The developmental regulation of mass cultures of free-living conchocelis for commercial net seeding of Porphyra leucosticta from Northeast America

The developmental regulation of mass cultures of “free-living” conchocelis (suspension cultures) of Porphyra leucosticta from Groton, CT (USA) has been studied in laboratory culture. The conchocelis filaments were vegetatively propagated and maintained in 15 l volumes at 15 °C, 40 μmol m− 2 s− 1 and 16 L:8 D. Conchosporangia formation was induced after four weeks by increasing the temperature up to 20 °C, maintaining a photon fluence rate of 40 μmol m− 2 s− 1 and decreasing the photoperiod to 8 L:16 D. Conchosporangial filaments were vegetatively propagated and maintained at these conditions for up to 24 weeks. Suspension cultures of conchosporangial filaments were induced to form and release conchospores (after 6-10 days) by decreasing the temperature to 15 °C, increasing the photon fluence rate to 60-100 μmol m− 2 s− 1 and lengthening the photoperiod to 12 L:12 D. Conchosporangial formation was found at all photoperiods, however, the ratio of conchosporangia to vegetative conchocelis increased as the photoperiod decreased. With higher photon fluence levels, conchospore release time was decreased, whereas at a temperature of 25 °C spore germination decreased. At their peak release, the quantity of conchospores increased from 7.14 to 18.3 million per gram of conchosporangia with a decrease in conchosporangia density from 1.582 to 1.125 mg ml− 1, respectively. On the average, one gram (dw) of free conchosporangia could release about 20 million conchospores at the peak period. These released conchospores were able to attach, germinate and develop into juvenile blades on the synthetic twine (3-5 mm in diameter) of standard nori nets (1.5 × 18 m). A total of 16 standard nets and eight small nets (2.0 × 2.5 m) were seeded by fixing the culture nets over a rotary wheel in a 2.5 × 2.5 × 0.5 m− 3 tank containing the mature conchospore inoculum from the free-living conchosporangia cultures. Four seeded standard nori nets were transferred to the sea for nursery culture in Long Island Sound (USA). Conchosporeling densities from 255 to 325 conchosporelings cm− 1 were produced. After 43 days of nursery culture, the blades grew to 1.49 ± 0.14 cm in length. Our results indicate that the use of “free-living” conchocelis suspension cultures may be an effective alternative technology in the commercial production of the Porphyra.