Fine scale variability in methanol uptake and oxidation in the micro-layer and near-surface waters of the Atlantic

The aim of this research was to make the first depth profiles of the microbial assimilation of methanol carbon and its oxidation to carbon dioxide and use as an energy source from the microlayer to 1000 m. Some of the highest reported methanol oxidation rate constants of 0.5–0.6 d−1 were occasionally found in the microlayer and immediately underlying waters (10 cm depth), albeit these samples also showed the greatest heterogeneity compared to other depths down to 1000 m. Methanol uptake into the particulate phase was exceptionally low in microlayer samples, suggesting that any methanol utilised by microbes in this environment is for energy generation. The sea surface microlayer and 10 cm depth also showed a higher proportion of bacteria with a low DNA content, and bacterial leucine uptake rates in surface microlayer samples were either less than or the same as those in the underlying 10 cm layer. The average methanol oxidation and particulate rates were however statistically the same throughout the depths sampled, although the latter were highly variable in the near-surface 0.25–2 m compared to deeper depths. The statistically significant relationship demonstrated between uptake of methanol into particles and bacterial leucine incorporation suggests that many heterotrophic bacteria could be using methanol carbon for cellular growth. On average, methanol bacterial growth efficiency (BGEm) in the top 25 m of the water column is 6% and decreases with depth. Although, for microlayer and 10 cm-depth samples, BGEm is less than the near-surface 25–217 cm, possibly reflecting increased environmental UV stress resulting in increased maintenance costs, i.e. energy required for survival. We conclude that microbial methanol uptake rates, i.e. loss from seawater, are highly variable, particularly close to the seawater surface, which could significantly impact upon seawater concentrations and hence the air–sea flux.

Fine-scale variability in methanol uptake and oxidation: from the microlayer to 1000 m.

The aim of this research was to make the first depth profiles of the microbial assimilation of methanol carbon and its oxidation to carbon dioxide and use as an energy source from the microlayer to 1000 m. Some of the highest reported methanol oxidation rate constants of 0.5–0.6 d−1 were occasionally found in the microlayer and immediately underlying waters (10 cm depth), albeit these samples also showed the greatest heterogeneity compared to other depths down to 1000 m. Methanol uptake into the particulate phase was exceptionally low in microlayer samples, suggesting that any methanol utilised by microbes in this environment is for energy generation. The sea surface microlayer and 10 cm depth also showed a higher proportion of bacteria with a low DNA content, and bacterial leucine uptake rates in surface microlayer samples were either less than or the same as those in the underlying 10 cm layer. The average methanol oxidation and particulate rates were however statistically the same throughout the depths sampled, although the latter were highly variable in the near-surface 0.25–2 m compared to deeper depths. The statistically significant relationship demonstrated between uptake of methanol into particles and bacterial leucine incorporation suggests that many heterotrophic bacteria could be using methanol carbon for cellular growth. On average, methanol bacterial growth efficiency (BGEm) in the top 25 m of the water column is 6% and decreases with depth. Although, for microlayer and 10 cm-depth samples, BGEm is less than the near-surface 25–217 cm, possibly reflecting increased environmental UV stress resulting in increased maintenance costs, i.e. energy required for survival. We conclude that microbial methanol uptake rates, i.e. loss from seawater, are highly variable, particularly close to the seawater surface, which could significantly impact upon seawater concentrations and hence the air–sea flux.

The impact of ocean acidification and warming on the skeletal mechanical properties of the sea urchin Paracentrotus lividus from laboratory and field observations

Increased atmospheric CO2 concentration is leading to changes in the carbonate chemistry and the temperature of the ocean. The impact of these processes on marine organisms will depend on their ability to cope with those changes, particularly the maintenance of calcium carbonate structures. Both a laboratory experiment (long-term exposure to decreased pH and increased temperature) and collections of individuals from natural environments characterized by low pH levels (individuals from intertidal pools and around a CO2 seep) were here coupled to comprehensively study the impact of near-future conditions of pH and temperature on the mechanical properties of the skeleton of the euechinoid sea urchin Paracentrotus lividus. To assess skeletal mechanical properties, we characterized the fracture force, Young's modulus, second moment of area, material nanohardness, and specific Young's modulus of sea urchin test plates. None of these parameters were significantly affected by low pH and/or increased temperature in the laboratory experiment and by low pH only in the individuals chronically exposed to lowered pH from the CO2 seeps. In tidal pools, the fracture force was higher and the Young's modulus lower in ambital plates of individuals from the rock pool characterized by the largest pH variations but also a dominance of calcifying algae, which might explain some of the variation. Thus, decreases of pH to levels expected for 2100 did not directly alter the mechanical properties of the test of P. lividus. Since the maintenance of test integrity is a question of survival for sea urchins and since weakened tests would increase the sea urchins' risk of predation, our findings indicate that the decreasing seawater pH and increasing seawater temperature expected for the end of the century should not represent an immediate threat to sea urchins vulnerability.

Quantifying pursuit diving seabirds' associations with fine-scale physical features in a high tidal energy environment

The rapid increase in the number of tidal stream turbine arrays will create novel and unprecedented levels of anthropogenic activity within habitats characterized by horizontal current speeds exceeding 2 ms−1. However, the potential impacts on pursuit‐diving seabirds exploiting these tidal stream environments remain largely unknown. Identifying similarities between the fine‐scale physical features (100s of metres) suitable for array installations, and those associated with foraging pursuit‐diving seabirds, could identify which species are most vulnerable to either collisions with moving components, or displacement from these installations. A combination of vessel‐based observational surveys, Finite Volume Community Ocean Model outputs and hydroacoustic seabed surveys provided concurrent measures of foraging distributions and physical characteristics at a fine temporal (15 min) and spatial (500 m) resolution across a tidal stream environment suitable for array installations, during both breeding and non‐breeding seasons. These data sets were then used to test for associations between foraging pursuit‐diving seabirds (Atlantic puffins Fratercula arctica, black guillemots Cepphus grylle, common guillemots Uria aalge, European shags Phalacrocorax aristotelis) and physical features. These species were associated with areas of fast horizontal currents, slow horizontal currents, high turbulence, downward vertical currents and also hard–rough seabeds. The identity and strength of associations differed among species, and also within species between seasons, indicative of interspecific and intraspecific variations in habitat use. However, Atlantic puffins were associated particularly strongly with areas of fast horizontal currents during breeding seasons, and European shags with areas of rough–hard seabeds and downward vertical currents during non‐breeding seasons. Synthesis and applications. Atlantic puffins’ strong association with fast horizontal current speeds indicates that they are particularly likely to interact with installations during breeding seasons. Any post‐installation monitoring and mitigation measures should therefore focus on this species and season. The multi‐species associations with high turbulence and downward vertical currents, which often coincide with fast horizontal current speeds, also highlight useful pre‐installation mitigation measures via the omission of devices from these areas, reducing the overall likelihood of interactions. Environmental impact assessments (EIA) generally involve once‐a‐month surveys across 2‐year periods. However, the approaches used in this study show that more focussed surveys can greatly benefit management strategies aiming to reduce the likelihood of negative impacts by facilitating the development of targeted mitigation measures. It is therefore recommended that these approaches contribute towards EIA within development sites.