Control of fouling in the aquaculture ofFucus vesiculosusandFucus serratusby regular desiccation

Fouling is a major problem in seaweed aquaculture and one of the main obstacles during the domestication process for new culture species. During first attempts to cultivateFucus vesiculosusandFucus serratusin the Kiel fjord (Western Baltic Sea), fouling by the epizoansElectra pilosa,Mytilussp., andAmphibalanus improvisusrendered the production of marketable biomass impossible. This study tested (1) if regular desiccation by air exposure is effective in decreasing the abundance and size of foulers and (2) if and how regular desiccation affects the growth performance of the cultivatedFucusthalli. For this purpose, thalli ofF. vesiculosusandF. serratuswere cultivated freely floating in baskets directly deployed in the fjord and desiccated to defined percentages of the wet weight (ww) by air exposure. The treatments comprised controls and desiccations of different intensities (from 90 to 40% of ww) and at different frequencies (1x week(-1), 3x week(-1)). Growth rates of bothFucusspecies were not or only slightly reduced by the desiccation treatments. The final harvested biomass ofF. vesiculosusunder frequent mild desiccations (3x week(-1)to 80% of ww) was even higher than the biomass of undesiccated controls. The size of the epizoansE. pilosaandA. improvisuswas significantly reduced by the desiccation treatments and the abundance of all epizoan species was drastically reduced by the desiccation regimes. Frequent mild desiccations (F. vesiculosus: 3x week(-1)to 80% of ww,F. serratus: 3x week(-1)to 90% of ww) proved to be most effective and decreased the epizoan ww share of the total harvest from 13.0 +/- 4.8% in the control to 1.8 +/- 0.2% forF. vesiculosusand from 19.1 +/- 2.7 to 1.0 +/- 0.1% forF. serratus.Thus, desiccation seems to be an effective measure for the production of cleanFucusbiomass in culture which is necessary for further valorization. A technical solution for the implementation of this procedure in large-scale cultures remains to be developed.