column spacer Defenses
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a grouper on a Caribbean reef

"Imagine you’re a grouper, this one, and you have a special taste for schoolmasters. That’s a job in itself and you work continually to improve your kills. But what about the schoolmaster?  It has not only you to contend with, but also lots of other predators, all with different attacking methods. How does it learn to defend against all of them?!" - Turneffe Island, Belize 2000. Video Courtesy Andy Stockbridge, Belize

NOTE Nassau grouper Epinephelus striatus

NOTE Lutjanus apodus

Seaweeds hot buttons for defense part of BCCR
This part of BCCR starts off the large subject of defenses of coral-reef organisms. Considered here are defenses of seaweeds, while defenses of other coral-reef organisms are accessible via the icons.
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of Caribbean seaweeds "This seaweed forest may look edible, but many of its members are defended with noxious chemicals or, as witnessed over there by the white bandings of Padina, at least with high levels of calcium carbonates.  My, Padina is abundant! It must have good defenses against the herbivores. " - Little Cayman 2002


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 structure are considered here, while the other seaweed-defensive topics can be accessed via the icons.
seahorse dive leader for Biology of Caribbean Coral Reefs photograqph of green alga Halimeda in cascading growth form "This type ofgreen seaweed is called Halimeda. Not only is it heavily calcified, but it is also chemically defended against being eaten by fishes" - Turks & Caicos 2003

illustration comparing different types of holdfasts of the green alga Halimeda depending on type of substratum it is anchored in
Structural protection for an alga starts with its holdfast. The holdfast of the green alga Halimeda is highly adaptable depending upon the substratum. Note in the illustration that a meshwork type of holdfast is better adapted for sand, while a mat type of holdfast is good for anchoring in rubble. Other roles played by the anchoring holdfasts of Halimeda spp. in the coral-reef ecosystem include providing surface for growth of encrusting coralline algae and providing a micro-environment conducive to calcium precipitation. This calcification has cement-like properties and benefits the reef ecosystem by its consolidating action, and also, through its provision of superior anchoring, may uniquely explain the success of Halimeda spp. in coral-reef areas. There is no root-like absorptive functions associated with the holdfast - only anchoring or attachment. Multer & Voltava 1992 Proc 7th Int Coral Reef Symp Vol. 2: 887.

NOTE anchoring or attachment structure of seaweeds


photograph of live Halimedaphotograph of dead and sun-dried Halimeda
Another structural defense in Halimeda, and other species of algae, is its high content of calcium-carbonate salts. After bleaching and erosion of the organic components, these structural parts of Halimeda spp. are important contributors to white "coral" sand-beaches.

Live Halimeda sp. 0.33X


Dead and sun-dried Halimeda consists
mostly of calcium carbonate 0.7X

  In the absence of other information, such as chemical makeup, the physical appearance of a seaweed can often providea clue as to its resistance to being eaten by herbivores such as fishes and sea urchins. Here are several common Caribbean seaweeds ranked in order of their "physical" edibility, starting with the most edible one on the Left. Littler et al. 1983 Coral Reefs 2: 111.
photograph of green alga Ulva photograph of green alga Cladophora photograph of red alga Acanthophora photograph of brown alga Turbinaria photograph of green alga Halimeda photograph of red coralline alga Peyssonnelia
sheet-like, soft, thin & fragile filamentous, forms stiff balls that are fragmentable coarsely branched, fleshy & easily fragmentable tough & leathery, with spine-like edges on "leaves" jointed segments, often heavily calcified crustose, heavily calcified & tough
hot button for seaweed defenses hot button for fishes defenses hot button for invertebrate defenses