Meiobenthos Assemblages as Bioindicators for Coastal Pollution Assessment

Coastal pollution assessment is a pressing matter as the anthropogenic pressure continues to increase worldwide. A leading approach to assess coastal pollution is using bioindicators. However, identifying species is time-consuming and demands profound morphological knowledge. Our goal was to find the meiobenthic composition in each pollution level. By utilizing the meiobenthic assemblage’s ratios, we will be able to indicate the pollution level. We examined the meiobenthos distribution at three sites exposed to a pollution gradient. We quantified the changes in the fauna assemblage in the community phylum level, focusing on nematodes and foraminifera (90% of the total population). Over 400 samples were examined, covering an annual seasonal cycle. Nematodes population dominated in the polluted coast. Nematodes density increased with the pollution level, up to seemingly harmful levels of pollution. In contradiction, the foraminifera flourished in the control site and exhibited an inverse relationship to the nematodes. We witnessed drastic changes in the entire meiobenthic population in the winter, which we speculate that originated from winter turbulences. We suggest that nematodes-foraminifers’ population ratios may be utilized as bioindicators for assessing coast intertidal zone pollution levels.

UV-B as a Photoacclimatory Enhancer of the Hermatypic Coral <i>Stylophora pistillata</i>

Photoacclimation processes are crucial for the survival of all photosynthetic organisms in the photic zone. Changes in photosynthetic active radiation (PAR) are however simultaneous to changes in UV-B radiation. The influence of UV-B levels on bio-optical and physiological parameters of deep (30 m) corals from the species Stylophora pistillata and their symbiotic algae, zooxanthellae, was examined during their gradual, stepwise acclimation to a shallow depth (3 m). Drastic exposure of deeper corals to higher UV-B levels in shallower depths is usually fatal. Hence, the acclimation process lasted 118 days and included 10 intermediate stations with an addition of similar amount of PAR at each depth transfer. Concomitantly, in an on-shore experiment, fragments from the same colonies were acclimated by changing shading nets corresponding in PAR levels to each in situ station. Since UV-B is attenuated more efficiently than PAR in seawater, the PAR: UV-B ratio changes in the depth experiment while remaining constant under the neutral density nets. This provided the opportunity to evaluate the importance of UV-B to photoacclimation. In both experiments all fragments survived, in spite of a four-fold difference in levels of PAR and a 140-fold difference in UV-B flux between the initial and final conditions. Both experimental designs resulted in reduction of zooxanthellae density, photosynthesis rates, and quantum yields of PSII, while cellular chlorophyll content remained unaffected. Zooxanthellae density and maximal photosynthetic rate was found decreased in correlation with UV-B radiation, whether it was elevated logarithmically with reducing depths or linearly with reducing shades. Conversely, quantum yields of PSII were adjusted according to the enhancement of PAR rather than UV-B. We conclude that UV-B enhances the magnitude of photoacclimation to higher PAR. This novel aspect of photoacclimation can provide the basis for our understanding of the underlying mechanisms that result in UV-related bleaching.

The Effect of Photoacclimation on Photosynthetic Energy Storage Efficiency, Determined by Photoacoustics

Photosynthesis rates in phytoplankton depend on light intensity and its spectral composition, however their relation changes with photoacclimation. During the photoacclimation process algal cells optimize their har-vesting and utilization of available light through series of related physical, biophysical, biochemical and physiological changes. These changes result in the ability of phytoplankton to survive under dim light when transported to the depth of the water column and avoid photodynamic damage when exposed to the intense radiation at the surface. Any reduction in the efficiency of light utilization results in decreased rates of pho-tosynthesis rate and slow growth. We present here the study of changes in photosynthetic energy storage efficiency of three phytoplankton species upon photoacclimation to low and high light, as measured by photo-acoustics. Our results illustrate the power of photoacoustics as a tool in aquatic ecology and in the physiological research of phytoplankton.

Natural Antioxidants: Function and Sources

The definition of antioxidants, given in 1995 by Halliwell and Gutteridge, stated that an antioxidant is “any substance that, when present at low concentrations compared with that of an oxidizable substrate, significantly delays or inhibits oxidation of that substrate” [1]. In 2007, Halliwell gave a more specific definition, stating that an antioxidant is “any substance that delays, prevents or removes oxidative damage to a target molecule” [2]. Oxidation reactions produce free radicals that can start multiple chain reactions that eventually cause damage or death to the cell. Antioxidants remove these free-radical intermediates by being oxidized themselves, and inhibit other oxidation reactions, thus stopping the harmful chain reactions. Such oxidative processes are dangerous for all living cells, especially those in proximity to sites where active oxygen is released by photosynthesis. Spontaneous oxidation causes food rancidity and spoilage of medicines. Furthermore, oxidative stress is an important part of many human diseases that can occur, inter alia, due to a lack of appropriate nutrition and exercise, air pollution, smoking, and more, leading to lethal diseases, such as cancer. Therefore, it is imperative to include antioxidants in our diets. Due to the fact that synthetically produced antioxidants are currently used in the food and pharmaceutical industries in order to prolong product shelf life, there is currently a strong trend to search for large, available, and efficient natural sources of antioxidants to replace the synthetic ones, thus minimizing damage to our cells.