Ecuadorian PhD student Denisse Dalgo discusses her research studying the ecology of marine iguana diet and the potential impacts of El Niño on the species with the support of the NGO Captain Darwin.
Denisse is a doctoral researcher working with the Iguanas from Above team. Her focus is on marine iguana diet and the potential impact of El Niño on the species' dietary patterns.
Captain Darwin is an NGO dedicated to documenting environmental and biodiversity changes in the places visited by world-famous naturalist Charles Darwin during his voyage on the HMS Beagle 189 years ago. This NGO provides logistical support, through the use of its vessel, to local researchers at each stop on Darwin’s historic voyage.
During his visit to Galapagos, Darwin was impressed by one species in particular, the Galapagos marine iguana. Two hundred years after Darwin’s visit, this species continues to fascinate scientists, such as myself, an Ecuadorian PhD student, who researches marine iguanas.
I am part of the research team for the project “Ecology of Marine Iguanas (Amblyrhynchus cristatus) of the Galapagos Islands (PC-01-24)”. This project is led by Universidad San Francisco de Quito (USFQ) and the University of Leipzig, with the Galapagos National Park Directorate as its counterpart. The project involves monitoring the population status and studying the ecology of the marine iguana’s diet.
This year, the project had the support of the Captain Darwin crew and Galapagos Conservation Trust to carry out an expedition in the Archipelago and continue research on marine iguanas during the El Niño climatic event.
Replacing Andrea Varela and Eduardo Sampaio on the next part of the expedition were myself and Isabel Damas. The aim of our expedition was to continue collecting iguana faecal samples and algae samples for dietary analysis, capture drone footage to assist with our population counts and count the number of deceased marine iguanas to monitor the impact of El Niño on the species.
We departed from Puerto Ayora and arrived at Puerto Velasco Ibarra, our first fieldwork site on Floreana island. Here, we observed marine iguanas foraging directly at the pier, where small algae covered the concrete walls. We immediately began collecting algae samples and flying the drones over the coastal landscape. We then continued our walk to search for fresh faecal samples and additional algae. Near the pier, over an exposed rocky area at the low tide, we could see iguanas foraging for algae, so we collected even more samples.
We also visited La Loberia, close to Puerto Velasco Ibarra. The landscape here is beautiful, covered with bright red terrestrial plants from the genus Batis, a drastic contrast from the black volcanic rocks and white sand. Although iguanas here were sparse, we managed to find a few faecal samples.
From the boat, we briefly explored Montura, a place named for the saddle-like shape of its rock formations. We landed in a rocky area of the island and had to climb a small cliff to reach our site. Once we’d arrived safely, we started taking aerial photos of the colony using the drones. We found a group of around 20-30 iguanas surrounded by their faeces which we collected. Many individuals were males with a bright red colouration. One male, in particular, was demonstrating territorial and aggressive behaviour towards the other males which is common during the reproductive season.
Early in the morning we left Floreana and set sail for Española island. Dolphins accompanied us along the 13-hour journey which added to the excitement. We arrived at Punta Suarez on Española at around 9pm. Early the next day, we explored a rocky beach and found many iguanas feeding in the intertidal zone. At first glance, it seemed like marine iguanas were foraging on green algae, which covered a great part of the rocks. However, upon a closer look, we saw that the iguanas were feeding on small, reddish-brownish algae found among the green algae.
Exploring the island further, we noted the presence of dead iguanas along the coast and many adult individuals looking small and malnourished. This year, El Niño has been creating warmer ocean temperatures, which may have resulted in a shortage of the marine iguanas’ food. Fortunately, we also found many healthy juvenile iguanas.
The next day, we completed the drone monitoring. Because this island is a nesting site for many marine bird species, we had to make sure we were careful when flying the drone to avoid disturbing the birds.
Iguanas from Above is an innovative project that combines drone technology with citizen science to monitor the health of marine iguana populations in Galapagos.
We continued our expedition to Gardner Islet off the coast of Española. We flew the drones around the islet’s perimeter to locate iguana colonies. We only spotted a small group of four marine iguanas, but further analysis of the aerial images might reveal more individuals camouflaged among the rocks.
Our next destination was San Cristobal. This island is particularly interesting because it is home to two subspecies of marine iguanas. We conducted aerial monitoring and sampling at four different locations: Montones de Arena, Punta Pitt, Isla Lobos and Lobería, to evaluate how these two subspecies differ in terms of diet and population status and understand how these differences occur along their habitat range.
We arrived at Santa Fe and anchored in a spot known as “La Bahía”. The next day, we proceeded to the sampling site called “El Miedo”. Upon landing, we began flying drones, which enabled us to observe iguanas in inaccessible areas. The drone footage revealed a cliffside, inaccessible on foot, where iguanas were feeding on algae. After completing the drone flights, we explored the island on foot, searching for iguanas and their faeces.
The final island on our expedition was Plaza Sur, which I was visiting for the first time. We carried out the drone monitoring and then walked along the coast in search of marine iguanas. On this island, the population of marine iguanas is relatively small. We found some individuals scattered along the rocky shore and collected faeces and algae samples. In contrast, land iguanas were abundant. Plaza Sur is unique in being the only place where hybrid iguanas are found, a result of crossbreeding between male marine iguanas and female land iguanas. After discovering a hybrid iguana, I took the opportunity to observe it closely and think about what its diet might consist of.
Overall, our expedition was a great success. The samples we collected will provide valuable information on how the diet of marine iguanas is changing in warmer climates – crucial information in the context of global climate change. In addition, the aerial images we collected will help us assess the status of the population following an event we know significantly affects this species.
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