The northern Gulf of Mexico (GoM) is a region strongly influenced by river discharges of freshwater and nutrients, which promote a highly productive coastal ecosystem that host commercially valuable marine species. A variety of climate and weather processes could potentially influence the river discharges into the northern GoM. However, their impacts on the coastal ecosystem remain poorly described. By using a regional ocean-biogeochemical model, complemented with satellite and in situ observations, here we show that El Nino - Southern Oscillation (ENSO) is a main driver of the interannual variability in salinity and plankton biomass during winter and spring. Composite analysis of salinity and plankton biomass anomalies shows a strong asymmetry between El Nino and La Nina impacts, with much larger amplitude and broader areas affected during El Nino conditions. Further analysis of the model simulation reveals significant coastal circulation anomalies driven by changes in salinity and winds. The coastal circulation anomalies in turn largely determine the spatial extent and distribution of the ENSO-induced plankton biomass variability. These findings highlight that ENSO-induced changes in salinity, plankton biomass, and coastal circulation across the northern GoM are closely interlinked and may significantly impact the abundance and distribution of fish and invertebrates.

https://aquila.usm.edu/cgi/viewcontent.cgi?article=17121&context=fac_pubs

ENSO-induced co-variability of Salinity, Plankton Biomass and Coastal Currents in the Northern Gulf of Mexico

There has been a dramatic increase in jellyfish biomass over the eastern Bering Sea shelf since the early 1990s, which was previously hypothesized to have been triggered by changing climate and ocean conditions. We examine the hypothesis that the presence of these large carnivores has affected fisheries resources, either through direct predation on larval stages, or through compe- tition for zooplankton prey. In this paper, we explore the impact of this jellyfish increase on zoo- plankton and fish communities based on field data on the composition of the jellyfish community, and the abundance, size, stable isotopic signatures, and feeding habits of the principal scyphomedusae in the region. These data, together with those on zooplankton biomass, are used to estimate the ecosys- tem impacts of this increase. The center of jellyfish biomass has shifted from the SE Middle Shelf Domain in the early 1980s to the NW in the late 1990s. In recent years, the species composition of large medusae caught in trawls was dominated (>80% by number and >95% by weight) by the scyphozoan Chrysaora melanaster. Dense aggregations of this species occupied the water column in daytime between 10 and 40 m. Their food habits consisted mainly of pelagic crustaceans (euphausi- ids, copepods, amphipods), although other jellyfish and juvenile pollock were also consumed. Based on stable isotope ratios, the trophic level of this scyphozoan is equivalent to, or higher than, that of Age 0 pollock. Preliminary estimates showed that medusae have a moderate grazing impact on zoo- plankton in the area around the Pribilof Islands; C. melanaster was estimated on average to consume seasonally about one-third of the standing stock and 4.7% of the annual production of zooplankton in this region. Daily consumption of Age 0 pollock was estimated to be 2.8% of the standing stock around the Pribilof Islands during 1999. A hypothesis for the increase in jellyfishes observed in the eastern Bering Sea, based on release from competition from planktivorous forage fishes, is proposed.

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Increases in jellyfish biomass in the Bering Sea: implications for the ecosystem

Distribution patterns of microplastics within the plankton of a tropical estuary.

Seasonal food web structures and sympagic–pelagic coupling in the European Arctic revealed by stable isotopes and a two-source food web model

Mesozooplankton are significant consumers of phytoplankton, and have a significant impact on the oceanic biogeochemical cycles of carbon and other elements. Their contribution to vertical particle flux is much larger than that of microzooplankton, yet most global biogeochemical models have lumped these two plankton functional types together. In this paper we bring together several newly available data syntheses on observed mesozooplankton concentration and the biogeochemical fluxes they mediate, and perform data synthesis on flux rates for which no synthesis was available. We update the equations of a global biogeochemical model with an explicit representation of mesozooplankton (PISCES). We use the rate measurements to constrain the parameters of mesozooplankton, and evaluate the model results with our independent synthesis of mesozooplankton concentration measurements. We also perform a sensitivity study to analyze the impact of uncertainty in the flux rates. The standard model run was parameterized on the basis of the data synthesis of flux rates. The results of mesozooplankton concentration in the standard run are slightly lower than the independent databases of observed mesozooplankton concentrations, but not significantly. This shows that structuring and parameterizing biogeochemical models on the basis of observations without tuning is a strategy that works. The sensitivity study showed that by using a maximum grazing rate of mesozooplankton that is only 30% higher than the poorly constrained fit to the observations, the model mesozooplankton concentration gets closer to the observations, but mesozooplankton grazing becomes higher than what is currently accounted for. This is an indication that food selection by mesozooplankton is not sufficiently quantified at present. Despite the amount of effort that is represented by the data syntheses of all relevant processes, the good results that were obtained for mesozooplankton indicate that this effort needs to be applied to all components of marine biogeochemistry. The development of ecosystem models that better represent key plankton groups and that are more closely based on observations should lead to better understanding and quantification of the feedbacks between marine ecosystems and climate.

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Biogeochemical fluxes through mesozooplankton

Publisher Summary The determination of the total plankton biomass or biovolume is rapid compared with the enumeration and identification techniques. Many samples can be processed in parallel. These measurements are suitable for mixed samples as well as for samples of selected individual species. There is a wide variety of biovolume and biomass measurements. The effort involved in sample treatment increases within the conventional methods and is generally large in biochemical procedures. The methodological bias decreases stepwise: when the amount of excess and interstitial water is reduced by measuring displacement volume or wet mass instead of settled volume, when body fluids are totally removed during dry mass determination, and when the inorganic substances are subtracted. Volumetric methods are the only choice if the samples are to be used for species identification as well. Volumetric methods are also recommended as a quick-look procedure; that is, on board a ship, and in cases where no microbalance or other sophisticated equipment is available. There are two principles related to the volumetric methods: the direct volume estimation of settled plankton and the measurement of the amount of water displaced by the plankton. The first method is more gentle but less precise.

W. Hagen

Papers

Biomass and abundance