Cave shrimps of the Typhlatya genus are common and widespread in fresh, brackish and marine groundwater throughout the Yucatan Peninsula (Mexico). These species are ideal models to test niche partitioning within sympatric species in oligotrophic systems. Nevertheless, their food sources remain unidentified, and despite their frequency and functional importance, distribution and abundance patterns of these species within caves have not been fully recognized. Here, we describe the abundance of three Typhlatya species in different temporal and spatial scales, investigate changes in water conditions, and potential sources of carbon as an indication of food origin. Species composition and abundance varied markedly in space and time revealing patterns that differed from one system to another and in relation to environmental parameters. Isotope analysis showed that each species reflects a particular δ 13 C and Δ 14 C fingerprint, suggesting they feed in different proportions from the available carbon sources. Overall, our findings suggest a niche partitioning of habitat and feeding sources amongst the three Typhlatya species investigated, where environmental characteristics and physiological differences could play an important role governing their distribution patterns.

New records of 14 stygobiont crustacean species pertaining to six Malacostraca orders from 32 cenotes are presented, with their associated caves of the state of Yucatan, Mexico, together with an individual account for each species. Species composition of most of the investigated cenotes is examined for the first time. A thermosbaenacean and two amphipod species were not formally recorded to the cenote ecosystems of the state of Yucatan prior to our research. Distribution data of a cirolanid isopod previously known only from its type locality is also provided. Barcodes of mitochondrial cytochrome c oxidase subunit I for the reported peracarid species previously lacking this information have been included in present study as tools for species identification and a baseline of further molecular genetic analyses.

Editorial on the Research TopicThe effects of environmental change on anchialine ecosystems Anchialine ecosystems comprise interconnected groundwater habitats at the land-sea aquatic continuum within karstic and volcanic geological settings. Here, crevicular and cavernous environments are flooded by the subterranean estuary, the region of coastal aquifers where seawater and terrestrial-borne freshwaters mix (Moore, 1999), creating globally dispersed habitats for characteristic aquatic fauna with subterranean adaptations (Bishop et al., 2015;van Hengstum et al., 2019). These cave-adapted organisms are primarily invertebrates, often endemic, with metabolic, physiologic, and morphologic adaptations that allow them to thrive in dark and energy-limited environments. Historically, these habitats have been considered particularly stable environments (e.g., Sket, 1996). However, there is growing evidence that the functioning of anchialine ecosystems is greatly influenced by external meteorological, hydrological, and oceanic conditions that closely link them with adjacent terrestrial and marine habitats (e.g., Brankovits et al., 2018;Tamalavage et al., 2018). For all these reasons, anchialine ecosystems may be more susceptible to short-and long-term effects of environmental change than previously thought.Organic matter availability is pivotal to the functioning of freshwater, estuarine, or marine habitats, because it regulates microbial community structure and dissolved oxygen concentrations in the water column and the sediments (e.g., Howarth et al., 2011). Anchialine ecosystems are typically oligotrophic environments with low dissolved oxygen content and, therefore, they can easily transition into anoxic eutrophic habitats when organic matter inputs increase from either terrestrial or marine sources (e.g., at sinkholes, cenotes, or other cave openings) (Pohlman, 2011). The inputs, composition, and bioavailability of organic matter are sensitive to changes in nearby surface habitats, human activities and pressures, tidal fluctuations, seasonal changes in precipitation, andFrontiers in Marine Science frontiersin.org 01

The Yucatán Peninsula, Mexico is a carbonate platform well-known for extensive karst networks of densely stratified aquifer ecosystems. This aquifer supports diverse anchialine fauna, including species of the globally distributed anchialine shrimp genus Typhlatya (Atyidae). Four species (T. campecheae, T. pearsei, T. dzilamensis and T. mitchelli) are endemic to the Peninsula, of which three are federally listed in Mexico. This first integrative evaluation (i.e., molecular, morphological, broad geographic and type locality sampling, and environmental data) of Yucatán Typhlatya reveals considerable species identity conflict in prior phylogenetic assessments, broad species ranges, syntopy within cave systems and five genetic lineages (of which two are new to science). Despite sampling from the type locality of endangered T. campecheae, specimens (and molecular data) were indistinguishable from vulnerable T. pearsei. Ancestral/divergence reconstructions support convergent evolution of a low-salinity ancestor for a post-Paleogene arc Yucatán + Cuba Typhlatya clade within the anchialine Atyidae clade. A secondary adaptation for the coastal-restricted euryhaline (2–37 psu), Typhlatya dzilamensis (unknown conservation status) was identified, while remaining species lineages were low-salinity (< 5 psu) adapted and found within the meteoric lens of inland and coastal caves. This study demonstrates the need for integrative/interdisciplinary approaches when conducting biodiversity assessments in complex and poorly studied aquifers.

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