Benthic Microhabitat Research Articles

Fine-scale drivers of extinction risk: tadpole occupancy dynamics of the Table Mountain Ghost Frog (Heleophryne rosei)

Over the last four decades much progress has been made towards recognising causes of global amphibian declines, but knowledge of fine scale drivers, particularly for specialised species, remains poor, inhibiting conservation effectiveness. The case of the Table Mountain Ghost frog (Heleophryne rosei) provides an example of this, listed as Critically Endangered for the last 15 years with limited conservation actions identified due to a lack of information about threat mechanisms and magnitude of declines. To address this, we investigated H. rosei tadpole occupancy dynamics over three years in stream pools on Table Mountain in Cape Town, South Africa, the only locality where this species occurs. Tadpole spatiotemporal distribution was examined as a function of abiotic and biotic factors to quantify habitat requirements, rank threats, and identify conservation actions. Heleophryne rosei tadpole occupancy was negatively correlated with levels of fine sediments (silt and sand), which embed larger substrates and decrease the diversity of benthic microhabitat. Increased abundance of these fine sediments was also associated with higher extinction probabilities. Localised habitat degradation from hiking paths, alien vegetation, and flow manipulation were identified as the primary threats to this species, increasing the sources of fine sediments and inhibiting the fluvial systems ability to effectively flush these sediments out. Our results demonstrate the importance of pore space refugia for mountain headwater stream-adapted amphibians and provides the required data to inform management decisions for this Critically Endangered species.

Benthic ecosystem determines jellyfish blooms by controlling the polyp colony development

The harmful irregular jellyfish blooms in recent years are difficult to be deciphered by macro hydrographic condition changes. To fundamentally explain the dynamic of jellyfish populations, we shifted the focus to the polyp stage of jellyfish life cycle and local benthic ecosystems. We monitored the population dynamics of Aurelia coerulea polyps in Jiaozhou Bay and other benthic biofouling species in situ to explore the adaptive mechanism of polyps and interspecific interactions in the benthic microhabitat. Our results showed that as temperature increased, the polyps multiplied on the bare substrate, however, other benthic fouling organisms simultaneously invaded the polyp colony according to their different colonisation methods and physiological characteristics. In addition, the polyps were extremely tolerant to food scarcity in the natural environment at low temperatures. Our study indicated that it is necessary to consider the local benthic ecosystem and implement ecosystem-based management strategies to predict and manage problematic jellyfish blooms.

Assessment of endangered freshwater pearl mussel populations in the Northern Iberian Plateau in relation to non–native species: xenodiversity as a threat

In the last two decades, small populations of freshwater pearl mussels, Margaritifera margaritifera, have been recorded in Mediterranean rivers of the Iberian Northern Plateau. A survey was carried out in Castilla and León in 2018 to assess the development of populations of this species in all the rivers of known distribution and to update the threat classification. Thirty sections in the rivers Negro, Tera, Alberche and Águeda were positive for its presence, and another 50 stretches of seven rivers were negative. The species is currently distributed over about 22.5 km. Águeda and Tera populations have decreased dramatically in the last 14 years and are on the threshold of extinction. The Negro river supports the largest population, although the species has now disappeared in at least 61 % of the stretches that were inhabited in 2004. All populations showed very low densities and an ageing population structure, with no recruitment for decades. The presence of non-native invasive alien species (NIS) was higher than in a previous regional survey, with the signal crayfish representing the greatest threat. We observed changes in benthic microhabitats and direct predation of adults and glochidia conglutinates. In the Alberche River, in strict syntopy with M. margaritifera and two other mussel species, 10 NIS were detected. The current hydrological and ecological conditions in the Duero watershed support the settlement of exotic species to the disadvantage of native mollusks, which are more demanding in terms of microhabitats.

First description of deep benthic habitats and communities of oceanic islands and seamounts of the Nazca Desventuradas Marine Park, Chile

Seamounts and oceanic islands of the Chilean Exclusive Economic Zone at the intersection of the Nazca and Salas y Gómez ridges lie within one of the least explored areas in the world. The sparse information available, mainly for seamounts outside Chilean jurisdiction and shallow-water fauna of the Desventuradas Islands, suggests that the area is a hotspot of endemism. This apparent uniqueness of the fauna motivated the creation of the large Nazca-Desventuradas Marine Park (NDMP, ~ 300,000 km2) around the small islands San Felix and San Ambrosio in 2015. We report for the first time a detailed description of benthic microhabitats (i.e., centimeter to meter scale), macrohabitats (i.e., meter to kilometer-scale) and associated megafauna within the NDMP. Descriptions were based on analysis of fauna collected by trawling and ROV video observations from ~ 50 to 370 m depth. Rocky, coarse sand and silty sediment bottom habitats were observed at island slopes. In contrast, rocky and coarse sandy bottom habitats with a predominance of rhodoliths, thanatocoenosis, and other biogenic components were observed at seamounts. Mobile fauna and predators dominated the oceanic islands and nearby seamounts, whereas seamounts farther from the islands were dominated by sessile and hemisessile fauna that were mainly suspension and deposit feeders. Based on the register of 118 taxonomic units, our results provide an expanded and updated baseline for the benthic biodiversity of NDMP habitats, which seemed pristine, without evidence of trawling or anthropogenic debris.

Taxonomic composition of mobile epifaunal invertebrate assemblages on diverse benthic microhabitats from temperate to tropical reefs

Anthropogenic drivers are flattening reef structure from 3-dimensional habitats composed of macroalgae and live branching corals towards low-profile turfing algae. Our current understanding of the consequences of widespread reef degradation currently fails to consider the responses of small mobile invertebrates (‘epifauna’) to patterns of change amongst reef structural elements (‘microhabitats’). Here, the taxonomic composition of 152 epifaunal assemblages was compared among 21 structurally diverse benthic microhabitats across an Australian temperate to tropical climatic gradient, spanning 28.6 degrees in latitude from Tasmania to the northern Great Barrier Reef. Epifauna varied consistently with different microhabitat types, and to a much lesser extent with latitude. Macroalgae, live branching coral and turfing algae represented 3 extremes for epifaunal community structure, with most microhabitats possessing epifaunal assemblages intermediate between these endpoints. Amongst structural characteristics, epifauna related primarily to the degree of branching and hardness of microhabitats. Mobile invertebrate communities are likely to transform in predictable ways with the collapse of large erect macroalgae and live coral towards low-lying turf-associated communities.

Local densities and habitat preference of the critically endangered spotted handfish (Brachionichthys hirsutus): Large scale field trial of GPS parameterised underwater visual census and diver attached camera.

The critically endangered spotted handfish (Brachionichthys hirsutus) is restricted to a limited number of locations in south-eastern Tasmania, Australia. As is often the case for rare species, conducting statistically adequate surveys for B. hirsutus can be costly and time consuming due to the low probability of encountering individuals. For the first time we used a highly efficient and rigorous Global Positioning System (GPS) parameterised underwater visual census (GUVC) to survey B. hirsutus abundance within all nine known local populations in the Derwent Estuary within one season. In addition, a benthic microhabitat assessment was conducted simultaneously using a GoPro® camera attached to diver to determine B. hirsutus microhabitat preferences. B. hirsutus local populations varied between sites, with densities ranging from 1.58 to 43.0 fishes per hectare. B. hirsutus demonstrates a strong preference for complex microhabitat features, such as depressions and ripple formations filled with biogenic substrates (e.g. shells) but avoids simple, low relief microhabitats (e.g. sand flats) and areas dominated by ephemeral, filamentous algae. Complex microhabitats may enable B. hirsutus to avoid predators, increase forage opportunities or provide higher quality spawning sites. This first wide-scale application of GUVC for B. hirsutus allowed us to survey a larger number of sites than previously possible to provide a robust reference point for future long-term monitoring.

Habitat complexity affects benthic harmful dinoflagellate assemblages in the fringing reef of Rawa Island, Malaysia

Few studies have investigated the effect of fine-scale habitat differences on the dynamics of benthic harmful dinoflagellate assemblages. To determine how these microhabitat differences affect the distribution and abundance of the major benthic harmful dinoflagellate genera in a tropical coral reef ecosystem, a field study was undertaken between April–September 2015 and January 2016 on the shallow reef flat of the fringing reef of Rawa Island, Terengganu, Malaysia. Sampling of benthic dinoflagellates was carried out using an artificial substrate sampling method (fiberglass screens). Benthic microhabitats surrounding the sampling screens were characterized simultaneously from photographs of a 0.25-m2 quadrat based on categories of bottom substrate types. Five taxonomic groups of benthic dinoflagellates, Ostreopsis, Gambierdiscus, Prorocentrum, Amphidinium, and Coolia were identified, and cells were enumerated using a light microscope. The results showed Gambierdiscus was less abundant than other genera throughout the study period, with maximum abundance of 1.2 × 103 cells 100 cm−2. While most taxa were present on reefs with high coral cover, higher cell abundances were observed in reefs with high turf algal cover and coral rubble, with the exception of Ostreopsis, where the abundance reached a maximum of 3.4 × 104 cells 100 cm−2 in habitats with high coral cover. Microhabitat heterogeneity was identified as a key factor governing the benthic harmful dinoflagellate assemblages and may account for much of the observed variability in dominant taxa. This finding has significant implications for the role of variability in the benthic harmful algal bloom (BHAB) outbreaks and the potential in identifying BHAB-related toxin transfer pathways and the key vectors in the food webs.

Microhabitat change alters abundances of competing species and decreases species richness under ocean acidification

Niche segregation allows competing species to capture resources in contrasting ways so they can co-exist and maintain diversity, yet global change is simplifying ecosystems and associated niche diversity. Whether climate perturbations alter niche occupancy among co-occurring species and affect species diversity is a key, but unanswered question. Using CO2 vents as natural analogues of ocean acidification, we show that competing fish species with overlapping diets are partially segregated across microhabitat niches and differently-orientated substrata under ambient CO2 conditions. Under elevated CO2, benthic microhabitats experienced a significant increase in non-calcifying turf and fleshy algae but a sharp reduction in calcareous algae. The increased availability of turf and fleshy algae supported increased densities of a competitively dominant species, whilst the reduction in calcifying algal microhabitats decreased densities of several subordinate species. The change in microhabitat availability also drove an increased overlap in microhabitat use among competing fishes at the vents, associated with a reduced fish species richness on horizontal substrates. We conclude that loss of preferred microhabitat niches, exacerbated by population proliferation of competitively dominant species, can drive population losses of less common and subordinate species, and reduce local species richness. The indirect effects of ocean acidification on microhabitat availability can therefore impair maintenance of species populations, and drive changes in local community and biodiversity patterns.

Progress in the discovery of amphipod crustaceans

At present, amphipod crustaceans comprise 9,980 species, 1,664 genera, 444 subfamilies, and 221 families. Of these, 1,940 species (almost 20%) have been discovered within the last decade, including 18 fossil records for amphipods, which mostly occurred in Miocene amber and are probably all freshwater species. There have been more authors describing species since the 1950s and fewer species described per author since the 1860s, implying greater taxonomic effort and that it might be harder to find new amphipod species, respectively. There was no evidence of any change in papers per author or publication life-times of taxonomists over time that might have biased apparent effort. Using a nonhomogeneous renewal process model, we predicted that by the year 2100, 5,600 to 6,600 new amphipod species will be discovered. This indicates that about two-thirds of amphipods remain to be discovered which is twice the proportion than for species overall. Amphipods thus rank amongst the least well described taxa. To increase the prospect of discovering new amphipod species, studying undersampled areas and benthic microhabitats are recommended.

Tectus (Trochus) niloticus search for suitable habitats can cause equivocal benefits of protection in village-based marine reserves.

In the Pacific, the protection of coral reef resources is often achieved through the implementation of village-based marine reserves (VBMRs). While substantial fisheries benefits are often reported, results of quantitative approaches are controversial for benthic macroinvertebrates, whose life history traits may cause low congruence with protective measures implemented at non-ecologically relevant scales. This study investigated the structural and behavioral responses of the exploited topshell Tectus niloticus within a very small (0.2 km2) VBMR in Vanuatu, south Pacific. The results of underwater surveys and a nine-month tagging experiment emphasized contrasted, scale-dependent responses. At the reserve scale, our results failed to demonstrate any positive effect of protection after three years of closure. In contrast, abundance, density and biomass increased more than ten-fold in the southern part of the reserve, along with significantly larger (25%) individual sizes. The dispersal of tagged specimens was also consistently lower after 2, 4 and 9 months in the latter zone. Analyses of 17 substratum variables revealed a marked small-scale patchiness delineating contrasted benthic microhabitats, the distribution of which closely matched that of trochus. We advocate that i) VBMRs have inherently unequal ecological potentials for protecting and managing highly habitat-dependent species such as trochus; ii) ‘success’ or ‘failure’ is to a certain extent pre-determined by the trajectory of species-specific microhabitats, which may outreach protection effects. This has strong implications in the Pacific where the location and size of reserves primarily depends upon marine tenure, and communities have little flexibility in setting reserve boundaries.

Microhabitat and biology of Sphaerium striatinum in a Central New York stream

In many lotic systems, drastic declines in freshwater bivalve populations, including fingernail clams (Sphaeriidae), have created concerns about biodiversity and future ecosystem services. We examined the local occurrence of the historically common fingernail clam, Sphaerium striatinum, in a central New York stream. We sampled the density of sphaeriids and measured the associated habitat variables (substrate, depth, water flow) to test within-stream multivariate benthic microhabitat association. Size distribution, density, and diel feeding periodicity were measured as focal aspects of fingernail clam biology and ecology. S. striatinum tended to be found in microhabitats that had harder substrates and faster flow. The Labrador Creek fingernail clam local population had positive indicators (size distribution, density). There was significant diel periodicity in feeding behavior. The clams fed most actively during the 0400–0800 h periods. This kind of behavioral periodicity can indicate a significant ecological interaction between predators and bivalve prey. Increased understanding of the behavioral ecology of small native freshwater bivalves in an unimpacted headwater stream is a fundamental building block for development of overall ecological conservation goals for freshwater bivalves and their lotic habitats.

Forest removal and the cascade of effects corresponding with an Ozark Hellbender population decline

Populations of the endangered Ozark Hellbender salamander (Cryptobranchus alleganiensis bishopi) in the North Fork of the White River (NFWR) in Missouri and other streams have declined precipitously in recent decades. Deforestation of the riparian and nearby upland habitat has corresponded with in-river habitat changes and other interacting stressors that coincide chronologically with the precipitous decline. We review the cascade of effects, including changes in water quality, benthic habitat, illegal and scientific harvesting, and introduced and reintroduced species occurrence that followed deforestation in the context of their impacts on hellbenders and relationship with other stressors such as climate change. In-river habitat changes since the 1960s include benthic microhabitat alterations associated with redistribution of gravel, siltation, and sedimentation and, in part, increases in nuisance vegetation, including periphyton. Deforestation of riparian and nearby upland habitats increased access and opportunities for human activities such as recreation, wildlife collection, and development. The subsequent degradation of stream habitat and water quality following deforestation reduced the carrying capacity for the NFWR Ozark Hellbender population and had negative consequences on population health.

Swimming behavior of marine cercariae: Effects of gravity and hydrostatic pressure

Many species of marine larvae use exogenous cues, such as gravity and pressure, for orientation and dispersal, but it is unclear if parasitic larvae exhibit comparable geotactic and barokinetic behaviors. Using two species of marine cercariae, Euhaplorchis sp. and Probolocoryphe lanceolata, which utilize the same first intermediate host, the mangrove snail Cerithidea scalariformis, the hypothesis that they use gravity and pressure to position themselves in the water column to increase the probability of contacting their respective second intermediate hosts was tested. In a test chamber under dark laboratory conditions, Euhaplorchis sp. cercariae ascended, and therefore displayed negative geotaxis, increasing the probability of finding their second intermediate host, salt marsh killifish (Fundulus spp.). In contrast, P. lanceoloata cercariae swam downwards towards the bottom of the chamber, and this positive geotactic behavior would place them in a benthic microhabitat consistent with their second intermediate host, fiddler crabs (Uca spp.). In a subsequent experiment testing swimming activity in response to step increases in pressure, no effect of pressure changes over the range tested (0.3–30kPa) was observed for either species. Collectively, these results suggest that while cercariae are unresponsive to changes in pressure, they are able to utilize gravity for orientation, placing them in the preferred microhabitat of the second intermediate host. This finding is consistent with published photobehavioral studies in which Euhaplorchis swam upwards towards light and P. lanceolata swam downward towards the bottom upon light stimulation. These complementary phototactic and geotactic behaviors optimize host contact, and thus completion of their complex life cycle.

The role of benthic microhabitats in determining the effects of hydromorphological river restoration on macroinvertebrates

Despite the large number of river restoration projects carried out worldwide, evidence for strong and long-term positive ecological effects of hydromorphological restoration on macroinvertebrates is scarce. To improve the understanding of the success and failure of restoration measures, a standardized field study was carried out in nineteen paired restored and degraded river sections in mid-sized lowland and mountain rivers throughout Europe. We investigated if there were effects of restoration on macroinvertebrate biodiversity, and if these effects could be related to changes in microhabitat composition, diversity and patchiness. Effects were quantified for all taxa combined, as well as Ephemeroptera, Plecoptera and Trichoptera separately. Additionally, species trait classifications of microhabitat preference types were used as a functional indicator. Restoration had no overall positive effects on the selected macroinvertebrate metrics. Rather, we did find positive relationships between the macroinvertebrate responses and the effect of restoration on the diversity and patchiness of microhabitats. Furthermore, the effects on macroinvertebrates could be related to changes in the cover of specific substrate types in the restored sections. We conclude that the limited effect of restoration on macroinvertebrate diversity overall reflected, at least in part, the limited effect of most restoration measures on microhabitat composition and diversity.

The role of surgeonfish (Acanthuridae) in maintaining algal turf biomass on coral reefs

Coral reefs are one of the most highly productive marine ecosystems, with a strong connection between herbivores and the production of benthic algae. The epilithic algal matrix (EAM) is a major source of primary production on coral reefs, and it is one of the dominant benthic microhabitats, covering up to 80% of reef flats and back reefs and up to 70% of reef slopes on outer-shelf sites of the Great Barrier Reef, Australia. Although herbivorous surgeonfish (Acanthuridae) are dominant members of most reef fish assemblages, there is a lack of quantitative information on their grazing impact, particularly those that feed upon the EAM in the Indo-Pacific. Therefore, the aim of this study was to investigate the role of surgeonfish in maintaining algal turf biomass on coral reefs. Spatial patterns of EAM productivity, and herbivorous fish biomass and grazing intensity were quantified at different depths (deep vs. shallow) and exposures (windward vs. leeward) of reef slope environments of Heron Island, southern Great Barrier Reef. Surgeonfish were the numerically-dominant EAM grazing fish family, and to identify the daily impact of surgeonfish species on the EAM, data on their biomass (gm−2) and grazing intensity (total bitesm−2day−1) were combined with EAM productivity estimates (gCm−2day−1). EAM productivity was greatest in windward and shallow sites, and herbivorous fish biomass mirrored this pattern. Yet, there was no difference in the EAM standing crop or grazing intensity among habitats. In the most productive habitat (windward-shallow), grazer/detritivore surgeonfish species accounted for 74% of the total herbivore biomass (gm−2), took 51% of the total bites (m−2day−1), and removed an estimated 73% of daily EAM productivity (gCm−2day−1). This study quantifies the role of surgeonfish in maintaining EAM biomass, and highlights their possible contribution to preventing shifts from coral- to algal-dominance following disturbance.

Microhabitat influences on stream insect emergence

Understanding the factors controlling insect emergence from streams has applications to ecological theory regarding cross-boundary flux, along with practical value for monitoring stream function after restoration projects. We hypothesized that stream microhabitat would have effects on emergence that were independent of those mediated by the local stock of benthic macroinvertebrates. We set 50 emergence traps in a third-order stream in northern Minnesota, USA, during two study periods and used structural equation modeling to examine direct and indirect effects of benthic stock and microhabitat features on emergence. Emergence by biomass showed direct positive relationships to substrates of fines and detritus in the first sampling period, and to shallow depth and wood area in the second period. Emergence by abundance had direct positive relationships with benthic stock, CPOM, and fewer macrophytes in the first period, and with benthic stock and periphyton in the second period. Fine substrates may act to concentrate burrowing larvae, whereas CPOM and particularly wood may intercept drifting pre-emergent insects and provide exiting surfaces. Shallow depths may reduce the extent to which resident insects drift downstream (and leave the sample area) while emerging. Periphyton may be an indicator for patches with greater illumination, which itself attracts emergers. Our results suggest emergence is sensitive to environmental conditions at the microhabitat scale, and that stream restoration activities should consider habitat for emerging insects when designing projects.

Associations between Non‐Lethal Injury, Body Size, and Foraging Ecology in an Amphibian Intraguild Predator

AbstractTheoretical treatments of intraguild predation and its effects on behavioral interactions regard the phenomenon as a size‐structured binary response wherein predation among competitors is completely successful or completely unsuccessful. However, intermediate outcomes occur when individuals escape intraguild (IG) interactions with non‐lethal injuries. While the effects of wounds for prey include compromised mobility and increased predation risk, the consequences of similar injuries among top predators are not well understood, despite the implications for species interactions. Using an amphibian IG predator, Ambystoma opacum (Caudata: Ambystomatidae), we examined associations between non‐lethal injuries and predator body size, foraging strategy, microhabitat selection, and intraspecific agonistic interactions. Wounds were common among IG predators, generally increasing in frequency throughout larval ontogeny. Non‐lethal injuries were associated with differences in predator body size and behavior, with injured predators exhibiting smaller body sizes, increased use of benthic microhabitats, reduced agonistic displays, and increased risk of intraspecific aggression. While such effects were not ultimately associated with reduced foraging success, non‐lethal injury could contribute to niche partitioning between injured and healthy predators via habitat selection, but injured predators likely continue to exert predatory pressure on IG and basal prey populations. Our results indicate that studies of top‐down population regulation should incorporate injury‐related modifications to both prey and predator behavior and size structure.

Influence of geomorphic setting on the metabolism of Lake Huron fringing wetlands

We measured gross primary productivity (GPP) and respiration (R) seasonally in benthic, water column, and epiphytic microhabitats of Lake Huron fringing wetlands. Spring areal GPP ranged from 33 to 103 mmol O2 m−2 d−1, spring R ranged from 16 to 110 mmol O2 m−2 d−1, and the water column was the most important microhabitat for both GPP and R on average. Summer GPP ranged from 40 to 131 mmol O2 m−2 d−1, R ranged from 25 to 155 mmol O2 m−2 d−1, and the water column and benthic microhabitats were equally important for GPP and R. Fall GPP ranged from < 1 to 19 mmol O2 m−2 d−1, and R ranged from < 1 to 47 mmol O2 m−2 d−1, with the benthic and water column microhabitats being equally important. Net metabolism (the difference between GPP and R) was close to zero at most wetlands, but when macrophyte productivity was accounted for, most wetlands appeared autotrophic. Both GPP and R were highest in deep wetlands protected from hydrologic energy and declined with increasing wave exposure. With increasing exposure, wetlands were restricted to shallower water and benthic GPP and R increased relative to water column GPP and R. This pattern persisted to intermediate levels of exposure, beyond which benthic GPP and R declined as a result of physical disturbance to the sediment. Coastal wetlands are hotspots of productivity in Lake Huron and hydrologic energy is an important driver of total metabolism rates, as well as the distribution of GPP and R among microhabitats.

Habitat attributes associated with short‐term settlement of Ozark hellbender (Cryptobranchus alleganiensis bishopi) salamanders following translocation to the wild

Summary1. Organisms associated with lotic systems rank among the most threatened because of global change. Although translocation is being increasingly applied as a conservation strategy, most studies have focused on survival and recruitment of individuals, and few have attempted to identify how habitat attributes influence short‐term settlement of animals during the critical post‐release period.2. We demonstrate the application of resource selection modelling in an information theoretic framework to identify release‐site characteristics that will increase the likelihood of settlement for a fully aquatic benthic stream salamander, the Ozark hellbender (Cryptobranchus alleganiensis bishopi). We fit discrete choice models using data from 29 radio‐tagged hellbenders that were translocated to two sites in the North Fork of the White River (NFWR), Missouri (U.S.A.). We defined resource availability at two spatial scales (stream reach and home range) and quantified abiotic habitat attributes at 3181 salamander locations and 6329 random available locations collected between May 2008 and August 2009.3. At both sites and spatial scales, a single model received substantially greater support (0.96–1.00 of total model weight) than all other models, and top‐ranked models were similar in form and predictive ability. At both spatial scales, selection was positively influenced by the presence of cobble‐boulder substratum relative to bedrock and finer substrata. We also noted a negative interactive effect between distance to the nearest substratum particle large enough to provide cover (i.e. at least one axis ≥15 cm in length) and an increase in either a direct or relative (i.e. pool, run, and riffle) measure of water velocity.4. Collectively, salamanders released in our study selected resources indicative of long‐term benthic microhabitat stability. However, despite strong selection of cobble‐boulder substratum, 8% (282 of 3181) of captive‐reared hellbender locations occurred in bank crevices and root masses. Although several studies have reported the importance of near bed hydraulics in determining occurrence of stream macroinvertebrates, our findings are the first to indicate that spacing among cobble‐boulder substrata may be important for hellbenders.5. To increase the likelihood of short‐term settlement of captive‐reared hellbenders in the wild, we recommend prioritising release sites where the average distance between cobble‐boulder particles within habitat patches is minimised. In general, average spacing among cobble and boulder substrata should be <1 m in habitat patches where mean benthic water velocity exceeds 0.1 m s−1, and <0.5 m where water velocity approaches 0.30 m s−1. Based on home range sizes of captive‐reared Ozark hellbenders, the collective extent of suitable cobble‐boulder habitat patches within release sites should approximate at least 10 m2 per salamander released.

Biological changes along the continuum of an agricultural stream: influence of a small terrestrial preserve and use of adult caddisflies in biomonitoring

We monitored benthic macroinvertebrates and adult caddisflies along an agricultural stream continuum upstream, within, and downstream of a small forested preserve. The habitat upstream of all sites was >60% disturbed by agricultural activities. The percentage of riparian disturbance was markedly lower adjacent to the sites inside the preserve than those outside. Water physicochemical factors did not exhibit clear changes among sites, except for nitrate concentration, which was highest upstream of the preserve. Biological diversity of adult caddisflies was significantly higher within the preserve. Biological diversity of benthic invertebrates exhibited similar results except for non-significance between the upstream and preserve sites. Pollution tolerance and percentage of filtering collector metrics were unchanged among sites for both assemblages. The percentage of adult caddisflies in the shredder functional group increased significantly within the preserve but remained small relative to that of pollution-tolerant filtering collectors. The small terrestrial preserve promoted a three-fold increase in species diversity, even without corresponding changes in water quality or trophic structure. Such an increase, however, may not be as detectable with traditional benthic biomonitoring techniques due to the difficulties of sampling benthic microhabitats representatively and identifying specimens to the species level.