Wellfleet Marina North and South
The North Marina features permanent docks with concrete-covered floats for fishing and recreational boats. The South Marina features the harbormaster seasonal docks and public docks that rest on modular floats composed of polyethylene plastic shells encasing polystyrene cores.
Wellfleet Marina North Facing the Mouth of Duck Creek
Permanent docks at the mouth of Duck creek provided a substrate for settlement by Diadumene lineata. The water was turbid with sediment, ranged 70-80 degrees in temperature, and had a favorable bay salinity of 32 parts per thousand.
In comparison to the other bays studied, Wellfleet marina had a relative low diversity of species on its docks. The dominant, year-around species was the common oyster, Crassostrea virginica which covered the intertidal rip rap and grew to mature size on the underside of the dock floats. The sides of the permanent docks also had a few mussels and empty shells, but not a new cohort of young oysters.
The Wellfleet oyster industry dates back prior to the Revolutionary War. In the 1700's, native oysters were harvested. During the mid 1800's, young oysters were shipped in from Chesapeake Bay and grown to maturity in Wellfleet Bay. During the late 1800 and 1900's, aquaculture techniques were developed, and today the bay is home to a thriving oyster industry that celebrates each fall with its Wellfleet OysterFest. The shallow bay that is so favorable to oyster beds is also probably one of the features that make it a favorable environment for the orange-striped anemone, Diadumene lineata (also listed as Haliplanella lineata).
Diadumene lineata - the orange striped anemone
Diadumene lineata is a small anemone about 3 cm in diameter, with a smooth, brown or green-gray body, with or without vertical orange stripes. The crown is topped with 50-100 slender, tapered, fully retractile tentacles that are transparent, pale yellow, beige, or light green. It is native to northeastern Asia but has spread around the world to temperate climates in both the northern and southern hemispheres. It is commonly found on pilings or floating docks of protected shallow waters such as harbors and is often associated with mussels or oysters. It is extremely tolerant to extremes in temperature, salinity, and water quality. This tolerance probably explains its distribution in Wellfleet in an area that is generally unpopulated by other attached and encrusting species.
Diadumene lineata - Portrait by Underwater Photography
A view of Diadumene as seen in the literature. This image by R. Manuel is from A Guide to Invasive Marine Species of Hawaii by Eldredge and Smith, 2001.
Within my monitoring areas in the Gulf of Maine, Wellfleet was the only site where we saw Diadumene, and within the Wellfleet Marina, it was most common along the long permanent dock in the north, protected bay. The permanent docks of Wellfleet Marina are dominated by oysters, in contrast to Provincetown Marina or Salem Sound where the mussel Mytilus edulis is the common bivalve. Diadumene is relatively inconspicuous to the eye but can been seen growing at moderate density in social groups on the vertical dock surfaces and on oyster shells.
Diadumene lineata Growing on Oyster Shell
Individuals were photographed shortly after collection (9/1/2011). Most individuals were fully open, but one is closed at the bottom center revealing the orange stripes.
Under the stereomicroscope, Diadumene took on a new look. The light colored tentacles had a luminescent glow, and with menthol anesthesia, the tentacles moved around in slow motion. The anemones were partially immobilized, and the tentacles appeared shorter and more stout (compare the length of the tentacles of the anemones below to the ones in the photo above). Two color variants were seen, a majority with light yellow tentacles and a less frequent variant with light brown tentacles.
Diadumene lineata Growing on an Oyster Shell
Diadumene lineata viewed with a stereomicroscope using fiber optic lighting.
The specimens were collected in July 2011 and anesthetized with menthol crystals.
The light colored tentacles had a luminescent glow. 2X zoom x 10X objective.
Diadumene lineata with Brown Translucent Tentacles
Diadumene lineata with Brown Translucent Tentacles
Diadumene lineata viewed from above showing the mouth and orange stripes. This individual was also anesthetized with menthol crystals. 2X zoom x 10X objective.
Color Variants of Diadumene lineata
The two color variants of Diadumene lineata detached from the substrate
after menthol relaxation. 1.5X zoom x 10X objective.
View of the Mouth of Diadumene lineata
Beige colored mouth surrounded by rings of brown tentacles
(above mouth, a small piece of adhering debris). 4X zoom x 10X objective.
Distribution of Diadumene in New England marinas (RI to Maine):
Pappal, A, Pederson, J, and Smith, JP. Marine Invaders in the Northeast. Rapid Assessment Survey of non-native and native marine species of floating dock communities. 7/25/2010 - 7/31/2010
Special thanks to Adrienne Pappal and Niels Hobbs for confirming the species identification of Diadumene from sterezoom micrographs.
Links providing further information on Diadumene lineata:
References on the history of Wellfleet:
1. Wright, D.B. The Famous Beds of Wellfleet. A Shellfishing History.The Wellfleet Historical Society, 153 pp., 2009.
2. Lombard, D. Wellfleet, A Cape Cod Village. Arcadia Publishing, 128 pp., 2000.
