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Bugula neritina (Linnaeus), 1758


Leslie Braberry 2016

Summary

Background

Bryozoans (Ectoprocta),also known as 'moss animals', are both freshwater and marine, and are generally hermaphroditic (Bishop museum 2002). Being benthic and colonial, these marine invertebrates are seen colonizing by attaching themselves onto hard substrates(Ruppert et al. 2004). Although colonies within bryozoans contain tiny zooids,these colonies can be large when numerous zooids come together. Having unobtrusive colonies within bryozoans deemed a physical appearance that resembles a plant, bryozoans usually go unnoticed by many, being commonly mistaken as mosses or seaweed. However, we fail to realize that the phylum bryozoa is a major animal taxon (Ruppert et al. 2004).

Zooids within colonies are less than a millimeter long.

These zooids are said to not bare any internal transport system (connecting individual zooids that are isolated via the interzooidal system (figure 13), allowing transport and communication amongst the zooids).
Nor do these zooids bare any coelom (a space where the introvert retracts in and a hydrostatic skeleton during protrusion same as above). It would be assumed that these are absent, when in fact, they are present (Ruppert et al. 2004).

The species, Bugula neritina (brown bryozoan) derived from the class gymnolaemata, is a fuzzy bryozoan that stands rigidly upright. It is known as an invasive, biofouling, marine invertebrate species that settles itself onto any substrate, colonizing itself, and are typically found in embayments and habours, especially at the base of shipping vessels (GISD 2015). They are also typically mistaken as seaweed due to their physically appearance, being bushy tufts, and physically small.

Classifications
Bryozoans, generally, have been classified into three taxa; Stenolaemata,Phylactolaemata, and Gymnolaemata (Ruppert et al. 2004).

Below lists the classification of the marine invertebrate species Bugula neritina, with the aid of pointers to illustrate the traits each group has; (Common Marine Organisms of Monterey Bay, California 2012) (figure 1)

Domain: Eukarya
  • A characteristic of having the presence of eukaryotic cells, with membrane-bound organelles and a true nucleus. Organisms can be multicellular, colonial or, unicellular (Domain Eukarya 2013).
Kingdom:  Animalia
  • Organisms in this Kingdom are eukaryotic and multicellular, They are also Heterotrophs (Kingdom Animalia, 2014).
  • Food consumed is stored in the fats or glycogen, which can either be ingested and digested, or, digested and absorbed, in the Kingdom, Animalia (Kingdom Animalia, 2014).

Phylum:  Bryozoa (Ectoprocta)

  • Bryozoans ("outside anus") have their anus situated at the external side of the lophophore structure (An Introduction to the Study of Invertebrate Zoology) (Figure 1).
  • Presence of Zooids and avicularium, which fends off predators (An Introduction to the Study of Invertebrate Zoology).

Class:  Gymnolaemata
  • Strictly marine invertebrates with the presence of a circular lophophore formation (Merriam Webster 2014). 
  • Bryozoans in this class are mainly marine.
  • Zooids in Gymnolaemata are usually flattened or cylindrical in shape (Classification of the Dutch freshwater bryozoan, 2007).
  • Protrusion of the lophophore at the frontal wall via the pulling muscle movement.

Order:  Cheilostomatida
  • Organisms in this order are defined by individuals within a colony based by having a chitonous covering or a calcareous, usually with opercula (Cheilostomata, 2014).
  • During reproduction, eggs tend to latch in ovicells.

Suborder:  Flustrina
Super-family: Buguloidea

Family:  Bugulidae
  • Ovicells within this family have a calcified outer layer membrane of the oecial wall, and are autonomous of each other (Cohen, 2011).

Genus:  Bugula
Species:  Bugula neritina
  • The only bryozoan species that is distinguished by its bushy tufts appearance, reddish-purple colour tone, the absence of avicularium and, presence of ovicells (Cohen, 2011).

The Phylogenetic Tree of Life provides a clear insight of the evolution of Bryozoans (Ectoprocta).
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Figure 1

Physical Description

Physical Appearance
Bugula neritina are branching biserial, flexible bushy colonial animals, that stand upright, with an estimated height of 15 cm (Bishop Museum 2002, Gordon and Mawatari, 1992, (Linnaeus, 1758)). Its colour varies, from dark red-purple to purple-brown, but in most cases, a dark or dull red color. Discoloration of the branches of B. neritina, is an indication of a dead or lifeless branch or section of the bryozoa with the absence of zooids, ovicells and with an appearance that is translucent or whitish in color.

Specificity on Zooids
Individuals within a colony are called zooids. These zooids consist of soft parts called polypides (Bishop Museum 2002, Gordon and Mawatari, 1992) (figures 2 and 3). These polypides are found enclosed in a rigid box called zooecium (Greek for ‘animal house’). Each branch within the colony comprises of a double row of zooecia, facing in one direction. These zooecia are stacked on top of one another in each row, and both rows in each branch, are staggered (Bishop Museum 2002,Gordon and Mawatari, 1992, (Linnaeus, 1758)). An individual zooecium is 0.2 – 0.3 mm wide and 0.6 – 1.1 mm long (Cohen 2011). With a flexible membrane front,and bearing no spines, the upper, outer corner of the zooecium extends to a sharp point.  Other species in the family Bugulae, bear distinctive, bird-head shaped structures with a jaw-like element, called avicularia, which opens and closes, this feature is absent in B.neritina. This distinguishing feature differentiates B. neritina from other bryozoans  (Cohen 2011).
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Figure 2
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Figure 3

Ecology

Habitat
B. neritina, lives in the marine environment, under salinity levels above 14 ppt and does not mature well under levels lower than 18 ppt. B. neritina are known as a fouling member in the marine environment due to their capacity to thrive from shallow subtitdal to intertidal depths in embayments, harbours and even bays (Bishop Museum 2002, Linnaeus, 1758).

Feeding
Bugula neritina has 20 – 24 white and translucent tentacles that sway and rotate in the water scanning for nutrients, forming a bell-shaped structure upon expansion (figure 5). B. neritina are suspension feeders, feeding on small phytoplankton by closing its tentacle tips around the prey to form a cage (Ruppert et al., 2004). Protrusion and expansion (figure 4) of the lophophore and polypide occurs from the zooecium through the membranous front orifice (Cohen 2011). Its lophophore bears cilia along each tentacle, producing currents, that draws water towards the open end of the bell-shaped funnel and travels outward between the tentacles (figure 6). This leads trapped micro-planktons and other organic particles into the mouth via the frontal cilia located at the inner surface of each tentacle (Eldredge and James 2002, GISD 2015 and, Ruppert et al., 2004). Food particles are transported to the mouth in all bryozoans through the process called tentacular flicking (Ruppert et al., 2004).

Two possible assumptions have been made in relation to the extraction of nutrients from water;
1) Ciliary reversal hypothesis
  • When food particles/nutrients come in contact with the cilia on the tentacles, it triggers a switch in motion causing the reversal of the beating of the cilia, kicking the particles back, transporting food particles via the frontal cilia (Ruppert et al., 2004)
2) Impingement hypothesis

  • Occurs due to the movement of food particles towards the mouth, flowing between into the funnel of tentacles, causing a straight movement into the mouth when water current bends sharply, exiting the tentacles (Ruppert et al., 2004).
The video here shows a close up view of the movement of the cilia, drawing both food and water currents, for nutrients.
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Figure 4
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Figure 5
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Figure 6

Importance: E.g. Indian River Lagoon
The Indian River Lagoon (IRL) holds vast array of habitats such as wetland, terrestrial, and estuaries, forming a compounded high ecosystem with high biodiversity. IRL holds economical, commercial and recreational benefits, generating millions to billions of dollars a year (Wright (2014).

Marine and freshwater bryozoans are generally suspension feeders in the benthic envrionment. They are relatively important in the Indian River Lagoon (IRL). Acting as a filtering system in the IRL in the marine environment, these bryozoans filter out excess waste and nutrients that flood the coastal, affecting the productivity of seagrasses, thus affecting the marine organisms in the area (Wright 2014).

According to Wright (2014), a typical bryozoan of colony, with an approximate size of 1m², has the capacity to filter up approximately 50,000 gallons of seawater per year.

Life History and Behaviour

Reproduction
Zooids are individual bryozoans occuring within a colony.

Ovaries of bryozoans are located at the distal end, whereas the testes are located on the funiculus at the basal end (Figure 4 or 10) (Ruppert et al., 2004).

The reproduction life cycle (figure 7) of the species B. neritina is a unique process, undergoing both sexual and asexual reproduction during its life cycle, thriving through warm waters and hard substrates(Fuchs, et al 2011).

A colony of the adult B. neritina is formed from a single, sexually produced, primary zooid, which undergoes asexual budding, producing a group of daughter cells, forming buds. Zooids of B. neritina, in general, are hermaphroditic.

Each zooid produces both sperm (only occurs towards the end of their lifespan, avoiding self-fertilization), and eggs (occurs in the middle of their lifespan). The sperm from the zooid is released into the coelom, with the fertilized eggs retained and brooded for a certain time period, before being released. (Eldredge and James 2002). 

A single dark-brown embryo is only produced at a time by the zooid, which is clutched onto a white, smooth globular complex, called ovicell (figures 8 and 9) (Bishop Museum 2002 (Linnaeus, 1758)). These ovicells are often distinct and bountiful as seen in the figures below. Ovicells tend to settle around the central, more mature,\ area within the colony. Upon release from the ovicell, "coronate" larvae of B. neritina do not have the capabilities nor function to feed themselves as they lack a complete gut, preventing to feed on any organisms during their developmental stages (Bishop Museum 2002 (Linnaeus, 1758)). According to Fuchs, et al 2011, because the larvae lacks a complete gut nor any feeding mechanism, it survives by relying heavily on the yolk sac surrounding the egg.

The fully developed larvae are then released from the ovicells and swims around with the aid of celiated coronal cells that surrounds the external layer of the larva (Lynch, 1947). After the time these larvae are released, they swim around in search of a hard substrate before attaching themselves to it tocommence the process of metamorphosim, which normally occurs within a day or two, into the first feeding colony, ancestrula, where the process of asexual budding occurs (Lynch, 1947, andSharp, et al 2007). 

The larvae of B. neritina tends to settle throughout the year except during the winter seasons (Sutherland and Karlson 1977). Keough and Chernoff, 1987; NEMESIS 2006 stated that the settlement behaviour of B. neritina larvae, is due to the likelihood of environmental and genetic variation effects.


Further illustration of the reproduction of B. neritina can be seen here.

Click here to view the movement of the larvae of Bugula neritina (tiny black ball-like shapes), which was placed in a dish filled with seawater, and viewed under a dissecting microscope.
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Figure 7
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Figure 8
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Figure 9
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Figure 10

Anatomy and Physiology
Gas Exchange:

According to Ruppert et al. 2004, gas exchange in all bryozoans does not only occur at the lophophore, but around its exposed body surface as well. Interzooidal pores in eurystomes are enclosed by rosette cells that controls the flow of organic materials, that are transported from the funicles of an individual zooid through the rosette cell cytoplasm to the funiculus of an individual zooid at the opposite side (Ruppert et at. 2004). 

Digestion:

Ruppert et al. 2004 explains that lophophores in eurystomes are protruded due to the contraction of the perietal muscles (figure 13) that squeezes the body, elevating the coelomic pressure within the body of a zooid. During the protrusion process of the lophophore, the perietal muscles are activated, causing the frontal membrane to bow inward. Retraction muscles retracts the lophphore and introvert into the zooid.

A U-shaped gut can be seen in the anatomy of a bryozoan as seen in figures 11 and 12. The U-shaped gut consist of a large, three-part stomach that has the cecum, ​pylorus, and cardia. The Cecum, like a large pouch, sits at the bottom of the stomach. The posterior pylorus, is partitioned by a second sphincter, from the intestine and rectum. The anterior cardia and shpincter valve are joined by the esophagus. (Ruppert et al. 2004). 

The funicular cord system, labelled in figure 13, not only aids in nutrient transport, it is also a crucial system for dispersing colony wide of the metabolites in cheilostomes (Ruppert et al. 2004).

Nervous System:

The dorsal side of figure 11 contains the brain (a ganglionic mass) of a bryozoan, and has a nervous system that consists of a nerve ring that goes around the pharynx (Ruppert et al. 2004). Presence of the ring and ganglion contributes to nerves that extends to other parts of the body, including the tentacles. Bryozoans in general do not have any specialized sense organs, however, individual sensory cilias, located along their tentacles serves as their means of sensing the surrounding environment.

The branches of B. neritina are positively phototropic, which indicates that there must be some form of phototropic responses capability in them. In colonies, nerves encircling the walls of zooids penetrates the interzooidel pores (figure 13), creating a form of communication and connection to adjacent zooids with similar nerves, which aids in the coordination of the retraction, protrusion, feeding and orientation of the lophphores within the colony (Ruppert et al. 2004).



Click here to see an illustration of B. neritina under a microscope.
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Figure 11
12
Figure 12
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Figure 13

Biogeographic Distribution
Bugula neritina can be found in subtropical, tropical, and temperate waters (The Exotic Guide, 2011). They usually attach themselves onto any hard substrate, such as rocks and floating docks (Collin, Wendt 2006) that is suitable to its needs, and begin metamorphosis to the first feed colony ancestrula (Sharp, et al 2007).  B. neritina are found globally, sometimes even on oyster beds and oyster shells (Conrad et al 2000 and The Exotic Guide, 2011). According to The Exotic Guide, 2011 and Cohen 2005, it was the intense attachment and hull fouling onto ships and oyster shells (oyster shippings), that began the widespread of B. neritina, allowing their movement to be on a gobal scale.

Evolution and Systematics

Bryostatin! An evolutionary occurance
Bryozoans are regarded as small, biofouling colonial marine invertebrates that coats most surfaces.B. neritina has been highly sought after amongst researches and scientists because it produces multiplex bryostatins (polyketides), which could be a potential cure for Alzheimer's diseases, and even, a cancer drug (Munn 20011). However, it is not the bryozoan that makes up the chemical. It is the bacterial endosymbiont Candidatus Endobugula sertula, found in the tissues of B. neritina,that secretes a chemical called bryostatin (figure 14). Candidatus Endonugula sertula (gammaproteobacterium) (Munn 2011), also plays a role by producing bryostatin which blots the surface layer of the larvae at really high concentrations, as a protection, leaving a bad taste to predators when preyed on (Sharp, Davidson, Haywood, 2007). 

The nature of the endosymbiont bacteria, is still unknown.
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Figure 14

Phylogeny of Bryozoa
The sister taxa to bryozoans are Gymnolaemata and Phylactolaemata (Ruppert et al. 2004). 
Gymnolaemata autapomorphies consist of epistome and body-wall muscle loss. Phylactolaemata autapomorphies comprise of a reduction in the hemal-funicular system, an open coelomic pores present between zooids, and statoblasts.  (Ruppert et al. 2004).

Sadly, there were no fossil records of phylactolaemata, therefore making it impossible to determine their relationship with the marine taxa. The only bryozoan fossils recorded occurred in the late Cambrian, however, there have been doubts over the species that was found. In the early period of Ordivician, rich fossil records were discovered, thus producing a vast array of species that were classified and described. In the Paleozoic era, cyclostomes were the dominant species and, it was the cheilostomes, emerging in the late Jurassic, that currently holds the dominant marine forms of today (Ruppert et al. 2004).

During the Paleozoic era, cyclostomes were dominating. In today’s dominant marine form, cheilostomes, began emerging in the late Jurassic. According to A. H. Cheetham, Jeremy B. C. Jackson, S. Lidgard, F. K. McKinney (2001), it is still a question that has yet been answered between the time of evolution that occurred between cyclostomes and cheilostomes.

Conservation and Threats

Management
B. neritina has been deemed as a top ten invasive and impacting species that has the capabilities to infect areas/regions that have yet been infected by it. This is determined based on its ability and potential to bring a huge impact environmentally and economically from infected to uninfected areas. B. neritina has been classified a 'medium priority species' that has a relatively high level of invasive impacts to a region (GISD 2005).

Wisely 1962, conducted a study which looks at the attachment and settlement of the larvae of B. neritina using chemical based paints such as mercury and copper, along with a control paint. The results shows that the control paint has a higher density of settlement and attachment of B. neritina larvae (NIMPIS 2001). This in turn brings in the idea of having implement chemical based paints onto the hulls of ships and vessels, controlling the widespread invasion of B. neritina globally (Piola and Johnston 2006).

Prince William Sound Regional Citizens Advisory Council 2004, suggests that ballast waters, in ships, via the oyster aquaculture industry should be taken into account in controlling the spread of B. neritina.

Conservation
B. neritina are not faced with any threats or extinction. But are deemed a biofouling invasive species worldwide. 

Predation threats
Nudibranchs are said to be consumers of B. neritina (NIMPIS 2002). B. neritina are preyed upon by grazers such as sea urchins and fishes. B. neritina larvae are sometimes preyed upon by fishes (Bishop Museum 2002, Linnaeus, 1758).

Competition

Competition is inevitable. Marine invertebrates face competition throughout their lifespan. The competition of space, food source, and even habitat. B. neritina usually face competition from the overgrowth of algae, tunicates and sponges (PWSRCAC 2004).

References

Citations
Alan H. Cheetham, Jeremy B. C. Jackson, Scott Lidgard, Frank K. McKinney. Evolutionary Patterns: Growth, Form, and Tempo in the Fossil Record. University of Chicago Press, 1 Aug. 2001.

An Introduction to the Study of Invertebrate Zoology n.d. 
<URL: http://www.faculty.ucr.edu/~legneref/invertebrate/bryozoa.htm> Accessed 27 May 2016.

Bishop Museum 2002. Bugula neritina (Linnaeus, 1758). Guidebook of introduced marine species of Hawaii.

Collin, H. and Dean E. Wendt. Availability of dissolved organic matter offsets metabolic costs of a protracted larval period for Bugula neritina (Bryozoa). Marine Biology 151: 301-311.
Common Marine Organisms of Monterey Bay, California 2012. <URL:http://seanet.stanford.edu/> Accessed 27 May 2016.

Cheilostomata 2014. <URL: http://www.britannica.com/EBchecked/topic/108357/Cheilostomata> Accessed 27 May 2016.

Classification of the Dutch freshwater bryozoan 2007. 
<URL:http://www.bryozoans.nl/algemeen/en/classification.html#gymnolaemata> Accessed 27 May 2016. 

Cohen, A.N. 2005. Guide to the Exotic Species of San Francisco Bay. San Francisco Estuary Institute: Oakland, USA.

Cohen, Andrew N. 2011. The Exotics Guide: Non-native Marine Species of the North American Pacific Coast. Center for Research on Aquatic Bioinvasions, Richmond, CA, and San Francisco Estuary Institute, Oakland, CA, Revised September 2011.

Davidson, S. K., S. W. Allen, G. E. Lim, et al. 'Evidence for the Biosynthesis of Bryostatins by the Bacterial Symbiont "Candidatus Endobugula Sertula" of the Bryozoan Bugula Neritina', Applied and Environmental Microbiology, vol. 67/no. 10, (2001), pp. 4531-4537.

Domain Eukarya 2013. 
<URL: http://comenius.susqu.edu/biol/202/domains/default.htm> Accessed 27 May 2016.

Eldredge, Lucius G. and James T. Carlton. "Hawaiian Marine Bioinvasions: A Preliminary Assessment". Pacific Science 56.2 (2002): 211-212. Web. 

Fuchs J. M.Q. Martindale and A. Hejnol. 2011. Gene expression in bryozoan larvae suggest a fundamental importance of pre-patterned blastemic cells in the bryozoan life-cycle. EvoDevo 2:13.  

Global Invasive Species Database (GISD) 2015. Species profile Bugula neritina.

Gordon, D.P. and S.F. Mawatari. 1992. Atlas of marine-fouling Bryozoa of New Zealand ports and harbours. Miscellaneous Publications of the New Zealand Oceanographic Institute 107:1-52 (pp. 30-31).

Hayes, Keith R. et al. "Sensitivity And Cost Considerations For The Detection And Eradication Of Marine Pests In Ports". Marine Pollution Bulletin 50.8 (2005): 823-834. Web.

The Indian River Lagoon: An Estuary Of National Significance. Sjrwmd.com. Web. 31 May 2016.

Keough, M. J. and Chernoff, H. 1987. Dispersal and population variation in the bryozoan Bugula neritina Ecology 68(1): 199-210.

Kingdom Animalia 2014. <URL:http://biology.tutorvista.com/organism/kingdom-animalia.html> Accessed 27 May 2016. 

Lynch, W.L. 1947. The behavior and metamorphosis of the larva of Bugula neritina (Linnaeus): experimental modification of the length of the free-swimming period and the responses of the larvae to light and gravity, Biological Bulletin 92: 115-150.

Merriam Webster 2014. 
<URL: http://www.merriam-webster.com/dictionary/gymnolaemata> Accessed 27 May 2016.
Munn, Collin. "Marine Microbiology". Google Books. N.p., 2011. Web. 27 May 2016.
National Introduced Marine Pest Information System (NIMPIS), 2002. Bugula neritina species summary. In: Hewitt, C.L., Martin, R.B., Sliwa, C., McEnnulty, F.R., Murphy, N.E., Jones, T. and Cooper, S. (eds). NIMPIS. Retrieved 7 December 2006, from NIMPIS database.

NEMESIS (National Exotic Marine and Estuarine Species Information System). 2006. Bugula neritina. The Smithsonian Environmental Research Center. Retrieved 7 December 2006, from Chesapeake Bay Introduced Species Database.

Prince William Sound Regional Citizens Advisory Council. 2004. Non-indigenous Aquatic Species of Concern for Alaska. Fact Sheet 9. Single Horn Bryozoan. 

Ruppert, E., Fox, R., Barnes, R (2004). Invertebrate Zoology: A Functional Evolutionary Approach, (7th Ed). Brooks/Cole Thompson Learning,Belmont, California.

Sharp K. H., S. K. Davidson and M.G. Haygood. 2007. Localization of Candidatus endobugula sertula and the bryostatins throughout the life cycle of the bryozoan Bugula neritina. The ISME Journal 1:693-702.

Sutherland, J.P. and Karlson, R.H. 1977. Development and Stability of the Fouling Community at Beaufort, North Carolina, Ecological Monographs 47(4): 425-446.

Wright, J. 2014. "Bryozoa" (On-line), Animal Diversity Web. Accessed May 31, 2016 at http://animaldiversity.org/accounts/Bryozoa/

    Video/s
    Bugula Neritina - The Life Cycle Of A Marine Bryozoan. Center for Marine Biology (CEBIMar), University of São Paulo, Sao Sebastiao, Brazil: Alvaro E. Migotto & Leandro M. Vieira, 2015. video. https://www.youtube.com/watch?v=FcvqEsLb23s

    Center for Marine Biology (CEBIMar), University of São Paulo (http://www.usp.br/cbm/), at São Sebastião, by Alvaro E. Migotto and Leandro M. Vieira.. (2015). Bugula neritina - the life cycle of a marine bryozoan. [Online Video]. 9 December 2015. Available from: https://www.youtube.com/watch?v=FcvqEsLb23s.
      
    GS's Biology Bonanza. (2007). Bryozoan feeding. [Online Video]. 19 January 2007. Available from:https://www.youtube.com/watch?v=4MI8kBLcRco. [Accessed: 27 May 2016].