Sammendrag
The use of macroalgae as a sustainable biomass for multiple applications has gained an
increased interest the last decades. The red algae Palmaria palmata is one of the species
in focus due to its vast characteristics. Compared to other macroalgae that have been
cultivated for decades, cultivation of P. palmata is in an infant stage with underdeveloped
cultivation techniques, inefficient for large-scale production. For successful cultivation,
further knowledge regarding the following steps is essential 1) production of fertile tissue
to provide spore-containing sori out of its main fertility season, 2) conditions and execution
of spore release, 3) the conditions and method for the nursing stage to grow robust
seedlings for deployment, and 4) the best suited substrates for cultivation at an open-sea
farm. These four steps were the focus of this master’s thesis, with the overall aim to
improve critical steps in the cultivation process of P. palmata.
An important finding in the present study was a demonstration of induction of fertility
outside the fertility season of P. palmata in Norway. Results revealed that a manipulation
of light regime to resemble short day conditions secured the highest number of fronds
induced with sori, compared to long day conditions. The same study revealed a possibility
of repeated spore release from the same fronds. For maturing, two different recovery times
between the repeated spore release rounds was tested: two and seven days. For two days
recovery time, sori could release spores up to five times when repeating the spore release
protocol. With seven days recovery time, the same fronds could release spores up to three
times. In the same experiment, different light regimes were tested during recovery time.
The light regime simulating short day conditions during seven days recovery time seemed
to have superior effect on spore density in spore release. However, a considerable number
of spores were released during recovery time as well. During seven days recovery time
and a light regime simulating long days, higher number of spores were released during
recovery time compared to the three days of spore release. Results from this experiment
indicate that two days recovery with short day conditions for maturing of the fronds seems
to be a recommended method. This approach enhanced the spore density retrieved from
the same sori and kept the spore release during recovery time to a minimum.
Two different methods for the nursing stage were tested to compare growth of seedlings
ready for deployment at an open-sea farm: free floating in bubble cultures and directly
seeded substrates. By comparing the two different methods, results revealed that the
method of nursing seedlings of P. palmata in bubble cultures seemed to give a higher
growth rate compared to seedlings directly seeded on substrates. In the method for nursing
seedlings in bubble cultures, three different treatments were tested to optimise the
conditions for growth. Nursing seedlings in bubble cultures treated with low light and low
nutrient content, resulted in a higher growth rate compared to seedlings nursed with high
light intensity or high nutrient treatments.
To test which substrates are best suited for P. palmata at an open-sea farm, the substrates
from nursing stage were deployed together with seedlings from bubble cultures glued to
algae ropes. Based on growth at the open-sea farm, the present study suggests using nets
as substrates when seeding P. palmata directly on substrates. Growth on algae ropes and
entwined ropes were not successful. Overall, the substrates were densely covered by
fouling and the cultivation trial was regarded as unsuccessful. The results amplify the
importance of high spore density in the nursing stage before deployment at an open-sea
farm.
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