Thermal reaction norms of growth in Atlantic and Pacific silverside fishes

How organisms may adapt to rising global temperatures is uncertain, but concepts can emerge from studying adaptive physiological trait variations across existing spatial climate gradients. Many ectotherms, particularly fish, have evolved increasing genetic growth capacities with latitude (i.e. countergradient variation (CnGV) in growth), which are thought to be an adaptation primarily to strong gradients in seasonality. In contrast, evolutionary responses to gradients in mean temperature are often assumed to involve an alternative mode, 'thermal adaptation'. We measured thermal growth reaction norms in Pacific silverside populations (Atherinops affinis) occurring across a weak latitudinal temperature gradient with invariant seasonality along the North American Pacific coast. Instead of thermal adaptation, we found novel evidence for CnGV in growth, suggesting that CnGV is a ubiquitous mode of reaction-norm evolution in ectotherms even in response to weak spatial and, by inference, temporal climate gradients. A novel, large-scale comparison between ecologically equivalent Pacific versus Atlantic silversides (Menidia menidia) revealed how closely growth CnGV patterns reflect their respective climate gradients. While steep growth reaction norms and increasing growth plasticity with latitude in M. menidia mimicked the strong, highly seasonal Atlantic coastal gradient, shallow reaction norms and much smaller, latitude-independent growth plasticity in A. affinis resembled the weak Pacific latitudinal temperature gradient.

Seawater carbonate chemistry and Ruditapes decussatus biological processes during experiments, 2011

We investigated the effects of ocean acidification on juvenile clams Ruditapes decussatus (average shell length 10.24 mm) in a controlled CO2 perturbation experiment. The carbonate chemistry of seawater was manipulated by diffusing pure CO2, to attain two reduced pH levels (by -0.4 and -0.7 pH units), which were compared to unmanipulated seawater. After 75 days we found no differences among pH treatments in terms of net calcification, size or weight of the clams. The naturally elevated total alkalinity of local seawater probably contributed to buffer the effects of increased pCO2 and reduced pH. Marine organisms may, therefore, show diverse responses to ocean acidification at local scales, particularly in coastal, estuarine and transitional waters, where the physical-chemical characteristics of seawater are most variable. Mortality was significantly reduced in the acidified treatments. This trend was probably related to the occurrence of spontaneous spawning events in the control and intermediate acidification treatments. Spawning, which was unexpected due to the small size of the clams, was not observed for the pH -0.7 treatment, suggesting that the increased survival under acidified conditions may have been associated with a delay in the reproductive cycle of the clams. Future research about the impacts of ocean acidification on marine biodiversity should be extended to other types of biological and ecological processes, apart from biological calcification.

Zooplankton community within the Titanic Polygon, Northwest Atlantic, summer 2003

In summer 2003 we continued our long-term series of observations over the zooplankton community within the Titanic Polygon (area of the frontal zone of Gulf Stream and the Labrador Current) in the North Atlantic, where interaction of ecosystems of subpolar and warm waters takes place. Depending on hydrological situation occurring in the frontal zone interrelated interannual variations in abundance and biomass of plankton species including Calanus hyperboreus and mesopelagic shrimps of Acanthephyra genus were observed. In different years contribution of two parallel trophic nets passing primarily through the larger and smaller plankters to formation of the community varied. Data on the size structure of population of macroplankton shrimps are presented.

Effect of acidification on an Arctic phytoplankton community from Disko Bay, West Greenland

Long-term measurements (i.e. months) of in situ pH have not previously been reported from the Arctic; this study shows fluctuations between pH 7.5 and 8.3 during the spring bloom 2012 in a coastal area of Disko Bay, West Greenland. The effect of acidification on phytoplankton from this area was studied at both the community and species level in experimental pH treatments within (pH 8.0, 7.7 and 7.4) and outside (pH 7.1) in situ pH. The growth rate of the phytoplankton community decreased during the experimental acidification from 0.50 ± 0.01/day (SD) at pH 8.0 to 0.22 ± 0.01/day at pH 7.1. Nevertheless, the response to acidification was species-specific and divided into 4 categories: I, least affected; II, affected only at pH 7.1; III, gradually affected and IV, highly affected. In addition, the colony size and chain length of selected species were affected by the acidification. Our findings show that coastal phytoplankton from Disko Bay is naturally exposed to pH fluctuations exceeding the experimental pH range used in most ocean acidification studies. We emphasize that studies on ocean acidification should include in situ pH before assumptions on the effect of acidification on marine organisms can be made.

Ketones in hydrothermal petroleums and sediments from Guaymas Basin

The polar compound (NSO) fractions of seabed petroleums and sediment extracts from the Guaymas Basin hydrothermal system have been analyzed by gas chromatography and gas chromatography-mass spectrometry. The oils were collected from the interiors and exteriors of high temperature hydrothermal vents and represent hydrothermal pyrolysates that have migrated to the seafloor by hydrothermal fluid circulation. The downcore samples are representative of both thermally unaltered and thermally altered sediments. The survey has revealed the presence of oxygenated compounds correlated with samples exhibiting a high degree of thermal maturity. Several homologous series of related ketone isomers are enriched in the interiors of the hydrothermal vent samples or in hydrothermally-altered sequences of the downcore sediments (DSDP Holes 477 and 481A). The n-alkanones range in carbon number from C11 to C33 with a Cmax from 14 to 23, distributions that are similar to those of the n-alkanes. The alkan-2-ones are usually in highest concentrations, with lower amounts of 3-, 4-, 5-, 6-, 7- (and higher) alkanones, and they exhibit no carbon number preference (there is an odd carbon number preference of alkanones observed for downcore samples). The alkanones are enriched in the interiors of the hydrothermal vent spires or in downcore hydrothermally-altered sediments, indicating an origin at depth or in the hydrothermal fluids and not from an external biogenic deposition. Minor amounts of C13 and C18 isoprenoid ketones are also present. Simulation of the natural hydrothermal alternation process by laboratory hydrous pyrolysis techniques provided information regarding the mode of alkanone formation. Hydrous pyrolysis of n-C32H66 at 350°C for 72 h with water only or water with inorganic additives has been studied using a stainless steel reaction vessel. In each experiment oxygenated hydrocarbons, including alkanones, were formed from the n-alkane. The product distributions indicate a reaction pathway consisting of n-alkanes and a-olefins as primary cracking products with internal olefins and alkanones as secondary reaction products. Hydrous pyrolyses of Messel shale spiked with molecular probes have been performed under similar time and temperature constraints to produce alkanone distributions like those found in the hydrothermal vent petroleums.