@article {5418, title = {Microbial parasites make cyanobacteria blooms less of a trophic dead-end than commonly assumed}, journal = {The ISME Journal}, volume = {12}, year = {2018}, pages = {1008-1020}, abstract = {

Les parasites sont pr{\'e}sents dans tous les {\'e}cosyst{\`e}mes et peuvent {\^e}tre {\`a} l{\textquoteright}origine de changements dans la structure et le fonctionnement des r{\'e}seaux trophiques. Cependant, {\`a} ce jour, nos connaissances concernant les effets des parasites sur la dynamique des r{\'e}seaux trophiques restent limit{\'e}es. Dans cette {\'e}tude, nous analysons le r{\^o}le de parasites microbiens (virus de bact{\'e}ries, phytoplancton et cyanobact{\'e}ries, et des chitrides parasites des cyanobact{\'e}ries) sur le transfert d{\textquoteright}{\'e}nergie et le fonctionnement du r{\'e}seau trophique au cours d{\textquoteright}un bloom de cyanobact{\'e}rie {\`a} l{\textquoteright}aide d{\textquoteright}un mod{\`e}le d{\textquoteright}Analyse Inverse Lin{\'e}aire. Cette mod{\'e}lisation a permis de mettre en {\'e}vidence l{\textquoteright}importance du broutage sur les bact{\'e}ries h{\'e}t{\'e}rotrophes {\`a} travers la voie microbienne (DOC -\> bact{\'e}ries -\> consommateurs), ainsi que la d{\'e}pendance des consommateurs vis {\`a} vis des bact{\'e}ries notamment pendant les blooms de cyanobact{\'e}ries. Au fur et {\`a} mesure que les bact{\'e}ries deviennent la principale source d{\textquoteright}{\'e}nergie des consommateurs, le syst{\`e}me adopte une structure plus complexe, en r{\'e}seau, s{\textquoteright}accompagnant d{\textquoteright}une augmentation de l{\textquoteright}omnivorie du syst{\`e}me. Cette derni{\`e}re pourrait {\^e}tre {\`a} l{\textquoteright}origine d{\textquoteright}une augmentation de la capacit{\'e} du syst{\`e}me {\`a} r{\'e}sister {\`a} l{\textquoteright}efflorescence des cyanobact{\'e}ries. Finalement, nous avons {\'e}galement mis en {\'e}vidence les effets de la destruction des cellules h{\^o}tes des cyanobact{\'e}ries par les chitrides sur la dynamique du r{\'e}seau trophique. En effet, cette derni{\`e}re faciliterait le broutage des cyanobact{\'e}ries et offrirait des voies alternatives aux consommateurs, ce qui augmenteraient la stabilit{\'e} du syst{\`e}me.

Parasites exist in every ecosystem and can have large influence on food-web structure and function, yet, we know little about parasites{\textquoteright} effect on food-web dynamics. Here we investigate the role of microbial parasitism (viruses of bacteria, phytoplankton and cyanobacteria, and parasitic chytrids on cyanobacteria) on the dynamics of trophic pathways and food-web functioning during a cyanobacteria bloom, using linear inverse food-web modeling parameterized with a 2-month long dataset (biomasses, infection parameters, etc.). We show the importance of grazing on heterotrophic bacteria (the microbial pathway: DOC -\> bacteria -\> consumer) and how consumers depended on bacteria during peak-cyanobacteria bloom, which abundance was partly driven by the viral activity. As bacteria become the main energy pathway to the consumers, the system takes a more web-like structure through increased omnivory, and may thereby facilitate the system{\textquoteright}s persistence to the cyanobacteria outbreak. We also showed how the killing of cyanobacteria host-cells by chytrids had important impact on the food-web dynamics by facilitating grazing on the cyanobacteria, and by offering alternative pathways to the consumers. This seemed to increase the system{\textquoteright}s ability to return to a mix of trophic pathways, which theoretically increases the stability of the system.

}, doi = {10.1038/s41396-018-0045-9}, url = {https://doi.org/10.1038/s41396-018-0045-9}, author = {Haraldsson, Matilda and M{\'e}lanie Gerphagnon and Bazin, Pauline and Samuele Tecchio and T{\'e}l{\'e}sphore Sime-Ngando and Nathalie Niquil} }