Effects of substrate, water flow, and turbulence in raceway culture of the high-value agarophyte Pterocladiella capillacea

Abstract

One reason most commercial seaweed aquaculture is done extensively is that land-based intensive culture is expensive. Seaweed growth in land-based raceways can be bolstered by high water flows and turbulence, and a better understanding of this may mitigate production costs. We investigated flow conditions in raceway culture of Pterocladiella capillacea, a source of pharmaceutical grade agar. We tested the effects of ploidy level (carpospores, tetraspores), substrate (rope, glass slide), and flow type in raceways (turbulent, laminar) and the laboratory (no flow) on the survival and growth of sporelings. We also assessed the effect of flow rates (1.5, 4, 10 cm s−1) and flow type (turbulent, laminar) on the growth of adult P. capillacea. Sporeling survival 48 h post-settlement was unaffected by flow type, and carpospores survived better than tetraspores on ropes. After four weeks, sporelings in raceways survived better on ropes than on glass slides, and sporelings derived from carpospores survived better on ropes than those from tetraspores. Sporelings grown in raceways were 5.8 times larger than those in the laboratory, but flow types had little effect within raceways. Seaweeds grown from carpospores grew 1.2 times larger than tetraspore in the raceways. Flow rate and type had little effect on the growth of adults, and their growth was slow possibly because of smothery by epiphytes. This study suggests P. capillacea spores are amenable to raceway culture, but adults do not fare as well in similar conditions.