Laminaria japonica |
Sporeling greenhouse |
Sporeling-curtains in a rearing tank |
Young seedlings attached to substrates (palm-fibre ropes) |
Farmers are managing the farmed kelp |
Sun-drying processing method |
Key: 1. main rope; 2. buoy; 3. anchor rope; 4. main anchor; 5. connecting rope; 6. culture rope with kelp; 7. weight
The vertical culture makes good use of water space and is a simple, easily managed procedure. Spacing between the kelp ropes allows currents to pass through them, thus stimulating sporophyte growth. As the plants hang downwards on the kelp ropes they shade each other from excess exposure to sunlight. However, because illumination decreases with water depth, the plants at the lower ends of the ropes may not get enough light to meet their requirements for good growth. This is a disadvantage of this system.Kelp grow-out system used in Japan. |
DISEASE | AGENT | TYPE | SYNDROME | MEASURES |
Malformation diseases | Macrococcus spp. (and other anaerobic sulphate-reducing saprophytic bacteria; also tannin poisoning, due to improper treatment of palm rope substrate materials) | Bacteria | Gametophyte metamorphosis disease: very slow gametophyte growth; cell wall thickening; chloroplast degeneration with pigment change to a yellowish colour; vacuolar contraction with cell protoplasm shrinkage; in serious cases, lipophanerosis occurs (chloroplasts & protoplasm form transparent or dark droplets in cell centre) Egg death: egg shrinks inside oogonium & is unable to extrude & attach to lip of oogonium in preparation for fertilization; as disease advances, egg further contracts & gradually dies; some eggs may extrude but, because of pronounced loss of vigour, fail to attach & drop off from the apical lip of the oogonium Rot & malformation of young sporelings: one or a group of cells expand abnormally to 3-6 times larger than normal; enlarged cells divide abnormally, leading to very disordered cell arrangement & deformed sporelings; grape-like malformed sporelings may be composed of several to a hundred cells; deformation is irreversible; infected sporelings unable to recover to normal shape & gradually die |
Avoid use of diseased & over-mature parent Laminaria; collect parents before temperature rises above 21ºC; avoid parent damage & improve transport & handling procedures; sterilise indoor water circulation system with bleaching powder before spore collection proceeds; separate mature sporophyte cultivation system from sporeling cultivation system; remove rotted spots on parent blades used for spore collection purposes; clean all sporeling substrates & culture tanks; change all seawater in indoor water system; reverse flush filtration tanks; lower circulating water temperature <10 °C; reduce stocking density |
Sporeling detachment disease | Pseudomonas spp. (& excessive illumination) | Bacteria | Sporelings detach from culture ropes; stipes become soft & faded in colour; holdfasts become hard, brittle & weakened; abnormal growth of holdfast rhizoids from sides of stipe; stipe & blade tips rot | Reduce excessive illumination; treat with antibiotics in rearing tanks |
Twisted frond disease | Not yet determined | Mycoplasma-like organisms | Coarsened, swollen & hollowed stipes; twisted or spiral-shaped fronds; withered or shortened holdfasts; frond surface rough or coarse; plants develop thick holdfasts with little branching; some stipes divide into two parts joining the blade to the holdfast; other stipes may appear unaffected | Remove all infected plants from culture ropes at raft site; improve ecological conditions, including reducing intensity of culture |
Green rot disease | Poor illumination | Environmental | Apical part of fronds turn greenish & become soft; symptoms gradually spread to lower part of fronds; serious spread of disease eventually results in decay & death of entire plant | Raise culture ropes; periodically reverse culture ropes |
White rot disease | Excessive illumination & insufficient nutrients | Environmental | Blades fade from brown to yellowish & finally to white; disease spreads from apical part to lower part; eventually whole frond decays & falls from the culture rope | Apply nitrogen-based fertilizers over seafarming area; lower culture ropes to decrease illumination |
Blister disease | Freshwater dilution of seawater after heavy rainfall; especially prevalent in shallow bays | Environmental | Blisters form on fronds, followed by decay | Lower culture ropes below the mass of freshwater run-off (which tends to be near surface) |
Twisted blade disease | Excessive illumination | Environmental | Typically affects young & robust sporophytes during mid-to late-stages of growout; blades show extensive twisting & edges develop convolutions or wrinkles & are crisp & hard; in serious cases, twisted fronds develop spiral-like turns, accompanied by extensive fading of colouration & rotting & disintegration along edges & tips | Reduce light intensity by adjusting height of culture ropes |
Red tide sporeling disease | Pollution/red tides | Thought to be environmental but unidentified pathogen my be implicated | Chloroplast pigmentation fades; cell plasma shrinks; cellular arrangement in tissues disordered; sporelings turn greenish yellow & quickly die | Spray-clean sporeling mats immediately; completely change seawater supply & reverse-flush filtration tanks |
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