Interaction of conspecific cues inBalanus amphitriteDarwin (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 < or =4 larvae well(-1). In untreated seawater, settlement rate increased linearly with larval density, levelling off at densities of > or =10 larvae well(-1). In conditioned seawater, settlement induction was observed at < or =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.

Effects of surface charge and Gibbs surface energy on the settlement behaviour of barnacle cyprids (Balanus amphitrite)

“…Adult barnacle brood-stock (supplied from the Duke University Marine Laboratory, North Carolina, USA) was allowed to release nauplii naturally and approximately 10,000 stage 1 nauplii were collected over a period of 2 to 3 h. The nauplii were attracted to a cold light source, according to the protocol of Elbourne et al (2008), and transferred at intervals to a dilute solution of Tetraselmis suecica for temporary storage. When sufficient numbers had been collected, all nauplii were transferred to a clean plastic bucket containing 10 l of 0.7 mm filtered seawater with 36.5 mg l 71 of streptomycin sulphate and 21.9 mg l 71 of penicillin G. The larvae were fed an excess of Skeletonema marinoi and T. suecica for 5 days until metamorphosis to the cyprid stage.…”

An improved barnacle attachment inhibition assay

“…A number of studies of cyprids have demonstrated that crowding will result in higher attachment rates (Clare et al 1994;Head et al 2004;Elbourne et al 2008). Under the assay conditions used in the present study, a high attachment rate of 84% was found when using 3-day old cyprids; the attachment rate was still 43% even when using 0-day old cyprids (Table 3).…”

“…Richardson 1998; Holm et al 2000;Thiyagarajan et al 2002;Head et al 2004;Hung et al 2005;Gribben et al 2006;Elbourne et al 2008). For instance, Harder et al (2001a) and Thiyagarajan et al (2002) demonstrated the importance of the food source of the nauplii (ie algae) in cyprid attachment rate.…”

“…It should be noted that a high baseline attachment rate is only desirable when investigating settlement inhibition. When investigating attachment induction, a different experimental design, such as the single-larva assay proposed by Elbourne et al (2008) that will have a low baseline settlement rate, should be adopted.…”

The density and spatial arrangement of the invasive oyster Crassostrea gigas determines its impact on settlement of native oyster larvae

“…Whereas solitary bivalves may enhance settlement by producing feeding currents that entrain larvae (Tamburri et al 2007), the stronger currents of clusters of bivalves might lead to ingestion and, in some cases, consumption of larvae (Smaal et al 2005; Troost 2010). Where negative effects of currents produced during suspension feeding overwhelm positive effects of bivalve habitat complexity, and innate recognitions of parent chemical cues by their larvae (e.g., Zimmer and Butman 2000; Elbourne et al 2008), reductions in the abundance and diversity of native flora and fauna may result.…”