Biological activity exceeds biogenic structure in influencing sediment nitrogen cycling in experimental oyster reefs

Oysters are estuarine ecosystem engineers, in that their physical structure and biological function affect ecosystem processes such as organic matter and nutrient cycling. Oysters deliver material to the sediments through biodeposition and sedimentation caused by modification of flow around the reef. We conducted an experiment to distinguish between biotic effects and physical structure of oyster reefs on sediment nitrogen cycling. Experimental reefs consisting of live oysters, oyster shells alone and mudflats (controls) were sampled for a period of 4 wk for sediment organic matter, C and N content and fluxes of nitrogen (NH4 +, NOX and N2) and oxygen (O2). We hypothesized that the biological activity of the oyster would deposit more, higher quality organic matter compared to deposition from flow modification alone, thus facilitating denitrification and having a larger impact on sediment nitrogen cycling. Compared to the controls, the live oyster experimental reefs increased sediment denitrification by 61% and the shell experimental reefs showed a 24% increase. The live oyster experimental reef also had the largest O2 demand and NH4 + production. Reef structure likely increased organic matter deposition, but the higher quality and larger quantity of organic matter associated with live oysters increased denitrification and microbial respiration. This experiment shows that the ecosystem service of nitrogen removal provided by oysters is primarily driven by the biological function of the oysters and secondarily from the physical structure of the reef. Our increased understanding of how oysters engineer ecosystems and modify nutrient cycling can help guide future oyster restoration effort

Phylogeographic analysis suggests a recent population Bottleneck in the rare Red Sea Tridacna squamosina

Giant clams are an important ecological component of coral reefs in the Red Sea, as they enhance the reef’s productivity and provide habitat that can increase diversity. Three species of giant clams, namely Tridacna maxima, T. squamosa, and T. squamosina have been described within the Red Sea. However, due to its scarcity, information about the distribution and ecology of T. squamosina in the Saudi Arabian Red Sea is still lacking. This study used DNA barcoding to confirm the identity of the rare T. squamosina in the Farasan Banks. Six mtCOI fragments (500 bp) of T. squamosina were successfully amplified using the SQUA-primers for the first time. We used our data along with 18 reference sequences (16S) from the online database to assess the genetic diversity and population structure of T. squamosina. Low genetic diversity among the T. squamosina populations inferred from the 16S sequences implies a recent bottleneck for this species, which is supported by their historically higher diversity based on the coalescent-based estimator. Given the small population abundance and limited genetic variation of T. squamosina, it may warrant immediate local protections such as biobanking and fertility preservation programs as well as effective integrated coastal zone management plans.info:eu-repo/semantics/publishedVersio

The small giant clam, Tridacna maxima exhibits minimal population genetic structure in the Red sea and genetic differentiation from the Gulf of Aden

The Red Sea serves as a natural laboratory to investigate mechanisms of genetic differentiation and population dynamics of reef organisms due to its high species endemism. Giant clams, important yet understudied coral reef engineering species, are ideal candidates for such study in this region. This paper presents the first population genetics study of giant clams covering the entire East coast of the Red Sea. Our study aimed to investigate the population structure of the small giant clam, Tridacna maxima, based on 501-bp fragment of the cytochrome c oxidase I gene from 194 individuals (126 new sequences from this study plus 68 sequences from GenBank), collected from 14 locations in the Red Sea and Gulf of Aden (RSGA). For the genetic analysis, each sampling site was treated as a population. T. maxima showed high genetic diversity, with high gene flow in almost all sampling sites. The insignificant global #ST-value of 0.02 (p > 0.05) suggests the presence of one large, panmictic population across a wide range of temperature and salinity gradients in the RSGA. Despite this, the population in Djibouti was genetically differentiated from the other 11 populations in the Red Sea, suggesting a connectivity break between the Red Sea and the Gulf of Aden. These results could be explained by the oceanographic features facilitating wide larval transport inside the Red Sea, and creating a dispersal barrier to the Gulf of Aden. Besides larval dispersal by currents, apparent successful establishment following dispersal is probably facilitated by the mode and time of reproduction as well as the ability of T. maxima to achieve high fitness in the highly variable environmental conditions of the Red Sea.King Abdullah University of Science & Technology: BAS/1/1071-01-01info:eu-repo/semantics/publishedVersio

Testing angular velocity as a new metric for metabolic demands of slow-moving marine fauna: a case study with Giant spider conchs Lambis truncata

BackgroundQuantifying metabolic rate in free-living animals is invaluable in understanding the costs of behaviour and movement for individuals and communities. Dynamic body acceleration (DBA) metrics, such as vectoral DBA (VeDBA), are commonly used as proxies for the energy expenditure of movement but are of limited applicability for slow-moving species. It has recently been suggested that metrics based on angular velocity might be better suited to characterise their energetics. We investigated whether a novel metric—the ‘Rate of change of Rotational Movement (RocRM)’, calculated from the vectoral sum of change in the pitch, roll and yaw/heading axes over a given length of time, is a suitable proxy for energy expenditure.ResultsWe found that RocRM can be used as an alternative energy expenditure proxy in a slow-moving benthic invertebrate. Eleven Giant spider conchs Lambis truncata (collected in the Red Sea) were instrumented with multiple channel (Daily Diary) tags and kept in sealed chambers for 5 h while their oxygen consumption, V̇O2, was measured. We found RocRM to be positively correlated with V̇O2, this relationship being affected by the time-step (i.e. the range of the calculated differential) of the RocRM. Time steps of 1, 5, 10 and 60 s yielded an explained variability of between 15 and 31%. The relationship between V̇O2 and VeDBA was not statistically significant, suggesting RocRM to provide more accurate estimations of metabolic rates in L. truncata.ConclusionsRocRM proved to be a statistically significant predictor of V̇O2 where VeDBA did not, validating the approach of using angular-based metrics over dynamic movement-based ones for slower moving animals. Further work is required to validate the use of RocRM for other species, particularly in animals with minimally dynamic movement, to better understand energetic costs of whole ecosystems. Unexplained variability in the models might be a consequence of the methodology used, but also likely a result of conch activity that does not manifest in movement of the shell. Additionally, density plots of mean RocRM at each time-step suggest differences in movement scales, which may collectively be useful as a species fingerprint of movement going forward

Fingerprinting blue carbon: Rationale and tools to determine the source of organic carbon in marine depositional environments

Blue carbon is the organic carbon in oceanic and coastal ecosystems that is captured on centennial to millennial timescales. Maintaining and increasing blue carbon is an integral component of strategies to mitigate global warming. Marine vegetated ecosystems (especially seagrass meadows, mangrove forests, and tidal marshes) are blue carbon hotspots and their degradation and loss worldwide have reduced organic carbon stocks and increased CO2 emissions. Carbon markets, and conservation and restoration schemes aimed at enhancing blue carbon sequestration and avoiding greenhouse gas emissions, will be aided by knowing the provenance and fate of blue carbon. We review and critique current methods and the potential of nascent methods to track the provenance and fate of organic carbon, including: bulk isotopes, compound-specific isotopes, biomarkers, molecular properties, and environmental DNA (eDNA). We find that most studies to date have used bulk isotopes to determine provenance, but this approach often cannot distinguish the contribution of different primary producers to organic carbon in depositional marine environments. Based on our assessment, we recommend application of multiple complementary methods. In particular, the use of carbon and nitrogen isotopes of lipids along with eDNA have a great potential to identify the source and quantify the contribution of different primary producers to sedimentary organic carbon in marine ecosystems. Despite the promising potential of these new techniques, further research is needed to validate them. This critical overview can inform future research to help underpin methodologies for the implementation of blue carbon focused climate change mitigation schemes

Projecting coral responses to intensifying marine heatwaves under ocean acidification

Over this century, coral reefs will run the gauntlet of climate change, as marine heatwaves (MHWs) become more intense and frequent, and ocean acidification (OA) progresses. However, we still lack a quantitative assessment of how, and to what degree, OA will moderate the responses of corals to MHWs as they intensify throughout this century. Here, we first projected future MHW intensities for tropical regions under three future greenhouse gas emissions scenario (representative concentration pathways, RCP2.6, RCP4.5 and RCP8.5) for the near-term (2021–2040), mid-century (2041–2060) and late-century (2081–2100). We then combined these MHW intensity projections with a global data set of 1,788 experiments to assess coral attribute performance and survival under the three emissions scenarios for the near-term, mid-century and late-century in the presence and absence of OA. Although warming and OA had predominately additive impacts on the coral responses, the contribution of OA in affecting most coral attributes was minor relative to the dominant role of intensifying MHWs. However, the addition of OA led to greater decreases in photosynthesis and survival under intermediate and unrestricted emissions scenario for the mid- and late-century than if intensifying MHWs were considered as the only driver. These results show that role of OA in modulating coral responses to intensifying MHWs depended on the focal coral attribute and extremity of the scenario examined. Specifically, intensifying MHWs and OA will cause increasing instances of coral bleaching and substantial declines in coral productivity, calcification and survival within the next two decades under the low and intermediate emissions scenario. These projections suggest that corals must rapidly adapt or acclimatize to projected ocean conditions to persist, which is far more likely under a low emissions scenario and with increasing efforts to manage reefs to enhance resilience

Integrating environmental variability to broaden the research on coral responses to future ocean conditions

Our understanding of the response of reef-building corals to changes in their physical environment is largely based on laboratory experiments, analysis of long-term field data, and model projections. Experimental data provide unique insights into how organisms respond to variation of environmental drivers. However, an assessment of how well experimental conditions cover the breadth of environmental conditions and variability where corals live successfully is missing. Here, we compiled and analyzed a globally distributed dataset of in-situ seasonal and diurnal variability of key environmental drivers (temperature, pCO2, and O2) critical for the growth and livelihood of reef-building corals. Using a meta-analysis approach, we compared the variability of environmental conditions assayed in coral experimental studies to current and projected conditions in their natural habitats. We found that annual temperature profiles projected for the end of the 21st century were characterized by distributional shifts in temperatures with warmer winters and longer warm periods in the summer, not just peak temperatures. Furthermore, short-term hourly fluctuations of temperature and pCO2 may regularly expose corals to conditions beyond the projected average increases for the end of the 21st century. Coral reef sites varied in the degree of coupling between temperature, pCO2, and dissolved O2, which warrants site-specific, differentiated experimental approaches depending on the local hydrography and influence of biological processes on the carbonate system and O2 availability. Our analysis highlights that a large portion of the natural environmental variability at short and long timescales is underexplored in experimental designs, which may provide a path to extend our understanding on the response of corals to global climate change

Noninvasive Featherlight Wearable Compliant “Marine Skin”: Standalone Multisensory System for Deep‐Sea Environmental Monitoring

Advances in marine research to understand environmental change and its effect on marine ecosystems rely on gathering data on species physiology, their habitat, and their mobility patterns using heavy and invasive biologgers and sensory telemetric networks. In the past, a lightweight (6 g) compliant environmental monitoring system: Marine Skin was demonstrated. In this paper, an enhanced version of that skin with improved functionalities (500–1500% enhanced sensitivity), packaging, and most importantly its endurance at a depth of 2 km in the highly saline Red Sea water for four consecutive weeks is reported. A unique noninvasive approach for attachment of the sensor by designing a wearable, stretchable jacket (bracelet) that can adhere to any species irrespective of their skin type is also illustrated. The wearable featherlight (<0.5 g in air, 3 g with jacket) gadget is deployed on Barramundi, Seabream, and common goldfish to demonstrate the noninvasive and effective attachment strategy on different species of variable sizes which does not hinder the animals' natural movement or behavior

Noninvasive Featherlight Wearable Compliant “Marine Skin”: Standalone Multisensory System for Deep‐Sea Environmental Monitoring

Advances in marine research to understand environmental change and its effect on marine ecosystems rely on gathering data on species physiology, their habitat, and their mobility patterns using heavy and invasive biologgers and sensory telemetric networks. In the past, a lightweight (6 g) compliant environmental monitoring system: Marine Skin was demonstrated. In this paper, an enhanced version of that skin with improved functionalities (500–1500% enhanced sensitivity), packaging, and most importantly its endurance at a depth of 2 km in the highly saline Red Sea water for four consecutive weeks is reported. A unique noninvasive approach for attachment of the sensor by designing a wearable, stretchable jacket (bracelet) that can adhere to any species irrespective of their skin type is also illustrated. The wearable featherlight (<0.5 g in air, 3 g with jacket) gadget is deployed on Barramundi, Seabream, and common goldfish to demonstrate the noninvasive and effective attachment strategy on different species of variable sizes which does not hinder the animals' natural movement or behavior