The Panama Canal region is susceptible to non-native species introductions due to the heavy international shipping traffic through the area. Ascidian introductions are occurring worldwide but little is known about introductions at the Panama Canal. Surveys were conducted in 2002, 2008, and 2009 within the Pacific and Atlantic entrances to the canal. We found a high diversity of ascidians on both sides of the canal, dominated by non-native species; six species occurred at both Pacific and Atlantic Panama sites. This is the first report of Polyandrocarpa anguinea and P. sagamiensis in Atlantic Panama waters and Ascidia incrassata, Ascidia sydneiensis, Botrylloides nigrum, Botryllus planus, Didemnum perlucidum, Diplosoma listerianum, Microcosmus exasperatus, Polyandrocarpa zorritensis, Polyclinum constellatum, Symplegma brakenhielmi, Symplegma rubra, and Trididemnum orbiculatum in Pacific Panama waters. The canal may serve as a major invasion corridor for ascidians and should be monitored over time.

Little is known about the ascidian fauna of Pacific Panama. Ascidian surveys were conducted in the southern Gulf of Chiriquí on the Pacific coast of Panama in January 2008 and 2009. Surveys along linear transects at 2-3 m depth (snorkel, 2008) and 5 and 12 m depth (SCUBA, 2009) were conducted at multiple sites within a chain of islands extending out from the mainland. Twelve different ascidian taxa were observed with mean densities of up to ~17 ascidians m-2. The most abundant species was Rhopalaea birkelandi. Two of the most abundant taxa (Ascidia sp., Pyura sp.) appear to represent previously undescribed species. Several species of didemnids were also abundant. Ascidians were most abundant near the coast of the mainland and were less abundant near the islands farthest offshore. These data on Panamanian ascidian communities provide a baseline of local biodiversity against which it will be possible to determine whether the communities change over time, if additional species become introduced to the region, or if native Panamanian species become invasive in other parts of the world.

The shellfish culture industry in Atlantic Canada has been adversely affected by the presence of non-indigenous, invasive tunicates since the mid-1990’s. A Fisheries and Oceans Canada Aquatic Invasive Species (DFO-AIS) monitoring program documented the presence, establishment, and spread of five tunicate species at geo-referenced coastal monitoring stations in Nova Scotian waters from 2006-2009. Styela clava (Herdman, 1881) and Didemnum vexillum (Kott, 2002) were not found in Nova Scotia during the course of this study, despite their problematic presence in Prince Edward Island and the Gulf of Maine, respectively. Botryllus schlosseri (Pallas, 1766) was the most widely distributed species, found at more than 69% of sites monitored in all years. Ciona intestinalis (Linnaeus, 1767) was present at about half of the stations in all years, and while its populations were heaviest and most persistent in the Halifax – St. Margaret’s Bay, Shelburne – Port La Tour, and Canso – Isle Madame areas, there was evidence of spread on the eastern and Fundy shores, and in Cape Breton. Botrylloides violaceus (Oka, 1927), was the least common tunicate encountered, but its distribution increased from 19% of stations in 2006 to 50% of stations in 2009. Tunicates occupied a wide variety of hard substrates (natural and artificial) in waters with 13.0 to 33.2 salinity and at oxygen saturations of 32.5 to 124.8%.

A monitoring programme was initiated in 2006 to detect invasive tunicates, especially Ciona intestinalis, Botryllus schlosseri, Didemnum vexillum, Botrylloides violaceus and Styela clava, in Atlantic Canada. Collectors were deployed at 11–21 monitoring stations in the southwestern New Brunswick portion of the Bay of Fundy from 2006-2009, starting in late May with some retrieved in August while others remained in the water until later in the fall. There was large variability between years and sites. C. intestinalis was detected through much of the southwest New Brunswick area, including Grand Manan Island, but not in the area from Dipper Harbour to Saint John. B. schlosseri was observed to be concentrated in the Dipper/Beaver Harbour areas and Grand Manan Island, St. Andrews Harbour, Fairhaven (Deer Island), and Harbour de Loutre (Campobello Island), with greatest settlement observed in 2009. During the study period, B. violaceus was first detected in 2009 and at only one location, Head Harbour, Campobello Island. S. clava and D. vexillum have not been detected from our sampling collectors to date. As the invasive colonial tunicate, D. vexillum, has rapidly extended its range in the northeastern United States of America and is within 2 km of Canadian waters, a rapid assessment was conducted around Deer Island and Campobello Island in September 2009 and failed to detect the species.

We tested the hypothesis that marine non-native fouling species are more abundant than native species on artificial structures, focusing on ascidians and using fouling plates deployed in various Dutch harbors. A more detailed study was conducted in the pleasure craft harbor of Breskens, in the south of The Netherlands, where a species assessment was done of iron harbor walls, wooden pilings, diagonal stone rip-rap dikes, fouling plates, and the inside, outside and underside of the floats of floating docks. Ascidians were found only on the floating structures. Non-native ascidians were not found to be significantly more abundant than native ascidians, however. Solitary and colonial tunicates were compared, assuming that they fundamentally differ in their abilities to occupy space. In general, colonial species like the native Botryllus schlosseri and the non-native Botrylloides violaceus were more abundant on fouling community plates, while solitary ascidians like the native species Ciona intestinalis and Ascidiella aspersa appeared to be more successful later in succession. The inside, outside and underside of a floating dock harboured significantly different species communities. Ascidiella aspersa for example was found significantly more often on the underside than on the inside and outside of the dock floats. When assessing the ascidian species diversity in a harbor it is therefore advised to search several different habitats on floating structures.

Approximately 200 grey PVC settlement plates were hung along at sites along the Dutch coast at a depth of 1 meter. The cover of each species that could be identified on the plates was recorded every three months from March 2009 to March 2010 to study the role of native versus non-native ascidians in the succession of marine fouling communities. Three native ascidian species, Ciona intestinalis, Ascidiella aspersa and Botryllus schlosseri, and five species of cryptogenic and/or non-native origin, Molgula socialis, Styela clava, Diplosoma listerianum, Botrylloides violaceus and Didemnum vexillum, were recorded. After the Cnidaria, Ascidiacea were found to be the group that explained most of the differences found in species communities on settlement plates at different stages in the succession. Regardless of the fact that non-native ascidian species were very abundant at times, their role in the succession of the studied marine fouling communities appears to be limited. After the polyp stage of the moon jelly Aurelia aurita and hydroid species of the genus Obelia, the two native ascidian species Ciona intestinalis and Ascidiella aspersa explained most of the differences that were found between the successive stages in the fouling communities. In general, the three native ascidian species appeared to determine the succession of the fouling communities more than the five cryptogenic and/or non-native ascidian species. Whether this is linked to species being either native or non-native is questionable however. The various ascidian species differed strongly in the period of settlement, the ability to settle on prior settlers and the ability to survive the winter. The non-native ascidians settled mostly in June to December, while the native ones settled from March to December. Although the native ascidians M. socialis and B. schlosseri were found to be restricted in their settlement by the presence of prior settlers, the non-native species B. violaceus and D. vexillum were not. Native and non-native ascidian species survived the winter equally well. Native C. intestinalis and A. aspersa and non-native B. botrylloides and D. vexillum were most successful in surviving winter water temperatures of just below 0°C. Thus the results of this study, based on one year of data, suggest that the roles of ascidian species in the succession of fouling communities vary, and that being native or non-native is not necessarily linked to the degree to which species influence the development of marine fouling communities. Their individual seasonality, abilities to overgrow prior settlers and survival of winter temperatures appear to be more important.

Settlement and competition for space of two colonial sea squirts, the non-native violet tunicate Botrylloides violaceus and the native golden star tunicate Botryllus schlosseri, were compared in The Netherlands. In each year, from March 2006 to March 2010, 125-150 grey, 14 ´ 14 cm, PVC plates were deployed along the Dutch coast at 13 localities, at a depth of 1 m, and checked for species after three and six months. New plates were deployed every three months. While comparing plates with only one species represented to plates with both species represented, it appeared that Botrylloides violaceus outcompeted Botryllus schlosseri for space. Botryllus schlosseri is nevertheless expected to remain abundant along the Dutch coast because it can inhabit places with low or fluctuating salinities where Botrylloides violaceus is at a disadvantage. Settlement and the interactions between these species in The Netherlands resembled the situation in North America where both of them are considered non-native. The interactions between the two species seemed to be independent of their being native or introduced in a particular area.

Didemnum perlucidum is a colonial ascidian that is cryptogenic in southern Brazil but introduced in many regions around the world. It is common in ports and marinas where it may form large colonies although its role in fouling communities is poorly understood. The goal of this study was to evaluate the role of D. perlucidum in a marine fouling community comprised mainly of non-indigenous species. Treatment pairs (D. perlucidum removal and unmanipulated controls) of experimental plates were exposed during 14 months at a mussel farm in southern Brazil. Taxonomic richness and percent cover of the species were compared between treatments (with and without D. perlucidum). D. perlucidum did not influence taxonomic richness or inhibit colonization by any species. Effects of this species on the abundance of others were sporadic, and suggest that it may be a weak competitor. The small effect of D. perlucidum in this community is explained by its low abundance and its occupation of secondary substrate without having detrimental effects on the species it grew over. Given that D. perlucidum is more abundant, and problematic, in other regions of southeastern and southern Brazil, continuous monitoring is desirable to better understand its fouling dynamics.

Didemnum vexillum is a globally invasive species and a major pest to the aquaculture industry. Like other colonial ascidians, D. vexillum can readily overgrow aquaculture nets and cultured species. Recently, the species has been found in great abundance on seafloor habitats, where it is often associated with commercially important shellfish species such as sea scallops, Placopecten magellanicus. Despite the increasing abundance of D. vexillum in areas that are regularly fished for sea scallops, little work has been conducted on the ascidians impact on scallop behavior. This study examined the effect of overgrowth of the sea scallop by D. vexillum using four measures: time to initial exhaustion, swimming speed, horizontal and vertical displacement. Scallops covered by D. vexillum became exhausted more quickly, and were not able to swim as far in either the horizontal or vertical direction as the control sea scallops without D. vexillum encrustation. The expansion of D. vexillum into sea scallop habitat may increase the vulnerability of sea scallops to predation and limit their ability to access food rich habitats.

The colonial ascidian Didemnum vexillum has become relatively widespread in New Zealand, since its initial discovery in 2001. Despite the potential economic and ecological impacts of D. vexillum, there are still considerable knowledge gaps surrounding its key biological attributes. The ability to obtain larvae and culture colonies in the laboratory is crucial to research into larval longevity and dispersal potential, and the factors affecting colony survivorship and growth. Here we present methods for spawning and culture of D. vexillum under laboratory conditions. A ‘light shocking without cycles’ technique was used to stimulate larval release in adult colonies, with > 500 larvae being produced from ~ 100 g of tissue at the peak of the reproductive season. Following release, the larvae were allowed to metamorphose and the juveniles were cultured under controlled conditions for four weeks. Recruit survival during the four weeks of culture was > 85 % with the majority having formed small colonies of 4 to 6 zooids with a dense cover of white spicules throughout the tunic. The most effective laboratory spawning conditions are described with respect to light and temperature. The ability to obtain D. vexillum larvae on demand will enable increased research into several aspects of this species’ reproductive biology and ecology.

The development of effective mitigation techniques against Botryllus schlosseri and Botrylloides violaceus colonizing blue mussel aquaculture operations has not been well studied. The objectives of our research were to determine the efficacy of using pressurized seawater in the mitigation of colonial tunicate fouling and to identify optimal treatment timing and frequencies in reducing tunicate biomass. Treatment trials using high- (~700 psi) and low-pressure (~40 psi) seawater spraying were conducted in St. Peters Bay and Savage Harbour, PEI, from May to November 2009. The use of high-pressure seawater was an effective anti-fouling measure for these species, causing significant reductions in tunicate biomass. In contrast, low-pressure seawater had no discernable effect. The timing of treatment was found to be the most important factor affecting efficacy, with reductions in tunicate biomass increasing in magnitude the closer the treatment occurred to harvest. Treatment frequency did not affect tunicate biomass. In addition, fewer treatments also resulted in less nuisance mussel spat fouling the mussel socks. Colonial tunicate fouling did not affect adult mussel growth and productivity, and no evidence of smothering or crop loss was observed.

Life history processes, such as reproduction, survival and growth, are known to be strongly affected in ascidians by different types of environmental factors including temperature and salinity. In a field study conducted from 2005 to 2009 in southern Nova Scotia, an area affected by invasions of Ciona intestinalis, low winter and high summer temperatures were shown to be strongly associated with intra- and inter- annual variation in larval recruitment. No clear patterns of association were seen with other environmental variables such as chlorophyll and indices of nutrient concentrations. In a 12 week challenge experiment in the laboratory, survival and growth of juvenile C. intestinalis were affected by both salinity and temperature. Individuals exposed to high temperature (25°C) and low salinity (20) did not survive the sustained exposure. In addition, Individual Specific Growth Rates were shown to decrease as salinity decreased. Temperature and salinity are factors which will subsequently influence distribution, persistence and potential for spread of adult populations. New favourable temperature and salinity conditions (e.g., potentially resulting from global climate change) will likely alter the distribution patterns of C. intestinalis. Conversely, infestation management techniques or site selection could benefit from unfavourable sustained temperature and salinity conditions.

Despite sporadic observations of the vase tunicate, Ciona intestinalis, on boats and mooring structures in Charlottetown Harbour, Prince Edward Island, the species has not established a population in the harbour nor dispersed the ~12 km downstream to Hillsborough Bay, an important source of blue mussel (Mytilus edulis) spat for the PEI aquaculture industry. A population matrix model used in conjunction with an oceanographic model suggests that advection of larvae from the harbour to the spat production area requires more than one or two generations, and the use of intermediate settlement nodes, such as navigational aids and aquaculture sites located in the upper part of Hillsborough Bay, as ‘stepping stones’. Maintaining potential settlement nodes in a tunicate-free condition could delay oceanographic dispersal of C. intestinalis within the estuary. According to observations of colonial tunicate dispersal in 2010, most likely originating from colonies established in the same locations where C. intestinalis inoculations have been detected, dispersal was occurring in the vicinity of one of the nodes identified by the model as priorities to be monitored for early detection of tunicate settlement, but had not yet reached the other node. A major finding is that the dispersal of solitary tunicates by oceanographic processes, often considered uncontrollable, is evidently amenable to management through monitoring and cleaning of the intermediate settlement nodes.

Mussel growers in Prince Edward Island (PEI), Canada, currently use high-pressure water spraying (~700 psi) to mortally injure or dislodge invasive tunicates from mussel product and gear. An added benefit of this process may be the stimulation of byssal thread production, leading to improved mussel attachment. This study measured byssal thread abundance and thickness in cultured blue mussel Mytilus edulis exposed to high-pressure spraying either once, five times (every three weeks), or not at all (control). No significant differences were observed in number or width of byssal threads between treatments indicating routine high-pressure spraying does not affect mussel attachment strength.

The toxicity of the synthetic catemine medetomidine to <12 h-old larval clubbed tunicate, Styela clava, was assessed in 2-h laboratory bioassays. Exposure to medetomidine resulted in increasing rates of larval immobility with increasing concentration. The 2-h EC50 was 3.8 mg/L medetomidine. Larval settlement was highest at a concentration of 0.1 mg/L medetomidine. At higher concentrations of medetomidine, metamorphosis was initiated but not all larvae settled. The ability of medetomidine to reduce S. clava larval mobility and interfere with settlement suggests that it has potential as a management tool for controlling subtidal invasive S. clava populations.

The Australian native colonial ascidian Eudistoma elongatum has spread throughout harbours and oyster farms in Northland, New Zealand. This paper summarizes results of a study on the biology, ecology and potential methods of control of this recently introduced species. Colonies were reproductive for nine months of the year and embryos were present in zooids at water temperatures above 14°C. Low salinity was most likely the cause of variation in reproductive status observed. Larvae were able to swim for up to 6 hours, and remain viable at temperatures as low as 10°C at salinities above 20 psu. Only acetic acid was effective at killing colonies. Control using heat or other chemicals was not feasible for shallow subtidal populations identified in the study. E. elongatum has the potential to spread further within already occupied harbours, and to more southern harbours in New Zealand.

Along the coast of Maine, recruitment of most invasive marine ascidians follows a generalized regional pattern, with higher recruitment rates at western sites. Using artificial collectors we found that Botryllus schlosseri, Botrylloides violaceus, Ciona intestinalis, Ascidiella aspersa and Styela clava were more abundant in the western (southwestern) sites than in the eastern (northeastern) sites. This general pattern also applies to a number of other recruiting species including native mussels, Mytilus spp., and the invasive crab, Carcinus maenas. While recruitment of many marine organisms can appear stochastic in space, there can be some consistent regional patterns. Higher recruitment in the western sites of Maine may be the result of greater oceanographic dispersal due to the westward flow of the Maine coastal current, higher seawater temperatures in the west, and more anthropogenic introductions having occurred in the western harbors.