There are no whole truths in meta-analyses: all their truths are half truths

In a recent letter, Thomsen & Wernberg (2015) rean-alyzed data compiled for our recent paper (Lyonset al., 2014). In that paper, we examined the effectsof macroalgal blooms and macroalgal mats on sevenimportant measures of community structure and eco-system functioning and explored several ecologicaland methodological factors that might explain someof the variation in the observed effects. Thomsen &Wernberg (2015) re-analyzed two small subsets of the data, focusing on experimental studies examining effects of blooms/mats on invertebrate abundance.Their analyses revealed two interesting patterns.First, they showed that macroalgal blooms reducedthe abundance of communities that Thomsen andWernberg categorized as ‘mainly infauna’, whileincreasing the abundance of communities categorized as ‘mainly epifauna’. Second, they showed that theimpacts of macroalgal blooms on ‘mainly infauna’communities increased with algal density in experiments that included multiple levels of algal density.These findings, as well as the conclusions that Thomsen & Wernberg (2015) draw from them, are largely consistent with our own expectations and interpretations. However, we also feel that some caution is required when interpreting the results of their analyses.

The combined effects of seasonal community succession and adaptive algal physiology on lipid profiles of coastal phytoplankton in the western English channel

Lipids are key constituents of marine phytoplankton, and some fatty acids (key constituents of lipids) are essential dietary components for secondary producers. However, in natural marine ecosystems the interactions of factors affecting seasonal phytoplankton lipid composition are still poorly understood. The aim of this study was to assess the roles of seasonal succession in phytoplankton community composition and nutrient concentrations, on the lipid composition of the phytoplankton community. Fatty acid and polar lipid composition in seston was measured in surface waters at the time series station L4, an inshore station in the Western English Channel, from January to December 2013. Redundancy analyses (RDA) were used to identify factors (abiotic and biotic) that explained the seasonal variability in phytoplankton lipids. RDA demonstrated that nutrients (namely nitrogen) explained the majority of variation in phytoplankton lipid composition, as well as a smaller explanatory contribution from changes in phytoplankton community composition. The physiological adaptations of the phytoplankton community to nutrient deplete conditions during the summer season when the water column was stratified, was further supported by changes in the polar lipid to phytoplankton biomass ratios (also modelled with RDA) and increases in the lipid to chlorophyll a ratios, which are both indicative of nutrient stress. However, the association of key fatty acid markers with phytoplankton groups e.g. 22:6 n-3 and dinoflagellate biomass (predominant in summer), meant there were no clear seasonal differences in the overall degree of fatty acid saturation, as might have been expected from typical nutrient stress on phytoplankton. Based on the use of polyunsaturated fatty acids (PUFA) as markers of ‘food quality’ for grazers, our results suggest that in this environment high food quality is maintained throughout summer, due to seasonal succession towards flagellated phytoplankton species able to maintain PUFA synthesis under surface layer nutrient depletion.

Impacts of ocean acidification in a warming Mediterranean Sea: An overview

Mediterranean Sea fisheries supply significant local and international markets, based largely on small pelagic fish, artisanal fisheries and aquaculture of finfish (mainly seabass and seabream) and shellfish (mussels and oysters). Fisheries and aquaculture contribute to the economy of countries bordering this sea and provide food and employment to coastal communities employing ca 600,000 people. Increasing temperatures and heat wave frequency are causing stress and mortality in marine organisms and ocean acidification is expected to worsen these effects, especially for bivalves and coralligenous systems. Recruitment and seed production present possible bottlenecks for shellfish aquaculture in the future since early life stages are vulnerable to acidification and warming. Although adult finfish seem able to withstand the projected increases in seawater CO2, degradation of seabed habitats and increases in harmful blooms of algae and jellyfish might adversely affect fish stocks. Ocean acidification should therefore be factored into fisheries and aquaculture management plans. Rising CO2 levels are expected to reduce coastal biodiversity, altering ecosystem functioning and possibly impacting tourism being the Mediterranean the world’s most visited region. We recommend that ocean acidification is monitored in key areas of the Mediterranean Sea, with regular assessments of the likely socio-economic impacts to build adaptive strategies for the Mediterranean countries concerned.

Algal Calcification and Silicification

The algae represent major producers of calcium carbonate and silica among the world's biota. Calcification involves the precipitation of CaCO3 from Ca2+ and CO32− ions. Algal calcification by coccolithophores may account for up to half of global oceanic CaCO3 production. Silicification, the transformation of silicic acid into skeletal material, occurs in a few algal groups. The abundant diatoms represent the major silicifiers, playing a key role in marine silica cycling. Fossilised diatomaceous deposits have long been exploited for building and filling materials. Biomineralisation of calcium and silicon require homeostatic ion controls that are well characterised for Ca2+ and H+ in coccolithophores. Calcification occurs in an alkalinised vesicle, while silicification requires an acidic pH. Research on silicification remains focused upon cell wall development. Initiation and development of structures that are mineralised intracellularly requires initiation and regulation by organic components within the vesicles. Low-temperature, low-pressure biogenic formation of silica and calcite has potential for biotechnological application in novel industrial processes.