Anchialine Habitats Research Articles

Phytoplankton in the Anchialine Habitat of Red Shrimp (Parhippolyte uveae) at Mangrove Ecosystem Waters

The anchialine habitat waters of this study is located at mangrove ecosystem around Koguna Beach area, Buton Island, Indonesia. It is a closed water, isolated from the sea, and inhabited by Parhippolyte uveae red shrimp. The existence of phytoplankton in this habitat can be used to determine the availability of natural food and the water quality of this shrimp’s habitat. This study was conducted to examine the presence of phytoplankton in the anchialine habitat of red shrimp. Phytoplankton samples were obtained by filtering water using Plankton Net. Meanwhile, several biological indexes such as the diversity index, evenness index, and dominance index were used to analyze the phytoplankton community. The result showed that this habitat was dominated by phytoplankton from the classes Bacillariophyceae, Florideophyceae, and Globothalamea with a total of 13 genera in September 2021 and Bacillariophyceae, Cyanophyceae, Dinophyceae, and Globothalamea with a total of 18 genera in December 2021. The most common type of phytoplankton found in the red shrimp habitat during the study was Navicula sp. with a ban of 1436 cells L-1 and 479 cells L-1 in September 2021 and December 2021, respectively. The diversity index of phytoplankton in this habitat was low, meanwhile, the index of evenness and dominance indicated that this habitat was of good quality (evenness index was high and dominance index was low). This study can be used as a basic information for further research on the management control for this species habitat.

Anchialine pool shrimp (Halocaridina rubra) as an indicator of sewage in coastal groundwater ecosystems on the island of Hawai'i.

Groundwater is a primary pathway for wastewater and other pollutants to enter coastal ecosystems worldwide. Sewage associated pathogens, pharmaceuticals, and other emerging contaminants pose potential risks to marine life and human health. Anchialine pool ecosystems and the endemic species they support are at risk and provide an opportunity to sample for presence of contaminants prior to diffusion in the marine environment. In this study, we tested the potential use of nitrogen isotopes in the tissues of a dominant anchialine pool grazing shrimp (Halocaridina rubra), as a bioindicator for sewage in groundwater flowing through their habitats. Water quality parameters and shrimp tissue isotopes (N and C) were collected from pools exposed to a range of sewage contamination along the West Hawai'i coastal corridor from 2015 to 2017. Data were used to test for spatial and temporal variability both within and among pools and to examine the relationship between stable isotopes and water quality parameters. Within 22 pools, mean δ15N from whole tissue samples ranged between 2.74‰ and 22.46‰. Variability of isotope values was low within individual pools and within pool clusters. However, δ15N differed significantly between areas and indicated that sewage is entering groundwater in some of the sampled locations. The significant positive relationship between δ15N and dissolved nitrogen (p<0.001, R2 = 0.84) and δ15N and phosphorus (p<0.001, R2 = 0.9) support this conclusion. In a mesocosm experiment, the nitrogen half-life for H. rubra tissue was estimated to be 20.4 days, demonstrating that the grazer provides a time-integrative sample compared to grab-sample measurements of dissolved nutrients. Ubiquitous grazers such as H. rubra may prove a useful and cost-effective method for δ15N detection of sewage in conjunction with standard monitoring methods, enabling sampling of a large number of pools to establish and refine monitoring programs, especially because anchialine habitats typically support no macroalgae.

South(East) by Southwest: Identification of a New Halocaridina rubra Holthuis, 1963 (Decapoda: Atyidae) Genetic Group From O‘ahu, Hawai‘i

The anchialine ecosystem, comprised of coastal landlocked habitats containing brackish water, experiences tidal fluctuations due to simultaneous underground connections with the sea and terrestrial aquifer system. Anthropogenic impacts have led to substantial habitat degradation and loss, potentially making the anchialine ecosystem and its biota one of Hawai‘i’s most threatened. Prior analyses of mitochondrial (mtDNA) cytochrome oxidase subunit I (COI) sequences from the Hawaiian anchialine atyid shrimp Halocaridina rubra revealed a potential cryptic species complex with strong regional endemism. This study hypothesized that a Halocaridina population discovered in 2018 in southeast O‘ahu, an area with no historically documented anchialine habitats but where a specimen was collected in 1998, represents a unique lineage or genetic group endemic to the region. Comparison of newly generated mtDNA COI sequences to previous ones identified the population as belonging to the South O‘ahu lineage of Halocaridina. However, fixed mutations and significant genetic differentiation distinguish it from the closely related ‘Ewa genetic group of southwest O‘ahu. Given this, we propose the new Maunalua genetic group for Halocaridina from southeast O‘ahu, with an apparent split between groups occurring at approximately the Holocene-Pleistocene Epoch boundary, corresponding well to the geological age of where the new population was discovered. Notably, the 1998 specimen shared the same distinctive coloration as the Maunalua and ‘Ewa genetic groups, implying inclusion within the South O‘ahu lineage. Conservation efforts should consider the currently recognized 15 Halocaridina genetic groups since they represent unique units from all others in both their genetics and geographic distribution.

Primary Microbial Succession in the Anchialine Ecosystem

When new land is created, initial microbial colonization lays the foundation for further ecological succession of plant and animal communities. Primary microbial succession of new aquatic habitats formed during volcanic activity has received little attention. The anchialine ecosystem, which includes coastal ponds in young lava flows, offers an opportunity to examine this process. Here, we characterized microbial communities of anchialine habitats in Hawaii that were created during volcanic eruptions in 2018. Benthic samples from three habitats were collected ∼2 years after their formation and at later time points spanning ∼1 year. Sequence profiling (16S and 18S) of prokaryotic and eukaryotic communities was used to test whether communities were similar to those from older, established anchialine habitats, and if community structure changed over time. Results show that microbial communities from the new habitats were unlike any from established anchialine microbial communities, having higher proportions of Planctomycetota and Chloroflexi but lower proportions of green algae. Each new habitat also harbored its own unique community relative to other habitats. While community composition in each habitat underwent statistically significant changes over time, they remained distinctive from established anchialine habitats. New habitats also had highly elevated temperatures compared to other habitats. These results suggest that idiosyncratic microbial consortia form during early succession of Hawaiian anchialine habitats. Future monitoring will reveal whether the early communities described here remain stable after temperatures decline and macro-organisms become more abundant, or if microbial communities will continue to change and eventually resemble those of established habitats. This work is a key first step in examining primary volcanic succession in aquatic habitats and suggests young anchialine habitats may warrant special conservation status.

New arietellid copepods (Calanoida, Arietellidae) from anchialine caves in the Eastern Adriatic Sea.

Two new species of calanoid copepods are described; Metacalanus adriaticus sp. nov. from an anchialine cave on Vis Island, and Paramisophria tvrtkovici sp. nov. from Orljak Cave, located in the lower part of River Krka estuary, near the town of Šibenik (Croatia). This is the first report of arietellid copepods found in any anchialine cave along the coast of the Adriatic Sea. In M. adriaticus sp. nov. the antennules are asymmetrical in both sexes (the female left antennule is 18-segmented, right 20-segmented; male left 16-segmented and right 20-segmented); the uniramous fifth legs of the female are 2-segmented; the terminal segment of the fifth leg in both sexes is the longest; and in the male the fifth leg exopod is 2-segmented. In P. tvrtkovici sp. nov. the antennules of both sexes are asymmetrical with the left antennule longer than the right, the female antennule is 21-segmented on both sides; the male left antennule is 19-segmented, the right 21-segmented; the armature of the terminal exopod segment of leg 1 is II, 2 ,2; the male fifth legs have a rudimentary endopod on the left leg, the third exopodal segment is smallest and bears three unequal processes on its outer margin, and the terminal spine is completely separated from the segment. On the right leg the third segment carries two short, unequal processes on its outer distal margin, as well as a long sigmoidal spine which is fused to the segment. It is inferred that, after the last glaciation, these new Arietellids moved out from their southern Adriatic refuge, colonizing first the anchialine habitats of the outer eastern Adriatic islands and then spreading along the coast.

Disparate responses to salinity across species and organizational levels in anchialine shrimps.

Environmentally induced plasticity in gene expression is one of the underlying mechanisms of adaptation to habitats with variable environments. For example, euryhaline crustaceans show predictable changes in the expression of ion-transporter genes during salinity transfers, although studies have typically been limited to specific genes, taxa and ecosystems of interest. Here, we investigated responses to salinity change at multiple organizational levels in five species of shrimp representing at least three independent invasions of the anchialine ecosystem, defined as habitats with marine and freshwater influences with spatial and temporal fluctuations in salinity. Although all five species were generally strong osmoregulators, salinity-induced changes in gill physiology and gene expression were highly species specific. While some species exhibited patterns similar to those of previously studied euryhaline crustaceans, instances of distinct and atypical patterns were recovered from closely related species. Species-specific patterns were found when examining: (1) numbers and identities of differentially expressed genes, (2) salinity-induced expression of genes predicted a priori to play a role in osmoregulation, and (3) salinity-induced expression of orthologs shared among all species. Notably, ion transport genes were unchanged in the atyid Halocaridina rubra while genes normally associated with vision and light perception were among those most highly upregulated. Potential reasons for species-specific patterns are discussed, including variation among anchialine habitats in salinity regimes and divergent evolution in anchialine taxa. Underexplored mechanisms of osmoregulation in crustaceans revealed here by the application of transcriptomic approaches to ecologically and taxonomically understudied systems are also explored.

Comparing the community structure of Bacteria and micro-Eukarya from the Hawaiian anchialine ecosystem during wet and dry seasons

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 82:87-104 (2018) - DOI: https://doi.org/10.3354/ame01884 Comparing the community structure of Bacteria and micro-Eukarya from the Hawaiian anchialine ecosystem during wet and dry seasons Stephanie K. Hoffman1,*, Kiley W. Seitz1,2, Justin C. Havird1,3, David A. Weese1,4, Scott R. Santos1 1Department of Biological Sciences and Molette Laboratory for Climate Change and Environmental Studies, Auburn University, Auburn, Alabama 36849, USA 2Marine Science Institute, University of Texas at Austin, Port Aransas, Texas 78373, USA 3Department of Biology, Colorado State University, Fort Collins, Colorado 80523, USA 4Department of Biological and Environmental Sciences, Georgia College & State University, Milledgeville, Georgia 31061, USA *Corresponding author: ski0003@auburn.edu ABSTRACT: The anchialine ecosystem, defined as tidally influenced, nearshore bodies of water with subterranean freshwater and seawater connections, has been relatively unstudied regarding its microbial communities. Notably, anchialine habitats of the Hawaiian Archipelago, specifically the Cape Kinau (Maui) and Kona (Hawaii) regions, can possess distinctive, laminated orange cyanobacterial-bacterial crusts found nowhere else worldwide. However, nearly nothing is known about the degree to which seasonal fluctuations in water chemistry might influence shifts in their community composition. To test the hypothesis that taxonomic diversity and relative sequence abundance exhibit dynamics correlating to particular seasonal environmental factors, benthic and water column microbial communities from 6 habitats in these 2 geographical regions were examined during 2 wet and 2 dry seasons via high-throughput sequencing of hypervariable V6 (Bacteria-specific) and V9 (micro-Eukarya-biased) regions from rRNA genes. Although significant seasonal variation occurred in water chemistry characteristics such as salinity, ammonium, dissolved organic carbon, total dissolved nitrogen, and nitrite + nitrate during the same period, overall benthic and water column microbial community structure instead correlated with spatial factors such as latitude and annual rainfall. Despite this, approximately half of the identified third-level clades (i.e. approximately class-level nomenclatures) within these communities exhibited variation in relative sequence abundances between wet and dry seasons. Furthermore, relative abundance changes for approximately three-quarters of these clades correlated with at least one seasonally varying factor. Thus, while microbial communities in the Hawaiian anchialine ecosystem did not show stable composition year-round, overall community structure correlated more strongly with the spatial, rather than temporal, context of any given habitat. KEY WORDS: Illumina amplicon sequencing · Microbial diversity · Seasonal variation · Sediment · V6 hypervariable region 16S rRNA gene · V9 hypervariable region 18S rRNA gene · Water Full text in pdf format Supplementary material PreviousNextCite this article as: Hoffman SK, Seitz KW, Havird JC, Weese DA, Santos SR (2018) Comparing the community structure of Bacteria and micro-Eukarya from the Hawaiian anchialine ecosystem during wet and dry seasons. Aquat Microb Ecol 82:87-104. https://doi.org/10.3354/ame01884 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 82, No. 1. Online publication date: September 20, 2018 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2018 Inter-Research.

Global correlates of diversity in aquatic subterranean fauna

Subterranean aquatic systems are island-like habitats spread all over the world consisting of many caves linked by a common geological history but displaying different ecological parameters (e.g. distance to the sea, topography, depth). Therefore, they comprise numerous, discrete, and varied entities that facilitate independent colonization events by epigean biota, providing many replicates of comparable evolutionary processes. The data produced over the past 100 years of research collectively indicates that subterranean aquatic systems harbor a high percentage of local endemism and disharmonic animal communities when comparing them to surrounding epigean environments. However, it remains unclear whether those are general trends, or whether confounding effects such as sampling bias may produce misleading results. We investigate these two problems by analyzing a global dataset of ca. 50,000 records for ca. 4,000 species in 2,000 caves with two goals. We search for global correlates of diversity in cave aquatic animals by testing the effect of ecological and geological parameters on the number of species, species composition and functional diversity in each cave and subterranean system; We account for the influence of sampling intensity on the analyses by including the number of samples and number of published papers explicitly in the analyses. We search for global correlates of diversity in cave aquatic animals by testing the effect of ecological and geological parameters on the number of species, species composition and functional diversity in each cave and subterranean system; We account for the influence of sampling intensity on the analyses by including the number of samples and number of published papers explicitly in the analyses. The highest species diversity was found in the Caribbean and Mediterranean basins: two areas with many caves covering a wide range of ecological conditions, as both basins include marine, anchialine and freshwater subterranean habitats. However, the number of papers per area explained a high proportion of the variation observed of our data, with a taxonomical bias favoring crustaceans. Our results indicate that sampling bias should be carefully considered when drawing conclusions from large-scale analyses, and that we still need further sampling, especially in groups different to crustaceans, to better understand the generality of the processes driving global patterns in subterranean biodiversity.

First record of a sea spider (Pycnogonida) from an anchialine habitat

The anchialine fauna from the Yucatan Peninsula has been extensively studied since the 1980´s. “Sea spiders” or Pycnogonida, have never been found in these systems before. A record for Anoplodactylus batangensis (Helfer, 1938) from a cenote (sinkhole) in the Yucatan Peninsula, Mexico is presented herein. The pycnogonid was found in waters of the cenote Nohoch Nah Chich, part of the Sac Actun anchialine system, in the State of Quintana Roo. This species was already reported from the northeastern shore of the Yucatan Peninsula, however the record we present herein constitutes the first time a pycnogonid is reported from an anchialine habitat. A brief description of the female A. batangensis is presented for the first time.

Mitochondrial OXPHOS genes provides insights into genetics basis of hypoxia adaptation in anchialine cave shrimps.

Cave shrimps from the genera Typhlatya, Stygiocaris and Typhlopatsa (TST complex) comprises twenty cave-adapted taxa, which mainly occur in the anchialine environment. Anchialine habitats may undergo drastic environmental fluctuations, including spatial and temporal changes in salinity, temperature, and dissolved oxygen content. Previous studies of crustaceans from anchialine caves suggest that they have possessed morphological, behavioral, and physiological adaptations to cope with the extreme conditions, similar to other cave-dwelling crustaceans. However, the genetic basis has not been thoroughly explored in crustaceans from anchialine habitats, which can experience hypoxic regimes. To test whether the TST shrimp-complex hypoxia adaptations matched adaptive evolution of mitochondrial OXPHOS genes. The 13 OXPHOS genes from mitochondrial genomes of 98 shrimps and 1 outgroup were examined. For each of these genes was investigated and compared to orthologous sequences using both gene (i.e. branch-site and Datamonkey) and protein (i.e. TreeSAAP) level approaches. Positive selection was detected in 11 of the 13 candidate genes, and the radical amino acid changes sites scattered throughout the entire TST complex phylogeny. Additionally, a series of parallel/convergent amino acid substitutions were identified in mitochondrial OXPHOS genes of TST complex shrimps, which reflect functional convergence or similar genetic mechanisms of cave adaptation. The extensive occurrence of positive selection is suggestive of their essential role in adaptation to hypoxic anchialine environment, and further implying that TST complex shrimps might have acquired a finely capacity for energy metabolism. These results provided some new insights into the genetic basis of anchialine hypoxia adaptation.

Diversity and the environmental drivers of spatial variation in Bacteria and micro-Eukarya communities from the Hawaiian anchialine ecosystem

Little is currently known regarding microbial community structure, and the environmental factors influencing it, within the anchialine ecosystem, defined as near-shore, land-locked water bodies with subsurface connections to the ocean and groundwater aquifer. The Hawaiian Archipelago is home to numerous anchialine habitats, with some on the islands of Maui and Hawaii harboring unique, laminated orange cyanobacterial–bacterial crusts that independently assembled in relatively young basalt fields. Here, benthic and water column bacterial and micro-eukaryotic communities from nine anchialine habitats on Oahu, Maui, and Hawaii were surveyed using high-throughput amplicon sequencing of the V6 (Bacteria-specific) and V9 (Eukarya-biased) hypervariable regions of the 16S- and 18S-rDNA genes, respectively. While benthic communities from habitats with cyanobacterial–bacterial crusts were more similar to each other than to ones lacking it on the same island, each habitat had distinct benthic and water column microbial communities. Analyses of the survey data in the context of environmental factors identified salinity, site, aquifer, and watershed as having the highest explanatory power for the observed variation in microbial diversity and community structure, with lesser drivers being annual rainfall, longitude, ammonium, and dissolved organic carbon. Our results epitomize the abiotic and biotic uniqueness characteristic of individual habitats comprising the Hawaiian anchialine ecosystem.

Reproduction and development in Halocaridina rubra Holthuis, 1963 (Crustacea: Atyidae) clarifies larval ecology in the Hawaiian anchialine ecosystem.

Larvae in aquatic habitats often develop in environments different from those they inhabit as adults. Shrimp in the Atyidae exemplify this trend, as larvae of many species require salt or brackish water for development, while adults are freshwater-adapted. An exception within the Atyidae family is the "anchialine clade," which are euryhaline as adults and endemic to habitats with subterranean fresh and marine water influences. Although the Hawaiian anchialine atyid Halocaridina rubra is a strong osmoregulator, its larvae have never been observed in nature. Moreover, larval development in anchialine species is poorly studied. Here, reproductive trends in laboratory colonies over a 5-y period are presented from seven genetic lineages and one mixed population of H. rubra; larval survivorship under varying salinities is also discussed. The presence and number of larvae differed significantly among lineages, with the mixed population being the most prolific. Statistical differences in reproduction attributable to seasonality also were identified. Larval survivorship was lowest (12% settlement rate) at a salinity approaching fresh water and significantly higher in brackish and seawater (88% and 72%, respectively). Correlated with this finding, identifiable gills capable of ion transport did not develop until metamorphosis into juveniles. Thus, early life stages of H. rubra are apparently excluded from surface waters, which are characterized by lower and fluctuating salinities. Instead, these stages are restricted to the subterranean (where there is higher and more stable salinity) portion of Hawaii's anchialine habitats due to their inability to tolerate low salinities. Taken together, these data contribute to the understudied area of larval ecology in the anchialine ecosystem.

Genetic lineage and environmental conditions as drivers of chromatosome variation in the anchialine shrimp Halocaridina rubra Holthuis, 1963 (Caridea: Atyidae)

Color variation among and within crustacean species is primarily due to morphological and physiological differences in specialized cells called chromatophores. Within Atyidae, individuals of Halocaridina rubra Holthuis, 1963, which is endemic to anchialine habitats (coastal ponds of mixohaline water under marine and terrestrial influences) of the Hawaiian Islands, range from bright red to nearly translucent in color. While H. rubra encompasses (at least) eight genetically diverged lineages based on analyses of mitochondrial genes, whether this phenotypic variation in coloration correlates to genetic background or if it statistically differs between lineages is unknown. Furthermore, if such properties in H. rubra exhibit plasticity under the environmental extremes that can be encountered in anchialine habitats has not been determined. Using previously published protocols for another atyid species, chromatosomal morphology and chromatic properties were quantified and statistically analyzed from 240 individuals of H. rubra, representing seven of the eight genetic lineages as well as one naturally mixed population (n=30 per group), maintained under standardized laboratory conditions for >6 years. Analogous analyses were also conducted on animals before and after exposure to environmental extremes, including anoxia, desiccation, decreased salinity and high and low temperatures. Overall, the genetic lineages of H. rubra statistically differed from one another in varying numbers of chromatosomal properties while exposure to environmental extremes also elicited significant changes. Furthermore, these properties statistically differed among body parts of H. rubra in a manner inconsistent with previous studies. Notably, data on chromosomal properties generated via a streamlined protocol were well correlated with those from the previously published approach utilized here, suggesting such analyses for H. rubra (or other crustacean/atyid species) might be successfully conducted under field settings.

Taking their breath away: Metabolic responses to low-oxygen levels in anchialine shrimps (Crustacea: Atyidae and Alpheidae)

Crustaceans generally act as oxy-regulators, maintaining constant oxygen uptake as oxygen partial pressures decrease, but when a critical low level is reached, ventilation and aerobic metabolism shut down. Cave-adapted animals, including crustaceans, often show a reduced metabolic rate possibly owing in part to the hypoxic nature of such environments. However, metabolic rates have not been thoroughly explored in crustaceans from anchialine habitats (coastal ponds and caves), which can experience variable oxygenic regimes. Here, an atypical oxy-conforming pattern of oxygen uptake is reported in the Hawaiian anchialine atyid Halocaridina rubra, along with other unusual metabolic characteristics. Ventilatory rates are near-maximal in normoxia and did not increase appreciably as PO2 declined, resulting in a decline in VO2 during progressive hypoxia. Halocaridina rubra maintained in anoxic waters survived for seven days (the duration of the experiment) with no measureable oxygen uptake, suggesting a reliance on anaerobic metabolism. Supporting this, lactate dehydrogenase activity was high, even in normoxia, and oxygen debts were quickly repaid by an unusually extreme increase in oxygen uptake upon exposure to normoxia. In contrast, four related anchialine shrimp species from the Ryukyu Islands, Japan, exhibited physiological properties consistent with previously studied crustaceans. The unusual respiratory patterns found in H. rubra are discussed in the context of a trade-off in gill morphology for osmoregulatory ion transport vs. diffusion of respiratory gasses. Future focus on anchialine species may offer novel insight into the diversity of metabolic responses to hypoxia and other physiological challenges experienced by crustaceans.

Anchialine crustaceans (Crustacea: Decapoda) from Siquijor Island, Philippines

Crustaceans occurring in the anchialine ponds of Siquijor Island are reported for the first time. The crustacean fauna in anchialine habitats consist of two species of shrimps and four species of crabs. Physico-chemical parameters measured in situ during the survey show typical characteristics of tropical anchialine habitats, i.e., subsurface temperatures ranged from 25°C to 29.6°C (mean ± standard deviation, throughout = 28.26 ± 1.87°C); pH of about 7.0; low dissolved oxygen (DO) level from 4.5 mg/L to 6.63 mg/L (5.93 ± 0.87 mg/L); and higher salinity in an open anchialine pool (21.7‰, Cambakjaw) than in anchialine caves, from 5.5‰ to 13.3‰ (12.18 ± 6.21‰). Degradation of anchialine habitats were observed as a result of agriculture run-off, human utilization (e.g., bathing and laundry) and, in one case, introduction of Tilapia Oreochromis niloticus.

Osmoregulation in the Hawaiian anchialine shrimp Halocaridina rubra (Crustacea: Atyidae): expression of ion transporters, mitochondria-rich cell proliferation and hemolymph osmolality during salinity transfers.

Studies of euryhaline crustaceans have identified conserved osmoregulatory adaptions allowing hyper-osmoregulation in dilute waters. However, previous studies have mainly examined decapod brachyurans with marine ancestries inhabiting estuaries or tidal creeks on a seasonal basis. Here, we describe osmoregulation in the atyid Halocaridina rubra, an endemic Hawaiian shrimp of freshwater ancestry from the islands' anchialine ecosystem (coastal ponds with subsurface freshwater and seawater connections) that encounters near-continuous spatial and temporal salinity changes. Given this, survival and osmoregulatory responses were examined over a wide salinity range. In the laboratory, H. rubra tolerated salinities of ~0-56‰, acting as both a hyper- and hypo-osmoregulator and maintaining a maximum osmotic gradient of ~868 mOsm kg(-1) H2O in freshwater. Furthermore, hemolymph osmolality was more stable during salinity transfers relative to other crustaceans. Silver nitrate and vital mitochondria-rich cell staining suggest all gills are osmoregulatory, with a large proportion of each individual gill functioning in ion transport (including when H. rubra acts as an osmoconformer in seawater). Additionally, expression of ion transporters and supporting enzymes that typically undergo upregulation during salinity transfer in osmoregulatory gills (i.e. Na(+)/K(+)-ATPase, carbonic anhydrase, Na(+)/K(+)/2Cl(-) cotransporter, V-type H(+)-ATPase and arginine kinase) were generally unaltered in H. rubra during similar transfers. These results suggest H. rubra (and possibly other anchialine species) maintains high, constitutive levels of gene expression and ion transport capability in the gills as a means of potentially coping with the fluctuating salinities that are encountered in anchialine habitats. Thus, anchialine taxa represent an interesting avenue for future physiological research.

Invasive fishes in the Hawaiian anchialine ecosystem: investigating potential predator avoidance by endemic organisms

Globally, introductions of alien species are increasingly common, with invasive predators potentially having detrimental effects via predation on native species. However, native prey may avoid predation by adopting new behaviors. To determine whether invasive fish populations consume endemic shrimp in invaded Hawaiian anchialine habitats or if adopted patterns of diel migration prevents predation as previously hypothesized, a total of 183 invasive poeciliids (158 Gambusia affinis and 25 Poecilia reticulata) were collected for gut content analyses from four anchialine sites during wet and dry seasons on the islands of Hawai'i and Maui. Predation on shrimp was not detected in habitats where they retreat exclusively into the underlying aquifer diurnally and only emerge nocturnally. However, low levels of predation were detected (7/65 fishes, only by Gambu- sia affinis) at Waianapanapa Cave, Maui, where shrimp retreat into both the aquifer and a cave during the day. Thus, adopted behavioral responses to invasive fishes generally, though not universally, prevent predation on endemic Hawaiian anchialine shrimps. However, non-consumptive effects resulting from behavioral modification of shrimps may have appreciable impacts on the Hawaiian anchialine ecosystem and warrant further study.

A Diel Comparison of the Unique Faunal Assemblage in Remote Anchialine Pools on Hawai‘i Island

Anchialine pools, which are defined as land-locked mixohaline pools with tidal influence, are unique and increasingly rare habitats in the Hawaiian Islands. Particularly, anchialine pools in Manukā on the island of Hawai‘i are home to a diverse, rare, and unique assemblage of decapod crustaceans. Diurnal and nocturnal surveys of motile aquatic species were conducted across 81 anchialine habitats in the Manukā watershed to perform diel comparisons of species assemblages, richness, abundances, distributions, and hydrography. Nocturnal surveys revealed significant increases in abundances, distributions, and species richness throughout Manukā's anchialine habitats. Of particular interest are six native anchialine decapods, Halocaridina rubra, Metabetaeus lohena, Calliasmata pholidota, Antecaridina lauensis, Procaris hawaiana, and Palaemonella burnsi, that exhibited notable diel patterns in abundance and distribution. In addition, a recent new record of a caridean shrimp and two unidentified species were documented. Factors influenced by diel period (i.e., behavior of introduced predators and sun exposure) and various hydrographic and habitat characteristics were suspected to affect patterns in the biological parameters that were measured. The addition of nocturnal surveys can provide valuable biological information to anchialine habitat resource management that would not have been obtained with diurnal surveys alone.

The Long and Short of It: Genetic Variation and Population Structure of the Anchialine Atyid Shrimp Caridina rubella on Miyako-jima, Japan

One of the most threatened ecosystems on many islands may be anchialine habitats, or coastal land-locked water bodies with no surface connection to the sea yet containing brackish water that fluctuates with the tides. To better manage these habitats, it is important to develop a broader understanding of the biodiversity within them since such knowledge plays critical roles in establishing conservation strategies. In this study, the genetic variation and population structure of an anchialine atyid shrimp, Caridina rubella Fujino and Shokita, 1975 was investigated in the Southern Ryukyu Archipelago, Japan. Given a planktotrophic larval stage and its potential amphidromous life cycle, populations of C. rubella on the island of Miyako-jima (to which it is apparently restricted) were hypothesized to have little to no structure across the island. To test this, 61 individuals were collected from four anchialine caves and sequence variation examined at the cytochrome c oxidase subunit I (COI) region of the mitochondrial DNA (mtDNA). Surprisingly, significant genetic structure was exhibited across distances ranging from 10 km. Additionally, deep (∼17% p-distance) genetic divergence correlating with distinct variation in rostrum lengths was found between closely situated, but more-or-less completely isolated, populations. This implies “C. rubella ”m ay actually represent two distinct species on Miyako-jima. Given that this atyid is already listed as a threatened species by the Japanese government, the results presented here are useful in the formulation and implementation of future conservation plans for populations of C. rubella on Miyako-jima.

Void development on carbonate coasts: creation of anchialine habitats

Anchialine caves in coastal locations develop in two ways: by pseudokarst processes that form talus caves, sea caves, tafoni, fissure caves and lava tubes, and by karst dissolutional processes that form stream caves, flank margin caves, and blue holes. Pseudokarst caves are of minor importance in anchialine cave habitat development, with some lava tubes being notable exceptions. Dissolution caves provide the most extensive, variable, and long-term environments for anchialine habitats. The Carbonate Island Karst Model (CIKM) allows dissolutional cave development in carbonate coasts to be understood as the interplay between freshwater and marine water mixing, sea-level change, rock maturity, and interaction with adjacent non-carbonate rocks. Glacioeustatic sea-level changes of the Quaternary have moved all coastal anchialine cave environments repeatedly through a vertical range of over 100 m, and modern anchialine environments could not develop at their current elevations until ~4,000 years ago when sea level reached its present position. Blue holes form by a variety of mechanisms, but the most common is upward stoping and collapse from deep dissolutional voids. As a result, they provide vertical connection between different levels of horizontal cave development produced by a variety of earlier sea-level positions. Blue holes are overprinted by successive sea-level fluctuations; each sea-level event adds complexity to the habitats within blue holes and the cave systems they connect. Blue holes can reach depths below the deepest glacioeustatic sea-level lowstand, and thereby provide a refugia for anchialine species when cave passages above are drained by Quaternary sea-level fall. Blue holes represent the most significant anchialine cave environment in the world, and may provide clues to anchialine cave species colonization and speciation events.