Coastal hypoxia is increasing in the global coastal zone, where it is recognized as a major threat to biota. Managerial efforts to prevent hypoxia and achieve recovery of ecosystems already affected by hypoxia are largely based on nutrient reduction plans. However, these managerial efforts need to be informed by predictions on the thresholds of hypoxia (i.e. the oxygen levels required to conserve biodiversity) as well as the timescales for the recovery of ecosystems already affected by hypoxia. The thresholds for hypoxia in coastal ecosystems are higher than previously thought and are not static, but regulated by local and global processes, being particularly sensitive to warming. The examination of recovery processes in a number of coastal areas managed for reducing nutrient inputs and, thus, hypoxia (Northern Adriatic; Black Sea; Baltic Sea; Delaware Bay; and Danish Coastal Areas) reveals that recovery timescales following the return to normal oxygen conditions are much longer than those of loss following the onset of hypoxia, and typically involve decadal timescales. The extended lag time for ecosystem recovery from hypoxia results in non-linear pathways of recovery due to hysteresis and the shift in baselines, affecting the oxygen thresholds for hypoxia through time.
Abstract Estimation of marine macrophyte contribution to coastal sediments is key to understand carbon sequestration dynamics. Nevertheless, identification of macrophyte carbon is challenging. We propose environmental DNA (eDNA) metabarcoding as a new approach for identification of sediment contributors, and compared this approach against stable isotopes—the traditional approach. eDNA metabarcoding allowed high‐resolution identification of 48 macroalgae, seagrasses, and mangroves from coastal habitats. The relative eDNA contributions of macrophytes were similar to their contributions of organic carbon based on stable isotopes; however, isotopes were unreliable for taxonomical discrimination among macrophyte sources. Additionally, we experimentally found that eDNA abundance in the sediment correlates with both the DNA (84%, R 2 = 0.71, p = 0.001) and the organic carbon content (76%, R 2 = 0.58, p = 0.006) per macrophyte lineage. These results demonstrate the unparallel resolution of eDNA as a method for estimation of the organic carbon contribution of marine macrophytes to blue carbon stocks.
We investigated the occurrence of the sea skater Halobates spp. from samples collected at a fixed time series station and from six cruises along the north-south extend of the Red Sea during 2016-2018. Halobates germanus White, 1883 was the only species found during our study, its distribution ranging between 17° 9´ N - 27° 27´ N and between 35° 67´ E - 41° 49´ E. Total H. germanus abundance ranged between zero to 158,610 individuals km-2 with a considerable temporal (at the fixed station) and spatial (cruises) variation. In general, nymphs of different instar stages dominated the population, followed by females and males. The sex ratio was female-biased, with a higher number of females than males. Presence and prevalence of eggs, exuviae (moults) and early nymphal stages indicate a year round breeding cycle by H. germanus. The apparent optimum temperature for H. germanus occurrence in the central Red Sea was at 28.2°C, corresponding to peak abundances in spring and fall. Absence of any significant correlation of the abundances with environmental parameters indicate relative resilience of H. germanus to changes in environmental conditions.
Hurricanes are large-scale disturbances with the potential to exert extensive damage in coastal ecosystems. On August 29, 2005 Hurricane Katrina catastrophically impacted a large area of the Gulf of Mexico spreading from coastal Alabama to Louisiana. For five months before hurricane landfall we were assessing the structure and functioning of a mixed seagrass bed located in an area greatly affected by the hurricane. The storm provided an opportunity to assess the effect of a large-scale disturbance on the structure and functioning of that seagrass bed. A comparison of surveys before and after the hurricane showed no decreases in seagrass density, associated fauna, or the microalgal abundance in the water column and sediment. We found no major impact on gross primary productivity, respiration, or net productivity of the water column or the sediment, suggesting that the hurricane had little impact on the metabolism of the seagrass bed studied. Overall, natural temporal changes recorded before the storm were larger than any post-hurricane changes. These findings indicate that this seagrass meadow was naturally highly dynamic and very resistant to Hurricane Katrina.
MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 532:101-109 (2015) - DOI: https://doi.org/10.3354/meps11343 Combined effect of warming and infection by Labyrinthula sp. on the Mediterranean seagrass Cymodocea nodosa Ylva S. Olsen1,*, Carlos M. Duarte1,2,3 1The UWA Oceans Institute, University of Western Australia, 35 Stirling Highway, Crawley 6009, Australia 2Department of Global Change Research. IMEDEA (CSIC-UIB), Institut Mediterrani d'Estudis Avançats, Miquel Marquès 21, 07190 Esporles, Spain 3Faculty of Marine Sciences, King Abdulaziz University, PO Box 80207, Jeddah 21589, Saudi Arabia *Corresponding author: ylva.olsen@uwa.edu.au ABSTRACT: Global warming is predicted to alter host-pathogen relationships and increase disease outbreaks in terrestrial and marine environments. We evaluated the effect of warming on the susceptibility of Cymodocea nodosa to infection by Labyrinthula sp. (the causative agent of seagrass wasting disease) by monitoring disease symptoms and seagrass photobiology. Seagrass shoots were incubated at temperatures between 24 and 32°C, encompassing maximum summer seawater temperatures projected for the Mediterranean during the 21st century, and exposed to Labyrinthula sp. for 2 wk. The effect of temperature on pathogen growth was also tested by growing Labyrinthula sp. in liquid medium for 24 h. Disease severity, measured as lesion size, decreased with warming, but the presence of lesions had a negative effect on quantum yield, quantum efficiency, optimum irradiance and the maximum electron transport rate (ETRmax) in adjacent tissue across the full range of temperatures. The direct effect of increased temperature on photochemical efficiency was positive in terms of quantum yield, whereas compensation and optimum irradiances and ETRmax decreased slightly with warming. Warming stimulated Labyrinthula sp. growth up to a threshold of around 26 to 28°C, beyond which cell division and elongation of the ectoplasmic network decreased. At 32°C almost no growth was observed. Our results indicate that warming does not make C. nodosa more susceptible to infection by Labyrinthula sp. and that the disease is unlikely to pose a serious threat to C. nodosa, but that the pathogen is able to persist during forecasted warm periods. KEY WORDS: Wasting disease · Pathogen · Host · Seagrass · Photosynthetic performance · Temperature · Climate change Full text in pdf format PreviousNextCite this article as: Olsen YS, Duarte CM (2015) Combined effect of warming and infection by Labyrinthula sp. on the Mediterranean seagrass Cymodocea nodosa. Mar Ecol Prog Ser 532:101-109. https://doi.org/10.3354/meps11343 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 532. Online publication date: July 21, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.
We provide evidence, based on the assessment of bactenal abundance in a series of samples representing geometncally decreasing volumes (5 1 to 0.25 ml), for the existence and scale dependence of patchiness in mixed-layer marine bacterioplankton.Our results demonstrate the existence of strong bacterioplankton patchiness at centimetre scale, the bacterioplankton community appearing as homogeneous when sampling at larger or smaller scales.We also provide, based on the inferred frequency distribution of bacterial densities, a representation of the in situ s p a t ~a l distribut~on of the bacterioplankton population sampled This dlstrlbution depicts the bacterioplankton community as composed of high density (> 107 bacteria ml-l) bacterial patches scattered within a 'matrix' of low bactenal density (105 bacteria ml-l).These results imply that the processes regulating bactenal abundance operate at centimetre scale.
Seagrass meadows are highly productive habitats found along many of the world's coastline, providing important services that support the overall functioning of the coastal zone. The organic carbon that accumulates in seagrass meadows is derived not only from seagrass production but from the trapping of other particles, as the seagrass canopies facilitate sedimentation and reduce resuspension. Here we provide a comprehensive synthesis of the available data to obtain a better understanding of the relative contribution of seagrass and other possible sources of organic matter that accumulate in the sediments of seagrass meadows. The data set includes 219 paired analyses of the carbon isotopic composition of seagrass leaves and sediments from 207 seagrass sites at 88 locations worldwide. Using a three source mixing model and literature values for putative sources, we calculate that the average proportional contribution of seagrass to the surface sediment organic carbon pool is ∼50%. When using the best available estimates of carbon burial rates in seagrass meadows, our data indicate that between 41 and 66 gC m −2 yr −1 originates from seagrass production. Using our global average for allochthonous carbon trapped in seagrass sediments together with a recent estimate of global average net community production, we estimate that carbon burial in seagrass meadows is between 48 and 112 Tg yr −1 , showing that seagrass meadows are natural hot spots for carbon sequestration.
