The metabolic carbon requirements and excretion rates of three major zooplankton groups in the Southern Ocean were studied in February 2009. The research was conducted in the framework of the ATOS research project as part of the Spanish contribution to the International Polar Year. The objective was to ascertain the possible consequences of the predicted zooplankton shift from krill to salps in the Southern Ocean for the cycling of biogenic carbon and the concentration and stoichiometry of dissolved inorganic nutrients. The carbon respiratory demands and NH4-N and PO4-P excretion rates of < 5 mm size copepods, krill and salps were estimated by incubation experiments. The carbon-specific metabolic rates and N:P metabolic quotients of salps were higher than those of krill (furcilia spp. and adults) and copepods, and as expected there was a significant negative relation between average individual zooplankton biomass and their metabolic rates, each metabolic process showing a particular response that lead to different metabolic N:P ratios. The predicted change from krill to salps in the Southern Ocean would encompass not only the substitution of a pivotal group for Antarctic food webs (krill) by one with an indifferent trophic role (salps). In a zooplankton community dominated by salps the respiratory carbon demand by zooplankton will significantly increase, and therefore the proportion of primary production that should be allocated to compensate for the global respiratory C-losses of zooplankton. At the same time, the higher production by salps of larger, faster sinking fecal pellets will increase the sequestration rate of biogenic carbon. Similarly, the higher N and P excretion rates of zooplankton and the changes in the N:P stoichiometry of the metabolic products will modify the concentration and proportion of N and P in the nutrient pool, inducing quantitative and qualitative changes on primary producers that will translate to the whole Southern Ocean ecosystem.
Abstract. The relationship between the percent extracellular carbon release (PER) and the specific lysis rates of phytoplankton was examined across a range of communities spanning from highly oligotrophic ones in the subtropical Atlantic Ocean to productive ones in the N. African upwelling and the Southern Ocean. Communities in oligotrophic waters supported high phytoplankton cell lysis rates and low particulate primary production rates but high dissolved primary production and PER. The percent extracellular carbon released increased with increasing lysis rates to reach an asymptote at about 80% PER with specific lysis rates > 1.5 d−1, observed in the most oligotrophic conditions tested. These results confirm that high phytoplankton mortality in the oligotrophic ocean leads to high PER, accounting for the large fraction of the photosynthetic carbon channelled through bacteria characteristic of oligotrophic marine communities.
The constraints imposed by the geometry of Codium bursa, a balloon-like Mediterranean macroalga with a thick (= 5.6 mm) thallus enclosing a lumen filled with water, on its functional properties were tested by examining the scaling of its form, composition (pigmentation and nutrient content), light absorption, metabolism (respiration rate, light use efficiency, and maximal photosynthetic rate), and growth to individual size.We found that C. bursa absorbs most (98 % ) of the incident light, due to its high area1 pigment density (0.52 pg chl a mm-2), but that light absorption was very inefficient, as seen from the low values of absorption per unit carbon (0.045 mZ g-' C), which suggest a low intrinsic growth rate.The pigment and nutrient content of C. bursa increase more slowly than the macroalgal weight, so that large C. bursa balloons have lower pigment and nutrient contents than smaller individuals.As a consequence, photosynthetic capacity declines with increasing size, and light compensation points increase with increasing individual size, suggesting increasing light requirements and reduced potential growth rate as C. bursa grows.This was confirmed by in situ estimates of growth rate that showed C. bursa to rank amongst the slowest-growing macroalgae (specific growth rate 1.8 * 0.3 X lO-= d-') as well as by the significant decline of specific growth rate with increasing algal size.The results obtained confirm the slow growth rates and the strong size-dependence of biochemical composition and metabolism imposed by the spherical geometry of C. bursa.
Study of 2 diatom species, Leptocylindrus danicus and Skeletonema costatum, growing in a n enclosed plankton community showed that most of the variability in the extent of epialgal colonization (i.e.bacteria algal cell-') was attributable to differences within species, compared to small among-species and temporal vanability.Within-species variability was related to the populahon dynamics of the diatom species examined, because the extent of colonization increased with the time algal cells had been exposed to colonization.Thus, modelling of algal colonization by bacteria requlres both consideration of encounter probabilities and phytoplankton demography.
On the basis of a broad compilation of data on p CO 2 in surface waters, we show tropical lakes to be, on average, far more supersaturated and variable in CO 2 (geometric mean ± SE p CO 2 = 1804 ± 35 μ atm) than temperate lakes (1070 ± 6 μ atm). There was a significant negative relationship between p CO 2 and latitude, resulting in an average decrease of p CO 2 by 2.8 ± 0.5% per degree latitude. In addition, we found a general positive relationship between p CO 2 and water temperature across lakes involving an average increase (±SE) in 6.7 ± 0.8% per °C. A conservative annual efflux from global lakes to the atmosphere was reestimated to 0.44 Gt C. Our results show tropical lakes maintain large CO 2 disequilibria with the atmosphere, playing a disproportionate and variable role in the flux of CO 2 between lakes and the atmosphere, thereby being a significant component of the global C cycle.
We examined the importance of pigment content and packaging within plant t~ssues for light absorption by Posidonia oceanica leaves from different locations along the Spanish Mediterranean coast.Pigments of P. oceanica leaves absorbed 70.5 to 97.1 % of incident Light (at 675 nm); the light absorbed by pigments increased with increasing chlorophyll density.The efficiency of chlorophyll a in absorbing light (i.e. the chlorophyll a-specific light absorption) also decreased significantly (p < 0.001) with increasing pigment packaging (i.e.concentration) within the leaves, although the light absorbed per unit biomass increased with increasing pigment concentration.The positive trend between light absorption and chlorophyll density found for P. oceanica leaves was also found to apply to 12 other seagrass species from the Atlantic, Pacific, Caribbean, South China and Mediterranean Seas.The similarity between the patterns in light absorption by seagrass leaves described here and those previously described for phytoplankton suggests that these patterns reflect constraints on light absorption by phototrophic organisms which may apply to most aquatlc plants
The planktonic metabolic balance that is the balance between gross primary production (GPP) and community respiration (CR) was determined in Matilda Bay (estuarine) and Woodman Point (coastal) in Perth, Western Australia. The rates of net community production (NCP = GPP - CR) and the ratio between GPP and CR (P/R) were assessed to evaluate whether the metabolic balance in the two coastal locations tends to be net autotrophic (production exceeding community respiration) or net heterotrophic (respiration exceeding production). We also analyzed environmental variability by measuring temperature, salinity, and nutrients and chlorophyll a concentration. Samples were collected biweekly from March 2014 to March 2015. During the study period the metabolic rates were three times higher in Matilda Bay than in Woodman Point. The predominant metabolism was net autotrophic at both sites with P/R ratios >1 in the majority of the sampling dates. In Matilda Bay, the metabolic rates were negatively correlated with salinity denoting river dynamics influence, and positively with chlorophyll a. In Woodman Point only the GPP was positively correlated with chlorophyll a. The positive correlation between P/R ratio and GPP in Matilda Bay and the positive correlations between the metabolic rates and chlorophyll a suggest that factors controlling autotrophic processes are modulating the planktonic metabolic balance in the coastal marine ecosystem in Perth. Significant correlations were found between CR and GPP-standardized to chlorophyll a and water temperature. The net autotrophic metabolic balance indicates that in both ecosystems planktonic communities are acting as a sink of CO2 and as a source of organic matter and oxygen to the system and are able to export organic matter to other ecosystems.
