General Information

Habitat Requirements

Procaris hawaiana occupies anchialine pools, which are defined as a body of water with mixed salinity within a geological formation (coastal lava flows or limestone exposures) that exposes the underlying water table (Hiromasa-Browning et al. 2019, p. 4). These include typical small bodies of water such as water in lava fields, tubes, cracks, and under rock overhangs, and open wells, and may occur singly or in groups (Maciolek and Brock 1974, entire). Pools display tidal dampening with some pools only having water at high tide. These pools have subterranean connections to the groundwater and ocean but have no regular surface connection to the sea (Holthuis 1973, p. 3; Sakihara 2012, pp. 83-84). Water chemistry is highly variable with salinities ranging from zero to 41 parts per thousand (ppt) and surface temperatures ranging from 17 to 36 °C (Yamamoto et al. 2015, entire; Hiromasa-Browning 2019, p. 4). Hypogeal shrimp are usually found in waters with salinities between 2 and 30 ppt and temperatures between 22 and 30 °C (Wiegner et al. 2006, p. 29). While some species of anchialine shrimp may not be able to tolerate low salinity (Maciolek 1983, p. 611-612), Procaris hawaiana has never been found in pools with salinities below 10 ppt, despite the accessibility of fresher waters at their habitat sites. Therefore, salinity is likely a strong driver of P. hawaiana’s distribution and may be central to their occurrences in particular pools and/or geographic areas (Maciolek 1983, pp. 611-612; Brock 2004, pp. 6, 31-32). Pool volume also appears to be linked with P. hawaiana distribution. For example, at Manukā the distribution of P. hawaiana was negatively correlated with pool volume. Sakihara (2012, pp. 89-90) suggested that this might be attributable to P. hawaiana’s elusive behavior and constant movement throughout the interstitial habitat.

Food Habits

Based on limited field studies and observations of captive individuals, Procaris hawaiana is known to be a filter feeder, using setae covered appendages to trap plankton and other food particles as they swim through the water column (USFWS 2008, entire; Yamamoto et al. 2015, p. 35). While extensive studies on the feeding behavior of P. hawaiana are lacking, the endemic P. hawaiana has also been observed feeding on moribund shrimp in a laboratory setting (Holthuis 1973, pp. 12-19; Maciolek 1983, p. 612). Although the closely related Procaris ascensionis, found in anchialine pools on Ascension Island in the South Atlantic Ocean, has been observed feeding on amphipods and other small shrimp (Abele and Felgenhauer 1985, pp. 20-24), Procaris hawaiana lacks conspicuous claws or chelipeds and has poorly developed eyes, which supports the idea that these shrimp are not specialized hunters but rather opportunistic predators. Still, it is likely that the Halocaridina shrimp, as well as amphipods, still may serve as a significant food source to P. hawaiana (Chan 1995, p. 11). If P. hawaiana does rely on the shrimp Halocaridina rubra as a consistent food source, the depletion of H. rubra populations due to over-harvesting as part of the aquarium trade may have cascading trophic consequences on P. hawaiana.

Movement / Home Range

Procaris hawaiana was first discovered at Lua O Palahemo during a survey by Maciolek and Brock in 1974. three individuals were discovered at Manuka during a 1989-1992 survey (Chan 1995, p.3). The area was not surveyed again until 2004 during which time the species was observed but no population size was recorded (Brock 2004, p.28). Eventually through more widespread surveys, Procaris hawaiana was documented within 24 anchialine pools within the Manuka watershed, which is located in south Kona on the island of Hawaii. Nineteen of these pools are located within the Manuka NAR, which encompasses an area of 25,500 acres. The remaining five pools are located on unencumbered state land that is adjacent to the NAR boundary(Conry 2012, in litt). Procaris hawaiana was only observed twice within a single pool at Kaloko-Honokohau, once on 9/12/2016 and again on 9/27/2016 (USFWS 2019, in litt). Ahihi-Kinau is the location where P. hawaiana was initially discovered during a 1973 survey by Holthuis (1973, pp. 12-19). During that survey, at least two individuals were found (Holthuis 1973, pp. 12-19). A survey of the area from 1979-1980 only mentions that they observed P. hawaiana but did not specify abundance (Maciolek 1980, p. 124). However, Maciolek (1983, pp. 607-614) mentioned that out of the four documented species of anchialine shrimp found at Ahihi-Kinau, P. hawaiana was the least common. Finally, a re-survey of the area in 1986, again did not specify abundance but did identify the pools in which P. hawaiana was found. Maciolek (1986, p. 121) found two pool groups occupied by P. hawaiana which were less than 1 km (0.62 miles) apart; however, because there were at least seven pools or groups of pools between these that were unoccupied by P. hawaiana, this suggests two separate populations of P. hawaiana at Ahihi-Kinau. Of the 700 known anchialine pools in the State of Hawaii, Procaris hawaiana has only been documented in two pools at Ahihi-Kinau NAR (formerly referred to as Cape Kinau) on Maui island (Holthuis 1973, entire; Maciolek 1983, entire; USFWS 1998, 2003, entire) and in 26 pools on the island of Hawaii (1 at Lua O Palahemo, 24 at Manuka, and 1 at Kaloko-Honokohau National Historical Park on the island of Hawaii) (Maciolek and Brock 1974, entire; Chan 1995, entire; Brock 2004, p. 28; Sakihara 2009, entire). The most recent surveys at Lua O Palahemo for Procaris hawaiana was from 2012 where 7 individuals were observed (Wada 2012, in litt). Similarly, in 2009-2010, 8 individuals were observed (Wada 2010, in litt) (Population Unit A). No numbers like the >1,000 recorded by Kensley and Williams (1986, p. 418) have been documented since their survey. This pool has been recorded as undergoing natural senescence (Wada 2010, in litt; Brock 2012, in litt). Additionally, while Lua O Palahemo is only 9.3 miles (15 km) away from Manuka (Chan 1995, p. 11), the Manuka watershed is not directly connected to Lua O Palahemo (Fransen et al. 2013, p. 630). Since 2004, the anchialine pools at Manuka have been formally surveyed twice more, once from 2008-2009 and another from 2009-2010. During the 2008-2009 survey, no population size was recorded but Procaris hawaiana was observed in four different pools (Sakihara 2009, p. 4). Then during the 2009-2010 survey by Conry (2012, in litt), again no specific population size was recorded, but 19 pools within the NAR were found to contain P. hawaiana and 5 pools located on unencumbered State land adjacent to the coastal NAR boundary was also found to contain P. hawaiana. In 2016, P. hawaiana was observed but no numbers were recorded (Shizuma et al. 2016, p. 33). The sighting at Kaloko-Honokohau is one of the most recent documented observations of Procaris hawaiana. However, after P. hawaiana was sighted in September 2016, the species has not been observed since then despite quarterly water quality monitoring (USFWS 2019, in litt).

Reproductive Strategy

Little is known of either the reproductive biology or ontogeny of the genus Procaris and even less is known about Procaris hawaiana. Maciolek (1983, p. 613) suggested that based on the absence of egg bearing females in the epigeal portion of the anchialine pool, Procaris hawaiana likely restricts their reproduction to the interstices of the water table. However, nothing is known about the larval stages. Females of the closely related P. ascensionis have been documented carrying up to 60 large bright orange eggs (Felgenhauer et al. 1988, p. 334). While the large eggs suggest the existence of a zoeal larval stage (usually meant for planktonic dispersal) (Felgenhauer et al. 1988, p.334), no studies on Procaris dispersal have been done.

Other

Procaris hawaiana (Holthuis 1973, pp. 12-19) is an anchialine pool shrimp that is endemic to the Hawaiian Islands. These shrimp are a part of the Procarididae family, which was once thought to be a superfamily within the infraorder Caridea, and only includes one other genus, Vetericaris (Kensley and Williams 1986, p. 428; Fransen et al. 2013, p. 625). The genus Procaris has a global distribution and includes at least five known species, including P. hawaiana (Bruse and Davie 2006, pp. 23-24).