ABSTRACT
The continuing expansion of seaweed cultivation could assist in ensuring future global food security. The Laminariales species Alaria esculenta and Saccharina latissima are each cultivated for food across their European ranges. The predominant method for cultivating European kelps involves growing juveniles on twine within a hatchery which is then deployed at a farm site. The associated hatchery and deployment cost of this approach are relatively high. A new and innovative methodology-called binder-seeding-can reduce these costs, but, has yet to be validated. We compare the biomass yield and morphology of A. esculenta and S. latissima cultured using either the traditional twine-longline method or binder-seeding onto AlgaeRope and AlgaeRibbon, specially designed textiles. In a controlled growth experiment, A. esculenta had a similar biomass yield on all materials, but fronds were shorter (23 ± 7%) and thinner on the AlgaeRibbon (42 ± 4%) due to a 3-4-fold higher density of developing sporophytes compared to the twine-longline. In contrast, S. latissima gave a 4-fold higher biomass yield on the AlgaeRibbon in June (4.0 kg m-1), but frond morphology was not different between materials, despite a 4-fold higher sporophyte density on the AlgaeRibbon. The stipe length of both species also increased at the higher sporophyte density on the AlgaeRibbon. The AlgaeRope gave an intermediate response or was similar to the twine-longline. These results show that binder-seeding onto the AlgaeRibbon significantly increases the achieved biomass yield in S. latissima. These results can assist cultivators to select the most appropriate method of kelp cultivation depending on morphological/yield requirements of the end use. Further study is needed on the optimisation of the binder-seeding density and its impact on thallus morphology.
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.
