Fertilization and normal development inAscidiella aspersa (Tunicata) studied with Nomarski-optics

Niermann-Kerkenberg, Eva; Hofmann, D. K.

doi:10.1007/bf02367902

Cited by 13 publications

(7 citation statements)

References 15 publications

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“…Ascidiella aspersa is a protandric hermaphrodite. Gametes are released in spring and the larvae go through a brief free-swimming stage and then quickly metamorphose into a settled juvenile (Niermann-Kerkenberg & Hofmann, 2006). Ascidiella aspersa has a lifespan of 18 months, lasting from mid-summer to winter of the following year.…”

Section: Resultsmentioning

confidence: 99%

The biology and functional morphology ofModiolarca subpicta(Bivalvia: Mytilidae: Musculinae), epizoically symbiotic withAscidiella aspersa(Urochordata: Ascidiacea), from the Kattegat, northern Jutland, Denmark

Morton

Dinesen

2010

J. Mar. Biol. Ass.

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This study of the little known north-eastern Atlantic mytilid Modiolarca subpicta suggests a more intimate relationship with ascidians and, especially, Ascidiella aspersa, than has hitherto been appreciated. Both live for 18 months and the reproductive cycle of both is approximately co-ordinated so that juvenile ascidians become available as hosts to the settling spat of the symbiotically epizoic M. subpicta each summer. Settling spat of M. subpicta are thought to be attracted to the exhalant flow from the ascidian's anal siphon. After the ascidian's death, the liberated mussels may adopt a wandering, free-living, lifestyle they have occasionally been reported to pursue. Anatomically, M. subpicta is of the typical mytilid plan, albeit simplified commensurate upon its normal lifestyle of protective envelopment within the host's tunic. The foot, however, is highly mobile and in addition to being used for locomotion, especially in juveniles, is responsible for the planting of byssal threads, typically dorsally above the shell, so that each individual stimulates the ascidian to produce an epidermal pocket into which it manoeuvres itself and reposes, securely attached, but dorsal side down Modiolarca subpicta, epizoic in the tests of ascidians, could have evolved from a more isomyarian, equivalve, ancestor via a nestling, epibyssate, Trichomusculus-like shaped intermediary with ventral flattening and, hence, stability characteristic of the more familiar heteromyarian mytilids of rocky shores and lotic freshwaters being achieved through living dorsal side down.

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Section: Resultsmentioning

confidence: 99%

The biology and functional morphology ofModiolarca subpicta(Bivalvia: Mytilidae: Musculinae), epizoically symbiotic withAscidiella aspersa(Urochordata: Ascidiacea), from the Kattegat, northern Jutland, Denmark

Morton

Dinesen

2010

J. Mar. Biol. Ass.

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“…All of these invaders are similar in feeding mode and growth habit (they are all sessile suspension feeders), but they differ considerably in their ecology and life history (Berman et al 1992, Osman and Whitlatch 1996). Botrylloides and Diplosoma brood very short‐lived larvae (a few minutes to hours) that appear capable of settlement almost immediately upon release (Worcester 1994; J. Stachowicz, H. Fried, R. Osman, and R. Whitlatch, personal observations ), whereas Ascidiella and Styela are broadcast spawners whose larvae generally become competent to settle within 12–24 h after fertilization (Niermann‐Kerkenberg and Hoffmann 1989). Thus, there may be differences in the scales over which populations of each species represent open vs. closed systems.…”

Section: Methodsmentioning

confidence: 99%

Biodiversity, Invasion Resistance, and Marine Ecosystem Function: Reconciling Pattern and Process

Stachowicz

Fried

Osman³

et al. 2002

Ecology

492

304

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A venerable generalization about community resistance to invasions is that more diverse communities are more resistant to invasion. However, results of experimental and observational studies often conflict, leading to vigorous debate about the mechanistic importance of diversity in determining invasion success in the field, as well as other ecosystem properties, such as productivity and stability. In this study, we employed both field experiments and observational approaches to assess the effects of diversity on the invasion of a subtidal marine invertebrate community by three species of nonindigenous ascidians (sea squirts). In experimentally assembled communities, decreasing native diversity increased the survival and final percent cover of invaders, whereas the abundance of individual species had no effect on these measures of invasion success. Increasing native diversity also decreased the availability of open space, the limiting resource in this system, by buffering against fluctuations in the cover of individual species. This occurred because temporal patterns of abundance differed among species, so space was most consistently and completely occupied when more species were present. When we held diversity constant, but manipulated resource availability, we found that the settlement and recruitment of new invaders dramatically increased with increasing availability of open space. This suggests that the effect of diversity on invasion success is largely due to its effects on resource (space) availability. Apart from invasion resistance, the increased temporal stability found in more diverse communities may itself be considered an enhancement of ecosystem function. In field surveys, we found a strong negative correlation between native‐species richness and the number and frequency of nonnative invaders at the scale of both a single quadrat (25 × 25 cm), and an entire site (50 × 50 m). Such a pattern suggests that the means by which diversity affects invasion resistance in our experiments is important in determining the distribution of invasive species in the field. Further synthesis of mechanistic and observational approaches should be encouraged, as this will increase our understanding of the conditions under which diversity does (and does not) play an important role in determining the distribution of invaders in the field.

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“…These species are all important occupiers of hard substrata of coastal areas of South Africa (Branch et al 2010). The larvae of 4 species have well-developed statocytes and ocelli (Griffiths 1976, Niermann-Kerkenberg & Hofmann 1989, Jacobs et al 2008 but S. plicata has a highly reduced ocellus (Ohtsuki 1990), and M. squamiger is unusual among Pyuridae in lacking an ocellus (authors pers. obs.…”

Section: Introductionmentioning

confidence: 99%

Larval settlement behaviour in six gregarious ascidians in relation to adult distribution

Rius¹,

Branch²,

Griffiths³

et al. 2010

Mar. Ecol. Prog. Ser.

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Settlement influences the distribution and abundance of many marine organisms, although the relative roles of abiotic and biotic factors influencing settlement are poorly understood. Species that aggregate often owe this characteristic to larval behaviour, and we investigated whether this predisposes ascidians to becoming invasive, by increasing their capacity to maintain their populations. We explored the interactive effects of larval phototaxis and geotaxis and conspecific adult extracts on settlement rates of a representative suite of 6 species of ascidians that form aggregations in the field, including 4 aliens with global distributions, and how they relate to adult habitat characteristics. In the laboratory, the larvae were (1) held in light or dark, (2) offered the choice of settling in the light or dark, or (3) held in the presence or absence of adult extract. When confined in either light or dark conditions, all species settled equally in dark and light. Four showed strong geotaxis, 3 settling preferentially on the bottom of experimental chambers, and one on the top. Offered a choice between dark and light, 2 species settled preferentially in the dark with no geotactic preferences and another 2 showed an interaction between light and geotaxis. For 4 of the species, the responses of settlers accorded with, and may contribute to, adult orientation patterns in the field. Adult extracts inhibited settlement of 3 species and failed to influence settlement of the other 3, arguing against conspecific attraction being a cause of aggregation and an explanation of the propensity of ascidians to become invasive.

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Fertilization and normal development inAscidiella aspersa (Tunicata) studied with Nomarski-optics

Cited by 13 publications

References 15 publications

The biology and functional morphology ofModiolarca subpicta(Bivalvia: Mytilidae: Musculinae), epizoically symbiotic withAscidiella aspersa(Urochordata: Ascidiacea), from the Kattegat, northern Jutland, Denmark

The biology and functional morphology ofModiolarca subpicta(Bivalvia: Mytilidae: Musculinae), epizoically symbiotic withAscidiella aspersa(Urochordata: Ascidiacea), from the Kattegat, northern Jutland, Denmark

Biodiversity, Invasion Resistance, and Marine Ecosystem Function: Reconciling Pattern and Process

Larval settlement behaviour in six gregarious ascidians in relation to adult distribution

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