Abstract
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 cultivate Fucus vesiculosus and Fucus serratus in the Kiel fjord (Western Baltic Sea), fouling by the epizoans Electra pilosa, Mytilus sp., and Amphibalanus improvisus rendered 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 cultivated Fucus thalli. For this purpose, thalli of F. vesiculosus and F. serratus were 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 (1× week−1, 3× week−1). Growth rates of both Fucus species were not or only slightly reduced by the desiccation treatments. The final harvested biomass of F. vesiculosus under frequent mild desiccations (3× week−1 to 80% of ww) was even higher than the biomass of undesiccated controls. The size of the epizoans E. pilosa and A. improvisus was 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: 3× week−1 to 80% of ww, F. serratus: 3× 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% for F. vesiculosus and from 19.1 ± 2.7 to 1.0 ± 0.1% for F. serratus. Thus, desiccation seems to be an effective measure for the production of clean Fucus biomass 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.
Highlights
Seaweed cultivation has become a large industry in the course of the past decades having reached an annual worldwide harvest of about 30 million t wet weight in 2016 (FAO 2018a)
The onset of the larval fall at the beginning of July allowed to test the effect of desiccation on Fucus growth rates before the occurrence of epizoans on the thalli, especially since A. improvisus and E. pilosa did not occur before that time either (Fig. 1)
The results show that growth rate as well as epizoan size and number are influenced by regular desiccation and that choosing the right desiccation regime allows for cultivation at growth rates comparable to non-desiccated cultures, but with significantly less epizoan biomass and abundance
Summary
Seaweed cultivation has become a large industry in the course of the past decades having reached an annual worldwide harvest of about 30 million t wet weight (ww) in 2016 (FAO 2018a). In 2015, an experimental cultivation of Fucus vesiculosus L. and Fucus serratus L. has been established at the Kiel fjord in the Western Baltic Sea. Hitherto, Fucus biomass has been harvested exclusively from wild stocks e.g. at the Atlantic coast of Ireland and France (Mac Monagail et al 2017). At the German Baltic Sea coast, harvesting of wild Fucus biomass for commercial purposes is prohibited (Bundesamt für Naturschutz 2013) due to dramatic stock declines in the twentieth century (Kautsky et al 1986; Torn et al 2006; Rohde et al 2008). The experiments in the Kiel fjord are among the first trials to cultivate Fucus species for commercial purposes (but see FAO 2018b; Haglund and Pedersen 1988)
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