A new encrusting interstitial marine fauna from Brazil

Abstract. This paper reports the second occurrence of a sand‐grain encrusting interstitial epifauna dominated by bryozoans and polychaetes at a site thousands of kilometers from the first described occurrence of such a fauna 20 years ago. Such faunas seem to have gone almost unrecorded in the marine ecological literature, but they are potentially geographically widespread and ecologically significant, deserving recognition and further study by benthic ecologists. Although rooted‐erect and free‐living lunulitiform bryozoans can be abundant in soft‐bottom habitats, the presence of encrusting forms was, until recently, considered to be limited to patches of hard substrata. In 1985 and 1988, a new and seemingly unique habitat for encrusting bryozoans and other organisms on single grains of shell or sand was reported from the coastal waters of Florida, USA. Here we report a second discovery of an interstitial encrusting fauna from the continental shelf off the state of São Paulo, Brazil. In addition to the cupuladriid Discoporella umbellata, several species of bryozoans (9 cheilostomes, 3 ctenostomes, and 1 cyclostome) were found encrusting on or boring into sand grains from the 4 stations examined. Four species were found exclusively on sand to gravel size grains. The most abundant colonies, with ～1300–1500 colonies m^?2, belonged to a new species of Cleidochasma. New species of Trypostega and Reginella, each with up to 200–300 colonies m^?2, were also discovered. The grain‐encrusting bryozoans were characterized by their small size, and by the fact that sexual reproduction was initiated very early in colony growth; brood chambers (for the development of embryos into larvae) occurred in colonies having only a few zooids. Colonies of boring ctenostome and cheilostome bryozoans were even more abundant than those of grain encrusting forms, being present in almost every piece of shell (～5000–5500 colonies m^?2). The fauna also included representatives of other groups of encrusting organisms, especially tubeworms (11,000–13,000 tubes m^?2). Planned work on samples from additional stations on the São Paulo shelf will no doubt yield a larger number of species from various taxa and perhaps show some overlap in sand fauna species between the Brazilian and Floridian sites. In addition to the unique species of single grain encrusters, colonies of bryozoan species characteristic of larger subtidal hard substrata were also found on sand or gravel size grains, indicating that an interstitial refuge may be available to some epifaunal taxa and suggesting that this interstitial refuge, which remains almost completely unknown to benthic ecologists, may play a large role in determining distributions of those taxa.     

Serpulids and other calcareous tube-dwelling encrusting polychaetes from the Early Cretaceous Agrio Formation (Neuquén Basin,Argentina)

Serpulids and other related tube-dwelling polychaetes are often ignored when found as fossil remains. They are, however, a widespread and important group today, and abundant literature has been published on them. Knowledge of fossil serpulids is centered on European material, and little has already been done on South American fossil calcareous tubes. In this paper, seven serpulid and sabellid morphotypes are described from the Early Cretaceous marine Agrio Formation of Argentina, revealing a diversity of worms recorded as encrusters on bivalves, ammonites and corals. Sabellids are represented by Glomerula cf. serpentina. Serpulids are represented by two subfamilies: “Serpulinae” includes Mucroserpula mucroserpula, Parsimonia antiquata, Placostegus cf. conchophilus, Propomatoceros semicostatus and P. sulcicarinatus; Spirorbinae is represented by heavily worn tiny coiled tubes assigned to ?Neomicrorbis. Serpulids and sabellids are one of the main components of the mollusk-encrusting fauna recorded in the Agrio Formation, along with small oysters but much more diverse. They are most commonly found as post-mortem encrusters, but some cases of unquestionable living interaction are also found, such as serpulid tubes embedded on coral branches. They are often overgrown by bryozoans, and sometimes by oysters; they frequently occur aggregated.     

Larger foraminifera as a substratum for encrusting bryozoans (Late Oligocene,Tethyan Seaway,Iran)

Considering the diversity and abundance of larger foraminifera examined from a wide range of Late Oligocene to Early Miocene palaeoenvironments in the Tethyan Seaway, encrusting bryozoans make extremely little use of their tests as substratum. Significant encrustations by bryozoans were exclusively found on large (ø c. 6 cm), undulating tests of Lepidocyclina spp., on which, however, a remarkable 34 taxa of encrusting bryozoans were recorded. This shallow-water fauna of Chattian age was analyzed in respect of the bryozoan taxa present, colony growth type, and mode of budding, colony size, as well as onset of reproduction. Taxic and morphological similarities between the fossil assemblage and modern faunas encrusting mobile substrata indicate a long history of bryozoans as part of the interstitial habitat, while the tests of certain larger foraminifera may have played a significant role in the evolution of shallow-water bryozoans by providing substrata for encrusting species in otherwise unfavorable environments.     

Les sclérobiontes des huîtres du Cénomanien supérieur du Mans (Sarthe,France)

Oysters of the Marnes à Pycnodonte biauriculata Formation, Upper Cenomanian (Guerangeri biozone) were significantly sampled in building works within the town of Le Mans (Sarthe, France). They are colonized by episkeletobionts (encrusting organisms) and endoskeletobionts (boring and bioeroding organisms). First ones include bivalves, polychaetes, foraminiferans and bryozoans. Second ones are represented by about fifteen ichnotaxa, the producers of which, when they are known, belong to ten taxa. The oysters, some of which have a large fixation surface, are allochtonous or at least parautochtonous. The settlement of sclerobionts began when the oysters were alive (Entobia isp.) and continued post-mortem on isolated valves, transported in their final depositional environment (Gnathichnus pentax). The significance of the coexistence of both Entobia and Gnathichnus ichnocoenosis is discussed.     

Palaeoecological analysis of a sclerobiont fauna on a single basibiont across the Valanginian of the Neuquén Basin,west‐central Argentina

Sclerobiont communities have proven their environmental and taphonomic value in extant and past settings; studies are beginning to quantify and evaluate their changes across time. Through the Valanginian of the Neuquén Basin, Argentina, trigonioids of the genus Steinmanella present an almost continuous record. Materials were collected from shales and shell beds across second‐order systems tracts (LST, TST and HST). Their sclerobiont communities were characterized and compared across systems tracts and facies. In addition, a link between them and coeval oyster mass occurrences (OMOs) was investigated, since studies on other local sclerobiont communities have consistently shown pronounced oyster dominance. Eleven sclerobiont taxa were found on Steinmanella (bryozoans, bivalves, foraminifers and polychaetes), of which oysters are usually strongly dominant but for the TST, in which their dominance is diminished. The sclerobiont community has a simple structure and interspecific relationships and competition for space seem to have had little importance. Few differences in richness, taxonomy and other parameters were found between facies. Across systems tracts, features of the sclerobiont communities are differentiated mostly from swings in relative abundance of taxa. The lowered oyster dominance in the TST may reflect a source–sink dynamics between OMOs (sources) and Steinmanella as sinks in shallower, soft substrate settings. Likely the sea‐level rise temporally drowned the oyster carbonate factory, resulting in decreased larvae emigration to the sinks and lowered oyster dominance during the TST.     

Hettangian (Early Jurassic) Dinosaur Tracksites from the Mecsek Mountains,Hungary

A rare example of a North American Jurassic hardground is found in the Carmel Formation of southwestern Utah. The Carmel hard‐ground was formed across a carbonate lagoon from an oolitic shoal seaward to a subtidal shelly facies landward. It has an abundant bivalve fauna consisting of thick layers of encrusters (the oyster Liostrea and the plicatulid Plicatula), borers (the ichnofossil Gastro‐chaenolites with the mytilid Lithophaga often preserved inside), and nestlers (the mytilid Modiolus). A rare soft‐bodied bryozoan (Arach‐nidium) is preserved by bioimmuration in the attachment scars of Liostrea; this is the first bioimmuration recorded from the Jurassic of North America, and the first bioimmuration recorded from a hard‐ground. The phoronid boring Talpina is present in some Liostrea shells; it was apparently excavated after the death of these oysters. The Carmel hardground community does not contain other fossils, such as serpulids, brachiopods, foraminiferans, and skeletal bryo‐zoans, typical of Jurassic hardgrounds elsewhere. It represents a low diversity molluscan community developed in a restricted marine environment.     

Large gryphaeid oysters as habitats for numerous sclerobionts: a case study from the northern Red Sea

The shell of a living specimen of the Indo-Pacific gryphaeid giant oyster Hyotissa hyotis was colonized by numerous encrusting, boring, nestling and baffling taxa which show characteristic distribution patterns. On the upper valve, sponge-induced bioerosion predominates. On the lower valve intergrowth of chamid bivalves and thick encrusting associations—consisting mostly of squamariacean and corallinacean red algae, acervulinid foraminifera, and scleractinian corals—provides numerous microhabitats for nestling arcid and mytilid bivalves as well as for encrusting bryozoans and serpulids. Such differences between exposed and cryptic surfaces are typical for many marine hard substrata and result from the long-term stable position of the oyster on the seafloor. The cryptic habitats support a species assemblage of crustose algae and foraminifera that, on exposed surfaces, would occur in much deeper water.     

Bryozoans as taphonomic engineers,with examples from the Upper Ordovician (Katian) of Midwestern North America

A combination of encrusting calcitic bryozoans and early seafloor dissolution of aragonitic shells recorded in the Cincinnatian Series of the upper Midwest of North America allowed the preservation of abundant moulds of mollusc fossils bioimmured beneath the attachment surfaces of the bryozoans. We here call this preservational process ‘bryoimmuration’, defined as a bryozoan‐mediated subset of bioimmuration. The bryozoans moulded very fine details of the mollusc shells, usually with more accuracy than inorganic sediment moulds. Most of the bryozoans are heterotrypid trepostomes with robust low‐Mg calcite skeletons. The molluscs are primarily bivalves, gastropods, nautiloids and monoplacophorans with their originally aragonitic shells now dissolved. Many of the encrusting bryozoans are so thin and broad that they give the illusion of calcitic mollusc shells clinging to the moulds. Some molluscs in the Cincinnatian, especially monoplacophorans and epifaunal bivalves, would be poorly known if they had not been bryoimmured. Unlike internal and external moulds in sediment, bryoimmured fossils could be transported and thus record aragonitic faunas in taphonomic assemblages (e.g. storm beds) in which they would otherwise be rare or absent. In addition, bryoimmurations of aragonitic shells often reveal the ecological succession of encrustation on the shells by exposing the earliest encrusters and borings that were later overgrown. Bryoimmuration was common during the Late Ordovician because the calcite sea at the time quickly dissolved aragonitic shells on the seafloor before final burial, and large calcitic bryozoans very commonly used molluscs as substrates. Bryoimmuration is an important taphonomic process for preserving aragonitic faunas, and it reveals critical information about sclerobiont palaeoecology. Several Cincinnatian mollusc holotypes are bryoimmured specimens. Bryozoans involved in bryoimmuration enhance the preservation of aragonitic fauna and thus act as taphonomic engineers.     

Microtaphonomy of bioclasts and paleoecology of microencrusters from Upper Jurassic spongiolithic limestones (External Prebetic,Southern Spain)

Microencrusters and microtaphonomic features of the Oxfordian spongiolithic limestones of the External Prebetic were studied using thin-section analysis. The spongiolithic limestone is a bioclastic-rich packstone with common echinoderm, mollusc and brachiopod remains. The bioclasts show a high fragmentation index and frequent microborings. The encrustation index (E _i) is higher for fragments of serpulids, ammonoids and bivalves, and increases with the initial grain-size of bioclasts. The main microencrusters consist of benthic microbial communities (BMC) and nubeculariids, as well as subordinate calcareous and siliceous agglutinated foraminifera, serpulids and bryozoans. BMC are usually the first colonizers, and encrusting foraminifera mainly appear on bioclasts larger than 2 mm. BMC dominate in well-developed encrustations on upward facing surfaces of larger bioclasts that are also colonized by foraminifera (nubeculariids and Subdelloidina). Bullopora, serpulids and bryozoans are more common on lower surfaces. The fact that the values of encrustation index, encrustation thickness and diversity of the microencrusters increase with the size of bioclasts is related to a higher stability and exposure time of the available bioclastic substrate. The microencruster distribution on upper and lower surfaces of large bioclasts may be related to photic control, space competition and/or predation avoidance.     

Microconchid tubeworms across the upper Frasnian – lower Famennian interval in the Central Devonian Field,Russia

Abstract: Microconchid tubeworms (Tentaculita) encrusting brachiopod shells have been investigated from the upper Frasnian – lower Famennian (Upper Devonian) deposits of the Central Devonian Field, Russia. The condition of microconchids and associated encrusting taxa is reported for the first time from the early Famennian recovery interval (crepida Chron) following the Frasnian–Famennian mass extinction. Two species, one new (Palaeoconchus variabilis sp. nov.) and the second one in open nomenclature (Palaeoconchus sp.), are described. Compared to lower Famennian specimens, they seem to be preferentially grouped on the anterior parts of the brachiopod host shells, which are interpreted as the most suitable sites away from the sea‐bottom and sediment. During the late Frasnian (Late rhenana Chron), microconchids, outnumbered by cornulitids and as abundant as foraminifers, were also associated with trepostome bryozoans, tabulates, rugose corals and various problematic encrusters. During the early Famennian recovery interval encompassing the crepida Chron, microconchids greatly outnumbered all associated encrusters, including the previously dominant cornulitids, while foraminifers, tabulates and rugose corals vanished. Early Famennian microconchids, represented by the single, albeit very abundant, species Palaeoconchus variabilis sp. nov., were opportunists that rapidly colonised the environment during the ongoing transgression following the regression‐driven biotic crisis in the area of the Central Devonian Field. In comparison to their late Frasnian predecessors and even other Middle Devonian specimens, no size reduction (the so‐called Lilliput effect) of early Famennian microconchid tubes was observed. It is probable that microconchids either rapidly attained their ‘normal’ sizes or they did not suffer any dwarfism following the Frasnian–Famennian event.     

Encrusting patterns and life habit of Mesozoic trigonioids: a case study of Steinmanella quintucoensis (Weaver) from the Early Cretaceous of Argentina

Luci, L. 2010: Encrusting patterns and life habit of Mesozoic trigonioids: a case study of Steinmanella quintucoensis (Weaver) from the Early Cretaceous of Argentina. Lethaia, 10.1111/j.1502‐3931.2009.00210.x. Trigonioid bivalves of the genus Steinmanella Crickmay are abundant at the top of the Vaca Muerta Formation, Neuquén Basin of Argentina, of Early Valanginian age. The species Steinmanella quintucoensis (Weaver) is frequently encrusted by oysters, serpulids and mytilids. Oysters are the most conspicuous encruster, followed by serpulids and then mytilids. A taphonomic, palaeoecological and taxonomic analysis was performed on the encrusting fauna of S. quintucoensis. An analysis of encrusting preference was performed on the basis of differences in ornamentation of the host shell, which was divided in a strongly tubercled flank and a smoother ribbed corselet and escutcheon zone. A higher encrustation frequency was found for the corselet and escutcheon zone, over the larger flank. Possible explanations are differences in the sculpture of each part of the valve, closeness to the respiratory openings of the host, and relation to life position of the trigonioids. In this respect, a palaeoecological analysis of the life position of the genus Steinmanella was made on the basis of functional morphology, encrustation patterns and comparison with related fossil forms as well as living representatives, finding that the most suitable position to explain encrustation patterns and functional morphology is one with the flanks below the water–sediment interface, and the corselets exposed above the substrate. □Early Cretaceous, encrustation, Neuquén Basin, trigonioids.     

Paleoecology of epizoans and borings on some Upper Cretaceous chalk oysters from the Gulf Coast

Analysis was made of a hard substrate fauna found on right valve interiors and exteriors of the epifaunal reclining oyster Pycnodonte mutabilis from the Maastrichtian (Navarroan) Saratoga Formation (southwestern Arkansas). Comparison of boring and encrustation patterns on both sides of valves indicates that a major portion of colonization on valve exteriors occurred while host oysters were alive. Paleoautecologic information derived from such valve exterior patterns includes evidence of rheotropic orientation by encrusting juvenile P. mutabilis and preferential location of Trypanites sp. borings in surficial shell grooves. Valve exteriors supported a hard substrate paleocommunity which had the following non-interactive progressive colonization sequence: (1) Trypanites sp. and P. mutabilis juveniles; (2) Entobia sp., serpulid worm tubes, and Bullopora sp.; and (3) cheilostome bryozoans. This sequence could have been caused by low seasonality and ranked success of colonizing encrusters and borers. Colonization of valve interiors generally differed from exteriors only in that many interiors were first colonized by the clionid sponge that created Entobia sp., which had already occupied the exterior, and which quickly bored through the valve to occupy the interior upon the host's death. □ Trace fossils, epizoans, borings, Gryphaeidae, palaeoecology, communities, colonization sequence, Late Cretaceous, Maastrichtian, Navarroan, Arkansas.     

Benthic Invertebrates Associated with a Serpulid Polychaete Assemblage in a Temperate Estuary

Hydroides dianthus (Verrill), a serpulid polychaete which secretes calcareous tubes, provides microhabitats for a variety of benthic invertebrates in Delaware Bay. These microhabitats function as biologically generated refuges and physical heterogeneities for at least 54 species. Dominance was measured by the biological index value which yielded 12 taxa that comprised 90% by number of the serpulid assemblage. These taxa included seven polychaetes, two amphipods, Nematoda, Oligochaeta, and Harpacticoida. In addition to the refuges provided by the serpulids, it was concluded that this temperate serpulid assemblage was comparable in function but not scale to calcareous biogenic assemblages in lower latitudes.     

Encrustation patterns on Late Cretaceous (Turonian) echinoids from southern Poland

This study focuses on sclerobionts from a large collection of epibenthic echinoids (>2,000 specimens) of the genera Conulus and Camerogalerus. Samples were collected from five localities in southern Poland (Polish Jura and Miechów Trough), where Turonian carbonates with terrigenous input are exposed. Low intensity (mean ca. 5 %, maximum ca. 10 %) and slight encrustation (“loosening effect”) exclusively by episkeletozoans probably resulted from low productivity of encrusters while the importance of other factors cannot be excluded unambiguously. Echinoids served as a main substratum and after death formed shellgrounds (‘echinoid carpet’) offering abundant benthic islands for encrusters in an otherwise soft-bottom environment. The moderate abundance but low-diversity assemblage is represented by bivalves, sedentary polychaetes, foraminifera, bryozoans, corals, and sponges. This assemblage is similar to a nearly contemporaneous assemblage from the Bohemian Basin. The presence of numerous spirorbins offers insights into their early evolution and may indicate that their first peak in abundance after origination was not prior to the earliest Turonian. This is regarded as one of the important ecological steps towards the rise of modern sclerobiont communities. Encruster diversities are independent of their abundance and, as shown in our novel planar projections, lateral parts of tests were preferentially encrusted. This pattern is explained by the combination of largest flat area and stable orientation. Encrusting bivalves and serpulids dominated hard substrate environments in the Turonian of Poland.     

The dispersal and colonisation behaviour of the marine polychaete <Emphasis Type="Italic">Nereis diversicolor</Emphasis> (O. F. Müller) in south-east England

Recent submarine caves are inhabited by endemic faunas adapted to oligotrophism, darkness and a tranquil environment. Many of their representatives are archaic types of animals resembling fossils from very early times in evolution. This article compares fossil fauna from Jurassic neptunian dykes (originally sea bed clefts) from the Western Carpathians with the Recent cave-dwelling fauna. The ostracods Pokornyopsis feifeli are particularly important. In the Western Carpathians, these were exclusively found in the Middle/Late Jurassic fissure fillings, but in the non-Tethyan Germanic Jurassic this species was found in deep-marine claystones. They are phylogenetic forerunners of the recent genus Danielopolina inhabiting both anchialine caves and deep seas. This indicates a Jurassic migration of deep-marine fauna to cryptic habitats. Other examples of cryptic communities include the Upper Jurassic cavity-dwelling fauna dominated by serpulids and scleractinian corals. Associated suspension feeders include thecideidine brachiopods, oysters, bryozoans, sponges, crinoids and sessile foraminifers. Serpulid-dominated bioconstructions have recent analogies in the Mediterranean and Carribean seas. Different type of dyke communities represent the Late Jurassic fauna of small sized ammonites which originated from both Tethyan and Boreal paleobioprovinces. It has not been established whether these amonites were juvenile, dwarfed specimens adapted to limited cave space or size-sorted adult specimens.     

Structural and taphonomic analysis of a columnar coralline algal build-up from SE Sicily

Unusual “coralligenous” build-ups were found at the infra–circalittoral boundary from SE Sicily. They are columnar, rising up perpendicularly from the bottom, and consist of an inter-growth of encrusting algae and invertebrates. A selected build-up and its longitudinal section, together with some thin sections of selected parts, were studied to detail the growth structures, composition and fabric of the trapped sediments. The coralline algae show a succession of “concentric”, “fruticulose” and “foliaceous” structures. The framework delineates cavities bounded by algal thalli, sometimes filled by sediments. The organisms constituting the framework were grouped into functional guilds (Fagerström, 1991): “primary frame builders” (mainly coralline algae); “secondary frame builders” (vermetids, serpulids and some bryozoans); “bafflers” (erect, flexible bryozoans, some sponges and soft algae); “binders” (encrusting bryozoans, some crustose coralline algae and serpulids); “destroyers” (a few endolithic algae, rare sponges and bivalves); “dwellers” (brachiopods, foraminifers, bivalves, small bryozoans and some motile organisms). The distribution pattern of taphonomic features (composition, grain size and distribution of sediments filling cavities; presence of cement and its location; mineralogical composition and crystal size), together with interactions between growth structures and functional guilds, allowed one to distinguish three taphofacies, each recording different environmental conditions. They have been tentatively related with cyclic sequences testifying to local hydrodynamic regimes, with subsequent slighter and stronger intensity phases, during the last 2200 years.     

The encrustation of fossil and recent sea-urchin tests: ecological and taphonomic significance

A comparison of fossil ( Echitwlampas sp. from the Lower Miocene Zogelsdorf Formation, Austria) and Recent ( Schizaster canaliferus from the northern Adriatic Sea) irregular sea-urchin tests shows that, upon their death, burrowing echinoids can serve as a substrate for a dense epigrowth. Size, shape, stable orientation, and surface residence-time were identified as key factors governing encrustation. The encrusters on fossil Echinolampas were bryozoans, serpulid polychaetes, barnacles, and coralline algae, while the recent material was initially encrusted by serpulids and hydrozoan colonies, and ultimately covered by the full range of sessile, hemi-sessile, and vagile species characterizing the benthic community in the Adriatic. In Echinolampas , epigrowth was more abundant on the lower (oral) surface; this specific distribution was echoed in S. canaliferus , where epigrowth started on the bottom side and grew upward. This indicates that the tests have a stable orientation and a surface residence-time long enough to allow intense encrustation. A taphonomic model is developed, and the role of encrustation on such special substrates for overall community structure is discussed. The Recent/fossil comparison provides new insights for both fields of study: the recent material indicates the role of soft-bodied faunas as well as the complexity of small-scaled ecological processes; the fossil material reflects many of the above phenomena and adds important taphonomic details on the fate of encrusted biogenic structures and on encruster growth patterns and distributions.     

Long-term trends of subtidal macrobenthos in North Inlet,South Carolina

Analyses of seasonal and yearly trends in subtidal macrobenthic samples collected bi-weekly at a sandy site (1981–1984) and a muddy site (1981–1985) in North Inlet, South Carolina, show large fluctations in abundance and high variability between replicate samples. Sampling variability at the sandy site, thought to be influenced more by physical disturbance than by biotic interactions, was especially high and prevented the interpretation of seasonal trends in abundance. Increased replication at the muddy site in 1985 revealed abundance patterns of winter/spring maxima and summer minima. Despite short-term (seasonal) and high year-to-year variability, the fauna at both sites were characterized by long-term stability in abundance. That is, although abundances varied considerably between seasons or years only 9 of 22 taxa analyzed showed a directional change in abundance. These 9 taxa increased in abundance over the four (sandy site) or five (muddy site) years of examination while the other 13 taxa fluctuated about a mean value. The taxonomic composition of benthic fauna at both sites was also very stable through time, with the sandy site always numerically dominated, in order, by polychaetes, amphipods, and bivalves and the muddy site by polychaetes, oligochaetes, and bivalves.     

Effects of two marinas on the composition of fouling assemblages

The composition of fouling assemblages was surveyed inside and near two fully enclosed marinas using settlement plates. The location of a plate, inside or outside the marina, influenced the abundances of four functional groups of fouling organisms (solitary ascidians, arborescent bryozoans, encrusting bryozoans and colonial ascidians). Transplantation of mature assemblages revealed that reductions in the abundance of arborescent bryozoans inside marinas might be explained by increased growth and recruitment of these bryozoans outside the marina. Surveys of settlement revealed decreased recruitment of encrusting bryozoans inside the marinas, a result consistent with patterns of adult abundance. It is proposed that an increased abundance of solitary ascidians inside marinas may be due to decreased competition. A second survey of adult assemblages was performed with multiple ‘Outside’ sites per marina. Effects of location consistent with the first survey were found for arborescent bryozoans, and in one marina area for solitary ascidians and encrusting bryozoans, but not in the other. Although mechanisms can be proposed to explain the effects of the marina (inside or outside) on the abundances of solitary ascidians, arborescent bryozoans and encrusting bryozoans, the second survey revealed that the effects may vary among marinas.     

Patterns of sclerobiont colonization on the rugose coral Schlotheimophyllum patellatum (Schlotheim, 1820) from the Silurian of Gotland,Sweden

Analysis of mushroom-shaped rugose corals Schlotheimophyllum patellatum (Schlotheim, 1820) from the Silurian (Upper Visby Beds, Lower Wenlock, Sheinwoodian) of Gotland, Sweden, showed that they were colonized on both the upper (exposed) and lower (cryptic) sides by a variety of encrusting and boring (sclerobiont) biotas, represented by 10 taxa and at least 23 species. Bryozoans and microconchid tubeworms, the most abundant encrusters, dominated on the cryptic undersides of the corals, while the dominant endobionts responsible for Trypanites borings overwhelmingly dominated the exposed surfaces. Except for cnidarian sphenothallids, which were exclusive colonizers of the underside of only one coral host, no other encrusters could be referred to as obligate cryptobionts. Because the upper surface of these corals was likely covered by soft-tissues during life, in specimens lifted off the sea-floor sclerobionts must have settled on the cryptic sides first. They could colonize the upper side only after the coral’s death, unless it was covered by sediment as could be the case in some flat specimens. With time, the space on the underside of the coral skeleton may have progressively been filled by sediment as well, precluding further colonization by sclerobionts. In that respect, the colonization patterns of these corals by encrusters and borers were controlled by the complex interplay of environmental factors, sclerobiont dynamics and coral growth in a given Silurian habitat. Compared with Silurian stromatoporoid hosts, the sclerobiont diversity and abundance noted on the Schlotheimophyllum corals may be regarded as representative for the Silurian as a whole.