Carrie L. Tyler

Predation on Modern and Fossil Brachiopods: Assessing Chemical Defenses and Palatability

ABSTRACT The post-Paleozoic decline of the diversity and abundance of rhynchonelliform brachiopods has been attributed to a variety of factors. Of the possible mechanisms invoked to explain the evolutionary decline and cryptic or antitropical distribution of brachiopods, predation has frequently been dismissed due to the potentially low energetic value and suspected nonpalatability or toxicity of brachiopod tissues. Herein we demonstrate that multiple invertebrate marine predators (crustaceans, echinoderms, and gastropods) are willing and able to consume brachiopods in laboratory settings without observable negative effects after ingestion. In addition, field samples indicate predation pressure on the living brachiopod population may be substantial. Although feeding trials are consistent with previous reports that bivalves are preferred prey relative to brachiopods, predation should not be dismissed as a potentially important factor in brachiopod ecology and evolution. The results presented herein reveal that in some cases brachiopods may be the intended target of predatory attacks, especially in habitats where mollusks are rare or absent. Examination of the fossil record of predation on rhynchonelliform brachiopods is consistent with this interpretation: evidence for drilling and repair of brachiopod shells is found throughout the fossil record in multiple lineages. While it is likely that predation traces on post-Paleozoic brachiopods are generally rare, there are multiple reports of fossil localities with anomalously high drill-hole or repair-scar frequencies. This suggests that although brachiopods may be unwanted prey in the presence of energetically more desirable targets, they do appear to be edible and subject to intense predator-prey interactions under certain conditions.

Utility of Marine Benthic Associations as a Multivariate Proxy of Paleobathymetry: A Direct Test from Recent Coastal Ecosystems of North Carolina

Benthic marine fossil associations have been used in paleontological studies as multivariate environmental proxies, with particular focus on their utility as water depth estimators. To test this approach directly, we evaluated modern marine invertebrate communities along an onshore-offshore gradient to determine the relationship between community composition and bathymetry, compare the performance of various ordination techniques, and assess whether restricting community datasets to preservable taxa (a proxy for paleontological data) and finer spatial scales diminishes the applicability of multivariate community data as an environmental proxy. Different indirect (unconstrained) ordination techniques (PCoA, CA, DCA, and NMDS) yielded consistent outcomes: locality Axis 1 scores correlated with actual locality depths, and taxon Axis 1 scores correlated with actual preferred taxon depths, indicating that changes in faunal associations primarily reflect bathymetry, or its environmental correlatives. For datasets restricted to taxa with preservable hard parts, heavily biomineralized mollusks, open ocean habitats, and a single onshore-offshore gradient, the significant correlation between water depth and Axis 1 was still observed. However, for these restricted datasets, the correlation between Axis 1 and bathymetry was reduced and, in most cases, notably weaker than estimates produced by subsampling models. Consistent with multiple paleontological studies, the direct tests carried out here for a modern habitat using known bathymetry suggests that multivariate proxies derived from marine benthic associations may serve as a viable proxy of water depth. The general applicability of multivariate paleocommunity data as an indirect proxy of bathymetry is dependent on habitat type, intrinsic ecological characteristics of dominant faunas, taxonomic scope, and spatial and temporal scales of analysis, highlighting the need for continued testing in present-day depositional settings.

Categorization of shell fragments provides a proxy for environmental energy and predation intensity

Shell fragments are extremely abundant in many marine environments; the origins of these fragments can largely be attributed to either crushing by predators or post-mortem processes such as transport. We present and test a new approach to identifying the origin of shell fragments in marine environments by examining modern mollusc assemblages from three wave-exposed, low-predation and three wave-sheltered, high-predation intertidal localities in Bamfield, British Columbia. We hypothesized that fragments with all-rounded edges (AR) or a combination of rounded and sharp edges (R&S) are indicative of taphonomic processes such as transport and so should occur more often in wave-exposed, low-predation localities whereas fragments with all sharp edges (AS) or a combination of intact and sharp edges (I&S), indicative of predation, should be more common in wave-sheltered, high-predation settings. In keeping with the prediction, All-Rounded (AR) and Rounded and Sharp (R&S) fragments are more abundant at the wave-exposed localities than at wave-sheltered localities whereas Intact and Sharp (I&S) and All-Sharp (AS) fragments are more abundant at high-predation localities than at low-predation localities. The two types of localities were statistically distinguishable for either gastropod or bivalve fragments. This supports the hypothesis that I&S and AS result from predation, whereas AR and R&S have a taphonomic genesis.

Surrogate taxa and fossils as reliable proxies of spatial biodiversity patterns in marine benthic communities

Rigorous documentation of spatial heterogeneity (β-diversity) in present-day and preindustrial ecosystems is required to assess how marine communities respond to environmental and anthropogenic drivers. However, the overwhelming majority of contemporary and palaeontological assessments have centred on single higher taxa. To evaluate the validity of single taxa as community surrogates and palaeontological proxies, we compared macrobenthic communities and sympatric death assemblages at 52 localities in Onslow Bay (NC, USA). Compositional heterogeneity did not differ significantly across datasets based on live molluscs, live non-molluscs, and all live organisms. Death assemblages were less heterogeneous spatially, likely reflecting homogenization by time-averaging. Nevertheless, live and dead datasets were greater than 80% congruent in pairwise comparisons to the literature estimates of β-diversity in other marine ecosystems, yielded concordant bathymetric gradients, and produced nearly identical ordinations consistently delineating habitats. Congruent estimates from molluscs and non-molluscs suggest that single groups can serve as reliable community proxies. High spatial fidelity of death assemblages supports the emerging paradigm of Conservation Palaeobiology. Integrated analyses of ecological and palaeontological data based on surrogate taxa can quantify anthropogenic changes in marine ecosystems and advance our understanding of spatial and temporal aspects of biodiversity.

The utility of wax replicas as a measure of crab attack frequency in the rocky intertidal

Crabs are thought to play a vital role in structuring gastropod populations. Studies quantifying the frequencies with which crabs attack gastropods in natural settings are, however, scarce. Although a wide variety of techniques exist with which predator–prey interactions can be investigated (e.g. laboratory experiments, exclusion caging, tethering and population surveys), there is a need for methods that can provide large amounts of quantitative data, particularly documenting the frequency with which crabs attack gastropods. This study examines the utility of using wax replicas of gastropods to determine crab attack frequencies. Replicas of Chlorostoma funebralis, Nucella ostrina and Nucella lamellosa were bolted to mesh screens and deployed in the rocky intertidal. Crabs attacked wax replicas of gastropods, leaving characteristic marks in the wax. In most cases, the appendage used in the attack could be identified from the marks (i.e. chelae vs walking legs). The effectiveness of this technique was verified using surveys of repair scar frequencies of the gastropod populations; patterns in attack frequency, determined from the number of marked wax replicas, were consistent with those of repair frequency, in that both were greater at the wave protected, quiet water locality. This study confirms the value of wax replicas in investigations of crab predation to determine the frequency and type of attack, and illustrates the potential of this method for quantifying predation intensity. The development of techniques that quantify the magnitude and exact nature of the effects of crab predation on intertidal communities is pivotal, given the intensity of commercial fishing of some species of crabs.

Regional surveys of macrobenthic shelf invertebrate communities in Onslow Bay, North Carolina, U.S.A.

Despite its importance for quantifying ecosystem responses to environmental and anthropogenic drivers, our understanding of spatial heterogeneity in marine communities remains inadequate. Studies in coastal marine benthic habitats are sparse, and predominantly target single higher taxonomic groups. Here we describe macrobenthic marine invertebrate community surveys from 52 localities in Onslow Bay (Beaufort, North Carolina, U.S.A.), over an extensive geographic area (~200 km2). The data consist of 11,467 individuals, 175 species, and 7 phyla. The data include species abundance data for each sample at all localities, and corresponding species lists and locality information. The metadata describe the sampling protocols and localities. The data provided here will facilitate examination of assemblage heterogeneity with regards to spatial and temporal patterns, and depth gradient analyses.

An Overview of Conservation Paleobiology

The field of conservation paleobiology was formally established in the early 2000s, as a growing body of literature substantiating the fidelity of paleontological data on a variety of spatial and temporal scales emerged, and paleontologists became increasingly aware of the potential insights that the fossil record could provide into the current biodiversity crisis. Conservation paleobiology contributes a temporal scope and historical perspective lacking from the relatively short time spans covered by modern ecological studies, progressively in demand in the face of changing climate and environmental degradation. The increasing number of conservation paleobiology studies in the past decade validates the potential contributions of this field to conservation efforts, and fall within a range of temporal categories (e.g., “near-time” and “deep-time”). Data are not restricted to fossils, but can also include historical reports and archeological evidence (conservation archeobiology). Although temporal resolution often declines with increased assemblage age, ancient ecosystems document responses to, and recoveries from, global crises. Thus, the field of conservation paleobiology, when considered in concert with historical ecology and conservation biology, has the potential to positively affect future ecosystems and biodiversity.

A Conceptual Map of Conservation Paleobiology: Visualizing a Discipline

Disciplinary boundaries frame the basic questions and central issues of research, providing the context for the evolution of prevailing theories or paradigm shifts. This chapter aims to outline the development and scope of conservation paleobiology using bibliometrics. Publication records relating to research on conservation paleobiology were downloaded from Web of Science to generate two datasets, one aimed at producing a more conservative representation of conservation paleobiology, and the other more expansive. Bibliographic maps were created to provide insight into the development and structure of the discipline for both characterizations of conservation paleobiology research (conservative versus expansive). Bibliographic maps indicated that individual researchers working on conservation paleobiology specialize in several fields. Regardless of how conservation paleobiology is defined, research involving both paleontology and conservation appears to be highly multidisciplinary, including at least three main research domains broadly categorized as: (1) environmental history and conservation archeobiology, (2) genetics and evolutionary biology, and (3) ecology. Furthermore, paleontological publications did not form a distinct cluster, but rather were integrated within conservation science. This supports the proposition that, in practice, conservation paleobiology is a field of study within conservation science, and not a sub-discipline within paleontology. Analyses also revealed emerging research fronts in several topics and confirmed the need for long-term data that pre-dates human activities.