Based on isotope analysis, a team of scientists from the ICM, the IEO and the ULPGC has demonstrated, for the first time, the importance of microbes in the entire marine food chain.
Scientists from the Spanish Institute of Oceanography (IEO), the Institut de Ciències del Mar (ICM) and the University of Las Palmas de Gran Canaria (ULPGC) have published a paper in the specialised journal Scientific Reports in which, applying isotope analysis techniques, they have demonstrated and quantified the important influence that microbes have in the marine food chain, not only on primary producers as previously believed, but also on higher organisms such as fish.
Ocean food webs have for a long time been understood as two distinct systems: one subsystem comprising primary producers -mainly microalgae in the case of the oceans- and herbivorous and carnivorous organisms that successively feed on each other, and another subsystem comprising microbes that recycle organic matter.
Until now, the two subsystems were considered to be linked mainly through the influence of these microbes on primary producers, as they make available nutrients resulting from the remineralisation of organic matter. However, the influence of microbes at higher levels of the food chain was considered to be very small.
This new study has, for the first time, quantified the influence of the microbial trophic system on 13 species of small fish, thus demonstrating its importance. To carry out the investigation, the scientific team has applied techniques of analysis of stable isotopes of nitrogen in amino acids obtained from micronecton fish (small fish that are the main food of larger fish, many of them commercially exploited) captured during an expedition in the central Atlantic, from the Canary Islands to Iceland.
These analyses make it possible to know the origin of the organic matter analysed and to quantify the trophic position of the organism analysed, that is, whether its diet is more herbivorous or more carnivorous. In this way, it has been estimated that microbes contribute up to 25% in defining the trophic position of these fish. In addition, the work shows that the trophic position estimates obtained through this method are very similar to those determined from the analysis of their diets.
"This research opens the door to a revision of the known trophic positions of all marine organisms, allowing the ecosystem to be monitored through the application of more precise performance indicators", explains Antonio Bode, a scientist at the IEO's A Coruña Oceanographic Centre and first author of the study.
In addition, the results of the study indicate that part of the diet of fish inhabiting the bathypelagic zone of the water column (between 1000 and 2000 m) consists of aggregates of detritus. "In these trophically impoverished habitats where there is no primary production and zooplankton concentrations are low, the so-called 'marine snow' emerges as a trophic resource that complements the diet of bathypelagic fish", states Pilar Olivar, researcher at the ICM and co-author of the study.