Calothrix
Calothrix spp.
Morphology and Cellular Structure
Calothrix represents a highly resilient, filamentous genus of Cyanobacteria distinct from standard 'red slime'. It features prominent morphological asymmetry: basal heterocysts (specialized cells responsible for nitrogen fixation via the nitrogenase enzyme) taper out into long, hair-like vegetative filaments. Biochemical Defenses: The exterior is sheathed in a tough, mucilaginous matrix constructed from complex polysaccharides. This extracellular envelope shields the organism from intense ultraviolet (UV) radiation, oxidative stress, and renders it utterly unpalatable to standard herbivorous invertebrates (e.g., Trochus, Astrea snails).
Symptoms
Visual Pathology
- Filamentous Matting: Appears as dense, fuzzy, or furry patches resembling dark, wiry hair algae but possessing a mucilaginous, slimy texture upon tactile inspection.
- Tapered Strands: Microscopically, individual strands taper from a bulbous base to a fine point.
- Gas Entrapment: Copious production of trapped $O_2$ and $N_2$ gas bubbles within the microbial mat, often resulting in sections tearing off and floating in the water column.
- Coloration: Typically presents in shades of deep brown, olive-green, or black, obscuring aragonite substrate and encrusting corals.
Main Causes
Pathogenic Drivers
- Nitrogen Imbalance: The possession of terminal heterocysts allows Calothrix to outcompete standard eukaryotic algae in extreme nitrogen-limited environments (e.g., zero nitrate readings on standard hobbyist assays) while phosphate remains available.
- Suboptimal Flow Dynamics: Settlement of detrital organics in low-velocity zones provides a rich micro-ecosystem supporting localized blooms.
- Trace Element Saturation: Over-administration of trace elements, particularly Iron (Fe) and Molybdenum (Mo)—critical cofactors for the nitrogenase enzyme—can hyper-accelerate Calothrix proliferation.
Treatments & Solutions
Eradication Strategies
- Chemical Oxidants: Extreme resilience necessitates targeted spot-treatment utilizing 3% Hydrogen Peroxide ($H_2O_2$) delivered directly to the mat via syringe with filtration pumps temporarily disabled. The oxidation destroys the protective mucilaginous sheath.
- Erythromycin Application: Standard anti-cyanobacterial treatments (e.g. Chemiclean) are effective, though higher dosages or successive rounds may be required relative to standard red slime.
- Competitive Exclusion: Intentional, controlled raising of Nitrate ($NO_3$) levels to ~2-5 ppm to restore the Redfield Ratio, enabling harmless green algae and beneficial bacteria to competitively exclude the diazotrophs.
Prevenzione & Biologia
Preventive Maintenance
- Nutrient Rationing: Rigorous monitoring to prevent 'bottoming out' nitrates while phosphates remain elevated. Employ nitrate dosing if heterotrophic activity is over-efficient.
- Vigorous Circulation: Eliminating hypoxic zones through the deployment of randomized, high-velocity gyre flow.
- Trace Element Moderation: Temporarily ceasing the supplementation of multi-mineral complexes, specifically halting external sources of Molybdenum and Iron.