Defenses
 
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Invertebrates
hot buttons for invertebrate defenses part of BCCR hot button for behavioral defenses part of invertebrate defenses in BCCR hot button for toxic chemicals part of invertebrate defenses in BCCR hot button for structure part of invertebrate defenses in BCCR
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 can be generally encompassed in the icon-topics shown.

This "hide away" part of invertebrate behavioral defenses includes use of camouflage, considered here, and

SMOKE SCREENS,
HIDE AWAY (as in a shell or crevice), and
MINIMISE CONTACT WITH PREDATORS (a sort of "hiding away"),
considered in other sections.

 
 

Invertebrate defenses: behaviour: camouflage

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of decorator crab taken from a video

"This little decorator crab has done a nice job of camouflaging itself in hydroids and other organisms. Pretty neat, huh?!. Now all it needs to do is choose a good backdrop." - Turneffe Island, Belize. Video courtesy Andy Stockbridge, Belize.

NOTE also known as a neck crab Podochela sp.

 
 

photograph of decorator crab Podochela sp. courtesy Anne Dupont, Florida
Camouflaging
is quite common in coral-reef invertebrates, and employs combinations of colour, behaviour, and morphology to hide from predators. Camouflaging involves pattern-disruption, well-known from military applications, and mimicry, the attempt to match something else perfectly. The camouflaging of certain decorator crabs, such as Podochela sp. shown in the photo below Left, is accomplished by the crab encouraging settlement of larvae of hydroids and other organisms onto its exoskeleton, or in some way actually attaching them to itself. Photographs courtesy Anne Dupont, Florida.

photograph of sacoglossan opisthobranch Elysia crispataNOTE also known as crypsis (lit. "hidden" Gr.). The use of colour in pattern-disruption and mimicry are dealt with in more detail in FUNCTIONS OF COLOURS: DEFENSE: CAMOUFLAGE:

Podochela sp. 1X

 

 

The ruffled surface and colours of the sacoglossan sea-slug
Elysia crispata may help disguise it amongst its algal foods 0.5X

 
 

Cephalopods are masters of camouflaging, using combinations of behaviour, skin texture, and chromatophore-colour change to blend into their habitat. These images of an Octopus vulgaris. disguising itself as seaweed on a rock in Grand Cayman Island were taken from a video by Roger Hanlon, Marine Biological Laboratory, Woods Hole, Massachusetts. CLICK HERE to see the actual video, courtesy of Roger Hanlon.

Note in the video the double-whammy effect of smoke-screen camouflaging as the octopus escapes, followed when it stops swimming by immediate spreading out and matching its colour and pattern to the coral-reef background. More on colour- and pattern-camouflaging in octopuses and other cephaloppods can be found at COLORATION OF REEF ORGANISMS: HOW COLOURS ARE CREATED: CHROMATOPHORES

photograph taken from a video of Octopus sp. camouflaging itself against a seaweed-covered rock

See it?

...now you don't...

photograph taken from a video of Octopus sp. camouflaging itself against a seaweed-covered rock ...now you do
 
  photo collage of camouflaged Caribbean crabs including the tear-drop crab Pelia mutica
 
 

Carrier shells cement other shells and calcareous debris to their own shells as they grow. Although it seems like camouflaging, the problem of determining its functional significance is made difficult by the fact that we know little about the snail's life. Here is a list of possible functions for the behaviour, only 3 of which have any merit. Take a moment to study the merits of each, then CLICK HERE to see explanations.

1. visual camouflage

2. armour

3. stability in currents

4. mimicry

5. tactile camouflage

6. locomotory stability in soft sand

7. chemical camouflage

NOTE as a hint, assuming that the decorations have a defensive function, possible predators could be fishes, sharks, certain turtles, sea stars, and perhaps octopuses

photograph of carrier shell Xenophora sp.

Caribbean carrier shell Xenophora sp. 1X. Can anything be learned about the snail by study of what it uses for decoration? A completely unscientific review of published images of different species of Xenophora suggests the following:

1. although molluscan shells are commonly used as decoration, as shown in the photograph above of a Caribbean species, most anything available in the habitat may be attached
2. by the number of broken shells attached, especially bivalves, it seems that inanimate material is preferred
3. bivalve shells are attached singly, suggesting that if a complete pair of valves is encountered, the valves are separated before being attached
4. however, sequential attachment of a matched pair of shells does not occur, indicating that the snail: a) moves away between attachments, or b) discards complete valve sets when encountered
5. bivalve shells are invariably attached with the inner side upwards
6. snail shells are more often than not attached aperture upwards
7. interesting...yes? Any other observations or comments? If so, send them along for inclusion here or, better still, do a proper study.

  photograph of transparent planktonic invertebrates, adults and larvaeTransparency is a camouflaging strategy commonly employed by invertebrates inhabiting open-water habitats - a region notably devoid of hiding places. Such invertebrates include jellyfishes, hydromedusae, siphonophores, and others, and include both adults and larvae.
 

photographs of adult and juvenile jellyfish Aurelia aurita
Examples of larger transparent planktonic invertebrates include ctenophores (comb jellies) and jellyfishes.photograph of ctenophore

Ctenophore 1X


Adult (0.6X) and juvenile ephyra (7X) of a moon jelly Aurelia aurita. The ephyra is sometimes
referred to as a "larva". The true larva of a jellyfish is the planula

 
 
Let's hear from the jellies on the matter: cartoon 1 in a series of 7 dealing with the evolutionary strategy of transparency for life in the plankton
cartoon 2 in a series of 7 dealing with the evolutionary strategy of transparency for life in the plankton cartoon 3 in a series of 7 dealing with the evolutionary strategy of transparency for life in the plankton
cartoon 4 in a series of 7 dealing with the evolutionary strategy of transparency for life in the plankton cartoon 5 in a series of 7 dealing with the evolutionary strategy of transparency for life in the plankton
cartoon 6 in a series of 7 dealing with the evolutionary strategy of transparency for life in the plankton cartoon 7 in a series of 7 dealing with the evolutionary strategy of transparency for life in the plankton
 
 

Possible explanations for function(s) of Xenophora's "decorations". The 3 most likely ones are highlighted:

1. visual camouflage This is a likely possibilty, as the snail blends in visually with the debris on the sand. However, this presumes that the snail's predators are using mainly vision to identify their prey, and this we do not know

2. armour Yes, but only from shell-crushing predators that might find the attached bits difficult or irritating to bite down on. It would not help against sea-star predators

3. stability in currents. No, this is unlikely. The increased surface area of the added material might actually increase the snail's instability in currents

4. mimicry. No. What is being mimicked? Unless it is the sea bottom, and that comes under topic #1: "visual camouflage"

5. tactile camouflage. Possibly. The attached bits might make the carrier shell feel like something quite different when touched by a predator. However, what fish or invertebrate predator would "touch" the host snail so casually as not to able to sense that there is a live snail within? Also, if this were the function, wouldn't it be better for the snail to attach living matter such as algae, hydroids, and the like, better to mimic a rock on the sea bottom?

6. locomotory stability in soft sand. No. The increased surface area might provide greater support on soft sand, but it would also likely increase frictional drag and thus lead to greater cost of locomotion

7. chemical camouflage. No. It's a good idea, but the shells and other attached debris are dead materials, and would offer no chemical stimulation to confuse a potential predator. The carrier shell might be better off to attach live snails and other organisms as "offerings/distractions" for predators (perhaps it does, but these may eventually die from lack of food)

CLICK HERE to return to the list.

 
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