Steven J. Hageman

Bryozoan growth habits; classification and analysis

Bryozoans are an important part of the benthic marine fauna in a wide variety of modern environments and are found in rock forming abundance in a number of settings throughout much of the Phanerozoic. Bryozoologists and nonspecialists have grouped taxa into colonial growth forms (e.g., erect fenestrates or encrusting sheets), both to simplify analyses and because correlations exist between some colony growth forms and the environmental conditions in which the organism lived. These correlations allow for the possibility of paleoenvironmental analyses based on skeletons alone. Existing bryozoan colonial growth from classifications do not, however, fully exploit the ecological information present in colony form. A new scheme is proposed here (Analytical Bryozoan Growth Habit Classification), which provides a list of colony-level morphological characteristics for bryozoan growth habits. This differs from previous approaches to bryozoan growth form analysis in that it is a classification of growth habit characteristics rather than a classification of morphological groups as such. The classification is based on eleven character classes, which describe the orientation of the colony and its occupation of, and placement in space. The overall colony shape is described based on the arrangement of modules in colonial growth. This classification provides a common ground for systematic comparison of character states among varied bryozoan growth habits. This approach allows for the evaluation of correlations among observed morphological character states and specific environmental conditions in which they develop. In addition, these growth habit characters can be used to recognize, characterize, evaluate, and apply more traditional growth form groups in broader studies.

Cool-water Carbonate Production from Epizoic Bryozoans on Ephemeral Substrates

Abstract Bryozoan skeletons are a dominant constituent of cool-water carbonate sediments in the Cenozoic of southern Australia. The primary substrate on much of the modern continental shelf is loose sediment that is reworked intermittently to 200+ m water depth by storm waves. Availability of stable substrate is a limiting factor in the modern distribution of bryozoans in this setting. As a result, a significant proportion of the sedimentologically important modern bryozoans (30–250 m water depth) live attached to sessile, benthic invertebrate hosts that possess organic or spicular skeletons. Hosts such as hydroids, ascidian tunicates, sponges, soft worm tubes, octocorals, and other lightly-calcified and articulated bryozoans provide ephemeral substrates; after death, host skeletons disarticulate and decay, leaving little or no body fossil record. The calcareous sediments produced by these epizoic bryozoans from ephemeral substrates result in loose particles that rarely preserve substratal relationships, but potentially retain diagnostic basal attachment morphologies. Although the best known examples of epizoic carbonate production on ephemeral substrates are from the southern Australian margin, this may be an important phenomenon both globally and in the fossil record. Bryozoan sediment production from epizoans on ephemeral substrates would seem, however, to have a scant record prior to the Cretaceous.

Bryozoan colonial growth-forms as paleoenvironmental indicators; evaluation of methodology

Bryozoans have played a significant ecological role in many shallow marine benthic communities since the Ordovician and are important contributors to carbonate sediment production in many modern cool-water marine environments. Correlation between bryozoan colonial growth forms and environments in which the organisms lived allows for the application of growth forms as paleoenvironmental indicators. This can be done as either (1) a characterization of regional environmental or distributional data within a comprehensive study; or (2) as a predictive tool applied in an unknown setting using limited data. A number of workers have demonstrated this potential in biological, paleontological, and sedimentological studies. Growth-form distributions established independently from, and later compared to, environmental factors provide for the greatest predictive utility. Problems encountered in methodology need to be addressed before bryozoan colonial growth forms can achieve their full potential as paleoenvironmental indicators. Methodological problems include those associated with specimen abundance versus species richness, numeric versus volumetric frequency, relative versus absolute abundance, and changes within growth forms among localities versus changes among growth forms within localities (facies). A procedure is proposed that combines species richness and specimen abundance, as well as information about distributions within growth forms and within localities, into a single, comparable data set. An example is provided using bryozoans from the cool-water Lacepede Shelf of southern Australia.

APPROACHES TO SYSTEMATIC AND EVOLUTIONARY STUDIES OF PERPLEXING GROUPS: AN EXAMPLE USING FENESTRATE BRYOZOA

Recognition of discrete taxa is an enduring problem in the biological sciences, especially for taxonomists who work with groups that display a great degree of homeomorphy at low taxonomic levels. Selection of the type and number of characters used to make taxonomic distinctions is important because it reflects taxonomic concepts for a group as a whole. Often the validity of characters used to develop classifications is not documented and resulting classifications are therefore suspect. However, classifications can be tested for their objectivity with numerical analysis and characters can be evaluated for their relative value for making taxonomic splits by a variety of statistical techniques. In addition, evaluation of the distribution of character states can lead to insights into evolutionary histories of any group. This study provides such an analysis. Fenestrate cryptostome Bryozoa are abundant and diverse in many upper Paleozoic rocks, and are therefore potentially highly useful for a variety of paleontologic studies. However, study of fenestrates is hampered by necessary complex preparation techniques and problems encountered with homeomorphy. In addition, inconsistent applications of inadequate methodologies have contributed to an unsatisfactory taxonomy. Results from cluster and discriminant analyses demonstrate that fenestrate species can be objectively recognized. Species distinctions are most clear when all available characters are used, although some characters are more diagnostic than others. Results from cluster and discriminant analyses suggest that fenestrate genera represent major evolutionary shifts associated with the development of key character(s) that allowed entry into new adaptive zones. Key characters allow for an oligothetic classification of genera, which is not merely an artifact created to simplify taxonomic analysis. Diversification of species within adaptive zones resulted in a natural hierarchy of genus-level and species-level characters. Iterative evolution at the species level within separate adaptive zones resulted in a great deal of homeomorphy. Morphometric analysis provides insights into several aspects of the paleobiology of this traditionally problematic group. Similar comprehensive studies may prove equally productive for other groups.

Paleoenvironmental Significance of Celleporaria (Bryozoa) from Modern and Tertiary Cool-water Carbonates of Southern Australia

Abstract Certain members of the bryozoan genus Celleporaria form large, erect colonies of hollow branches (∼10–30 cm tall and 1–3 cm diameter). These are common and conspicuous in Pleistocene and Cenozoic neritic strata of the southern margin of Australia. Most of these basins are characterized by decimeter-scale cycles through subtidal, heterozoan, cool-water, carbonate sediments. Several intervals are further characterized by pervasive celleporarid bryozoan thickets (10–30 cm thick), individual units of which can be traced for many tens of kilometers. Study of modern, live celleporarid bryozoans from the continental shelf of the Great Australian Bight (GAB), Pleistocene celleporarid mounds stranded below the shelf break of the Australian margin, and Miocene celleporarid thickets from the Murray and Torquay Basins indicates that Celleporaria thickets form under specific environmental conditions: i.e., low-energy or sub-swell wave-base settings, mud-silt substrate, medium-high mesotrophy, and moderate sedimentation rate. These conditions, however, are not site specific. They are manifested here in two different environmental settings: (1) a deep-water (>200 m), upwelling nutrient source, below the shelf break during extreme sea-level low stands; and (2) shallow-water (<50 m), terrestrial nutrient source, in embayments, far inland from the shelf break during relative high stands of sea-level. The celleporarid growth habit (species specific—not an ecomorph) allows their populations to proliferate in spatially restricted, transitional, geologically short-lived environments where most other bryozoans cannot cope. Their environmental sensitivity means that Celleporaria have great potential for paleoenvironmental analysis of Cenozoic carbonate Tethyan sediments.

Partitioning phenotypic variation: genotypic, environmental and residual components from bryozoan skeletal morphology

Using morphometric studies of colonial (clonal) organisms such as Bryozoa grown as replicates in controlled laboratory experiments, phenotypic variation (hard part morphology) can be partitioned into its genotypic and environmental (ecophenotypic) components. The interaction between these, i.e. different genotypic responses to the same environmental change, can also be recognized. Palaeobiological studies are inherently constrained by species concepts based on morphotypes (preserved morphological phenotype). Uncertainties associated with fossil species concepts restrict the deductive resolution potential of fossil taxa in discussions of the broader biological questions of species evolution, ecology, biogeography and phylogeny. The relationship between species-level morphological variation and genetic variation in modern taxa is central to evaluating the viability of fossil morphotypes as biological species. Results from a preliminary study of three genotypes of Electra pilosa L., grown as replicate coloni...

Paleozoic to modern marine ecological shift displayed in the northern Adriatic Sea

One of the major changes in the history of life was the decline from abundant sedentary, suspension-feeding animals living on the seafloor during the Paleozoic to their relative scarcity afterward, while animal life within the sediment burgeoned after the end-Paleozoic extinction. In the northern Adriatic Sea there is a quantitative change from abundant exposed sedentary suspension feeders in eastern oligotrophic water to their virtual absence under western higher-nutrient waters, where prolific animal life occurs within sediments. This geographic gradient supports the hypothesis that an increase in neritic nutrients drove—and continues to drive—the Paleozoic to post-Paleozoic marine ecological transition.

Complexity generated by iteration of hierarchical modules in Bryozoa

Abstract Growth in colonial organisms by iteration of modules inherently provides for an increase in available morpho-ecospace relative to their solitary relatives. Therefore, the interpretation of the functional or evolutionary significance of complexity within groups that exhibit modular growth may need to be considered under criteria modified from those used to interpret complexity in solitary organisms. Primary modules, corresponding to individuals, are the fundamental building blocks of a colonial organism. Groups of primary modules commonly form a second-order modular unit, such as a branch, which may then be iterated to form a more complex colony. Aspects of overall colony form, along with their implications for ecology and evolution, are reflected in second-order modular (structural) units to a far greater degree than by primary modular units (zooids). A colony generated by modular growth can be classified by identifying its second-order modular (structural) unit and then by characterizing the nature and relationships of these iterated units within the colony. This approach to classifying modular growth habits provides a standardized terminology and allows for direct comparison of a suite of functionally analogous character states among taxa with specific parameters of their ecology.

Magnetic susceptibility measurements to detect coal fly ash from the Kingston Tennessee spill in Watts Bar Reservoir

An estimated 229,000 m(3) of coal fly ash remains in the river system after dredging to clean-up the 2008 Tennessee Valley Authority (TVA) spill in Kingston, Tennessee. The ash is heterogeneous with clear, orange and black spheres and non-spherical amorphous particles. Combustion produces iron oxides that allow low field magnetic susceptibility (χ(LF)) and percent frequency dependent susceptibility (χ(FD)%) to be used to discriminate between coal fly ash and sediments native to the watershed. Riverbed samples with χ(LF) greater than 3.0 × 10(-6) m(3)/kg, have greater than 15% ash measured by optical point counting. χ(LF) is positively correlated with total ash, allowing ash detection in riverbed sediments and at depth in cores. The ratio of ash sphere composition is altered by river transport introducing variability in χ(LF). Measurement of χ(LF) is inexpensive, non-destructive, and a reliable analytical tool for monitoring the fate of coal ash in this fluvial environment.

Modern bryozoan assemblages and distribution on the cool‐water Lacepede Shelf, southern Australian margin

Modern and relict sediments on the cool‐water Lacepede Shelf are dominated by fragments of bryozoans, molluscs and foraminifers. This study evaluates the distribution of modern bryozoan sediment on the Lacepede Shelf based on 88 species from 16 localities using cluster analysis and principal component analysis. Six bryozoan faunal assemblages, corresponding roughly to physiographic position on the shelf, are recognized objectively. Assemblages are robust and generally defined by the changing diversity and relative abundance of the bryozoan fauna across the shelf. Slope assemblages can be differentiated from shelf assemblages based on presence or absence of a few key species. Lateral variation along the three transects is associated with: (i) differences in shelf geometry (shelf width, depth of shelf edge and angle of the slope); (ii) previous influx of continental sediments; and possibly (iii) presence of upwelling and long‐shelf currents. Data were also evaluated to determine the level of detail required...