Defenses
 
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Invertebrates
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The topic considered here reating to defenses of invertebrates deals withbehaviour. Other invertebrate defenses are accessible via the icons.

 

 
 

Invertebrate defenses: behaviour

hot buttons for behavioural-defense part of BCCR

Behavioural defenses in Caribbean invertebrates are many and varied, but are broadly represented by the topics indicated by the icons.

This part of behavioral defenses includes the use of smoke screens, considered here, and CAMOUFLAGE,
HIDE AWAY as in a shell or crevice, and hide away as in the sense of
MINIMISE CONTACT WITH PREDATORS,
considered in other sections.

 
 

Invertebrate defenses: behaviour: smoke screens

 
 
seahorse dive leader for Biology of Caribbean Coral-Reef website photograph of cephalopod ink released in open water, taken from a video "Whoa! What's this?. This mucousy dark cloud is all that can be seen after the quick withdrawal of either an octopus or squid." - Curacao 2008
 
 


When disturbed, cephalopods release black ink from a special gland-sac that opens into the rectum. The rectum discharges the ink into the siphon, where it is flushed out, usually in several strong pulses as the animal jets away backwards. All that is left for the predator is an inky cloud. The ink consists primarily of mucus and melanin pigment, along with several minor chemical components.

The ink has 3 possible defensive functions, one being the obvious one of a smoke screen. Laboratory experiments using moray eels suggest that a predatory fish's vision can be blocked by the ink-cloud. Even under natural conditions where an ink-cloud disperses rapidly, the fast jet-propelled escape of the cephalopod will take it quickly out of view of the predator.

The other defensive functions are: 1) when released as a blob, the ink may act as a decoy to distract a predator while the cephalopod escapes, and 2) the ink may act to anaesthetise the chemical-detecting ability of a potential predator. This last function is discussed in another section: DEFENSE: BEHAVIOUR: TOXIC CHEMICALS.

NOTE melanin (lit. "black" Gr.) is a pigment ubiquitous in the animal kingdom. In humans it is what contributes to the colour of skin, eyes, hair, and so on

 
 

school of squids Sepioteuthis sepioides
Recent research has disclosed another possible function of ink in cephalopods, and that is as an alarm cue for conspecifics. Thus, ink release by one member of a school of squids may act as a visual signal to other members to initiate defensive behaviours. This has been demonstrated for reef squids Sepioteuthis sepioidea in laboratory experiments in Bermuda. Defensive behaviours include chromatophore flashing, eyespot mimicking, and camouflaging, postural mimicking of seaweeds, and sometimes jetting to safety. Whether or not the ink also carries chemical alarm cues is considered by the authors but not conclusively tested. Perhaps injection of ink into a container of squids in the dark could have helped answer this question. Wood et al 2008 J Exp Mar Biol Ecol 367: 11. Photograph courtesy Captain K. Gastrich.

NOTE members of the same species

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of an octopus inking during disturbance by SCUBA divers "Oh, that's not very nice. How would you like to chased and squeezed, you big bully? Still, it does give us a good demonstration of the effectiveness of the ink of an octopus, and the octopus seems to be okay. Still, shame on you...you terrible diver!" - Turks & Caicos 2005.
 
 

photograph of Humboldt squid Dosidicus gigas releasing ink in the Sea of Cortez
Octopuses are bottom-dwelling and are preyed upon by moray eels and large groupers, while squids inhabit open water and are preyed upon by various pelagic fishes, and by several types of mammals including toothed whales, seals, and dolphins.

 

 

 

 

A little ink goes a long way. Ink being released
from a stranded, post-spawning and moribund,
Humboldt squid Dosidicus gigas in the Sea of Cortez

 
 

photograph of an inking sea hare Aplysia brasiliana Anne Dupont
Sea hares Aplysia spp. release a purple ink when disturbed, but whether it serves a similar camouflaging role as in cephalopods is not known. The ink does hang around for a time, and the individual releasing it may quickly crawl away by "galloping" on its foot (Aplysia dactylomela), or swim away by flapping its parapodia (A. brasiliana). On release, the ink may form a smoky photograph of a sea hare Aplysia dactylomela inkingcloud or, depending upon the amount of mucus released along with it, a more cohesive blob that could be visually distracting to a predator. Alternative ideas regarding the function of the ink include irritation or even toxicity to the molesting fish or invertebrate. Photograph of A. brasiliana courtesy Anne Dupont, Florida.

Sea hare Aplysia brasiliana inking.
The ink is released from a gland at
the base of the mantle cavity,
positioned between the 2 parapodia


Sea hare A. dactylomela inking 0.5X

 
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