Measuring Alloxanthin as a Proxy Approach in a Study of Trophic Relationships between Zooplankton and Cryptophyte Algae in Lake Shira

Cryptophyte algae are an important trophic link in many aquatic ecosystems, but they remain insufficiently studied in terms of trophic interactions with other components of ecosystems. They are better quality food than most other algae and, therefore, can be subject to selective grazing by zooplankton; thus, direct measurements of the dynamics of their concentration in lakes may give very low productivity indicators. One way to assess the consumption of cryptophyte algae by zooplankton is to determine the content of alloxanthin, a carotenoid specific for cryptophyte algae, in zooplankton. The present study investigated the alloxanthin content of sedimentary silts, sedimentation traps, and zooplankton of Lake Shira using high performance liquid chromatography. A significant correlation was found between the abundance of some zooplankton species capable of consuming cryptophyte algae and the flux of precipitated alloxanthin recorded in sedimentation traps. Analysis of zooplankton samples (the largest contribution to the biomass of which was made by the copepod Arctodiaptomus salinus (Daday, 1885)) for the content of carotenoids during the spring-summer season showed the presence of alloxanthin amounts reaching 80 μg/g, which decreased by the end of the season, and that correlated with the biomass of cryptophyte algae in the lake. Carotenoids associated with other groups of algae were observed in considerably smaller amounts. Thus, the copepod A. salinus exhibits high selective consumption of cryptophyte algae, which may serve as a confirmation of a close trophic relationship between them

Prospects for using the preparation “Aldofix” as a substitute for formalin in studies of juvenile fish

The study of juvenile fish is a necessary component of fishery research, is of great theoretical interest and is widely used in the study of ontogeny, influence of various environmental factors on the final trophic link of aquatic ecosystems. Traditionally, fry samples are fixed with a 4–5 % formalin solution. However, formalin is a toxic compound, which entails special requirements for the organization of work in laboratory. In order to search for alternative means of fixing biological preparations, an experimental assessment of the possibility of using the drug “Aldofix” as a substitute for formalin in studies of juvenile fish. It was shown that the fixation of juvenile fish with the “Aldofix” preparation immediately after collection of samples is possible only for the subsequent analysis of the length and weight of the specimens. For species identification and for the study of the morphology of fish specimens, fixed with the preparation “Aldofix” immediately after capture unsuitable. However, the re-fixation of fish juvenile samples with “Aldofix”, initially fixed with formalin, seems reasonable, since the quality of the material does not decrease, but at the same time, due to the non-toxicity of the “Aldofix” preparation, there is no negative impact on the health of specialists and students who process these wet preparations.

Surface transport of DOC acts as a trophic link among Mediterranean sub-basins

Characterizing carbon cycling and redistribution in the ocean is an important issue for Mankind, because it may affect key ecosystem services, e.g., support to climate system and food provision. In this paper, using an integrated approach, we explore the impact of the surface circulation on carbon dynamics in the Western Mediterranean Sea, where strong inter-basin differences in primary production do exist. Detailed information on the surface circulation, derived from high-resolution model simulations, is combined with the analysis of accurate, repeated dissolved organic carbon (DOC) data. Our work indicates that the advection of the Atlantic Water acts as a trophic link between the Algerian Basin and the Tyrrhenian Sea, determining a flux of 8.8–37.9 × 1012 g DOC yr−1 into the basin. Thus, surface transport of DOC can redistribute chemical energy among regions with different trophic regimes. We hypothesize that this overlooked mechanism plays an important role also in the global ocean.

Protistan microzooplankton and the trophic position of tuna: quantifying the trophic link between micro- and mesozooplankton in marine foodwebs

The importance of the trophic link between <200-µm protistan microzooplankton and mesozooplankton is a cornerstone of modern understanding of foodweb structure of marine pelagic ecosystems that is well demonstrated in experimentally measured contributions of protistan consumers to mesozooplankton diets, in constrained global budgets, and in regional studies that show the inadequacies of meeting zooplankton metabolic requirements by herbivory alone. Nonetheless, protistan trophic steps are poorly reflected in stable isotope analyses by standard methods and systematically neglected in fisheries-related trophic research, which focuses instead on interactions that can be measured in stomach contents. Here, we apply recent advances in compound-specific isotope analysis of amino acids (CSIA-AA) based on alanine as a trophic indicator of protistan foodweb steps to evaluate the implications of lower foodweb structure on trophic position (TP) estimates of tunas. CSIA-AA results for mesozooplankton of the subtropical North Pacific suggest that tuna TPs are underestimated by 0.9, which give rise to new TP estimates of 4.7–5.4 for the three main tuna species of that region. These, in turn, are used to compute a trophic enrichment factor (TEF = 4.45) based on alanine that includes 15N enrichments for protistan consumers and can be applied more broadly in the region. Accounting for the magnitude and variability of protistan trophic steps in the foodwebs supporting pelagic fisheries has important implications for understanding regional variability in energy flows and foodweb structure and their temporal responses to climate change.