Marine biofouling is regarded to be problematic in mariculture incurring businesses direct costs in clearing biofouling from sea cages and reducing efficiencies. Marine biofouling on sea cages is predominantly composed of opportunistic marine macroalgae, with microphytobenthos, hydroids and other settling fauna that make up the remainder of the community. When the settlement duration is <5 months, biofouling is predominantly marine macroalgae that thrive in a high nutrient environment from intensive fin-fish farming. This study highlights the real commercial opportunity presented by biofouling macroalgal biomass when transformed into a premium liquid fertiliser in addition to nutrient trading credits (NTC) through bio-assimilation of carbon, nitrogen and phosphorus from the adjacent marine environment.
This presentation will encompass settlement of marine macroalgae on mooring lines of Southern bluefin tuna cages of a farm in Port Lincoln, South Australia. Results reveal close to 70 species of marine macroalgae that make up the assemblage with settlement ranging from 0.04 to 26.19 gDW m-1 (depth integrated) on the mooring lines over an 8-month settlement period. Polysiphonia, Uronema, Vaucheria and Dasya dominated the algal community on the mooring lines. Higher settlement was observed at 20-24m depth equivalent dominated by Rhodophyceae.
A scaled-up pilot was undertaken with 0.8 ha of seaweed settlement lines deployed adjacent to the tuna cages. Results reveal a very different community composition with Sarconema dominating (~95%) the assemblage followed by Dasya (2%) and Claviclonium (2%). Mean settlement of 115 gDW m-1 was recorded with tissue carbon, nitrogen and phosphorus content of 27%, 3% and 0.35%, respectively. Based on these preliminary outcomes, harvesting marine macroalgae from the settlement lines present a commercial opportunity ranging between $9,600-18,000 ha-1 annum-1 from premium liquid fertiliser in addition to $1,300-3,600 ha-1 in nutrient trading credits.