Effects of increased CO2 concentration on nutrient limited coastal summer plankton depend on temperature

Increasing seawater temperature and CO2 concentrations both are expected to increase coastal phytoplankton biomass and carbon to nutrient ratios in nutrient limited seasonally stratified summer conditions. This is because temperature enhances phytoplankton growth while grazing is suggested to be reduced during such bottom-up controlled situations. In addition, enhanced CO2 concentrations potentially favor phytoplankton species, that otherwise depend on costly carbon concentrating mechanisms (CCM). The trophic consequences for consumers under such conditions, however, remain little understood. We set out to experimentally explore the combined effects of increasing temperature and CO2 concentration for phytoplankton biomass and stoichiometry and the consequences for trophic transfer (here for copepods) on a natural nutrient limited Baltic Sea summer plankton community. The results show, that warming effects were translated to the next trophic level by switching the system from a bottom-up controlled to a mainly top-down controlled one. This was reflected in significantly down-grazed phytoplankton and increased zooplankton abundance in the warm temperature treatment (22.5°C). Additionally, at low temperature (16.5°C) rising CO2 concentrations significantly increased phytoplankton biomass. The latter effect however, was due to direct negative impact of CO2 on copepod nauplii which released phytoplankton from grazing in the cold but not in the warm treatments. Our results suggest that future seawater warming has the potential to switch trophic relations between phytoplankton and their grazers under nutrient limited conditions with the consequence of potentially disguising CO2 effects on coastal phytoplankton biomass.

Temperature-dependent phenology of Plutella xylostella (Lepidoptera: Plutellidae)

Temperature-dependent population growth of diamondback moth (DBM) Plutella xylostella (L.), a prolific insect pest of crucifer vegetables, was studied under six constant temperatures in the laboratory. The objective of the study was to predict the impacts of temperature changes on the population of DBM at high-resolution scales along altitudinal gradients and under climate change scenarios. Non-linear functions were fitted on the data for modeling the development, mortality, longevity and oviposition of the pest. The best-fitted functions for each life stage were compiled for estimating the life table parameters of the species by stochastic simulations. To quantify the impacts on the pest, three indices (establishment, generation and activity) were computed using the estimates of life table parameters and temperature data obtained at local scale (current scenario 2013) and downscaled climate change data (future scenario 2055) from the AFRICLIM database. To measure and represent the impacts of temperature change along the altitude on the pest; the indices were mapped along the altitudinal gradients of Kilimanjaro and Taita Hills, in Tanzania and Kenya, respectively. Potential impact of the changes between climate scenarios 2013 and 2055 was assessed. The data files included in this database were utilized for the above analysis to develop temperature dependent phenology of Plutella xylostella to assess current and future distribution along eastern African Afromontanes.