Defenses
 
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Seaweeds hot buttons for seaweed defenses part of BCCR hot button for structural defenses of seaweeds part of BCCR hot button for toxic chemicals of seaweeds part of BCCR hot button for growth strategies of seaweeds part of BCCR
Seaweed defenses relating to growth strategies are considered here, while those relating to TOXIC CHEMICALS and STRUCTURE can be accessed via the icons.
 
 

Growth strategies

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of Caribbean seaweeds taken from a video "These are pretty seaweeds. I see some HalimedaHalimeda is interesting in that it grows its new segments at night, and they become defended by morning, just as the awakening algivorous fishes are looking for breakfast.  Neat, huh? ." - Little Cayman 2003
 
 

photograph of green alga Halimeda showing freshly grown tips produced overnight
Growth of the calcified green alga Halimeda is at the tips, with production of new segments occurring mainly at night. The new segments are high in levels of diterpenoids. Photosynthetic pigments are not added to the new growth until sunrise and, by the following day, calcification is well underway. The strategy allows the new tips to grow a bit before being exposed to herbivores, and indicates that calcification plays a secondary role to diterpenoid chemicals with respect to deterrence of herbivores. Perhaps calcification is more important for structural support of the plant. Hay et al. 1988 Oecologia 75: 396.

NOTE this subject is considered in another part of SEAWEED DEFENSES: TOXIC CHEMICALS

 

Nighttime growth of new segments of Halimeda
showing lack of pigmentation 0.8X

 

photograph of brown alga Padina sp.Some tropical seaweeds are known to exhibit different physical structure depending upon the intensity of grazing. For example, in back-reef areas in Jamaica the brown alga Padina adopts a prostrate turf form in areas of intense grazing by surgeonfishes and parrotfishes. But, if the herbivorous fishes are experimentally removed, within a few days the alga begins to grow fan-shaped blades, and after a few weeks of reduced grazing the familiar calcified foliose blades are evident. Lewis et al. 1987 Ecology 68: 636.

 

 

Brown alga Padina sp. 0.33X

 
drawing of morphological form of the seaweed Padina when grazing pressure is great drawing of morphological form of the seaweed Padina a few days after release of grazing pressure by fishes drawing of seaweed Padina several weeks after release of grazing pressure by fishes
Padina has a prostate form under intese grazing pressure by fishes Within 4d of removal of the fishes, fan-shaped blades appear By 10wk after removal of fishes, typical large foliose blades are present
 
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