Evaluación del cangrejo fantasma como bioindicador de impacto antropogénico en el litoral costero de Manta, Ecuador de octubre 2021 septiembre 2022.

Abstract

The ghost crab, Ocypode gaudichaudii, has been considered a bioindicator species of anthropogenic impact on sandy beaches, which comprise highly valuable coastal resources in the world and represent a direct relationship between the marine and terrestrial systems. The objective of the present study was to evaluate the changes in the density of the ghost crab as a bioindicator of anthropogenic impact of three beaches of Manta Canton, Manabí, Ecuador; Murciélago (MU), San Lorenzo (SL) and La Tiñosa (TS). Monthly samplings were carried out between Oct. 2021 and Sept. 2022 and in each one two anthropic impact zones were chosen, low (BI) and high (AI) impact. Three transects perpendicular to the coastline were located as replicates in each zone, to count the number of burrows, and the amount of macroplastics (MAP), organic (OM) and inorganic matter (MI), counted in 5 x 3 m cuadrats contiguous, from the place where burrows began to be observed to the place where they disappeared. Ambient and soil temperature at a depth of 10 cm, and the number of people observed at the time burrows was observed in the first half of the year and in the areas with the least anthropogenic of sampling were measured. In each area, samples of sand and pellets derived from crab feeding were collected to observe the presence of microplastics (PM). The results revealed significant differences in the monthly densities for burrows, macroplastics, organic and inorganic matter. The highest density of impact, but only in SL-BI was found an inversely proportional correlation of crab density with the number of people observed (r= -0.6181). The macro plastic and organic matter contaminants were observed in greater density between June and September, coinciding with the highest number of visitors on the beaches. On the other hand, in the BI zone, the number of burrows was significantly higher in SL than in TS and this greater than MU; while in the AI zone, the density of burrows was similar in SL and TS, and these were higher than MU. Regarding the contaminants (MAP, MO, MI), SL showed a higher density than TS and MU, which did not differ from each other, while in AI, SL was similar to TS and these were higher than MU. No significant difference was observed in the MP content in the sand and the pellets in the three beaches, but the MP content in the pellets was 44% lower than in the sand, although a significant correlation was found only in TS (r= 0.65) between the PM content of the pellets and the sand. It was evidenced that natural impacts also directly influenced the density of ghost crabs, such as the limited number of burrows in TS associated with natural morphodynamic changes in the availability of sandy areas. Therefore, anthropic activities (sports, tourism, among others) that take place on the beach can generate the displacement of crabs, which is why O. gaudichaudii is presented as a bioindicator of disturbed environments in these natural systems.