While baseline in nature, this study represents the most detailed arthropod study of Salas y Gómez. At least 15 morphospecies exist on this remote island. Of the 46 individuals collected, two morphospecies (E. atrocincta and L. americana) were identified to species level (Fig. 4). Additionally, the Segestriidae morphospecies (Fig. 3b) is being formally described as a new species (D. Cotoras, pers. comm. 2018). It is likely to be the first endemic arthropod species discovered on Salas y Gómez and may ultimately represent the first terrestrial species of management concern.
For the remaining 12 morphospecies, there were various obstacles in achieving higher taxonomic resolution. For the pseudoscorpion, we collected one tritonymph of the genus Garypus (Fig. 3a). While this also likely represents a new and endemic species (M. Harvey, pers. comm., 2019), examination of adult characters is required to properly identify arachnids to species level. To both confirm whether this is a new endemic species and to formally describe it, we will require additional specimens (i.e., multiple adult males and females). The Staphylinid beetle, Atheta sp. (Fig. 3d), cannot be identified beyond the genus level because Chilean Aleocharinae are presently unidentifiable. Original descriptions of congeners are insufficient to reliably identify the specimen, and aside from a few select genera, no one is actively working on this group (V. Assing, pers. comm. 2019). Regarding the two terrestrial isopod morphospecies (Halophilosciidae? sp. 1 and 2), we suggest these two isopod morphospecies may belong to the genus Littorophiloscia (S. Taiti, pers. com. 2020); however, these specimens will require examination by an isopod systematist to confirm.
As would be expected, avian species richness (i.e., total number of species) increased as additional surveys (i.e., when more time was allocated) were conducted [4,5,6, 12]. Schlatter [12] reported six species based upon brief site visits by naturalists; unfortunately, no survey methods were presented. Today, 16 seabird species are known from the island [6]. The arthropod inventory results presented here were similarly constrained by time. Because the primary objective of the 2016 work was to census seabirds, observers spent only two person hours collecting arthropods. Through this abbreviated effort, at least 15 morphospecies were identified, which stands as a testament to the significance of continuing this work. Importantly, we identified several research questions that should be addressed to best guide future conservation and management efforts.
First, what options exist for expanding this inventory work and/ or developing future arthropod monitoring strategies for Salas y Gómez island? To best capture diversity and identify potential management concern species, a multi-day sampling frame, which employ multiple techniques, is highly recommended. This could be accomplished by focusing future efforts on examining the different habitat types. Harrison and Jehl [4] identified at least five different topographic features on the island (which may serve as a proxy for different habitats); these include (1) the eastern half of the island, which is relatively uniform and flat; (2) a sandy beach on the northeastern extent of the island; (3) steep-sided rocky cliffs to the south rising to ~ 10 m elevation; (4) a sandy depression approximately 70 m in diameter in the west-central section of the island; and, (5) the more rocky western half of the island. We have identified a sixth area, pelagic bird nesting areas, which could reveal unique taxa. Each of these sites likely supports different species. Sampling techniques to consider include conducting timed searches within 1 m2 quadrats and surface pitfall trapping similar to previous work on Rapa Nui [16], which would maximize our ability to best capture diversity, provide a robust sampling frame, and establish a framework for future monitoring efforts. These sampling locations could be marked and revisited should monitoring be required. Alternatively, if an intensive effort cannot be supported in the near future, we recommend CONAF Rapa Nui personnel continue sampling arthropods during their annual pelagic bird censuses. Sampling arthropods annually would require a diminutive time investment for CONAF (i.e., an additional 1 to 2 h per visit to search for and collect arthropods). Elements of the above mentioned sampling design could be incorporated whereby researchers establish a systematic framework for sampling the different habitat types during each visit. Both of these repeatable approaches and the derived data may ultimately be modified to monitor endemic and/or indicator species.
The prevalence of Cryptamorpha desjardinsii should be further examined and potentially monitored by CONAF and SAG. Native to “tropical Asia” [17], this nonnative species is predaceous in its larval stage [18]. As virtually nothing is known concerning the entomofauna of Salas y Gómez island, it is unknown whether this species is competing with and/or predating upon endemic arthropod populations.
Additionally, understanding the relationship between pelagic birds and arthropods could both improve monitoring of avian populations, as well as shed additional light on bird-arthropod phoresy in the South Pacific. Pseudoscorpions have been widely documented using birds for dispersal [19,20,21]. Because nothing is known about pelagic bird phoresy in this part of the South Pacific Ocean, it is possible Garypus sp. (a potentially undescribed species) arrived to Salas y Gómez island via this method. Currently, no pseudoscorpions have been identified on Rapa Nui [22,23,24]. We suggest conducting arthropod surveys (to search for pseudoscorpions) on Motu Nui (a small islet off the southwestern coast) and Rano Raraku crater, the two primary pelagic bird rookeries of Rapa Nui. If present on both islands, this could launch an exciting investigation into another ecological connection between these two geographical regions.
This study represents the small first step toward characterizing the arthropod community of Salas y Gómez. Although Motu Motiro Hiva Marine Park is a protected area, little is known regarding the natural history of the terrestrial fauna – with the exception of avian species. As it is infeasible to manage what is unknown, a future management plan will benefit from a baseline understanding of the terrestrial flora and fauna on the island. We hope this project will serve to inspire future workers to expand upon our efforts and acquire the data necessary to most effectively manage the island’s terrestrial ecosystem. Through such an initiative, researchers will both collect the information necessary to characterize the natural history, as well as contribute to the protection of sensitive natural resources on Salas y Gómez island.