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1.
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. 相似文献
2.
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. 相似文献
3.
Bryozoans are colonial invertebrates that often dominate epibenthic assemblages on the lower surfaces of hard substrata. Competition
among neighbouring organisms is usually a critical process regulating biodiversity, and hard substrata have proved to be a
suitable model habitat to analyse spatial interactions. We explored the relationships among abundance, species richness, diversity,
competitive ability, coverage, available surface, depth and substratum size in an assemblage of bryozoans encrusting pebbles
and cobbles in a bank off the eastern mouth of the Strait of Magellan. We also tested whether overgrowth competition can be
regarded as hierarchical, and whether the species abundance distribution shows a mode of rare species and a decreasing frequency
of increasingly abundant species. Abundance, species richness, diversity and overgrowth competition were highest on the largest
substrata. Smaller pebbles tended to be encrusted by the commonest bryozoans, while the rarest species were mainly found on
relatively larger clasts. A high proportion of the lower surfaces of most substrata was available for growth. Diversity values
of relatively shallow stations were lower than expected under Caswell’s neutral model. Interspecific competition was hierarchical,
but the abundance of colonies was not related to the competitive ability of each species. The species abundance distribution
was bimodal, with a main mode of rare species and a second one partly composed of relatively abundant bryozoans with poor
competitive abilities. This study shows that even in an encrusting assemblage where competition is hierarchical, the weakest
competitors persist and the dominant species are far from being capable of monopolizing space. 相似文献
4.
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. 相似文献
5.
The macrofauna associated with Fucus serratus at Dale in south-west Wales contained 30 taxa of which five were common: these comprised four encrusting bryozoans and a hydroid. The bryozoans Flustrellidra hispida and Electra pilosa showed significant variations in abundance according to the size and structure of plants colonised. Electra was most abundant on plants where other bryozoans were least numerous. Colony growth in Electra was proportional to the amount of space provided by individual plant segments whilst growth in competitively superior species appeared to be independent of the size of the plant segments colonised. Dynamena pumila was larger and more abundant on larger segment faces where competition was presumably weaker. Each species showed a specific pattern of zonation along the fronds. The dominant species were generally more abundant on the concave surfaces of the plants. There was some evidence for the tendency for certain taxa to co-occur but the degree of association between species was weak and probably of limited biological significance. Species diversity varied with plant structure. More species occurred on concave surfaces at all plant levels but the overall pattern of diversity on the two segment faces was similar; diversity was greatest in the shrubbier mid-frond regions. Differential distribution of the dominant encrusting taxa within this Fucus community results in a considerable degree of niche segregation and ecological isolation. 相似文献
6.
The Paleocene–Eocene Taleh Zang Formation of the Zagros Basin is a sequence of shallow-water carbonates. We have studied carbonate platform, sedimentary environments and its changes based on the facies analysis with particular emphasis on the biogenic assemblages of the Late Paleocene Sarkan and Early Eocene Maleh kuh sections. In the Late Paleocene, nine microfacies types were distinguished, dominated by algal taxa and corals at the lower part and larger foraminifera at the upper part. The Lower Eocene section is characterised by 10 microfacies types, which are dominated by diverse larger foraminifera such as alveolinids, orbitolitids and nummulitids. The Taleh Zang Formation at the Sarkan and Maleh kuh sections represents sedimentation on a carbonate ramp. The deepening trends show a gradual increase in perforate foraminifera, the deepest environment is marked by the maximum occurrence of perforate foraminifers (Nummulites), while the shallowing trends are composed mainly of imperforate foraminifera and also characterised by lack of fossils in tidal flat facies. Based on the facies changes and platform evolution, three stages are assumed in platform development: I; algal and coralgal colonies (coralgal platform), II; coralgal reefs giving way to larger foraminifera, III; dominance of diverse and newly developing larger foraminifera lineages in oligotrophic conditions. 相似文献
7.
Living on an island: characterization of the encrusting fauna of large pectinid bivalves from the Lower Cretaceous of the Neuquén Basin,west‐central Argentina
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Leticia Luci Darío G. Lazo 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2015,48(2):205-226
Exposed mollusc shells may act as benthic islands in soft bottoms, and the analysis of their encrusting faunas provides unique palaeoecological information. In the late Valanginian of the Agrio Formation (Neuquén Basin, west‐central Argentina), the large pectinid Prohinnites acted as a benthic island on soft substrates. Inequivalved Prohinnites adults with small, smooth cementing scars on the right valve suggest that a free reclining life habit followed the epibyssate juvenile and cementing phases. The encrusting fauna on Prohinnites was studied taxonomically and palaeoecologically by means of a quantitative approach. Over 90% of 123 valves presented encrusters. Encrustation was equally common in both valves. Internal encrustation was rare. The left umbonal region was less encrusted probably due to sediment accumulation or early colonization by soft‐bodied taxa. The fauna was composed of 14 encrusting taxa, including oysters, serpulids, sabellids and cyclostome bryozoans. Oysters exceeded 50% of the total abundance, but serpulids and bryozoans were more diverse. Serpulids and particularly oysters showed a gregarious life habit. Few interactions took place among encrusters and most were post‐mortem, involving the overgrowth of already dead oysters. The oysters were early settlers that took advantage of their gregarious behaviour to rapidly cover available hard surfaces. However, they were unable to exclude bryozoans and polychaetes, which settled on the pectinid's valves regardless of the presence of oysters. The studied fauna corresponds to a climax community that was structured by larval abundance rather than by competitive interactions; oysters settled first and replenished themselves while polychaetes and bryozoans settled over or alongside them 相似文献
8.
Bryozoans are among the most important groups of the Southern Ocean benthic macrofauna, both in terms of species richness and abundance. However, there is a considerable lack of ecological research focused on their distribution patterns and species richness on smaller scale, especially in the soft bottom habitats of Antarctic glacial fjords. The aim of this study was to describe those patterns in the Admiralty Bay. Forty-nine Van Veen grab samples were collected at the depth range from 15 to 265 m, in the summer season of 1979/1980, at three sites distributed along the main axis of the fjord. Among 53 identified species of bryozoans, 32 were recorded in the Admiralty Bay for the first time. The most common and abundant species were Himantozoum antarcticum, Inversiula nutrix and Nematoflustra flagellata. Genera such as Arachnopusia, Cellarinella and Osthimosia were the most speciose taxa. It was demonstrated that depth was important for the distribution of the bryozoans. More than half of the recorded species were found only below 70 m. An influence of glacial disturbance was reflected in the dominance structure of colony growth-forms. The inner region of the fjord was dominated almost entirely by encrusting species, while the diversity of bryozoan growth-forms in less disturbed areas was much higher. In those sites the highest percentage of branched, tuft like species represented by buguliform and flustriform zoaria was observed. 相似文献
9.
Lower Oligocene, shallow-water carbonates of the Calcareniti di Castelgomberto formation (Monti Berici, Italy, Southern Alps) are studied in detail with respect to fabric and component distributions in order to trace paleoecological changes along a monotonous sedimentary stacking pattern. The carbonates are dominated by coralline algal rudstones with a packstone to wackestone matrix. Non-geniculate coralline algae include six genera: Lithoporella melobesioides, Mesophyllum, Neogoniolithon, Spongites, Sporolithon, and Subterraniphyllum. The algae are found in the form of encrusting thalli, rhodoliths, and coralline debris. Non-algal components include larger, small benthic, and planktonic foraminifera associated with bryozoans, zooxanthellate corals, and echinoderms. Four carbonate facies are distinguished: (1) coralline algal facies, (2) coralline algal-coral facies, (3) coralline algal-larger foraminiferal facies, and (4) coralline algal debris facies. Marly horizons also occur in the section. The facies and coralline algal content are interpreted with respect to light intensity, hydrodynamic energy, biotic interactions, and substrate stability. Facies development along the studied section shows systematic variations, suggesting asymmetric sea-level changes with rapid regressions and gradual transgressions. 相似文献
10.
Lars Siln 《Acta zoologica》1981,62(4):219-232
Encrusting forms presumably represent the original mode of growth in the bryozoans. They usually exhibit a relatively low degree of colony integration. The numerous different erect colony types, certainly independently derived from this stage, show a higher degree of integration. Eventually forms arise with a strict pattern only little influenced by the environment. The Flustra foliacea colony holds an intermediate position in this respect. It forms an initial crust on a foreign substratum such as rock. The crust forms marginal lobes. The lobes collide two and two. The two components of each collision then rise back to back, owing to lack of space, into bilaminar fronds. The two zooid layers composing these erect branches and mutually encrusting the “auto-substratum” of their respective basal walls, grow much more rapidly than the initial crust on the “heterosubstratum” of the rock to finally comprise more than 95 % of the colony volume. The different rate of growth on “auto-” and “heterosubstratum” respectively is interpreted as indicating a preference for the “autosubstratum” and as the main force in the formation of erect branches. The Fl. foliacea case indicates one of the pathways from encrusting to erect colonies in the bryozoans. It is probably valid for at least some of the erect bilaminar colonies appearing in different parts of the bryozoan system. 相似文献
11.
Within the Gavrovo–Tripolitza area (southern continental Greece), marine carbonate platforms existed from the Late Triassic
to the Late Eocene. The Middle–Upper Eocene marine shallow-water carbonates of the Klokova Mountain represent remnants of
the large volumes of sediment that were produced on a middle ramp sedimentary system which culminated in the Lower Oligocene
terrigenous deposits. Facies analysis of Bartonian–Priabonian shallow-water carbonate successions and the integration with
palaeoecological analysis are used to produce a detailed palaeoenvironmental model. In the proximal middle ramp, porcelaneous
foraminiferal packstone facies is characterised by larger foraminifera such as Praturlonella and Spirolina. These forms thrived in a shallow-water setting with low turbidity, high-light intensity and low-substrate stability. The
foraminiferal packstone facies, the thin coralline wacke–packstone facies and the rhodolith packstone facies deposited approximately
in the same depth range adjacent to one another in the middle-ramp. Nummulitids (Nummulites, Assilina, Pellatispira, Heterostegina and Spiroclypeus) increase in abundance in the middle to distal mid-ramp together with the orthophragminids. Coralline algae, represented
by six genera, are present in all facies. Rhodoliths occur in all facies but they show different shapes and growth forms.
They develop laminar sub-ellipsoidal shapes in higher turbulence conditions on mobile sand substrates (foraminiferal packstones
and rhodolith rudstones), whilst sub-discoidal shapes often bound by thin encrusting coralline plants in lower hydrodynamic
settings. The distinctive characteristics of the palaeoecological middle-ramp gradient are an increase in dominance of melobesioids,
a thinning of the encrusting coralline plants and a flattening of the larger benthic foraminiferal shells. 相似文献
12.
Abstract: Abundant and diverse bioerosion trace fossils in the Lower Devonian of the Rade de Brest, France, were produced by boring ctenostomate bryozoans, polychaete annelids and algae. Two unidentifiable traces of encrusting sclerobionts are also considered. Two new taxa are described: Pinaceocladichnus cristatus ichnosp. nov. and Ichnogutta erectus ichnogen. et ichnosp. nov. Both are attributed to the work of boring bryozoans. Sedimentary condensation during intervals of sea-level rise seems to have had an important influence in promoting infestation by organisms, the activities of which are now preserved as trace fossils. A zonation of bioerosion trace fossils within the offshore zone, in the Lower Devonian of the Armorican Massif, is also suggested. 相似文献
13.
Paleontological and biostratigraphical studies on carbonate platform succession from southwest Iran documented a great diversity of shallow-water benthic foraminifera during the Oligocene–Miocene. Larger foraminifera are the main means for the stratigraphic zonation of carbonate sediments. The distributions of larger benthic foraminifera in two outcrop sections (Abolhayat and Lali) in the Zagros Basin, Iran, are used to determine the age of the Asmari Formation. Four assemblage zones have been recognized by distribution of the larger benthic foraminifera in the study areas. Assemblage 3 (Aquitanian age) and 4 (Burdigalian age) have not been recognized in the Abolhayat section (Fars area), due to sea-level fall. The end Chattian sea-level fall restricted marine deposition in the Abolhayat section and Asmari Formation replaced laterally by the Gachsaran Formation. This suggests that the Miocene part of the formation as recognized in the Lali section (Khuzestan area) of the Zagros foreland basin is not present in the Abolhayat outcrop. The distribution of the Oligocene larger benthic foraminifera indicates that shallow marine carbonate sediments of the Asmari Formation at the study areas have been deposited in the photic zone of tropical to subtropical oceans. Based on analysis of larger benthic foraminiferal assemblages and microfacies features, three major depositional environments are identified. These include inner shelf, middle shelf and outer shelf. The inner shelf facies is characterized by wackestone–packstone, dominated by various taxa of imperforate foraminifera. The middle shelf is represented by packstone–grainstone to floatstone with a diverse assemblage of larger foraminifera with perforate wall. Basinwards is dominated by argillaceous wackestone characterized by planktonic foraminifera and large and flat nummulitidae and lepidocyclinidae. Planktonic foraminifera wackestone is the dominant facies in the outer shelf. 相似文献
14.
Ehrhard Voigt 《Pal?ontologische Zeitschrift》1988,62(3-4):193-203
The genusGrammothoa, growing on the interior walls ofThalassinoides burrows in the Maastrichtian Chalk-tuff, has developed a special growth strategy for spatial competition with other encrusting species which has not been previously recorded in bryozoans. The zoarium consists of auto-zooecia, gynozooecia and chains of smaller zooeciules, the latter forming stolon-like outgrowths from the distal edge of the colony. New areas of substratum are explored and colonized by the growth of these zooeciules. At the branching points of the zooeciules, autozooecia and gynozooecia are budded and may coalesce to form the main part of the colony. 相似文献
15.
Epi- and endobiontic organisms on Late Jurassic crinoid columns from the Negev Desert, Israel: Implications for co-evolution 总被引:1,自引:0,他引:1
HOWARD R. FELDMAN CARLTON E. BRETT 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1998,31(1):57-71
Columns of the articulate crinoids Millericrinus and Apiocrinites from the Upper Jurassic (Upper Callovian) Zohar and Matmor formations of the Negev Desert of Israel display abundant encrusting organisms of about ten species, as well as diverse trace fossils produced by endobionts. Pluricolumnals were colonized by epi- and endobiontic organisms both during life and post-mortem. Skeletonized encrusting organisms include abundant ostreid bivalves (which evidently colonized both live and dead crinoid columnals), two types of serpulid worms, encrusting foraminifera, three species of bryozoans, and small encrusting sclerosponges. Several types of borings are present: Trypanites (possibly produced by sipunculids), Gastrochaenolites (crypts of boring lithophagid bivalves), elliptical barnacle? borings, and channel-like annelid? borings. In addition, approximately 16% of the pluricolumnals display circular parabolic embedment pits assignable to the ichnogenus Tremichnus. They are associated with substantial deformation of the containing columnals and were probably the work of host-specific ectoparasitic organisms. Discovery of Tremichnus on Jurassic crinoids extends the range of this trace by almost 100 million years, providing evidence for one of the longest-ranging host-parasite interactions documented thus far (over 200 million years). The relationship of epibionts to the Jurassic crinoids thus ranged from simple utilization of dead hard substrate to probable opportunistic commensalism in forms that colonized the live upright stems, as in some oysters, through host-specific parasitism in the case of Tremichnus. 相似文献
16.
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. 相似文献
17.
Drop stones with lithophyllic macrofauna from Belgica Bank, Greenland Sea (79–81°N and 5–17°W) were collected during the Polarstern
cruise in August 2000. The investigation focussed on species richness, diversity, abundance, and interactions of organisms
colonizing rocks. On 101 stones collected by 10 dredges from nine sites, 113 taxa (58 genera, 38 families, 12 orders and 8
phyla) were recognized. Among the most abundant groups of organisms were foraminiferans, bryozoans and polychaetes, while
the least abundant were anthozoans and ascidians. Abundance ranged from 1239 to 11,383 individuals m−2 of rock surface area. Bryozoans were the most species-rich group, while anthozoans and ascidians were represented by the
least number of species. Colonization occurred at various topographical levels and was classified into two categories. Stones
were classified as primary space and were colonized by erect membranous, erect flexible, erect rigid, and flat encrusting
organisms. The second level of colonization by epibionts occurred on erect forms of organisms (e.g. erect bryozoans) and was
classified as a secondary space. Species composition and abundance between faunal assemblages of primary and secondary space
differed greatly. Colonization occurred only on the top of stones and was considered a special adaptation to avoid burial
by sedimentation and to enhance food supply. Only 3% of recruits were involved in any competitive interactions. Competition
was considered to be of minor importance in structuring lithophyllic assemblages. 相似文献
18.
19.
During the Pliocene and Pleistocene, the Monte Cetona (Northern Apennines, central Italy) was part of an elongated island.
The Middle Pliocene deposits around the Monte Cetona are represented by shallow-water marine carbonates rich in coralline
red algae and bryozoans. These skeletal carbonates, characterising a coralline algal-dominated factory, were analysed in terms
of microfacies, taxonomy, and growth-forms of coralline red algal assemblage. Three microfacies were distinguished on the
basis of component distribution and fabric analysis: coralline algal rudstones, coralline algal floatstones, and bioclastic
packstones. Skeletal components are commonly abraded, bioeroded, and encrusted. The shallow-water skeletal carbonates are
strongly bioturbated and any primary sedimentary structure is obliterated. The distribution of the coralline growth-forms
suggests a decreasing hydrodynamic gradient from the coralline algal rudstone, through the coralline algal floatstone to the
bioclastic packstone microfacies. The coralline algal flora consists of eight species representing the subfamilies Lithophylloideae,
Mastophoroideae and Melobesioideae. The assemblage is dominated by lithophylloids. Other biogenic components are bryozoans,
barnacles, echinoderms, and benthic foraminifera. These coralline algal assemblages were deposited just above the fair-weather
wave base and indicate a shallow-marine temperate water setting for the eastern Tyrrhenian Sea during the Mid Pliocene. 相似文献
20.
Sixty specimens of the giant marine isopod Glyptonotus antarcticus Eights, collected from Borge Bay, Signy Island, Antarctica were examined for epizoans. Ten species of cheilostomatid bryozoans
were found on the isopods. The purpose of the study was to quantify the prevalence, intensity, abundance, and spatial distribution
of the bryozoans on the isopods. The proportion of isopods colonized was 42%. The larger isopods had both significantly more
epizoic bryozoan colonies and species. The greatest density of bryozoans was on the fused pleon and telson. There was no significant
difference between the dorsal and ventral abundance of bryozoan colonies. The diversity of epizoic bryozoans on the isopods
is higher than on other host organisms from more stable environments. This may be because of active selection by settling
larvae. The frequency of local substrata being scoured by ice is high around Signy Island, so there may be a selective advantage
in colonizing a motile host.
Accepted: 20 June 1998 相似文献