Johann Hohenegger

Habitats of larger foraminifera on the upper reef slope of Sesoko Island, Okinawa, Japan

Larger foraminifera living in the upper 50 m in front of the fringing coral reef northwest off Sesoko Island, Japan show strong habitat differences. This study closely examines the distributions of larger foraminifers and relates these to a number of key environmental factors using rigorous statistical methods. Since all larger foraminifera house symbiotic algae, light attenuation by the water column is the most important limiting factor that must be dealt with wall structures. Water energy is also countered by test structure. The local topography is responsible for different intensities of hydrodynamic forces, which are expressed in various substrates, mostly coral rubble and coarse-grained sand. The genus Peneroplis, very common on the reef flat, clearly prefers hardgrounds of the shallowest slope parts down to 30 m, while Dendritina is restricted to sandy bottoms and avoids the uppermost meters of the slope. It can be found down to 50 m at least. Alveolinella shows a similar depth distribution to Dendritina, but is common on hard bottom. The distribution of Parasorites, which is restricted to sandy substrates, starts at 20 m and extends to 80 m. Sorites, on the other hand, was found only on firm substrates between the reef edge and 50 m. The same depth distribution was recorded for Amphisorus, but this genus is not correlated with specific substrates. Most of the Amphistegina species prefer hardgrounds, while Amphistegina radiata is also common on sand. The calcarinids, capable of withstanding high water energy, are abundant on firm substrates close to the reef edge. Only Baculogypsinoides inhabits deeper parts of the slope on sandy bottom and avoids the shallowest parts. Sections with hard substrates are settled by Heterostegina, even down to 80 m, although this genus was occasionally found on sandy bottoms. Nummulites, in contrast, is restricted to sands between 20 and 70 m. Operculina, starting at 20 m, also prefers sandy substrates, but rare individuals were detected on coral rubble and macroids.

DEPTH COENOCLINES AND ENVIRONMENTAL CONSIDERATIONS OF WESTERN PACIFIC LARGER FORAMINIFERA

Symbiont-bearing benthic foraminifera are restricted to the euphotic zone of tropical and warm-temperate seas. Species distribution is correlated with depth, and the continuous alteration of community structures represents a coenocline. Since depth is a composite environmental gradient, the coenocline of larger foraminifera is not stable but alters with changes in primary limiting factors: temperature, light, water movement, substrate, and nutrients. Temperature determines geographic distribution and affects the depth distribution of larger foraminifera by the development of a shallow thermocline that truncates the distribution of shallower species and excludes species adapted to the deepest euphotic zone. Within these constraints, light is the most important primary factor because larger foraminifera are at least partly dependent upon photosynthesis by their algal endosymbionts for growth and calcification. The microalgae show distinct intervals along the light gradient and the foraminiferal host develops various strategies for regulating light intensity. First, well-structured environments in shallow waters allow shelter against irradiation by protecting in shadow areas. Second, wall and test structures enable regulation of light penetration. A range of mechanisms allows species to resist the highest energies in the breaker zone of the reef edge and crest, where foraminifera attach to inorganic or organic hard substrates. Concentrations of dissolved and particulate organic matter in the water column, as well as sediments or other inorganic particles, influence depth distributions by changing water transparency and, therefore, photosynthesis. Permanent or episodic elevations of concentrations therefore compress the coenocline upward. Species adapted to hard substrates must compete for the reduced space, while species living in the deepest euphotic zone are at a disadvantage because they are insufficiently motile to surmount large depth differences. Changing light transparencies due to nutrient input and different hydrodynamic conditions alter relations between the light coenocline and water depth. Thus, paleodepth interpretations based on larger foraminiferal assemblages should be based not only on foraminiferal taxa and ecology, but also on environmental evidence for climate, terrigeneous influence, water transparency, and hydrodynamic conditions based on sedimentology, geochemistry, and associated fossil biota.

Taphonomy of larger foraminifera: Relationships between living individuals and empty tests on flat reef slopes (Sesoko Island, Japan)

SummaryThe depth distributions of larger foraminifera (27 species) were investigated along two transects in the fore reef areas of a NW Pacific fringing reef. One transect is distinguished by a strong flattening below the steep reef slope (−30 m), whereas further steepening characterizes the equivalent part in the other transect. According to the different taphonomic processes affecting foraminiferal tests before final sedimentation, empty tests were classified into the three categories ‘optimally’, ‘well’ and ‘poorly’ preserved. The depth distribution of each preservation state was compared with living individuals. While distributions of optimally preserved tests almost coincide with living individuals, well-preserved tests are characterized by significant depth shifts that are stronger at the upper-most slope compared with the deeper parts. Since the time-averaged traction forces are similar in both investigated transects, differences between the distributions of living individuals and well-preserved tests are more intensive on steep versus flat slopes. Poorly preserved tests signalize allochthonous origin or reworking of relict sediments.

REMARKS ON WEST PACIFIC NUMMULITIDAE (FORAMINIFERA)

Living Nummulitidae achieve their highest diversity in the subtropical and tropical West Pacific. Although all house symbiotic microalgae, they avoid highly illuminated areas near the water surface, since their flat tests could be easily damaged by the hydrodynamic regime. The preference for calm water conditions extends their depth distribution down to the base of the photic zone. West Pacific Nummulitidae can be differentiated into ten species belonging to six genera according to an ecological species concept. The genus Operculina d’Orbigny is represented by three species. While O. discoidalis (d’Orbigny) prefers a fine-grained bottom under medium light conditions (10% surface intensity), O. ammonoides (Gronovius) prefers a coarser substrate and sometimes can be found on hard bottoms. Light dependence ranges from 1.5% to 68% surface intensity. Less illuminated coarse sands are inhabited by Operculina cf. O. complanata (Defrance), which is the dominant symbiont-bearing foraminifer between light intensities of 0.2% to 12% surface illumination. The genus Planostegina Banner and Hodgkinson demonstrates transitions to the genus Operculina in test form and surface, while the division into chamberlets is similar to Heterostegina. Planostegina operculinoides (Hofker) is distinguished by flat tests and delicate chamberlets. It lives on sandy bottoms restricted to light intensities between 0.45% and 26% surface illumination. The more robust Planstegina aff. P. operculinoides (Hofker) prefers light intensities between 0.4% and 2.7% surface illumination. Planoperculina heterosteginoides (Hofker) shows morphological transition to Operculina cf. O. complanata in developing incomplete septula. This species lives in low illuminated areas (0.3% to 2.5% surface intensity) and prefers medium to fine-grained sands. Heterostegina depressa d’Orbigny spans a broad range in light intensities (2% to 70% surface illumination), and is protected against irradiation by thick tests and a cryptic life mode near the surface. Test construction enables life under strong hydrodynamic regimes. This species lives firmly attached to hard substrates, thus counteracting transportation by water movement. Nummulites venosus (Fichtel and Moll) differs from H. depressa in having undivided chambers. It lives exclusively on coarse sand and avoids high sediment movement, thus starting its distribution beneath the fair weather wave base. According to light intensities, the upper limit may be similar to O. ammonoides (80%), while the lower limit is 2.5% surface illumination. Operculinella cumingii (Carpenter) inhabits coarse to medium sand in deeper regions between 1.2% and 25% surface illumination. Tests of the cyclic, large-sized species Cycloclypeus carpenteri Brady are easily transported due to the thin, plate-like form. The upper distribution limit correlates with the storm wave base, restricting C. carpenteri to depths below 50 m. The lower distribution limit depends on light intensity and is located near the base of the photic zone (0.4% surface illumination).

A comparison of living and dead molluscs on coral reef associated hard substrata in the northern Red Sea — implications for the fossil record

Fidelity of death assemblages to live shelly faunas is one of the major palaeontological questions, but quantitative data are scarce and most case studies on this topic have been performed in non-reef sediments. Therefore we studied diVerent types of subtidal reef-associated hard substrata (reef flats, reef slopes, coral carpets, coral patches, rock grounds), each with diVerent coral associations, in order to determine the agreement of assemblages of living and dead shell-bearing molluscs. A total area of 340.5 m2 was investigated and 2846 individuals were counted at 68 sample localities ranging from shallow subtidal to 40 m water depth. Most taxa found dead in the study area were also found live and vice versa; diVerences in this respect can be related to quantitatively unimportant taxa. However, strong diVerences exist in the proportion of living and dead fauna, dominant taxa, and molluscan distribution patterns. The ratio of live to dead molluscs is high. Living molluscs are strongly dominated by taxa with distinct relations to corals, mainly Pedum, Coralliophila and Tridacna, and the encrusting gastropod Dendropoma. Five distinct groups of living molluscs can be diVerentiated and related to specific hard substrata, which are characterized by distinct molluscan life habits. In contrast, the death assemblages are always strongly dominated by encrusting bivalves, mainly Chamoidea and Spondylidae, and cerithiid gastropods in varying dominances. Correspondingly there is no significant correlation of the total abundance of living and dead molluscs and their overall similarity is only 6%. Similarity between living and dead faunas is above 50% at only 12 of the 68 sample locations, and at 17 sample locations significant correlations of living and dead molluscs were recognized. These correlations are mainly based on Chamoidea, which dominate both the living and dead fauna, on rock grounds. Therefore rock grounds are the only bottom type with consistent correlations and similarities of living and dead molluscs. The observed bias is due to the close relationship of molluscan life habits and post-mortem history of shells. Molluscs that live permanently attached to or within living corals (mostly bivalves and encrusting Dendropoma) can easily be overgrown after death by the large amounts of living substrata available. Rapid transport of dead shells into surrounding sediments or into crevices within corals is typical of gastropods that feed on corals. Molluscs that colonize dead surfaces preferentially accumulate on rock grounds. The ecologic information that can be derived from the shells depends on the diVerent post-mortem histories of the faunas.

Molluscan assemblages on coral reefs and associated hard substrata in the northern Red Sea

Abstract Information on spatial variability and distribution patterns of organisms in coral reef environments is necessary to evaluate the increasing anthropogenic disturbance of marine environments (Richmond 1993; Wilkinson 1993; Dayton 1994). Therefore different types of subtidal, reef-associated hard substrata (reef flats, reef slopes, coral carpets, coral patches, rock grounds), each with different coral associations, were investigated to determine the distribution pattern of molluscs and their life habits (feeding strategies and substrate relations). The molluscs were strongly dominated by taxa with distinct relations to corals, and five assemblages were differentiated. The Dendropoma maxima assemblage on reef flats is a discrete entity, strongly dominated by this encrusting and suspension-feeding gastropod. All other assemblages are arranged along a substrate gradient of changing coral associations and potential molluscan habitats. The Coralliophila neritoidea–Barbatia foliata assemblage depends on the presence of Porites and shows a dominance of gastropods feeding on corals and of bivalves associated with living corals. The Chamoidea–Cerithium spp. assemblage on rock grounds is strongly dominated by encrusting bivalves. The Drupella cornus–Pteriidae assemblage occurs on Millepora–Acropora reef slopes and is strongly dominated by bivalves associated with living corals. The Barbatia setigera–Ctenoides annulata assemblage includes a broad variety of taxa, molluscan life habits and bottom types, but occurs mainly on faviid carpets and is transitional among the other three assemblages. A predicted degradation of coral coverage to rock bottoms due to increasing eutrophication and physical damage in the study area (Riegl and Piller 2000) will result in a loss of coral-associated molluscs in favor of bivalve crevice dwellers in dead coral heads and of encrusters on dead hard substrata.

Subtropical coral-reef associated sedimentary facies characterized by molluscs (Northern Bay of Safaga, Red Sea, Egypt)

SummaryThe shallow marine subtropical Northern Bay of Safaga is composed of a complex pattern of sedimentary facies that are generally rich in molluscs. Thirteen divertaken bulk-samples from various sites (reef slopes, sand between coral patches, muddy sand, mud, sandy seagrass, muddy seagrass, mangrove channel) at water depths ranging from shallow subtidal to 40m were investigated with regard to their mollusc fauna >1mm, which was separated into fragments and whole individuals.Fragments make up more than 88% of the total mollusc remains of the samples, and their proportions correspond to characteristics of the sedimentary facies. The whole individuals were differentiated into 622 taxa. The most common taxon,Rissoina cerithiiformis, represented more than 5% of the total mollusc content in the samples. The main part of the fauna consists of micromolluscs, including both small adults and juveniles. Based on the results of cluster-, correspondence-, and factor analyses the fauna was grouped into several associations, each characterizing a sedimentary facies: (1) “Rhinoclavis sordidula—Corbula erythraeensis-Pseudominolia nedyma association” characterizes mud. (2) “Microcirce sp.—Leptomyaria sp. association” characterizes muddy sand. (3)”Smaragdia spp.-Perrinia stellata—Anachis exilis—assemblage” characterizes sandy seagrass. (4) “Crenella striatissima—Rastafaria calypso—Cardiates-assemblage” characterizes muddy seagrass. (5) “Glycymeris spp.-Parvicardium sueziensis-Diala spp.-assemblage” characterizes sand between coral patches. (6) “Rissoina spp.-Triphoridae —Ostreoidea-assemblage” characterizes reef slopes. (7) “Potamides conicus—Siphonaria sp. 2—assemblage” characterizes the mangrove.The seagrass fauna is related to those of sand between coral patches and reef slopes with respect to gastropod assemblages, numbers of taxa and diversity indices, and to the muddy sand fauna on the basis of bivalve assemblages and feeding strategies of bivalves. The mangrove assemblage is related to those of sand between coral patches and the reef slope with respect to taxonomic composition and feeding strategies of bivalves, but has a strong relationship to those of the fine-grained sediments when considering diversity indices. Reef slope assemblages are closely related to that of sand between coral patches in all respects, except life habits of bivalves, which distincly separates the reef slope facies from all others.

Molecular phylogeny of large miliolid foraminifera (Soritacea Ehrenberg 1839)

Abstract The foraminiferal superfamily Soritacea belongs to the suborder Miliolina and is divided in two families, Peneroplidae and Soritidae, the latter one comprising two subfamilies, Archaiasinae and Soritinae. Phylogenetic relationships of 11 genera of soritid foraminifera were investigated by sequencing the complete SSU rDNA gene for 25 specimens. Additionally, partial SSU rDNA sequences were obtained from another 15 specimens of Soritinae. DNA sequence analysis confirms the monophyly of each family. Caribbean Archaiasinae form a monophyletic clade with Pacific Laevipeneroplis at the base. The genus Parasorites apppears as a sister taxa to Soritinae. Complex morphological features that characterize the genus Marginopora seem to have evolved independently at least twice, as the examined representatives cluster within two other soritine genera. Molecular analysis further shows that Sorites orbiculus and Sorites marginalis represent two different morphotypes of one species. Our data indicate that morphological changes and acquisition of new endosymbiont types in each group played an important role in the adaptation and radiation of Soritacea.

Timing of the Middle Miocene Badenian Stage of the Central Paratethys

Abstract A new and precisely defined chronometric subdivision of the Badenian (Middle Miocene, regional stage of Central Paratethys) is proposed. This uses global events, mainly geomagnetic polarity reversals as correlated chronometric boundaries, supported by climatic and sea-level changes in addition to isotope events and biostratigraphic data. The Karpatian/ Badenian boundary lies at 16.303 Ma, at the top of Chron C5Cn.2n, which is near the base of the Praeorbulina sicana Lowest-occurrence Zone (LOZ). The Badenian/Sarmatian boundary is placed at the top of polarity Chron C5Ar.2n, thus at 12.829 Ma. In relation to three sea level cycles TB 2.3, TB 2.4 and TB 2.5 and astronomically confirmed data, the Badenian can be divided into three parts of nearly equivalent duration. The Early Badenian as newly defined here ranges from 16.303 to 15.032 Ma (top of polarity Chron C5Bn.2n). The younger boundary correlates roughly to the base of the planktonic foraminifera Orbulina suturalis LOZ at 15.10 Ma, the HO (Highest Occurrence) of the nannofossil Helicosphaera ampliaperta at 14.91 Ma (NN4/NN5 boundary) and the Lan2/Ser1 sequence boundary at 14.80 Ma. The subsequent Mid Badenian ranges from 15.032 Ma to 13.82 Ma; the latter datum correlates with the base of the Serravallian, characterized by a strong global cooling event reflected in the oxygen isotope event Mi3b. The main part of cycle TB 2.4 falls into the Mid Badenian, which can be subdivided by a short cooling event at 14.24 Ma during the Middle Miocene Climate Transition (14.70 to 13.82 Ma). The HCO (Highest common occurrence) of the nannofossil Helicosphaera waltrans at 14.357 Ma supports this division, also seen in the tropical plankton Zones M6 Orbulina suturalis LOZ and M7 Fohsella peripheroacuta LOZ that correspond roughly to the lower and upper Lagenidae zones in the Vienna Basin, respectively. The Late Badenian is delimited in time at the base to 13.82 Ma by the Langhian/Serravallian boundary and at the top by the top of polarity Chron C5Ar.2n at 12.829 Ma. The Mediterranean Langhian/Serravallian boundary can be equated with the Mid/Late Badenian boundary at 13.82 Ma. However, the Karpatian/Badenian boundary at 16.303 Ma, a significant event easily recognizable in biostratigraphy, paleoclimate evolution and sequence stratigraphy, cannot be equated with the proposed global Burdigalian/Langhian, and thus Early/Middle Miocene boundary, at 15.974 Ma

Depth estimation by proportions of living larger foraminifera

Abstract Estimation of environmental gradients by proportions of species using transfer functions is a viable and proven method. Two new methods enabling exact point estimation of the gradients are developed. The “minimum distance function”, like simple transfer equations, results in a single value, whereas the “transformed proportions method” based on logit-transformed density functions allows additional diagnosis of the coenoclines under investigation. Depth estimations in sublittoral coral reefs using larger foraminifers demonstrate the high precision of both methods.