Crevice occupation by musk turtles: taxonomic distribution and crevice attributes

Musk turtles, Sternotherus, of all taxa preferentially used crevices as resting sites in laboratory pools. Crevice use was greater during the day. Larger, darker crevices that were low enough to touch the carapace were preferred. Positional preferences within crevices were for full coverage of the shell despite the head being exposed, for the low half of crevices, and for axial orientation that maximized contact between the carapace and crevice ceiling. Light but touchable portions of crevices were preferred over dark but untouchable portions, so the possibility of establishing carapacial contact with the ceiling is the definitive attribute of a satisfactory crevice. The behavioural tendency to use the lowest possible crevice may have an anti-predator function, and it is one necessary condition for existence of a selective regime in favour of depressed shells.     

Selective settlement of the barnacle Semibalanus balanoides (L.) facilitates its growth and reproduction on mussel beds in the Wadden Sea

On the unstable sedimentary tidal flats of the Wadden Sea, a suitable attachment substrate for sessile organisms is generally lacking. Epibenthic mussel beds (Mytilus edulis L.) provide the only and strongly limited settlement sites available for the barnacle, Semibalanus balanoides (L.). Field investigations showed that barnacles were non-randomly distributed within a mussel bed. They preferentially occurred near the siphonal apertures of living mussels but rarely grew on dead mussels or shell fragments. Field experiments revealed that this was due to selective settlement of barnacle cyprid larvae. Growth of barnacles was significantly higher upon living mussels than on empty mussel shells. Moreover, a higher reproductive output was obtained by individuals on living mussels which produced twice as many nauplii larvae than barnacles attached to empty shells. This study shows that selective settlement of S. balanoides cyprid larvae on living mussels is adaptive with respect to individual fitness. Received in revised form: 15 January 2001 Electronic Publication     

Non-linear density-dependent effects of an intertidal ecosystem engineer

Ecosystem engineering is an important process in a variety of ecosystems. However, the relationship between engineer density and engineering impact remains poorly understood. We used experiments and a mathematical model to examine the role of engineer density in a rocky intertidal community in northern California. In this system, the whelk Nucella ostrina preys on barnacles (Balanus glandula and Chthamalus dalli), leaving empty barnacle tests as a resource (favorable microhabitat) for other species. Field experiments demonstrated that N. ostrina predation increased the availability of empty tests of both barnacle species, reduced the density of the competitively dominant B. glandula, and indirectly increased the density of the competitively inferior C. dalli. Empty barnacle tests altered microhabitat humidity, but not temperature, and presumably provided a refuge from wave action. The herbivorous snail Littorina plena was positively associated with empty test availability in both observational comparisons and experimental manipulations of empty test availability, and L. plena density was elevated in areas with foraging N. ostrina. To explore the effects of variation in N. ostrina predation, we constructed a demographic matrix model for barnacles in which we varied predation intensity. The model predicted that number of available empty tests increases with predation intensity to a point, but declines when predation pressure was strong enough to severely reduce adult barnacle densities. The modeled number of available empty tests therefore peaked at an intermediate level of N. ostrina predation. Non-linear relationships between engineer density and engineer impact may be a generally important attribute of systems in which engineers influence the population dynamics of the species that they manipulate.     

Mass mortality in a population of the mussel Mytilus edulis L. Caused by high temperature on rocky shores

Mass mortality in a population of the mussel Mytilus edulis L. occurred in early August, 1981, on rocky intertidal shores in Mutsu Bay, northern Japan, due to unusually high temperatures. The decomposed tissues disappeared within 3 days after death. Higher mortality was observed in the upper part of the Mytilus zone than in the lower zone. As temperatures rose the mussels expelled water contained in the shells and 50% individuals died within 1 h from high body temperature rising up to >40°C. Septifer (Mytilisepta) virgatus (Wiegmann), which occupied the zone above Mytilus, showed low mortality (maximum 16.8%). Heat tolerance seems stronger in Septifer than in Mytilus. Many small animals including polychaetes, amphipods and nemerteans etc., lived among the empty shells and when the shells were removed by wave action, these animals disappeared from the bared rock surface. One year after the mass mortality the rock surface was covered by the barnacle Chthamalus challengeri Hoek. The ecological effect of mass mortality on the intertidal community is discussed.     

The importance of crevices to the intertidal snail Littoraria articulata (Philippi) in a tropical mangrove forest

The intertidal gastropod, Littoraria articulata (Philippi), is common on the trunks of mangroves at Coorooman Creek, Central Queensland. Individuals of shell length less than 3 mm were only found in empty tests of the barnacle Hexaminius popeiana (Foster). Larger snails were exposed on the trunk or occasionally in crevices such as knot holes. The relationship between shell length and shell strength differed between barnacle dwelling and larger L. articulata: in both cases it was linear, but the rate of increase of strength with increasing length was significantly greater for barnacle dwelling snails than for exposed ones. In contrast, there was an exponential relationship between shell strength and length for the weaker shelled Littoraria filosa (Sowerby), which occurs higher on the tree and does not inhabit barnacles. The survival of L. articulata was affected by the presence of crevices: significantly fewer disappeared from posts with artificial crivices than from those which lacked them, and some snails testhered to posts appeared to have been eaten by fish. The importance of crevices is discussed in relation to predation pressure, growth and habitat selection by larval L. articulata. This revised version was published online in July 2006 with corrections to the Cover Date.     

The influence of some symbionts on the shell-selection behaviour of the hermit crabs, Pagurus pollicarus and Pagurus longicarpus

The influence of some symbionts on the shell-selection by the hermit crabs Pagurus pollicarus and P. longicarpus was examined by placing individual hermit crabs with two similar shells in a choice situation and recording the shell occupied after 12 hr. One shell contained a symbiont species and the other did not. The results indicated that organisms normally found on or in empty shells influence the shell-section by these species of hermit crab. P. pollicarus preferred shells occupied by the sea anemone Calliactis tricolor or by the hydroid Hydractina echinata as opposed to bare shells. P. longicarpus also preferred shells with H. echinata. Both crab species rejected shells with the barnacle Balanus amphitrite. Shells containing the molluscs Crepidula fornicata or C. plana were rejected by the smaller hermit crab P. longicarpus. These molluscs appeared to exert no influence on P. pollicarpus unless they were large or abundant, at which point their weight or occlusion of available space possibly has negative effects on the crab.     

Shell use by juvenile fiddler crabs Uca pugnax and U. pugilator

The present study documents for the first time shell use by juvenile fiddler crabs in the salt marsh. Twenty visits were made to six salt marsh sites at Tybee Island, Georgia between 2007 and 2009. One hundred empty Littorina irrorata shells were collected at each site on each field trip. Juvenile carapace width was measured, crabs sexed, and species identification completed using RFLP analysis. Shell use of up to 79% was observed. Two species of fiddler crabs were found in empty shells, Uca pugnax and U. pugilator. U. pugnax was the dominant species at all sites representing 62-84% of the juvenile fiddler crab population. Juvenile sex ratios were female-biased (1.7:1) at all six sites. Juvenile size did not vary significantly between species but males of both species were significantly larger than females. Size frequency distribution of carapace width revealed that shell use varied with size and sex. In the 3 to 4 mm size class, juvenile females outnumbered juvenile males in empty L. irrorata shells while in the 5 to 6 mm size class and greater, juvenile males outnumbered juvenile females in shells. Significantly more juvenile fiddler crabs were found in empty shells during flood than ebb tide at 3 of the sites. This discovery illuminates the resourcefulness of juvenile fiddler crabs and provides another mechanism that might enhance survival.     

Patches of barnacles and ascidians in soft bottoms: Associated motile fauna in relation to the surrounding assemblage

Epibenthic patches dominated by barnacles Balanus crenatus Bruguiere and solitary ascidians Styela spp., Bolthenia echinata (L.) and Molgula spp. in the White Sea shallow subtidal develop on bivalve shells and small stones surrounded with muddy sand. The space between barnacles and ascidians is filled with muddy sediment inhabited by motile taxa. We hypothesized that (i) epibenthic patches and unstructured sediment would attract different motile fauna and (ii) motile fauna of the patches would be affected by local abundances of epibenthic foundation species. Most dominant motile species demonstrated a significant difference in abundance between the two microhabitats. In contrast to the fauna of the sediment, species composition observed in aggregations of barnacles and ascidians was stable across different locations. In the field experiment initially clear bivalve shells after 5 years of exposure developed barnacle clusters with motile fauna similar to that observed in natural aggregations. Amphipods, isopods and bivalves, capitellid polychaets, Cirratulus cirratus (Müller) and Pholoe minuta Fabricius (Polychaeta) dominated in the sediment inside epibenthic patches. The proportion of capitellids, known to be sensitive to organic enrichment, was much higher within the patches than outside. The abundances of motile taxa found in aggregations were mostly determined by the number of barnacles of different size and of their empty shells, the biomass of ascidians, and the effect of location. Different dominant species demonstrated sensitivity to different parameters.Physical structure of the habitat, provided by barnacles and ascidians, as well as their biodeposition activity are regarded as the main factors structuring the motile fauna in the community studied. The spatial pattern observed seems to imply a range of pattern-generating biogenic processes, similar to those previously revealed in patches of filter-feeding bivalves, tube-building worms and seagrass.     

Experiments on factors influencing settlement,survival, and growth of two species of barnacles in new south wales

Adult Tesseropora rosea (Krauss) and Tetraclitella purpurascens (Wood) are mostly found in the eulittoral (barnacle) zone of rocky seashores in New South Wales. Below this zone most space is occupied by the tube-worm Galeolaria caespitosa (Lamarck) or by various species of macroalgae. Within the eulittoral zone, T. rosea are mostly on sunny areas of rock exposed to relatively strong wave-action. T. purpurascens are present mainly in crevices, caves, and under ledges where there is considerable shade.Cyprids of both species settled on sandstone plates and on experimentally cleared areas in the barnacle and Galeolaria zones. Neither species settled where the substratum was already covered by algae or Galeolaria. No spat of T. purpurascens were found in sunny areas of the barnacle zone. T. rosea, however, settled in cleared substrata in sunny and shaded areas. Neither species settled in the littoral fringe above the upper limit of distribution of adults. On boulders transferred to high levels of the shore during a storm, small T. purpurascens died within a few weeks.Barnacles of both species which had settled in experimentally cleared areas in the Galeolaria zone survived and grew. In these areas some T. purpurascens were killed by being smothered by tube-worms which settled after the barnacles. This probably happens to T. rosea, but was not demonstrated experimentally. In the Galeolaria zone, both species of barnacles were very quickly smothered and killed by macroalgae growing over them, except where these were experimentally removed.Within the barnacle zone, all newly-settled spat of T. purpurascens transferred to sunny sites died within two months, whilst many of those in shaded sites survived. In areas where wave-action was strong, spat of T. rosea survived and grew well in sunny areas, but survived better in the shade. Under a ledge, however, where wave-action was reduced, all the T. rosea in sunny sites, and most of those in shaded sites died within two months; many newly-settled T. purpurascens survived in the shade in this area.The grazing limpet Cellana tramoserica (Sowerby) dislodged and crushed some newly-settled T. rosea and reduced survival in some sunny areas. T. rosea settled preferentially on bare rock and were rarely found on the shells of adult barnacles. Thus, the density of spat was greater where adult barnacles were absent. In contrast, many newly-settled T. purpurascens were found on the shells of adults of their own species in shaded areas; they also settled on cleared rock. Because T. purpurascens tended to settle amongst and on adults, and in crevices and confined areas, they were not much affected by limpets. When newly-settled T. purpurascens were in high densities, they had lower survival than in areas with reduced densities, because of squashing and smothering by each other.The upper and lower limits of vertical distribution (zonation) of these two species of barnacles are determined primarily by the settlement of cyprids. Neither species settled at the highest levels on the shore. Whether this was due to the decreasing time of submersion during high tide towards the top of the shore, or a result of preferences for settlement site is unknown. Even if cyprids were to settle in the littoral fringe, the spat would die very quickly probably as a result of desiccation. Below the barnacle zone, the entire substratum is usually occupied by other sessile species, particularly macroalgae, on which the barnacles do not settle. In experimentally cleared areas below the barnacle zone, or in any naturally cleared areas both species settled, and could survive the physical conditions. Newly-settled spat were, however, overgrown and killed by algae and Galeolaria.Within the barnacle zone, T. purpurascens is restricted to shaded areas because of the inability of newly-settled spat to survive the physical stresses of high temperature and desiccation in sunny habitats. T. rosea appears to be excluded from shaded areas by a combination of the lack of suitable substrata on which to settle, and the effects of reduced water-flow in many crevices and under ledges. T. rosea survived better in areas with strong wave-action and can survive in shaded areas where water-flow is not reduced by the topography of the substratum.     

The size and shape of shells used by hermit crabs: A multivariate analysis of Clibanarius erythropus

Shell attributes such as weight and shape affect the reproduction, growth, predator avoidance and behaviour of several hermit crab species. Although the importance of these attributes has been extensively investigated, it is still difficult to assess the relative role of size and shape. Multivariate techniques allow concise and efficient quantitative analysis of these multidimensional properties, and this paper aims to understand their role in determining patterns of hermit crab shell use. To this end, a multivariate approach based on a combination of size-unconstrained (shape) PCA and RDA ordination was used to model the biometrics of southern Mediterranean Clibanarius erythropus populations and their shells. Patterns of shell utilization and morphological gradients demonstrate that size is more important than shape, probably due to the limited availability of empty shells in the environment. The shape (e.g. the degree of shell elongation) and weight of inhabited shells vary considerably in both female and male crabs. However, these variations are clearly accounted for by crab biometrics in males only. On the basis of statistical evidence and findings from past studies, it is hypothesized that larger males of adequate size and strength have access to the larger, heavier and relatively more available shells of the globose Osilinus turbinatus, which cannot be used by average-sized males or by females investing energy in egg production. This greater availability allows larger males to select more suitable shapes.     

Coexistence in a sea urchin guild and its implications to coral reef diversity and degradation

Summary Coexistence between the coral reef inhabiting sea urchins Echinometra mathaei, Diadema savignyi and D. setosum was studied by comparing differences in body morphology, distribution, diet, susceptibility to predators, intra- and interspecific competition and settlement. The three species share similar diets and broad within-habitat distributions but differ in their microspatial preferences. E. mathaei is the smallest species, has the highest settlement rates and lives territorially within small burrows or crevices. D. savignyi is intermediate in size and lives frequently in intermediate size crevices or occassionally in social groups. D. setosum is the largest species and occassionally lives in large crevices or more frequently in social groups. Both Diadema have similarily low settlement rates. Competition experiments showed that E. mathaei was consistently the top competitor for crevice space. Diadema species shared larger crevices but competition occured within smaller crevices and was frequently won by the largest individual, regardless of species. D. savignyi may be the top competitor for crevice space between the Diadema species due to a reduced spine length/test size ratio which gives it a larger test for the same crevice size requirement. Predation rates were high for E. mathaei and low for both Diadema species. Coexistence is mediated by predation on the competitive-dominant while predation coupled with different body morphologies and behavior allows spatial resource partitioning of the reef's variable topography. Consequently, the three variables of predation, topographic complexity and differing body shapes create the observed species diversity. A reduction in predators due to stochastic fluctuations or from fishing pressure can lead to E. mathaei population increases and competitive exclusion of Diadema.     

Visual selection of shell colour in two littoral prosobranchs

The rough periwinkle Littorina “saxatilis” exhibits a wide range of shell colours. In current literature it is claimed that these colours are not related to the environment, that they arise randomly as genetic accidents and that they have little positive survival value. In a previous paper it has been shown that, in Wales, “saxatilis” consists of four separate, fully sympatric species. This paper reports an investigation as to whether the colour of two of these species, nigrolineata and rudis, is related to the colour of the background. Because of difficulties in quantitatively describing the colour of the background it was decided to concentrate mainly upon one aspect: whether or not the frequency of red shells is larger upon shores consisting of red sandstone than elsewhere in Wales. In both species the association between red shells and red sandstone is highly significant. All nigrolineata samples in which red was found at a frequency above 15% are from red sandstone. On red sandstone, red shells of this species were found mainly upon sheltered shores, their frequency decreasing and that of white shells increasing with exposure. This may be because barnacles, which occupy the same vertical zone as nigrolineata, are more abundant upon exposed shores. Partly covering the red rock, barnacles create a white background upon which white shells, rather than red, are cryptic. Yellow shells are found mainly on sheltered shores, where the brown alga Fucus is abundant. It was observed that when the tide is in and the algae spread out, a yellow shell situated beneath them is well concealed. Yellow is also found upon barnacles which because of fungal and lichen infections, are dirty yellow. It is suggested that a striped (“nigrolineated”) pattern breaks up the shape of the shell. It also resembles the colour of the dark rock and the dark sutures between barnacle plates. In rudis 80% of the samples containing over 25% red are from red sandstone. Contrast to nigrolineata, in this species the relative frequency of red decreases on sheltered shores. This could be because the brown alga Pelvetia, which occupies the same vertical zone as rudis, is more abundant in sheltered conditions and its colour partly covers over that of the rock beneath. The fact that in both species red shells are more frequent upon red sandstone than elsewhere in the study area, suggests that visual selection is restricting their distribution to the background that they match most. Rock pipits and shore-crabs prey upon winkles. They have colour perception and could be partly responsible for this selection.     

Point pattern analysis as a tool for assessing disease spread and population features in remaining sanctuaries of the critically endangered bivalve Pinna nobilis

An emergent disease has relegated populations of the Mediterranean pen shell, Pinna nobilis L. critically endangered to sanctuaries featuring salinities outside the 36.5 to 39 range. Point pattern analysis was used in three areas of the Alfacs Bay (Ebro Delta) still hosting pen shells to assess the possible undergoing of disease spread by comparing the spatial distribution of live individuals vs. empty shells across spatial scales. We also evaluated the importance of other ecological aspects of conservation relevance such as the size distribution of individuals, and the possible association to seagrass habitats. The population assessment showed no recent mortality and a clear dominance of large adults among empty shells (97.3%) pointing to no disease spread during the study period. At the low spatial scale Nearest Neighbor (NN) analyses evidenced significant clustering (NN Ratios of 0.4–0.8), but in one of the zones NN distances were closer in empty shells than in live individuals, suggesting a former localized outbreak. At the larger spatial scale, MDSCA confirmed clustering patterns up to distances of 115 to 190 m, with higher aggregation of empty shells at the same study zone. The bay also featured low juvenile availability (3.2%), which risks the continuity of the population. No evidence for habitat or conspecific selection could be observed from abundance patterns and variation in NN across study regions. Our research provides a tool for assessing population condition in paralic environments, where salinity conditions tend to slow down disease spread, thus allowing a time gap for undertaking conservation decisions.     

Mechanisms and consequences of shell fouling in the kelp snail,Norrisia norrisi (Sowerby) (Trochidae): Indirect effects of octopus drilling

The kelp snail, Norrisia norrisi (Sowerby), dwells on the large kelps Macrocystis pyrifera (L.) and Eisenia arborea Areschoug, and is rare on benthic substrata. Approximately 4% of the snail population is dislodged from plants each day. Per capita mortality of snails on the benthos is an order of magnitude greater than individuals on kelp. Even though snails displaced to the bottom actively seek a plant to climb, we found that between 20–40% of marked snails released on the bottom were killed over a 24-day period. While most N. norrisi are free of epibionts on their shells, ≈30% of the population are encrusted by the barnacle Megabalanus californicus (Pilsbry). The majority of barnacle fouling was the result of failure by Octopusbimaculatus (Verrill) to kill Norrisia norrisi; barnacle cyprids settled in octopus drill holes in the shells of live kelp snails. N. norrisi encrusted by barnacles were less effective in exploiting kelp compared with unfouled snails. Moderately to heavily fouled snails were dislodged from kelp twice as frequently and remained on the benthos much longer than snails without epibionts. Laboratory tests revealed that escape velocities of N. norrisi from asteroid predators were much reduced by shell fouling, and that snails carrying barnacles were most likely to be captured and consumed. Hence octopus increase mortality of kelp snails in two ways. First, octopus can kill N. norrisi encountered on the bottom. Second, kelp snails drilled by octopus, but not killed outright, will become fouled by barnacles. This results in a subsequent risk of mortality from all benthic predators that is at least 8-fold greater than for unfouled kelp snails.     

Resource allocation,demography and the radiation of life histories in rough periwinkles (Gastopoda)

Applicability of life-history theory to higher levels of comparison (from populations, through ecotypes to sibling species) was investigated in rough periwinkles, whose life histories have diversified since colonization of the North Atlantic by an oviparous ancestor in the upper Pliocene. Comparisons were made among populations of the ovoviviparous Littorina saxatilis, between L. saxatilis and its ecotype, L. neglecta (with an annual life history) and between the sibling species L. saxatilis and L. arcana, the latter of which retains the ancestral oviparity. Resource-allocation priority, reproductive effort and related trade offs were compared between the ecotypes and the sibling species by measuring changes in flesh mass and reproductive output in snails subjected to different degrees of food deprivation, and by measuring mortality rate of snails stressed by desiccation, high temperature and low salinity. Body size had a marked effect on all parameters, but after statistically removing this effect there remained no significant differences in allocation among ecotypes or species. Published demographical data were reviewed for correlations between habitat, mortality regime and life-history characteristics. Populations of L. saxatilis varied principally in size at birth and in adult size. Theoretical premises based on density-dependent versus density-independent mortality regimes could not explain these trends. Instead, size at birth may have reflected the mechanical, physiological or biological nature of mortality risk rather than its density dependence or independence. Adult size reflected the available sizes of crevices used for shelter and perhaps also the quality of feeding conditions. Radiation of life histories within the rough periwinkles is interpreted as a series of adaptations to a progressively wider range of habitats. The transition from oviparity to ovoviviparity allows colonization of estuaries, saltmarshes and pebble beaches too hazardous for naked egg masses. The transition from a perennial to an annual life history in barnacle ecotypes follows from allometric re-scaling of morphological and physiological parameters, enabling reproduction and brooding to occur at the small body size necessary for life within empty barnacle tests. This suite of adaptations allows exploitation of a relatively benign microhabitat that occurs almost ubiquitously on exposed rocky shores of the temperate North Atlantic. The persistence of oviparous forms, presumably in the face of competition from sympatric ovoviviparous forms, remains unexplained.     

The effects of exposure and predation on the shell of two British winkles

Changes in shell size and shell shape of the two British winkles Littorina nigrolineata and L. rudis were studied in relation to exposure and to crab-size. In both species, shells from exposed shores are smaller and more globose than those from sheltered shores. Also, in rudis of exposed shores the mouth is relatively wider. In shores of equally sheltered conditions, shells are bigger at those localities where crabs are large than at those localities where they are small. The largest shells are found in those localities where it is extremely sheltered, and the crabs are very large.
It is argued that on exposed shores, small shells are favoured because they have more possibilities than large ones to shelter in crevices and in barnacle interspaces, from the impact of winds and waves. A globose shell could accommodate more foot muscle and thus enable a stronger adherence to the rock; and an increased mouth diameter would increase the area of foot adherence to the rock. On sheltered shores, on the other hand, large, narrow-mouthed shells are favoured because they discourage crab predation, large crabs being abundant mainly on sheltered shores.
The possible significance of shell size and shape in relation to zonation is discussed, in view of the different predatory and physical conditions which prevail in different zones of the shore, and the different shell specializations which these conditions would require.     

Predatory behaviour of juvenile shore crab Carcinus maenas (L.)

Juvenile shore crabs Carcinus maenas (L.) were observed feeding on rock barnacles Semibalanus balanoides (L.) on a Bay of Fundy rocky shore. This previously unreported predatory behaviour was further investigated in the laboratory. When given a choice of three common and abundant gastropods, Nucella lapillus (L.), Littorina littorea (L.), and Littorina obtusata (L.), and the rock barnacle Semibalanus balanoides, juvenile shore crabs of both sexes ate mainly barnacles and consumed proportionately more barnacles than gastropods compared with adults, which ate mainly gastropods. The rock barnacle is an abundant and readily available food source which may be important in sustaining the juvenile crab through periods of moults and rapid growth. As the shore crab attains a certain age (size), it must forage lower on the shore as gastropods become more important in its diet.     

Initial Effects of Wildfire on Freshwater Turtle Nesting Habitat

Natural wildfire regimes are important for ecosystem succession but can have negative ecological effects depending on fire characteristics. A portion of a granite rock barrens landscape that extends along the eastern shoreline of Georgian Bay, Lake Huron to eastern Ontario, Canada, burned in 2018 during a wildfire that affected >11,000 ha. This landscape is a biodiversity hotspot providing habitat for many species at risk where freshwater turtles nest in soil deposits in cracks and crevices in the bedrock dominated by moss (Polytrichum spp.) and lichen (Cladonia spp.) cover. To assess the initial effect of wildfire on freshwater turtle nesting habitat, we measured soil depths and estimated moss, lichen, and vascular plant cover at 2 morphology types (crevice, flat) in burned and unburned areas of the landscape. The probability that burned flat plots supported soil was near zero; the burned flat plots had 98% less soil volume compared to unburned flat plots. Although crevices were more resistant to soil loss, burned crevices still had a 15% lower probability of having soil and 35% less soil volume compared to unburned crevice plots. We estimated nest site availability by calculating the number of locations with shallow (5–10 cm), intermediate (10–20 cm), and deep (>20 cm) soils required for a small (5 cm × 5 cm) or medium (10 cm × 10 cm) nest chamber. Overall, the burned open rock barrens had 71–73% fewer sites with suitable soil depth and volume for a nest chamber of either size. Furthermore, burned plots had almost no lichen and moss cover but were dominated by bare soil, forbs, and jack pine (Pinus banksiana) seedlings. Although the loss of tree cover in previously forested areas may increase nest site availability for freshwater turtles in newly open areas, we suggest that organic soil combustion and soil erosion may require restoration activities in the post-fire landscape to support successful nesting of at-risk turtles. © 2020 The Wildlife Society.     

Gastropod shells: A potentially limiting resource for hermit crabs

The availability of gastropod shells to hermit crabs in the Newport River Estuary, Beaufort, N.C. has been assessed by determining the numbers of usuable shells occurring in characteristic subtidal habitats and by measuring shell size adequacy. The proportion of useable shells occupied by hermit crabs ranged from 58–99 % and many of the shells not used by hermit crabs were judged unavailable because they were occupied by sipunculids or only uncovered by the dredge. The shell adequacy index (shell size occupied/shell size preferred) was significantly below 1.0 for the largest species (Pagurus pollicaris Say) in the one location where sufficient numbers were collected and for the next largest species (P. longicarpus Say) in three of the four locations where it was collected. The shell size adequacy index for the smallest species (P. annulipes Stimpson) did not differ significantly from 1.0 in either of the two locations in which it was found. These observations suggest that the availability of gastropod shells plays a significant rôle in limiting the abundance of at least the larger hermit crabs.