Monitoring Review 2015-17

Highlights of the MacMillan Pier Visits

A few years ago during a monitoring trip to Provincetown, I took a tour of the 250 ft Pilgrim Monument (350 ft above the harbor) and climbed to the top to discover an outstanding view of the marina and harbor that gave a different perspective on the monitoring site.  The outer harbor has a deep channel 50 to 70 ft deep that curves around the west end of the Cape (Lands End), making Provincetown one of the deepest marine fishing harbors along the north Atlantic coast.  The inner harbor is formed by a 2,500 foot long stone breakwater built by the Army Corps of Engineers in the early 1970's about 835 ft off the end of the Provincetown Wharf complex. 

View of Provincetown Harbor from Pilgrim Monument

View of Provincetown Harbor and Wharf from the Pilgrim Monument.  MacMillan Pier on the left, Fisherman's Wharf on the right.  The stone breakbeakwater is seen beyond the end of the piers.  Truro is seen a few miles across the harbor in the far background.  The tip of Lands End is shown on the right.

View of MacMillan Pier from Pilgrim Monument

MacMillan Pier showing the docks, fishing vessels, and tour boats.  View from the Pilgrim Monument looking south.  On the east side (left), two floating dock complexes are closest to shore followed by two finger piers near the end of the main pier.  On the west side (right), a long row of tour boats line the pier.  The ferry terminal to Boston is located at the end of the pier on the west side (right).  

Both floating dock complexes are monitored each July and August for invasive species. The salinity and temperature are recorded and photographs are taken to document salient features.  Salinity is typically fairly high and ranged from 31 to 35 parts per thousand between 2012 and 2017.  Temperatures ranged from 22 to 27 degrees C (approximately 70 to 80 degrees F).

Measuring Salinity on the North Floating Dock

Holding a refractometer toward the light to make a reading.  Ready for monitoring with my checklist, thermometer, refractometer, camera, jeweler's loupes for magnifying, buckets, shallow pan for documentation, and small net for capturing crustaceans.

Ascidians
During the 2015-2017 summer seasons, the docks were inspected for invasive species in the MIMIC program (Coast Watch 2011, Coast Watch 2012).  The most abundant attached species were the colonial ascidians Botryllus, Botrylloides, Didemnum, and Diplosoma, and the solitary ascidian Styela.  The one exception to the general abundance of ascidians was the rare ocurence of the solitary species Ascidiella aspersa, which has been periodically seen at low frequency in Provincetown (several years only 1 specimen), but not seen in 2017.  Interestingly, the translucent solitary species Ciona intestinalis and Molgula manhattensis, cryptogenic species not included in the survey have also been observed at low frequency whereas the colonial species and the solitary Styela are common all over the marina.  Perhaps these three translucent species are out-competed and crowded out by the colonial species which spread throughout the marina in the summer.  Interestingly, Molgula manhattensis is abundant in Wellfleet marina, a location with very low species diversity and few colonial species of any kind. 

Crustaceans

The skeleton shrimp Caprella mutica and the European rock shrimp Paleomon elegans were seen with low frequency.  The skeleton shrimp prefers hydroids and algae like Ulva in the more protected waters near the pier and has been consistently observed since its disappearance after Hurricane Irene in August 2011.  

The rock shrimp Paleomon is easiest seen in late summer when they have grown larger than Paleomonetes shrimp and the blue bands on their legs are prominently displayed.  Unlike the other species in the program, Paleomon requires an active search for individuals by running a net along the sides of the floating docks where algae and hydroids are numerous and closely inspecting the shrimp for morphological features.  

Algae
The Asian red alga Grateloupia has been a consistent member of the floating dock community albeit at relatively low frequency in comparison to other invasives.  It is usually found on the same docks where Codium is located near the pilings that hold the docks in place.  An analysis of of the MIMIC data presented on the MORIS website for the distribution of Grateloupia along the MA/NH/ME coast indicates that it has not yet been reported yet at MIMIC sites north of Boston and has remained in southern New England since it was first observed in the Gulf of Maine in 2007.  Other MA sites where it has been observed include the east end of the Cape Cod Canal at Sandwich, Onset and New Bedford on Buzzards Bay, and Fall River on the upper Naragansett Bay.  

Codium fragile on Floating Dock 

A large clump of Codium fragile growing at the waterline on a polystyrene float under one of the secondary docks, Provincetown, July, 2016.  The attachment site is clearly shown and there are no epiphytes growing on its surface.  

Grateloupia turuturu on Floating Dock

A cluster of Grateloupia turuturu growing on a floating dock right below the water line, Provincetown, August 2017.

Bryozoans
During the last 2 years, the bryozoan Bugula neritina has remained a common species on the docks along with a newly identified invasive bryozoan Tricellaria inopinata.  The bryozoan Tricellaria was first identified in Massachusetts in 2010 in Eel Pond, Woods Hole, lower Cape Cod (Johnson et al, 2012) and was reported in the Gulf of Maine during the 2013 Rapid Assessment Survey (RAS), where it was given the common name "unexpected bryozoan".  I have seen Tricellaria since I started monitoring (unidentified beige bryozoan in my November 2012 Bugula neritina post (MIS Branching Bryozoan), but I only became aware that it was an invasive species in 2016.  On the floating docks, Bugula and Tricellaria grow in the same niche and frequently cohabitate together.  Last July, the colonies were typically only a few cm high and newly settled juveniles were common. Tricellaria has a distinctly different microscopic growth pattern from other native, beige Bugula species (zooids point toward the anterior whereas they are alternately opposed to each other in Bugula).  This pattern could be discerned in the lab under a dissecting microscope and can be seen at the docks with a 20x or 30x magnifying lens.  During the summer of 2017, Tricellaria was particularly abundant and overgrew other species like the green algae Ulva and Codium.  

In contrast to the branching bryozoa, the encrusting bryozoan Membranipora membranacea has not been seen much in Provincetown despite the expectation that it might be seen on a floating dock. The rare times it has been seen has been on kelp growing on the dock or plastic dock trim that was submerged in the water.  The marina does not seem conducive to other encrusting bryozoans either, since the native encrusting broyzoans Electra pilosa and Schizoporella unicornis, are also rarely seen.

Bugula and Tricellaria Growing on Dock Float and Algae

Purple Bugula and light beige Tricellaria growing with green alga Ulva and orange chain tunicate Botrylloides, August, 2017.  Recently settled juvenile Tricellaria can be seen growing on the Ulva surfaces.  

Closer View of Bugula and Tricellaria

A clump of Bugula and Tricellaria growing out from the dock float on a mass of undergrowth.  The notched branches of Bugula, which represent alternating left and right facing zooids, can be discerned at the outer edges of the bush.

Tricellaria Overgowth on Codium

Tricellaria and Neosiphonia growing on Codium in an area of docks where Codium and Grateloupia are common, August 2017.  Heavy growth on the base of Codium obscurs the holdfast and lower branches. 

LINKS:

Marine Invasive Species in the MIMIC Program: Coast Watch 2011, Coast Watch 2012
Mathieson, AC, Dawes, CJ, Pederson, J, Gladych, RA, and Carlton, JT. The Asian red seaweed Grateloupia turuturu (Rhodophyta) invades the Gulf of Maine.  Biol. Invasions 10: 985-988, 2008.
Johnson, CH, Winston, JE, and Woollacott, RM. Western Atlantic introduction and persistence of the marine byrozoan Tricellaria inopinata.  Aquatic Invasions 7: 295-303, 2012.

RAS Report: Report on the 2013 Rapid Assessment Survey of Marine Species at New England Bays and Harbors.   
MORIS: CZM's Online Mapping Tool.

Tricellaria Sighting in Provincetown, 2012: MIS Branching Bryozoan 

Native Ghost Anemone in Wellfleet

Diadumene leucolena on Docks in the North Marina

A few years ago, a second, larger anemone, Diadumene leucolena, appeared at the Wellfleet marina and has remained on the north dock joining Diadumene lineata. The north marina is a protected, shallow estuary at the end of a creek that has limited species diversity.  The north side of the dock sits on the tidal flat at low tide limiting marine growth to anemones like D. lineata and D. leucolena, the solitary tunicate Molgula manhattensis, and a few sponges and algae.  Specimens of Diadumene leucolena, commonly known as the ghost anemone, are a pale beige color and several times longer than wide without colored stripes. They also form social groups on their own or sometimes mixed among groups of D. lineata.

Diadumene leucolena on the North Dock at Wellfleet Marina

Live Diadumene leucolena photographed off the north side of the floating dock in the north marina.  Top, a group of 4 anemones right below the water line.  Bottom, an enlargement of an individual anemone showing details of the tentacles and translucent body.  

LINKS: 

NEMESIS: The ghost anemone Diadumene leucolena. 

"Diadumene leucolena is commonly known as the Ghost Anemone because of its translucent white color. It is native to the East Coast of North America spanning from Georgia, USA to New Brunswick, Canada.  It is known from estuaries and sheltered waters, where it grows on oysters, rocks, seaweeds, pilings, and floats. It can also occur in sheltered tide pools, and is especially tolerant of variable salinities."

Global Biodiversity Information Facility: Diadumene leucolena (Verrill, 1866)

Harbor Watch Sep. 2013 post: Striped Anemone's Life in Wellfleet.  In situ photos of Diadumene lineata.

Harbor Watch Dec. 2011 post: Striped Anemone at Wellfleet Marina.  In situ and dissecting microscopic views of D. lineata.  

YouTube Video of Diadumene leucolena: Ghost Anemone (Diadumene leucolena). From Kevin Wilson.  A ghost anemone in Kevin's Chesapeake Bay Oyster Reef Biotope aquarium. 

Floating Dock Videos

Bugula, Grateloupia, and Bryopsis:

Capturing Moving Targets with Greater Clarity 

During the summer of 2016, I tried my hand at making videos of species on the docks that are moving in time with the wave action.  The live observation of some species just didn't seem to be realistically captured by a static image.  I was surprised at the detail that was shown by a video in comparison to a photo, especially on a day when the water was choppy.  Two of these videos featuring the invasive bryozoan Bugula neritina, the invasive Asian red alga Grateloupia turuturu, and the native green alga Bryopsis plumosa are shown below.  Bugula, which occurs at relatively high frequency on the docks, and Grateloupia, which is seen at low frequency, have been consistent parts of the floating dock community since I started monitoring Provincetown.  

Bryozoa and Algae at the Waterline

Floating dock species growing along the waterline.  The purple bryozoan Bugula neritina (center) is flanked by the bryopsid green alga Bryopsis plumosa (left) and the red alga Grateloupia turuturu (right).  A single solitary ascidian Styela clava with open siphons is seen in the center background.  MacMillan Pier, 2016. 

Asian Red Alga Waving with the Water Action

Another group of the same species focusing on the movement of the Asian red alga Grateloupia turuturu. The soft, leafy structure of the fronds is displayed by its flexibility with the rhythmic surge of the water.  The alga is growing among the purple Bugula neritina and green Bryopsis plumosa.  Red and green algae compete with tunicates, bryozoa, mussels, and hydroids for space along the waterline.

Since taking these videos, I searched YouTube for videos of these species and found several outstanding microscopic videos of feeding bryozoan zooids and bryozoan reproduction and development.  These terrific videos are definitely worth viewing and are listed below the Links.

LINKS:

MIS Branching Bryozoan:  Bugula neritina. 
Branching Bryzoan and Red Alga:  Bugula neritina and Neosiphonia harveyi.  Includes more information about Bugula and a photo of Grateloupia turuturu from MacMillan Wharf.

Mathieson, A.C., Dawes, C.J., Pederson J., Gladych R.A. and Carlton J.T.   The Asian red seaweed Grateloupia turuturu (Rhodophyta) invades the Gulf of Maine. 
Coast Watch 2012:   Marine Invasives Overview.  Shows all 11 species on the MIMIC list including Bugula neritina and Grateloupia turuturu. 
Floating Dock Bryopsid Green Alga:  Bryopsis plumosa.

YOUTUBE VIDEOS:
Short Video of Bugula Zooids:  Briozous (Bugula neritina).  From Eric Badosa.  Microscopic close-ups of feeding zooids featuring upbeat music.

Excellent Video of Feeding Bugula Zooids:  Bugula.  From Gulf Specimen Marine Laboratory.  Silent Video.
Educational Video Showing Development of Embryos:  Bugula neritina - the life cycle of a marine bryozoan.  From Alvaro Migotto.  Labeled, fast motion, microscopic live action featuring pleasant background music.
Sperm Release in a Bryozoid:  Through the tips of Tentacles.  From Alvaro Migotto.  Fascinating video showing ciliated tentacles and release of spermatozoa from the tips. 

Microscopic Photo Acccessory

Cell Phone Macro Lens Attachment

In a previous post, I wrote about the advantages of using jeweler's loupes in the 20-40X range to identify species when anatomical structure cannot been determined with the naked eye.  Since then, I always have taken along my 20X and 30X lenses to view the microstructure of colonial ascidians, bryozoans, red algae, and small crustaceans.  One of the disadvantages of the jeweler's loupe is that, although they are terrific for identifying and recording, they do not provide satisfactory in-focus images for documentation. 

Last fall, I had the opportunity to try a macro lens mobile phone attachment for my iPhone 6s, the olloclip Macro for 6/6s, which offers a 7x, 14x, and 21x lens adapter.  It proved valuable for producing quality in-focus images worthy of cataloging with the caveat that numerous, multiple images need to be taken to get suitable photos.  The focal plane is fairly narrow, so the camera needs to be held at the exact distance from the object, and any movement will give an out-of-focus image.  Ideally, structures with three dimensional features will have in-focus features in the center and out-of-focus features around the periphery.  The seawater around the subject also needs to be shallow so the camera lens can get close enough to the object to obtain focus such as in a shallow tray.  It is best to have the subjects as close to the surface as possible without disrupting the smooth surface level. 

Olloclip Macro Lens Attachment

 

These images show the Olloclip Macro lens attachments for the iPhone 7/8 Series.  The adapter has a 2 piece 7x and 14x (7x + 2x) lens on one side, and a single 21x objective lens on the other side (a single 15x Macro lens is available for the iPhone X).  Note that the case must be removed in order to place the adapter on the camera lens.   These lenses were useful for approximating images possible by a stereoscopic light microscope.  

Macro Images of Botrylloides violaceus

Macro images of Botrylloides violaceus collected from the floating docks at MacMillan Pier, November, 2017 showing chains of orange zooids against a contrasting dark background.  Numerous incurrent siphons and several shared excurrent siphons are evident. Also shown are orange ampullae of the blood vessel system in the common tunic.  Images were edited with Photoshop by cropping and slightly adjusting brightness and contrast.

Enlarged Macro Images of Botrylloides violaceus

Enlarged macro images of Botrylloides violaceus collected from the floating docks at MacMillan Pier.  In the upper photo, the solid orange endostyle can be discerned on a few zooids.  These photos were more cropped and resized, giving an enlargement effect. 

LINKS:  

Olloclip Macro Lens for iPhone available from Apple or online retailers:  Apple adapter for iPhone 7/8. Adapter for iPhone 6/6s being phased out.  A 10x + 15x macro lens pair also available as part of a 4-in-1 lens.
Olloclip Macro Lens for iPhone X:  Fisheye + Macro 15x Lens
Review of the Olloclip 4-in-1 Wide-Angle/Macro Lens:  https://9to5mac.com/2014/12/22/review-olloclip-4-in-1-lens-for-iphone-6/.
Olloclip Macro Lens Introduced:  Macro 3-in-1 lens.
Helpful Monitoring Accessories:  Jeweler's Loupe for Specimen Identification.
Tunicarium:  Microscopic images of Botrylloides violaceus.

Spring 2018 at MacMillan Pier

Overwintering Floating docks

Farewell to the Winter of 2017-18.  My blog has been on break since January 2014, but summer monitoring in Provincetown and Wellfleet has continued each year on schedule.  In the months ahead, I'll review the highlights of the last few seasons and discuss some of the current issues being considered for the marine invasives program.  In early April, I visited the McMillan Pier and was able to photograph some of the changes in the configuration of the floating docks during winter's off-season.  Below is a series of photos of the two floating dock complexes and a third finger pier on the east side of the main pier.  

First Floating Dock Out of Service

Floating dock complex nearest shore on the east side of the Pier.  Most of the seasonal docks on the north side (including the dinghy dock), which have no securing pilings, have been removed or moved parallel to the main dock.  No commercial vessels moor on this side of the dock, which is reserved for small boats and skiffs. Several of the secondary docks for the berths on the south side as well as the gangway from the pier have been removed (see below), preventing vessels from docking.

Several Secondary Docks Removed During Winter

Several secondary docks on the south side of the primary dock have been removed leaving their securing pilings behind.  While out of the water, the polyethylene floats can be thoroughly cleaned, which will provide a clean surface for settling plants and animals once the docks are back in the water.  The docks sit fairly low in the water so the the sides of the floats on docks still in the water can also be cleaned in place.  In April, the docks were home to numerous seagulls, so there will be plenty of clean-up to perform in preparation for the summer fishing and boating season.

Second Floating Dock Complex In Service

Second floating dock complex, which has berthing spaces on both sides of the main floating dock, has most of the secondary docks in place (a few are missing on the south side) and a functional gangway from the pier (see below).   During the summer, invasive seaweeds are common on these docks (the green alga Codium and red alga Grateloupe).

Finger Pier with No Floating Docks

The first of two finger piers on the east side of MacMillan pier is a permanent structure at the same height as the main pier and has no floating docks.  It is reserved for larger commercial vessels in the marina.  Access to the vessels is gained by wood ladders on the side of the pier.  This dock is not monitored for invasives, which are attached to the pilings below the low tide level and are accessible only by diving.   

ADDITIONAL IMAGES:

Satellite View of Pier Similar to April Visit

Missing Gangway to First Floating Dock

Gangway to Second Floating Dock

(See also MacMillan Pier Images in the Sidebar).

LINKS:

Summer at MacMillan Pier:  Photos of Floating Dock Complexes
Winter at MacMillan Pier:  I am Provincetown

Town of Provincetown Harbor and Pier Website: Harbor and Pier Homepage.

Town of Provincetown Harbor Rgulations and Documents:  Harbor, MacMillan Pier, and Mooring Regulations.

Sea Stars at MacMillan Wharf

Grazing the Pilings and Harbor Floor

Sea stars are not usually seen on the floating docks, but this summer when I visited the marina at low tide, the docks had lowered on the pilings to the upper subtidal zone. On my last visit, I encountered several sea stars crawling over marine life on the pilings. From the morphology, coloration of the madreporite, and size, they appeared to be Asterias forbesi.

Sea stars prey on mussels and other species on the pilings and harbor floor. When feeding on a mussel, the sea star attaches its tube feet to each shell and exerts force to separate them slightly. A tug of war ensues, and only a small gap is sufficient for the sea star to insert a fold of its stomach and start digesting the body. When the mussel is sufficiently digested, the sea star brings its stomach back into its body with the food inside. The sea star has a well-developed sense of smell and can detect the odor of mussels and crawl towards them.

Sea stars are able to move around via a water vascular system of tube feet that act as suction cups to walk over the surface or pull prey into the mouth. The tube feet are located on the ventral surface and the water intake structure, called a madreporite, is located on the dorsal surface.

Docks and Pilings at MacMillan Wharf

Docks slide up and down on the pilings as the tide rises and lowers about 10 feet. Permanent growth of most algae and invertebrates can only be sustained below the low tide line.

Sea Star Near the Water Line of a MacMillan Wharf Piling

 

The center of the sea star is raised up as though it is feeding on a prey, or it is about to feed on the mussel wedged between two arms. When the sea star was lifted, it was not feeding on another meal, so perhaps is was headed towards the mussel.

Dorsal Surface of the Sea Star Asterias forbesi

Dorsal surface of the same Asterias showing the red madreporite and numerous spines covering the arms.

Ventral Surface of the Sea Star Star Asterias forbesi

Ventral surface of the same sea star showing the mouth and radiating rows of tube feet. The outline of the tube feet can clearly be seen in the shadow of the upper arm.

  

Sea Star Righting Itself after Being Place on its Ventral Surface

Sea stars can rapidly right themselves by flipping over using their tube feet and flexible bodies. This photo was taken 1-2 minutes after the photo above.

LINKS: 

Echinoblog:  Feeding: What and How do Starfish Eat.

Echinoblog:  Madreporite and Water Vascular System





Global Biodiversity Information Facility: GBIF.ORG: Asterias forbesi (Desor, 1848)

Caprellid Amphipods Return to Docks

Caprella mutica back in Provincetown after Hurricane Irene

After Hurricane Irene passed through New England in late August, 2011, much of the growth on the docks at MacMillan Wharf was washed away, particularly delicate algae and invertebrates. One species that I failed to see in the following days and month was the amphipod Caprella mutica, also called the Japanese skeleton shrimp, which was observed fairly commonly on the docks earlier in 2011.  In 2012, Caprella had not re-established itself during my summer monitoring, but this year, groups of Caprella were found during July and August at several locations on the docks.   Most of the caprellids were attached to bushy hydroids and were not commonly observed on other filamentous (e.g., algae) or bushy species (e.g., bryozoa).   

My observations motivated a visit to the CZM MORIS website where species maps can be created for MIS species in previous years.  Confirming my previous observations, sighting of Caprella mutica decreased at different moriting sites from Narragansett Bay to Wells, Maine.   

 Groups of Caprella mutica living on branched hydroids

 

Populations of Caprella attached by their hind legs crawl over branched hydroids. Larger males and a few smaller females with mid-body brooding pouches can be identified. 

  

Caprella mutica MIMIC sightings in 2011 and 2012     

MORIS website-generated map of the locations where populations of Caprella mutica were found during invasive species monitoring in 2011 (top) and 2012 (bottom).  Caprella sightings decreased by about one-third.   No reports were made in 2012 in Narragansett Bay, Buzzards Bay, or Cape Cod Bay, and fewer sightings were reported in Salem Sound.  Website: MORIS: CZM’s Online Mapping Tool.  Credit: "Massachusetts Office of Coastal Zone Management (CZM), Executive Office of Energy and Environmental Affairs."

 

LINKS:

Harbor Watch:  Coastwatch 2012

"Caprella mutica (Caprellid amphipod a.k.a. skeleton shrimp) - Very common living on algae and bryozoa. These small amphipods look and act like miniature preying mantis.  They hold tight to surfaces and do not "swim around" like typical amphipods and shrimp." 

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.
Massachusetts Office of Coastal Zone Management (CZM): Home page
CZM - Aquatic Invasive Species (AIS) Program

MORIS: CZM’s Online Mapping Tool
WILD Shores of Singapore: Workshop on Bryozoans and Hydroids: 29 April- 4 May, 2013.  "Tiny skeleton shrimps are commonly seen on some hydroids!"

Floating Dock Mussel Beds

Provincetown Mussels and Ascidians

I've been monitoring floating docks at MacMillan Wharf in Provincetown for a few years now, and each season has been slightly different and yet broadly similar regarding the associations of different species.  One of the abundant species in the marina is the common blue mussel, Mytilus edulis.  It is abundant under the floats and variable in number on the sides depending on competition with other species and cleaning activities by marina personnel.  Each Spring, cleaned float surfaces provide opportunities for larval settlement. 

Mytilus normally lives on rocky shores in the intertidal zone attached to rocks and other hard substrates by strong, somewhat elastic structures called byssal threads.  These threads are secreted by byssal glands located in the foot of the mussel.  The mussels are firmly attached, but they have the ability to detach and reattach to the substrate allowing them to reposition themselves relative to their neighbors. They are usually found clumping together on wave-washed rocks, which helps hold the mussels firmly on the rocks against the force of the waves.

When the mussel larva first settles, it first secretes a thin shell and then develops an elongated foot with byssal glands. If the substrate is suitable, it will metamorphoses into a juvenile form and attach byssal threads. This attachment is a prerequisite for the foundation of the blue mussel population. On the sides of the Provincetown docks, large numbers of mussels will often settle on a clean surface and form masses of juvenile mussels which are striking because most of the individuals are about the same size, indicating that they settled around the same period of time.  These juvenile beds are apparently seasonal, because the beds do not mature over winter, and new beds of young mussels are seen the next Spring.  
 

Mussels can move slowly by extending a byssal thread, using it as an anchor and then shortening it.  A thread is formed by the foot by creating a vacuum at the contact site and secreting a foamy mixture of proteins into the formed chamber, producing sticky threads about the size of a human hair.

Mussels and ascidians frequent colonize together on floating docks, ropes, and fishing gear.  Ascidians compete for substrate, limiting colonization by mussels, and colonial ascidians will grow over the surface of the shell, limiting growth and food supply.  Co-colonization and competition of ascidians with mussels has had an impact on mussel aquaculture throughout the northeast.

Juvenile Mussels Beds on the Sides of Floating Docks

Mussel beds of young Mytilus edulis on the sides of floating docks at MacMillan Wharf, Provincetown, August, 2013.  Individual mussels averaged about 1-1.5 cm long.  In July, the mussels were covered by the colonial ascidian Diplosoma listerianum (which was extremely abundant), but most mussels were clean in August.  The soft ascidians were presumable removed by predation, an idea support by the observation in August of torn sections of Diplosoma colonies pulled off the substrate.  In these photos, small colonies of orange Botylloides violaceus and green-grey Diplosoma can be seen at the water surface, and two small colonies of Botryllus schlosseri (star tunicates) can seen deeper in the water in the top photo.  (Images in this post were taken with a 14 megapixel camera and can be enlarged without losing detail by zooming into the photo).

 

Mixed Floating Dock Communities of Mussels, Colonial Asicidans, and Algae

Botrylloides violaceus, green algae (Ulva), red algae (Neosiphonia harveyi), bryozoans (Bugula neritina), and other ascidians (Botryllus schlosseri, Diplosoma listerianum, Didemnum vexillum) form a colorful blend of species along with mussels.  Green-gray areas in top photo are Diplosoma.  Milky white areas in both photos are probably Didemnum.    

 

Mussels and Orange Colonial Ascidians Cohabitate Hanging Ropes 

Outside the juvenile beds, mussels grow and mature in small groups along with ascidians, especially Botrylloides violaceus.  Growth can become so extensive that the colony forms orange "hanging gardens."

 

LINKS:

A Snails Oddessy:  Learn about Mussels. Anchoring.

Van Winkle, W.  Effect of environmental factors on byssal thread formation.  Marine Biology 7: 143-148, 1970. 

Lane, DJW, AR Beaumont, and JR Hunter.  Byssus drifting and the drifting threads of the young post-larval mussel Mytilus edulis.  Marine Biology 84: 301-308, 1985.

Striped Anemone's Life in Wellfleet

Surviving Adverse Tidal Conditions

 

After I first started monitoring Wellfleet Marina in 2011, I wrote a post on the striped anemone, Diadumene lineata, on docks in the North Harbor, noting that few other species were found (see December 2011 post).  A monitoring study on MIS species along the New England coast reported that Diadumene was extremely tolerant to extremes in temperature, salinity, and water quality (Pappal et al, 2003).  Interestingly, temperature and salinity readings in Wellfleet during the summer of 2011 appeared normal, similar to those in Provincetown.  I did notice, however, that the turbidity of the water was much higher than that in Provincetown, and visibility was greatly reduced.

The following year, I learned more about the harbor when I coincidentally visited the harbor about 30 minutes before low tide.  The North Marina was already drained of water, and, in the South Marina, the receding water under the docks was rapidly disappearing.  I realized that the twice-daily exposure at low tide and high sediment levels were probably the most significant contributing factors to the distribution of species (see additional images in Footer at bottom of Blog).

High tidal variation is characteristic of the Gulf of Maine, and in the North Harbor, the shallow bay is filled and emptied during each tidal cycle. This variation has a positive effect on marine life (e.g., oyster beds) in that it brings in fresh seawater twice a day.  At the highest tides, the harbor is filled and Duck Creek is a shallow bay.  At the lowest tide, Duck Creek is drained and the marina is transformed into a mudflat.  Tidal variation in the summer averages over 10 feet, and this July, the tidal variation peaked at over 14 feet.  

 

On the north marina, Diadumene lineata, a yellow sponge (keyed as Halichondria bowerbankia), and an occasional oyster have most of the floating docks to themselves.  At high tide, sediment in the water produces a layer of sediment and organic matter on the sides of the floats.  At low tide, the floats sink into the mudflat.  This adds an additional layer of dark mud to the float.  Most of the anemones are in the upper layer near the waterline.     

 

On the South Marina, most of the docks are seasonal, and Molgula, algae, and distinctive color variations of Botryllus schlosseri form the dominant species on the sides of docks.  Other species that are commonly observed are sea lettuce Ulva, filamentous green algae, an occasional Codium, and branched red algae such as Neosiphonia harveyi. 

Satellite Views of Wellfleet Harbor at High and Low Tide

Tidal variation in Wellfleet Harbor taken from different satellite images of Wellfleet.  Left, high tides.  Right, mid-to-low tide.  At the lowest low tides, the entire north estuary is drained. 

View of the North Wellfleet Harbor at Low Tide

Evening low tide in the Duck Creek estuary on the North Side of Wellfeet Marina, September 16, 2012.  The entire area is drained and converted into a mud flat of dark brown, wet sediment.  At low tide, the docks rest partially submerged in sediment. This year, the marina was monitored at high tide and will be henceforth.

 
Diadumene Habitat on the Side of the Main Dock in the North Marina 

Digital photos and enlarged details of Diadumene lineata on the North Marina docks (August, 2013).  Diadumene lives in social groups distributed along the length of the docks right below the water line.  Wellfleet was monitored at high time this summer.  The floats were stratified into three regions: the upper, dry float above the water water (bottom of top image), a light brown zone containing sediment below the water line that is exposed at low tide, and a dark brown zone zone that sinks into the dark sediment at low tide (top of top image).  Most of the anemones live in the light brown region, but a few individuals can also be found in the dark brown zone.    

 

LINKS:

Pappal, A, J Pederson, JP Smith.  Marine Invaders in the Northeast, 2003.

In this study, Diadumene was commonly found at Marinas in Naragansett Bay and Buzzards Bay and at certain locations in the Gulf of Maine. 

Harbor Watch:  Striped Anemone at Wellfleet Harbor.  Features stereomicroscopic views of collected anemones.