The marine iguana, a species found exclusively in the Galápagos Islands, is the only lizard globally that forages in the sea. These reptiles, known for their unique ability to “sneeze” out excess salt, spend significant time basking on volcanic rocks to absorb heat after cold ocean dives. While they are an iconic part of the Galápagos ecosystem, their population faces numerous challenges that have led to their vulnerable status. Understanding the threats to this distinctive species offers insight into broader conservation concerns in delicate island environments.
Threats from Introduced Species
Non-native species, brought to the Galápagos by human activity, pose substantial threats to marine iguanas. Feral animals like cats, dogs, and rats prey on marine iguana eggs, hatchlings, and smaller adults. On islands with invasive rats, successful hatching of marine iguana eggs can be severely reduced, leading to an aging population with reduced reproductive success.
Introduced herbivores such as goats and donkeys degrade the terrestrial habitats that marine iguanas use for nesting and basking. These grazing animals compete for vegetation, impacting the availability of suitable nesting sites and cover. The removal of vegetation by grazers can also expose nests to harsh weather conditions and make them more accessible to predators.
Impacts of Climate Change and Natural Events
Broader environmental challenges, particularly those intensified by climate change, significantly impact marine iguanas. Rising sea temperatures directly affect their primary food source, marine algae. Warmer waters can cause a reduction in the red and green algae that marine iguanas prefer, sometimes replacing them with brown algae that are indigestible. This shift in algal composition can lead to widespread starvation, even if their stomachs are full.
Extreme weather events, such as El Niño, intensify these food scarcity issues. During strong El Niño events, ocean temperatures rise, leading to a significant decline in the growth of edible algae, and can cause mass starvation for iguana populations, with mortality rates reaching up to 90% on some islands. Sea level rise and increased storm intensity, also linked to climate change, threaten coastal habitats and destroy nesting sites. This loss of crucial shoreline areas reduces the available space for iguanas to bask and lay their eggs, further stressing populations.
Direct Human Activities
Direct human activities, distinct from the introduction of invasive species, also contribute to the marine iguana’s vulnerability. Coastal development leads to habitat degradation, reducing the available areas for basking and nesting. As human populations and tourism grow, there is increased pressure on these limited coastal zones.
Pollution, including plastic waste and oil spills, poses another significant threat. Oil spills can have significant immediate effects, as seen with the MV Jessica oil spill in 2001, which caused a 62% mortality rate in one marine iguana colony, potentially by killing essential gut bacteria. Plastic pollution poses a risk, as marine iguanas can ingest microplastics or become entangled in larger debris. Unregulated tourism activities can disturb iguana populations, particularly in sensitive nesting areas, impacting reproductive success.
Unique Vulnerabilities of the Species
The marine iguana’s inherent biological and ecological characteristics make it more vulnerable to these threats. Its endemic status limits its ability to escape threats by migrating to other regions. This geographic confinement makes the entire species vulnerable to localized environmental changes or disasters.
The species’ specialized diet, relying almost exclusively on specific marine algae, makes it highly dependent on the stability of its food source. Changes in algal availability or composition, whether from climate events or pollution, directly impact their survival.
Marine iguanas have a slow reproductive rate, with females laying only one to six eggs per clutch and breeding every other year, which hinders population recovery after significant declines. These factors collectively mean that even minor disturbances can have disproportionately large and lasting impacts on marine iguana populations.