THE EFFECTS OF INTRODUCED FISH SPECIES ON THE ENDEMIC SHRIMP OF ANCHIALINE PONDS Meredith F. Acly Senior Thesis Department of Marine Science University of Hawaii at Hilo May 6,2003 Advisors: Dr. Karla McDermid and Dr. Cedric Muir Abstract Anchialine ponds, or tidally influenced coastal ponds, are common along the coasts of Hawai 'i Island. yet rare worldwide. The endemic species Halocaridina ruhra (Red Pond Shrimp) when in high abundance, can create red carpets along the bottom of anchialine ponds. Unfortunately, many ponds contain introduced species of fish which reduce or displace native shrimp populations. Of the estimated 650 anchialine ponds on Hawai'i Island, 300 were surveyed in this study. Forty-three percent of the ponds no longer contain evident shrimp populations. Twelve ponds were visited monthly from August 2002 to April 2003 to measure shrimp density, and physical parameters in the presence and absence of Poecilia reticulata (Trinidadian Guppy), an introduced fish. Shrimp densities in the presence of fish were significantly lower. In the presence of fish, various unusual behaviors were observed such asshrimp present only in cracks or crevices at pond edges. The rate and frequency of subterranean shrimp migration between ponds due to introduced fish or natural behaviors is unknown. The study included preliminary work to extract, amplify. and sequence DNA from individuals living in different ponds. By comparing the frequency of alleles in different ponds one can assess the degree to which gene flow (migration) occurs between these ponds. Introduction The island of Hawai'i, like all Hawaiian Islands, faces extinction of native species and damaged ecosystems due to habitat loss and the introduction of exotic species. Exotic species introduced into Hawaiian ecosystems typically lack natural predators, resulting in fast-growing populations existing alongside and out-competing native species. These processes have occurred on land and in nearshore habitats, resulting in an extinction of numerous plant and animal species. One ecosystem in particular, anchialine ponds, though common around the island of Hawai'i, is rare worldwide. Characterized as land-locked brackish water pools, this distinctive habitat does not have surface connections to ocean water, but connects directly to the sub-surface water table, which controls daily tidal fluctuations in the ponds (Brock, 1985). Anchialine ponds are most common throughout the newer lava flows of the Kona coast on Hawai'i and Maui Islands, as well as a bomb crater on Kaho'olawe, a lake on Moloka'i, and in limestone formations on O'ahu (Bailey-Brock and Brock, 1993). Over the last twenty years, the loss of suitable anchialine pond habitat has totaled more than 95%, making the habitat one of the rarest in the country (Brock, personal communication, 2001). The most common source of degradation has been the introduction of alien fish species, mainly Oreochromis mossnmbicus (Tilapia), and various types of topminnows including Gambusia affinis (Mosquito Fish), Poecilia reticulata (Trinidadian Guppy), and Poecilia mexicana (Shortfin Molly). Intentional introduction of an exotic fish may be for its later harvest as fish bait, insect control, or food; accidental introductions can occur when one pond in a system is intentionally stocked and the introduced species colonizes other ponds (Brock, 1985). Once topminnows have been introduced into one anchialine pond, fish eventually migrate to ponds in close proximity, traveling through porous basalt walls separating pond clusters (Chai, personal communication, 2002). Other sources of degradation include human use and impact. Construction of resorts and small industrial developments along popular coastal stretches has already caused an unknown quantity of ponds to be filled in. At least 130 ponds were destroyed in 1985, during the construction of the Waikoloa Resort Village (Brock et al., 1987). Resorts have also increased human accessibility to some ponds. resulting in decreased pond water quality or the further destruction of ponds. Ponds have become bathtubs or trash receptacles, and most are impacted by fertilizers and chemicals washed down from golf courses, malls, and homes. Over time pond awareness has increased, and now all coastal development near anchialine pools must now include detailed pool inventories and management plans (Chai, 1993). Numerous ponds have been surveyed on land and using aerial photography, and between 600 and 650 were been counted (Brock, 1985). The estimate is conservative, as there may be hundreds of ponds on the island undetectable from the air, or completely unknown to scientists. Exact numbers of ,. anchialine ponds and their health status is crucial information in the preservation of this native habitat. Among many unique flora and fauna, Hawai'i's anchialine ponds are home to endemic shrimp species, the two most common being Halocaridina rubra (Family Atyidae) or Opae 'ula and Metabetaeus lohena (Family Alpheidae). The shrimp are hypogeal, meaning that they utilize both the pond habitat as well as subterranean rock interstices linking ponds to the underIying water table. Many of the shrimp display a tidally linked migration, emerging and returning to rock interstices with the incoming and ebbing tide (Brock, 1985). Shrimp have been recorded with higher abundances during night hours versus daylight hours, indicating a definite preference for nocturnal activity (Chai, 1993). H. rubra is characterized as a small, red L herbivorous shrimp commonly seen grazing along the algal substrate of the ponds. The larger M. Iohena reaches lengths of approximately 16 mm, about twice the size of H. rubra, and is most often observed hunting H. rubra (Banner and Banner, 1960). Typically M. Iohena and H. rubra exist in a 1 :100 ratio. * No native fish are known to successfully reproduce in anchialine ponds (Brock, 1992) but in recent years, it is suspected that the total number of anchialine ponds containing reproducing introduced fish species has increased. The actual effect introduced fish have on anchialine shrimp is only hypothesized, but many believe fish prey upon native shrimp. Studies have indicated lower or absent populations of shrimp exist when introduced fish are present (Brock, 1985; Chai, 1993). In order to return native ponds back to anchialine species, information on the total numbers of anchialine ponds containing alien fish must be determined, and data on how these fish affect shrimp distribution and abundance is needed. Few ponds have been observed where shrimp and introduced fish co-exist, but Brock (1 985) calculated shrimp to inhabit 18% of the ponds containing introduced fish in the one study. In the absence of herbivorous H. rubra, ponds are overgrown by algae which has the potential to fill in ponds (Brock, 1992). Ponds over run by introduced fish can be chemically treated to destroy introduced fish and restore the habitat. In one treatment of rotenone, shrimp returned to the fish-free ponds (pers. obs., 2002), thus exhibiting their hypogeal nature. It is unknown to what extent shrimp move freely between undisturbed ponds and locations. Morphological differences in cheliped shape, spination, length of pereopod joints, and rostrum length (Bailey-Brock and Brock, 1993) have been noted between samples of H. rubra raising the question of possible genetic differences between anchialine pond populations. To date, published work on anchialine ponds and shrimp have been general surveys of the physical and chemical aspects of ponds (Aquatic Resources Management and Consulting, 1994, 1995; Brock, 1985; Brock, 1985; Brock et al., 1987), and the description and classification of the known endemic shrimp species (Bailey-Brock and Brock, 1993; Banner and Banner, 1960; Couret and Wong, 1978; Holthius, 1973; Kensley and Williams, 1986) Methods Thirteen anchialine ponds located along the Kona coast of the island of Hawai'i (Figure I) were visited from July, 2002 to April, 2003. Temperature, salinity, dissolved oxygen, and shrimp density were recorded at each visit. Three ponds at each of the sites, Kaloko-Honokohau National Historical Park (KAHO), Four Seasons Resort, Waikoloa Resort Village (Waikoloa Anchialine Pond Preservation Area (WAPPA)), and four ponds at Makalawena Beach were included in this study. Physical parameters were measured using a YSI Model 85, which tests temperature, salinity, and dissolved oxygen. Measurements were taken at the bottom of the pond, or if the pond is deep, at five meters depth which is the length of the YSI cable. Shrimp density was taken using a 10 X 10 cm quadrat placed randomly around the circumference of each pond. The edges of the pond were tested to prevent destruction of fragile algae often growing throughout -. _. the center of the ponds. At each pond, five density counts were taken: the number of shrimp inside each quadrat during the span of one minute. The five counts were averaged on each sampled day and used in comparisons between ponds. Shrimp density at Makalawena Beach was estimated by counting visible shrimp around the entire circumference of the pond. The circumerference is defined in this study as the perimeter into one half meter of the pond. This - --- area of each pond at Makalawena Beach was measured, and shrimp density was calculated to shrimp/m2. Shrimp densities at all other locations were extrapolated from 10 x 10 cm quadrat counts to shrimp/m2 densities. Pond across the island were located using a previous aerial survey (Biological Database, -- 1987). Latitude, longitude, and estimated position error of each pond were recorded using a Gamin eTrex Legend handheld GPS. Temperature, salinity, and dissolved oxygen were taken - using a YSI, and species present were noted. All surveying was performed during daylight hours. Tidal delay for anchialine ponds was approximated using data from one pond in Hilo. A PVC pipe with marked intervals was placed standing up in the middle of the pond at the time of high tide. The still rising water was observed until it began to fall, and the difference between coastal high tide and the pond's high tide (tidal delay) was used in later analysis.