An official website of the United States government
Abstract During the Early Jurassic, reefs in the shallow seas of the Atlas Rift experienced substantial changes as they recovered from the end-Triassic mass extinction. Excellent Lower Jurassic reef deposits documenting this change occur in the Central High Atlas region of Morocco, and herein we describe Owl Olistolith, a micro-olistolith found in lower Pliensbachian-aged (∼ 188.7 million years ago) Moroccan strata. The olistolith records the composition of a reef that grew within the Atlas rift zone and represents a snapshot of reef recovery ∼ 10 million years after the end-Triassic mass extinction. Owl Olistolith is derived from a reef that was originally situated on an outer platform within fair weather wave base; it broke loose and was transported to deeper water and deposited amongst marls. Corals and microbialites formed the primary framework of the reef; microproblematica, foraminifera, and other minor components were also present. The reef can be divided into two dominant facies: a microbialite facies that contains no corals (54%–94% microbialites), and a coral-microbialite facies with substantial proportions of both microbialite (23%–50%) and corals (14%–72%). The micro-olistolith contains at least 15 distinct coral types. In this study, seven coral genera were identified, three of which represent taxa that span the Triassic/Jurassic boundary, including Coryphyllia, Stylophyllopsis, and Margarosmilia. These results indicate that, although surviving taxa played a significant role, newly evolved corals were the most important taxa in the reestablishment of reef ecosystems in the Early Jurassic of Morocco.
more »
« less
This content will become publicly available on April 1, 2026
Ecological differences in upper Pliensbachian (Early Jurassic) reef communities determined by environmental conditions in carbonate settings
Reef communities changed dramatically during the Early Jurassic as they recovered from the End-Triassic Mass Extinction. The Atlas Rift Zone in Morocco provided expansive shallow water substrate, which allowed a variety of reef communities to develop, such as lithiotid bivalves that established themselves as new and prolific reef builders alongside corals, microbialites, and sponges in the Sinemurian and Pliensbachian stages. To better understand the dynamics between these reef builders and their environments, a detailed facies analysis of upper Pliensbachian reefs and a quantitative analysis of their composition was undertaken. We describe two distinct environmentally controlled reef types in the Central High Atlas Mountains. Lithiotid bivalves dominated reef construction in lagoonal environments and, together with phaceloid corals, commonly built bioherms and biostromes that ranged from 1 to 2 m tall and up to several hundred meters wide. Meanwhile, on the platform edge, microbialites, corals, and sponges constructed patch reefs up to 7 m tall and 20 m wide. These two reef types share common facies, as many of the same reef inhabitants, and some framework builders, grew in both environments. Despite the facies overlap, the communities in these two environmental settings are distinct, which is likely a result of environmental controls on the dominant reef framework builders. Moderately turbid waters and soft substrate in lagoons were ideal conditions for lithiotids but excluded many corals, sponges, and microbialites. Conversely, the clear, oligotrophic waters at the platform edge allowed photosynthetic and photosymbiotic organisms to thrive (e.g., coral and microbial reefs), while firmer substrate and higher wave energy may have prevented lithiotids from establishing dense populations.
more »
« less
- Award ID(s):
- 1848393
- PAR ID:
- 10585076
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Journal of African Earth Sciences
- Volume:
- 224
- Issue:
- C
- ISSN:
- 1464-343X
- Page Range / eLocation ID:
- 105547
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Microorganisms are central to the functioning of coral reef ecosystems, but their dynamics are unstudied on most reefs. We examined the microbial ecology of shallow reefs within the Federated States of Micronesia. We surveyed 20 reefs surrounding 7 islands and atolls (Yap, Woleai, Olimarao, Kosrae, Kapingamarangi, Nukuoro, and Pohnpei), spanning 875053 km 2 . On the reefs, we found consistently higher coral coverage (mean ± SD = 36.9 ± 22.2%; max 77%) compared to macroalgae coverage (15.2 ± 15.5%; max 58%), and low abundances of fish. Reef waters had low inorganic nutrient concentrations and were dominated by Synechococcus, Prochlorococcus, and SAR11 bacteria. The richness of bacterial and archaeal communities was significantly related to interactions between island/atoll and depth. High coral coverage on reefs was linked to higher relative abundances of Flavobacteriaceae, Leisingera, Owenweeksia, Vibrio, and the OM27 clade, as well as other heterotrophic bacterial groups, consistent with communities residing in waters near corals and within coral mucus. Microbial community structure at reef depth was significantly correlated with geographic distance, suggesting that island biogeography influences reef microbial communities. Reefs at Kosrae Island, which hosted the highest coral abundance and diversity, were unique compared to other locations; seawater from Kosrae reefs had the lowest organic carbon (59.8-67.9 µM), highest organic nitrogen (4.5-5.3 µM), and harbored consistent microbial communities (>85% similar), which were dominated by heterotrophic cells. This study suggests that the reef-water microbial ecology on Micronesian reefs is influenced by the density and diversity of corals as well as other biogeographical features.more » « less
-
null (Ed.)Abstract Background The microbiomes of foundation (habitat-forming) species such as corals and sponges underpin the biodiversity, productivity, and stability of ecosystems. Consumers shape communities of foundation species through trophic interactions, but the role of consumers in dispersing the microbiomes of such species is rarely examined. For example, stony corals rely on a nutritional symbiosis with single-celled endosymbiotic dinoflagellates (family Symbiodiniaceae) to construct reefs. Most corals acquire Symbiodiniaceae from the environment, but the processes that make Symbiodiniaceae available for uptake are not resolved. Here, we provide the first comprehensive, reef-scale demonstration that predation by diverse coral-eating (corallivorous) fish species promotes the dispersal of Symbiodiniaceae, based on symbiont cell densities and community compositions from the feces of four obligate corallivores, three facultative corallivores, two grazer/detritivores as well as samples of reef sediment and water. Results Obligate corallivore feces are environmental hotspots of Symbiodiniaceae cells: live symbiont cell concentrations in such feces are 5–7 orders of magnitude higher than sediment and water environmental reservoirs. Symbiodiniaceae community compositions in the feces of obligate corallivores are similar to those in two locally abundant coral genera ( Pocillopora and Porites ), but differ from Symbiodiniaceae communities in the feces of facultative corallivores and grazer/detritivores as well as sediment and water. Combining our data on live Symbiodiniaceae cell densities in feces with in situ observations of fish, we estimate that some obligate corallivorous fish species release over 100 million Symbiodiniaceae cells per 100 m 2 of reef per day. Released corallivore feces came in direct contact with coral colonies in the fore reef zone following 91% of observed egestion events, providing a potential mechanism for the transfer of live Symbiodiniaceae cells among coral colonies. Conclusions Taken together, our findings show that fish predation on corals may support the maintenance of coral cover on reefs in an unexpected way: through the dispersal of beneficial coral symbionts in corallivore feces. Few studies examine the processes that make symbionts available to foundation species, or how environmental reservoirs of such symbionts are replenished. This work sets the stage for parallel studies of consumer-mediated microbiome dispersal and assembly in other sessile, habitat-forming species.more » « less
-
Seawater microorganisms play an important role in coral reef ecosystem functioning and can be influenced by biological, chemical, and physical features of reefs. As coral reefs continue to respond to environmental changes, the reef seawater microbiome has been proposed as a conservation tool for monitoring perturbations. However, the spatial variability of reef seawater microbial communities is not well studied, limiting our ability to make generalizable inferences across reefs. In order to better understand how microorganisms are distributed at multiple spatial scales, we examined seawater microbial communities in Florida Reef Tract and US Virgin Islands reef systems using a nested sampling design. On 3 reefs per reef system, we sampled seawater at regular spatial intervals close to the benthos. We assessed the microbial community composition of these waters using ribosomal RNA gene amplicon sequencing. Our analysis revealed that reef water microbial communities varied as a function of reef system and individual reefs, but communities did not differ within reefs and were not significantly influenced by benthic composition. For the reef system and inter-reef differences, abundant microbial taxa were found to be potentially useful indicators of environmental difference due to their high prevalence and variance. We further examined reef water microbial biogeography on a global scale using a secondary analysis of 5 studies, which revealed that microbial communities were more distinct with increasing geographic distance. These results suggest that biogeography is a distinguishing feature for reef water microbiomes, and that development of monitoring criteria may necessitate regionally specific sampling and analyses.more » « less
-
Abstract BackgroundMicrobes play vital roles across coral reefs both in the environment and inside and upon macrobes (holobionts), where they support critical functions such as nutrition and immune system modulation. These roles highlight the potential ecosystem-level importance of microbes, yet most knowledge of microbial functions on reefs is derived from a small set of holobionts such as corals and sponges. Declining seawater pH — an important global coral reef stressor — can cause ecosystem-level change on coral reefs, providing an opportunity to study the role of microbes at this scale. We use an in situ experimental approach to test the hypothesis that under such ocean acidification (OA), known shifts among macrobe trophic and functional groups may drive a general ecosystem-level response extending across macrobes and microbes, leading to reduced distinctness between the benthic holobiont community microbiome and the environmental microbiome. ResultsWe test this hypothesis using genetic and chemical data from benthic coral reef community holobionts sampled across a pH gradient from CO2seeps in Papua New Guinea. We find support for our hypothesis; under OA, the microbiome and metabolome of the benthic holobiont community become less compositionally distinct from the sediment microbiome and metabolome, suggesting that benthic macrobe communities are colonised by environmental microbes to a higher degree under OA conditions. We also find a simplification and homogenisation of the benthic photosynthetic community, and an increased abundance of fleshy macroalgae, consistent with previously observed reef microbialisation. ConclusionsWe demonstrate a novel structural shift in coral reefs involving macrobes and microbes: that the microbiome of the benthic holobiont community becomes less distinct from the sediment microbiome under OA. Our findings suggest that microbialisation and the disruption of macrobe trophic networks are interwoven general responses to environmental stress, pointing towards a universal, undesirable, and measurable form of ecosystem change.more » « less
