Growth kinetics related to physiological parameters in young Saccorhiza dermatodea and Alaria esculenta sporophytes exposed to UV radiation

Young sporophytes of Saccorhiza dermatodea and Alaria esculenta cultured from Spitsbergen isolates were exposed in the laboratory to either only photosynthetically active radiation (PAR) or to a spectrum including UV-radiation (PAR+UVA+UVB) by use of cutoff glass filters. The plants were grown at 8±2°C and 16:8 h light-dark cycles with 6 h additional UV exposure in the middle of the light period. Growth was measured every 10 min using growth chambers with online video measuring technique for 18-21 days. Tissue morphology and absorption spectra were measured in untreated young sporophytes while tissue chlorophyll-a content and DNA damage were measured from treated thalli at the end of the experiment. Under UVR, growth rates of S. dermatodea were significantly reduced while A. esculenta have a potential to acclimate. Tissue chlorophyll-a contents in both species were not significantly different between treatments suggesting that these algae may acclimate to moderate UVR fluence. Higher DNA damage in S. dermatodea effectively diverted photosynthetic products for repair constraining growth. Tissue optics (opacity and translucence) was correlated to the tissue absorbance in the UVR region characteristics of phlorotannin, an important UV-absorbing compound in brown macroalgae. Growth rates of sporophytes of both species exposed to PAR without UV was similar during day and night. The results showed that both species can recruit and inhabit a similar coastal zone when appropriate strategies are expressed to minimize damage in response to the stress factor. © Springer-Verlag 2005

Seaweeds and their communities in polar regions

Polar seaweeds typically begin to grow in late winter-spring, around the time of sea-ice break up. They can grow under very low light enabling distributions to depths of ≥40 m. Moreover, they are physiologically adapted to low temperatures. Intertidal species exhibit a remarkable stress tolerance against freezing, desiccation and salinity changes. Endemism is much greater in the Antarctic compared to the Arctic species. On rocky shores of the Antarctic Peninsula and of Spitsbergen >80% of the bottom can be covered by seaweeds with standing biomass levels ≥20 kg wet wt m-2. Species richness and biomass declines, however, towards higher latitudes. Seaweeds are the dominant organisms in coastal waters and thus play important roles in benthic food webs and are likely to be of particular importance to benthic detrital food chains. Chemical defenses against herbivores are common in Antarctic, but not in Arctic seaweeds. More research is needed especially to study the effects of global climate changes

The diversity of population responses to environmental change

The current extinction and climate change crises pressure us to predict population dynamics with ever‐greater accuracy. Although predictions rest on the well‐advanced theory of age‐structured populations, two key issues remain poorly explored. Specifically, how the age‐dependency in demographic rates and the year‐to‐year interactions between survival and fecundity affect stochastic population growth rates. We use inference, simulations and mathematical derivations to explore how environmental perturbations determine population growth rates for populations with different age‐specific demographic rates and when ages are reduced to stages. We find that stage‐ vs. age‐based models can produce markedly divergent stochastic population growth rates. The differences are most pronounced when there are survival‐fecundity‐trade‐offs, which reduce the variance in the population growth rate. Finally, the expected value and variance of the stochastic growth rates of populations with different age‐specific demographic rates can diverge to the extent that, while some populations may thrive, others will inevitably go extinct

Effects of hydrogen peroxide on the content of major volatile halogenated compounds in the red alga Asparagopsis taxiformis (Bonnemaisoniaceae)

The genus Asparagopsis is a prolific source of halogenated metabolites. Due to its commercial applications, it has been intensively cultivated in southern Portugal. In the present study, we assess if the internal levels of the major halogenated metabolites (bromoform and dibromoacetic acid) in Asparagopsis taxiformis can be increased with hydrogen peroxide (H2O2) addition. Previous studies with red algae showed that the production/release of bromoform can be enhanced by exogenously supplying H2O2. However, no study has assessed if H2O2 supply enhances the content of secondary metabolites within the biomass. This detail is important as the objective of the proposed research is to enhance the content of these valuable metabolites in the produced biomass. Both the activity of the haloperoxidase enzyme and the metabolite content were assessed on short-term and long-term incubation periods to H2O2. To determine the susceptibility of A. taxiformis photosynthetic performance to the imposed oxidative stress, the in vivo fluorescence of photosystem II was monitored. A. taxiformis was shown to be physiologically vulnerable to H2O2, given the observed decrease of the maximum quantum yield of photosynthesis (F v/F m). Contrary to what was expected, the presence of H2O2 inhibited the activity of the iodoperoxidase enzyme. Nevertheless, the extracted halogenated metabolites were higher over the first hours of exposure to H2O2, decreasing after 48 h. These results are probably related to the prosthetic group of the halogenated enzyme in A. taxiformis and the long-term oxidative stress damage of H2O2 exposure. Considering the objective of the proposed research, addition of H2O2 to the cultures, prior (3 h) to biomass harvesting, increases the metabolite content

Volatile halocarbon emissions by three tropical brown seaweeds under different irradiances

The emission rates of eight volatile halogenated compounds by three tropical brown seaweed species collected from Cape Rachado, west coast Peninsular Malaysia, under different irradiances have been determined. A purge-and-trap sample preparation system with a gas chromatograph and mass-selective detector was used to measure a suite of halocarbons released by Sargassum binderi Sonder ex J. Agardh, Padina australis Hauck, and Turbinaria conoides (J. Agardh) Kützing. All species are widely distributed in Peninsular Malaysia, with S. binderi a dominant seaweed species at our survey site. Release of few halocarbons was found to be influenced by irradiance. Correlations were also observed between emission of certain halocarbons with photosynthetic activity, especially bromo-and iodinated compounds (0.6 < r <0.9; p < 0.01) suggesting that environmental factors such as light can affect the release of these volatile halogenated compounds by the seaweeds into the atmosphere. Compared with temperate and polar brown seaweeds, tropical species, such as T. conoides, may emit higher levels of bromoform, CHBr3, and other halocarbons. It is therefore important to investigate the contribution of tropical seaweeds towards the local atmospheric composition of halocarbons