Banca de QUALIFICAÇÃO: EWALDO LEITÃO DE OLIVEIRA JÚNIOR

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
DISCENTE : EWALDO LEITÃO DE OLIVEIRA JÚNIOR
DATA : 07/11/2017
HORA: 14:30
LOCAL: Sala de reuniões do DECOL
TÍTULO:

Grazer controls on phytoplankton dynamics – copepods reduce toxic-filamentous cyanobacteria biomass and size

PALAVRAS-CHAVES:

tropical zooplankton, Notodiaptomus iheringi, Thermocyclops decipiens, predator-prey dynamics, Cylindrospermopsis raciborskii, competition, allelopathy, artificial food-webs

PÁGINAS: 21
GRANDE ÁREA: Ciências Biológicas
ÁREA: Ecologia
RESUMO:

Selective grazers feed on most edible prey releasing less edible prey from competition. Zooplankton copepods are selective grazers that demonstrate active selection for nutritious eukaryotic phytoplankton and rejection for toxic cyanobacteria, and this mechanism is likely to contribute to cyanobacteria bloom and dominance. Moreover, in tropical environments, copepods commonly co-occur with cyanobacteria blooms, raising the question whether they can facilitate cyanobacteria dominance. Thus we experimentally tested the effects of two groups of copepods with different feeding modes – calanoid Notodiaptomus iheringi (feeding current) and cyclopoid Thermocyclops decipiens (ambush feeders) – on the competition of an eukaryotic phytoplankton Cryptomonas and the filamentous cyanobacteria Cylindrospermopsis raciborskii. First, growth rates of Cryptomonas and Cylindrospermopsis were compared in single and co-cultures in different ratios to assess for competition in batch cultures for ten days. We found no decrease in growth rates in controls and treatments, despite initial differences in algal ratios. Further, we assessed grazing on 1L batch co-cultures for seven days, starting with 10-fold initial dominance of Cryptomonas. During the experiment, dominance was reversed to Cylindrospermopsis at day 2, showing preference for Cryptomonas cells. However, at days 4 and 7, grazers fed on Cylindrospermopsis filaments, decreasing both biomass and filament size. N. iheringi had a stronger impact on Cylindrospermopsis biomass at final day, jointed with reestablishment of Cryptomonas biomass. T. decipiens, though initially rejected Cylindrospermopsis at day 2, fed on both phytoplankton similarly throughout the rest of the experiment. Despite differences on body size, both zooplankton shredded cyanobacteria filaments, reducing filament size in ~70%. These findings suggest little rejection by copepods for filamentous cyanobacteria, and may not facilitate their dominance. Instead, in nature, mechanisms other than selective grazing by copepods are benefiting filamentous cyanobacteria bloom and dominance. Yet significant reduction on cyanobacteria biomass is surprising, and more grazing studies of tropical copepods on filamentous cyanobacteria are necessary.

MEMBROS DA BANCA:
Interno - 1714892 - ADRIANO CALIMAN FERREIRA DA SILVA
Presidente - 1345773 - RENATA DE FÁTIMA PANOSSO
Interno - 1177742 - RONALDO ANGELINI