Percorrer por autor "Cordes, Aaron Johannes"
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- Mono-trophic seaweed polyculture of sea grapes (Caulerpa lentillifera) and Kappaphycus alvarezii: a case study from Van Phong Bay, Viet NamPublication . Stuthmann, Lara Elisabeth; Costa, Beatrice Brix da; Cordes, Aaron Johannes; Du, Hoang Trung; Kunzmann, Andreas; Springer, KarinKappaphycus alvarezii and Caulerpa lentillifera are economical important seaweeds cultivated in Van Phong Bay, Viet Nam, respectively. The complementary light and nitrogen requirements of the seaweeds introduce the opportunity for a mono-trophic seaweed polyculture. Three different set-ups were tested, namely the integration of K. alvarezii in sea grape ponds, the integration of sea grape plastic cages on longlines and the polyculture of both species in net cages. The relative growth rates (RGRs) of K. alvarezii were highest on longlines, compared to net cages in mono- and polyculture (4.4 ± 0.8 % day− 1 vs 2.1 ± 0.6, 0.6 ± 0.5 % day− 1 ), whereas fragments died off due to warm temperatures and absence of water movement in ponds. Strong recurring water movements at the experimental site caused high losses of K. alvarezii fragments (39 % of initial) and impaired growth of delicate C. lentillifera causing negative RGRs in all treatments (plastic cages without gauze: − 9.8 ± 0.6 % day− 1 , net cages: − 6.4 ± 0.9 % day− 1 ), but with least loss in plastic cages with gauze wrapping (-1.3 ± 0.8 % day− 1 ). Fv´/ Fm´values of both species showed typical midday depression and C. lentilliferas´Fv/Fm were influenced especially by gauze wrapping. Here, we show that the K. alvarezii cultivation on longlines with C. lentillifera integrated below in inexpensive, self-made, customizable plastic cages with additional gauze protection is the most promising set-up from a physiological and economic point of view for Van Phong Bay and beyond. However, further research is needed before implementation of the system.
- Production of nama seaweed (Caulerpa spp.) in an experimental lagoon cultivation setting and landbased system – Influence of cultivation depth and nutrient load on growth and morphologyPublication . Cordes, Aaron Johannes; Engelen, Aschwin; Kunzmann, AndreasWith the increasing impacts of climate change and declining fishery yields, interest in aquaculture is growing in Pacific Island Countries (PICs). One promising solution to produce nutritious and sustainable food without further exploiting the environment is the cultivation of seaweeds, which provide valuable biomass while simultaneously removing carbon dioxide and excess nutrients from the water. To offer fishers an economic alternative to high-value fishery products, seaweeds of the genus Caulerpa are particularly promising due to their comparatively high market price. In Fiji, these edible seaweeds, locally known as nama, are traditionally handharvested from shallow lagoon waters and reefs. However, rising demand has placed increasing pressure on natural stocks, making sustainable cultivation an important alternative. This study evaluated two cultivation approaches for nama. First a lagoon-based system using submerged trays at different depths, and secondly a land-based tank system with and without fertilizer supplementation. Because nama is highly sensitive to environmental parameters such as light intensity, nutrient availability, salinity, temperature, and hydrodynamics, the central aim was to determine which approach provides the most favorable conditions for optimal growth and desirable morphology. Replicated floating trays were deployed at four depths in lagoon waters, while land-based tanks were used to assess the effects of nutrient enrichment. Over a four-week period, relative growth rate (RGR), frond weight, ramuli density, and frond coloration were measured. To provide a benchmark for cultivated biomass, commercial nama sold in Fijian markets was also analyzed for the same parameters. The results suggest that nutrient limitation may be the primary bottleneck preventing successful cultivation in lagoon waters, as nama did not have access to sediment nutrient deposits. In contrast, fertilizer addition in the land-based system promoted growth but also caused pronounced morphological changes, resulting overall in a poor quality of the cultivated biomass. This study underscores the critical influence of nutrient availability on the successful cultivation of nama and can serve as a valuable proxy for future research. Particular attention should be directed toward the identification of the cultivated nama species and the composition of the applied fertilizer.