Effects of ocean acidification on macroalgal communities

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Proceedings of the Mediterranean Seagrass Workshop 2006

The Mediterranean Seagrass Workshop 2006 was convened in response to the need to promote a periodic event that would host scientists interested in Mediter- ranean seagrasses, and international scientists who are involved in projects that are focused on the Mediterranean marine environment, to discuss current knowl- edge and present the findings of their latest research. The concept of holding an international meeting originated during the Inter- national Seagrass Biology Workshop (ISBW6) held in 2004 in Queensland, Aus- tralia. In particular, one of the goals of ISBW6 was to identify key ecological issues and environmental trends within a number of geographical regions. This stimulated the idea of taking such topic to a higher level; the Mediterranean scale. The Mediterranean Sea is a rare and vulnerable ecoregion, one of the planet’s biodiversity hot spots, where many of the species present are endemic (around 20%). The Mediterranean Sea also has a millenarian history of human use of its coasts. However, the current exponential increase of human pressure on the coastal zone for living space, transportation, recreation and food production is expected to have dramatic long-term impacts on the Mediterranean marine envi- ronment. Being located in shallow coastal areas close to human settlement, sea- grasses are bearing the brunt of disturbance from such anthropogenic activities, with the result that degradation and loss of seagrass habitats is widespread in the whole Mediterranean Sea. Thus, there is great concern that the functions which seagrasses have performed in the Mediterranean marine ecosystem will be weak- ened or, in some places, lost altogether.peer-reviewe

Nutrient Loading Fosters Seagrass Productivity under Ocean Acidification

The effects of climate change are likely to be dependent on local settings. Nonetheless, the compounded effects of global and regional stressors remain poorly understood. Here, we used CO2vents to assess how the effects of ocean acidification on the seagrass, Posidonia oceanica, and the associated epiphytic community can be modified by enhanced nutrient loading. P. oceanica at ambient and low pH sites was exposed to three nutrient levels for 16 months. The response of P. oceanica to experimental conditions was assessed by combining analyses of gene expression, plant growth, photosynthetic pigments and epiphyte loading. At low pH, nutrient addition fostered plant growth and the synthesis of photosynthetic pigments. Overexpression of nitrogen transporter genes following nutrient additions at low pH suggests enhanced nutrient uptake by the plant. In addition, enhanced nutrient levels reduced the expression of selected antioxidant genes in plants exposed to low pH and increased epiphyte cover at both ambient and low pH. Our results show that the effects of ocean acidification on P. oceanica depend upon local nutrient concentration. More generally, our findings suggest that taking into account local environmental settings will be crucial to advance our understanding of the effects of global stressors on marine systems

Arsenic concentrations in seagrass around the Mediterranean coast and seasonal variations

Arsenic’s occurrence in the environment could be due to human activities as well as to natural sources. In this study, Posidonia oceanica and Cymodocea nodosa are collected in 84 sites around the Mediterranean basin. In addition, both seagrass are collected monthly, in two sites (Calvi in Corsica and Salammbô in Tunisia). Arsenic concentrations in C. nodosa present seasonal variations in relation with spring phytoplankton blooms. For both species arsenic concentration is higher in the vicinity of geological sources (mining), lagoon outlets and industrial activities. Moreover, Mediterranean islands (Balearic, Sardinia, Corsica, Malta, Crete and Cyprus) and the Southern basin coastline exhibit lower concentrations in Arsenic than the rest of the Mediterranean basin. The wide spread distribution of these two species would encourage their use in a global monitoring network devoted to Arsenic contamination.peer-reviewe

A MSFD complementary approach for the assessment of pressures, knowledge and data gaps in Southern European Seas : the PERSEUS experience

PERSEUS project aims to identify the most relevant pressures exerted on the ecosystems of the Southern European Seas (SES), highlighting knowledge and data gaps that endanger the achievement of SES Good Environmental Status (GES) as mandated by the Marine Strategy Framework Directive (MSFD). A complementary approach has been adopted, by a meta-analysis of existing literature on pressure/impact/knowledge gaps summarized in tables related to the MSFD descriptors, discriminating open waters from coastal areas. A comparative assessment of the Initial Assessments (IAs) for five SES countries has been also independently performed. The comparison between meta-analysis results and IAs shows similarities for coastal areas only. Major knowledge gaps have been detected for the biodiversity, marine food web, marine litter and underwater noise descriptors. The meta-analysis also allowed the identification of additional research themes targeting research topics that are requested to the achievement of GES. 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.peer-reviewe

In situ experiments on the effect of low pH on the ultrastructure of the seagrasses Cymodocea nodosa and Posidonia oceanica

The present study investigates the impacts of low pH on the cell structure of the seagrasses Posidonia oceanica (L.) Delile and Cymodocea nodosa (Ucria) Ascherson. The study was applied with in situ experiments at the Castello Aragonese of Ischia (Naples, Italy), where shallow submarine vents, lowering the pH, can be used as natural laboratories. Shoots of the seagrasses were transferred from the control area (pH 8.1) to the two venting areas (pH 7.8 and 6.8) for different times. Epidermal cells of young leaves were examined using transmission electron microscopy (TEM) and tubulin immunofluorescence. After one week at pH 7.8, the cell structure of Posidonia oceanica was normal, while in Cymodocea nodosa microtubule (MT) network and cell structure were affected. In addition, in C. nodosa, ultrastructural analysis revealed a gradual degradation of the nuclei, a disorganization of the chloroplasts, and an increase in the number of mitochondria and dictyosomes. The exposure of both plants for 3 weeks at pH 6.8 resulted in the aggregation and finally in the dilation of the endoplasmic reticulum (ER) membranes. Tubulin immunofluorescence revealed that after three weeks, the MT cytoskeleton of both plants was severely affected. All these alterations can be considered as indications of an apoptotic like programmed cell death (AL-PCD) which may be executed in order to regulate stress response

Dinámica de la estructura y crecimiento de praderas de Cymodocea nodosa

The seasonal changes in the structure and growth dynamics of a Cymodocea nodosa meadow off the island of Ischia (Tyrrhenian Sea) were studied from July 1988 to August 1989 using leaf and rhizome marking methods. High levels of leaf production (3.1 g dw m-2 d-1) significantly related to water temperature regimes, were observed. The number of new leaves per year (16 leaves y-1), the leaf Plastochrone Interval (23 days) and the life span of the single leaves (from 2 to 6 months) were also calculated. Relevant yearly fluctuations of the leaf canopy, representing about 20% of the total meadow biomass, testify the strong seasonal variability of leaf phenological parameters and shoot density (the latter, between 925 ± 323 and 1925 ± 267 shoots • m-2). On the other hand, a constant and well developed layer of rhizomes and roots is present throughout the year (80% of total biomass), with an annual rhizome elongation of about 30 cm. In spite of the temporal variability of the above-ground compartment (CV=55%), the below-ground portion represents the conservative compartment of the meadow (CV=7%). Nevertheless, the remarkable number of seeds present in this meadow (up to 2112 m-2), does not seem to effect the stability of the system through the sexual reproduction. Although similar growth trends have been reported for C. nodosa meadows from different geographical areas and habitats (eutrophic zones, confined shallow waters, estuaries), remarkable differences may be found in the highest and lowest values of growth rate. This comparison highlights the ability of this species to grow in different habitats and that growth process seems to be amplified by a high influence of environmental constraints. Moreover, differences from P. oceanica, both in the growth rate and reproductive patterns, are identified in order to explain the dynamics of these vegetated systems and their role in the Mediterranean basin.Se estudiaron los cambios estacionales de la dinámica de la estructura y crecimiento de las praderas de Cymodocea nodosa fuera de la Isla de Ischia (Mar Tirreno) desde Julio 1988 a Agosto 1989 utilizando métodos de marcaje de hojas y rizomas. Se observaron elevados niveles de producción de hojas (3.1 g dw m-2 d-1) significativamente relacionados con el régimen de temperatura del agua. También se determinó el número de hojas nuevas por año (16 hojas y-1) el intervalo de plastocrono de la hoja (23 días) y el período de vida de las hojas (desde 2 a 6 meses). Las persistentes fluctuaciones anuales de la cobertura de hojas, que representan alrededor del 20% del total de la biomasa de la pradera, confirman la fuerte variabilidad estacional de los parámetros fenológicos de la hoja y la densidad de los tallos (entre 925 ± 323 and 1925 ± 267 tallos • m-2). En cambio, una capa constante y bien desarrollada de rizomas y raíces está presente a lo largo del año (80% de la biomasa total), con una elongación anual del rizoma, alrededor de 30 cm. A pesar de la variabilidad temporal del compartimento de la parte superficial (CV = 55%), la porción de bajo tierra representa el compartimento conservativo de la pradera (CV = 7%). Sin embargo, el extraordinario número de semillas presentes en la pradera (hasta 2112 m-2) no parece reforzar la estabilidad del sistema a través de la reproducción sexual. Aunque patrones similares de crecimiento han sido descritos para praderas de C. nodosa en diferentes áreas geográficas y hábitats (zonas eutróficas, aguas someras confinadas, estuarios), se pueden encontrar notorias diferencias en los más elevados y más bajos valores de tasas de crecimiento. Esta comparación pone de manifiesto la habilidad de estas especies para crecer en distintos hábitats y que el proceso de crecimiento parece estar amplificado por la influencia de las condiciones ambientales. Además se han identificado diferencias con P. oceánica, en cuanto tasas de crecimiento y patrones reproductivos con el fin de explicar la dinámica de estos sistemas con vegetación y su papel en la cuenca Mediterránea

Risposta fotosintetica di alcune specie macroalgali in ambiente acidificato

A causa delle continue emissioni di biossido di carbonio nell'atmosfera, è stata stimata per il 2100 una diminuzione del pH della superficie oceanica di circa 0,5 unità. Le ricerche effettuate fino ad oggi in questo ambito non consentono di trarre conclusioni univoche sugli effetti che acidificazione del mare può provocare sulle comunità bentoniche. Per fornire un contributo a questa tematica, uno studio di tali effetti sulla componente macroalgale, particolarmente vulnerabile alle modificazioni di origine antropica, è stato intrapreso in un sito naturalmente acidificato per la presenza di emissioni di CO2 sottomarine. In questo lavoro è stata caratterizzata l’attività fotochimica, come marcatore di efficienza fotosintetica, di alcune specie macroalgali presenti lungo il gradiente naturale di acidificazione. I dati preliminari mostrano che le specie studiate hanno una diversa capacità di utilizzare la radiazione luminosa assorbita nei processi fotochimici ed una differente ripartizione di tale energia nei processi non-fotochimici