Motile organisms

hot button for motile competition part of Biology of Caribbean Coral Reefs hot button for motile-organism space/territory competition hot button for motile-organism food competition hot button for motile-organism mate competition
Competition for space/territory is considered in this section, while other types of competition in motile organisms can be accessed via the icons.

Motile organisms: space/territory competition

  The topic of space/territory competition is divided into a smaller part on BUTTERFLYFISHES/GRUNTS/STINGRAYS/TILEFISHES/JAWFISHES/HERMIT CRABS, considered here, and a larger one on PARROTFISHES/DAMSELFISHES, considered in its own section.

Motile organisms: space/territory competition: butterflyfishes


pair of 4-eye butterflyfishes patrolling the reef
Butterflyfishes also appear to maintain territories and studies in several areas of the Caribbean suggest that butterflyfishes pair up for better defense of these. Pair-partners nearly always remain in visual contact, and experimental removal of a partner leads to speedy replacement. The advantage of pairing in this circumstance is thought simply to be in the doubling of territorial "presence" over that of a single fish.




A pair of four-eye butterflyfishes
Chaetodon capistratus move
about the reef 0.25X

seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a pair of 4-eye butterflyfishes taken from a video

"Here's a pair of spotfin butterflyfishs. Butterflyfishes are monogamous and like to swim in pairs. In some species a pair will defend a loosely defined feeding territory. " - Cayman Islands 2001

NOTE Chaetodon ocellatus


photograph of a pair of banded butterflyfishes
Labours are shared within the butterflyfish pair. The male's duty is to defend the territory containing a female from other males, while the female's duty is to defend food resources from other females. Males attempting to defend an area containing more than one female are generally unsuccessful; hence, leading to the evolutionary selection for monogamous systems. Fricke 1985 Ethology 73: 307; Hourigan 1989 Envir Biol Fishes 25: 61.



A monogamous pair of banded
butterflyfishes Chaetodon striatus 0.5X


Motile organisms: space/territory competition: grunts


photograph of school of Frensh grunts
Members of this shoal of grunts seem relaxed and restful, but note the even spacing between individuals. Juvenile grunts are thought to stake out specific territories within the shoal where they can find refuge from predators.

NOTE a shoal is a less disciplined gathering of fishes than a school




A shoal of French grunts
Haemulon flavolineatum


Unlike other species of Caribbean rays, southern stingrays Dasyatis americana rarely seem to form aggregations.  A recent study in Glover’s Reef, Belize on habitat utilization by this species shows a mean spacing distance between individuals of about 100m, slightly smaller during nighttime (see photograph of southern stingray Dasyatis americanaphoto/diagram).  With an approximate lagoon area of 250 km2 and a mean annual density of 245 individuals per square km, the standing stock of stingrays is high, reaching and even exceeding 60,000.   Inroads photo composite showing day and night habitat areas for southern stingrays Dasyatis americana in Glover's Reef, Belizeon prey stocks of molluscs, crustaceans, and worms at such densities must be great.  Tilley et al. 2013 Mar Ecol Prog Ser 482: 169.

NOTE  the study involved 32h of observation of 12 individuals

Habitat use by a single female southern stingray
Dasyatis americana
on the shallow fringe reef of
Glover's Reef. Pink = daytime use; blue = nighttime use
Dark lines represent 95% occupation; light colours, 50%


Motile organisms: space/territory competition: tilefishes/jawfishes


photograph of a sand tilefish Malacanthus plumieri swimming near its burrow
Sand tilefishes Malacanthus plumieri are territorial and also keep harems.  They prefer to inhabit open sandy terrain with exposed coral rubble that they can gather and use to construct home burrows.  A male’s burrow defends an area that may encompass up to six or so female burrows.  The females apparently defend their own burrow refuge and surrounding feeding space, and thus space in suitable sand/rubble habitat may be hotly contested.  Males defend their own territories, which appear to photograph of rocks and coral rubble around burrow of a sand tilefish Malacanthus plumieribe similarly sized whether there be no females or up to 3 females present in a harem.  Baird & Liley 1989 Anim Behav 38: 817.  Photograph of rubble courtesy Colin 1973 Copeia (1): 84.

Rubble surrounding burrow of a sand
tilefish Malacanthus
in Jamaica

photograph of yellowhead jawfish Opistognathuys aurifrons hovering over burrow entrance

Burrows are similarly constructed by yellowhead jawfishes Opistognathus aurifrons.  Construction takes place during daytime and takes about 8h.  Major steps are removal of sand to create a pit, collection of rocks and coral bits, and “masonry” (see drawings below).  Burrow depth is about 15cm and the fish takes care not to exceed this by much.  This is likely because a 1cm increase in depth at 20cm requires that 4 times more material must be removed than at 10cm owing to sand subsidence.  Mucus cementation appears not to be involved in the construction.  If not destroyed by weather events or other calamitous events, an individual may occupy the same burrow for its entire life.  Colin 1973 Copeia (1): 84.

NOTE  3 types of burrows are actually constructed: under-rock, open chamber, hole-in-rock.  The second of these is described here

Yellowhead jawfish Opistognathus aurifrons hovers
over its burrow opening on a Bahamian reef

drawing 1 in a series of 4 showing burrow construction by a yellowhead jawfish Opistognathus aurifrons drawing 1 in a series of 4 showing burrow construction by a yellowhead jawfish Opistognathus aurifrons drawing 1 in a series of 4 showing burrow construction by a yellowhead jawfish Opistognathus aurifrons drawing 1 in a series of 4 showing burrow construction by a yellowhead jawfish Opistognathus aurifrons
Hours 0-2: sand is removed by fanning of body and anal fin to form burrow opening Hours 2-5: rocks and rubble collected from area surrounding burrow Hours 3-6: rocks and rubble positioned at mouth of burrow Hours 5-8: final adjustment of materials to make the opening level with surrounding surface

Motile organisms: space/territory competition: hermit crabs

  photographs of terrestrial hermit crabs Coenobita in their domiciles
On the shoreline of the back-reef area, fights over habitable shells ("space/territory") are common amongst terrestrial hermit crabs Coenobita sp., for shell resources large enough to accommodate their also large adult size are usually in short supply.