Cobble Substrate Research Articles

Habitat-specific effects of interstitial space between stream substrate particles on the colonization of aquatic organisms

We examined the effects of interstitial space between stream substrate particles on the colonization of aquatic organisms using three types of substrates (gravel, a cobble, and a cobble on gravel) in a riffle and pool of a temperate stream. Significantly greater abundance, wet weight, diversity (H′), taxonomic richness, and evenness of aquatic organisms were found in the riffle than in the pool, and the interstitial space substrate (i.e., a cobble on gravel) had significantly greater abundance, wet weight, and taxonomic richness of aquatic organisms than did the cobble substrate. Of the 13 families observed in the experiments, larval net-spinning caddisfly (Hydropsychidae) dominated the riffle in terms of the abundance and wet weight; chironomid larvae dominated both the riffle and the pool in terms of abundance. Simple main effect tests indicated significant effects of substrate on the abundance and wet weight of larval caddisfly in the riffle, and post hoc tests on substrate in each habitat indicated that the abundance and wet weight of larval caddisfly on interstitial space substrate were significantly greater than those on cobble substrate in the riffle. Our results suggest the importance of interstitial space between stream substrates in riffles to ensure higher colonization rates of aquatic organisms such as larval net-spinning caddisflies characterized as filter feeders.

Effects of Substrate on Movement Patterns and Behavior of Stream Fish through Culverts: An Experimental Approach

Culverts can provide a significant barrier to fish passage by fragmenting fish habitats and impeding the passage success of small-bodied fish. Geographical connectivity is critical to the maintenance of diverse fish assemblages. Culverts with high cross-sectional velocity can cause population fragmentation by impeding passage of small, freshwater fish. Behavioral responses of small fish to high velocities can differ among functional groups, and swimming behavior of many species is not well known. We tested effects of substrate type on swimming behavior in two small, freshwater fish species—southern leatherside chub (Lepidomeda aliciae, a midwater species), and longnose dace (Rhinichthys cataractae, a benthic species)—across three substrate treatments: (1) a bare flume, (2) large flow obstacles, and (3) a natural cobble substrate. Both longnose dace and southern leatherside chub used paths of low velocity and swam in the near-substrate boundary area. Fish in the bare flume and large obstacle treatments swam along the corners of the flume in a straight swim path, whereas fish in the natural substrate treatment used all parts of the flume bed. There was no relationship between passage success of fish and substrate type, fish species, or their interaction. In contrast, substrate type, fish species, and their interaction were significant predictors of passage time. Southern leatherside chub passed through the test section about two to four times faster than longnose dace. Both species took longer to pass through the large flow obstacle treatment compared to the bare flume or natural substrate. The natural substrate created a complex velocity profile with areas of low velocity throughout the entire flume, in contrast to the other two treatments. Our data suggest natural substrates can improve the passage of small fish in high-velocity culverts for both benthic and midwater functional groups.

Characteristics of a Naturalized Kokanee Salmon Oncorhynchus nerka Population in Atypical Habitat

Kokanee salmon are a dwarf freshwater form of the anadromous sockeye salmon (Oncorhynchus nerka) native to the Pacific coast of North America and Asia and widely introduced in western North America as a sport and prey fish. Few kokanee salmon introductions have succeeded in eastern North America. A naturalized population of kokanee salmon has persisted for over 50 yr in Florence Lake, Wisconsin, an unlikely location given its relatively small size (21.4 ha), shallow maximum depth (7.6 m), low elevation (381 m), and southerly latitude (45.12°N). Kokanee salmon completed their entire life cycle within the lake and rarely entered an accessible coldwater inlet stream. Spawning occurred during late October and early November along the lake shoreline. Spawning redds with defending males were observed in 1–2 m of water on sand/gravel/ cobble substrate. Kokanee salmon growth in the lake was relatively rapid, and fish had a mean total length of 117 mm after their first growing season (age 0+), 212 mm after their second (age 1+), begin to mature and spawn after their third (age 2+) at 317 mm for females and 324 mm for males, and were at 344 mm for females and 354 mm for males after their fourth (age 3+). Few fish reproduced at age 4+. Despite limited oxy-thermal habitat during summer, kokanee salmon appear to thrive in Florence Lake, perhaps because of cold inflows from the inlet and springs within the lake.

Changes in the distribution of Michigan crayfishes and the influence of invasive rusty crayfish (Faxonius rusticus) on native crayfish substrate associations

Invasive crayfishes have a strong negative effect on multiple trophic levels, including other crayfishes. However, documentation of the spread of non-native crayfish species and their impact on native crayfishes could be improved, particularly over large spatial scales in stream ecosystems. We collected crayfish and quantified habitat at 461 stream sites throughout Michigan in 2014–2016 and compared our collections to a historical account of crayfish collections published in 1975. Our objectives were to: (1) quantify the change in non-native rusty crayfish (Faxonius rusticus) and native species distributions from 1975 to 2014–2016; (2) quantify how rusty crayfish affect the habitat associations of native species in Michigan streams; and (3) determine the effectiveness of dipnets, our primary sampling method. We found all species in more watersheds compared to 1975, likely due in part to increased sampling. However, we found rusty crayfish in 22 more HUC-8 watersheds than in 1975, a larger increase than all other species. Habitat associations of native species also shift in the presence of rusty crayfish. In instances where native species co-occurred with rusty crayfish, most obligate aquatic native species were found in less-preferred habitat such as sand or macrophytes compared to cobble substrate when the species is in isolation. Our results indicate a broad range expansion by rusty crayfish over the last 40 years, suggesting that surveys of crayfish diversity and habitat occupancy should be more routine to inform management of native crayfish species.

Efficiency of Sampling Sunfishes Using Snorkeling in Clear, Warm-Water Streams of the South-Central United States

AbstractThe continued evaluation of fish-sampling gears and methods is essential to identify their applicability across environmental conditions and among species. Although limited by visibility, snorkeling has potential advantages relative to other fish-sampling gears in wadeable streams (e.g., minimally intrusive, cost effective, and appropriate in deeper areas). Clear water is common to warm-water streams; however, the use of snorkeling for monitoring stream-fish populations has largely focused on cold-water systems. To assess relative snorkeling efficiency in warm-water streams, we compared standardized single-pass snorkel counts to tow-barge electrofishing abundance estimates for six sunfishes (Centrarchidae) in the Ozark Highlands ecoregion of northwest Oklahoma and southwest Missouri under relatively similar environmental conditions (i.e., clear water, cobble substrates, low-flow conditions). Snorkeling efficiency was variable among sunfishes and consistently low for species with cryptic traits and habitat use. We also did not detect cryptic sunfishes (i.e., a single individual was not encountered) using snorkeling at multiple stream reaches where estimated abundance was > 50 within a 0.5- to 1.0-km stream reach. Our findings indicate that snorkeling has applications for monitoring sunfish populations and assemblages when using an abundance estimator or accounting for imperfect detection; however, it is inappropriate for estimating population size of cryptic sunfishes. We encourage continued research into the applicability of snorkeling to estimate warm-water stream fish abundance.

Lake sturgeon (Acipenser fulvescens) spawning habitat: a quantitative review

The loss of spawning habitat has been identified as a limiting factor to population growth for lake sturgeon, Acipenser fulvescens, the most widely distributed species of the family in North America. While local information exists about lake sturgeon spawning habitat, a synthesis of all available data is needed across its range. Our study used meta-analytical techniques to describe the mean and range of critical spawning habitat characteristics based on data from 48 sites across all major watersheds in which lake sturgeon are found. Data were compiled into univariate habitat suitability indices to describe the spawning niche. Results indicate that peak suitability occurred at depth-averaged velocities of 0.6 m·s−1, depths of 0.55–0.85 m in small rivers (<100 m3·s−1 annual average discharge) and 0.75–5.25 m in large rivers (>100 m3·s−1), over cobble substrates (64–256 mm), and that suitable water temperatures decreased with increasing latitude. This study provides a comprehensive review of critical spawning criteria from which future habitat suitability models can be adapted.

Life history and habitat preference in the Darling hardyhead, Craterocephalus amniculus (Teleostei, Atherinidae) in the northern Murray‐Darling Basin, Australia

AbstractThe Darling hardyhead, Craterocephalus amniculus (Atherinidae), is a threatened fish species inhabiting upstream reaches of a number of northern Murray‐Darling Basin catchments. Little is known of its life history. Our goal was to determine patterns of seasonal size structure, interannual and spatial variation in diet, and habitat selection in this species across multiple sites and years in the upper Macintyre River, northern New South Wales. Preserved specimens from a separate study were used to obtain information on diet and size structure. Size structures suggested a single annual spawning season in late September or early October. Diets varied significantly, both between years at the downstream site and among the three sites although the underlying cause of this was untested. Dietary diversity increased with distance downstream. At the two upstream sites, aquatic invertebrates made up most of the diet while over half the gut contents at the downstream site was unidentified detritus. Preference was shown for pool habitats with a sand or cobble substrate, increased channel depth and width and distance from the bank, and reduced flow velocity. Overhanging exotic riparian vegetation and in‐stream woody debris were non‐preferred. This species may be vulnerable to further population decline in light of its restricted habitat preferences and narrow spawning season. However, comparable data from nearby catchments will be necessary to ascertain the species’ conservation status across its broader distribution.

Substrate preferences of coexisting invasive amphipods, Dikerogammarus villosus and Dikerogammarus haemobaphes, under field and laboratory conditions

Two Ponto-Caspian amphipods, Dikerogammarus villosus and Dikerogammarus haemobaphes, have expanded their geographical ranges from eastern Europe into Great Britain in recent years. This study represents one of the first examining the distribution and habitat preferences of coexisting populations of D. haemobaphes and D. villosus via field and laboratory experiments in the UK. Field surveys of a recently invaded lowland reservoir in the UK are complimented with ex situ laboratory mesocosm experiments examining the substrate preferences of coexisting populations of D. villosus and D. haemobaphes. Results from the field study indicated that D. haemobaphes dominated the macroinvertebrate community within the reservoir and demonstrated a strong affinity for large cobble and artificial substrates. D. villosus occurred at lower abundances but displayed a strong preference for coarse cobble substrates. A third invasive amphipod, Crangonyx pseudogracilis, was largely confined to sand/silt habitats. Laboratory mesocosm experiments clearly supported the field observations of D. villosus and D. haemobaphes with both species demonstrating a preference for cobble substrates. Results from the study highlight the importance of characterising physical habitat when investigating biological invasions and suggest that habitat availability may influence the extent and speed at which range expansion of new amphipod invaders occurs.

Distribution and habitat associations of the California moray (Gymnothorax mordax) within Two Harbors, Santa Catalina Island, California

While kelp forests are some of the best-surveyed ecosystems in California, information on cryptic inhabitants and their role within the community are lacking. Kelp itself provides overall structure to the habitat; however the rocky reef to which the kelp attaches is known to provide additional structure for cryptic species. Gymnothorax mordax, the California moray, is an elusive predatory species that is considered abundant in the waters around Catalina Island. However, no life history data exists for this species. We examined habitat composition, relative abundance, size pattern distributions, and biomass of G. mordax within Two Harbors, Catalina Island. Habitats were sampled using a combination of baited trap collection and transect surveys using SCUBA. A total of 462 G. mordax were captured, primarily in shallow (< 10 m) waters. Individuals of G. mordax were associated with mostly boulder and cobble substrates. Measurements of relative abundance and density indicate that G. mordax is more prevalent than reported in previous studies. We also discovered that the 6 trapping sites from which all morays were collected, differed in size structuring and density while the relatively high biomass did not change across sites. In general, southern facing sites exhibited higher densities of morays, while northern facing sites showed more size structuring. We show how the structural complexity of the rocky reef habitat in an already diverse kelp forest ecosystem, can support a high biomass of a cryptic elongate predatory fish.

Evidence for Substrate Influence on Artificial Substrate Invertebrate Communities.

Cobble baskets are frequently used as a tool to measure differences in benthic macroinvertebrate communities between waterbodies; however, underlying differences in substrate type may influence the resultant colonization of baskets, misrepresenting communities. This study tests the hypothesis that cobble basket placement influences the resulting benthic macroinvertebrate community. Cobble basket arrays (n = 4) were deployed in Dog Lake, Saskatchewan, in 2011 (97 d) and 2012 (95 d) on cobble habitats and soft or sandy substrates ∼100 m apart. Baskets placed on cobble substrate had significantly higher Shannon-Weaver diversity relative to those placed on soft substrate in both years, and higher % EPT (Ephemeroptera Plecoptera Trichoptera) in 2011, but total density was not significantly different. Nonmetric multidimensional scaling revealed that the community was different between both treatments, characterized by higher densities of Gammarus lacustris Sars in baskets placed on soft sediment in both years, higher densities of Aeshna sp. and Mystacides sp. on cobble substrate in 2011, and higher densities of Helobdella stagnalis (L.) and Glossophinia complanata (L.) on cobble substrate in 2012. The results were consistent with the hypothesis that baskets placed on cobble substrate versus soft substrate will result in differing community colonization. The resulting recommendation for monitoring and assessment using cobble baskets in lakes is that baskets be placed on comparable substrate type when comparing between lakes, and that cobble beds be chosen as a more appropriate substrate for deployment, as the added habitat complexity of baskets on soft sediment may act as an attractant and not reflect the true community composition of that habitat.

Conspecific tolerance and heterospecific competition as mechanisms for overcoming resistance to invasion by an intertidal crab

The success of the invasive Asian shore crab, Hemigrapsus sanguineus, stems partly from its ability to exclude established crab species from preferred rocky and cobble intertidal habitat. Here, we assessed preference and competition for habitat types (cobble vs. sand) for H. sanguineus and two competitor species; the previous invasive green crab, Carcinus maenas, and the native rock crab, Cancer irroratus, in New England. In simple laboratory experiments, we paired similarly sized heterospecifics and conspecifics from each species, and also grouped combinations of C. maenas and H. sanguineus in a series of four-individual sets in order to dissect the outcome of intra- and inter-specific competition at different densities. Individually, all three species preferred cobble substrate. With paired conspecifics, H. sanguineus individuals would cohabitate in cobble, whereas C. maenas and C. irroratus individuals each excluded conspecifics from cobble. In heterospecific pairs, H. sanguineus excluded both C. maenas and C. irroratus from cobble. C. maenas and C. irroratus, were equally likely to exclude the other species, but rarely excluded H. sanguineus. In larger assemblages, H. sanguineus preferentially grouped under cobble, whereas C. maenas were more evenly distributed among habitat types. These observations demonstrate that conspecific tolerance and heterospecific competition can be effective, complementary mechanisms for overcoming invasion resistance. Such mechanisms help explain the well-studied success of H. sanguineus following its introduction into New England coastal habitats, and the resulting exclusion of preexisting crab species.

Short-term colonization dynamics of macroinvertebrates in restored channelized streams

Macroinvertebrate colonization of restored rivers is a function of dispersal into the restored reach and its suitability for population establishment. To maximize potential for colonization success, spatial considerations such as distance to colonizer source pools and dispersal pathways must be included in restoration planning. Unfortunately, the dispersal abilities of macroinvertebrates and ecological importance of different dispersal modes for colonization are still poorly understood. We used a field experiment that controlled colonization by passive drift and allowed distinction between active upstream aquatic and active/passive aerial dispersal, thus testing their differential importance during colonization of experimentally restored stream reaches. Two agricultural streams emanating below culverts were longitudinally separated along the first 30 m and one stream side each was covered with a fine-mesh net to limit aerial dispersal. Colonization of manually disturbed background and experimentally introduced cobble substrate was investigated over 6 months. We found that upstream in-stream dispersal, especially in these agricultural streams, can be rapid (days) and play an important role in the short-term colonization of restored streams. We conclude that a landscape perspective, in addition to in-stream measures, must be considered when attempting to restore streams dominated by agricultural and urban land use that constrains available species pools and limits dispersal pathways.

Habitat Preferences and Distribution of the Freshwater Shrimps of the Genus Caridina (Crustacea: Decapoda: Atyidae) in Lake Lindu, Sulawesi, Indonesia

The objectives of this study were to reveal ecological preferences and distribution of all species of Caridina found in Lake Lindu and their catchment area. Specimens from 39 sampling sites were caught using tray net and hand net. There are three species of Caridina found in the lake system, i.e. Caridina linduensis, Caridina kaili and Caridina dali. There is no overlapping distribution among the species. Caridina kaili is a true riverine species and it is never encountered sympatric with C. dali nor C. linduensis. This species is abundant in streams and ditches with moderate flow running water and gravel–cobble substrate. It is mainly spread within streams west to the lake. Both C. dali and C. linduensis can be found in the lake and streams with very slow current to almost stagnant water, muddy sand substrate and associated with roots of water plants and leaf litter. However, C. dali is never occurred together with C. linduensis and they are less abundant compare to C. kaili. Distribution of Caridina spp. in Lake Lindu is probably affected by the temperature of their habitats and the occurrence of introduced fish such as Mozambique tilapia (Oreochromis mossambicus), common carp (Cyprinus carpio), and an alien riceland prawn (Macrobrachium lanchesteri). These introduced and alien species can have the potency to become predators or competitors for the Caridina spp. It is also the first record for M. lanchesteri present in Lake Lindu.

Patch occupancy of stream fauna across a land cover gradient in the southern Appalachians, USA

We modeled patch occupancy to examine factors that best predicted the prevalence of four functionally important focal stream consumers (Tal- laperla spp., Cambarus spp., Pleurocera proxima, and Cottus bairdi) among 37 reaches within the Little Tennessee River basin of the southern Appalachian Mountains, USA. We compared 34 models of patch occupancy to examine the association of catchment and reach scale factors that varied as a result of converting forest to agricultural or urban land use. Occupancy of our taxa was linked to parameters reflecting both catchment and reach extent character- istics. At the catchment level, forest cover or its conversion to agriculture was a major determinant of occupancy for all four taxa. Patch occupancies of Tallaperla, Cambarus, and C. bairdi were positively, and Pleurocera negatively, correlated with forest cover. Secondarily at the reach level, local availability of large woody debris was important for Cambarus, availability of large cobble substrate was important for C. bairdi, and stream calcium concentration was important for P. proxima. Our results show the abundance of stream organisms was determined by the taxon-dependent interplay between catchment- and reach-level factors.

American eel (Anguilla rostrata) substrate selection for daytime refuge and winter thermal sanctuary

We addressed hypotheses that anguillid eels use mud as a substrate refuge only in the absence of substrate cavities, and that the winter distribution of eels in coastal bay and estuarine habitat is limited to waters warmer than the freezing point of fish tissue (~–0.7°C). In the seasonally ice-covered southern Gulf of St Lawrence, Canada, locations of summer fyke and winter spear fisheries indicate that American eels (Anguilla rostrata) are widely distributed in both summer and winter in shallow soft-bottomed bay and estuarine habitat. Captive eels in fresh water preferred mud substrates during summer, during pre-winter cooling and during post-winter warming periods, but in winter chose mud and cobble substrates at approximately equal frequencies. Plasma antifreeze was not detected in blood sampled from eels speared in mud under winter ice. Winter bottom water temperatures in an eel wintering site were below the approximate freezing point of fish tissue 29.9% of the time. Mud of eel wintering grounds is warmer than overlying water and appears to serve as a thermal sanctuary that allows eels to safely overwinter under ice-covered waters. American eels in the southern Gulf of St Lawrence spend ~67% of their annual cycle within the substrate.

Cannibalism among green sea urchins Strongylocentrotus droebachiensis in the laboratory and field

The green sea urchin Strongylocentrotus droebachiensis plays an important ecological role as a consumer of kelp in temperate subtidal ecosystems, but is known to be omnivorous, and recent studies suggest it is potentially cannibalistic. This study ex- amined cannibalism of small juvenile S. droebachien- sis by larger conspecifics in the laboratory, and esti- mated rates of inter-cohort cannibalism in the field based on gut contents of adult sea urchins collected from subtidal sites in the Mingan Archipelago, St. Lawrence Estuary, Canada. Initial 48 h trials investi- gated factors (substratum, presence of food) that may influence cannibalism, and a subsequent 4 wk laboratory experiment found that adults and larger juveniles consumed 21 and 24% of small juveniles (3.5�6 mm test diameter), respectively, on cobble substratum when kelp was provided ad libitum. Fre- quencies of cannibalism from gut contents of urchins in the field were combined with an estimate of gut passage time determined in the laboratory and the densities of sea urchins at each site to estimate rates of cannibalism. The proportion of adults that had can- nibalized ranged from (mean ± SD) 0 ± 0 to 0.31 ± 0.12 across sites in 2013 and 2014, resulting in estimated rates of cannibalism from 0 ± 0 to 68.3 ± 0.60 small juveniles cannibalized m �2 wk �1 . This is the first study to report size-structured cannibalism among S. droe- bachiensis, and suggests that cannibalism can be a major source of mortality for small juvenile sea urchins in subtidal barren grounds.

Invasive predator influences habitat preferences in a freshwater fish

Invasive species are an important contributor to global biodiversity loss. This is particularly true in freshwater ecosystems, where introduced species have contributed to native fish extinctions, altered native fish communities and modified aquatic ecosystem structure and function. Native species can potentially mitigate the impact of invasive predators and competitors by altering their behaviour, for example by reducing activity such as foraging or by increasing their use of shelter. This study investigated interactions between an introduced salmonid, the rainbow trout (Oncorhynchus mykiss), and a native fish, the riffle galaxiid (Galaxias arcanus), that currently co-inhabit streams in parts of south-eastern Australia. We used three separate sets of behavioural experiments to test whether riffle galaxiids avoided trout under different substrate conditions. We hypothesised that habitat selection in the presence of a predator could be an important factor in facilitating galaxiid and trout co-existence. We found that interactions between the two fish differed depending on substrate. Galaxiids avoided trout when only sand substrate was available, but did not avoid trout when cobble substrate was available. The complex structure of cobbles may afford riffle galaxiids protection from trout, thereby facilitating their current existence in trout-inhabited streams.

Spawning and rearing behavior of bull trout in a headwater lake ecosystem

Numerous life histories have been documented for bull trout Salvelinus confluentus. Lacustrine-adfluvial bull trout populations that occupy small, headwater lake ecosystems and migrate short distances to natal tributaries to spawn are likely common; however, much of the research on potamodromous bull trout has focused on describing the spawning and rearing characteristics of bull trout populations that occupy large rivers and lakes and make long distance spawning migrations to natal headwater streams. This study describes the spawning and rearing characteristics of lacustrine-adfluvial bull trout in the Quartz Lake drainage, Glacier National Park, USA, a small headwater lake ecosystem. Many spawning and rearing characteristics of bull trout in the Quartz Lake drainage are similar to potamodromous bull trout that migrate long distances. For example, subadult bull trout distribution was positively associated with slow-water habitat unit types and maximum wetted width, and negatively associated with increased stream gradient. Bull trout spawning also occurred when water temperatures were between 5 and 9 °C, and redds were generally located in stream segments with low stream gradient and abundant gravel and cobble substrates. However, this study also elucidated characteristics of bull trout biology that are not well documented in the literature, but may be relatively widespread and have important implications regarding general characteristics of bull trout ecology, use of available habitat by bull trout, and persistence of lacustrine-adfluvial bull trout in small headwater lake ecosystems.

Response of crayfish to hyporheic water availability and excess sedimentation

Crayfish in many headwater streams regularly cope with seasonal drought. However, it is unclear how landscape changes affect the long-term persistence of crayfish populations. We designed two laboratory experiments to investigate the acute effects of common landscape stressors on crayfish: water withdrawal and sedimentation. The first experiment tested the interaction among water withdrawals (four 24-h water reductions of 0, 15, 30, or 45 cm) and two substrate treatments (pebble and cobble) on the burrowing depth of crayfish. The second experiment evaluated the effects of excess fine sediment (three treatments of 0, 45, and 90% sediment) and substrate type (cobble and pebble) on crayfish burrowing depth. Crayfish were able to burrow deeper into the simulated hyporheic zone in cobble substrate when compared to pebble. Crayfish subjected to greater water withdrawals in the pebble treatment were not able to reach the simulated hyporheic zone. Excess fine sediment reduced the depth that crayfish burrowed, regardless of substrate type. Results from this study suggest excess fine sediment may reduce crayfish persistence, particularly when seeking refuge during prolonged dry conditions.

First record and habitat associations ofSpongilla cenota(Class Demospongiae) within streams of the Edwards Plateau, Texas, USA

We report the first record of Spongilla cenota occurrence among drainages of the Edwards Plateau, a large karst area within the western gulf slope drainages of central Texas, and provide the first quantitative habitat description for this species. Spongilla cenota was common in the two rivers of the Edwards Plateau, occurring within 23% of the quadrats surveyed in the Devils River and 31% of the quadrats surveyed in the Llano River. Among multivariate gradients, S. cenota was positively associated with moderate current velocities and coarser substrates and negatively associated with vegetation. The majority (74%) of the quadrats with S. cenota had boulder or bedrock substrates with the remaining sponges attached to aquatic macrophytes and cobble substrate. Among univariate gradients, S. cenota were observed at water depths from 0.5 to 2.5 m and current velocities from 0.1 to 0.6 m/s. Occurrence and abundance of S. cenota potentially provides a novel bioindicator of a sound ecological environment within streams of the Edwards Plateau.