Article

A GUIDE TO THE LARVAL AND JUVENILE STAGES OF COMMON LONG ISLAND SOUND ASCIDIANS AND BRYOZOANS

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... 18. Place the bag for Genetic Archive into a second plastic bag. 19. Store this Genetic Archive at 4 C. 20. ...
... 3. Induce spawning in marine bryozoans by sudden exposure to bright light; freshwater species will spawn overnight, but must be watched as the larvae can be very short-lived. The time until larval release can vary between 5 and 60 min depending on the species [19][20][21][22][23][24][25] (see Note 29). ...
... Most gymnolaemates, and all stenolaemates, produce lecithotrophic (nonfeeding) coronate larvae, but other species produce planktotrophic (feeding) cyphonautes [34]. Refer to [19] to identify the two larva types. A pilot study might be required prior to spawning the species of interest, in order to understand the type of larvae produced and potential settlement intervals. ...
Chapter
Full-text available
Among marine invertebrates, bryozoans are small, not well known, and complex to identify. Nevertheless, they offer unique opportunities for whole-body generation research, because of their colonial, modular mode of growth. Here, we describe detailed methods for collection of bryozoans from a range of environments, sample preparation and identification, culture and feeding, spawning and breeding, marking colonies for growth studies, and histological preparation.Key wordsBryozoansCultureCollection Growth Feeding Whole-body regeneration Budding Regression Brown bodies Anatomy Histology Larvae Spawning Settlement
... Fertilization of C. intestinalis eggs occurs in the water column following gamete release during summer and fall months. The duration of embryonic development is highly dependent upon temperature and can range from 18 h at 18-20°C to 48 h at 12°C (Dybern, 1965;Bullard and Whitlatch, 2004). C. intestinalis larvae are very small (0.88-1.28 mm in length) and nearly transparent with a larval phase ranging from 24 h at high temperatures (18-20°C) to 5 days at low temperatures (10-12°C; Dybern, 1965;Bullard and Whitlatch, 2004). ...
... The duration of embryonic development is highly dependent upon temperature and can range from 18 h at 18-20°C to 48 h at 12°C (Dybern, 1965;Bullard and Whitlatch, 2004). C. intestinalis larvae are very small (0.88-1.28 mm in length) and nearly transparent with a larval phase ranging from 24 h at high temperatures (18-20°C) to 5 days at low temperatures (10-12°C; Dybern, 1965;Bullard and Whitlatch, 2004). ...
... B. violaceus is a common fouling organism and is found on both man-made and natural substrates including floating docks, pilings, subtidal rocks and algae, and Mytilus edulis shells (Carver et al., 2006). This species produces very large (length b3 mm) and often brightly colored orange, red, pink, or purple tadpole larvae that are brooded within the colony and released throughout the summer and fall (Bullard and Whitlatch, 2004). The B. violaceus larval phase is very short, lasting from several minutes to hours after release from the parent colony (Lambert, 1990). ...
... Fertilization of C. intestinalis eggs occurs in the water column following gamete release during summer and fall months. The duration of embryonic development is highly dependent upon temperature and can range from 18 h at 18-20°C to 48 h at 12°C (Dybern, 1965;Bullard and Whitlatch, 2004). C. intestinalis larvae are very small (0.88-1.28 mm in length) and nearly transparent with a larval phase ranging from 24 h at high temperatures (18-20°C) to 5 days at low temperatures (10-12°C; Dybern, 1965;Bullard and Whitlatch, 2004). ...
... The duration of embryonic development is highly dependent upon temperature and can range from 18 h at 18-20°C to 48 h at 12°C (Dybern, 1965;Bullard and Whitlatch, 2004). C. intestinalis larvae are very small (0.88-1.28 mm in length) and nearly transparent with a larval phase ranging from 24 h at high temperatures (18-20°C) to 5 days at low temperatures (10-12°C; Dybern, 1965;Bullard and Whitlatch, 2004). ...
... B. violaceus is a common fouling organism and is found on both man-made and natural substrates including floating docks, pilings, subtidal rocks and algae, and Mytilus edulis shells (Carver et al., 2006). This species produces very large (length b3 mm) and often brightly colored orange, red, pink, or purple tadpole larvae that are brooded within the colony and released throughout the summer and fall (Bullard and Whitlatch, 2004). The B. violaceus larval phase is very short, lasting from several minutes to hours after release from the parent colony (Lambert, 1990). ...
... Larvae hatch after ~12 hours and are planktonic for a further 12-36 hours (Holmes 1969, Svane 1984, Minchen et al. 2006). An individual produces relatively few, lecithotrophic, medium-sized, snake-like larvae (Bullard & Whitlatch 2004) that are negatively buoyant (sink), negatively geotactic (swim up), positively phototactic (move towards light) (Davis 1997), and do not seem capable of spreading far as they seldom travel more than a few centimetres by sustained swimming activity (Minchin et al. 2006). Little is known about egg and larval ability frogs, in relatively small steps, from highly localised small populations to expand. ...
... shown that Styela reaches maturity quickly (Lützen 1999, Parker et al. 1999, and although it has a relatively low reproductive output (Bullard & Whitlatch 2004), by forming dense populations it can exert relatively high propagule pressure (Bourque et al. 2007). In estuaries off Prince Edward Island, Styela exhibits a distinct annual cycle with recruitment beginning at the end of June and ending in late October (Bourque et al. 2007). ...
... Within clearance plots recruitment of Styela was monitored monthly. The guide by Bullard & Whitlatch (2004) was used to help in identification of recently recruited Styela (Figure 2.1). It was hoped that this part of the clearance experiment would make detection of smaller individuals easier and allow some insight into the temporal patterns of recruitment in Styela. ...
Article
Full-text available
This thesis is about the demography of the tunicate Styela clava, a species of some notoriety because of its invasiveness and impacts in many parts of the world. Species assemblages have continuously changed throughout evolutionary history, but the rate of today’s anthropogenically facilitated dispersal is unparalleled in history. Non-indigenous species (NIS) are now considered one of the most important risks to native biodiversity. NIS become invasive by becoming both widespread and locally dominant. This requires that a species becomes established, spreads locally, and increases in abundance. In the early stages of invasion, its demography and life history characteristics are of crucial importance. In New Zealand, Styela has established populations in several places, but none of these populations has yet reached the high densities found in other countries. In Lyttelton Port, where this study was located, Styela was first noticed in 2005. It therefore presented an ideal situation to study an invasive species in its early stages of establishment and provided a potentially good model for understanding how invasive species get local traction and spread from initial infestation points. Therefore, I set out to determine demographic features of Styela to understand the numbers game of population dynamics. This study used empirical data on growth rates, size-frequencies through time, and size and age to maturity to test several models, including von Bertalanffy, Logistic dose-response, Ricker and power models of individual growth. The most useful proved to be the von Bertalanffy model. Styela individuals shrink frequently, so average growth rates were often quite low, even though some individuals reached 160 mm or more in total length. Mortality was greatest in summer, presumably after reproduction, and lowest in winter. Fewer than 5% of individuals survived 12 months, and most or all of these died soon afterwards. Populations were, therefore, essentially annual. Recruitment was difficult to determine because of the cryptic nature of small juveniles. However, size-frequency, abundance and mortality data indicated that recruitment most likely occurred in early spring (late-October), and then again in late summer, with growth to maturity (at c. 50 mm total length) within < 5 months. Several manipulative experiments showed that Styela did not readily capitalise on provision of free space but the other non-native ascidian, Ciona intestinalis, rapidly recruited. Transplants of Styela were greatly affected by C. intestinalis, which overgrew them, similar to a localised replacement of Styela by Ciona seen overseas. Lefkovitch modelling was used to test whether Styela had an “Achilles heel” in its life history, whereby managed removal could impact future populations. This showed that under several scenarios intervention would most likely be ineffectual. Overall, this study showed that the original populations in Lyttelton Port are either static or in decline, somewhat contrary to original expectations. Nevertheless, it appears that these small populations may be acting as stepping stones for spread of this species outside of the port.
... A and C. intestinalis sp. B take anywhere from a few hours up to 5-6 days to undergo settlement and metamorphosis (Dybern 1965;Svane & Young 1989;Havenhand & Svane 1991;Svane & Havenhand 1993;Carver et al. 2003;Bullard & Whitlatch 2004). The species is thought to be native to the Northwest Pacific Ocean (Nydam & Harrison 2007, 2010, and was probably introduced into California in the 1930s (Lambert & Lambert 1998;Blum et al. 2006) and to the east coast of North America in the early 2000s (Ramsay et al. 2008;Therriault & Herborg 2008). ...
... A, high connectivity among populations is likely maintained through sea-current mediated drift of gametes and larvae and by hull fouling of adults and aquaculture transport. Mature C. intestinalis can spawn daily and produce approximately 500 tadpole larvae that metamorphose and settle as sessile adults after 1-6 days of free-swimming (Dybern 1965;Svane & Young 1989;Havenhand & Svane 1991;Svane & Havenhand 1993;Carver et al. 2003;Bullard & Whitlatch 2004). Natural dispersal can therefore be considered to be active locally yet insufficient to homogenize genetic variation at larger scales (Dupont et al. 2010;Zhan et al. 2010Zhan et al. , 2012. ...
Article
Understanding the factors that cause population divergence has long been of interest to marine biologists in their attempts to interpret the effect of human-mediated vectors. Broadcast-spawning species with limited dispersal capability are excellent candidates to measure the present-day patterns of genetic diversity. The tunicate Ciona intestinalis (Ascidiacea) is comprised of a complex of morphologically cryptic species that form vigorous aggregates in eutrophic habitats (harbors, gulfs and lagoons) where they can compete with the epibenthic community and cause biofouling problems. This study investigated biogeographic variability and migration patterns of C. intestinalis sp. A along Northeast Atlantic and Mediterranean coasts using microsatellite markers. Data presented here on 371 specimens collected from 17 populations reveal high genetic polymorphism, but with a deficit of heterozygote deficiency. Absence of evidence for isolation by distance suggests that the genetic patterns do not reflect the geographic distribution of sampled populations. Substantial gene flow and artificial potential for dispersal boost high levels of within-population genetic variability and prevent genetic differentiation within and between seas. A predominant eastward migration pattern was revealed by the data set, with very limited opportunity for C. intestinalis sp. A to travel westward. This directional movement indicates that other properties (e.g. habitat quality, genetic traits, mating system, life cycle) may cause adaptive divergence at a large biogeographic scale.
... Recent studies have examined settlement of invasive ascidians in Atlantic Canada and southern New England (e.g., Bullard & Whitlatch 2004, Howes et al. 2007, Ramsay et al. 2009, Valentine et al. 2009). Less work has been conducted at sites between these 2 regions, especially in Maine (Valentine et al. 2009, McNaught & Norden 2011. ...
... This may have been a result of warmer water temperatures in 2006 (Valentine et al. 2009). Regardless, D. vexillum settled consistently later in the year than other fouling species (see also Bullard and Whitlatch (2004)). This late-season settlement has a potential benefit for aquaculture growers. ...
Article
Full-text available
Biofouling ascidians represent a serious and costly problem for aquaculture. Although the subject of intensive study for the past decade, little is still known about the timing, intensity, and duration of ascidian settlement, especially in coastal Maine. To assess ascidian settlement, PVC panels were deployed in the Damariscotta River, Maine, on a weekly basis during the summers of 2007 and 2008. Long-term fouling panels were deployed from June to October 2007 to assess the development of mature fouling communities. Settlement of fouling organisms largely occurred during 2 seasonal phases. Early summer (May to July) was dominated by settlement of hydroids and bivalve molluscs; late summer and early fall (August to September) was dominated by ascidian settlement. Overall, ascidians accounted for ;50–80% of total settlement. The solitary ascidian Ciona intestinalis dominated mature fouling panels, but had low and intermittent settlement levels. The invasive colonial ascidian Didemnum vexillum settled later in the year (starting at the end of July) than other taxa. Specific knowledge of settling patterns of biofouling organisms may provide growers with a means of determining opportune times for deployment of gear to avoid excess fouling.
... Didemnum vexillum now occurs in temperate waters in many parts of the world, including: Japan; northern Europe (France, Netherlands, Ireland); the U.S. east coast (from Long Island, NY to Eastport, ME near the border with Canada); the U.S. and Canadian west coasts (California, Washington, British Columbia); and New Zealand (North and South Islands). For further background and source materials for this description of D. vexillum see: Coutts (2002), Bullard and Whitlatch (2004), Bullard et al. (2007), Coutts and Forrest (2007), Minchin (2007), Valentine et al. (2007a, b), Whitlatch and Bullard (2007), U.S. Geological Survey (2008), Woods Hole Oceanographic Institution (2008), Lengyel et al. 2009 (this issue). ...
... The most distinctive features of the D. vexillum oozooid are the paired, white crescent-shaped LOTs which are easily distinguished with a magnifying lens ( Figure 11). We have not yet determined the time period required for settled tadpole larva of D. vexillum to metamorphose into an oozooid and for the oozooid to bud into a colony, but see Bullard and Whitlatch (2004). ...
Article
Full-text available
The invasive colonial ascidian Didemnum vexillum occurs in Japan, North America, northern Europe, and New Zealand. It forms adhering mats on living and non-living hard substrates and alters seabed habitats. We examined the relationship of the first and last occurrences of D. vexillum recruits to water temperature and suggest it is possible to identify coastal and offshore locations that are at risk of colonization by the species based on seasonal water temperature trends. Temperature loggers and settlement plates for recruits were deployed and monitored at three shallow coastal settings in New England, including an open harbor, a marine estuary, and a nearshore island. In addition, the distribution of D. vexillum at sites on Georges Bank, an offshore fishing ground (where settlement plates could not be deployed), was compared to long-term bottom temperature data. Recruits of D. vexillum are small (0.2 to 1.0 mm) but easy to identify, and photographs illustrating the developmental stages of oozooids are presented. Recruits of D. vexillum did not appear on settlement plates at the same water temperature at the three coastal sites. Recruitment occurs in the range of 14 to 20°C and apparently is dependent on local climatic conditions. At coastal sites where we have complete records, recruitment persisted for 3.5 to 5 months; and recruits continued to appear as waters cooled to below the temperature of first occurrence. Recruitment ceased in the range of 9 to 11°C. On Georges Bank, the yearly temperature range (4 to 16-17°C) is the same in areas where D. vexillum is present and in a nearby area where D. vexillum is absent. However, in the reproductive season on the bank, temperature variability is but a few degrees in areas where the species is present; whereas it is high (11°C) where the species is absent. It is known from previous studies that in extremely cold conditions in shallow water D. vexillum colonies degenerate and all but disappear, only to regenerate as waters warm. We suggest that: 1) the degree to which colonies degrade in the cool season influences the length of time they require to regenerate, reproduce sexually, and brood larvae; 2) larval recruits will be released at the end of a developmental period as water temperatures warm, not necessarily when a particular water temperature is reached; 3) larvae likely will appear at different temperatures at climatically different sites, and at approximately the same time and temperature at climatically similar sites; 4) highly variable temperatures during the warm season likely inhibit the reproductive process; 5) the time required for a colony to develop and release larvae and the length of the warm season probably affects the length of the recruiting period at a site; 6) as waters cool, larval release by healthy colonies and recruitment might be regulated chiefly by declining temperature and therefore could end at approximately the same temperature at all sites. At deeper water sites, where minimum temperatures are warmer than at shallow sites, it is possible that D. vexillum colonies are not as affected in the cool season (i.e., do not degenerate) and thus could have a longer recruiting season. This may explain the species' successful colonization of several large areas of gravel habitat on Georges Bank.
... During the course of the experiment, a total of 22 benthic taxa were observed and identified to the lowest level possible, usually to species (Supplementary Table 1). For taxonomic identifications, we primarily consulted Pollock (1998) and Bullard and Whitlatch (2004). Further, we deployed six additional (i.e., sacrificial) settlement plates that were not part of our experiment design to periodically observe the development of newly recruited fouling organisms to aid in taxonomic identification, because more mature (and larger) specimens can exhibit additional morphological features (or render features more visible) that were key to identification. ...
Article
Full-text available
The choice of the duration and frequency of sampling to detect relevant patterns in field experiments or for environmental monitoring is always challenging since time and material resources are limited. In practice, duration and frequency of sampling are often chosen based on logistical constraints, experience, or practices described in published works but are rarely justified and almost never optimized before initiating sampling. Settlement plates are commonly used as a passive sampling tool to study recruitment patterns of fouling organisms (including non-indigenous species) and their deployment is amenable to experimentation with respect to manipulating duration and frequency of sampling. This study aimed to determine the optimal sampling strategy to detect rare species (e.g., a non-indigenous species early in the invasion process when its population size is still small). To do so, we deployed a series of settlement plates of various durations (1–32 days) and sampling frequencies (daily to biweekly) during the seasonal onset of recruitment, when larval supply was low, a situation that mimics the low propagule pressure of the early stages of the invasion process. We demonstrated that a combination of longer sampling duration and higher sampling frequency was the best strategy to maximize taxonomic richness. However, we found that an intermediate sampling duration of 1–2 weeks was optimal for detecting most species. These results can guide species-specific and assemblage-level sampling strategies using settlement plates. Additionally, this study can serve as a practical template for optimizing sampling of other taxonomic groups that were not examined in the present study as well as for the use of other methods.
... Colonies were maintained in a controlled temperature room at 15°C with aerated, natural seawater. Larval release was induced by shining a light onto the colonies after an overnight period of darkness (Bullard & Whitlatch, 2004); swimming tadpoles were collected with a pipette and randomly placed in the respective salinity treatments. Because previous studies report a very short pelagic period (a few hours, Saito et al., 1981), larvae were assumed not to be acclimatized to lower salinities. ...
Article
Full-text available
Coastal and estuarine ecosystems exhibit extreme fluctuations in abiotic factors that influence the success and distribution of many introduced marine invertebrates. The frequency of these fluctuations may worsen under the scenario of climate change due to more intense storm events or greater precipitation. While many studies have focused on the response of adult ascidians to salinity, few have examined the response of larvae to low salinity events or post‐metamorphic asexual reproduction after larval exposure to low salinity. Here we tested the effect of low salinity on larval metamorphosis and post‐metamorphic growth of the introduced ascidian Botrylloides violaceus. We exposed tadpole larvae to salinities ranging 0–30 ppt. Tadpoles metamorphosed in salinities as low as 16 ppt and percent metamorphosis of larvae was not significantly different at salinities >20 ppt. A few tadpoles metamorphosed within 2–4 hr after release, and larval metamorphosis continued for 3–4 days, suggesting that larvae could disperse considerable distances. We then tested post‐metamorphic survival, growth, and asexual reproduction of larvae exposed (5–7 days) to varying salinities (18, 20, 25, and 30 ppt), and placed the resulting colonies in full‐salinity natural seawater; colony growth was monitored for 9 weeks post‐metamorphosis. Results indicated that colonies whose larvae were exposed to low salinity (<25 ppt) had fewer zooids than colonies from larvae exposed to seawater at 30 ppt, but total area occupied by each colony was similar among salinity treatments. Because each individual zooid within a colony filter‐feeds and reproduces through asexual budding, fewer feeding individuals within a colony will likely reduce future growth and reproduction. Due to the likelihood of more frequent heavy rain events and low‐salinity conditions for the northwest Atlantic Ocean, there is need for continued research to assess the response of ascidians to factors like salinity and to evaluate the spread of ascidians and their adaptation to estuarine and coastal habitats.
... Plates revealing the presence of any organisms were then processed with 70 × and/or 100 × magnification for further identification. All organisms were photographed using a Leica M205C stereo microscope with a DFC 295 (3MP) digital camera and identified to the lowest taxonomic level possible using taxonomy keys (Gordon & Mawatari 1992;Hayward & Ryland 1995;Bullard & Whitlatch 2004). For each identified taxon, abundance was assessed by counting the number of recruits (individual or a colony) on plates. ...
Article
In this experimental study the patterns in early marine biofouling communities and possible implications for surveillance and environmental management were explored using metabarcoding, viz. 18S ribosomal RNA gene barcoding in combination with high-throughput sequencing. The community structure of eukaryotic assemblages and the patterns of initial succession were assessed from settlement plates deployed in a busy port for one, five and 15 days. The metabarcoding results were verified with traditional morphological identification of taxa from selected experimental plates. Metabarcoding analysis identified > 400 taxa at a comparatively low taxonomic level and morphological analysis resulted in the detection of 25 taxa at varying levels of resolution. Despite the differences in resolution, data from both methods were consistent at high taxonomic levels and similar patterns in community shifts were observed. A high percentage of sequences belonging to genera known to contain non-indigenous species (NIS) were detected after exposure for only one day.
... The D. vexillum larvae produced in this study were obtained using a 'light shocking' technique (Bullard and Whitlatch 2004) that stimulates and enables control of the time of larval release through the manipulation of a dark adaptation period. The colonies need to be maintained in constant darkness for a duration that is long enough to induce sufficient larval release, but not so long as to lead to deterioration of colony health. ...
Article
Full-text available
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 similar to 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.
... This result is consistent with laboratory work by Epelbaum et al. (2009), who found C. mutica did not prey on 7-day old Botrylloides violaceus recruits (the only stage investigated), which were relatively large (4.25 mm in diameter). The fast growth rate of Ciona (0.26-0.76 mm in diameter in 7 days; Bullard and Whitlatch 2004) suggests that the time period during which newly-settled tunicates are vulnerable to predation is limited (ca. 1-2 days)once the larvae have metamorphosed and begin to grow, they probably become too large to be consumed (''ontogenetic vulnerability'' sensu Osman and Whitlatch 2004). ...
Article
Full-text available
As the number of introductions of non-indigenous species (NIS) continues to rise, ecologists are faced with new and unique opportunities to observe interactions between species that do not naturally co-exist. These interactions can have important implications on the invasion process, potentially determining whether NIS become widespread and abundant, survive in small numbers, or fail to establish and disappear. Although many studies have naturally focused on the interactions between NIS and native species to examine their effects and the biological resistance of the recipient community to invasion, few have examined the effects that NIS have on each other. In some cases, interactions can facilitate the invasion process of one or both species (i.e., “invasional meltdowns”), but competition or predation can lead to negative interactions as well. The introduction of the vase tunicate, Ciona intestinalis, in Prince Edward Island (Canada) has harmed mussel aquaculture via heavy biofouling of equipment and mussels. Through both a broad-scale survey and small-scale field experiments, we show that Ciona recruitment is drastically reduced by caprellid amphipods, including the NIS Caprella mutica. This study provides an exciting example of how established invasive species can negatively impact the recruitment of a secondary invader, highlighting the potential for non-additive effects of multiple invasions.
... All individuals that settled upon adult individuals and free space on the panels were counted and identified to species (Pollock 1998, Bullard & Whitlatch 2004. A randomized complete-block 1-way ANOVA, with treatment levels as the independent factor, site as the block term, and recruitment (species and individuals) as the dependent variable, was used to test for differences in community structure on secondary space (bivalves and colonial ascidians) and primary space (free space on panels with adult individuals) ( Table 1). ...
Article
Full-text available
Diversity can be maintained by the biological characteristics of species within communities, particularly dominant species, Invasions often result in shifts of dominant species. Despite the number of studies on invasion ecology, few have determined their long-term effect on diversity. In the present study, we coupled short- and long-term studies to examine the relationship between invasive species (colonial ascidians or sea squirts) and diversity and to discuss their implications for species coexistence. Diversity patterns between 2 panel studies (1979 to 1982; 2003 to 2006), one conducted before the establishment of invasive colonial ascidians, revealed an increase in species diversity. Short-term recruitment studies designed to elucidate mechanisms behind the patterns observed in our long-term studies suggest contrasting methods of maintaining diversity, Between 1979 and 1982, Mytilus edulis was a consistent spatial occupant whose hard shell provided secondary space for colonization by other species. In contrast, the 2003 to 2006 community was dominated by the seasonally abundant invasive colonial ascidians Botrylloides violaceus and to a lesser extent Didemnum vexillum, which do not provide secondary substrate. These species either senesce after reproduction or undergo seasonal regression and free space for colonization by other species. These studies suggest that the coexistence of species has shifted from a community in which diversity was maintained by secondary substrates to a community in which diversity is maintained by primary substrates. Additionally, they suggest that the community is undersaturated and could support more species, particularly those that seasonally utilize a limited resource (free space).
... A transparent grid was used to count juvenile tunicates on the collector plates. Species identification followed Bullard and Whitlatch (2004). In this study, collector plates were deployed without preconditioning, i.e., they were not soaked in sea water to allow biofilm to develop prior to deployment (Osman and Whitlatch 1995;Bourque et al. 2007). ...
Article
Full-text available
In 2004, an exotic tunicate, Ciona intestinalis, was detected in Montague River, Prince Edward Island. Since it was first detected, this exotic species has become an invasive nuisance species creating production problems in bivalve aquaculture industries including handling difficulties and resource competition with the cultured blue mussel, Mytilus edulis. Ciona intestinalis has become a challenging species to manage because of its long reproductive period and rapid biomass accumulation. Population development of C. intestinalis in a single season was investigated to inform the aquaculture management of this fouling species. The study focused on seasonal recruitment patterns and the subsequent development of the C. intestinalis population after settlement. Recruitment on experimental collectors occurred from mid-June until late November, with a peak in late August. A rapid increase in biomass was documented in late July, six weeks after the initial recruitment. No substantial increase in C. intestinalis biomass was observed in new recruits after mid-August.
Conference Paper
Full-text available
Each year, the aquaculture industry experiences significant economic losses as a result of pathogens that cause disease, pests that render product unmarketable, operational mishaps, adverse weather events, and closures of harvest areas due to the presence of organisms with the potential to cause human illness. Collectively, we refer to these as aquaculture production hazards, which present considerable risk to operations. Massive loss of farmed product and human illness caused from ingestion of unknowingly contaminated product both adversely impact profitability, trade, and public perception. The ability of professionals to assist farmers is often limited by a lack of farm-level monitoring, record keeping, and farmer knowledge of hazards and hazard management strategies. Frequently, the causes of mortality events remain unknown or are identified when it is too late to prevent, control, correct or mitigate. Often, key pieces of information are missing from requests to identify and correct the hazard, limiting the response from extension and aquatic animal health professionals. To respond to this problem, a group of extension professionals from universities and industry associations across the northeastern U.S., together with researchers, aquatic animal health professionals, and industry members developed a publication, the Northeast Aquaculture Management Guide that identifies strategies to address aquaculture production hazards. The manual includes science-based information about major production hazards facing farmers, including: predators, diseases, parasites, organisms that have the potential to cause aquatic animal illness and human illness (e.g. toxic algae), biofouling, spread of invasive species, and other operational and environmental hazards. The manual also includes guidelines for environmental monitoring, evaluation and sampling of stocks, record-keeping procedures, and state-by-state contact information for whom to call when a problem occurs. The manual incorporates best management practices and biosecurity measures developed through research and outreach efforts. Improved knowledge of hazards associated with aquaculture production is the first step towards developing or improving risk management strategies. Use of appropriate farm monitoring protocols and record keeping will help aquatic animal health professionals respond better and more efficiently to illness or mortality events. If the causes of such events are identified quickly and definitively, future losses may be minimized or prevented, leading to increased production and profitability. The potential for realized economic benefits is significant; operators who plan proactively to minimize production hazards may have a competitive advantage in the marketplace.
Article
Planktivory is believed to be a major selective force in marine systems, but little is known about how the intensity of planktivory risk varies spatially or temporally. We assessed seasonal daytime planktivory patterns over fifteen months (Apr 2003 to Jun 2004) at a temperate site in eastern Long Island Sound, CT. Planktivory was measured using modified Plankton Tethering Units (PTUs) deployed from floating docks and baited with live brine shrimp. Planktivory risk varied throughout the year. The highest levels of risk occurred in Aug, Sept and Oct (85%, 75% and 42.5% of brine shrimp consumed, respectively), the lowest levels of risk occurred from Dec to Apr. Mean monthly consumption of brine shrimp strongly correlated with the presence of planktivorous fish. Many species of benthic invertebrates exhibited high levels of recruitment during times of the year when planktivory risk was high, although some species recruited when planktivory risk was low. These seasonal planktivory patterns (highest risk occurring during the late summer and early fall) may be typical for many temperate near-shore habitats, especially those associated with man-made structures (e.g., floating docks, pilings).
Thesis
Full-text available
An invasive colonial tunicate Didemnum sp. was observed in Narragansett Bay, Rhode Island, beginning in 2000. Preliminary observations, which showed tunicate colonies overgrowing mussel (Mytilus edulis) beds and restricting the ability of individual mussels to open their valves, prompted this study. The study had four goals: 1) to measure percent cover of Didemnum sp. at three sites in Narragansett Bay and to compare this abundance with percent cover abundance of native species.; 2) to compare larval recruitment of species in Narragansett Bay on artificial substrates; 3) to compare recruitment abundances of the tunicate Didemnum sp. in Narragansett Bay with another estuary, Long Island Sound, and 4) to understand the extent of the colonial tunicate Didemnum sp. settlement in select intertidal areas along Narragansett Bay and the Rhode Island coastline, including fishing areas, boat ramps and marinas. Locations with the highest percent cover of Didemnum sp. had the highest recruitment and rates of growth. The Graduate School of Oceanography site showed the highest abundance overall of the tunicate, compared with other sites in Narragansett Bay and Long Island Sound. At this site, a decrease of M. edulis individuals occurred as Didemnum sp. percent cover and recruitment increased. Mussels, as a biogenic secondary substrate, provided additional substrate for Didemnum sp. growth, and did not slow the growth of the tunicate in experimental studies. Didemnum sp. abundance also increased at the GSO with the decrease of the other colonial tunicates. The environmental factors that correlated most positively with Didemnum sp. abundances were temperature and salinity; these correlations varied by site. Finally, the areas in the bay (included in a bay-wide survey) with intertidal growth were more likely to have high boat traffic and be close to a site where Didemnum sp. had been initially observed in former studies.
Article
Full-text available
Colonization rates of mussels (Mytilus trossulus and M. edulis) were measured on natural substrata in tidepools and on emergent rock in recently ice-scoured and non-scoured regions of a rocky shore near Halifax, Nova Scotia, Canada. The relative importance of initial settlement/colonization, compared to subsequent dispersal and mortality, in determining the distribution and abundance of mussels was examined by comparing patterns and rates of mussel colonization at sampling intervals of days to months over a 17 mo period. Less than 4% of mussels which colonized the quadrats sampled at short (2 to 7 d) intervals were settling larvae (<0.5 mm shell length), indicating the importance of postsettlement dispersal of mussels on this shore. Most colonists were >2 mm, too large to be dispersed by byssal drifting, suggesting they were redistributed by wave dislodgment and deposition. At both short (2 to 7 d) and long (5 to 16 mo) sampling intervals, colonists were most abundant in ice-scoured tidepools and least abundant on ice-scoured emergent rock, probably reflecting differences in the macrobenthic assemblage, the substratum for colonization. In addition, the long term abundance of colonists was linearly related to the cumulative short term abundance during all but one of the intervals. Therefore, our results indicate that, over time scales up to 16 mo, patterns of initial colonization by settlers and larger post-larval mussels were more important than post-colonization mortality and dispersal in determining patterns of distribution and abundance of mussels on this shore.
Article
Full-text available
Newly settled invertebrates usually are subject to high rates of mortality (Type ill survivorship). Therefore, knowledge of early post-settlement events is critical in determining if and when patterns of abundance and distribution of juveniles reflect settlement patterns. Causes of mortality of early juvenile invertebrates include delay of metamorphosis, biological disturbance, physical disturbance and hydrodynamics, physiological stress, predation, and competition. Predation is the best documented cause of early mortality, particularly for mobile species. Other possible causes which have not yet been investigated are developmental abnormalities, insufficient energy reserves, disease and. parasitism. In most studies of sessile invertebrates, early post-settlement mortality did not obscure the relationship between recruit and settler abundance. This relationship appears to be more variable among mobile species for which migration also can modify the distribution of settlers. There is still insufficient data to support general conclusions about the conditions under which recruitment rate can be predicted from settlement rate. Studies have found evidence of the effects of both settlement and early post-settlement mortality on the distribution of some sessile species at small spatial scales, but mortality appears to have less influence at larger scales. Much of the present knowledge of the early postsettlement period has come from studies of barnacles and ascidians and more information is needed for other groups of benthic marine invertebrates, particularly mobile species. The relative importance of mortality during the early post-settlement period compared to other life history stages can only be determined in studies which examine several stages.
Article
Full-text available
Biological invasions of marine habitats have been common, and many patterns emerge from the existing literature. In North America, we identify 298 non-indigenous species (NIS) of invertebrates and algae that are established in marine and estuarine waters, generating many "apparent patterns" of invasion: (a) The rate of re-ported invasions has increased exponentially over the past 200 years; (b) Most NIS are crustaceans and molluscs, while NIS in taxonomic groups dominated by small organisms are rare; (c) Most invasions have resulted from shipping; (d) More NIS are present along the Pacific coast than the Atlantic and Gulf coasts; (e) Native and source regions of NIS differ among coasts, corresponding to trade patterns. The va-lidity of these apparent patterns remains to be tested, because strong bias exists in the data. Overall, the emergent patterns reflect interactive effects of propagule supply, invasion resistance, and sampling bias. Understanding the relative contribution of each component remains a major challenge for invasion ecology and requires standardized, quantitative measures in space and time that we now lack.
Article
Full-text available
Biological invasions are an increasing agent of change in aquatic systems, and ballast-water transfer in ships is a leading pathway of these invasions. During sequential stages of ballast transfer (uptake, transport, and release), the density and diversity of the plankton assemblage is selectively filtered, determining the pool of potential invaders. Understanding taxon-specific patterns of mortality along the invasion pathway is key to understanding and predicting successful invasions. We quantified taxon-specific trends in plankton mortality during a 16 d trans-Atlantic ballast water voyage. In the ballast tanks, we collected a miminum of 50 live taxa. Over 50 % of taxa and > 98% of organisms collected in initial samples were not detected at the end of the voyage. No ballasted organisms survived experimental transfer to coastal harbor water. We suggest that the invasion success of a particular taxon may be predicted both by high density at the end of a voyage (which is comparatively easy to measure) and by low mortality during a voyage (which may indicate good body condition, but is harder to measure). These 2 predictors were not, however, correlated across taxa. Mid-ocean exchange, the most widely used method for reducing ballast-mediated invasion risk, alters the pool of potential invaders. In an experimental test of mid-ocean exchange, 93 to 100 % of the coastal water and 80 to 100 % of the coastal organisms were removed. However, the total density and diversity of plankton in the ballast tanks increased significantly following exchange and in laboratory experiments ocean water was not lethal to coastal organisms.
Article
Full-text available
Organisms living in the marine rocky intertidal zone compete for space. This, together with predation, physical disruption, and differing species tolerances to physiological stress, explains the structure of the ecological communities at some sites. At other sites the supply of larvae is limiting, and events in the offshore waters, such as wind-driven upwelling, explain the composition of intertidal communities. Whether the community ecology at a site is governed by adult-adult interactions within the site, or by limitations to the supply of larvae reaching the site, is determined by the regional pattern of circulation in the coastal waters. Models combining larval circulation with adult interactions can potentially forecast population fluctuations. These findings illustrate how processes in different ecological habitats are coupled.
Article
Full-text available
Kelp forests along the coast of central California harbor juvenile rockfish that prey on the larvae of invertebrates from the rocky intertidal zone. This predation reduces recruitment to barnacle populations to 1/50 of the level in the absence of fish. The dynamics of the intertidal community are thus strongly coupled to the dynamics of the offshore kelp community.
Article
In a New England (USA) subtidal hard-substrate community, 2 species of very small gastropods, Anachis lafresnayi and Mitrella lunata, prey on several species of newly settled ascidians. Preliminary experiments indicated that this predation drastically changes ascidian recruitment patterns. In order to examine this phenomenon more fully, an extensive series of field experiments using artificial substrates was performed over a 2 yr period between 1991 and 1992. In 1992, weekly experiments were conducted over the complete recruitment season between July and October. Comparisons of the experiments were made to test for any weekly or annual variation in the effect of these micro-predators on recruitment. Results demonstrated that the predators (1) were fairly specific in their prey preferences, (2) could eliminate prey species regardless of their settlement density, (3) switched prey in response to changes in prey species abundance, and (4) affected recruitment throughout the entire settlement season. These results indicate that processes affecting post-settlement life stages contribute significantly to the overall dynamics of communities and must be considered along with the much better documented effects of larval supply, adult predators, and physical disturbance.
Article
Residents within any community can affect the larval settlement of both their own and other species. In marine sessile communities resident adults can affect larval settlement by preying on settling larvae, removing or adding space for the larvae to colonize, or stimulating or prohibiting larval settlement on available substratum nearby. To examine those processes by which residents affect settlement, we exposed experimental substrata with three densities of adults of a single species at a site in eastern Long Island Sound, USA for a 24-h period. Four species of common ascidians, Botryllus schlosseri (Pallas), Botrylloides diegensis Ritter and Forsyth, Diplosoma macdonaldi Herdman, and Molgula manhattensis (De Kay), were used in 11 separate experiments. Few individuals of any species settling attached to the surfaces of these species and this resulted in the main effect of these residents being the usurpation of space and the restricting of settlement to unoccupied areas. A model is also presented to explain the apparent aggregated settlement of several species in open areas adjacent to the resident ascidians. From this model we suggest that the aggregated settlement can result from limited larval mobility such that some larvae that contact and reject the resident species as settlement sites may subsequently contact open surfaces of the same substratum and increase settlement densities there over those observed on control substrata. Finally, settlement data for several species indicate that Molgula may influence settlement by preying on larvae.
Article
The larval morphology of the marine bryozoan Bowerbankia gracilis has been investigated by light and electron microscopy. The barrel-shaped larva (200 µm long and 150 µm in diameter) is light yellow without any apparent eyespots, although it is positively phototactic during its brief free-swimming existence. The primary morphological characteristics of the larva are: (1) a large corona that forms most of the larval surface, (2) a small apical disc without blastemas, (3) a deep pallial sinus lined by an extensive pallial epithelium, (4) an internal sac without regional specializations, and (5) a polypide rudiment in the oral hemisphere. This organization is characteristic of larvae of the ctenostome superfamily Vesicularioidea, and differs radically from the organization of all other bryozoan larvae examined. The major morphological differences occur in the size and organization of the apical disc, the pallial epithelium, and the internal sac. In most bryozoans, these regions of the larval epithelium represent rudiments of the polypide and the body wall epidermis of the ancestrula. The oral polypide rudiment, the extensive pallial epithelium, and the reduced internal sac in vesicularioid larvae indicate that their pattern of metamorphosis also differs radically from the metamorphoses of other bryozoans.
Article
For species recruiting into established sessile communities, the adult colonies and individuals already present form a significant part of the environment and have the potential to alter both larval settlement rates and post-settlement mortality. Settlement rates can be reduced by predation on larvae, by the removal or addition of substratum space, or by stimulation or prohibition of larvae from settling on adjacent substratum. Once attached, the recruiting individual can still be influenced by predation or overgrowth by residents, by the added physical structure for firmer attachment, or by being camouflaged from motile predators. To examine those processes by which residents affect recruitment we exposed experimental substrata with three densities of adults of a single species at a site in eastern Long Island Sound, USA for a 1-wk period. Seven different species of common invertebrates were used in nine separate experiments. The major effect of most resident species was the usurpation of space and the restricting of recruitment to adjacent unoccupied areas. This was particularly true for resident ascidians and bryozoans, but less so for barnacles and oysters. In fact several species recruited in higher densities on or next to oysters and barnacles. Comparison to 1-day settlement experiments indicated that the encrusting ascidian species Diplosoma and possibly Botryllus reduced recruitment relative to settlement, probably by overgrowing newly-settled individuals. However, in the presence of most resident species, recruitment patterns were not greatly different from settlement patterns, indicating that the effects of the attached community on recruitment may result from influences on settlement.
Article
Young juveniles of many motile benthic species are concentrated in structurally complex habitats, but the proximate causes of this distribution are usually not clear. In the present study, I assessed three potentially important processes affecting distribution and abundance of early benthic stages in the shore crab (Carcinus maenas): (1) selection of habitat by megalopae (postlarvae); (2) habitat-specific predation; and (3) post-settlement movements by juveniles. These processes were assessed concurrently over 3–9 days at two spatial scales: at the scale of square meters using cage techniques within nursery areas, and at the scale of hectares using isolated populations of juvenile shore crabs in small nursery areas as mesocosms. The results were compared to habitat-specific distribution in the field.
Article
The spread of exotic species and climate change are among the most serious global environmental threats. Each independently causes considerable ecological damage, yet few data are available to assess whether changing climate might facilitate invasions by favoring introduced over native species. Here, we compare our long-term record of weekly sessile marine invertebrate recruitment with interannual variation in water temperature to assess the likely effect of climate change on the success and spread of introduced species. For the three most abundant introduced species of ascidian (sea squirt), the timing of the initiation of recruitment was strongly negatively correlated with winter water temperature, indicating that invaders arrived earlier in the season in years with warmer winters. Total recruitment of introduced species during the following summer also was positively correlated with winter water temperature. In contrast, the magnitude of native ascidian recruitment was negatively correlated with winter temperature (more recruitment in colder years) and the timing of native recruitment was unaffected. In manipulative laboratory experiments, two introduced compound ascidians grew faster than a native species, but only at temperatures near the maximum observed in summer. These data suggest that the greatest effects of climate change on biotic communities may be due to changing maximum and minimum temperatures rather than annual means. By giving introduced species an earlier start, and increasing the magnitude of their growth and recruitment relative to natives, global warming may facilitate a shift to dominance by nonnative species, accelerating the homogenization of the global biota.
Few or no perforations on zooecium. If perforations present they are located between operculum and side of zooecium closest to operculum (this contrasts to Cryptosula were perforations are on side of zooid farthest from operculum). Light orange in color. Often with three dark orange spots
  • One-Day Old
  • Juvenile
One-Day Old Juvenile: Single shield-shaped zooecium with 8 spines surrounding operculum. Size = 0.40 mm. Few or no perforations on zooecium. If perforations present they are located between operculum and side of zooecium closest to operculum (this contrasts to Cryptosula were perforations are on side of zooid farthest from operculum). Light orange in color. Often with three dark orange spots; one spot on each side of zooecium and one at base.
Size approximately 0.200 mm. Barrel shaped. Narrow slit on the median plane of the larva
  • Larvae
Larvae: Paraphrased from Reed (1980). Light yellow coronate larva. Size approximately 0.200 mm. Barrel shaped. Narrow slit on the median plane of the larva.
Ectoproct and entoproct type material: reexamination of species from New England and Bermuda named by
  • F J S Maturo
  • T J M Schopf
Maturo, F.J.S. Jr., Schopf, T.J.M. (1968) Ectoproct and entoproct type material: reexamination of species from New England and Bermuda named by A. E. Verrill, J. W. Dawson, and E. Desor. Postilla 120:1-95
Polyzoa (Bryozoa) order Cheilostomata cyphonautes larvae
  • J S Ryland
Ryland, J.S. (1965) Polyzoa (Bryozoa) order Cheilostomata cyphonautes larvae. Cons. Int. Explor. Mer. Sheet 107:1-6
Marine animals of southern
  • H M Weiss
Weiss, H.M. (1995) Marine animals of southern New England and New York. State Geol. Nat. History Survey Connecticut, Hartford, CT, USA. Bulletin 115
Rocky subtidal communities
  • J D Witman
  • P K Dayton
Witman, J.D., Dayton, P.K. (2001) Rocky subtidal communities. In: Bertness, M.D., Gaines, S.D., Hay, M.E. (eds) Marine Community Ecology. Sinauer Associates, Inc, Sunderland, MA, p 339-366