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3. Assessment of trophic relationships between symbiotic tropical ophiuroids using C and N stable isotope analysis

Author

Fourgon, Didier, Lepoint, Gilles, Eeckhaut, Igor, Fourgon, Didier, Lepoint, Gilles, and Eeckhaut, Igor

Abstract

Analyses of the natural abundance of carbon and nitrogen stable isotopes were performed to investigate the feeding habits of two ophiuroids, Ophiomastix venosa and Ophiocoma scolopendrina, and to assess the potential benefit obtained by the symbiotic Ophiomastix venosa juveniles. A tracer experiment was also carried out to clarify the contribution of algae to the nitrogen uptake amongst the tested ophiuroids. Our results suggest that Ophiocoma scolopendrina adults occupy a higher position in the food web than Ophiomastix venosa and mainly feed on neuston. In contrast, O. venosa adults feed on the alga Sargassum densifolium and on organic matter associated with sediment. Free juveniles and symbiotic juveniles of O. venosa have intermediate δ13C values between both adult species. The high proportion of 13C in the symbiotic juveniles compared to the one in their conspecific adults indicates that their diet slightly differs from the latter and is closer to that of Ophiocoma scolopendrina. This raises the hypothesis that symbiotic juveniles steal neuston from their associated host, O. scolopendrina., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
2006

6. Population dynamics, infestation and host selection of Vexilla vexillum, an ectoparasitic muricid of echinoids, in Madagascar.

Author

Vaïtilingon, Devarajen, Eeckhaut, I., Fourgon, Didier, Jangoux, Michel, Vaïtilingon, Devarajen, Eeckhaut, I., Fourgon, Didier, and Jangoux, Michel

Abstract

The symbiotic interaction, population and infestation dynamics of the muricid Vexilla vexillum (Gmelin, 1791) on 2 echinoid species, Tripneustes gratilla (Linnaeus, 1785) and Echinometra mathaei (Blainville, 1825), was investigated on the barrier reef off Toliara (Madagascar). V. vexillum is an ectoparasitic muricid which was exclusively found in association with sea urchins, on which it moves freely and browses over the integument. Host recovery from damage caused by muricid grazing was dependent on lesion size. Small lesions regenerated while larger ones were subjected to secondary infections, which led to host death. A 27 mo survey (2000 to 2003) of the muricid's population dynamics revealed annual recruitment episodes during the mid-summer season (December to January). Patterns of recruitment peaks were apparently linked to its reproductive cycle. Demographic parameters including growth and mortality rates of the muricid were estimated from analysis of size-frequency distributions. Growth was described by the von Bertalanffy function. The model predicts that V. vexillum is a fast-growing species in which asymptotic shell length (L infinity = 1.024 cm) is reached 6 to 7 mo after recruitment. The growth rate constant K, and shell length at settlement L0, were estimated from the model. Estimated mortality rate was 55% yr(-1); V. vexillum has a short lifespan. The observed high growth rate together with the high mortality rate suggest that V. vexillum is a semelparous species. A field survey of the infestation dynamics of V. vexillum was performed during 3 consecutive years, with seasonal variation in parasite prevalence on both echinoid host species. Although both T. gratilla and E. mathaei were infested, a preference towards T. gratilla was noted. This was attributed to T. gratilla's test morphology (which allows better accessibility for grazing), to the muricid's higher recognition capacity of T. gratilla (as determined by olfactory experiments) and to the high r, Comparative Study, Journal Article, Research Support, Non-U.S. Gov't, info:eu-repo/semantics/published

Published
2004

9. Lecithotrophic development and metamorphosis in the Indo-West Pacific brittle star Ophiomastix venosa(Echinodermata: Ophiuroidea)

Author

FOURGON, DIDIER

Abstract

SummaryThe larval development of the ophiocomid ophiuroid Ophiomastix venosais described using SEM. The gastrula transforms into a uniformly ciliated early larva which progressively changes into a lecithotrophic late premetamorphic larva with a continuous bilateral ciliated band. This stage is short-lived and equivalent to a highly reduced ophiopluteus. Comparisons between O. venosaand other ophiuroid species whose development has been investigated suggest that, whatever the developmental mode (lecithotrophic or planktotrophic), a pluteus stage always occurs in ophiuroids with planktonic development. Two metamorphic stages were identified, the late metamorphic larva differing from the early one by the closure of the larval mouth. The appearance of the permanent mouth marks the end of the metamorphosis. The postlarva still possesses remnants of larval features. The transformation of the reduced ophiopluteus into a barrel-shaped metamorphic larva with transverse ciliated bands, a vitellaria larva, is followed. The possible occurrence of a unique type of metamorphic larva in non-brooding ophiuroids is discussed. Verification of this, however, needs further SEM investigations on metamorphic larva from species having “regular” planktotrophic development.

Published
2005
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10. Population dynamics, infestation and host selection of Vexilla vexillum, an ectoparasitic muricid of echinoids, in Madagascar.

Author

Vaïtilingon D, Eeckhaut I, Fourgon D, and Jangoux M

Subjects
Animals, Body Weights and Measures, Host-Parasite Interactions, Indian Ocean, Madagascar, Population Dynamics, Seasons, Species Specificity, Temperature, Models, Biological, Sea Urchins parasitology, Snails physiology, Symbiosis
Abstract

The symbiotic interaction, population and infestation dynamics of the muricid Vexilla vexillum (Gmelin, 1791) on 2 echinoid species, Tripneustes gratilla (Linnaeus, 1785) and Echinometra mathaei (Blainville, 1825), was investigated on the barrier reef off Toliara (Madagascar). V. vexillum is an ectoparasitic muricid which was exclusively found in association with sea urchins, on which it moves freely and browses over the integument. Host recovery from damage caused by muricid grazing was dependent on lesion size. Small lesions regenerated while larger ones were subjected to secondary infections, which led to host death. A 27 mo survey (2000 to 2003) of the muricid's population dynamics revealed annual recruitment episodes during the mid-summer season (December to January). Patterns of recruitment peaks were apparently linked to its reproductive cycle. Demographic parameters including growth and mortality rates of the muricid were estimated from analysis of size-frequency distributions. Growth was described by the von Bertalanffy function. The model predicts that V. vexillum is a fast-growing species in which asymptotic shell length (L infinity = 1.024 cm) is reached 6 to 7 mo after recruitment. The growth rate constant K, and shell length at settlement L0, were estimated from the model. Estimated mortality rate was 55% yr(-1); V. vexillum has a short lifespan. The observed high growth rate together with the high mortality rate suggest that V. vexillum is a semelparous species. A field survey of the infestation dynamics of V. vexillum was performed during 3 consecutive years, with seasonal variation in parasite prevalence on both echinoid host species. Although both T. gratilla and E. mathaei were infested, a preference towards T. gratilla was noted. This was attributed to T. gratilla's test morphology (which allows better accessibility for grazing), to the muricid's higher recognition capacity of T. gratilla (as determined by olfactory experiments) and to the high recruitment predictability of that particular host. This study provides novel information on the biology of V. vexillum, an echinoid epidermal grazer, and its relationship with 2 ecologically and economically important echinoid species.

Published
2004
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