Defenses
 
column spacer Defenses
 
 
Invertebrates
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The topic considered here reating to defenses of invertebrates deals with toxic chemicals. Other invertebrate defenses are accessible via the icons.
 
 

Invertebrate defenses: toxic chemicals

Chemical defenses of invertebrates fall into a category of toxic/noxious tissues or secretions, considered here, and 3 other categories accessible via the icons.

 

hot buttons for chemical-defenses part of BCCR
 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of reef taken from a video "The flesh of many Caribbean reef invertebrates is chemically protected. Sometimes the toxicity is associated with bright coloration, but oftentimes not, as we can see in these drably coloured gorgonians." - Turks & Caicos 2005
 
 

Invertebrate defenses: toxic chemicals: toxic/noxious tissues or secretions

  Toxic or noxious tissues or secretions are employed as defenses by many reef invertebrates. Sponges, and zoanthids, & gorgonians are dealt with here in 2 subsections, while SNAILS, CRABS, CEPHALOPODS, & SEA CUCUMBERS are considered elsewhere.
 
 

Sponges

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of Caribbean sponge taken from a video "Sessile reef invertebrates may seem vulnerable. These sponges, for example, are doubly protected, by spicules and deterrent chemicals." - Little Cayman 2001
 
 

photograph of brown tube-sponge Agelas conifera
Sponges contain abundant spicules of many different types. The spicules are made of glass, and in certain deep-water species form a rigid supporting skeleton. Similarly, data on defenses of shallow-water species suggest that the spicules in the tissues of the sponges are mainly for structural support and not for defense. If so, what defenses does a sponge have against being eaten by fishes? Well, the answer is not difficult given the topic being considered in this section. Sponges have a range of toxic chemicals that are known to be deterrent to fishes. For example, crude extracts from dried tissues of brown tube-sponges are known to deter feeding by bluehead wrasses and other reef fishes. Chanas et al. 1996 J Exp Mar Biol Ecol 208: 185.

 

 

Brown tube-sponge
Ageles conifera 0.1X

 

In one such study researchers collect 71 species of Caribbean sponges from reef, mangrove, and seagrass habitats. Each sponge is dried, ground to a fine consistency, extracted with solvents, and the solvents evaporated to yield the component organic toxins. This dried matter is combined with fish-food pellets at physiological levels and tested for edibility with bluehead wrasses Thalassoma bifasciatum. The following results are obtained:

1. 69% of the sponges yield extracts that deter feeding by the wrasses (i.e., unpalatable).
2. Of the 10 most common reef sponges, 4 yield extracts that are palatable to the wrasses.
3. Of these 4, two are regularly eaten by species of angelfishes.
4. Of the 49 unpalatable sponges (= 69% of total), there is no significant correlation of colour with unpalatability.
Pawlik 1995 Benthic Ecol Meet Abstr; Pawlik et al. 1995 Mar Ecol Progr Ser 127: 183.

NOTE levels at which the materials would be found naturally in the sponges

NOTE the idea here is to see if there is evidence of warning coloration (known also as aposematism) in sponges. Fishes have excellent colour vision and thus have the potential for learning to associate certain colours with bad taste. This topic is considered elsewhere in BCCR: COLOURS: FUNCTIONS OF COLOURS: DEFENSE: WARNING OF TOXICITY.

 

photograph of several Caribbean reef sponges
So, the results from the experiment show that chemical defenses are important to sponges, but also show that not all sponges have evolved this strategy. Also, there appears to be no evolution of warning coloration, at least from what our eyes can detect. Some reef fishes are known to see portions of the light spectrum, such as ultraviolet, that are invisible to us. Thus, it is possible that in addition to a reef fish seeing sponge colours as we see them, they may be perceiving cues hidden to our vision that contain completely different messages.

 

 

Colorful Caribbean reef sponges, including
pink vase sponge Niphates digitalis, tube sponge, and chicken-liver sponge Chondrilla nucula

 

photograph of tube sponge Pseudoceratina crassa with a bite wound
Another "wrinkle" in our undestanding of chemical defenses in sponges is that several common Caribbean species possessing deterrent chemicals (based on laboratory studies using extracts) are nonetheless eaten by spongivorous fishes. Such sponges may rely on quick regeneration as a survival strategy, much like terrestrial plants do after being partially eaten by a herbivore. For example, studies in the Bahamas show that certain tube sponges can regenerate fish-bite wounds at 1mm or more per day, with complete regeneration being completed in a matter of weeks. Swearingen & Pawlik 1998 Mar Biol 131: 619.

 

 

 

Tube sponge Pseudoceratina
crassa
with bite wound 0.3X

  Simulated time-schedule of healing of bite wound:
 
photograph 1 in a series of 9 showing regeneration of a bite wound by a tube sponge Pseudoceratina crassa photograph 1 in a series of 9 showing regeneration of a bite wound by a tube sponge Pseudoceratina crassa photograph 1 in a series of 9 showing regeneration of a bite wound by a tube sponge Pseudoceratina crassa photograph 1 in a series of 9 showing regeneration of a bite wound by a tube sponge Pseudoceratina crassa photograph 1 in a series of 9 showing regeneration of a bite wound by a tube sponge Pseudoceratina crassa photograph 1 in a series of 9 showing regeneration of a bite wound by a tube sponge Pseudoceratina crassa photograph 1 in a series of 9 showing regeneration of a bite wound by a tube sponge Pseudoceratina crassa photograph 1 in a series of 9 showing regeneration of a bite wound by a tube sponge Pseudoceratina crassa photograph 1 in a series of 9 showing regeneration of a bite wound by a tube sponge Pseudoceratina crassa
Time 0d 2d 4d 6d 8d 10d 12d 14d 16d
 

photograph of hawksbill turtle and French angelfish eating sponge
Chemicals in sponge known to deter feeding by reef fishes include alkaloids, terpenes, and brominated compounds. None of these chemicals, however, deters feeding by hawksbill turtles, and some of the sponge foods most favoured by turtles are ones that are highly toxic to fishes. Meylan 1988 Science 239 (4838): 393

 

 

Hawksbill turle Eretmochelys imbricata and French angelfish Pomacanthus paru join
in eating a sponge Geodia neptuni, a species that is known to lack chemical defenses.
The 2 types of spongivores are competing, but in an amicable way...made easier for
the angelfish by the turtle having to go to the surface periodically to breathe 0.1X

 

photograph of touch-me-not sponge Neofibularia nolitangere
Because of toxic chemicals produced by its cells, contact with " touch-me-not" sponge can cause severe allergic reaction in humans. Whether it similarly affects reef invertebrates and fishes is not known.

 

 

 

 

"Touch-me-not" sponge Neofibularia
nolitangere
0.15X

 
 

Zoanthids & gorgonians

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of mat zoanthid taken from a video

"These light blue colonial polyps are zoanthids. They're very aggressive, overgrowing other reef organisms. They're apparently very toxic." - Bonaire 2003

NOTE this one looks to be the mat zoanthid Zoanthus pulchellus

 
 

photograph of zoanthid Zoanthus pulchellus
Zoanthids contain a powerful toxin known as palytoxin and there is evidence that it is deterrent to at least some reef fishes but, if eaten by certain invertebrates, can pass up the food chain. For example, palytoxin has been found in bristleworms known to eat zoanthids and in some reef fishes that may be consuming the bristleworms. Mebs & Gleibs 1997 Toxicon 35: 814; Gleibs & Mebs 1999 Toxicon 37: 1521.

 

 

 

 

Mat zoanthid Zoanthus pulchellus 1X

 


Gorgonians contain chemicals known as prostaglandins that are thought to deter predation by fishes. The effect of these defensive chemicals on flamingo-tongue snails, which like to eat gorgonians, is not known, but the snails do tend to be found more commonly on species of gorgonians, such as black sea-rods, that contain lower concentrations of the prostaglandin chemicals. The snails are also known to have evolved special enzymes to convert ingested prostaglandins into different, perhaps less toxic, form. Gerhart 1986 Mar Ecol Progr Ser 31: 255; Vrolijk & Targett 1992 Mar Ecol Progr Ser 88: 237.

NOTE a type of lipid. In humans prostaglandins are involved in tissue inflammation and, because of their effect on swelling of blood vessels in the brain, are implicated in the cause of headaches

Flamingo-tongue shells Cyphoma gibbosum eating a
gorgonian. Note the extent of tissue destruction by
the snails and also the extent of fouling of the
eaten surfaces by algae and other colonisers 0.4X

  Let's hear from the flamingo-tongues on the matter:
 
cartoon 1 in a series of 6 on flamingo-tongue shells dealing with aspects of feeding on gorgonians cartoon 2 in a series of 6 on flamingo-tongue shells dealing with aspects of feeding on gorgonians
cartoon 3 in a series of 6 on flamingo-tongue shells dealing with aspects of feeding on gorgonians cartoon 4 in a series of 6 on flamingo-tongue shells dealing with aspects of feeding on gorgonians
cartoon 5 in a series of 6 on flamingo-tongue shells dealing with aspects of feeding on gorgonians cartoon 6 in a series of 6 on flamingo-tongue shells dealing with aspects of feeding on gorgonians
  More on the distastefulness of flamingo-tongue shells to fishes can be found at SNAILS, CEPHALOPODS, & SEA CUCUMBERS.
 
  cartoon showing responses of predatory fishes to prostaglandin-containing artificial food
Experiments in the Bahamas using extracts from tissues of various gorgonians in feeding trials with predatory fishes, such as yellowtail snappers Ocyurus chrysurus and bluehead wrasses Thalassoma bifasciatum, confirm that a lipid-soluble fraction has feeding-deterrent properties. Pawlik & Fenical 1992 Mar Ecol Progr Ser 87: 183.
 
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