Posts Tagged 'Mediterranean'

Ocean acidification alters meiobenthic assemblage composition and organic matter degradation rates in seagrass sediments

Seagrass meadows are an important organic matter (OM) reservoir but, are currently being lost due to global and regional stressors. Yet, there is limited research investigating the cumulative impacts of anthropogenic stressors on the structure and functioning of seagrass benthic assemblages, key drivers of OM mineralization and burial. Here, using a 16‐month field experiment, we assessed how meiobenthic assemblages and extracellular enzymatic activities (as a proxy of OM degradation) in Posidonia oceanica sediments responded to ocean acidification (OA) and nutrient loadings, at CO2 vents. P. oceanica meadows were exposed to three nutrient levels (control, moderate, and high) at both ambient and low pH sites. OA altered meiobenthic assemblage structure, resulting in increased abundance of annelids and crustaceans, along with a decline in foraminifera. In addition, low pH enhanced OM degradation rates in seagrass sediments by enhancing extracellular enzymatic activities, potentially decreasing the sediment carbon storage capacity of seagrasses. Nutrient enrichment had no effect on the response variables analyzed, suggesting that, under nutrient concentration unlikely to cause N or P imitation, a moderate increase of dissolved nutrients in the water column had limited influence on meiobenthic assemblages. These findings show that OA can significantly alter meiobenthic assemblage structure and enhance OM degradation rates in seagrass sediments. As meiofauna are ubiquitous key actors in the functioning of benthic ecosystems, we postulated that OA, altering the structure of meiobenthic assemblages and OM degradation, could affect organic carbon sequestration over large spatial scales.

Continue reading ‘Ocean acidification alters meiobenthic assemblage composition and organic matter degradation rates in seagrass sediments’

Ocean acidification and elevated temperature negatively affect recruitment, oxygen consumption and calcification of the reef-building Dendropoma cristatum early life stages: evidence from a manipulative field study

Highlights

• Effects of pH and temperature in a Mediterranean intertidal reef-building species were tested for the first time;

• Portions of vermetid reefs have been transplanted in a natural CO2 vent and air-temperature was manipulated;

• The combination of high temperature and low pH reduced the oxygen consumption of the vermetid D. cristatum;

• Reproductive success, recruitment, and calcification of early life stages of D. cristatum were impacted by temperature and pH;

• Shell of embryos and recruits exposed to high pCO2 showed an increase in Mg concentration and a higher dissolution.

Abstract

Expected temperature rise and seawater pH decrease may affect marine organism fitness. By a transplant experiment involving air-temperature manipulation along a natural CO2 gradient, we investigated the effects of high pCO2 (~1100 μatm) and elevated temperature (up to +2 °C than ambient conditions) on the reproductive success, recruitment, growth, shell chemical composition and oxygen consumption of the early life stages of the intertidal reef-building vermetid Dendropoma cristatum. Reproductive success was predominantly affected by temperature increase, with encapsulated embryos exhibiting higher survival in control than elevated temperature conditions, which were in turn unaffected by altered seawater pH levels. Decreasing pH (alone or in combination with temperature) significantly affected the shell growth and shell chemical composition of both embryos and recruits. Elevated temperatures along with lower pH led to decreases of ~30% oxygen consumption and ~60% recruitment. Our results suggest that the early life stages of the reef-builder D. cristatum are highly sensitive to expected environmental change, with major consequences on the intertidal vermetid reefs they build and indirectly on the high biodiversity levels they support.

Continue reading ‘Ocean acidification and elevated temperature negatively affect recruitment, oxygen consumption and calcification of the reef-building Dendropoma cristatum early life stages: evidence from a manipulative field study’

Mediterranean cold-water corals as paleoclimate archives

Scleractinian cold-water corals preserve in their aragonite skeleton information on the past changes of the physico-chemical properties of the seawater in which they grew. Such information is stored as geochemical signals, such as changes in trace elements concentration (B/Ca, Li/Mg, P/Ca, Sr/Ca, Ba/Ca, U/Ca) or stable and radiogenic isotopes composition (δ11B, δ13C, δ18O, 14C, εNd), that are usually converted into environmental parameters using empirical calibration equations. The aragonite skeleton of cold-water corals is sufficiently uranium-rich to be suitable for U-series dating, providing precise and accurate ages for the last 600–700 kyrs. This opens the possibility to obtain reconstructions of key oceanographic parameters for the intermediate and deep water masses at sub-decadal scale resolution for climatically-relevant time windows in the past. However, part of the geochemical signal incorporated into the coral skeleton is modulated by the physiology of the coral, which complicates the interpretation of the geochemical proxies. This “vital effect” needs to be taken into account and corrected for to obtain reliable reconstructions of past changes in seawater temperature, pH and nutrient content. On the other hand, these biologically-induced geochemical signals can be used to investigate the processes controlling coral biomineralisation and better understand the resilience of cold-water corals to environmental and climate changes.

In the recent years, Mediterranean cold-water corals have been targeted for geochemically-oriented studies and their trace elements and isotopes composition has contributed significantly to developing and understanding new and established coral proxies. Living in an environment characterised by relatively warm seawater temperatures (13–14 °C) and high pH (8.1), the Mediterranean cold-water corals provide the end-member geochemical composition useful to derive empirical calibration equations. In particular, the analysis of several specimens of the cold-water corals species Lophelia pertusa, Madrepora oculata and Desmophyllum dianthus live-collected in the western, central and eastern Mediterranean Sea, has contributed to the development of the Li/Mg thermometer, boron isotopes pH proxy and P/Ca nutrient proxy, as well as a better understanding of the neodymium isotopic composition of cold-water corals as a water mass tracer. A multi-proxy approach has been recently applied to precisely U/Th-dated cold-water corals fragments from coral-bearing sediment cores retrieved in the western and central Mediterranean Sea, showing large changes in the dynamics of the intermediate waters during the Holocene. Further investigations of fossil cold-water corals specimens from different Mediterranean locations will open new perspectives on the reconstruction of past changes in the physico-chemical properties of sub-surface waters and their potential role in modifying the Mediterranean climate.

Continue reading ‘Mediterranean cold-water corals as paleoclimate archives’

A case study: variability in the calcification response of Mediterranean cold-water corals to ocean acidification

The Mediterranean Sea has certain characteristics that make it especially sensitive and vulnerable to changes in atmospheric CO2 and its gradual acidification. Some of the organisms that may be the first to be threatened by this impact are the cold-water corals. The few studies carried out up to date with these organisms by simulating in aquarium the acidified conditions expected for the year 2100 revealed a high variability between and within species. This chapter shows this highly variable response in the calcification of four of the most abundant cold-water coral species in the Mediterranean to low-pH conditions and their potential ecological implications.

Continue reading ‘A case study: variability in the calcification response of Mediterranean cold-water corals to ocean acidification’

Fate of Mediterranean Scleractinian cold-water corals as a result of global climate change. A synthesis

This chapter addresses the question as to how Mediterranean cold-water corals might fare in the future under anthropogenically-induced global climate change. The focus on three most prominent scleractinian cold-water corals species, the two branching and habitat-forming forms Madrepora oculata, Lophelia pertusa and the solitary cup coral Desmophyllum dianthus. We provide an introduction to climate change principals, highlight the current status of the marine environment with regard to global climate change, and describe how climate change impacts such as ocean acidification are predicted to affect key calcifiers such as scleractinian cold-water corals in the Mediterranean region. A synthesis of the experimental cold-water coral studies conducted to date on climate change impacts: The present state of knowledge reviewed in this chapter takes into account the number of experiments that have been carried out in the Mediterranean as well as for comparative purposes in other parts of the world, to examine the effects of climate change on the corals. We assess the statistical robustness of these experiments and what challenges the presented experiments. A comprehensive multi-study comparison is provided in order to inform on the present state of knowledge, and knowledge gaps, in understanding the effects of global climate change on cold-water corals. Finally we describe what the fate could be for the important scleractinian coral group in the Mediterranean region.

Continue reading ‘Fate of Mediterranean Scleractinian cold-water corals as a result of global climate change. A synthesis’

Ocean acidification influences plant-animal interactions: the effect of Cocconeis scutellum parva on the sex reversal of Hippolyte inermis

Ocean acidification (O.A.) influences the ecology of oceans and it may impact plant-animal interactions at various levels. Seagrass meadows located at acidified vents in the Bay of Naples (Italy) are considered an open window to forecast the effects of global-changes on aquatic communities. Epiphytic diatoms of the genus Cocconeis are abundant in seagrass meadows, including acidified environments, where they play key ecological roles. A still-unknown apoptogenic compound produced by Cocconeis triggers the suicide of the androgenic gland of Hippolyte inermis Leach 1816, a protandric hermaphroditic shrimp distributed in P. oceanica meadows located both at normal pH and in acidified vents. Feeding on Cocconeis sp. was proven important for the stability of the shrimp’s natural populations. Since O.A. affects the physiology of diatoms, we investigated if, in future scenarios of O.A., Cocconeis scutellum parva will still produce an effect on shrimp’s physiology. Cell densities of Cocconeis scutellum parva cultivated in custom-designed photobioreactors at two pH conditions (pH 7.7 and 8.2) were compared. In addition, we determined the effects of the ingestion of diatoms on the process of sex reversal of H. inermis and we calculated the % female on the total of mature individuals-1 (F/mat). We observed significant differences in cell densities of C. scutellum parva at the two pH conditions. In fact, the highest cell densities (148,808 ±13,935 cells. mm-2) was obtained at day 13 (pH 7.7) and it is higher than the highest cell densities (38,066 (±4,166) cells. mm-2, day 13) produced at pH 8.2. Diatoms cultured at acidified conditions changed their metabolism. In fact, diatoms grown in acidified conditions produced in H. inermis a proportion of females (F/mat 36.3 ±5.9%) significantly lower than diatoms produced at normal pH (68.5 ±2.8), and it was not significantly different from that elicited by negative controls (31.7 ±5.6%).

Continue reading ‘Ocean acidification influences plant-animal interactions: the effect of Cocconeis scutellum parva on the sex reversal of Hippolyte inermis’

Seagrass Posidonia oceanica diel pH fluctuations reduce the mortality of epiphytic forams under experimental ocean acidification

Highlights

• Forams epiphyte of Posidonia oceanica are resistant to ocean acidification scenarios.

• Seagrasses may provide “refugia” from ocean acidification to associated biota.

• There is an urgent need to incorporate pH fluctuations in the experimental designs.

Abstract

It is hypothesized that pH fluctuations produced by seagrasses metabolism may confer marine calcifiers resistance to ocean acidification. Here, we tested this thesis by comparing the net population growth rate (NPGR) of a foraminifer species (Rosalina sp.) epiphytic of Mediterranean seagrass (Posidonia oceanica) to average current and projected pH scenarios under either stable conditions or diel fluctuations in pH of 0.3 units; variations similar to that experienced in their habitat. No significant differences were found in NPGRs between the fluctuating and stable pH treatments at current pH levels. NPGRs in treatments where pH fluctuated did not present significant differences to the treatment with high and stable pH conditions. In contrast, foraminifers exposed to stable low pH regimes experienced a steep decline in NPGR. These results suggest that diel pH fluctuations generated by P. oceanica photosynthetic activity could confer resistance to ocean acidification to Rosalina sp.

Continue reading ‘Seagrass Posidonia oceanica diel pH fluctuations reduce the mortality of epiphytic forams under experimental ocean acidification’


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Ocean acidification in the IPCC AR5 WG II

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