The red seaweed Delesseria sanguinea (D.s.) is the dominating macroalga populating a man-made large-scale reef, which has been installed near Rostock, Germany. D.s. showed to contain biologically active sulfated polysaccharides (SP) with an interesting activity profile. Important prerequisites for a potential economic use of these SP are the availability of sufficient amounts and a reproducible high quality. To evaluate this, D.s. has been monthly harvested over the course of more than one year and the SP were isolated using two optimized extraction procedures, one with water, the other one with 0.1M NaOH at 85°C. The only parameter showing a clear seasonal variation is the dry mass of D.s., ranging form 12% in spring up to 23% in late autumn. In general, water extraction leads to ˜50% lower yields (1.9±0.5% of fresh algae) than the alkaline extraction (3.1±0.9%), but the obtained SP have a higher degree of sulfation (DS) (0.48 vs. 0.40), a lower protein contamination (0.5% vs. 1.4%), and ˜50% higher elastase inhibitory and anticoagulant activities. Moreover, the quality of the SP extracted with water is highly reproducible, whereas the SP extracted with NaOH show considerable batch-to-batch variation. This partly tends to be dependent on the season, as the yield increases from spring to autumn, whereas the DS decreases. Main reason seems to be the coextraction of starch-like polysaccharides by NaOH, which are accumulated over the year and contribute to the increasing dry mass of D.s. This has been confirmed by acetylation analysis of the SP, indicating a glucose content rising from spring to autumn. In conclusion, by using an optimized extraction procedure, SP of reproducible and high quality can be isolated from D.s.. Compared to NaOH, the extraction with water is more specific and allows an extraction of D.s. batches harvested throughout the whole year.