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 & DEG; 00 & PRIME; 05.63 & DPRIME; N; 81 & DEG; 36 & PRIME; 36.41 & DPRIME; 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 (delta C-13 and delta N-15) assessment of 403 samples (107 terrestrial and 296 marine) collected between 2017 and 2021. Isospaces were estimated based on delta C-13 and delta N-15 values, contribution of terrestrial sources in consumer diets (mixing model), (15) N enrichment in C-3 plants, and interactions among environments (overlap). delta C-13 and delta N-15 values showed a larger terrestrial isospace (134.7 parts per thousand (2)) than the marine isospace (117.2 parts per thousand (2)). The mixing model indicated that detritus(Terrestrial) (median: 30.2%) contributed more to the food web than C-3 plants (0.2%), reflecting high delta C-13(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.