Botrylloides giganteus

Invasion History

First Galapagos Record: 2015

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General Invasion History:

The colonial tunicate Botrylloides giganteus was first described from Senegal in 1949. In the 1980s, it was found in Brazil, over a limited range from Sao Paulo to Vittorio (Aron and Sole-Cava 1991, Rodrigues and da Rocha 1993, Da Rocha and Costa 2005). In 1997, a colonial tunicate, first identified as B. perspicuum, was found on the coast of southern California (Lambert and Lambert 2003). Recent morphological and genetic studies (in preparation) indicate that the Southern California form was conspecific with B. giganteus and with a colonial tunicate described from the Gulf of Taranto, Italy, B. pizoni (Brunetti and Mastrotaro 2012). It has also been identified in New Zealand (Riding et al. 2014, Ministry of Primary Studies 2015, Rocha et al. 2019). The native and introduced ranges of this tunicate are unresolved. 

Invasion History in the Galapagos:

Botrylloides giganteus was collected on settling plates in 2015 and 2016 in Tortuga Bay, Santa Cruz Island, and on Baltra Island. Two color morphs, purple and red, were found. These were the first records from the Galapagos (Lambert 2019).

Invasion history elsewhere in the world:

The native range of Botrylloides giganteus is unknown. The type locality was Senegal (Peres 1949, cited by (Aron and Sole-Cava 1991), but it was subsequently found on the Indian Ocean coast of South Africa and Mozambique (Millar 1955, Millar 1961, Millar 1963, cited by Monniot et al. 2001; Rocha et al. 2019). In Brazil, it was first found in 1986, and is known largely from artificial substrates, and is especially abundant in mussel cultures. It was not seen in previous surveys and is considered introduced and established in Brazil (da Rocha et al. 2009; Rocha et al. 2019; Oricchio et al. 2019). In 2014, B. giganteus was found in Whangarei Harbor, New Zealand (Riding et al. 2014; Rocha et al. 2019), and on Santa Cruz and Baltra Islands, in the Galapagos Archipelago, in 2015 (Lambert 2009; Rocha et al 2019).

Description

Botrylloides giganteus is a colonial tunicate. Colonial tunicates are communities of individuals, called zooids, which share a protective cellulose layer called a tunic. Each zooid is an individual, but they are such an intricate part of the colony that they cannot be separated from it. In fact, the zooids are connected to one another by a network of blood vessels and work together to make the colony function like a single animal.

The colonies of B. giganteus are 2-5 mm thick, translucent, and variable in size and shape, ranging from 30 to 150 mm in diameter. They can grow on algae or other debris. Botrylloides giganteus has linear systems of zooids, which are visible through the tunic. The colonies are red to orange or violet in color. The body walls of its zooids are very delicate and transparent and lack longitudinal or circular musculature. The oral siphon is round, with a smooth margin. There are 24 branchial tentacles in mature zooids. On the branchial sac there are 11-17 pairs (usually 14) of stigmata. The atrial siphon develops a languet, a tongue-like structure, which varies in shape and length. The esophagus is short and curved, and the stomach has 9-10 longitudinal folds. A mature zooid can have a single developing embryo. Description based on: Rodrigues and da Rocha 1993, and da Rocha and Costa 2005.

This tunicate, discovered in Southern California, was initially identified as B. perspicuum (1997, Lambert and Lambert 2003). Recent observations indicate that it is actually B. giganteus (Gretchen Lambert and Rosana da Rocha, personal communications). We are in the process of revising the morphological description and biogeographical history of this species (Rodriques and da Rocha 1993; da Rocha and Costa 2005; Rocha et al. 2019).

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Taxonomy

Ecology

General:

Life History- A colonial (or compound) tunicate consists of many zooids, bearing most or all of the organs of a solitary tunicate, but modified to varying degrees for colonial life. Colonial tunicates of the genera Botrylloides have small zooids, usually not organized in systems, and fully embedded in a mass of tunic material. Each zooid has an oral siphon and an atrial canal, opening to a shared cloacal chamber. Water is pumped into the oral siphon, through finely meshed ciliated gills on the pharynx, where phytoplankton and detritus is filtered, and passed on mucus strings to the stomach and intestines. Excess waste is expelled in the outgoing atrial water (Van Name 1945; Barnes 1983). 
 
Colonial tunicates reproduce both asexually, by budding, and sexually, from fertilized eggs developing into larvae. Buds can form from the body wall of the zooid. Colonies vary in size and can range from small clusters of zooids to huge spreading masses. The zooids are hermaphroditic, with eggs and sperm being produced by a single individual. Eggs may be self-fertilized or fertilized by sperm from nearby animals, but many species have a partial block to self-fertilization. Eggs are internally fertilized, and embryos are incubated in a brood pouch. Once they are mature, fertilized eggs hatch into a tadpole larva with a muscular tail, notochord, eyespots, and a set of adhesive papillae. The lecithotrophic (non-feeding, yolk-dependent) larva swims briefly before settlement. Swimming periods are usually less than a day, and some larvae can settle immediately after release, but the larval period can be longer at lower temperatures. Once settled, the tail is absorbed, the gill basket expands, and the tunicate begins to feed by filtering (Van Name 1945; Barnes 1983). 

Food:

Phytoplankton

Consumers:

fishes, crabs

Trophic Status:

Suspension Feeder

SusFed

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Habitats

General Habitat	Rocky	None
General Habitat	Coral reef	None
General Habitat	Marinas & Docks	None
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Tidal Range	Low Intertidal	None
Vertical Habitat	Epibenthic	None

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Life History

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Tolerances and Life History Parameters

Broad Temperature Range	None	Warm temperate-Tropical
Broad Salinity Range	None	Polyhaline-Euhaline

General Impacts

Competition: The colonial tunicate Botrylloides giganteus (then identified as B. perspicuum) covered extensive areas crowding out other species. This was seen in San Diego Bay in 1997 (Lambert and Lambert 2003).

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References

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