The green–blue swing: plasticity of plankton food‐webs in response to coastal oceanographic dynamics

Abstract

The internal organization of plankton communities plays a key role in biogeochemical cycles and in the functioning of aquatic ecosystems. In this study, the structure of a marine plankton community (including both unicellular and multicellular organisms) was inferred by applying an ecological network approach to species abundances observed weekly at the long‐term ecological research station MareChiara (LTER‐MC) in the Gulf of Naples (Tyrrhenian Sea, Mediterranean Sea) in the summers of 2002–2009. Two distinct conditions, characterized by different combination of salinity and chlorophyll values, alternated at the site: one influenced by coastal waters, herein named ‘green’, and the other reflecting more offshore conditions, named ‘blue’. The green and blue ‘phases’ showed different keystone biological elements: namely, large diatoms and small‐sized flagellates, respectively. Several correlations amongst species belonging to different trophic groups were found in both phases (connectance ~0.30). In the green phase, several links between phytoplankton and mesozooplankton and within the latter were detected, suggesting matter flow from microbes up to carnivorous zooplankton. A microbial‐loop‐like sub‐web, including mixo‐ and heterotrophic dinoflagellates and ciliates, was present in the green phase, but it was relatively more important in the blue phase. The latter observation suggests a more intense cycling of matter at the microbial trophic level in the blue phase. These results show that different modes of ecological organization can emerge from relatively small changes in the composition of aquatic communities coping with environmental variability. This highlights a significant plasticity in the internal structure of plankton webs, which should be taken into account in predictions of the potential effects of climatic oscillations on aquatic ecosystems and biogeochemical cycles therein.

Improved marine‐derived POM availability and increased pH related to freshwater influence in an inland sea

“…Environmental conditions affect the FA content of algae (Dalsgaard et al ; Galloway and Winder ) leading to declines in EFA and food quality under increased p CO2 (Rossoll et al ), high temperature and low salinity (Galloway and Winder ). However, growing evidence suggests the plasticity in community composition in response to environmental changes observed in this study will be of greatest importance for determining energy cycling (D'Alelio et al ), effects on consumers (Rossoll et al ) and the abundance of EFA synthesized by photoautotrophs (Galloway and Winder ). Indeed, POM composition varied greatly with oceanographic conditions in this study, and changes in the phytoplankton species composition can explain more than 70% of the variation in POM fatty acid composition (Lowe et al ).…”

Why large cells dominate estuarine phytoplankton

“…Although the model used here is a highly simplified representation of diverse and complex communities and trophic linkages (e.g., D'Alelio et al ), it apparently captures key processes through which temperature, nutrients, and plankton size shape these communities. This might reflect two things.…”

Bivalve Grazing Can Shape Phytoplankton Communities

“…The species makeup of phytoplankton communities is highly variable over time (D'Alelio et al, 2015), within (Cloern and Dufford, 2005) and between marine ecosystems (Carstensen et al, 2015). A grand challenge of aquatic ecology is developing a mechanistic understanding of the processes that select which species are present at a particular time and location.…”