Biological traits, and egg and fecal pellet production of Calanus finmarchicus and Calanus glacialis in situ and during experiments

The effects of temperature and food was examined for Calanus finmarchicus and C. glacialis during 3 phases of the phytoplankton spring bloom in Disko Bay, western Greenland. The 2 species were collected during pre-bloom, bloom, and post-bloom and exposed to temperatures from 0 to 10°C, combined with deficient or excess food. Fecal pellet and egg production were measured as indices for grazing and secondary production, respectively. Furthermore, changes in body carbon, nitrogen, and lipid content were measured. C. glacialis sampled before the bloom and incubated with excess food exhibited high specific egg production at temperatures between 0 and 2.5°C. Higher temperatures did not increase egg production considerably, whereas egg production for C. finmarchicus more than tripled between 2.5 and 5°C. Starved C. glacialis produced eggs at all temperatures stimulated by increasing temperatures, whereas starved C. finmarchicus needed temperatures above 5°C to produce eggs fueled by their lipid stores. Few C. finmarchicus had mature gonads at the initiation of the pre-bloom and bloom experiment, and egg production of C. finmarchicus therefore only increased as the ratio of individuals with mature gonads increased. During the bloom, both C. glacialis and C. finmarchicus used the high food availability for egg production, while refueling or exhausting their lipid stores, respectively. Finally, during the post-bloom experiment, production was low by C. finmarchicus, whereas C. glacialis had terminated production. Our results suggest that a future warmer ocean will reduce the advantage of early spawning by C. glacialis and that C. finmarchicus will become increasingly prevalent.

(Table 1) Egg laying and hatching dates and guarding duration of Adélie penguins (Pygoscelis adeliae) on Petrel Island, Antarctica

1. In Polar Regions, the extent and dynamics of sea-ice are changing. This affects the ocean productivity which consecutively impacts plankton communities and polar top predators like penguins. Yet, the underlying behavioural and physiological mechanisms remain poorly understood. 2. Here we monitored the ecophysiological responses of Adelie penguin (Pygoscelis adeliae) pairs during two seasons of contrasting timing of sea-ice retreat. Beside classical breeding parameters like foraging trip duration, body mass and reproductive success, we also investigated food-related stress (via plasma corticosterone concentration), nutritional state (via metabolite levels) and the use of penguins' habitat (via blood isotopic values). 3. Body mass and reproductive success remained unchanged but foraging trips were shorter when sea-ice retreated earlier. Constant plasma corticosterone concentrations indicated that none of the feeding conditions resulted in a food-related stress. However metabolite levels were lower when sea-ice retreated early, suggesting that the foraging performance and the quality/quantity of food differed. Indeed isotopic ratios indicated that coastal prey like fish contributed more to the penguins' diet when sea-ice retreated prematurely. 4. The early sea-ice retreat was related to higher chlorophyll concentrations, known to favour krill recruitment. Paradoxically, this was not associated to a higher krill contribution in the penguins' diet. We propose that a shift in the phytoplankton quality (rather than quantity), affecting krill recruitment, forced penguins to switch to more available prey like coastal fish. 5. In some Antarctic regions, sea-ice is retreating earlier and earlier. In the present study, even though the timing of sea-ice retreat and the consecutive ocean productivity differed drastically between the 2 years, Adelie penguins were not severely affected because they were able to adjust their at-sea behaviour and thus maintained their body condition and reproductive success unchanged. 6. This suggests that the timing of sea-ice retreat does not represent an important threat to populations of Adelie penguins at least as long as alternative resources are still available and other environmental parameters like winter sea-ice extent are not dramatically altered.

Seawater carbonate chemistry and Astrangia poculata mass and zooxanthellate during experiments, 2012

The effects of nutrients and pCO2 on zooxanthellate and azooxanthellate colonies of the temperate scleractinian coral Astrangia poculata (Ellis and Solander, 1786) were investigated at two different temperatures (16 °C and 24 °C). Corals exposed to elevated pCO2 tended to have lower relative calcification rates, as estimated from changes in buoyant weights. Experimental nutrient enrichments had no significant effect nor did there appear to be any interaction between pCO2 and nutrients. Elevated pCO2 appeared to have a similar effect on coral calcification whether zooxanthellae were present or absent at 16 °C. However, at 24 °C, the interpretation of the results is complicated by a significant interaction between gender and pCO2 for spawning corals. At 16 °C, gamete release was not observed, and no gender differences in calcification rates were observed - female and male corals showed similar reductions in calcification rates in response to elevated CO2 (15% and 19% respectively). Corals grown at 24 °C spawned repeatedly and male and female corals exhibited two different growth rate patterns - female corals grown at 24 °C and exposed to CO2 had calcification rates 39% lower than females grown at ambient CO2, while males showed a non-significant decline of 5% under elevated CO2. The increased sensitivity of females to elevated pCO2 may reflect a greater investment of energy in reproduction (egg production) relative to males (sperm production). These results suggest that both gender and spawning are important factors in determining the sensitivity of corals to ocean acidification, and considering these factors in future research may be critical to predicting how the population structures of marine calcifiers will change in response to ocean acidification.

Egg and early larval stages of Baltic cod, Gadus morhua duirng ocean acidification experiments, 2012

The accumulation of carbon dioxide in the atmosphere will lower the pH in ocean waters, a process termed ocean acidification (OA). Despite its potentially detrimental effects on calcifying organisms, experimental studies on the possible impacts on fish remain scarce. While adults will most likely remain relatively unaffected by changes in seawater pH, early life-history stages are potentially more sensitive, due to the lack of gills with specialized ion-regulatory mechanisms. We tested the effects of OA on growth and development of embryos and larvae of eastern Baltic cod, the commercially most important fish stock in the Baltic Sea. Cod were reared from newly fertilized eggs to early non-feeding larvae in 5 different experiments looking at a range of response variables to OA, as well as the combined effect of CO2 and temperature. No effect on hatching, survival, development, and otolith size was found at any stage in the development of Baltic cod. Field data show that in the Bornholm Basin, the main spawning site of eastern Baltic cod, in situ levels of pCO2are already at levels of 1,100 µatm with a pH of 7.2, mainly due to high eutrophication supporting microbial activity and permanent stratification with little water exchange. Our data show that the eggs and early larval stages of Baltic cod seem to be robust to even high levels of OA (3,200 µatm), indicating an adaptational response to CO2.