ELFT HÍRADÓ

[szpl <szpl AT metal.elte.hu>]

ELTE Fizikai Intézet

                                ORTVAY KOLLOKVIUM

                    2015. október 15., csütörtök, 15:00-kor
                Az ELTE Pázmány Péter s. 1/A alatti épületében
                           földszinti 0.81 előadóban

                                Ulrike Feudel
        (Institute for Chemistry and Biology of the Marine Environment
         Carl von Ossietzky University Oldenburg, Oldenburg, Germany)

        "Harmful algal blooms: combining excitability, competition
                            and hydrodynamic flows"


Kivonatos ismertetés:
Harmful algal blooms (HABs) are rare events which are characterized by a 
sudden large abundance of potentially toxic plankton species which can 
alter the dynamics of the whole ecosystem. Since as a consequence of 
climate change, the frequency of HABs is increasing, there is a strong 
need in understanding the possible causes for such bloom events. The 
phenomenon itself will be introduced and possible essential factors for t
he emergence of HABs will be discussed.

To develop a model which mimics basic properties of HABs and includes 
different environmental and biological factors we use ideas which are 
inspired by neuron dynamics describing a neuronal excitation. In neurons, 
this excitation is a result of an interplay between an activator and an 
inhibitor leading to the formation of a neuronal pulse. For HABs the 
activator is the phytoplankton – the plants of the ocean – forming the 
pulse-like bloom, while the inhibitor is the zooplankton grazing on 
phytoplankton. While many models of HABs focus on the growth of a single 
species, we discuss the emergence of such blooms from the perspective of 
plankton communities. This involves the competition between toxic and 
non-toxic species as well the preference of grazing zooplankton for 
certain species. We show how the interplay of the competition and 
environmental factors like increasing nutrient input result in a sudden 
growth of toxic species. Our models based on experiments reflect several 
features of HABs in nature.

Hydrodynamic flows are also important determinants for the emergence and 
the spread of HABs in the real ocean. Analzying data from observations in 
the Southern California Bight we demonstrate, that particularly mesoscale 
hydrodynamic vortices are of crucial importance for the spread of HABs. 
Moreover, such vortices can lead to heterogeneous dominance patterns of 
different plankton species in the ocean. We illustrate the mechanism of 
the emergence of spatially localized HABs using a simplified kinematic 
flow giving rise to appearing and disappearing vortices.