Cell growth and calcification result from uncoupled physiological processes in the soft coral Litophyton arboreum

E Tentori,R Shepherd,D Allemand

doi:10.3354/meps276085

Abstract

Cellular growth and calcification were measured in branch tips of the soft coral Litophyton arboreum (Cnidaria, Octocorallia, Alcyonacea). We measured cell growth rates as 3 H-thymidine incorporated into tissues, and calcification as 45 Ca incorporated into sclerites, during 2 h incubations in labelled seawater. Both parameters were normalised against soft coral protein content and analysed separately as stem and polyp responses. The experiments were run at various points during coral recovery from dissection. Stems and polyps showed their lowest cell growth rate immediately after injury due to cutting (Days 1 to 3), and their highest cell growth rate during recovery time (Days 7 to 49). In all experiments, the cell growth rate of stems was significantly higher than that of polyps. By contrast, no significant difference was detected between calcification rates of stems and polyps of the fully recovered microcolonies (Days 7 to 81). This study documents for first time the independent progress of cell growth and calcification mechanisms in tropical corals. It also demonstrates the contrasting physiological potential between the body regions of soft coral colonies.

Highlights

One of the most striking features of Indo Pacific coral reefs is the presence and diversity of soft corals (Cnidaria: Alcyonacea)
Using Litophyton arboreum as a model in this study, we address the following questions: (1) Do all parts of the colony grow/calcify at similar rates? (2) Is cell growth coupled to calcification? (3) How does experimental fragmentation of a colony affect cell and skeletal growth?
In contrast to the cell growth rate responses, the fully recovered microcolonies did not show a clear difference in calcification potential between regions (Fig. 4)

Summary

Introduction

One of the most striking features of Indo Pacific coral reefs is the presence and diversity of soft corals (Cnidaria: Alcyonacea). Soft corals are important space competitors, assisted by the production of metabolites that can arrest their neighbours’ growth by causing cell necrosis on contact, by triggering zooxanthellae expulsion, or by preventing larval settlement (see review by Coll 1992). Apart from affecting their neighbours, soft corals must grow fast to occupy the space made available by interspecific competition. While biomass gain represents cellular growth, calcium carbonate gain represents calcification Both processes cause colony growth, these 2 functions may respond to different needs and have different metabolic requirements.

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Discussion

Conclusion