Posts Tagged 'Mediterranean'

Linking internal carbonate chemistry regulation and calcification in corals growing at a Mediterranean CO2 vent

Corals exert a strong biological control over their calcification processes, but there is a lack of knowledge on their capability of long-term acclimatization to ocean acidification (OA). We used a dual geochemical proxy approach to estimate the calcifying fluid pH (pHcf) and carbonate chemistry of a Mediterranean coral (Balanophyllia europaea) naturally growing along a pH gradient (range: pHTS 8.07–7.74). The pHcf derived from skeletal boron isotopic composition (δ11B) was 0.3–0.6 units above seawater values and homogeneous along the gradient (mean ± SEM: Site 1 = 8.39 ± 0.03, Site 2 = 8.34 ± 0.03, Site 3 = 8.34 ± 0.02). Also carbonate ion concentration derived from B/Ca was homogeneous [mean ± SEM (μmol kg–1): Site 1 = 579 ± 34, Site 2 = 541 ± 27, Site 3 = 568 ± 30] regardless of seawater pH. Furthermore, gross calcification rate (GCR, mass of CaCO3 deposited on the skeletal unit area per unit of time), estimated by a “bio-inorganic model” (IpHRAC), was homogeneous with decreasing pH. The homogeneous GCR, internal pH and carbonate chemistry confirm that the features of the “building blocks” – the fundamental structural components – produced by the biomineralization process were substantially unaffected by increased acidification. Furthermore, the pH up-regulation observed in this study could potentially explain the previous hypothesis that less “building blocks” are produced with increasing acidification ultimately leading to increased skeletal porosity and to reduced net calcification rate computed by including the total volume of the pore space. In fact, assuming that the available energy at the three sites is the same, this energy at the low pH sites could be partitioned among fewer calicoblastic cells that consume more energy given the larger difference between external and internal pH compared to the control, leading to the production of less building blocks (i.e., formation of pores inside the skeleton structure, determining increased porosity). However, we cannot exclude that also dissolution may play a role in increasing porosity. Thus, the ability of scleractinian corals to maintain elevated pHcf relative to ambient seawater might not always be sufficient to counteract declines in net calcification under OA scenarios.

Continue reading ‘Linking internal carbonate chemistry regulation and calcification in corals growing at a Mediterranean CO2 vent’

Fish assemblages cope with ocean acidification in a shallow volcanic CO2 vent benefiting from an adjacent recovery area

Highlights

• pH played a role in shaping nekto-benthic fish assemblages.

• Fish diversity did not show unique spatial patterns or significant pH-relations.

• Species richness and abundance correlated with seagrass canopy, regardless of pH.

• Unexpected among-site similarity was found in the abundance of juveniles.

• The area close to low pH site seems to work as a recovery area for fish.

Abstract

Shallow CO2 vents are used to test ecological hypotheses about the effects of ocean acidification (OA). Here, we studied fish assemblages associated with Cymodocea nodosa meadows exposed to high pCO2/low pH conditions at a natural CO2 vent in the Mediterranean Sea. Using underwater visual census, we assessed fish community structure and biodiversity in a low pH site (close to the CO2 vent), a close control site and a far control site, hypothesising a decline in biodiversity and a homogenization of fish assemblages under OA conditions. Our findings revealed that fish diversity did not show a unique spatial pattern, or even significant relationships with pH, but correlated with seagrass leaf canopy. Among-site similarity was found in the abundance of juveniles, contrary to the expected impacts of OA on early life stages. However, pH seems an important driver in structuring fish assemblage in the low pH site, despite its high similarity with the close control site. This unexpected pattern may represent a combined response of fish mobility, enhanced food resources in the acidified site, and a ‘recovery area’ effect of the adjacent control site.

Continue reading ‘Fish assemblages cope with ocean acidification in a shallow volcanic CO2 vent benefiting from an adjacent recovery area’

Coralline algae in a changing Mediterranean Sea: how can we predict their future, if we do not know their present?

In this review we assess the state of knowledge for the coralline algae of the Mediterranean Sea, a group of calcareous seaweeds imperfectly known and considered highly vulnerable to long-term climate change. Corallines have occurred in the Mediterranean area for ~140 My and are well-represented in the subsequent fossil record; for some species currently common the fossil documentation dates back to the Oligocene, with a major role in the sedimentary record of some areas. Some Mediterranean corallines are key ecosystem engineers that produce or consolidate biogenic habitats (e.g., coralligenous concretions, Lithophyllum byssoides rims, rims of articulated corallines, maerl/rhodolith beds). Although bioconstructions built by corallines exist virtually in every sea, in the Mediterranean they reach a particularly high spatial and bathymetric extent (coralligenous concretions alone are estimated to exceed 2,700 km2 in surface). Overall, composition, dynamics and responses to human disturbances of coralline-dominated communities have been well-studied; except for a few species, however, the biology of Mediterranean corallines is poorly known. In terms of diversity, 60 species of corallines are currently reported from the Mediterranean. This number, however, is based on morphological assessments and recent studies incorporating molecular data suggest that the correct estimate is probably much higher. The responses of Mediterranean corallines to climate change have been the subject of several recent studies that documented their tolerance/sensitivity to elevated temperatures and pCO2. These investigations have focused on a few species and should be extended to a wider taxonomic set. Phylogeography, genomics, transcriptomics, and associated microbiomes are fields in which the information for Mediterranean corallines is very limited. We suggest that future work on Mediterranean corallines should be based on a multidisciplinary perspective combining different approaches, and that it should consist of large-scale efforts by scientists based both in western and eastern Mediterranean areas.

Continue reading ‘Coralline algae in a changing Mediterranean Sea: how can we predict their future, if we do not know their present?’

Elevated trace elements in sediments and seagrasses at CO2 seeps

Highlights
• Sandy CO2 seep sediments had higher concentration of trace elements.

• Metals can be more toxic in areas affected by CO2 acidification, with adverse effects on the sediment associated biota.

• Seagrasses element accumulation at CO2 seeps was highest in the roots.

Abstract
Seagrasses often occur around shallow marine CO2 seeps, allowing assessment of trace metal accumulation. Here, we measured Cd, Cu, Hg, Ni, Pb and Zn levels at six CO2 seeps and six reference sites in the Mediterranean. Some seep sediments had elevated metal concentrations; an extreme example was Cd which was 43x more concentrated at a seep than its reference. Three seeps had metal levels that were predicted to adversely affect marine biota, namely Vulcano (for Hg), Ischia (for Cu) and Paleochori (for Cd and Ni). There were higher-than-sediment levels of Zn and Ni in Posidonia oceanica and of Zn in Cymodocea nodosa, particularly in roots. High levels of Cu were found in Ischia seep sediments, yet seagrass was abundant, and the plants contained low levels of Cu. Differences in bioavailability and toxicity of trace elements helps explain why seagrasses can be abundant at some CO2 seeps but not others.

Continue reading ‘Elevated trace elements in sediments and seagrasses at CO2 seeps’

Environmental and biological controls on Na∕Ca ratios in scleractinian cold-water corals (update)

Here we present a comprehensive attempt to correlate aragonitic Na∕Ca ratios from Desmophyllum pertusum (formerly known as Lophelia pertusa), Madrepora oculata and a caryophylliid cold-water coral (CWC) species with different seawater parameters such as temperature, salinity and pH. Living CWC specimens were collected from 16 different locations and analyzed for their Na∕Ca ratios using solution-based inductively coupled plasma-optical emission spectrometry (ICP-OES) measurements.

The results reveal no apparent correlation with salinity (30.1–40.57 g kg−1) but a significant inverse correlation with temperature (0.31±0.04mmolmol1C1). Other marine aragonitic organisms such as Mytilus edulis (inner aragonitic shell portion) and Porites sp. exhibit similar results highlighting the consistency of the calculated CWC regressions. Corresponding Na∕Mg ratios show a similar temperature sensitivity to Na∕Ca ratios, but the combination of two ratios appears to reduce the impact of vital effects and domain-dependent geochemical variation. The high degree of scatter and elemental heterogeneities between the different skeletal features in both Na∕Ca and Na∕Mg, however, limit the use of these ratios as a proxy and/or make a high number of samples necessary. Additionally, we explore two models to explain the observed temperature sensitivity of Na∕Ca ratios for an open and semi-enclosed calcifying space based on temperature-sensitive Na- and Ca-pumping enzymes and transport proteins that change the composition of the calcifying fluid and consequently the skeletal Na∕Ca ratio.

Continue reading ‘Environmental and biological controls on Na∕Ca ratios in scleractinian cold-water corals (update)’

Influence of water quality parameters on the prevalence of Livoneca redmanii (Isopoda; Cymothoidae) infestation of Mediterranean Sea fishes, Egypt

The quality of water in the aquatic ecosystem is a very sensitive issue and is controlled by many physical and chemical factors. The deterioration of water quality has variable effect on parasitic population and their rate of infestation and consequently the negative impact can impede fish viability and productivity. The current study aimed to: i) Surveying the parasitic isopod infesting some of the edible fish species inhabit the Egyptian Mediterranean Sea water ii) Assess the seasonal variations in water quality parameters of Mediterranean coastal water of Egypt. iii) Investigating the effect of water quality parameters on the rate of parasitic isopod infestation among the examined fishes. Water samples during each season were analyzed for physico-chemical parameters using standard methods. The selected parameters namely: temperature, pH, salinity, oxidizable organic matter (OOM), ammonia, nitrite, nitrate and some heavy metals (Lead, Copper, Arsenic and Mercury). A total of 400 Mediterranean Sea fish of Tilapia zilli, Solea spp, Mugil capito and Sardinella species were examined for isopod parasites. Parasites were preserved and identified. The results revealed isolation of the isopod species Livoneca redmanii, with an infestation rate of 19% among the examined fish species with the highest rate among Mugil capito (36%) and reached its total maximum value during summer (32%). Correlation analysis revealed that infestation rates were highly correlated (positively) with certain water quality parameters, such as temperature, oxidzable organic matter (OOM) and nitrite. High water temperatures during summer and spring seasons, and high nitrite concentrations were significantly associated with high infestation rates in Tilapia zilli (R2=0.91, P=0.046 and R2 = 0.97, P=0.015). The findings suggested that deterioration of water quality with varying seasons was stressful to fish, and consequently increased the incidences of the parasitic Isopod (Livoneca redmanii) so considered as a predisposing agent to parasitism. The study recommended
periodical monitoring of water quality parameters in fish water resources and the need to take all measures by the responsible authorities to prevent pollution of these resources to minimized and control the prevalence of parasite
infestations particularly of isopods.

Continue reading ‘Influence of water quality parameters on the prevalence of Livoneca redmanii (Isopoda; Cymothoidae) infestation of Mediterranean Sea fishes, Egypt’

Ocean acidification impact on ascidian Ciona robusta spermatozoa: new evidence for stress resilience

Highlights

• Impact of ocean acidification on sperm quality of the ascidian Ciona robusta was investigated.

• Two experimental approaches were set up to simulate the ocean conditions predicted for the end of this century.

• Alteration of sperm motility, morphology and physiology was detected in short-term exposure.

• A rapid recovery of physiological conditions was observed within one week.

• New evidence of resilience in ascidian C. robusta spermatozoa in response to ocean acidification.

Abstract

Rising atmospheric CO2 is causing a progressive decrease of seawater pH, termed ocean acidification. Predicting its impact on marine invertebrate reproduction is essential to anticipate the consequences of future climate change on species fitness and survival. Ocean acidification may affect reproductive success either in terms of gamete or progeny quality threating species survival. Despite an increasing number of studies focusing on the effects of ocean acidification on the early life history of marine organisms, very few have investigated the effects on invertebrate gamete quality. In this study, we set up two experimental approaches simulating the ocean conditions predicted for the end of this century, in situ transplant experiments at a naturally acidified volcanic vent area along the Ischia island coast and microcosm experiments, to evaluate the short-term effects of the predicted near-future levels of ocean acidification on sperm quality of the ascidian Ciona robusta after parental exposure. In the first days of exposure to acidified conditions, we detected alteration of sperm motility, morphology and physiology, followed by a rapid recovery of physiological conditions that provide a new evidence of resilience of ascidian spermatozoa in response to ocean acidification. Overall, the short-term tolerance to adverse conditions opens a new scenario on the marine species capacity to continue to reproduce and persist in changing oceans.

Continue reading ‘Ocean acidification impact on ascidian Ciona robusta spermatozoa: new evidence for stress resilience’


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Ocean acidification in the IPCC AR5 WG II

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