Variability in diel and seasonal in situ metabolism of the tropical gastropod Tectus niloticus

A Lorrain,M Le Goff,J Clavier,F Houlbrèque,L Chauvaud,E Amice,J Thébault,L Tremblay-Boyer

doi:10.3354/ab00618

Abstract

Researchers often use metabolic measurements in the field over narrow time periods to estimate an organism's metabolism over large time scales. Here, we measured in situ respira- tion, calcification and excretion rates of the tropical gastropod Tectus niloticus L. through benthic chamber experiments. Our samples spanned a 21 h time frame and were taken during both the warm and cool seasons. We assessed diel and seasonal variability in metabolic rates, as well as the effect of individual size and the contribution of shell epi- and endobionts. Our results show that metabolic rates vary through time at both diel and seasonal scales, as measured fluxes for respira- tion and calcification were significantly higher at night during the warm season. This nocturnal pattern was not significant in the cool season. Size effects were significant with higher respiration and calcification rates for small individuals regardless of the season, although the difference tended to be more pronounced in the warm season. We also found that shell epi- and endobionts made an important contribution to respiration, as 40 and up to 100% of total measured fluxes for night and day, respectively, could be attributed to the shell community. More importantly, the direction of the measured flux was occasionally opposite that of the individual trochus, highlight- ing that the contribution of shell epi- and endobionts must be accounted for in order to achieve an accurate understanding of individual metabolism. Lastly, depending on the time of day and season when measurements are taken, ignoring diel or seasonal variations in metabolic rates could result in important under- or overestimation of the contributions of gastropods to carbon and calcium carbonate fluxes in coastal ecosystems.

Highlights

Respiration and biocalcification of marine animals such as molluscs can be a source of CO2 into the ecosystem and their role in the carbon cycle has been demonstrated in temperate environments (Chauvaud et al 2003, Clavier et al 2009, Lejart et al 2012, Mistri & Munari 2013)
This species is one of the most valuable and sought-after reef gastropods because its shell can be used in the manufacture of mother-of-pearl buttons (Castell & Sweatman 1997), which can be a valuable source of income for people in the Indo-Pacific region
Field work was conducted from the RV ‘Alis’ in the southwest New Caledonian lagoon on the Tabou reef (22° 28.861’ S; 166° 26.793’ E; Fig. 1) on 4−5 February and 23−24 August 2012, to sample 2 seasons with contrasting temperatures

Summary

Introduction

Respiration and biocalcification of marine animals such as molluscs can be a source of CO2 into the ecosystem and their role in the carbon cycle has been demonstrated in temperate environments (Chauvaud et al 2003, Clavier et al 2009, Lejart et al 2012, Mistri & Munari 2013). Trochus meat is a source of protein, while its shells have been traditionally used for ornaments by indigenous people (Castell & Sweatman 1997, Hoang et al 2008). Because of commercial interest and the risk of overfishing, this species has been the subject of numerous biological studies (e.g. Bour 1989, Castell & Sweatman 1997, Pakoa et al 2010, Purcell & Cheng 2010)

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