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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 carnivory deals with piscivores, that is, with coral-reef organisms that eat fishes. These include fishes, sharks, squids, marine mammals, and some pelagic invertebrates. Other topics relating to carnivory can be accessed via the icons.
 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of reef fishes taken from a video

"When I swim over a reef like this, with so many fishes, I tend to forget that each one of them requires a belly-full of food each day and, for fishes like these black groupers, the food is likely to be other fishes."- Turneffe Island, Belize 2000. Video courtesy Andy Stockbridge, Belize.

NOTE Mycteroperca bonaci

 
 

Carnivory: piscivores (eaters of fishes): roving piscivores

This section deals with piscivores that swim freely about the reef. Topics dealing with AMBUSH PISCIVORES and WOUNDED FISHES can be found in their own sections. Additionally, there is a section on COOPERATIVE HUNTING.

 
  Piscivorous vertebrates include fishes, sharks, and cetaceans (dolphins and toothed whales). Overall, about 38% of all Caribbean fishes subsist primarily on diets of other fishes. Some piscivores, such as barracudas and groupers, roam about the reef while others, such as scorpionfishes, toadfishes, and snake eels, are lie-in-wait ambush predators. Sierra et al. 2001 Ecology of the marine fishes of Cuba. Smiths Institute Press, Washington, D.C.
 
photo collage of several fish species that subsist mainly on diets of other fishes
 
 

photograph of siphonophore, a Portuguese-man-of-war Physalia physalis with captured fishesphotograph of sea anemone with captured juvenile surgeonfish, courtesy Linda Ianiello, Florida
As in other marine ecosystems, reef-inhabiting bottom-dwelling invertebrate piscivores are rare, but there are a few such as sea anemones and fast-moving portunid crabs that are known to eat juvenile fishes. The most "dedicated" fish-eating invertebrates are those that float avove the reef, such as siphonophores and jellyfishes.

A siphonophore, or "blue-bottle"
Portuguese-man-of-war Physalia
sp. with captured fish prey 0.4X


Unidentified anemone with captured juvenile whitespotted filefish Catherhines macroceros 1X. Photograph courtesy Linda Ianiello, Florida

 
 

photograph of reef squids Sepeoteuthis sepioidea courtesy George Lilly, Newfoundland
Squids swim in schools above the reef and catch fishes with their paired tentacles. The two tentacles are usually endowed with larger suckers than the ones on the arms, and may have accompanying hooks. When the prey fishes are pulled into the circle of 8 arms, photograph of armed tentacles of Humboldt squid Dosidicus gigasthey are killed by the beak or poisoned by a toxic secretion from the salivary glands, then swallowed whole or after being bitten into chunks.


Caribbean reef squids
Sepioteuthis sepioidea 0.15X
Photo courtesy George Lilly, Nfld

 

Club-headed and hooked ("armed") fishing
tentacles of a large Humboldt squid Dosidicus
gigas
photographed in the Sea of Cortez 0.5X

 
photograph of beak and radula of a Humboldt squid Dosidicus gigas
 

Beaks and radula of a Humboldt squid
Dosidicus gigas
photographed from a
moribund individual in the Sea of Cortez

 
 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of fish activity on a Caribbean reef taken from a video "It's rare to one fish capturing and eating the other. It happens in a split second and might be seen just as a flash of movement. There's a chase now, but it's probably just a territorial dispute since they all just screeched to a stop."- Turneffe Island, Belize 2000. Video courtesy Andy Stockbridge, Belize.
 
 

photograph of nurse shark Ginglymostoma cirratum courtesy Anne Dupont, Florida
The food of sharks is mostly fishes that they take bites from, slice up and eat portions of, or swallow whole.

 

 

 

 

 

Nurse sharks Ginglymostoma cirratum apparently
eat molluscs along with their main diet of fishes.
Photograph courtesy Anne Dupont, Florida

 

photograph of tame Nassau grouper in Cayman BracBarracudas are prototypal "burst" predators with fast acceleration, widely extensible jaws, and sharp teeth. Their attack velocity is so fast, and jaws photograph of a barracuda Sphyraena barracuda having just eaten half a large grouperand teeth so strong and sharp, that they can knife through their prey, slicing them in two.

"Fred" was a tame Nassau grouper
Epinephelus striatus that used to
schmooze with divers in Cayman
Brac, mostly looking for food
handouts. A split-second attack by a
barracuda moments after this photo
was taken ended Fred's life 0.25X

 


Barracuda Sphyraena barracuda
eyes the front half of Fred floating
at the surface moments after the
attack. The back half of Fred is
represented by the bulge in the
barracuda's stomach 0.1X

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of tiger grouper taken from a video

"Watch this tiger grouper. See how the grunts make room. So, if you're wondering, where do the tiger groupers swim? Well, the answer is, pretty much wherever they want to." - Little Cayman 2001

NOTE Mycteroperca tigris

 
  The chief determinant of diet in groupers is body size of the prey. Small grouper species favour small prey items, while large species specialise on fishes, lobsters, and even turtles. Shown in the graph are 18 grouper species arranged by body length and size-class of major prey. Photogaphs of 7 representative species are shown. Wainwright & Richard 1995. Envir Biol Fish 44: 97. Photograph of rock hind courtesy Anne Dupont, Florida.
 
photo collage of groupers showing relationship of grouper size with diet
 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of yellowfin grouper taken from a video, courtesy Andy Stockbridge, Belize

"Like other groupers, yellowfins eat almost anything. If it moves, eat it! Wrasses, grunts, parrotfishes, snappers, crabs, lobsters, octopuses, squids...all yummy." - Turneffe Island, Belize 2000. Video courtesy Andy Stockbridge, Belize

NOTE Mycteroperca venenosa

 
 

Studies on relative mouth sizes of predatory fishes show that in fishes that eat algae or small bottom-dwelling prey such as worms, crustaceans, and molluscs, mouth size in proportion to body size changes little over the life of the fish.  However, in fishes that consume larger prey such as crabs, lobster, cephalopods, and other fishes, mouth size relative to overall body size may increase over the life of the fish, signifying that diet is changing ontogenetically

If mouth size increases in direct proportion to body size during the life of a fish, then the relationship is said to be isometric (see graph below). Conversely, if mouth size increases out of proportion to body size during life of a fish, then the reltionship is said to be allometric. Karpouzi & Stergiou 2003 J Fish Biol 62: 1353.

NOTE referring to "during the life of" an organism; contrasting with phylogenetically, referring to "during the evolutionary history" of the organism

NOTE lit. "equal measure". For every unit that body size increases as the fish grows, mouth size increases also by one unit

NOTE lit. "different measure". Thus, in the example for fishes, for every unit that body size increases as the fishes grow, mouth size increases by more than one unit

 
graph comparing isometric and allometric growth in mouths of fishes
  graph showing isometry of growth of fish mouthsWith this in mind, let's now look at some fishes, specifically, a few Mediterranean species as examples. Note that as some species grow, notably seabreams and parrotfishes, mouth sizes change in direct proportion to body size; in other words, isometrically. These species tend to be small in size and have diets consistng of small invertebrates such as copepods, polychaetes, snails, and clams for seabreams, and algae for parrotfishes. The slopes shown do not differ significantly from isometry (i.e., a slope of 1). Karpouzi & Stergiou 2003 J Fish Biol 62: 1353.
  graph showing allometric growth of fish mouths in relation to changing diets with ageHowever, in other fishes such as scorpionfishes and lizardfishes, mouth sizes increase out of proportion to body size, in other words, they scale allometrically (i.e., a slope greater than 1). Such species go through one or more switches in dietary preferences during their lifetimes and, at adult size, are eating relatively large prey such as fishes, decapods, and cephalopods. In the cases shown here the slopes shown differ significantly from isometry. These examples for Mediterranean fishes are likely representative of similar changes to be found in Caribbean fishes. Karpouzi & Stergiou 2003 J Fish Biol 62: 1353.
 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a Nassau grouper investigating a spotted moray in its den

"Now this is interesting!  A Nassau grouper eyes the spotted moray, or vice versa…but look, the grouper goes around to the back…and you can see the moray’s tail sticking out…doesn’t get bitten, though, which is bad for us, but I guess is good for the moray…". - Bonaire 2005

NOTE Gymnothorax moringa

 
  photograph of Nassau grouper
Groupers have high trophic status on the reef; that is, they cap numerous different food webs. The Nassau grouper Epinephelus striatus shown here eats several other fish species that each caps its own particular sub-web. For example, a prey wrasse will eat planktonic crustaceans that in turn eat phytoplankton; a prey octopus will eat crabs and molluscs, both participants in other sub-webs; and so on. Such a grouper species, then, may have the status of a keystone species, one whose removal, such as by overfishing, will have profound effects on other members of the reef community.
 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of yellowfin grouper taken from a video

"Groupers are good candidates for keystone-predator status on the reef.  Their broad-spectrum diets mean that they “cap” a number of different food-chains…therefore, their feeding activities can have a disproportionately large influence on species composition and numbers in the reef community."  - Turneffe Island, Belize 2000. Video courtesy Andy Stockbridge, Belize

NOTE Nassau grouper Epinephelus striatus

 
 
Number 1 in cartoon series exploring the candidacy of groupers as keystone predators on the reef Number 2 in cartoon series exploring the candidacy of groupers as keystone predators on the reef
Number 1 in cartoon series exploring the candidacy of groupers as keystone predators on the reef Number 4 in cartoon series exploring the candidacy of groupers as keystone predators on the reef
Number 5 in cartoon series exploring the candidacy of groupers as keystone predators on the reef Number 6 in cartoon series exploring the candidacy of groupers as keystone predators on the reef
Number 7 in cartoon series exploring the candidacy of groupers as keystone predators on the reef Number 8 in cartoon series exploring the candidacy of groupers as keystone predators on the reef
Number 9 in cartoon series exploring the candidacy of groupers as keystone predators on the reef Number 10 in cartoon series exploring the candidacy of groupers as keystone predators on the reef
 
  STOP!  Let’s leave the discussion of keystone-predtor status for the grouper right there, looking down its onrushing gullet.  What do you see in the photo that gives you a clue as to the relative size of prey consumed by the grouper? 
 

photograph of large, open mouth of a Nassau grouper
Well, the big mouth is obvious, but did you also notice the large puckery opening to the esophagus, allowing extra-large size prey to be taken in?  If you thought the white structures on either side of the gullet to be teeth for grinding and crushing, then you are incorrect.  They are gill rakers and function to keep food and other particulate matter from clogging the gills (in planktivorous fishes they function to trap plankton).  The teeth in groupers are small, and are located (where else?) on the gums.

 
  graph showing distance that reef-based piscivorous fishes will swim out from their own reef to attack prey fishes
Piscivorous fishes may hang about the reef to feed or swim out from the reef after prey. In doing so, though, they risk being attacked by other piscivores, and the question arises as to how far out from the reef piscivorous fishes will roam. In one experiment to test this, 4 small surgeonfishes Acanthurus sp. are enclosed in sealed glass jars to act as prey for the reef-based piscivores. The graph shows the intensity of attacks on the surgeonfishes over a 90min daytime period. The results show a low rate of attack even as close as 2m from the reef, suggesting that the reef-based piscivorous fishes stay quite close to the reef, presumably because of their own risk of attack from still larger piscivores roaming further out. Sweatman & Robertson 1994 Mar Ecol Progr Ser 111: 1.
 
 

photograph of 2 bottlenose dolphins Tursiops truncatus and a bull shark Carcharhinus leucas preying on a group of spawning mutton snappers Lutjanus analisIn Belize, large spawning aggregations of mutton snappers Lutjanus analis may attract the attention of roving carnivores such as sharks and dolphins that consume the spawning fish, and of whale sharks that consume the spawned eggs. Graham & Castellanos 2012 Coral Reefs 31: 1017; photograph courtesy the authors.

 

 

 

An aggregation of mutton snappers Lutjanus
analis
receiving attention from 2 bottlenose
dolphins Tursiops truncatus and at least
one bull shark Carcharhinus leucas

 
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