Search

In marine soft-bottom environments, the availability of hard substrates may strongly influence the reproduction of benthic species. Most marine gastropods attach egg capsules to any hard object lying on the sediment surface, but some species may choose to deposit egg capsules on living organisms. This study reports deposition of egg capsules on shells of living Tivela mactroides. We collected T. mactroides individuals in six sampling sites along a morphodynamic continuum to investigate which species was using T. mactroides as oviposition substrate as well as looking at the pattern of capsule deposition on the shells. More than 90% of T. mactroides individuals had one to 55 egg capsules on their shells, all belonging to Olivella minuta —the first record of this interspecific relationship. Most egg capsules were concentrated closer to the umbo of the bivalve (dorsal region) and there was no evident relationship between the number of egg capsules and length of T. mactroides. The number of egg capsules strongly decreased in more reflective beach conditions; however, the pattern of egg deposition on the shells was roughly similar in all sites. These findings increase our understanding of the reproductive biology of O. minuta and demonstrate the ecological importance of T. mactroides ; they also emphasize that biological interactions and density-dependent relationships may influence the community ecology of soft-bottom habitats. [ABSTRACT FROM AUTHOR]

Archaeological investigations of the age and origins of marine shell beads are important for understanding the emergence and maintenance of long-distance trade networks in prehistory. In this paper we expand upon and re-examine the incremental carbon (14C and δ13C) and oxygen (δ18O) isotope data from two Olivella biplicata shell beads from the LSP-1 Rockshelter, Oregon, USA, to address two common problems in dating marine shell trade goods: (1) the source region is large, adding to uncertainty regarding the appropriate specification of ΔR; and (2) the 14C activity within individual specimens is variable. Although this combination of factors severely limits the dating precision that is possible, we recommend a sampling and calibration approach that accounts for these added sources of uncertainty and minimizes the loss of precision. We recommend (1) sequential sampling in order to quantify the range of variability in 14C within shells; (2) a Bayesian calibration procedure that models the 14C dates as an ontogenetic sequence, in this case constrained by stable isotope sclerochronology; and (3) specifying ΔR in a manner that accounts for the full range of possible reservoir offsets in the source region. [ABSTRACT FROM AUTHOR]

Beads manufactured from marine shells originating along the Pacific Coast have been found at numerous sites in the western United States. Because they were conveyed across substantial distances and widely exchanged during ethnographic times, researchers generally assume that shell beads were also traded prehistorically. By examining the spatial and temporal distribution of beads, researchers have reconstructed prehistoric exchange networks. In this report, we present stable isotope data and accelerator mass spectrometer (AMS) radiocarbon dates for six Callianax (previously Olivella) biplicata beads from the LSP-1 rockshelter in southcentral Oregon. Most of the beads were deposited during the early Holocene during a series of short-term occupations and the shells used to manufacture them were procured along the northern California, Oregon, or Washington coasts. [ABSTRACT FROM AUTHOR]

Predator-prey interactions can shape biological communities and drive evolutionary change. The assessment of predation rates in modern and ancient ecosystems presents many challenges. We examined the utility of one common predation metric, shell repair frequency, as a proxy for crushing predation on marine gastropod populations. Our six localities near Bamfield, British Columbia, represented two contrasting predation regimes: three high-wave-energy (exposed) environments have low predation rates, while three low-wave-energy (protected) environments exhibit high predation rates. We measured the occurrence of repair scars for local populations of the gastropod Chlorostoma funebrale, and recorded multiple independent variables (shell measurements, water velocity, predatory crab abundance) at each locality. Fisher's exact test established that the repair frequencies observed in the protected localities were significantly greater than those of the exposed environments. Factors important in predicting the likelihood of an individual having a repair scar were examined using binomial logistic regression. A model containing the main effects of crab abundance, shell height, shell thickness and water velocity provided the best fit in predicting the presence of repair scars, with crab abundance having the largest contribution. The strong relationship between the presence of repair scars and predator abundance indicates that repair frequency is a valid tool for assessing predation intensity in gastropod populations. [ABSTRACT FROM AUTHOR]

This is the very first checklist of the terrestrial gastropods of Nepal. It includes 138 species and six subspecies, of which 22 species are endemic and four are introduced. It highlights 34 species recorded for the first time in Nepal and provides new distribution records for another 30 species. [ABSTRACT FROM AUTHOR]

The structure, dynamics and production of two populations of the olivid gastropod Olivella minuta were analyzed through monthly sampling from November 2009 through October 2011 on two sandy beaches, Pernambuco (very sheltered) and Barequeçaba (sheltered) in São Paulo state (23°48'S), southeastern Brazil. On both beaches, samples were taken along five transects established perpendicular to the waterline. Parameters of the von Bertalanffy growth function were estimated for both populations from monthly length-frequency distributions. The production and turnover ratios were determined using the mass-specific growth rate method. The population on the less-sheltered Barequeçaba Beach was less abundant (120.02 ± 22.60 ind m −1 ) than on Pernambuco Beach (3295.30 ± 504.86 ind m −1 (±SE)), which we attribute to the greater environmental stability of the latter. Conversely, the mean length, size of the largest individual, and body mass were higher at Barequeçaba than at Pernambuco. The significant differences in the growth of individuals and the mortality rate (Z) between the beaches suggest that density-dependent processes were operating at Pernambuco Beach. The production and P / B ratio at Pernambuco (12.12 g AFDM m −1 year −1 and 1.91 year −1 ) were higher than at Barequeçaba (0.82 g AFDM m −1 year −1 and 1.06 year −1 ). The difference in production can be attributed to the higher abundance on Pernambuco, while the higher P / B ratio resulted from the scarcity of smaller individuals in the intertidal zone of Barequeçaba. The P / B ratio estimated for the Pernambuco population is the highest found so far for sandy-beach gastropods. This study reinforces the theory that biological interactions are important regulators of sheltered sandy-beach populations. Future studies with multi-beach sampling are needed to better understand the life-history variations of O. minuta along gradients of degree of exposure of sandy beaches. [ABSTRACT FROM AUTHOR]

Marine drilling predation, in which the predator bores a hole through shelled invertebrate prey, plays a role in the structure of benthic communities. As drilling often leaves the prey shell otherwise undamaged, the resulting holes are also an excellent proxy for drilling predation pressure in the fossil record. Considering that a large number of predation studies focus on drilling predation in the fossil record, it is crucial that we are able to distinguish true drilling predation from taphonomy. The purpose of this study is to determine damage onOlivella biplicatashells, drilled by naticid gastropods, is distinguishable from taphonomically produced damage to these shells. In addition, the potential for preferential breakage due to either the presence or whether absence of a drillhole was investigated. Drilled and non-drilledO. biplicatashells were tumbled to simulate wave action and were checked at intervals to record accumulated damage. Drilled and non-drilled shells do not show a significant difference in damage accumulated while undergoing simulated wave action. Taphonomic damage is unlikely to be mistaken for drilling damage, due to the jagged, irregular appearance of taphonomically produced holes. [ABSTRACT FROM PUBLISHER]

Predatory gastropod drill holes are an abundant and easily identifiable signal of predation in ancient and modern molluscan shell assemblages. Many workers have used drill holes to interpret patterns of predation intensity and success in fossil assemblages. These studies are predicated on the assumption that the relative abundances of drilled and undrilled shells in an assemblage accurately reflect those of the community from which the shells were originally derived. The underlying assumption is that drilled and undrilled shells are transported into shell accumulations in the same manner. If this assumption is false, shell accumulations do not represent taphonomically unbiased samples, but rather preferentially sorted deposits from which conclusions about drilling predation cannot be made. To test the hypothesis that drilled and undrilled gastropod shells transport at different flow velocities, multiple transport trials were conducted on two morphologically distinct taxa, Olivella biplicata and Euspira lewisii. Individual specimens were placed in a recirculating flume tank and observed from rest (in stable orientation) until they were transported downstream. During each trial, flow velocity was slowly and incrementally increased, so as to avoid pulses of acceleration, until shells began to move downstream. Drilled and undrilled specimens of both taxa demonstrate statistically significant correlations between shell mass and average transport velocity. Similarly sized drilled and undrilled specimens of both taxa do not exhibit significant differences in transport velocity. These results indicate that predatory drill holes do not change the hydrodynamic properties of gastropod shells. Therefore, gastropod shell assemblages are not likely to be affected by differential transport and sorting of drilled and undrilled shells. [ABSTRACT FROM AUTHOR]

Abstract: Vermeij Crushing Analysis allows researchers to estimate frequencies of fragmentation due to crushing predation by establishing a taphonomic fragmentation baseline using shells bearing predatory drillholes. We calculated the frequencies of several types of shell damage on groups of drilled and undrilled shells. Shells of the modern species Olivella biplicata, O. baetica, Nassarius perpinguis, and Euspira lewisii were collected at Torrey Pines State Beach, Del Mar, California. The shells were divided into drilled and undrilled groups and examined for multiple types of damage. The frequencies of damage in the drilled groups represent taphonomic damage, as the cause of death of these shells is known to be naticid gastropod predation. In cases where the damage frequencies were higher for the undrilled shells (cause of death unknown, possibly crushing), the differences in fragmentation between the two categories is attributed to crushing predation. The frequencies of damage due to crushing predation are used to estimate a minimum frequency of mortality due to crushing predation in the shell assemblage. Potential confounding factors were also examined, such as potential differences in taphonomic susceptibility and hermit crab habitation between drilled and undrilled shells. This technique bypasses the logistical difficulties of field predation studies and the problems of interpretation of shell repair frequencies, two common methods of assessing crushing predation in shelled prey. Most significantly, Vermeij Crushing Analysis can be performed on both modern and fossil shell assemblages, allowing the study of trends in crushing predation over both space and time. [Copyright &y& Elsevier]

Production of marine shell beads in island and coastal settings was an important activity in prehistory, with important political and economic ties. Currently, there are few methods to track beads to their locus of production. Examining the spatial distribution of bead types provides one method of doing so. Chemical and stable isotopic methods provide an additional and independent means of testing hypotheses generated by spatial distributions. We use stable oxygen, carbon, and strontium isotope data to reconstruct provenance zones for 18 Olivella biplicata beads from the Los Angeles Basin and San Nicolas Island, California. We compare the results to isotopic data from modern and radiocarbon-dated whole shells collected along the Pacific Coast. Results indicate that all 18 beads were manufactured from shells growing in open coast locations south of Point Conception. Differences in isotopic composition between bead types suggest that not all were produced in the same location. Some, such as callus beads (K1), have highly variable composition, suggesting production in a range of locations. Others, such as thin lipped (E1), seem to have been produced in more restricted regions. [ABSTRACT FROM AUTHOR]

The size-specific burrowing capacity of Olivella semistriata, an extremely abundant surfing gastropod of exposed sandy beaches in the tropical East Pacific, was investigated in terms of sediment grain size. For all investigated sand classes, there was a significant increase in burial time with size. Burrowing was fastest in sand with grain size between 150 and 355 μm, as well as in native sediment (median grain size 209 μm) and in field conditions (median grain size 223 μm). Values of the burrowing rate index (BRI) were found to be between 3 and 7, rating the burrowing capacity of O. semistriata to be fast to very fast. Data from previous qualitative and quantitative sampling campaigns were used to identify the macroscale (i.e., between beaches) distribution of O. semistriata in terms of sediment grain size and swash conditions. Swash period was shorter than burial time, excluding this as a factor limiting the distribution. Swash standstill time (the time between uprush and backwash), however, was just long enough on the beaches, where O. semistriata was present to allow for securing firm anchorage. On reflective beaches, the swash standstill time is as short as 1 or 2 s, denying O. semistriata the time to burry itself before being swept away by the backwash. As such, swash standstill time is advocated as a valuable part of the swash exclusion hypothesis. A survey of the available literature on the burrowing of surfers shows that mole crabs are by far the fastest burrowers and the only surfers that burrow sufficiently fast to withstand the extremely short swash standstill time on reflective beaches. Burrowing ability of surfing gastropods is found in the same range as surfing bivalves, both being insufficient to cope with coarse sediment on steep beaches. Finally, we suggest that neither burial time nor BRI, yet rather the minimal burial time—the time needed to anchor securely in a certain sand at a given swash velocity—should be used to judge the limitations of burial in terms of sediment and swash conditions. [ABSTRACT FROM AUTHOR]