Regrowth and biofouling in two species of cultivated kelp in the Shetland Islands, UK

Abstract

The meristem of the kelps Laminaria digitata and Saccharina latissima is located at the base of the blade, growth can therefore continue when the distal blade is lost due to erosion or harvesting. The aim of the study was to determine the regrowth potential of cultivated kelp in the Shetland Islands (UK) to assess feasibility of harvesting twice in one growing season. Laminaria digitata and S. latissima grown on longlines at sea were sampled between March and August, and harvested either at the stipe (whole) or 10 cm above the stipe-blade transition zone (partial) May-August. Image analysis was used to estimate blade length, width, area and fouled area. S. latissima increased in length more than L. digitata between March and August, and in August, while whole S. latissima experienced a net loss in length, partially cut blades had a net increase. Whole blades significantly increased in length for both species but only partially cut S. latissima significantly regrew. In late summer, severe biofouling by tunicates made up 12 and 27% of the biomass at two sites. Interestingly, S. latissima was less fouled than L. digitata. Consequently, S. latissima shows the greatest potential for the application of partial cutting to improve cultivated biomass yields. However, the period for regrowth is limited by low yields in early spring and blade degradation in late summer. In order to optimise biomass yields, further understanding is needed on the abiotic and biotic factors that control growth and biofouling on natural and farmed seaweed.

Latitudinal, seasonal and depth-dependent variation in growth, chemical composition and biofouling of cultivated Saccharina latissima (Phaeophyceae) along the Norwegian coast

“…The species composition of the epibionts, and thus possibly their effect on kelp biomass, varied among locations. At most locations, epibionts were dominated by the bryozoan M. membranacea like in many earlier studies across different regions (Lüning and Mortensen 2015;Førde et al 2016;Rolin et al 2017). At locations influenced by freshwater, however, hydroids and bivalves also covered the seaweed fronds to a high degree.…”

“…Undesirable for seaweed production, the seaweed frond provides a substratum for fouling organisms to settle on and grow. Fouling by epibionts usually occurs from spring to autumn (Peteiro and Freire 2013a;Førde et al 2016;Rolin et al 2017;Matsson et al 2019), depending on location (Matsson et al 2019), latitude (Rolin et al 2017) and interannual variation (Scheibling and Gagnon 2009). Epibionts can form a barrier inhibiting nutrient (Hurd et al 2000) and light absorption (Andersen 2013) and may cause loss of biomass through increased drag and friction and decreased flexibility (Krumhansl et al 2011).…”

Biofouling in marine aquaculture: a review of recent research and developments

“…Some fouling species, such as the encrusting bryozoans Membranipora membranacea and Electra pilosa, make the lamina of cultivated kelps brittle, which increases susceptibility to breakage (Førde et al 2016). In addition, the presence of tunicates, predominantly Ciona intestinalis, and the hydroid Obelia geniculata can deteriorate the appearance and quality of cultured kelp blades (Park and Hwang 2012;Rolin et al 2017). Furthermore, some epiphytic fouling species penetrate deep into the host cell tissues, causing disorganisation or even destruction of the host's cells close to the infection (Leonardi et al 2006).…”

“…Farming seaweed at exposed locations is one promising strategy, but it is highly species-specific. For example, exposed sites are linked with reduced levels of biofouling for the cultured kelps Undaria pinnatifida, Saccharina latissima and Laminaria digitata (Andersen et al 2011;Peteiro and Freire 2013;Rolin et al 2017) and increased water movement with less siltation is recommended for the cultivated red alga Kappaphycus alvarezii (Hurtado et al 2006). In contrast, softer-bodied seaweeds such as the red alga Gracilaria chilensis may lose biomass when cultured at exposed locations (reviewed in Buck et al 2018).…”

“…In contrast, softer-bodied seaweeds such as the red alga Gracilaria chilensis may lose biomass when cultured at exposed locations (reviewed in Buck et al 2018). However, cultivating seaweeds at exposed sites may also present other environmental challenges as severe storms can damage seaweeds and displace aquaculture structures, leading to reductions in biomass and farm productivity (Rolin et al 2017).…”