The inner Danish waters as suitable seaweed cultivation area- evaluation of abiotic factors

Increased production of macroalgae may contribute to solving e.g. the demand for food globally. Palmaria palmata and Saccharina latissima are at present demanded and cultivated in European waters, and can potentially be cultivated at even larger scale. The present study investigated suitable cultivation areas in Danish waters for these two algal species in regard to a variation in the abiotic conditions: light, temperature, and the unusual salinity gradient through the inner Danish waters towards the Baltic Sea.

Published tolerance levels of the abiotic conditions of the species were reviewed and compared to surveillance data on presence of the species and to empiric abiotic data at five sites in Denmark. Furthermore, in situ experiments were conducted at the locations by deployed vertical ropes with inserted adults of P. palmate and S. latissima at 1-6 m depth.

The analysis of the abiotic conditions showed, that light conditions are sufficient to meet the light saturation level of both algae, but large seasonal and a site specific variations in light attenuation determine optimal cultivation depth. Water temperatures were found to exceed the tolerance level for P. palmata in July, August, and September and for S. latissima in August at some sites.

A large geographical variation in salinity was seen between sites, with salinities below the tolerance level of P. palmata at most sites. The results the in situ experiments showed increased biomass over a seven months cultivation period for both species at salinities down to 21±3 PSU, and at the low salinity site (17±5 PSU) P. palmata turned green while continuing growing.

This most likely due to stress such as low salinity and light. Cultivation of P. palmata near Fredericia provided the highest specific growth rate of 0.038 d-1 which was significant from the other sites. These findings were further discussed and the inner Danish waters evaluated as suitable location for cultivation of the assessed species.