6 Summary and outlook
In relation to the investigated traits we identied several trade-os that provide insight
into the variety of survival strategies. The agellar force arrangement in biagellates
was related to a trade-o between swimming speed and hydrodynamic stealth on one
side and advective prey capture on the other, which demand dierent force arrangements
to be optimised (paper II). For a swimmer like Heterosigma akashiwo with
one transverse and one longitudinal agellum we can think of a trade-o between net
translational and rotational velocity depending on the distribution of forces between
the two agella, where the translational velocity can be related to propulsion, while
the rotational velocity might have dierent purposes and advantages for prey search
and capture that still need to be explored (paper I).
Filter feeders with constant driving forces seem to have developed lter spacings
that balance the lter permeability and the prey size range to optimise feeding rates
(paper III). Another general trade-o seems to exist between maximum force and
maximum power, or between maximum tension and maximum frequency of biological
motors. In lter feeders a force limit seems to dominate the overall scaling of clearance
rates. On the other hand, many choanoagellates seem to use vane-like structures on
the agellum, thus investing more force in slow motion, instead of moving a naked
agellum with less force, but higher frequencies to produce the needed clearance rate.
An important physical trade-o for planktonic lter feeders is the one between biomass
density and body size (paper IV). Large organisms need to be gelatinous, or dense
organisms should be small to lter-feed eciently.
For interception feeders we relate sloppiness, which comes with a decreased foraging
eort, to the reduction of capture rates. Organisms with a higher foraging rate capture
larger amounts of prey. However, even with innite eort in total absorption, the prey
encounter rate is limited by the physical prey transport and thus makes very high
absorption eciencies less lucrative.
The goal is to include the identied traits and trade-os into the research scheme of
the Centre for Ocean Life, i.e., we would like to connect to the Models, Nature and
Function themes in order to properly contribute to the predictive trait-based approach
discussed in section 1.1.
In order to relate agellate swimming modes to dierent trophic strategies one could
use grazing experiments together with kinematic and morphological observations. Are
biagellates with equatorial force arrangements specialised in photosynthesis or nonadvective
prey capture and thus focus on swimming and stealth as proposed? It is
hypothesised that prey capture is often only used to supplement additional nutrients
instead of carbon Nygaard and Tobiesen, 1993. Under which circumstances do haptophytes
and other mixotrophic organisms supplement their acquired carbon with carbon
from particulate prey? One could test the strategies of dierent agellates by grazing