Growth and survivorship of Phyllospora comosa (Phaeophyceae, Fucales) on different mariculture seeding twines in a hatchery setting

Seeding twines are convienient for outplanting cultured seaweeds, facilitating seeding in high densities. Twines are typically made of synthetic polymer fibres, likely for increased durability and economic benefits relative to natural fibres. However, synthetic twines can contribute to oceanic plastic pollution if fragmented or lost at sea, whereas natural-fibre twines will biodegrade over time. We compared the seeding success of zygotes and germlings of the fucoid Phyllospora comosa among different twines varying in diameter and composition (nylon (1 mm & 3 mm), Kuralon (2 mm & 3 mm) and Algae Twine™ (1 mm) and hemp (1 mm) in three separate experiments (A, B & C). For experiments A and B (both six weeks duration), equal densities of P. comosa embryos were seeded directly onto twines wrapped tightly around 20-cm lengths of 50-mm diameter PVC pipe and cultured indoors in controlled conditions. For experiment C (three-months duration) equal sections of each twine were wrapped in a randomised order around replicate quadrats (50 cm × 50 cm) and cultured in large flow through outdoor tanks. Successful seeding of P. comosa zygotes occurred on all twines in all three experiments, but differences in length, percentage cover and densities varied among twine types across times, and between experiments. Germlings had reached ~ 1-mm lengths by 9 weeks of age in Experiment A, but similar lengths were reached by 4 weeks in Experiment B. In Experiment C, germlings had attained ~1.7 mm by 12 weeks on all twines except hemp. This study demonstrates that whilst 2-mm Kuralon twine generally performed well, a range of twine types may be suitable for seeding and subsequent hatchery growth of P. comosa embryos, including the natural twine, hemp. Farmers may thus effectively base their choice of seeding twine on the cost of material versus environmental trade-offs of using natural versus synthetic twines. However, performance of the different twines at sea remain to be tested in future studies.