Oceanography and Marine Life of the Galápagos Islands

John M. Fitz
Biological Science/Marine Biology Major, University of Maryland
July 4, 2000


  • Introduction
  • Currents and Physical Oceanography
  • Upwelling
  • El Niño and its effects
  • Marine Life
  • Fish
  • Invertebrates
  • Mammals
  • Reptiles
  • Conservation
  • Additional Readings

  • Introduction

    The physical oceanographic processes in the eastern Pacific Ocean along the equator create a very unique setting in the Galápagos Islands. Several currents, counter currents, and subcurrents all converge to greatly affect the waters surrounding the archipelago. This complex system of currents also creates an upwelling, a surge of deep, cold water, which is very rich in nutrients to the surface that provides for an extraordinary marine ecosystem. Since the Galápagos waters contains a mix of tropical and cool water from the deep, many different kinds of marine fauna are found throughout the islands. This study will focus in great detail on the complex system of currents, upwelling, the unique diversity of marine life found in the Galápagos and briefly touch on the effects of the El Niño weather phenomenon on the marine ecosystem.

    Currents and Physical Oceanography

    A complex system of several currents surround the waters of the Galápagos Islands. The South Equatorial Current is the major surface current in the tropical Pacific and flows west between roughly five degrees north and ten degrees south. To the north of the South Equatorial Current lies the North Equatorial Countercurrent and to the south lies the South Equatorial Countercurrent, which is also known as the Cromwell Current. The Cromwell Current flows east, reaching the western islands of the Galápagos. The Southern Equatorial Current is supported by the Peru Current System from the east, which includes the Peru Coastal Current, also known as the Humboldt Current, the Peru Oceanic Current and the Peru Coastal Countercurrent. The Peru Current system brings in relatively cool, subtropical waters north to the equator. At the equator, the current changes direction towards the west and then joins the South Equatorial Current. The Peru Current System and the South Equatorial Current are mainly caused by the near constant southeast trade winds. There is also a warm water current flowing from north to south towards the Galápagos Islands, called the Panama Current or Niño Flow, which brings warmer, tropical waters to the islands. There are also three main subsurface flows near the Galápagos islands which flow east, the Equatorial Undercurrent near the equator and the Northern and Southern Subsurface Countercurrents, near five degrees north and five degrees south, respectively.

    The Galápagos platform is located approximately 900 meters (almost 3000 feet) below sea level and the average depth surrounding the islands is about 3,000 meters (9900 feet). The temperature of the waters surrounding the Galápagos is considered subtropical. The islands have been broken up into five temperature regions or zones. The water temperature around the northern islands are more tropical, the surrounding waters of the southern islands are more of a warm-temperate and the waters surrounding Fernandina and the western shores of Isabela Islands are much cooler, higher in salinity and have a much higher content of chlorophyll. The two central regions are considered a mix of different water temperature, salinity, and productivity. The currents mentioned above help to explain the reasons for these water temperatures.


    The several currents mentioned above caused by various winds along with the Coriolis effect causes a surge of cold water from very deep to be brought up to the sunlit layer of the surface. The Coriolis effect is the result of the Earth's eastward rotation and causes the deflection of air and water relative to the solid Earth below. This water is very high in nutrients, such as nitrates and phosphates, from the sinking of dead organic material which has been decomposed by bacteria and then released back into the water. This high content of nutrients and sunlight fuels large-scale phytoplankton (photosynthesizing or plant plankton) or algae blooms. This phytoplankton uses photosynthesis to create more plant material and is then fed upon by the zooplankton (animal plankton) and herbivorous fish. The phytoplankton is the primary producer of the ecosystem and is the key to food production which dramatically affects and supports the rest of the marine ecosystem.

    El Niño and its effects

    An atmospheric phenomenon know as El Niño that occurs at an interval ranging from every two to 15 years takes place along the northwest coast of South America. It usually occurs near Christmas time and literally means "the child." El Niño is similar to a reversal of the normal conditions found in the Galápagos and also affects the weather around the world. Upwelling stops, water temperatures go up, driving cold water species to migrate or to go deeper. The latest occurrence of this phenomenon to affect the archipelago was from June 1997 to June 1998. Scientific studies of those results have shown both extremely negative effects as well as some positive impacts on land. Most of the negative effects in the islands were found to be related to marine plants and animals. Some terrestrial plants thrived due to the increased rainfall, which was also good for land reptiles and birds. Of the marine life affected, Sea Lions suffered very badly because of the lack of their staple diet of sardines. An estimated 90% of Sea Lion pups and 76% of dominant males died from starvation. Marine Iguanas also suffered greatly because of a decrease of green algae (Hincksia mitchellae). Many species of fish, including some sharks species were found in deeper than usual waters because of a rise in water temperatures brought of by the cease of upwelling. Fish and other marine life are making a comeback, natural selection in action again, the life that sustained had the genetic makeup that enabled them to survive, adapt and pass on their genes by reproducing. The effects of El Niño can be viewed as compelling evidence of how fragile this and other ecosystems really are. During our excursion, we encountered waters that seemed to be quite chilly at times and observed abundant species of fish, both of which could be an indication that things seem to be heading back to normal. For more information on the El Niño phenomenon click here, for more on its effects on wildlife, click here.

    Marine Life

    An often overlooked component of the Galápagos Islands is the extraordinary marine life that flourishes there. When people think of the Galápagos, they often think of the usual (but also very exciting) land creatures such as the tortoises and guanas, or the physical geology and volcanic activity and of course Charles Darwin. Darwin is famous for his voyage to the islands in 1835 and his theory on evolution by means of natural selection. Strong scientific evidence of the natural selection among the finches of the islands also comes to mind. The Galápagos marine fauna and flora are equally isolated as the terrestrial plants and animals and evidence of natural selection can be seen in the waters. The Galápagos marine ecosystem is considered intermediate-to-high in terms of species richness with approximately 3000 species of marine plants and animals, of that number, about 21% are found no where else on Earth. When people investigate a little further into the life that surrounds the waters of the islands, they will find an equally as interesting and exciting life below the surface as they do on land. Darwin noticed, on a much smaller scale, but he was probably the first to collect and record some fish specimens, taking 15 species which were all new to science in 1835. A later study of those specimens by the Reverend Leonard Jenyns found five of the 15 were endemic and one even bears Darwin's name, the Goldspot or Galápagos Sheephead (Semicossyphus darwini). Many scientific expeditions focusing on fish and other marine life followed and the number of different fish species exceeds 400 (including fishes located further from the coast or pelagic fishes) from close to 100 families. There are a wide range of habitats located in the Galápagos, including mangroves, rocky shores and sandy bottoms. The marine life that made it to the islands by way of the currents were able to quickly adapt to these different environments.


    It is easy to recognize the great diversity of fish, it happened very soon after getting into the water. I saw an amazing array of fish, ranging in different size, form, function and lifestyle. During our Galápagos excursion, we saw dozens of species of fish in only five short snorkel dives and we were slightly limited because we didn't utilize SCUBA or spend a great deal of time in the water and we still saw incredible amounts of life below the surface. Many interesting fishes including the Chondrichthyan fishes (sharks and rays) and the Osteichthyan fishes (bony fishes) were observed by our teams.

    28 species of sharks from nine families are found in the waters of the Galápagos, including the one shown here, a White-tipped Reef Shark (Triaenodon obesus).Also, one of our National Park Guides, Lenin Villacís saw two Scalloped Hammerhead Sharks (Sphyrna lewini). During our last dive of the trip, two members of our team encountered about five smaller sharks (2 to 4 feet). I spotted at least four that looked to me like Blacktip Sharks (Carcharhinus limbatus). Due to distance and lower visibility, I won't discount the possibility of wrongly identifying them, as Blacktips are commonly mistaken for other sharks. The Rays were quite abundant, with several spottings of Spotted Eagle Rays (Aetobatus narinari), Golden cow-rays (Rhinoptera steindachneri),including at least two large schools, Diamond stingrays (Dasyatis brevis),and one Manta ray (Manta hamiltoni),spotted breaching the surface by the keen eye of one of our fearless leaders, Dr. John Merck.

    Far too many bony fish were observed to possibility list here, some links to great photos taken during the trip for the following species include: a King Angel Fish (Holacanthus passer), a Streamer Hogfish (Bodianus diplotaenia),a Belted Blenny (Malacoctenus zonagaster), a Blue-Chin Parrotfish (Scarus ghobban), and a Flag Cabrilla (Cratinus agassizii). One interesting encounter of a fish occurred on a dive from Baltra Beach, I spotted a Bullseye or Concentric Pufferfish (Sphoeroides annulatus), which are quite common in the archipelago. What was so interesting was the lack of fear of humans shown by this fish. The Galápagos wildlife are known for this characteristic of terrestrial animals, but this was quite evident in this marine species as well. This particular pufferfish (which I saw on at least three different occasions within a half hour) seems to be quite interested in me, investigating me instead of the opposite. Another interesting characteristic about this fish is that it employs some unique defense mechanisms, such as sucking in air and water to become larger and they also have a poisonous substance covering their skin. The diversity of this marine ecosystem is quite amazing and apparent , the cold upwelled waters converging with the warm tropical waters creates a unique diversification of cold, tropical and mixed water species of fish with numerous forms.

    Marine Invertebrates

    An interesting and often overlooked component of the Galápagos marine ecosystem is the marine invertebrates, such as this Panamic Cushion Sea Star shown here. These groups of animals, which are commonly found along the shores and below the surface are also extremely diverse and ecologically important. The highly recognizable Sally lightfoot crab (Grapsus grapsus) were often seen with their bright red and orange coloration among the black of the lava rocks along the shorelines. Although it would seem a disadvantage to be such a bright color and most commonly located on such a dark surface, they use a form of Batesian mimicry, not aposematic warning colors to divert possible predators. Other Arthropods observed were: three different species of hermit crabs, and many Ghost Crabs (Ocypode sp.) and the Princely Fiddler Crab. Occasional sea anemones and Orange Cup coral (Tubastrea coccinea) were also found. Corals and coral reefs are not commonly found throughout the islands, mainly because of the colder, upwelled water. Some corals and coral reefs are found, but are mostly limited to the central islands.

    Another interesting phyla of invertebrates observed by our teams were the echinoderms, huge numbers of sea stars were seen on every venture into the water. Pyramid (Pharia pyramidata), Panamic cushion (Pentaceraster cummingi),and Chocolate chip, (Nidorellaarmata) sea stars were commonly found. An interesting Panamic cushion star was spotted with six arms instead of five. Also the urchins were quite abundant as well, species of urchins observed included: the Green (Lytechinus semituberculatus) the Pencil (Ducidaris thouarsii) and the Crowned (Centrostephanus coronatus)sea urchins. Numerous sea cucumbers were also observed .

    Marine Mammals

    The Galápagos Sea Lion (Zalophus californianus) was the marine mammal most often seen during our excursion to the islands. They are quite abundant throughout the archipelago, living in large and small colonies along the sandy or rocky shores. They tend to feed offshore on squid and fish and can dive down to 200 meters (about 650 feet). Their only predators are sharks. Males, or bulls, can be easily recognizable by their larger size and can sometimes be quite aggressive in defending their territory, especially during mating season, which runs from May until January. Mating occurs in the water, while the females give birth on land. During our excursion, no mating behavior was observed, but we did see a few bulls on the shore, but again, no aggressive behavior was seen as we did not approach too closely. We were very fortunate to observe some sea lions underwater during our last snorkel dive off the shores of Bartolome Island. Not knowing exactly how long they would stick around, I frantically snapped the remaining film in my underwater camera. To my dismay (only because I snapped my last 10 photos in about 15 seconds) and my great pleasure, they hung around our group for close to twenty minutes. At least six were observed, including one bull, which we closely kept an eye on. They are such great swimmers, they would at times streak by you at such high speeds and at other times they would slowly approach you and even bump you. What an exciting conclusion to our trip, this truly turned out to be one of the coolest experiences of my life. Another species of Pinnipeds seen by our teams were the Fur Sea Lion (Arctocephalus galapagoensis).This is an endemic species and reached the islands by way of the Humboldt Current from the Southern Hemisphere. This species was not seen nearly as often as the Galápagos Sea Lions. Other marine mammals include the Cetaceans, or whales and dolphins. At least 16 different species of whales and seven species of dolphins inhabit the islands at least occasionally, but unfortunately, we did not see any.

    Marine Reptiles

    The marine reptiles found in the Galápagos Islands mainly consists of four species of marine turtles, the world's only sea going lizards, marine iguanas, and the yellow-bellied sea snake. The Pacific Green Sea Turtle, (Chelonia mydas) is the most abundant species of sea turtle found in the islands and the only marine turtle observed by our team. It is an endangered species but is quite abundant in the Galápagos because the islands are a major breeding site. The females are much larger than the males and are required to do the swimming of both during mating. The mating season begins during the hot season and the egg laying occurs in December and January. The female comes ashore at night to deposit 80 to 120 eggs the size of ping-pong balls into a nest in the sand along the shore. She then covers the nest, which can take up to an hour, by which point she is physically exhausted. The gestation period is approximately two months and the young turtles face almost insurmountable challenges to survive. They are often preyed upon by sea birds, crabs and sharks and are also affected by human activities such as nets and pollution. If these young turtles manage to survive, they will go on to reproduce themselves, they reach sexual maturity after about 20-25 years. They use very sophisticated navigation methods to reach the Galápagos Islands for mating and possibly find the very same beaches they hatched from to lay their eggs. It was a tremendous joy and a memory that I will always remember to be able to see these beautiful and graceful creatures gliding though the water below me off the coast of Bartolome Island or very quietly come up for air in Black Turtle Cove. It was extremely interesting to see endangered species with such abundant numbers around the islands. For more about Galápagos reptiles, click here.


    The coastal and marine wildlife of the Galápagos Islands are extremely vulnerable to illegal and inappropriate human activities, including fishing. Industrial fishing boats from Ecuador and other nations that fish for tuna are common despite new mandates that protect up to 40 miles of surrounding waters. During the 1990s, a high demand for sea cucumbers and shark fins among the Asian seafood markets drastically reduced numbers of those species. Many steps have been taken to help protect the marine environment such as coastal clean-up programs and the passing of the Galápagos Marine Reserve Management Plan by the Ecuadorian Congress. For more on conservation in the islands click here.

    Additional Readings

    Boyce, B. 1998. Traveler's Guide to the Galápagos Islands Galápagos Travel,

    Cambell, N., J. Reece, L. Mitchell. 1999. Biology Benjamin Cummings.

    Constant, P. 1992. Marine Life of the Galápagos Caloa Life Experience.

    Constant, P. 1999. The Galápagos Islands Odyssey Publications Ltd.

    Glynn, P. and G. Wellington. 1983. Corals and Coral Reefs of the Galápagos

    Grove, J. and R. Lavenberg. 1997. The Fishes of the Galápagos Islands Stanford

    Humann, P. 1993. Reef Fish Identification: Galápagos New World Publications

    James, M. (Ed) 1991. Galápagos Marine Invertebrates. Plenum Press,

    Levington, J. 1995. Marine Biology: Function, Biodiversity, Ecology. Oxford

    Charles Darwin Research Center website:

    Cornell University Galápagos Geology website:

    National Oceanic and Atmospheric Administration El Nino website: