Joachim Scholz

Paleoecology of a late Eocene mobile rockground biota from North Otago, New Zealand

A distinctive mobile pebble and cobble rockground biota of Late Eocene age is described from volcaniclastic sediments between Oamaru and Kakanui, North Otago, New Zealand. Thousands of subangular to subrounded basaltic pebbles and cobbles are encrusted with a diverse range of very well-preserved epibionts including crustose coralline algae, serpulids, bivalves, foraminifera, brachiopods, and more than 70 species of cyclostome and cheilostome bryozoans. The preservation of thin sediment layers beneath and between encrusting bryozoan colonies indicates the probable occurrence, during life, of agglutinating microbial mats. The abundance of subspherical rhodoliths, the diversity of epibionts, and their occurrence on all faces of the volcanic clasts reflect intermediate levels of overturning and rolling in a moderately current-swept channel adjacent to small volcanic islands and seamounts. The occurrence of large foraminifera (Asteroclyna), bryozoans (including two extant species), and brachiopods with warm-water affinities indicates subtropical sea temperatures and water depths of 25-50 m for this community, which represents one of the few described Cenozoic examples of a mobile rockground biota.

Reef-bryozoans and bryozoan-microreefs: Control factor evidence from the philippines and other regions

SummaryIn this paper, a preliminary concept on the interplay of local, regional and global control factors of bryozoan diversity and distribution pattern is introduced. Recent bryozoans from the Philippines, New Zealand and the Gulf of Aqaba are compared to the selected fossil specimens from the Oxfordian and Santonian.Reef bryozoan skeletons are studied in order to separate local control within the substrate-water interface from regional control. The latter originate mainly from the transport function of the water column (e.g. sediment load, wave energy, vagile predators). This is true especially for erect (tree-like) and massive (multilaminar) bryozoans which are subjected to the dynamics of the water body in the littoral area. This regional control, affects simultaneously several structural and substrate zones of a reef. Early life history of vertically growing reef bryozoans reflect local control, while older zoarial structures reflect the signals of regional influence. Three types of multiserial nodular bryozoans are cited: self-overgrowing sheets (‘S-Nodule’, derived from ‘S-Sheet’), circumlaterally budding colonies (‘C-Nodules’), and fungiform bryozoans.Bryozoan growth form selection allows the separation of two types of regional controls, long range control which favours the selection of specialized sheets, and slow rate control documented in the growth form modification of sheets changing into nodules.In the domain of local control epibiontic microorganisms, microbial mats and biofilms on hard substrata represent probably the most important elements, aside from the limited substrate space. Symbiotic and/or competitive bryozoan-microorganism interrelationships result in the distinct adaptations of bryozoan growth. It is apparent that bryozoan modifications of substrate micro-topography influence the character of epibiontic microbial settlement. The peak occurrence of microbial settlement on prominent external bryozoan skeleton parts is discussed as an effect of feeding currents. In contrast, smooth and unelevated exoskeletons are less favourable for micro-epibiontic colonization. Due to the high level of order in the spatial zonation patterns of epibionts on calcifying bryozoans, the term ‘bryozoan-microreef’ is introduced. Bryozoan-microreefs are locally controlled reefs. They are e.g. characterized by higher competitive abilities than bryozoans without ‘reefdwellers’. Local control has a fast rate of change and is reflected in morphologies of individual zooids and/or single zooid generations.Regional control has a slower rate but a higher range. It is important for growth modifications of the whole zoaria. The very slow rate of global control cannot be recorded within the life span of bryozoan zoaria unless it is expressed through regional control (such as monsoons). Nevertheless, global control is paleoecologically important because it is traceable in bryozoan (paleo-)biogeography. For practical purpose, we suggest to define those control factors of bryozoans as global which affect simultaneously at least one tropical and one non-tropical bryozoan community.

Microbial mats associated with bryozoans (Coorong Lagoon, South Australia)

SummaryBryostromatolites are laminated carbonate rocks composed of bryozoan zoarial laminae. The laminated texture is frequently caused by patterns of bryozoan self overgrowth as a regular defensive tactic against microbial fouling. In the Coorong Lagoon (South Australia), another type of bryostromatolite is present where the laminated growth of the weakly calcifying bryozoan speciesConopeum aciculata is postmortally stabilized by cyanobacterial mats at the surface, and fungal mats settling in the zooecial cavities.A tough extracellular slime network produced by benthic cyanobacteria is a trap for sediment particles, provides a method of adhesion to the bryozoan substrate, and produces a biological lamination by the vertical stratification of dead bryozoan skeletons. These slimes are also important for the preservation of cell structures and for their fossilization.Seasonal fluctuations in salinity and water level are the most important regional control factors, causing a phase displacement in the growth optima of microbial mats and bryozoans, thereby resulting in a rigid bryostromatolitic fabric.

Indications for microbial clues for bryozoans when settling

SummaryA correlation between skeletal growth of recent bryozoans and external environmental factors (e.g. abrasion, suspended sediment load) exists in ahermatypic tropical shallow water associations of the Philippines. Yet, the spatial zonation pattern of bryozoan species in a modern Philippine reef exhibits an amazingly high level of stability and order which cannot be readily correlated with external environmental factors. This is due to the observation that zonation correlates with the bryozoan taxa but not with their growth form categories (e.g. flexible-erect). Bryozoans are closely linked with their reef (micro)environment and reef microbiota by feedback control: Interacting biofilms, microbial mats, bryozoans and bryozoan larvae illustrate how such internal functions in a Philippine reef may stabilize the biotope structure as a whole

Fungal infections of a colonial marine invertebrate: Diversity and morphological consequences

SummaryColonies of the bryozoan speciesHippodiplosia insculpta collected from Grandmother’s Cove (American Camp, San Juan Island, Washington, USA) were analyzed in view of pathologic growth patterns. The species produced giant buds that were filled with extracellular polymeric substances and a dense microbial biofilm consisting of bacteria and fungal hyphae. Fungi were isolated from the colonies and were identified asPenicillium expansum, Peniillium brevicompactum, Sclerotinia sclerotiorum, Acremonium breve, andCladosporium sphaerospermum. The results of this study indicate that the formation of giant buds in the bryozoan is a defense mechanism against fungal infection.

Ristedtia vestiflua n. gen. et sp., a new bryozoan genus and species (Gymnolaemata: Cheilostomata) from an Arctic seamount in the central Greenland Sea

Ristedtia vestiflua is described as a new genus and species of cheilostomatous Bryozoa from the Arctic Vesterisbanken Seamount, located in the central Greenland Sea. The currently monospecific genus Ristedtia is included in the family Pyrisinellidae. It is characterised by a paired series of opesiules, interzooidal avicularia and hyperstomial, globular ovicells with a triangular endooecial frontal exposure. Its relationship to other members of this family as well as its habitat preference is discussed. It is suggested that the Recent genera of this family represent Tethyan relicts.

Distribution and Diversity of Erect Bryozoan Assemblages Along the Pacific Coast of Japan

To assess factors involved in the high diversity of benthic fauna in Sagami Bay, we examined the species composition of bryozoans forming rigidly erect colonies, possibly occuring in dense assemblages called bryozoan thickets. We identified erect bryozoans from collections made in the bay in four time intervals over ~125 years. To examine latitudinal effects on diversity, we also identified specimens in collections from near Otsuchi Bay to the north and the Nansei Islands to the south. In addition, we compared the composition and diversity of erect bryozoans in Sagami Bay with those in bryozoan thickets at Otago Shelf, New Zealand. We categorized erect bryozoans into five form categories based on the colony morphologies; detected 17 species in representing the five forms in Sagami Bay, five species representing four forms in the Nansei Islands, and three species representing two forms at Otsuchi Bay. Erect bryozoan diversity thus did not show a latitudinal gradient; it was higher in Sagami Bay than farther north or farther south, though we cannot rule out sampling effects. We speculate that the high diversity in Sagami Bay is due to greater environmental complexity than the other areas, including warming and cooling influences from the Kuroshio and Oyashio Currents, respectively, in different parts of the bay. We detected no clear differences in species composition between eastern and western Sagami Bay, but did detect an apparent loss of diversity of four species overall and nine species in western Sagami Bay between the 1928–1988 and the 2001–2005 intervals, suggesting differential environmental changes in different parts of the bay. Sagami Bay was richer in rigidly erect species than the bryozoan thickets at Otago Shelf, though the same colony morphologies were represented.