Growth and biochemical composition of green seaweed Chaetomorpha linum (O.F. Müller) Kützing (1845) cultured in a range of ionic profiles

Seaweed aquaculture in Inland Saline Water (ISW) can utilise degraded land to produce valuable products. ISW is characterized by its different ionic profile to ocean water (OW), particularly the ratios of sodium (Na⁺) to potassium (K⁺) ions, and magnesium (Mg²⁺) to calcium (Ca²⁺) ions. The feasibility of seaweed cultivation in varying ionic profiles is not yet well understood. This study investigates the growth of Chaetomorpha linum by length (SL) and biomass (TB), cultured in several ionic profiles by mixture of ISW with OW over two 15 day experiments. The first experiment (EXP 1) investigated growth across a broad range of ionic profiles. C. linum was then cultivated across a more specific range of profiles in the second experiment (EXP 2), based on EXP 1 results. Tanks (50 L) were randomly organised outdoors and salinity was maintained at approximately 25 ppt. SL and TB of seaweed was recorded every 3 days. The proximate and mineral composition of harvested seaweed on Day 15 was also analysed. A significant negative correlation (p < 0.001, r = −0.835, n = 13) was observed between non-discrete TB specific growth rate (SGR) and increasing K⁺ of media in EXP 1. A significant positive correlation (p < 0.001, r = 0.769, n = 28, EXP 1) was observed between potassium (K) in dry matter (mg.g⁻¹) and K⁺ in media, suggesting lower K⁺ in media causes increased TB due to higher water flow rate into cells. Calcium (Ca) content (% d.b.) was much higher in K⁺ deficient media, indicating Ca accumulation occurs in cells during ion homeostasis when K is not available. Positive SL SGR's across ionic profiles also indicate this species is capable of a high level of internal ion regulation. This study provides context for commercial cultivation of C. linum in varying water types, and presents an avenue for salinity-affected dryland farmers to diversify their income through ISW aquaculture.