Trophic connectivity between the terrestrial and marine ecosystems of Malpelo Island, Colombia, evaluated through stable isotope analysis

The trophic dynamics of islands with low terrestrial primary productivity often depend on marine allochthonous inputs from nearby donor habitats. For instance, on Malpelo Island, Colombia (4° 00′ 05.63″ N; 81° 36′ 36.41″ W), the Nazca booby Sula granti affects the productivity and trophic dynamics of the terrestrial ecosystem by delivering nutrients, primary in the form guano, chick carcasses, and eggs. This study evaluated the trophic connectivity between the terrestrial and marine ecosystems of Malpelo Island, Colombia based on the isotopic (δ¹³C and δ¹⁵N) assessment of 403 samples (107 terrestrial and 296 marine) collected between 2017 and 2021. Isospaces were estimated based on δ¹³C and δ¹⁵N values, contribution of terrestrial sources in consumer diets (mixing model), ¹⁵ N enrichment in C₃ plants, and interactions among environments (overlap). δ¹³C and δ¹⁵N values showed a larger terrestrial isospace (134.7‰²) than the marine isospace (117.2‰²). The mixing model indicated that detritus_Terrestrial (median: 30.2%) contributed more to the food web than C₃ plants (0.2%), reflecting high δ¹³C_Marine content. The high isotopic overlap (> 60%) between terrestrial and marine isospaces suggests a significant trophic connection between environments. These results show the role of the marine ecosystem on the terrestrial ecosystem and the importance of S. granti regarding nutrient transfer between environments. The conservation of this seabird is essential to maintain the balance of this insular ecosystem. Using stable isotopes, this study was able to reveal trophic relationships between ecosystems associated with small oceanic islands that host large seabird colonies but have low primary productivity.