Animal Diversity Web

Ge­o­graphic Range

The ma­rine iguana in­hab­its the Gala­pa­gos Is­lands which form an arch­i­pel­ago off the coast of South Amer­ica. The vol­canic Gala­pa­gos has never been at­tached to an­other land mass so it is be­lieved that igua­nas rafted over water from South Amer­ica (Cog­ger and Zweifel 1998). Some re­searchers be­lieve that the land igua­nas and the ma­rine iguana di­verged from a com­mon an­ces­tor at least 10 MY on the for­mer is­lands of the arch­i­pel­ago which are now below sea level (Rass­mann et. al. 1997).

• Biogeographic Regions
• oceanic islands
  • native

Habi­tat

The ma­rine iguana is found on the vol­canic is­lands of the Gala­pa­gos. Many of the is­lands have steep rock cliffs, low rock ledges and in­ter­tidal flats. A. crista­tus needs ac­cess to the ocean and a sandy area to lay eggs. They evolved in a habi­tat that is lim­ited in preda­tors. On Santa Fe an is­land in the Gala­pa­gos the preda­tor are hawks, short-eared owls, snakes, hawk-fish, and crabs. With so few nat­ural preda­tors the ma­rine iguana is very vul­ner­a­ble to feral preda­tors such as rats, dogs and cats. The feral an­i­mals can af­fect egg sur­vival and adult mor­tal­ity. Fe­males are es­pe­cially at risk of pre­da­tion when going to the open nest­ing areas.

Phys­i­cal De­scrip­tion

Am­bly­hynchus crista­tus is a grey to black iguana with pyra­mid-shaped dor­sal scales. They have shorter more blunt snouts than land igua­nas, and they have a slightly lat­er­ally com­pressed tail. The young have a lighter color dor­sal stripe (Rass­mann et. al. 1997).

Re­pro­duc­tion

Males de­fend mat­ing ter­ri­to­ries dur­ing the three-month an­nual breed­ing sea­son. Fe­males lay one to six eggs in bur­rows dug 30 to 80 cm deep. The eggs are laid in sand or vol­canic ash up to 300m or more in­land. Fe­males guard the bur­row for sev­eral days then leave the eggs to fin­ish in­cu­ba­tion, which is ap­prox­i­mately 95 days. Nest­ing months are Jan­u­ary through April de­pend­ing on the is­land.

Lifes­pan/Longevity

• Average lifespan
  Sex: male
  Status: captivity

  6.4 years

  Max Planck Institute for Demographic Research

Be­hav­ior

Am­blyrhynchus crista­tus faces a ther­moreg­u­la­tion dilemma. The ocean wa­ters that it re­lies on for food are very cold and since rep­tiles do not have the abil­ity to reg­u­late their body tem­per­a­tures phys­i­o­log­i­cally, they must bask in the sun­light to warm up. At low tem­per­a­tures the abil­ity of these an­i­mals to move ef­fec­tively is re­duced and they are vul­ner­a­ble to pre­da­tion. The ma­rine iguana be­hav­io­r­i­ally com­pen­sates for its in­abil­ity to move ef­fec­tively. At low tem­per­a­tures lizards are often highly ag­gres­sive, re­ly­ing on less en­er­get­i­cally ex­pen­sive bluffs or bites than es­cape. The dark color of the ma­rine iguana aids in heat re­ab­sorb­tion and males can change to full breed­ing dress for rapid re-warm­ing (Cog­ger and Zweifel 1998). Hy­bridiza­tion be­tween the Gala­pa­gos land and ma­rine igua­nas have been doc­u­mented on Plaza Sur. DNA ev­i­dence sug­gests that hy­bridiza­tion is not com­mon but pos­si­ble (Rass­mann et. al. 1997).

Food Habits

The ma­rine iguana feed al­most ex­clu­sively on ma­rine algae (Cog­ger and Zweifel 1998). Larger mem­bers of the species feed more often by div­ing at high tide while smaller an­i­mals are re­stricted to in­ter­tidal feed­ing at low tide (Lau­rie and Brown II 1990). A major change in the ma­rine algal flora oc­curred be­tween No­vem­ber 1982 and July 1983. This co­in­cided with ab­nor­mally high rain­fall, sea level, and sea sur­face tem­per­a­tures as­so­ci­ated with El Nino-South­ern Os­cil­la­tion Event (ENSO). ENSO events are de­scribed as a mass of low-salin­ity nu­tri­ent-poor sur­face water mov­ing south in the east­ern trop­i­cal pa­cific. This causes a de­crease in bi­o­log­i­cal pro­duc­tiv­ity and de­creases sur­vival and re­pro­duc­tion of an­i­mals de­pen­dant on the ef­fected ecosys­tem. This was fol­lowed by un­usu­ally high mor­tal­ity of maine igua­nas (Lau­rie and Brown II 1990).

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

The ma­rine iguana does not af­fect hu­mans be­cause hu­mans do not in­habit most of the is­lands they live on. The main food for the ma­rine iguana is algae and that is not re­source we com­pete for ei­ther.

Con­ser­va­tion Sta­tus

It is im­por­tant to con­serve the bio­di­ver­sity of the ma­rine iguana be­cause it is a unique and in­ter­est­ing an­i­mal. It is nec­es­sary to pro­tect their is­land refuges from feral pests and human ex­ploita­tion be­cause they are long lived an­i­mals that can not sus­tain added mor­tal­ity.

• IUCN Red List

  Vulnerable
  More information

• IUCN Red List

  Vulnerable
  More information

• US Federal List

  No special status

• CITES

  Appendix II

Other Com­ments

The ma­rine iguana has filled an in­ter­est­ing niche that no other liv­ing lizard does. It de­pends on the ma­rine en­vi­ron­ment. To rid it­self of the salt con­sumed while eat­ing, A. crista­tus ex­cretes con­cen­trated salt crys­tals from a nasal gland. The ma­rine iguana reg­u­lates its body tem­per­a­ture by al­ter­nat­ing from cold ocean water to bask­ing on rocks near shore.

Con­trib­u­tors

Kristi Roy (au­thor), Michi­gan State Uni­ver­sity, James Hard­ing (ed­i­tor), Michi­gan State Uni­ver­sity.

Ref­er­ences

Cog­ger, H., R. Zweifel. 1998. En­cy­clo­pe­dia of Rep­tiles and Am­phib­ians. San Diego, CA: Aca­d­e­mic Press.

In­di­viglio, F. 1997. Newts and Sala­man­ders. Haup­pauge, NY: Bar­ron's Ed­u­ca­tional Se­ries.

Lau­rie, W. 1990. Pop­u­la­tion Bi­ol­ogy of Ma­rine Igua­nas I. Changes in Fe­cun­dity Re­lated to a Pop­u­la­tion Crash. Jour­nal of An­i­mal Ecol­ogy, 59: 515-528.

Lau­rie, W., D. Brown. 1990. Phop­u­la­tion Bi­ol­ogy of Ma­rine Igua­nas III. Fac­tors Af­fect­ing Sur­vival. Jour­nal of An­i­mal Ecol­ogy, 59: 545-568.

Lau­rie, W., D. Brown. 1990. Pop­u­la­tion Bi­ol­ogy of Ma­rine Igua­nas II. Changes in An­nual Sur­vival Rates and the Ef­fects of Size, Sex, Age, and Fe­cun­dity in a Pop­u­la­tion Crash. Jour­nal of An­i­mal Ecol­ogy, 59: 529-544.

Rass­mann, K., F. Trillmich, D. Tautz. 1997. Hy­bridiza­tion be­tween the Gala­pa­gos land and ma­rine iguana on Plaza Sur. Jour­nal of Zo­ol­ogy Lon­don, 242: 729-739.