Responses of Marine Diatom-Dinoflagellate Competition to Multiple Environmental Drivers: Abundance, Elemental, and Biochemical Aspects

Abstract

Ocean-related global change has strongly affected the competition between key marine phytoplankton groups, such as diatoms and dinoflagellates, especially with the deleterious consequency of the increasing occurrence of harmful algal blooms. The dominance of diatoms generally shifts toward that of dinoflagellates in response to increasing temperature and reduced nutrient availability; however, contradictory findings have also been observed in certain sea areas. A key challenge in ecology and biogeochemistry is to quantitatively determine the effects of multiple environmental factors on the diatom-dinoflagellate community and the related changes in elemental and biochemical composition. Here, we test the interplay between temperature, nutrient concentrations and their ratios on marine diatom-dinoflagellate competition and chemical composition using bi-algal competition experiments. The ubiquitous diatom Phaeodactylum tricornutum and dinoflagellate Prorocentrum minimum were cultivated semi-continuously, provided with different N and P concentrations (three different levels) and ratios (10:1, 24:1, and 63:1 molar ratios) under three temperatures (12, 18, and 24°C). The responses of diatom-dinoflagellate competition were analyzed by a Lotka-Volterra model and quantified by generalized linear mixed models (GLMMs) and generalized additive models (GAMs). The changes in nutrient concentrations significantly affected diatom-dinoflagellate competition, causing a competitive superiority of the diatoms at high nutrient concentrations, independent of temperature and N:P supply ratios. Interestingly, the effect amplitude of nutrient concentrations varied with different temperatures, showing a switch back toward a competitive superiority of the dinoflagellates at the highest temperature and at very high nutrient concentrations. The ratios of particulate organic nitrogen to phosphorus showed significant negative correlations with increasing diatoms/dinoflagellates ratios, while lipid biomarkers (fatty acids and sterols) correlated positively with increasing diatoms/dinoflagellates ratios over the entire ranges of temperature, N and P concentrations and N:P ratios. Our results indicate that the integration of phytoplankton community structure and chemical composition provides an important step forward to quantitatively understand and predict how phytoplankton community changes affect ecosystem functions and biogeochemical cycles in the ocean.

All-In-One: Microbial Response to Natural and Anthropogenic Forcings in a Coastal Mediterranean Ecosystem, the Syracuse Bay (Ionian Sea, Italy)

“…Regarding the phytoplankton community, at Station 2 dinoflagellate abundance was on average 1.5 times higher than at control stations, while low concentrations of diatoms were found, confirming that several environmental factors-in addition to T and nutrient availability-may influence the diatom-dinoflagellate patterns and succession. The prevalence of diatoms independently on T and N:P supply ratios and a switchback towards the dinoflagellates' dominance at high T and nutrient concentrations have recently been observed [53].…”

“…Phytoplankton communities are known to influence water turbidity and the dissolved oxygen content, and, because of their responsiveness to nutrient or S changes in terms of their structure and distribution, they are regarded as sensitive proxies for several ecosystem processes [79,80]. Through symbiosis or resource competition, phytoplankton communities also interact with other planktonic components; the associations/interactions between microbial community members allow us to understand the effect of changing environmental conditions on ecosystem functioning [53,81]. Within the phytoplanktonic community inhabiting the Syracuse bay, dinoflagellates prevailed throughout the study period and, occasionally, diatoms in summer at marine stations; moreover, the negative association found between these two taxa could be explained by the high optimal N/P ratio of dinoflagellates in contrast to the low optimal N/P ratio that favors the growth of diatoms, by the different mechanisms of nutrient uptake [81].…”

Forecasting Prorocentrum minimum blooms in the Chesapeake Bay using empirical habitat models

“…Finally, the negative relationship with dissolved phosphorus complies with Li et al (2015) who showed that P. minimum blooms are associated with low phosphate concentrations in the Chesapeake Bay. Bi et al (2021) also found a negative relationship between the ratio of particulate organic nitrogen to particulate organic phosphorus and diatom to P. minimum ratio.…”

Soil legacy nutrients contribute to the decreasing stoichiometric ratio of N and P loading from the Mississippi River Basin

“…The level of eutrophication and resulting hypoxia reflect relative inputs of N, P, and silica (Si) over space and time (Justić et al, 1995; Turner et al, 2006). High N and Si inputs favor the production of large, rapidly sinking phytoplankton species, while higher relative P inputs promote small, slower sinking dinoflagellate communities (Bi et al, 2021; Glibert et al, 2011; Guo et al, 2014). However, how the decreasing N:P loading ratio would impact harmful algal blooms is still unclear and calls for more studies.…”