Nutrition
 
  Nutrition
 
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Carnivory hot buttons for carnivory part of Biology of Caribbean Coral Reefs website hot button for zooplanktivore part of BCCR hot button for spongivore part of BCCR hot button for corallivores & other cnidivores part of BCCR hot button for gorgonivores part of BCCR hot button for benthic invertebrate-eaters part of BCCR hot button for piscivores part of BCCR

This part of nutrition deals with carnivory, that is, with coral-reef organisms that eat animals. Other topics relating to nutrition of coral reefs can be accessed via the icons.

Major predators of sponges are vertebrates, including fishes and turtles, but a few invertebrates, includings sea stars and nudibranchs, also eat sponges. Fishes will be considered here, while TURTLES and SEA STARS/NUDIBRANCHS/SNAILS are dealt with in their own sections.

 
 

Carnivory: spongivores: fishes that eat sponges

Several species of reef fishes subsist, in whole or in part, on sponges, including most angelfishes and a few parrotfishes.

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of French angelfish taken from a video

"Hello, Mr. Angelfish...looking for your next meal of sponges? Sponges don't seem appetising to us, but angelfishes and other predators, most notably hawksbill turtles, find them quite tasty. You can often see healed bite-marks on sponges, such as these ones on a yellow tube sponge." - Turneffe Island, Belize 2000. Angelfish video courtesy Andy Stockbridge, Belize.

NOTE French angelfish Pomacanthus paru

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of sponge bearing many bite-marks, taken from a video

"Check out the big bite-marks on this sponge. It's old, though, and well healed. Most wounds to sponges heal without infection or opportunistic algal growth. The latter is probably testament to a sponge's strong chemical defenses." - Little Cayman 2002

NOTE possibly a brown tube-sponge Agelas conifera from above

 
  Underwater videotaping in Key Largo, Florida over 10h showed nearly 600 bites on several specimens of giant barrel sponges Xestospongia muta by 3 species of parrotfishes: princess, striped, and redband, and by several species of angelfishes. Dunlap & Pawlik 1998 Mar Ecol 19: 325.
 
photo collage showing several parrotfish species that eat giant barrel sponges Xestospongia muta
 
 
"Check out the big bite-marks on this sponge. It's old, though, and well healed. Most wounds to sponges heal without infection or opportunistic algal growth. The latter is probably testament to a sponge's strong chemical defenses." - Little Cayman 2002 photograph of an initial-stage stoplight parrotfish swimming over a sponge, taken from a video

"Lots of fishes eating this sponge. Oh, but wait! They're all herbivores. Even the princess parrotfish, which is known to eat sponges, seems only to be taking nips of the algae growing on the sponge." - Bonaire 2003

NOTE Scarus taeniopterus

 
 

In San Blas, Panama parrotfishes Sparisoma spp. that are normally algivorous will readily eat sponges residing in cryptic habitats when the habitats are experimentally excavated or exposed. Of over 9000 bitings by the 3 species of Sparisoma shown below, 72% are made on the freshly exposed cryptic sponges. Wulff 1997 Mar Biol 129: 41.

NOTE meaning "hidden"; referring here to sponges that occupy under-boulder and crevice habitats, protected from fish predators. When the sponges are exposed by the researchers, the fishes are curious and gather round to feed

  photo collage of 3 species of spongivorous parrotfishes Sparisoma aurofrenatum, S. viride, and S. chrysopterum
  So, does this mean that these parrotfishes are spongivores, not algivores? No, they are certainly algivorous; however, in this case when they are presented with novel and abundant food in the form of the newly exposed sponges, they eat them up. It also suggests that these cryptic sponges may lack, or have less, defenses than non-cryptic ones. This in turn may explain, in part, the prevalence of these particular sponges in cryptic habitats. That parrotfishes don't include more sponges in their diets may be explained by the presence of strongly aversive chemical defenses in most non-cryptic sponges.
 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of French angelfish Pomacanthus paru

"Who's this mincing along taking such small bites. Don't let the delicacy of this French angelfish's table manners fool you. It's a dedicated spongivore, whose jaws can take bites from even the toughest sponges." - Cayman Brac 2002

NOTE Pomacanthus paru

 
  Most angelfishes, including the 3 species shown here, eat sponges as their main dietary items. However, studies in St. Croix show that some algae are also eaten, and that French and gray angelfishes also eat gorgonians. Hourigan et al. 1989 Envir Biol Fish 24: 105.
 
photo collage showing several sponge-eating Caribbean angelfishes
  Of the 3 angelfish species shown above, 2 are fairly dedicated spongivores while the third actually eats more algae than sponges. Does mouth structure reflect this preference? Check out their mouth designs below, and see if you can select the one better able to tear algae from hard surfaces rather than biting at sponges. Hourigan et al. 1989 Envir Biol Fish 24: 105.

 
drawings of angelfish mouths in a study of morphological adaptation to diet
It's the rock beauty. Did you get it correct? The clue was in the symmetry of its jaws in comparison with the asymmetry of the other two. The authors consider the symmetrical jaws of a rock beauty to be more effective at biting and scraping at algae. In St. Croix a rock beauty's diet is 50% algae and 43% sponges.
 

photograph of sponge Geodia partly consumed by a queen angelfishOf the many sponges on the reef, leathery barrel sponges Geodia neptuni seem to be the ones most commonly eaten. The tidy job done on this one suggests that angelfishes rather than another possible culprit, a hawksbill turtle, may have been responsible.

 

 

 

 

Queen angelfish Holacanthus ciliaris swims close to a
partly eaten leathery barrel sponge Geodia neptuni 0.5X

 
Researchers in Key Largo, Florida use underwater-videotaping to assess the characteristics of sponges that are attractive to 18 species of bottom-feeding reef fishes. The authors select 8 species of sponges, 4 from the reef area and 4 from a nearby mangrove area. The 2 groups are matched as closely as possible in shape and colour. Eighteen species of fishes are videotaped for 52 daylight hours and 11 nighttime hours. Of the 18 species of fishes, 8 are found to be the most important spongivorous ones. In total, over 35,000 bites are taken, representing an average of about 680 bites per daylight hour. Now for some questions.

drawing of sponges used in Key-Largo field experiment on spongivorous fishes

1. Which type of fishes took the most bites?
array of reef fishes involved in spongivory experiment in Key Largo, Florida

5 species of parrotfishes took 35% of the bites 5 species of angelfishes took 51% of the bites, with blue angelfishes (27%) the most 2 species of cowfishes (scrawled) & filefishes (orangespotted) together took only 12% of the bites  
   
 

2. Which type of sponges was favoured?
drawing of sponges used in Key-Largo spongivory experiment

 
mangrove sponges received 96% of all bites, perhaps in part owing to their novelty, but mainly because they appeared to lack chemical defenses in contrast, reef sponges received only 4% of all bites. Most reef sponges have chemical defenses   The authors suggest that the apparent absence of defenses in mangrove fishes may relate to the absence of most reef fishes in this habitat as a selective pressure in evolution; thus, defenses against their depredatory attacks did not evolve.
   
 

3. What time of day did the fishes bite?
drawing of reef sponges used in Key-Largo spongivory experiment

 
100% occurred in daytime 0% occurred at nighttime Does this suggest that spongivorous fishes hunt by sight? Not necessarily. Perhaps the lack of feeding activity at night is because the fishes themselves are hiding from their own predators. Or perhaps they're just taking a rest from feeding in order to digest their spongy foods. In broader terms, it is interesting that the absence of algivorous fishes on the reef during nighttime is at least partly attributed to the need for the fishes to see their algal foods, so why isn't this equally applicable to spongivorous fishes to explain their daytime feeding habits?
   
   
 

4. What colour of sponge was preferred?
drawing of sponges used in Key-Largo spongivory experiment

 

The fishes had no preference for colour, neither avoiding nor preferring colorful varieties. Since half are reef sponges known to contain potent chemical defenses, this suggests that sponges are not warningly coloured as a strategy to ward off potential predators. Could there be too many colours of sponges, thus making it confusing for reef fishes to form and remember the associations? Or do spongivorous fishes rely more on other senses, such as scent, to identify which species of sponges are edible?

NOTE warning coloration is found commonly throughout the animal kingdom as a "don't touch me" signal to potential predators. A predator quickly learns through the negative association of becoming sick, not to eat a prey of a certain colour or colour-patter

 
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