Interaction of conspecific cues in Balanus amphitrite Darwin (Cirripedia) settlement assays: Continued argument for the single-larva assay

Abstract

Gregariousness in marine invertebrate larvae is an important regulator of benthic community structure. Previous laboratory settlement assays employing Balanus amphitrite Darwin cyprids found gregarious effects with as few as 3 larvae well⁻¹, together with modulation of such effects by chemical cues. Here, the relationship between settlement rate and larval density was rigorously tested through a fully randomised design. Seawater conditioned with adult B.amphitrite was tested alongside unconditioned seawater to determine the effect of a conspecific cue on gregarious interactions. Gregarious effects were detected in both conditioned and unconditioned seawater at ≤4 larvae well⁻¹. In untreated seawater, settlement rate increased linearly with larval density, levelling off at densities of ≥10 larvae well⁻¹. In conditioned seawater, settlement induction was observed at ≤4 larvae well⁻¹, switching to inhibition at 6, 8 and 10 larvae well⁻¹, before asymptoting at the highest densities tested. These results advocate the use of individual larvae in laboratory assays that investigate factors stimulating barnacle settlement.

Keywords:

• Balanus amphitrite
• barnacle cypris larva
• settlement
• gregariousness
• waterborne cue
• bioassay development

Acknowledgements

This study was funded by NERC studentships NER/S/A/2003/11884 and NER/S/A/2005/13338. We thank Jens Høeg for helpful comments on the manuscript, Sheelagh Conlan for larval culture and Dan Rittschof and Beatriz Orihuelia de Diaz for collecting and shipping B.amphitrite brood stocks from Beaufort, North Carolina.

Notes

1. The binomial Balanus amphitrite is retained here in preference to Amphibalanus amphitrite introduced during the systematic revision of Pitombo (2004) (see Perez-Losada et al. 2007).