Primary Production Respiration Research Articles

Research Article: Trophic dynamics analysis and ecosystem structure for some fish species of northern Oman Sea

In the present study, a trophic structure model for some fish species of the northern Oman Sea is developed through using mass balance modeling software, Ecopath with Ecosim (EwE). In this model, we simulated 16 functional groups spread across an area of 3998.20 km2 from 2017 to 2018. Mean trophic level in the area of the present study was 3.49. Values calculated for system omnivory and connectance indices were 0.42 and 0.44, respectively. However, the values of ecotrophic efficiency in the model were high (>0.5) for most consumers of high trophic levels except for sharks and rays because of their high fishing mortality. Accordingly, mixed trophic impact showed that phytoplankton and detritus positively impacted almost all ecological groups. Also bentho-pelagics, the medium demersals, benthos, and crustaceans had a very negative impact on themselves due to cannibalism. Furthermore, the highest realized trophic level was 4.34 for sharks. The maximum omnivory index is calculated as 0.99 for medium demersals for feeding on a wide variety of preys. Also, the average catch per net primary production, i.e., the gross efficiency of the system was around 0.000198 (lower than the global average) indicating that the fishery is harvesting fishes high in the food chain. The primary production/respiration (PP/R) ratio is found to be 3.57 and the values of ascendancy (45.40%) and overhead (54.60%) showed stability of the ecosystem. Thus northern Oman Sea can be classified as an immature ecosystem (in the developmental stage), although it has some kind of system maturity. Accordingly, the food web of northern Oman Sea is consisted mostly of detritivorous, planktivorous, and carnivorous fish species. Besides, Ecopath with Ecosim (EwE) software can be an excellent option to examine interactions among ecological groups, and the impact of fishing in northern Oman Sea which is unquestionably helpful to develop concrete management strategies. The proper ecosystem-based fisheries management practice can improve the efficiency of this overexploited ecosystem.

Drivers of the carbonate system seasonal variations in a Mediterranean gulf

The effects of different physical and biogeochemical drivers on the carbonate system were investigated in a semi-enclosed coastal area characterized by high alkalinity riverine discharge (Gulf of Trieste, Northern Adriatic Sea, Mediterranean Sea). Our 2-year time-series showed that a large part of the seasonal carbonate chemistry variation was controlled by the large seasonal change of seawater temperature, though air-sea CO2 exchange, biological activity (primary production-respiration), and riverine inputs also exerted a significant influence.With the exception of summer, the Gulf of Trieste was a sink of atmospheric carbon dioxide, showing a very strong CO2 fluxes from atmosphere into the sea (−16.10 mmol m−2 day−1) during high wind speed event of north easterly Bora wind. The CO2 influx was particularly evident in winter, when the biological activity was at minimum and the low seawater temperature enhanced CO2 solubility. During spring, the drawdown of CO2 by primary production overwhelmed the CO2 physical pump, driving a significant decrease of dissolved inorganic carbon (DIC), [CO2], and increase of pHT25 °C. In summer the primary production in surface waters occurred with the same intensity as respiration in the bottom layer, so the net biological effect on the carbonate system was very low and the further reduction of seawater CO2 concentration observed was mainly due to carbon dioxide degassing induced by high seawater temperature. Finally, during autumn the respiration was the predominant process, which determined an overall increase of DIC, [CO2], and decrease of pHT25 °C. This was particularly evident when the breakdown of summer stratification occurred and a large amount of CO2, generated by respiration and segregated below the pycnocline, was released back to the whole water column. Local rivers also significantly affected the carbonate system by direct input of total alkalinity (AT) coming from the chemical weathering of carbonate rocks, which dominate the river watershed. Our finding clearly demonstrates a high AT concentration in low salinity surface waters (AT max = 2742.8 μmol kg−1) and a negative AT-salinity correlation. As a result the Gulf of Trieste revealed a low Revelle factor (10.1) and one of the highest buffer capacities of the Mediterranean Sea (ßDIC = 0.31 mmol kg−1), which allows the system to store a significant amount of atmospheric CO2 with a small decrease of seawater pH.

Preliminary trophic network analysis of subalpine Lake Annecy (France) using an Ecopath model

Lake Annecy is the second largest natural lake in France, with intensive commercial and recreational fisheries. However, there is limited knowledge of its trophic interaction. A preliminary Ecopath model was fitted to study the trophic interaction in the lake using the available data on most of the ecosystem compartments. Fourteen functional groups were used in the present analysis. Most of the consumers have ecotrophic efficiency from 0.3 to 0.6. The results show that flow from detritus is as important as flow from primary producers. The overall transfer efficiency of the system is 9.6. The primary production/respiration (Pp/R) ratio, which is 3.253, shows that Lake Annecy's ecosystem is comparatively mature. The gross efficiency of fisheries is 0.001173. Catch trophic level and percentage of primary productivity required for catch show that fishery in Lake Annecy is stable. The values of ascendancy (31.2) and overhead (68.8) show the stability of the ecosystem. Mixed trophic analysis indicates that zoobenthos have a positive effect on most of the fish functional groups. This preliminary model can be helpful to pinpoint the gaps in the present knowledge about Lake Annecy.

Microbial respiration and trophic regimes in the Northern Adriatic Sea (Mediterranean Sea)

Remineralization in the Northern Adriatic Sea has been examined by studying the respiratory rates, through electron transport system activity, in four systems identified on the basis of different salinities, caused by riverine outflows, and different productivity regimes measured by apparent oxygen utilization. The sea waters influenced by river discharges were characterized by high respiratory activity while in fully marine waters respiration fell close to the typical value for the surface pelagic Mediterranean waters. A speculative approach to quantify the trophic balance in the examined sub-systems was adopted and the following ratios were computed: Primary Production/Respiration (PP/R); Primary Production/(Bacterial Production + Respiration) [PP/(BP + R)]; (Dissolved Organic Carbon + Particulate Organic Carbon)/Respiration [(DOC + POC)/R], using the data generated at the same time from the same multidisciplinary cruises. High variability of these metabolic ratios in the described subsystems occurred, so that shifting autotrophy and heterotrophy patterns through summer-winter and cross-productivity front trends occurred. Episodic heterotrophy has been found to happen in the North Adriatic Sea, although this is normally considered a productive ecosystem.