Biochemical descriptors for Posidonia oceanica and other seagrasses

Posidonia oceanica is an endemic seagrass in the Mediterranean Sea. It forms wide submerged meadows that constitute one of the most productive systems of the basin and plays a crucial role in the dynamics and maintenance of coastal marine ecosystems (oxygenation of water, food and shelter for many organisms, reduction of hydrodynamics and the coastal erosion). It is considered a keystone species and is listed in the Habitats Directive 92/43/EEC, and it is also a recognized indicator of the quality of coastal marine waters, according to the Water Framework Directive (WFD 2000/60/UE).Unfortunately, the growing impact of human activities in coastal areas is causing a widespread regression of Posidonia meadows. The decline of Posidonia oceanica meadows is mainly due to human-induced disturbances: the modification of the hydrological regime and littoral transport, pollution and eutrophication, aquaculture and anchoring. Growing evidence suggests that seagrass meadows are also vulnerable to climate change due to the impact of higher temperatures on shoot survival. Consequently, the development and combination/integration of sensitive and measurable descriptors, which may reveal environmental alterations, are becoming essential for monitoring the health of segrass meadows. Standard monitoring indicators are been applied at individual, population or community level; however, many of them lack sensitivity and often the combination/integration of indicators is necessary to obtain significant information. The identification of early warning indicators that give ecologically relevant information is still a critical issue. A new descriptor has been identified since 2004: a biochemical descriptor, the total phenol synthesis. Phenolic compounds are a class of secondary metabolites widely distributed in terrestrial and aquatic plants. They are present in all plant organs playing several structural and physiological roles, including the defense of plants. Total phenols works as biochemical markers of environmental stress: high phenol concentrations were found in Posidonia leaves exposed to different environmental pressures like competition with the invasive seaweed Caulerpa taxifolia, contamination by metals, and proximity to intensive fish aquaculture. The increase of phenolic compounds represents a generic response to different kinds of environmental stress and thus can be used to screen the meadow’s health state. Total phenol concentration varies in leaves with season due to leaves’ short lifespan and with depth. On the opposite, levels of synthesis and accumulation of phenolic compounds are more stable in rhizomes.

Associated with the determination of total phenols, the use of 2-D protein electrophoresis analysis was proposed to identify changes of protein expression in healthy vsstressed plants. This could be a possible way to identify new descriptors/biomarkers in stressed plants. The prototype was tested and set upon plants from Talamone (Grosseto) and S. Marinella (Rome) Posidonia oceanica meadows.

Moreover recently, along with the quantification of phenolic compounds in rhizomes, other descriptors were proposed: photosynthetic pigments, markers of oxidative stress and measures of genetic diversity, were successfully used as biomarkers of environment quality. All these markers can be evaluated on a single shoot; this allows (i) a more accurate evaluation of the conservation status of the plant, (ii) the reduction of the impact of sampling and, last but not least, (iii) a reduction of the costs of the monitoring sampling campaigns. Biochemical markers (phenolic compounds and photosynthetic pigments) have been successfully applied in other marine phanerogams such as Cymodocea nodosaZostera noltii and Halophila stipulacea collected from different sites and different environmental conditions (C. nodosa and Z. noltii, Ria formosa lagoon, Faro, Portugal; H. stipulacea, Gulf of Aqaba, Eilat, Israel, and Limassol, Cyprus).

A different application of total phenols determination in seagrass was aimed to study the herbivory pressure of Smaragdia souverbiana, a mollusc that exclusively feeds seagrass tissues, on two species of phanerogams, Zostera muelleri and Halophila ovalis, sympatric in different sites at different environmental conditions on the eastern coast of Australia. The work has shown the importance of total phenols concentration and its variation according to the environmental conditions, with respect to the herbivory pressure, showing how herbivores can determine top-down influences on the dynamics of marine phanerogams.




 Grazing influences the structure and function of seagrass meadows. Like terrestrial plants, seagrasses have evolved nutritional, structural and chemical mechanisms to either tolerate or resist grazing. Phenols are common secondary metabolites that have multiple roles, including grazing deterrence, and their content in seagrass tissues can vary both among species and within a single species in response to biotic and abiotic processes. Such variability influences the grazing behaviour of species that consume seagrass, but few studies have addressed mesograzers that consume or damage seagrass, such as the nerite Smaragdia souverbiana. We assessed the effect of environmentally-mediated differences in phenol concentration on these seagrass mesograzers by testing: (1) if phenol content is different between sites and seagrass species (Zostera muelleri vs Halophila ovalis) and (2) if S. souverbiana inflicts different amounts of damage on different seagrasses from different sites, according to their phenol content. Phenol content was consistently lower in Z. muelleri than H. ovalis, and concentrations were about 60% lower in both species at one of two sites in eastern Moreton Bay, Queensland. These differences corresponded to different foraging patterns of S. souverbiana, with the snails generally choosing the seagrass species with the lowest phenol content. These results suggest that S. souverbiana chooses among locally available seagrasses based on a trade-off between phenol content and digestibility (related to cell size). This work demonstrates how subtle local processes can create complex changes in seagrass–grazer interactions with potential ecological consequences at local and regional scales.

Rotini A., Belmonte A., Barrote I., Micheli C., Peirano A., Santos R.O., Silva J., Migliore L. (2013) EFFECTIVENESS AND CONSISTENCY OF A SUITE OF DESCRIPTORS FOR ASSESSING THE ECOLOGICAL STATUS OF SEAGRASS MEADOWS (POSIDONIA OCEANICA L. DELILE). Estuarine, Coastal and Shelf Science, 130: 252–259. DOI: 10.1016/j.ecss.2013.06.015
The increasing rate of human-induced environmental changes on coastal marine ecosystems has created a demand for effective descriptors, in particular for those suitable for monitoring the status of seagrass meadows. Growing evidence has supported the useful application of biochemical and genetic descriptors such as secondary metabolite synthesis, photosynthetic activity and genetic diversity. In the present study, we have investigated the effectiveness of different descriptors (traditional, biochemical and genetic) in monitoring seagrass meadow conservation status. The Posidonia oceanica meadow of Monterosso al Mare (Ligurian sea, NW Mediterranean) was subjected to the measurement of bed density, leaf biometry, total phenols, soluble protein and photosynthetic pigment content as well as to RAPD marker analysis. This suite of descriptors provided evidence of their effectiveness and convenient application as markers of the conservation status of P. oceanica and/or other seagrasses. Biochemical/genetic descriptors and those obtained by traditional methods depicted a well conserved meadow with seasonal variability and, particularly in summer, indicated a healthier condition in a portion of the bed (station C), which was in agreement with the physical and sedimentological features of the station. Our results support the usefulness of introducing biochemical and genetic approaches to seagrass monitoring programs since they are effective indicators of plant physiological stress and environmental disturbance.
Rotini A., Anello L., Di Bernardo M., Giallongo A., Valiante L., Migliore L. (2013) COMPARATIVE ANALYSIS OF BED DENSITY, TOTAL PHENOL CONTENT AND PROTEIN EXPRESSION PATTERN IN POSIDONIA OCEANICA (L.) Delile. Open Journal of Ecology, 3(6): 438-444. DOI: 10.4236/oje.2013.36050
Posidonia oceanica meadows are experiencing a progressive decline, and monitoring their status is crucial for the maintenance of these ecosystems. We performed a comparative analysis of bed density, total phenol content and protein expression pattern to assess the conservation status of Posidonia plants from the S. Marinella (Rome, Italy) meadow. The total phenol content was inversely related to maximum bed density, confirming the relationship between high phenol content and stressful conditions. In addition, protein expression pattern profiles showed that the number of differentially expressed proteins was dramatically reduced in the latest years compared to previous analyses. Our results support the usefulness of integrating solid descriptors, such as phenol content, with novel biochemical/molecular approaches in the monitoring of meadows.
The conservation status of the Posidonia oceanica meadow at Santa Marinella (Rome) was evaluated through both standard (bed density, leaf biometry, “A” coefficient, Leaf Area Index, rhizome production) and biochemical/genetic approaches (total phenol content and Random Amplified Polymorphic DNA marker). The biochemical/genetic results are in agreement with those obtained by standard approaches. The bed under study was ranked as a disturbed one, due to its low density, and high heterogeneity in leaf biometry, LAI values, “A” coefficient and primary production. This low quality ranking is confirmed by both mean phenol content in plants, quite high and scattered, and by the low genetic variability in the meadow, with a very high similarity of specimen at a local scale. Hence, these two putative approaches clearly identify the endangered conservation status of the meadow. They link plant biodiversity and ecophysiology to ecosystem ‘health’. Further- more, they are repeatable and standardizable and could be usefully introduced in meadows monitoring to check environmental quality.
Migliore L., Rotini A., Randazzo D., Albanese N.N., Giallongo A. (2007) PHENOLS CONTENT AND 2-D ELECTROPHORESIS PROTEIN PATTERN: A PROMISING TOOL TO MONITOR POSIDONIA MEADOWS HEALTH STATE. BMC Ecology, 7:6 doi:10.1186/1472-6785-7-6
The endemic seagrass Posidonia oceanica (L.) Delile colonizes soft bottoms producing highly productive meadows that play a crucial role in coastal ecosystems dynamics. Human activities and natural events are responsible for a widespread meadows regression; to date the identification of "diagnostic" tools to monitor conservation status is a critical issue. In this study the feasibility of a novel tool to evaluate ecological impacts on Posidonia meadows has been tested. Quantification of a putative stress indicator, i.e. phenols content, has been coupled to 2-D electrophoretic protein analysis of rhizome samples. The overall expression pattern from Posidonia rhizome was determined using a preliminary proteomic approach, 437 protein spots were characterized by pI and molecular weight. We found that protein expression differs in samples belonging to sites with high or low phenols: 22 unique protein spots are peculiar of "low phenols" and 27 other spots characterize "high phenols" samples. Posidonia showed phenols variations within the meadow, that probably reflect the heterogeneity of environmental pressures. In addition, comparison of the 2-D electrophoresis patterns allowed to highlight qualitative protein expression differences in response to these pressures. These differences may account for changes in metabolic/physiological pathways as adaptation to stress. A combined approach, based on phenols content determination and 2-D electrophoresis protein pattern, seems a promising tool to monitor Posidonia meadows health state.
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