The Plants of the Littoral Zone in the Galápagos Islands
Annette Y. Mitchell
July 6, 2004
The variety of animals in the Galápagos, especially birds, are well documented and well known. However, plants in the islands also experience variation according to their environments. The height, range, and presence of coastal plants on the different islands depended on, or changed with, the kinds of animals present and the age of the islands themselves. Some coastal plants were easy to recognize and take note of, while others were more difficult.
The plants that I found most recognizable on our trip were the mangroves, especially the red mangroves. Red mangroves ( Rhizophora mangle) are tree- or bush-like plants, depending on where they are located, that are compatible with salt water. A prominent feature of the red mangrove is the waxiness of their leaves that are unique to this type of mangrove. They showed up in various forms, alive and dead, young and old, all around the islands. Their presence was perhaps most noticeable on the 19th as we rowed around Elizabeth Bay off of Isabela. The red mangroves surrounded the river on either side, and Luis told us that they were among the tallest in the world. Their roots were visible and grew out of the saltwater and the turtles that swam around us feed on the algae that accumulates on the roots beneath the surface of the water. Our guide Luis remarked that it felt like we were in the middle of the Amazon rain forest. If it had not been for the penguins that we occasionally saw, incongruously swimming in front of the equatorial coastal plants, I would have agreed.
As we rode in the dinghies, we saw that Palo Santos and Prickly Pear Cacti, or Opuntia were growing just behind the mangroves. This juxtaposition of coastal and arid zone plants showed how limited the coastal zone can be. Luis found a mangrove seed, which looked like no other seed that I have ever seen. It was long and slender, and Luis told us could survive up to two years, until it found an appropriate place to take root. It was easy to see how this seed could grow into the small sapling that we saw in the lava flow on Santiago island the day before. The seed had probably slipped into a crack between rocks, perhaps brought in by the high tide or possibly windblown, and had managed to thrive. Since the lava flow on Santiago was only 50 years old, the mangroves were just now beginning to colonize, along with the sole lava cactus that we saw. However, we saw evidence of the presence of mangroves before the lava flow had appeared: the outline of a mangrove trunk lay in the cooled lava, preserved even after the actual trunk had disappeared. I could also venture to guess why mangroves were not as plentiful on Bartolomé, as we saw as we hiked there. The sand was probably not as hospitable an environment for the seeds to be able to stay before being washed out to sea again.
Also in Elizabeth Bay we saw the way that some animals make use of the mangroves. Although we didn't catch a glimpse of any turtles actually feeding, we did see a sea lion napping about four feet up on the trunk of a red mangrove. Later, at Urbina Bay we saw pelicans nesting in the leaves of a mangrove that was relatively small compared to the giants of Elizabeth Bay. In short, we saw nearly every stage of mangrove growth: a seed, a young plant, slightly older plants, mammoth ones, and the remains of dead ones.
We also saw white mangroves (Laguncularia racemosa), characterized not by waxy leaves but by "dots" on the other side. The white mangroves were not as common as red mangroves, or perhaps I was just not as skilled at recognizing them, but I noticed that where they occurred, red mangroves were often nearby. They occurred in the intertidal zone of Fernandina.
Saltbush (Cryptocarpus pyriformis) was another common plant we saw on most of the islands that we visited. It is a more shrub-like plant than the mangroves are, and has softer-looking, smaller leaves. According to Michael Jackson's Galápagos: A Natural History, the leaves are salty-tasting. On Espanola we saw blue-footed boobies mating in the shade of saltbush, and on North Seymour we saw frigate birds nesting in it. We also saw pelicans sitting on nests of saltbush. Espanola seemed somewhat unusual to me because of how far the coastal zone extended. Often on other islands it seemed that the coastal zone, if it even existed, lasted only for a short time before the mangroves and saltbush and sesuvium were replaced with Opuntia and Palo Santos. On Española, all through our walk through the "field of boobies" and "couples reserve" of albatrosses, saltbush was interspersed with rounded boulders.
Saltbush also seemed to be a fairly hardy plant. While we were walking along Urbina Bay, saltbush was present even where we saw the devastation that introduced goats had caused by eating everything in sight. On that same hike, I noticed that there seemed to be a great overlap between arid zone and littoral zone plants. Again, perhaps because the area was only 50 years old, the plants of different areas were not yet established and competed for the same space.
Wherever we went and coastal plants were present, animals seemed to use the saltbush in some way or another. Frigate birds stole nesting material made of saltbush from one another, we saw sea lions lying in the shade of the plant, and the first and only giant tortoise we saw in the wild looked like it was about to make its way through the plant.
At Urbina Bay it was extremely odd to see the results of the recent uplift. Among the plants and animals we had learned to identify as being terrestrial, even if they lived near the water, there was coral, surrounded by terrestrial plants. According to Dr. Merck, the relatively young coral looked much the same as 90 million year old coral he had seen.
One coastal plant that has an interesting survival technique is maytenus. Its leaves are turned vertically towards the sun rather than horizontally, in order to absorb as much sunlight as possible, and to ensure that the leaves higher up do not prevent the lower leaves from getting sunlight. When we saw the plant, it had small round green berries among the rounded green leaves. Luis first pointed out maytenus on Las Bachas, the first beach we visited, where it surrounded a lagoon and had mangroves and Palo Santos behind it.
Also on Las Bachas we saw sesuvium, a small colorful creeping plant. A yellow warbler finch was hopping through a patch of it. Sesuvium was harder for me to recognize unless it was pointed out to me as its color varied from island to island, and perhaps I was not as observant of the ground as I needed to be. Other plants that crept along the beach were beach morning glory, whose yellow dying leaves I first mistook for flowers, and scorpion weed. According to Jackson, beach morning glory is important for stabilizing sand dunes, and in the sand is where we found them, especially in the intertidal zone. Scorpion weed we found in close proximity to lakes like those in Santa Cruz.