Non-reef Environments Research Articles

Distribution and palaeoecology of scleractinian corals during the Maastrichtian (Late Cretaceous)

Abstract Maastrichtian scleractinian corals from 94 localities in 26 Maastrichtian regions world-wide with strata of that age are taxonomically and palaeobiogeographically evaluated. A total of 205 taxa, belonging to 116 genera and 37 families, are included in the present study. Most coral taxa have been recorded from non-reefal environments. A significant majority of these taxa (genera = 70.7%; species = 75.6%) appear to have been endemic during the Maastrichtian. The Maastrichtian coral fauna is dominated by solitary and cerioid-plocoid forms (both accounting for 41 genera = 70%), having mainly medium- and large-sized corallites. The most diverse coral assemblages are those that have been recorded from arid (Jamaica: 63 species, Mexico: 29 species), warm-temperate (the Netherlands-Belgium: 32 species) and tropical regions (Iran: 27 species). The occurrence of Cunnolites polymorphus (Goldfuss) is newly recorded for the Netherlands (southern Limburg). Compared to the microstructural composition of the coral fauna of the lowermost Cretaceous (Berriasian; 91% of the species and 83% of the genera belonged to previously established microstructural groups), in the Maastrichtian, corals belonging to previously established microstructural groups were of minor importance (genera = 26%; species = 29.3%). The majority of Maastrichtian scleractinian taxa (both solitary and colonial) from the type area of the Maastrichtian Stage in the southeast Netherlands and northeast Belgium are illustrated.

Discrimination Reef and Non-Reef Environments, Using REE Geochemistry

This research aims to distinguish the reef environment from the non-reef environment. The Oligocene-Miocene-succussion in western Iraq was selected as a case study, represented by the reefal limestone facies of the Anah Formation (Late Oligocene) deposited in reef-back reef environments, dolomitic limestone of the Euphrates Formation (Early Miocene) deposited in open sea environments, and gypsiferous marly limestone of the Fatha Formation (Middle Miocene) deposited in a lagoonal environment. The content of the rare earth elements (REEs) (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Ho, Tm, Yb, Lu, and Y) in reef facies appear to be much lower than of those in the non-reef facies. The open sea facies have a low content of REEs due to being a transitional phase. The facies investigated have ƩREEs lower than the PAAS. The lagoonal facies shows an average ƩREEs higher than the Global Standard of Carbonate Rocks (GSCR), whereas reefal and open sea facies contain lower. The Y/Ho, Y/Dy, and Er/Nd were used as distinctive indicators of facies diagnosis; reefal facies have a high value of Y/Ho, Y/Dy, and Er/Nd as compared to PAAS are higher than1. In contrast, non-reef facies (lagoonal) have a lower value of Y/Ho, and Y/Dy as compared to PAAS is lower than 1, but Er/Nd is higher than 1. While in open sea facies the Y/Ho and Y/Dy have moderate values as compared to PAAS are close to 1, but a high value of Er/Nd as compared to PAAS higher than 1.

Reef-dwelling brachiopods record paleoecological and paleoenvironmental changes within the Changhsingian (late Permian) platform-margin sponge reef in eastern Sichuan Basin, China.

The eastern Sichuan Basin area (China) is the representative locality for studies of the Late Permian Changhsingian platform to basin transition. However, details of the paleoecology and paleoenvironment of rich brachiopod fauna in this area are still unclear, especially regarding the reef-dwelling brachiopods. The reef-dwelling brachiopod specimens from the Panlongdong platform-margin reefal environment are first described herein. A detailed comparison is presented with the paleoecological features and sedimentological characteristics of the reef-dwelling brachiopods and brachiopods of the reported Zhongliang Hill and Huayingshan intraplatform nonreefal environments in the transitional zone. The reef-dwelling brachiopods are dominated by the spiriferids, such as Martinia and Permophricodothyris, which are mainly found in hypercalcified sponge-calcareous algae binding framestone from the second reef-building process of the Panlongdong reef. The brachiopods in the first and third reef-building processes of the Panlongdong reef often show clear indications of transportation. The comparison of paleoecological and sedimentological evidence indicates that the reef-dwelling brachiopod specimens, which have strong pedicle-attached convex shells and supporting body spines, are commonly preserved in live positions and form a hard-bottom fauna, showing low evenness, and high dominance in both taxonomical and lifestyle diversity. The association among reef-dwelling brachiopod individuals also represents potential biological interactions to prevent the shells from being swept away by constant currents and waves, forming extremely dense concentrations on the sea floor as reef ecosystem engineers. This case study of reef-dwelling brachiopods preserved within the platform-margin reefal environment was critical for filling various gaps in our knowledge of the complexity of the Changhsingian reef-related ecosystem.

Amsassia(calcareous alga) from the Lower Ordovician (Tremadocian) of western Newfoundland, and the biologic affinity and geologic history of the genus

AbstractModular coral-like fossils from Lower Ordovician (Tremadocian) thrombolitic mounds in the St. George Group of western Newfoundland were initially identified asLichenariaand thought to include the earliest tabulate corals. They are here assigned toAmsassia terranovensisn. sp. andAmsassia? sp. A from the Watts Bight Formation, andA.diversan. sp. andAmsassia? sp. B from the overlying Boat Harbour Formation.Amsassia terranovensisn. sp. andA.argentinafrom the Argentine Precordillera are the earliest representatives of the genus.Amsassiais considered to be a calcareous alga, possibly representing an extinct group of green algae. The genus originated and began to disperse in the Tremadocian, during the onset of the Great Ordovician Biodiversification Event, on the southern margin of Laurentia and the Cuyania Terrane. It inhabited small, shallow-marine reefal mounds constructed in association with microbes. The paleogeographic range ofAmsassiaexpanded in the Middle Ordovician (Darriwilian) to include the Sino-Korean Block, as well as Laurentia, and its environmental range expanded to include non-reefal, open- and restricted-marine settings.Amsassiaattained its greatest diversity and paleogeographic extent in the Late Ordovician (Sandbian–Katian), during the culmination of the Great Ordovician Biodiversification Event. Its range included the South China Block, Tarim Block, Kazakhstan, and Siberia, as well as the Sino-Korean Block and Laurentia, and its affinity for small microbial mounds continued during that time. In the latest Ordovician (Hirnantian), the diversity ofAmsassiawas reduced, its distribution was restricted to non-reefal environments in South China, and it finally disappeared during the end-Ordovician mass extinction.UUID:http://zoobank.org/ef0abb69-10a6-46de-8c78-d6ec7de185fe

Bleaching susceptibility of aquarium corals collected across northern Australia

There are a wide range of Scleractinian corals that are collected for the global reef aquarium market, often from non-reefal environments. The sustainability of coral harvesting is potentially threatened by increasing anthropogenic disturbances and climate change, though it is unknown to what extent many commonly harvested corals are susceptible to environmental change, or actually bleach during marine heatwaves. In this study, we experimentally tested the temperature sensitivity and bleaching susceptibility of six coral species (Homophyllia australis, Micromussa lordhowensis, Catalaphyllia jardinei, Trachyphyllia geoffroyi, Duncanopsammia axifuga, and Euphyllia glabrescens), which are important components of the aquarium coral fisheries across northern Australia, in Western Australia, the Northern Territory, and/or Queensland. Interspecific differences were evident in the temperature sensitivity and bleaching susceptibility among the study species. Homophyllia australis, and M. lordhowensis were found to be particularly susceptible to elevated temperatures, whereby all corals subjected to elevated temperatures died within the course of the experimental treatment (75 d). Catalaphyllia jardinei and E. glabrescens also exhibited significant increases in mortality when exposed to elevated temperatures, though some of the corals did survive, and C. jardinei mostly died only after exposure to elevated temperatures. The other species (T. geoffroyi and D. axifuga) exhibited marked bleaching when exposed to elevated temperatures, but mortality of these corals was similar to that of conspecifics held at ambient temperatures. This study highlights the potential for environmental change to impact the sustainability and viability of Australian coral harvest fisheries. More importantly, this study highlights the need for specific and targeted in situ monitoring for important stocks of coral fishery target species, to assess their vulnerability to fishery and fishery-independent effects.

A hermit crab preserved inside an ammonite shell from the Upper Jurassic of central Russia: Implications to ammonoid palaeoecology

The discovery of a hermit crab (superfamily Paguroidea) preserved in the likely immature shell of an ammonite, Craspedites nekrassovi is reported from the Upper Jurassic of Moscow, Russia. This is the oldest undoubtable symmetrical hermit crab to date which is known from non-reefal environments. This new occurrence combined with the documentation of numerous sublethal and lethal injuries on ammonite shells in the same beds (probably produced by such paguroids), all suggest that the hermit crabs not only lived in ammonite shells but also hunted these animals. The proportion of damaged shells (including healed ones) varies in different Upper Jurassic ammonite genera from 1.2% in Kachpurites up to 9.3% in Craspedites. Among damaged Kachpurites only 6.25% survived attacks whereas among Craspedites the percentage of survivors was 87.5%. These data imply that Craspedites likely lived near the sea bottom and often encountered hermit crabs, whereas Kachpurites likely lived in the water column.

Non-reef environments impact the diversification of extant jacks, remoras and allies (Carangoidei, Percomorpha).

Various factors may impact the processes of diversification of a clade. In the marine realm, it has been shown that coral reef environments have promoted diversification in various fish groups. With the exception of requiem sharks, all the groups showing a higher level of diversity in reefs than in non-reef habitats have diets based predominantly on plankton, algae or benthic invertebrates. Here we explore the pattern of diversification of carangoid fishes, a clade that includes numerous piscivorous species (e.g. trevallies, jacks and dolphinfishes), using time-calibrated phylogenies as well as ecological and morphological data from both extant and fossil species. The study of carangoid morphospace suggests that reef environments played a role in their early radiation during the Eocene. However, contrary to the hypothesis of a reef-association-promoting effect, we show that habitat shifts to non-reef environments have increased the rates of morphological diversification (i.e. size and body shape) in extant carangoids. Piscivory did not have a major impact on the tempo of diversification of this group. Through the ecological radiation of carangoid fishes, we demonstrate that non-reef environments may sustain and promote processes of diversification of different marine fish groups, at least those including a large proportion of piscivorous species.

The role of peripheral endemism and habitat associations in the evolution of the Indo-West Pacific tuskfishes (Labridae: Choerodon)

The unrivalled level of biodiversity across the tropical Indo-Australian Archipelago (IAA) has been the subject of wide debate. Attempts to understand its origins have focussed on the timing of speciation, rates of diversification and the directionality of colonisation across geographical and climatic gradients in an array of marine groups. We investigate origins and evolution in the Choerodon tuskfishes, a group of labrids whose centre of diversity coincides with this region. Mitochondrial (COI, 16S) and nuclear (RAG2, Tmo4c4) molecular phylogenies and biogeographic analyses, coupled with molecular clock dating, were inferred from 19 of the 23 valid Choerodon species. Two additional, undescribed Choerodon species were also included, showing reciprocal monophyly in both genomes, confirming their species level status. Choerodon diverged from their ancestral sister group, the Odacines, at the onset of the Miocene, coinciding with the collision of the Australian and Eurasian Plates when extensive areas of shallow-water habitat formed. Despite subsequent evolutionary patterns being partially obscured by overlapping distribution ranges between many species and a lack of clear evidence for climatically driven lineage divergences, our data support an evolutionary scenario of peripheral endemics budding from once widespread populations across this biodiversity hotspot. Interestingly, these peripheral endemics tend to occupy more specialised reef or non-reef habitats whereas widespread groups appear to generally take advantage of both reef and non-reef environments. Our results are discussed in light of the most accredited hypotheses proposed to explain species richness in the IAA, with some support for processes such as centrifugal speciation.

Encrusting strategies in a Cambrian nonreefal epibenthic community

Abstract Microfossils released by the action of acids from the Cambrian Valdemiedes Formation (Iberian Chains, NE Spain) contain evidence that encrusting microepifauna (foraminifers and serpulid tube worms) infested shelled hard substrates in nonreefal environments. They appear to have exploited parasitic and/or commensal ecological niches under medium- to low-energy bottom conditions. Despite the gregariousness character of the epifauna, skeletal overgrowths are rare, reflecting low-patterns on competitive interactions for space. Cambrian psammosphaerids (agglutinated foraminifers) were able to dissolve partly calcareous shells: although no evidence of pitting is observed, distinct depressed scars occur on the internal sides of host shells. The serpulids experienced a population bloom during the ecosystem recovery interval after the community turnover represented by the Valdemiedes event, and sharply disappeared during the ensuing return to background conditions. By contrast, the psammosphaerids are relatively abundant across the event, increasing in abundance during the same bloom of opportunistic taxa.

Is morphology a good way to understand the evolution of corals?

Within a family, genera are usually separated on the basis of their colonial structure. The periodic occurrence of transgeneric highly variable specific units (spectra) in the fossil record poses nomenclatural and phylogenetic problems. A detailed example among Jurassic montlivaltiids is presented in this paper involving the generaMontlivaltia, Coenotheca, Thecosmilia, LatiphylliaandComplexastrea.These spectra are related to peculiar unstable nonreefal environments and are characterized by the dominance of young stages of the colonial growth (astogeny). The arising nomenclatural difficulties are solved by way of spectral nomenclature which allows naming morphological types, as well as taxonomic units and keeping some stability within the general frame of nominal taxa. Genera correspond to grades (solitary, thamnasterioid, phaceloid, meandroid, cerioid) rather than clades and the colonial structure is a labile character. Several alternative phylogenetic hypotheses are proposed, among which, some can renew our vision of this group and emphasize that the iterative production of generic-level shapes is best explained by mean of heterochronic processes. It is suggested that testing of these hypotheses be extended to other families such as Microsolenidae, Stylophyllidae or Fungiidae.

Sedimentation control on growth of stromatoporoid reefs in the Silurian of Gotland, Sweden

Silurian stromatoporoid-dominated reefs of Gotland, Sweden, are bioherms and biostromes formed during phases of reduced clastic supply. Well-exposed examples are in the early Wenlock Högklint Formation and middle Ludlow Hemse Group. Reef development culminated in shallow water biostromes, laterally expanded over a stabilized substrate and associated with frequent erosion surfaces. Högklint reefs began as bioherms, to be replaced by biostromal phases as water shallowed, with vertically zoned communities. Biostromal phases are considered equivalent to the whole of individual stromato-poroid biostromes (without biohermal phases) of the Hemse Group, which developed in shallow, low to moderate energy water, on stabilized substrate. Low clastic supply associated with these reefs reduced not only the clay input, which is otherwise common in most non-reef environments on Gotland, but also is interpreted to have lowered available nutrient levels. Modern reefs develop best in conditions of low nutrients and also show (a) suppressed bioerosion, and (b) increased symbiosis between corals and algae which conserves nutrients in the reef biota. Högklint reefs show reduced bioerosion while Hemse reefs show almost complete lack of bioerosion. Symbiosis between stromatoporoids and corals, interpreted as a response to the need for nutrient conservation, occurs in the reefs, but is much more common in Hemse reefs. Both Högklint and Hemse reefs are regarded as having grown in nutrient-deficient conditions in line with modern reefs although the effect on Hemse reefs is believed to have been greater because they appear to have grown in quieter conditions on a broad shelf and may have had reduced access to nutrients in a regressive regime throughout the Ludlow. Reduced clastic supply while the Gotland reefs grew could have been due to regional tectonism controlling local sea-level change. However, the Högklint Formation and Hemse Group reef phases coincide with times of proposed eustatic sea-level falls. Reef growth on Gotland could therefore relate to eustatic tectonism by subduction-related or plate flexure processes, or climatic control. An oceanographic model for the Silurian proposed alternating wet and dry episodes, interpreted as CO 2 -driven, and could have controlled clastic input, permitting the development of fossiliferous reefs and the carbonate platforms on which they formed. These interpretations provide a revised framework for examining the reef growth.