Assessing Water-Saving Technologies and the Impact of Giant Tortoise Herbivory on the Restoration of Opuntia megasperma var. orientalis on Española Island—Galapagos

Abstract

The prickly pear (Opuntia megasperma var. orientalis), a pivotal species for the ecological balance of Española Island in Galapagos, has witnessed a severe decline in its population due to the enduring presence of introduced feral goats over several decades. Additionally, the inherent slow recovery of this species, requiring several years of development, has contributed to its population decline. Several attempts were carried out to restore this species, but they were not successful due to the island’s extreme arid conditions. Subsequently, innovative water-saving technologies were introduced to ensure the survival and growth of the Opuntia species. Two water-saving technologies, Groasis Waterboxx® and Hydrogel, were applied in two distinct treatments, the first involving Waterboxx solely, and the second combining Waterboxx with Hydrogel, alongside a control group. Planting involved two types of cacti: cladodes and seedlings. To safeguard against potential damage from giant tortoises and local birds, protective mesh fencing was installed around the plants. Each monitoring session recorded plant survival and growth, evaluating the impact of water-saving technologies on cactus survival, maximum plant height reached, age at the time of plant death, and growth achieved since planting. Additionally, the study assessed the influence of climate on plant survival and growth. Unfortunately, the employment of protective mesh fences and Waterboxx containers resulted in the unintended loss of specific bird species. Consequently, a decision was taken to remove these protective measures, resulting in a substantial rise in herbivorous activity, and the subsequent mortality of nearly all plants. Our findings underscore the efficacy of water-saving technologies in Opuntia restoration. However, successful application necessitates a better understanding of these technologies within the unique conditions of the island. Future endeavors should focus on refining these techniques to minimize avian mortality while fostering biodiversity and restoring ecological equilibrium.