Horizons Volume 5 Issue 1 Article 25 12-18-2020 Size and Population Dynamics of Native Ghost Crabs, Ocypode spp. In Response to an Invasive Ant Population in a Native Wildlife Refuge, Oʻahu, Hawaiʻi Haley Norma Anne Chasin University of Hawaiʻi at Mānoa Follow this and additional works at: https://kahualike.manoa.hawaii.edu/horizons Part of the Marine Biology Commons Recommended Citation Chasin, Haley Norma Anne (2020) "Size and Population Dynamics of Native Ghost Crabs, Ocypode spp. In Response to an Invasive Ant Population in a Native Wildlife Refuge, Oʻahu, Hawaiʻi," Horizons: Vol. 5 : Iss. 1 , Article 25. Available at: https://kahualike.manoa.hawaii.edu/horizons/vol5/iss1/25 This Article is brought to you for free and open access by Kahualike. It has been accepted for inclusion in Horizons by an authorized editor of Kahualike. For more information, please contact [email protected]. Size and Population Dynamics of Native Ghost Crabs, Ocypode spp., in Response to an Invasive Ant Population in a Native Wildlife Refuge, O‘ahu, Hawai‘i Haley Norma Anne Chasin Biology 400 (Marine Option Program Skill Project) (OPIHI Internship) Mentor: Patrick Nichols, Joanna Philippoff, and Dr. Cynthia Hunter Invasive species are harmful to ocean environments especially fragile ecosystems, like intertidal island environments. Ant populations are among the most aggressive invaders. Ants have been known to cause individual harm to endangered birds, plants and other arthropods in Hawai‘i. The yellow crazy ant (YCA), Anoplolepis gracilipes, is one of the worst invasive ants as it can form supercolonies and spew out formic acid. This study investigates the effect of YCA on the abundance, sizes and distribution of ghost crabs, Ocypode spp., at James Campbell National Wildlife Refuge (JCNWR), a native wildlife restoration area. Ghost crab’s burrows were counted and measured (a proxy for crab size), in order to see if there is a relationship between ghost crab size/number to the density of ants (both invasive YCA and others) present. Ghost crabs are vital to sandy intertidal regions as they are the link to land and water ecosystems and are opportunistic. This study is important because it tell us how the ants are affecting the ghost crab popula- tions and the ecosystem in general. This study can be used in future research to determine conservation techniques in order to control invasive ant populations, like the YCA. traffic from humans and risk of desiccation (Przeslawski 2004; Introduction Nordlund et al. 2014; Pombo et al. 2017). As temperature in- creases or decreases it can have an effect on the embryonic Intertidal zones are areas between the ocean and land ecosys- development which may reflect how a species in the intertidal tems that encompasses a more sensitive to change area com- zone is distributed (Przeslowski 2004). Organisms are affect- pared to other terrestrial environments (Ansari et al. 2014). ed by both abiotic and biotic factors, some of which affect spe- The challenges of the intertidal zone come from its many hard- cies in the intertidal zone more so than others (Brancho et al. ships including, temperature extremes, wave intensity, foot 2010). Sandy intertidal zones are characterized by variations in This has been an amazing opportunity to show how an invasive species changes the ecology of an ecosystem. I learned more about research in the field and learn more about crabs and ants. I also learned how to do better data analysis and come up with my own research question, hypothesis and other scientific method processes. It was a great way to meet new people and develop a network of friends in the community. Thank you to OPIHI (Our Project in Hawaii’s Intertidal) and NSF (Nation- al Science Foundation). Horizons, Vol. 5, 2020, pp. 124–132 Copyright © 2020 by the University of Hawaiʻi at Mānoa 124 Chasin Size & Population Dynamics of Native Ghost Crabs in a Native Wildlife Refuge 125 sand grain size, sun exposure time, differences in the swash densities or supercolonies causing ‘invasional meltdowns’ of spe- zone width, temperature variations and inter/external species cies in the area (Abbott 2005). There are about 45 different ant interactions (Zardi et al. 2007; Przesclowski 2004). In the san- species in Hawaiʻi all of which are non-native and invasive with dy intertidal zone species like the ghost crab (Ocypode spp.) are about half found in urban, agricultural and natural environments affected by wind and human traffic as well as the other factors (Reimer 2004; Kirschenbaum 2007). The invasive ant species, mentioned, which may reflect fragility in their species which Anoplolepis gracilipes or the yellow crazy ant, originated from West could allow for better management tactics as well (Chan et al. Africa, India or China. They are found mostly in tropical, moist 2006; Brancho et al. 2010). lowlands environments but not found in areas above 1200m or Included in the biotic factors, is organismal competition in arid environments. A. gracilipes has been known to have affects which may dictate the spatial distribution of the intertidal zone on nesting birds and native invertebrates in Seychelles as well as (Connell and Gillanders 2007; Nordlund et al. 2014). For the endemic crabs found on Christmas Island, Australia (Wetterer genus, Ocypode, some spatial distributions are based on gender 2005). A. gracilipes forms a mosaic of high-density supercolonies differences, where the males are found in the upper intertid- that can last for more than 24 hours a day, year-round as well as al/dry areas and females/juveniles are found in the vegeta- their ability to spit out formic acid into the eyes or weak areas of tion zone (Fellows 1975), though some indicate that juveniles birds and crabs (Abbott 2005; Gül 2017). On Christmas Island are found more towards the wet swash zone due to desicca- they have had the ability to kill the native red land crabs within tion awareness, which may be an indication of differences in 24 hours (Abbott 2005), which makes YCA a substantial threat burrow diameters as adult males tend to leave behind larger to native Hawaiian crabs. burrows (Chan et al. 2006). It may also indicate gender-based Ocypode spp. is an ecologically important part of the sandy pyramidal formation, an important sign of colony formation intertidal food webs. They are highly mobile and feed on a variety where males build burrows with pyramid-like sand pellet be- of foods which making them an important balance in the food hind them, in order to attract females (Trott 1998; Fellows web ecosystem. Ocypode spp. are also a key link between inland 1975). Lighter (1977) describes how Ocypode used all three ecosystems and the marine environment as they are the predator/ kinds of spatial dispersal patterns, randomness, aggregation prey item for higher level consumers like birds, as well as some and uniformity based on sex and crowding distances. He used of their food is obtained through terrestrial resources (Rae et al. a similar method to this study to characterize the sizes of crabs, 2019). Ghost crabs are also an important part of bioindication of by measuring their hole diameter (Lighter 1977; Pombo et al. oil spills and other such chemical contamination (Ghost Crabs . 2007). Species distribution and spatial variation can change unknown copy-right date). Hawai‘i has two ghost crab species, based on different biotic and abiotic factors and can be based Ocypode ceratophthalmus (horn-eyed ghost crab) and Ocypode lae- on species interactions as well (Brancho et al. 2010). vis or Ocypode pallidula (pallid ghost crab), The horn-eyed ghost Species interactions can be beneficial, harmful, or neither crab is found all over the world whereas the pallid ghost crab is (Connell and Gillanders 2007). Sometimes species that are found on different islands throughout the pacific (Lighter 1977). more dominant ‘take-over’ or invade an area. If invaders are un- Invasive species have become one of the causes for the 91 manageable, they can compromise the spatial distribution and/ (54%) extinctions of the 680 extinct species around the world or densities of Ocypode, interfering with their natural processes of which 34 (20%) of the extinctions, invasive species were the (Bergstrom et al. 2009; Dejean et al. 2010). Due to the fragil- only cause of extinction (Clavero and Garcia-Berthou 2005). ity of island-like environments, allowing many generations for Many species have become introduced, since the first arrival species to evolve and co-exist together, invasive species are a of humans over 1,000 years ago and many have also become detriment to these environments, like in Hawaiʻi (Reimer 2004; extinct including the important land-dwelling crab, Geoprapsus Bergstrom et al. 2009). This phenomenon threatens Hawaiian severnsi, once common on the Hawaiian islands. The loss of the ecosystems as there are 30% endangered and rare species and land-dwelling crab allowed for there to be an ecological imbal- more than 1000 native Hawaiian species already extinct (Al- ance, that was once harmonious, in an ecosystem (Gonzaga len 2000). Therefore, it is vital that conservation efforts go into 2011). This emphasizes the importance of understanding inva- place in order to protect the remaining species present. sive species ecology as ecosystems do not want to allow more Many ant species including Solenopsis invicta (Red Fire Ant), species to go extinct as well as disrupt the normal harmony of Linepithema humile (Argentina Ant), Pheidole megacephala (Big the ecosystem present. The effect of invasive species could influ- Headed Ant), Wasmannia auropunctata (Electric Ant) and Ano- ence the environment and species around them in the refuge. plolepis gracilipes (Yellow Crazy Ant), which have been known to Therefore, this study was focused on James Campbell cause detrimental ecological effects around the world (Wetterer National Wildlife Refuge (JCNWR) where a restoration of four 2005; Invasive ants .