Marine Invertebrates of the Galápagos Islands

Angela Gruenfelder

July 5, 2004

Marine invertebrates are a vital part of the Galápagos Islands ecosystem. The evidence of their existence is everywhere, from the beaches you walk upon to the snapping crackling noise you hear the moment you put your head beneath the surface of the ocean. The Galápagos archipelago is no exception and is home to an array of marine invertebrates.

Our first day aboard the San José, June 17th, we made our first trip onto the islands, Santa Cruz Island at Las Baches beach, named from the water barges that used to bring fresh water to the isle. Before we even landed in the dingy, we saw the presence of marine invertebrates, possibly the most obvious invertebrate in the isles, a bright orange, red, and yellow crab that stands out vividly upon the basaltic rocks. The Sally lightfoot crabs are easy to spot and are there in force. In many cases, the bright creatures dot the dark basaltic rocks. Their predators are within the water and every now and then one will run across the surface of the water, hence their name lightfoot. A juvenile Sally lightfoot crab is black becoming more colorful as it gets older. Upon closer inspection, there are many different stages of this type of crab upon the rocks. The juveniles blend in with the basalt, making them hard to see. This beach was a white sand beach, much of which came from a calcium bicarbonate origin. Taking a closer look at the sand you can spot small purple rods, often broken short. Pencil urchin spines, that have since become part of the beach. There is also an array of shells that one can spend all day identifying the variety. The sand is spotted by holes, where you can't necessarily see the bottom; and occasionally you can spot the inhabitant trying to dig in deeper. Often little tracks originate or end at the holes. They are ghost crab holes, within each whole a single or multiple of the fast shy creature wait for you to move on.

Visitors are only allowed on the islands during the daylight hours from six am to six pm. Back on the boat at night, we watched the wildlife around us. Hanging over the side and sitting on the stern of the boat, we were able to see, with the use of a flashlight, many fish, a sea lion chasing a flying fish, a snake eel, and a baby squid, a marine invertebrate. The squid is also fed upon by sea lions. In fact, the seal lions would follow our boat to catch the squid the boat turns up.

Our second day, June 18th, we spent the morning on Bartolomé Island, near pinnacle rock. From the zodiacs, we saw ghost crabs or what we assumed to be ghost crabs scuttling across the shore. Sally lightfoots were easily spotted on the basaltic rocks, and snails as well, although were unidentifiable at this distance. After a hike, we went snorkeling. From the moment you enter the water you are aware of the marine invertebrates due to the crackling snapping noises you here when your head is underneath the surface. This is caused by the constant scraping and scavenging of the marine invertebrates on the ocean floor. Slate pencil urchins could be found in crevasses of rock formations, Green sea urchins and white sea urchins were also in abundance, occasionally you can spot them with rocks and debris on top of them, attempting to hide themselves, or that is the assumption. Panamic cushion stars spot the bottom, from the surface, they appear brown, but when one dives to come in close, they are actually an orange-red color with darker spots. Although I did not see one on this day, I did hear of another student spotting the chocolate chip sea star.

Our afternoon was spent exploring Santiago Island and its lava flows. Once again, Sally light foot crabs were easily spotted along the shores and in the intertidal zones we saw many gastropods including limpets. While attempting to identify the type of limpet by memory, we were unable to decide whether it was De Roy Keyhole Limpet or a Sculptured Keyhole Limpet. It is against park rules to remove anything from the isles including seashells, sand, or crab molts; this does make it difficult to identify types of shells found on the beaches. There are many variations and similarities between many of the shells. There were also many small snails sealed into their shells until the next high tide. Their shells were small grayish purplish and dotted the intertidal zone with a high frequency. Purpura shells, larger snails used to create a purple dye were also present.

On June 19th, Isabela Island, the largest of the Galápagos Isles, we started out on a dingy tour of shoreline, which consisted of many small channels lined by basalt and red mangrove trees. The red mangrove trees were easily identified by their long prop roots that created an extensive ecosystem within them. Algae, oysters, and barnacles were all growing on them and easily spotted from the zodiacs. We then snorkeled around the Mariela Islets. While snorkeling we saw many blue sea stars, and I saw my first chocolate chip sea star, they are yellow with darker brownish spots. This type of sea star is easily spotted and identified from the surface. There were many encrusted sea cucumbers to be found and even several non-encrusted. I did not have the luck to see the 'pepiños' sea cucumber, but our Professor Dr. Holtz did. This sea cucumber is currently the center of an ongoing debate between local fisherman and conservationists. The fishermen are protesting the limitation on the harvesting of the pepiños, because they are currently receiving very high prices for them due to the Asian market. However, given the chance the fisherman could fish the pepiños right out of the area. Evidence of this dispute was evident later on, as the fisherman threatened to kill the giant tortoises, according to our tour guide Luis, at the Darwin research station, there were indeed armed guards.

We spent our afternoon in Urbina bay, a black sand beach. Beaches are an excellent place to observe an areas marine invertebrates, especially those with calcium carbonate armor or shells. They wash up or are left by sea birds, and their shells remain long after they have gone. There was a red spiny lobster tail on the beach, large in size the size of an average boys shoe. We also spotted and unusual crab carapace on the beach, green with algae and it appeared furry. The amazing thing about Urbina bay is that fifty years ago it experienced a sudden uplift. Sea floor became part of the island stranding much sea life that could not just swim away, including many marine invertebrates. Evidence of this uplift is most obvious from the marine invertebrates that inhabited the area. Shells lined the pathways and made up many of the pathways. Limpets, snail shells, barnacles, oysters, and others I could not identify had been crushed beneath the shoes of past visitors. There were small pieces of coral ground into the pathways and huge coral heads in the undergrowth.

June 20th began with a hike on Fernandina Island. The usual sSally lightfoot crabs awaited our arrival on the lava rocks. We eventually arrived at an intertidal zone, an area where the rocks are exposed every time the tide goes out, ultimately making it a difficult environment to survive in. Many black lumps with a slimy appearance inhabited cracks or crevasses in the rocks. At first, we thought these to be anemones, which had withdrawn their tentacles, but we later identified them as oval sea slugs. Anemones were also present but their color was not as dark making them more easily identifiable. Sculptured chitons were spotted. Their patterned exterior allowed us to identify them easily, also dark in color, but flatter than the sea slugs. Along with sally Light Foots we saw orange tipped hermit crab and purple bristle crabs. The purple bristle crabs were shy and attempted to hide in deep holes as soon as they sensed our presence. These were only occasionally spotted. When you leaned forward close to crevasses filled with crabs one could hear the clicking of their mouthparts. One of the most exciting things to spot was beneath the lava rocks. Attached to the bottom of one was a red sun star. This mutlirayed echinoderm was the first I had ever seen and the only starfish I had ever seen with more than five feet. Purpura (small mouth) shells of gastropods were often stuck beneath basalt ledges. Red mangroves lined the intertidal zones. Their prop roots become home to many palmate oysters. Barnacles dotted the lava rocks as well as baby clams.

That evening we set sail for our next island after dinner. The crew agreed to turn off the lights so we could see bioluminescence the boat turned up. Bright blue and green hues, sometimes in bright spots sometimes or in large duller clouds were turned up. It was best seen from the stern of the boat. The cause of this bioluminescence was mainly marine invertebrates including squids, crustaceans, and phytoplankton. The bioluminescence is why the sea lions followed the boat. When stirred or jostled, squid give off the light, making them an easily seen meal for the sea lions.

June 21st was split between James Island and Rábida Island. In the morning, we landed on Puerto Egas on James Island, a black sand beach. We hiked across the island to a series of grottoes that were actually collapsed lava tubes. The occasional rock bridge crossed over these flooded tubes. Coralline algae lined the water line. Its pink and yellow color very visible and vibrant against the dark basaltic rock it clung to. However, coralline algae are not marine invertebrates. There was the ever-present Sally light foot crabs. In fact, a previous visitor had left two Sally lightfoot crab molts on a rock so we could examine the difference between the male and female. The male has a triangular piece on the underside of its carapace. This was his genital.

Snorkeling in this area gave us the opportunity to see an area that was heavily inhabited by green, white, slate pencil urchins. There was also a large quantity of starfish; both the panamic cushion sea star and some blue sea stars.

We spent our afternoon on the Red Island of Rábida. We took the zodiacs to the point then snorkeled toward the beach. We stayed close to the rocks, diving to see what was hiding within the crevasses. We saw an octopus here, reddish brown in color, hidden beneath one rock ledge and many of the species that we had seen earlier in the isles. After our snorkel, we landed on the red sand beach for a hike. We walked down the beach toward the pelican nesting grounds. On this beach there were the small air holes formed near the tide line, evidence of sand crabs. We dug for them and found many. Although we only truly unearthed one, about the size of a silver dollar, it was dark in color, making it difficult to identify. The sand crab's coloration is usually specific to their location, or beach. This one did not have a large set of pincers. Continuing on the walk along the beach, we found a panamic cushion sea star. This starfish had washed up probably several hours ago, as it was already experiencing bleaching from the sun. We were unable to try and save it by sending it back out to sea because it is against park rules to interfere with any of the wildlife. A green sea urchin had also washed upon shore, although already deceased, shockingly the Aristotle's lantern, the radial mouthpiece of this creature was still intact, or at least the outward beak portion was.

June 22nd we arrived in Puerto Ayora, on Santa Cruz. This port is home to the Darwin Research Station, and a town. What was interesting to see though, was despite its civilization; there were still Sally lightfoots to be seen as well as other wildlife. The rest of the day was spent in the Research Station, and the highlands, which both lack marine invertebrates.

June 23rd was spent with a morning hike seeing mostly sea birds. As usual, Sally Light foot crabs were present, as well as the usual shell collection on the beaches. Farther along our walk we saw lava rocks and cliffs where the surf meets the cliffs harshly creating blowholes, large barnacles were evident. Even in harsher conditions, marine invertebrates can survive. We also snorkeled that afternoon around what Luis identified as Turtle Island due to its shape. Once again many of the same marine invertebrates were seen, urchins, sea stars, and more of the encrusted sea cucumbers.

The Galápagos isles are an amazing place to visit. Here you can learn to identify many of the things you see on sight. For marine invertebrates, one receives the totally awesome experience. You can see, hear, and in some cases actually feel these creatures. Many you see repeatedly but occasionally you spot a rare or new creature, which once again sends you back to the field guides to identify. We were able to see the islands' ecosystems as a whole, and how everything interconnected between the different species, especially the marine invertebrates.