The Invasive Club Tunicate

An Abundant Resource for Ascidian Research

Styela clava and its cousin Styela plicata have been getting some pretty bad press over the last 10 years due to their circumglobal distribution and classification as Marine Invasive Species.  As a Styela biologist, I'd like to spend some time discussing some of the positive aspects to the Styela story. They may be be ugly ducklings on the outside (literally), but because of their recent world-wide distribution, they have also been the subject of scientific investigation by several research labs.  They are an attractive research model because they are readily available to researchers around the temperate world (in both hemispheres), and they are an important group of ascidians biologically in terms of their relationships to colonial botryllid species and other solitary ascidians.  In Asia (Korea), S. clava is part of the regional cuisine (Mideodok-chim) and is grown in aquaculture. The biology of Styela has become important for understanding diseases that have threatened commercially-cultured ascidians (soft-tunic syndrome in Halocynthia roretzi).  Inside, they are fascinating to study because their internal organs are bright orange and easy to examine.   S. clava is particularly useful because it is slender with a relatively thin, easily-cut tunic, whereas S. plicata is globular in shape and has a thick, less pliable tunic.  S. clava cohabitates with S. plicata in bays where their ranges overlap on both the East and West US coasts. 

Successful MIS Species:  S. clava and S. plicata

Styela clava and Styela plicata have made a home in Marinas and Bays around the world and are two of the most commonly studied Styela species.  In North America, both species have been established on both coasts for several decades.  S. clava has a more northern distribution than S. plicata, and the two co-habitate where their ranges overlap.  

Native American Styelids (Pacific Coast):  S. montereyensis, and S. gibbssi.

 

Styela montereyensis and Styela gibbsii, two Styela species from the Pacific coast were the two Styela research species of choice before the two MIS species became established in North America and Europe.  S. montereyensis and S. gibbsii have stayed within their ranges in the North American Pacific and prefer the cooler waters of the open coast. 

Styela clava showing orange-colored internal organs

   

Dissection of Styela clava with branchial sac (bs) on left and digestive tract on the right.  All the internal organs are located in the upper portion of the individual and not in the stalk whose function is essentially to raise the siphons and body above the growth of encrusting invertebrates and algae.  st, stomach; int, intestine;  os, oral siphon. as, atrial excurrent siphon. 

Diagram of the internal organs of Styela clava

Diagram of the internal organs of Styela clava.  Branchial sac, digestive tract consisting of esophagus, stomach, and intestine; reproductive organs in the body wall (both sides); and heart.   en, endostyle; bf, branchial folds; dl, dorsal lamina; rb, retropharyngeal band; ht, heart; es, esophagus; st, stomach; in, intestine; ov, ovary; t, testis.

Styela clava has a number of advantages as a model system for the study of solitary ascidians.  It is abundant, grows up to 4-5 inches (12 cm), and is easy to dissect.  It is adaptable for a wide range of studies and has a firm, flexible tunic that supports the internal organs during dissection.  In coastal marinas, S. clava individuals on docks show a range of sizes depending on the season and whether the substrate has been recently cleared.  During my 2011 MIS monitoring from Cape Cod to Salem Harbor, the population density was kept at a moderate level by competition with other encrusting invertebrates and colonial ascidian species, especially Didemnum vexillum and Diplosoma listerianum, which can aggressively overgrow solitary ascidians.  When fully mature, large individuals are easy to spot (unless totally covered by Didemnum).  However, small, young individuals may not be counted in the field when if they are not recognized. This is particularly important in marinas with new or cleaned docks. 

Young and Fully-Grown Individuals of Styela clava

Size distribution of Styela clava (the field is approx 5 inches [12.5 cm] high). The 6 smallest individuals were covered with Diplosoma listerianum, which was manually removed, revealing a smooth, light-tan tunic. The 3 medium sized individuals show typical bumpy brown corrugated tunic. The 3 largest individuals are covered with colonial ascidians and other attaching invertebrates. Left, complete coverage with Didemnum vexillum except for the siphons.  Center, patch-work collection of orange Botrylloides and Botryllus. Right, coverage by Didemnum and Botrylloides. Siphons and the upper body can contract within the tunic of the colonial species maintaining water flow and inhibiting overgrowth.

Styela has been used as a model system for studying filter feeding, the anatomy, histology, and ultrastructure of tunicates, cell biology (such as the function of the endostyle), blood cell formation, and the production of anti-bacterial peptides (styelins, clavanins, and clavaspirin).  The ovaries and testes are located in the body wall on both sides of the body instead of along the digestive tract and are arranged in radiating rows that are ideal for morphological and developmental studies.  Styela is a good control solitary ascidian for the study of coloniality in botryllid ascidians and is therefore important from an evolutionary point of view.  The styelids are located at a cross road linking more distantly related solitary ascidians such as Ciona, Ascidia, and Ascidiella, and other more closely related advanced ascidians such as Pyura (on the West Coast), Halocynthia (sea peach), and Boltenia (sea potato).  Some of these topics will be discussed in more detail in upcoming posts.

Granulocytes in Blood-Forming Tissue of Styela clava

Granulated blood cells in ascidians contain antimicrobial peptides that are important in fighting off bacterial and fungal infections.  The peptides are made in the cytoplasm and are concentrated into secretion granules that are released from the cell when they detect microorganisms.  This process is a part of the innate immune response and serves a similar function to the granulated blood cells in vertebrates that fight infections.  

Antibacterial Peptides from Blood Cell Granules of Styela clava

Styelins share amino acid sequences with each other and with cecropins in the domestic pig Sus scrofa domesticus (P1) and Drosophila virilis (Dv1).  Clavanins also share similar amino acid sequences.   

WEB AND LITERATURE SEARCH TERMS:

Styela, branchial sac, filter feeding, endostyle, stigmata, cilia, mucus, digestive tract, stomach, blood cells, hemocytes, granulocytes, cell renewal, reproduction, ovary, testis, innate immunity, styelin, clavanin, etc.

REFERENCES:

1.  Ermak TH. Cell proliferation in the digestive tract of Styela clava (Urochordata: Ascidiacea) as revealed by autoradiography with tritiated thymidine. J. Exp. Zool., 194: 449-466, 1975.

2.  Ermak TH. The hematogenic tissues of tunicates. In, The Phylogeny of Thymus and Bone Marrow-Bursa Cells, RK Wright and EL Cooper, Eds., Elsevier/North Holland, Amsterdam, pp. 45-56, 1976.

3.  Ermak TH. The renewing cell populations of ascidians. Amer. Zool. 22: 795-805,1982.

4.  Jiang AI, Lin J, Wang CH. Physiological energetics of the ascidian Styela clava in relation to body size and temperature. Comp. Biochem. Physiol. 149: 129-136. 2006.

5.  Kumagai A, Suto A, Ito H, Tanabe T, Takahashi K, Kamaishi T, Miwa S. Mass mortality of cultured ascidians Halocynthia roretzi associated with softening of the tunic and flagellate-like cells. Dis. Aquat. Org. 90: 223-234, 2010.

6.  Lambert G. New records of ascidians form the NE Pacific: a new species of Trididemnum, range extension and redscription of Aplidiopsis pannosum (Ritter, 1899) including is larva, and several non-indigenous species. Zoosystema 25: 665-67X, 2003 (includes an updated description of Styela clava).
7.  Lee IH, Cho Y, and Lehrer RI.  Styelins, broad-spectrum antimicrobial peptides from the solitary tunicate, Styela clava.  Comp Biochem. Physiol. 118B: 515-521, 1997.
8.  Lehrer RI, Lee IH, Menzel L, Waring A, and Zhao C.  Clavanins and styelins, alpha-helical antimicrobial peptides from the hemocytes of Styela clava.  Adv. Exp. Med. Biol. 484: 71-76, 2001.

9.  Lehrer RI, Tincu JA, Taylor SW, Menzel LP, and Waring J.  Natural Peptide Antibiotics from Tunicates: Structures, Functions and Potential Uses. Integr. Comp. Biol. 43: 313-322, 2003.
10.  Menzel LP, Lee IH, Sjostrand B, and Lehrer RI.  Immunolocalization of clavanins in Styela clava hemocytes.  Dev. Comp. Immunol. 26: 505-515, 2002.
11.  Raftos DA, and Cooper EL. Proliferation of lymphocyte-like cells from the solitary tunicate, Styela clava, in response to allogeneic stimuli. J. Exp. Zool., 260: 391–400, 1991.
12.  Raftos DA, Stillman DL, and Cooper EL. In vitro culture of tissue from the tunicate Styela clava.  In Vitro Cell. Dev. Biol. 26, 962-970, 1990.
13. Sawada T, Zhang J, and Cooper EL. Classification and characterization of hemocytes in Styela clava. Biol. Bull. 184:87-96,1993.
14. Thorndyke MC. Observations on the gastric epithelium of ascidians with special reference to Styela clava.  Cell Tiss. Res. Volume 184, 539-550, 1977.

15. Thorndyke MC.  Comparative studies on the effects of cholecystokinins, caerulein, bombesin 6-14 nonapeptide, and physalaemin on gastric secretion in the ascidian Styela clava.  Gen. Comp. Endocrinol., 1984. 

LINKS:

National System for the Prevention and Management of Marine Pest Incursions

Korean Mideodok-chim (Steamed Styela with beef, clams, vegetables, and ground rice over noodles)
iTunicate Newsletter (Invasive Tunicate Network in Alaska):  Plate Watch.  Includes a recipe for steamed Mideodok-chim.

Botryllus: Burgundy Color Variants

At the beginning of the season, the typical star-shaped Botryllus schlosseri color variants with a burgundy body and white inter-siphon pigment bands forming an actual white star was one of the most prevalent color variants.  But as the summer progressed, the number and variations of color variants increased, including the burgundy colonies.  Their appearance in daylight or under incandescent light varied depending on substrate (light green sea lettuce, dark green Codium, brown algae, red algae, mussel shell, Styela) and background setting (on the dock, in collection containers, or on a black or white microscope stage). In this post, I show a few of the burgundy color variants collected from Provincetown and Salem Sound during the summer.

   Burgundy Botryllus schlosseri Variant on Green Algae - White Star

Botryllus schlosseri on Ulva, MacMillan Wharf, Provincetown, MA, September, 2011.  Green back-lighting through the algae clearly outlines the zooids.   White pigment cells form a pair of curved bands between the branchial and excurrent siphons giving the bands a daisy-star appearance.  Stereozoom 1.0 x 10x.  

Burgundy Variants with Inter-siphon White Shield

 

Botryllus schlosseri on Codium, MacMillan Wharf, September, 2011. White pigment cells form a shield-shaped pattern filling the space between the branchial and excurrent siphons of the cluster. The zooids also have a tiny patch of white cells on the opposite, outer side of the branchial siphon at the anterior end of the endostyle.  Othewise, the branchial siphons are burgundy like the rest of the zooid body. Stereozoom 3.0 x 10x.

 Burgundy Variant on Red Algae, White Branchial Crescent with Atrial Ring

 

Nine-zooid cluster of Botryllus schlosseri on red algae, MacMillan Wharf, October, 2011. Scattered white pigment cells encircle the orange-colored branchial siphon, more heavily on the outer side of the cluster. The common excurrent siphon is outlined by a dashed ring of white pigment cells formed by a short, white stripe at the atrial opening of each zooid.  Stereozoom 1.5 x 10x.

Ampullae of Burgundy Variant on Red Algae - White-Capped

 

Same colony of Botryllus schlosseri on red algae as shown above.   The zooids share a common vascular system that consists of blood vessels and enlarged club-shaped vascular ampullae along the periphery. The ampullae have the capacity to reconstruct the colony by vascular budding if all the zooids are lost.  Top, ampullae define the edge of the colony and separate clusters of zooids.    Bottom, white pigmented cells concentrate at the distal ends of burgundy ampullae like snow-capped boulders. 

Burgundy Variant on Red Algae - Diffuse White Branchial Stripe

Botryllus schlosseri on red algae, MacMillan Wharf, September, 2011.  White pigment cells form a short stripe through the branchial siphon above the endostyle and dorsal lamina.  Pigment cells also lightly speckle the body of the zooid.  Branchial siphons are orange-colored. Top, two 7-zooid and 10-zooid clusters.  Stereozoom 2.0 x 10x.  Bottom, close-up view of branchial siphons and diffuse white stripe.  Stereozoom 3.0 x 10x.  

LINK:

CE Carver, AL Mallet, and B Vercaemer, Biological Synopsis of the colonial tunicates, Botryllus schlosseri and Botrylloides violaceus

Identifying the Native Encrusting Bryozoan

Electra pilosa

Electra pilosa is a native encrusting Bryozoans found in the Gulf of Maine co-habitating with the cosmopolitan, MIS species Membranipora membranacea. Both of these encrusting colonies have a lacy appearance and are typically found on brown algae such as Laminaria sharing space on the same blade. Upon inspection, established colonies may look similar but they can be distinguished from each other by specific differential features. 

Colony growth pattern is an important clue to differentiating Electra from Membranipora.  Electra in its first stages of growth forms star-shaped colonies whereas Membranipora grows in a uniform, radial pattern (what Silén called "unitary multiserial", see LINK below).  In contrast, the colony of Electra is separated into sectors divided by radial axes that extend beyond the margins of the colony forming a multi-pointed star (what Silén called "composite multiserial" growth).  Each sector has a central growth axis composed of 2 or more parallel rows of rectangular zooids (approximately 0.33 by 0.5 mm in dimensions) flanked on each side by wings of oval or ovate zooids which fill in the area between the axes. The side walls of the calcified enclosure do not directly abut each other like in Membranipora (see February 12, 2012 post), but are separated by a translucent, calcareous surface membrane. Each enclosure is surrounded by several spines that vary in length. However, the median, proximal spine is larger than the rest and can be easily seen with a magnifing lens. 

The bottom line when identifying encrusting Bryozoans in New England is to check for growth pattern (composite vs. uniform), boundary morphology (jagged vs. smooth), zooid skeletal structure (ovate vs. rectangular), arrangement of spines (larger pointed, proximal spine vs. 6 short, blunt spines, 4 at each corner of the rectangular enclosure) for Electra vs Membranipora, respectively.  

Growth Pattern of Electra vs. Membranipora

Comparison of growth pattern of Electra vs. Membranipora in small colonies where the axial structure of Electra is most pronounced.  Modified image from Silén, 1987 (see LINK below).  

Axial Growth Pattern of Electra pilosa

Outer border of Electra pilosa colony growing on Laminaria collected from Hawthorne Cove, Salem Sound, MA.  The colony illustrates composite multiserial growth.  At the bottom, two axial strands of rectangular zooids curve toward each other encircling inter-axial ovate zooids. At the top, several axial strands join each other to form a single 5-zooid wide strand.   Stereozoom 1.0 x 10x objective. 

Calcareous Enclosures of Electra pilosa

Electra pilosa zooids showing axial (left and right) and inter-axial zooids (center) with conspicuous proximal spines and translucent calcareous membranes between walls of the enclosures.  Stereozoom 3.0 x 10x objective

LINKS:

L. Silén. Colony Growth Pattern in Electra pilosa (Linnaeus) and Comparable Encrusting Cheilostome Bryozoans. Act. Zool. 68: 17-34, 1987.

Electra pilosa: MarLIN - The Marine Life Information Network



Electra pilosa (Linnaeus, 1767): WoRMS - World Register of Marine Species

MIS Encrusting Bryozoan

Membranipora membranacea

Bryozoans are tiny colonial organisms characterized by the presence of a tentacled feeding structure called a lophophore that filters food particles out of the sea water and transfers them to the mouth. The tentacles of Bryozoans differ from those of anemones and corals in that they contain a body cavity and the anus is located outside the circle of lophophore tentacles.  Encrusting Bryozoans in the Gulf of Maine include the cosmopolitan Membranipora membranacea and the native Electra pilosa.  Encrusting colonies have a lacy appearance and are typically found on brown algae such as Laminaria species but are also found on red algae and solid flat surfaces in marinas.

Membranipora forms mat-like calcareous colonies of small, closely packed zooids living inside a rectangular sheath that secretes a protective, calcified enclosure.  Each rectangular compartment is composed of lateral calcified walls and ventral uncalcified bands, which provide flexibility.   A membrane completely roofs the space between the supporting side walls. The enclosure has an orifice through which the lophophore extends into the water column for feeding. In Membranipora, the orifice is covered by an operculum. 

Membranipora membranacea Growing on a Blade of Laminaria

A small colony of Membranipora membranacea growing on a blade of the brown algae Laminaria longicruris collected from Beverly Marina  The point of origin (the ancestrula) is in the upper left quadrant.  Membranipora is characterize by rectangular enclosures and a smooth edge lacking zooids along the growing colony edge.  1x zoom x 10x objective.

Smooth Growth Zone at the Edge of Membranipora membranacea Colony

Growing edge of Membranipora membranacea lacks zooids and provides a smooth edge for excurrent water flow away from the colony.  1.5x zoom x 10x objective.

Diagram of an Encrusting Bryozoan: Retracted (left) and Feeding (right)

Diagram of two encrusting zooids, one retracted and one with the lophophore extended.  The lophophore circulates water through the tentacles, filters food particles, and transfers them by ciliary motion to the mouth.  Because the zooids are closely packed, the lophophores of the colony work cooperatively to circulate water through tentacles and to remove waste and unwanted particles.  When disturbed, the retractor muscles pull the zooid and lophophore into the safety of the enclosure. From www.earthlife.net - bryozoa.

Membranipora membranacea Rectangular Zooid Chambers

Calcified rectangular walls of the colony of Membranipora membranacea.  The units are arrange in staggered rows that give the structure additional strength.  Short tubercles (spines) occur at the corners of the rectangular enclosures, 6 spines per enclosure.  4x zoom x 10x objective.

Links:
Beyond the Human Eye

Marine Invaders in the Gulf of Maine: Membranipora

MarLIN: Membranipora membranacea
Marine Invasions Research Lab

WoRMS: Membranipora membranacea

Web Photo, showing Colony Enclosures by Scanning Electron Microscopy:

Bryozoa: Cheilostomata

Membranipora organization by SEM Dennis Gordon

Web Photo Favorites, showing colony formation:

Marney Pratt's Home Page, Duke Univ

Lovell and Libby Lanstroth, California Academy of Science
Ann-Margret Amui-Vedel's Webpage, NUI Galway

Twin Ancestrula Marney Pratt 

Emerging Colony Lovell and Libby Lanstroth Collection, CalPhotos

Small Colony Marney Pratt

Colony in Culture showing lophophores Ann-Margret Amui-Vedel

References on Feeding and Water Flow:

1. Pratt, MC. Effect of zooid spacing on bryozoan feeding success: is competition or facilitation more important? Biol. Bull. 207:17-27, 1004.

2. Pratt, MC. Consequences of coloniality: influence of colony form and size on feeding success in the bryozoan Membranipora membrancea. Mar. Ecol. Prog. Ser. 303: 153-165, 2005.

3. Von Dassow, M. Effects of ambient flow and Injury on the morphology of a fluid transport system in a Bryozoan. Biol. Bull 208:47-59, 2005.

3. Winston, JE. Current related morphology and behavior in some Pacific coast Bryozoans. In Advances in Bryozoology: Proceedings of the 4th International Conference on Bryozoa, GP Larwood & MB Abbott, eds. Systematics Association Special Volume, 13:, 247-268, 1979.

Diplosoma Ascidian Up Close

Diplosoma listerianum is a cryptogenic species of almost cosmopolitan distribution that is found from the low-tide mark until about 80 m deep and is a close relative of Didemnum vexillum.  Both species have rapidly spread throughout New England waters and have become dominant species in many localities.  They are members of the same ascidian family, the Didemnidae, and and have a similar zooid body structure but differ primarily by the presence of stellate spicules and a coiled sperm duct in Didemnum.  The lack of spicules gives Diplosoma a smooth, gelatinous feel to it, whereas Didemnum has a tougher, slightly calcareous surface.  By eye, the two species would rarely be confused because they differ dramatically in color.  Dilosoma is an inconspicuous green-grey whereas Didemnum is a bright tan or cream color.  The feel of Diplosoma comes into play when trying to determine the identity of an amorphous green gelatinous mass, particularly when feeling the out-of-view but within-reach under-surfaces of docks. 

Diplosoma listerianum Colony showing Distinctive Green-Grey Color.

Numerous, small openings in the surface of the colony are incurrent branchial siphons of individual zooids.  Less frequent, large openings are common, excurrent apertures.  

Diving photograph by Rokus Groeneveld, Diverosa.com

During the monitoring season, Diplosoma was seen throughout the summer in Salem Sound but did not make its first appearance at the Provincetown Docks until August and continued to spread through September. I never saw it on the sides of docks in Wellfleet.  Earlier in the season, most of the Diplosoma specimens I brought to the lab were not very photogenic because of their dark color, lack of contrast, or poor viability in standing sea water.  However, in September, I collected a colony growing on red algae that I kept in replenished sea water until it was examined in the lab the next morning.  This colony showed beautiful light-blue structural features and white pigmented cells in the surface that glowed like stars in the sky.  The zooids, which are only about 2 mm long, afforded great views of the branchial siphons and stigmata in the branchial sac.   

Diplosoma listerianum on Red Alga Glows Light Blue by Stereomicroscopy

This view is from above, looking almost directly down on the branchial siphons, which have 6 lobes and up to 24 thin branchial tentacles of variable size.  The branchial sac bears 4 rows of stigmata, which can be clearly seen through the opened branchial siphon arranged in a ring around the opening. 

Diplosoma  listerianum Zooids showing Rows of Light Blue Stigmata

 This view is looking at a slight angle through the branchial opening showing some stigmata from the side.  The upper rows of stigmata are in clear focus.  The digestive tract, ovary, and testis are localed deeper in the colony below the plane of focus. 

Links providing further information on Diplosoma listerianum:
Guide to Marine Invaders in the Gulf of Maine: Diplosoma listerianum
Marine Invasive Species Benthic Fouling Study
Tunicarium: Diplosoma
MarLIN - The Marine Life Information Network: Diplosoma listerianum
WoRMS: World Register of Marine Species: Diplosoma listerianum
Nemesis: National Exotic Marine and Estuarine Species Information System
Pattern of Cell Proliferation During Budding in the Colonial Ascidian Diplosoma listerianum, N Sköld et al., The Biological Bulletin, 221: 126-136, 2011.

Marine Event of the Year - 2011 Tropical Storm Irene

Tropical Storm Irene hit New England on August 28th, 2011 with onshore winds on the east side of the storm battering coastal areas with large waves and a destructive storm surge.  After the storm, I traveled to Provincetown during calm weather and monitored the docks at Provincetown and Wellfleet on August 31st and September 1st.

Tropical Storm Irene Hits New England

 Tropical storm Irene over New England brought onshore easterly winds

 and turbulent waters to the Massachusetts coastline.  

 

Satellite view over the Northeastern US with outlines of the states superimposed. The image was taken when the eye of the storm was near New York City.

  Left, projected path of Hurricane Irene when it was in the Carribean.  Irene started its journey as a hurricane in Puerto Rico, made landfall over eastern North Carolina's Outer Banks, and was downgraded to a tropical storm as it passed over Long Island, NY.  Right, it continued through western New England battering CT and VT.  The threat level through the Northeast was extreme with widespread damaging winds through August 29th.

The storm had a significant effect on marine life on the sides of docks, scouring off loosely attached organisms and battering firmly attached species.  Most of the colonial species and algae that extended away from their attachment site were pruned or torn off and some species appeared bruised or damaged.  Firmly attached species like Styela clava and Codium fragile survived the storm, but filamentous and leafy algae were washed away or pruned shorter taking with them the species (e.g., amphipods) that grew on or among them. Outgrowths of Didemnum vexillum were torn off at the base, as were large colonies of Botryllus schlosseri and Botrylloides violaceus.  In Wellfleet, an almost solid covering of a spring cohort of Molgula sp.(manhattensis?) on portions of the seasonal docks was decimated resulting in large areas of the docks being cleared of the ascidian.

Monitoring at MacMillan Wharf, Provincetown, 2 Days after the Storm

Inspecting colonial organisms on August 31st using the palm of my hand to make a small pool of water and preparing to magnify the field with a jeweler's loupe. 

A month later, by the September monitoring visit, there was a clear re-colonization of the depleted areas in Provincetown by algae, ascidians, and other invertebrates.  Didemnum vexillum grew up the sides of the dock from established areas lower on the dock, and Diplosoma listerianum, not found at the beginning of the season, surged in its colonization from its first sighting in August.  Botryllus and Botrylloides repaired their torn edges and resumed their previous growth.  Near the water line, small individuals of Styela clava (under 1 or 2 inches) were scattered along the dock on newly exposed substrate.  In Wellfleet, there was no noticable re-colonization of cleared surfaces by Molgula, but Botryllus schlosseri growing on the remaining Molgula continued to grow and spread, and there was some regrowth of algae and other attached species along the water line. 

Striped Anemone at Wellfleet Marina

Wellfleet Harbor and Marina
                     

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 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:

Guide to Marine Invaders in the Gulf of Maine

A Guide to the Exotic Species of San Francisco Bay

Introduced Marine Species of Hawaii

Actiniaria.com

Nemesis: National Exotic Marine and Estuarine Species Information System

WoRMS: World Register of Marine Species

WILD Singapore Fact Sheets 

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.  

New Ascidian Images on Tunicarium

Botryllus schlosseri is another beautiful colonial ascidian whose single and multi-color variants make for an amazing number of color morphs.  These colorful ascidans, like Botrylloides violaceus (Nov. 11 Post), make for terrific underwater photographs that I thought would transcend directly to the stereomicroscope.  It did to an extent; however, like with Botrylloides, structural detail was easier to capture with the lighter color variants.  Some of the stereomicrographs from this summer's monitoring of Cape Cod and Salem Sound marinas are now featured on Tunicarium, including images of the invasive ascidians Botrylloides violaceus, Botryllus schlosseri, and Didemnum vexillum.  

Botryllus schlosseri was a challenging colonial to capture under fiber optic lighting. The variants with dark-colored zooids blended in with the backgrounds making difficult the photography of structural detail.  With the light color variants against a darker background, the two-toned beige, which formed a mosaic-patterned colony, and single-colored orange colonies proved to be highly photogenic.

To capture the zooids with open siphons, I tried Gretchen Lambert's technique for relaxation with menthol crystals.  It was terrific for relaxing ascidians as well as other invertebrates.  But as with any approach, I found relaxation had its pros and cons for viewing as well as photomicrography.  Relaxation greatly reduced contraction ability, but also inhibited the ability of zooids to fully expand. Lack of anesthesia was challenging under bright light because individual zooids reacted to the light independently, each zooid in a cluster randomly closing and re-opening during photography.  My objective was to obtain images where all the branchial siphons in the field of view were fully open.  It made for some interesting and entertaining time-sequence shots.    

The images below are two of my favorites.  They demonstrate the difference between the information revealed capturing images of light vs. dark Botryllus color variants and show zooid structural and pigment cell details that cannot be seen solely by underwater photography.  The 40X original magnification generated images with the greatest resolution and zooid detail (4X zoom + 10X objective lens).  These details can also be seen out in the field with the 30-40X jeweler's loupe magnifying glasses that I discussed in the Nov. 25 Post.  The beige variant gave vivid zooid detail, whereas the typical white star on dark purple was outstanding for showing cells in the pigment bands.

Botryllus schlosseri Beige-Rust Mosaic Variant

Botryllus schlosseri growing on the green algae Codium fragile collected from MacMillan Wharf, Provincetown, MA. Zooids have a translucent beige color revealing the tips of the branchial tentacles and pale rust-orange cells in the pigment bands. 

Botryllus schlosseri White Star Variant with Parallel Pigment Bands.

Botryllus schlosseri growing on Codium collected from MacMillan Wharf, Provincetown, MA.  Four branchial openings are seen at the top with 4 pairs of white pigment bands leading to the single, common atrial aperture at the bottom center.  

The full collection of images on Tunicarium can be seen all together on Google Images that has been web-searched using the word "Tunicarium".  The photos are featured in thumbnail view and can be "double-clicked" to see the jpg files saved on the website.  Larger sized micrographs can be obtained from me by request at tomermak@rcn.com.