Coral microatolls and a probable Middle Ordovician example

1990 ◽  
Vol 64 (1) ◽  
pp. 39-43 ◽  
Author(s):  
David R. Kobluk ◽  
Iqbal Noor
Keyword(s):  
Coral Reefs ◽  
Fossil Record ◽  
Scleractinian Coral ◽  
Regional Scale ◽  
Southern Ontario ◽  
Middle Ordovician ◽  
Reef Environments ◽  
Maximum Water ◽  
Water Depths ◽  
Tabulate Corals

A disk-shaped massive colony of Tetradium, from the Middle Ordovician Bobcaygeon Formation in southern Ontario, displays features of a coral microatoll. This is the first pre-Holocene coral microatoll yet described, indicating that some tabulate corals in level-bottom communities were growing as microatolls as do many modern colonial skeleton-secreting organisms.The microatoll therefore is not strictly a Quaternary or even Cenozoic phenomenon, but has a fossil record that may span most of the Phanerozoic. This indicates that the special conditions necessary for microatoll growth have existed outside of reef environments, and were present before the advent of scleractinian coral reefs. It may be possible to use ancient microatolls to estimate absolute water depths at low tide, thereby providing a means for estimating maximum water depths on a local and regional scale.

In situ lingulids from deep-water carbonates of the Middle Ordovician Table Head Group of Newfoundland and the Trenton Group of Quebec

1984 ◽  
Vol 21 (2) ◽  
pp. 194-199 ◽  
Author(s):  
R. K. Pickerill ◽  
T. L. Harland ◽  
D. Fillion
Keyword(s):  
Deep Water ◽  
Fossil Record ◽  
Environmental Indicators ◽  
Outer Shelf ◽  
Head Group ◽  
Middle Ordovician ◽  
Trenton Group ◽  
Water Depths ◽  
Upper Slope

Specimens of in situ lingulids have been discovered in carbonates of the Middle Ordovician Table Head Group of northwestern Newfoundland and Trenton Group of the St. Lawrence Lowland of Quebec. The discoveries have two important implications regarding Palaeozoic lingulid ecology. First, they represent one of the few recordings of in situ lingulids in carbonate substrates of Palaeozoic age and, second, they occur mainly in outer shelf and upper slope sediments (Grondines Member of Neuville Formation, Trenton Group, and Table Cove Formation, Table Head Group), deposited in presumed considerable water depths. Caution must be observed with the use in the fossil record of lingulids as palaeo-environmental indicators.

scholarly journals Multi-Temporal UAV Data and Object-Based Image Analysis (OBIA) for Estimation of Substrate Changes in a Post-Bleaching Scenario on a Maldivian Reef

2020 ◽  
Vol 12 (13) ◽  
pp. 2093 ◽  
Author(s):  
Luca Fallati ◽  
Luca Saponari ◽  
Alessandra Savini ◽  
Fabio Marchese ◽  
Cesare Corselli ◽  
...  
Keyword(s):  
Image Analysis ◽  
Coral Reefs ◽  
Shallow Water ◽  
Regional Scale ◽  
Spatial And Temporal Patterns ◽  
Coral Rubble ◽  
Object Based Image Analysis ◽  
Object Based ◽  
Reef Environments ◽  
Multi Temporal

Coral reefs are declining worldwide as a result of the effects of multiple natural and anthropogenic stressors, including regional-scale temperature-induced coral bleaching. Such events have caused significant coral mortality, leading to an evident structural collapse of reefs and shifts in associated benthic communities. In this scenario, reasonable mapping techniques and best practices are critical to improving data collection to describe spatial and temporal patterns of coral reefs after a significant bleaching impact. Our study employed the potential of a consumer-grade drone, coupled with structure from motion and object-based image analysis to investigate for the first time a tool to monitor changes in substrate composition and the associated deterioration in reef environments in a Maldivian shallow-water coral reef. Three key substrate types (hard coral, coral rubble and sand) were detected with high accuracy on high-resolution orthomosaics collected from four sub-areas. Multi-temporal acquisition of UAV data allowed us to compare the classified maps over time (February 2017, November 2018) and obtain evidence of the relevant deterioration in structural complexity of flat reef environments that occurred after the 2016 mass bleaching event. We believe that our proposed methodology offers a cost-effective procedure that is well suited to generate maps for the long-term monitoring of changes in substrate type and reef complexity in shallow water.

The Evolutionary Diversity and Ecological Complexity of Coral Reefs

2011 ◽  
Vol 17 ◽  
pp. 111-120 ◽  
Author(s):  
Nancy Knowlton ◽  
Jeremy Jackson
Keyword(s):  
Coral Reefs ◽  
Small Proportion ◽  
Fossil Record ◽  
Marine Species ◽  
Foreseeable Future ◽  
Ecological Complexity ◽  
The Face ◽  
Open Question ◽  
Trophic Linkages ◽  
Bounce Back

Coral reefs are the most biodiverse marine ecosystems on the planet, with at least one quarter of all marine species associated with reefs today. This diversity, which remains very poorly understood, is nevertheless extraordinary when one considers the small proportion of ocean area that is occupied by coral reefs. Networks of competitive and trophic linkages are also exceptionally complex and dense. Reefs have a long fossil record, although extensive reef building comes and goes. In the present, coral reefs sometimes respond dramatically to disturbances, and collapses are not always followed by recoveries. Today, much of this failure to recover appears to stem from the fact that most reefs are chronically stressed by human activities, judging by observations of recovery at exceptional locations where local human activity is minimal. How long reefs can continue to bounce back in the face of warming and acidification remains an open question. Another big uncertainty is how much loss of biodiversity will occur with the inevitable degradation of coral reefs that will continue in most places for the foreseeable future.

scholarly journals A ‘Giant Microfossil’ from the Gunflint Chert and its Implications for Fungal and Eukaryote Origins

2019 ◽  
Author(s):  
Mark A. S. McMenamin ◽  
Aurora Curtis-Hill ◽  
Sophie Rabinow ◽  
Kalyndi Martin ◽  
Destiny Treloar
Keyword(s):  
Thin Section ◽  
Asexual Reproduction ◽  
Alternaria Alternata ◽  
Fossil Record ◽  
Iron Formation ◽  
Southern Ontario ◽  
Large Size ◽  
Early Evidence

We report here a giant microfossil resembling the conidium of an ascomycete fungus (cf. Alternaria alternata). The specimen is preserved in stromatolitic black chert of the Gunflint Iron Formation (Paleoproterozoic Eon, Orosirian Period, ca. 1.9-2.0 Ga) of southern Ontario, Canada, and the rock that provided the thin section may have been collected by Elso Barghoorn as part of the original discovery of the Gunflint microbiota. The large size of the fossil sets it apart from other, tiny by comparison, Gunflint microfossils. The fossil is 200 microns in length and has cross walls. Individual cells are 30-46 microns in greatest dimension. The apical ‘spore’ is cap-shaped, and has partly separated from the rest of the structure. Cloulicaria gunflintensis gen. nov. sp. nov. may provide early evidence for eukaryotes (fungi) in the fossil record, and may also represent the earliest evidence for asexual reproduction in a eukaryote by means of mitospores.

scholarly journals A ‘Giant Microfossil’ from the Gunflint Chert and its Implications for Eukaryote Origins

2019 ◽  
Author(s):  
Mark McMenamin
Keyword(s):  
Thin Section ◽  
Asexual Reproduction ◽  
Alternaria Alternata ◽  
Fossil Record ◽  
Iron Formation ◽  
Southern Ontario ◽  
Large Size ◽  
Early Evidence

We report here a ‘giant microfossil’ resembling the conidium of an ascomycete fungus (cf. Alternaria alternata). The specimen is preserved in stromatolitic black chert of the Gunflint Iron Formation (Paleoproterozoic Eon, Orosirian Period, ca. 1.9-2.0 Ga) of southern Ontario, Canada, and the rock that provided the thin section may have been collected by Elso Barghoorn as part of the original discovery of the Gunflint microbiota. The large size of the fossil sets it apart from other, tiny by comparison, Gunflint microfossils. The fossil is 200 microns in length and has cross walls. Individual cells are 30-46 microns in greatest dimension. The apical ‘spore’ is cap-shaped, and has partly separated from the rest of the structure. Cloulicaria gunflintensis gen. nov. sp. nov. may provide early evidence for eukaryotes (fungi) in the fossil record, and may also represent the earliest evidence for asexual reproduction in a eukaryote by means of mitospores.

scholarly journals A modern scleractinian coral with a two-component calcite–aragonite skeleton

2020 ◽  
pp. 202013316
Author(s):  
Jarosław Stolarski ◽  
Ismael Coronado ◽  
Jack G. Murphy ◽  
Marcelo V. Kitahara ◽  
Katarzyna Janiszewska ◽  
...  
Keyword(s):  
Calcium Carbonate ◽  
Southern Ocean ◽  
Phylogenetic Relationship ◽  
Fossil Record ◽  
Scleractinian Coral ◽  
Scleractinian Corals ◽  
Marine Organisms ◽  
Close Phylogenetic Relationship ◽  
Two Component ◽  
Selection Of

One of the most conserved traits in the evolution of biomineralizing organisms is the taxon-specific selection of skeletal minerals. All modern scleractinian corals are thought to produce skeletons exclusively of the calcium-carbonate polymorph aragonite. Despite strong fluctuations in ocean chemistry (notably the Mg/Ca ratio), this feature is believed to be conserved throughout the coral fossil record, spanning more than 240 million years. Only one example, the Cretaceous scleractinian coral Coelosmilia (ca. 70 to 65 Ma), is thought to have produced a calcitic skeleton. Here, we report that the modern asymbiotic scleractinian coral Paraconotrochus antarcticus living in the Southern Ocean forms a two-component carbonate skeleton, with an inner structure made of high-Mg calcite and an outer structure composed of aragonite. P. antarcticus and Cretaceous Coelosmilia skeletons share a unique microstructure indicating a close phylogenetic relationship, consistent with the early divergence of P. antarcticus within the Vacatina (i.e., Robusta) clade, estimated to have occurred in the Mesozoic (ca. 116 Mya). Scleractinian corals thus join the group of marine organisms capable of forming bimineralic structures, which requires a highly controlled biomineralization mechanism; this capability dates back at least 100 My. Due to its relatively prolonged isolation, the Southern Ocean stands out as a repository for extant marine organisms with ancient traits.

scholarly journals Divergence of seafloor elevation and sea level rise in coral reef ecosystems

2017 ◽  
Vol 14 (6) ◽  
pp. 1739-1772 ◽  
Author(s):  
Kimberly K. Yates ◽  
David G. Zawada ◽  
Nathan A. Smiley ◽  
Ginger Tiling-Range
Keyword(s):  
Coral Reef ◽  
Coral Reefs ◽  
Sea Level Rise ◽  
Sea Level ◽  
Anthropogenic Impacts ◽  
Regional Scale ◽  
Coastal Hazards ◽  
Carbonate Production ◽  
Coral Reef Ecosystems ◽  
Study Sites

Abstract. Coral reefs serve as natural barriers that protect adjacent shorelines from coastal hazards such as storms, waves, and erosion. Projections indicate global degradation of coral reefs due to anthropogenic impacts and climate change will cause a transition to net erosion by mid-century. Here, we provide a comprehensive assessment of the combined effect of all of the processes affecting seafloor accretion and erosion by measuring changes in seafloor elevation and volume for five coral reef ecosystems in the Atlantic, Pacific, and Caribbean over the last several decades. Regional-scale mean elevation and volume losses were observed at all five study sites and in 77 % of the 60 individual habitats that we examined across all study sites. Mean seafloor elevation losses for whole coral reef ecosystems in our study ranged from −0.09 to −0.8 m, corresponding to net volume losses ranging from 3.4  ×  106 to 80.5  ×  106 m3 for all study sites. Erosion of both coral-dominated substrate and non-coral substrate suggests that the current rate of carbonate production is no longer sufficient to support net accretion of coral reefs or adjacent habitats. We show that regional-scale loss of seafloor elevation and volume has accelerated the rate of relative sea level rise in these regions. Current water depths have increased to levels not predicted until near the year 2100, placing these ecosystems and nearby communities at elevated and accelerating risk to coastal hazards. Our results set a new baseline for projecting future impacts to coastal communities resulting from degradation of coral reef systems and associated losses of natural and socioeconomic resources.

Early radiation of echinoderms

1997 ◽  
Vol 3 ◽  
pp. 205-224 ◽  
Author(s):  
James Sprinkle ◽  
Thomas E. Guensburg
Keyword(s):  
Mass Extinction ◽  
Fossil Record ◽  
Early Paleozoic ◽  
Soft Substrate ◽  
Middle Cambrian ◽  
Middle Ordovician ◽  
Late Cambrian ◽  
Low Diversity ◽  
Early Radiation ◽  
Ways Of Life

Echinoderms underwent a major two-part radiation that produced all of the major groups found in the fossil record between the Early Cambrian and the Middle Ordovician. A small initial radiation in the Early and Middle Cambrian produced about nine classes containing low-diversity members of the Cambrian Evolutionary Fauna. These were characterized by primitive morphology, simple ambulacral feeding structures, and the early development of a multiplated stalk or stem for attachment to skeletal fragments on a soft substrate. Several groups became extinct at the end of the Middle Cambrian, leaving the Late Cambrian as a gap of very low diversity in the fossil record of echinoderms with only four classes preserved and very few occurrences of complete specimens, mostly associated with early hardgrounds. The survivors from this interval re-expanded in the Early Ordovician and were joined by many newly evolved groups to produce a much larger radiation of more advanced, diverse, and successful echinoderms representing the Paleozoic Evolutionary Fauna on both hard and soft substrates. At least 17 classes were present by the Middle Ordovician, the all-time high point for echinoderm class diversity, and nearly all of the major ways-of-life (except for deep infaunal burrowing) had been developed. With the rise to dominance of crinoids, many less successful or archaic groups did not survive the Middle Ordovician, and echinoderm class diversity dropped further because of the mass extinction at the end of the Ordovician. This weeding-out process of other less-successful echinoderm groups continued throughout the rest of the Paleozoic, and only five classes of echinoderms have survived to the Recent from this early Paleozoic radiation.

Were bivalves ecologically dominant over brachiopods in the late Paleozoic? A test using exceptionally preserved fossil assemblages

Paleobiology ◽  
2019 ◽  
Vol 45 (02) ◽  
pp. 265-279 ◽  
Author(s):  
Shannon Hsieh ◽  
Andrew M. Bush ◽  
J Bret Bennington
Keyword(s):  
Fossil Record ◽  
Energy Use ◽  
Regional Scale ◽  
Late Paleozoic ◽  
Ecosystem Structure ◽  
Relative Importance ◽  
Clear Trend ◽  
Fossil Assemblages ◽  
Ecological Importance ◽  
Preferential Dissolution

AbstractInterpreting changes in ecosystem structure from the fossil record can be challenging. In a prominent example, the traditional view that brachiopods were ecologically dominant over bivalves in the Paleozoic has been disputed on both taphonomic and metabolic grounds. Aragonitic bivalves may be underrepresented in many fossil assemblages due to preferential dissolution. Abundance counts may further understate the ecological importance of bivalves, which tend to have more biomass and higher metabolic rates than brachiopods. We evaluate the relative importance of the two clades in exceptionally preserved, bulk-sampled fossil assemblages from the Pennsylvanian Breathitt Formation of Kentucky, where aragonitic bivalves are preserved as shells, not molds. At the regional scale, brachiopods were twice as abundant as bivalves and were collectively equivalent in biomass and energy use. Analyses of samples from the Paleobiology Database that contain abundance counts are consistent with these results and show no clear trend in the relative ecological importance of bivalves during the middle and late Paleozoic. Bivalves were probably more important in Paleozoic ecosystems than is apparent in many fossil assemblages, but they were not clearly dominant over brachiopods until after the Permian–Triassic extinction, which caused the shelly benthos to shift from bivalve and brachiopod dominated to merely bivalve dominated.

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