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Marine Iguana
Marine Iguana taking in the sun on the beach at Punta Carola on San Cristobal Island

Imps of darkness

The black Lava rocks on the beach are frequented by large … most disgusting, clumsy Lizards. They are as black as the porous rocks over which they crawl & seek their prey from the Sea. — Somebody calls them “imps of darkness”

Charles Darwin, 17 September 1835

In the morning, black marine iguanas (Amblyrynchus cristatus) lay strewn haphazardly across the beach, warming themselves in the early sun. Within a few hours, as the heat becomes unbearable, they slowly make their way down to the rocky shore, tracing a distinctive trail through the sand with an alternating waggle of their hind legs and a swish of their tails.

They perch on the lava rocks in large colonies, maintaining a serene stoicism even as other lizards climb over top of them or small birds symbiotically pick parasites from their backs. From there, one by one they slip into the water and out to sea, where they gnaw on the red and green algae attached to rocks on the sea floor. Darwin describes their aquatic ballet in his Voyage of the Beagle,

It is a hideous-looking creature, of a dirty black color, stupid, and sluggish in its movements…. Their tails are flattened sideways, and all four feet partially webbed … [but] when in the water this lizard swims with perfect ease and quickness by a serpentine movement of its body and flattened tail – the legs being motionless and closely collapsed on its sides.

Marine Iguanas

Marine Iguanas in assorted sizes lounging on the rocks on San Cristobal (Photo/Rebecca Keim)

One moment they are awkwardly lumbering over the rocks; the next they are gliding gracefully through the water. Once they begin feeding, they may remain on the bottom for 10 minutes or more before coming up for air. By feeding at sea, marine iguanas accumulate a lot of salt, which they extract and periodically expel. In what appears to be a sneeze, a short spray of cloudy water streams simultaneously from each nostril. With one lizard I was close enough to catch a bit of it in the face.

As with many other Galapagos genera, marine iguanas come in distinct subspecies on each island. Of the islands’ seven varieties, I observed three. A.c. venustissimus on Espanola was the most colorful of the group, its black undercoat highlighted with red and sometimes turquoise accents. The others were more difficult to tell apart.  For me, A.c. mertensi on San Cristobal and A.c. hassi on Santa Cruz were indistinguishable, especially considering the variation I saw within the same subspecies.

Calling them stupid because of their sluggishness is unfair, but there’s a much better case to be made for ugly. Their leathery skin hangs loosely on them as if it were at least one size too big. They are not uniformly black but mottled with irregular patches of buff, gray and brown. The spines along their back are often askew, and their blunt head is crowned in short spikes that are sometimes a chalky white.

Marine Iguanas

Marine Iguanas with red and turquoise accents on the rocks at Espanola

The marine iguana has two terrestrial cousins: Conolophus subcristatus, which is resident on Santa Cruz and its adjacent islands, and C. pallidus, which is confined to nearby Santa Fe. The land iguana is similar in general appearance and demeanor to the marine iguana, except for its yellow to sandy brown color, rounded tail and lack of webbed feet. They feed on Opuntia cactus, other plants and insects. The one I saw on Santa Cruz was a bright yellow.

About Scott Clark

I'm a former journalist and graduate student working toward a Ph.D. in Ecology.