Dissolved Compounds Excreted by Copepods Reshape the Active Marine Bacterioplankton Community Composition

Abstract

Copepods are important suppliers of bioreactive compounds for marine bacteria through fecal pellet production, sloppy feeding, and the excretion of dissolved compounds. However, the interaction between copepods and bacteria in the marine environment is poorly understood. We determined the nitrogen and phosphorus compounds excreted by copepods fed with two natural size-fractionated diets (<20-and 20-150-µm) in the upwelling zone of central/southern Chile in late summer and spring. We then assessed the biogeochemical response of the bacterial community and its structure, in terms of total and active cells, to enrichment by copepod-excreted dissolved compounds. Results revealed that copepods actively excreted nitrogen and phosphorus compounds, mainly in the form of ammonium and dissolved organic phosphorus (DOP), reaching excretion rates of 2.6 and 0.05 µmol L −1 h −1 , respectively. In both periods, the maximum excretion rates were associated with the 20-150-µm size fraction, but particularly during spring, when a higher organic matter quality was observed in excretion products compared to late summer. There were higher excretion rates of dissolved free amino acids (DFAAs) from copepods fed with the <20-µm size fraction, mainly histidine (HIS) in late summer and glutamic acid (GLU) in spring. A shift in the composition of the active bacterial community was observed between periods and treatments, which was associated with the response of the common seawater surface phyla Proteobacteria and Bacteroidetes. The specific bacterial activity (16S rRNA:rDNA) suggested a different response to the two size-fractionated diets. In late summer, Betaproteobacteria and Bacteroidetes were stimulated by the treatment enriched with excretion products derived from the 20-150-µm and <20-µm size fractions, respectively. In spring, Alphaproteobacteria were active in the treatment enriched with the excretion products of copepods fed with the <20-µm size fraction, whereas they were inhibited in the treatment enriched with excretion products in the 20-150-µm size fraction. Our findings indicate that different Valdés et al. Copepod Excretion and Bacterial Community Structure copepod diets can have a significant impact on the quantity and quality of their excretion compounds, which can subsequently generate shifts in the active bacterial composition. The bacterial response is probably associated with common-opportunistic sea surface microbes that are adapted to rapidly reacting to environmental offers.

Mesozooplankton taurine production and prokaryotic uptake in the northern Adriatic Sea

“…Hence, although crustacean zooplankton are synthesizing taurine, the elevated taurine and DFAA release rates during the fall–winter period might also be attributed to taurine‐ and DFAA‐enriched diet and/or harmful phytoplankton. Additionally, the quality, quantity, composition, and the size of the available diet can strongly influence the release rates of DOM compounds by copepods (Frangoulis et al 2004; Valdés et al 2017) and thus, the organic C, N, and S available to heterotrophic prokaryotes (Valdés et al 2018 a , b ). The diversity of copepod species was higher in the fall–winter period, especially of small‐sized species, than in the spring–summer period (Supporting Information Table S1).…”

Hidden in plain sight: The importance of cryptic interactions in marine plankton

“…Thus, with sufficient data on stoichiometric parameters and metabolic potential, models can be used to establish the sensitivity of ocean characteristics to cryptic interactions. In addition, iterative quality-control processes help determine those interactions that are essential to the overall skill of the model and identify which relationships are most important (Van Nes and Scheffer 2005). Ultimately, the quality of the data and level of complexity that goes Table 1.…”

Chitin distribution in the Oithona digestive and reproductive systems revealed by fluorescence microscopy

“…A recent study, based on the Tara Oceans metagenomic data, has shown the global distribution of Oithona in coastal and open ocean waters ( Madoui et al, 2017 ), which highlighted its key role as a major secondary producer of the marine food chain ( Beaugrand et al, 2003 ; Zamora-Terol et al, 2014 ). The important contribution of copepods in the biological carbon pump has also been demonstrated ( Jonasdottir et al, 2015 ), in particular through the excretion of faecal pellets ( Steinberg & Landry, 2017 ) that sink, provide organic and inorganic compounds to microplankton ( Steinberg, Goldthwait & Hansell, 2002 ; Valdés et al, 2017 ), and deposit on the sediments where they could remain as fossils for several thousand years ( Bathmann et al, 1987 ; Haberyan, 1985 ). The biochemical analysis of the copepod faecal pellets has revealed a high amount of chitin ( Kirchner, 1995 ), a β-1-4- N -acetylglucosamine polymer, the most abundant biopolymer in nature after celluloses ( Kirchner, 1995 ), and mostly known in copepods as a component of the exoskeleton.…”