Preprint volume - SIBM

Pre-print Volume - Oral presentations
Topic 2: MARINE ORGANISMS AND ECOSYSTEMS AS MODEL SYSTEMS
Materials and methods – Experiments characterising physiological parameters were
designed to examine individual tolerance, adaptive mechanisms and ecological
relevance in the field. Tolerance: Cell burst assays recorded species survival following
exposure to a severe (10‰ S) hypo-osmotic treatment throughout the first 48h of
development. Species survival was assessed following a period of induced desiccation
and re-immersion into natural seawater. Adaptive Mechanisms: Cell volume
measurements monitored volumetric changes occurring at within zygotes during and
immediately after mild (15‰ S) hypo-osmotic exposure. Sub-lethal effects of hypoosmotic
exposure were tested by exposing zygotes to several dilute salinity
concentrations over varying lengths of exposure time, measuring the ratio between
length/width growth over seven days. Field studies: involved both manipulative and
descriptive experiments. Manipulative experiments transplanted laboratory released
zygotes to high, mid and low shore levels for 24h. Descriptive sampling monitored the
supply of propagules versus percentage recruitment. Wild fucoid embryos were
identified to species level using a pioneered technique relying on auto-fluorescence
using confocal microscopy and ratio image analysis identification.
Results – Tolerance: Resistance to hypo-osmotic shock varied throughout
development in all three fucoid species. Inter-specific differences in tolerance were
also apparent. Embryos of the high shore alga, Fucus spiralis, as expected burst
significantly less than the mid shore, F. vesiculosus, and low shore, F. serratus,
embryos respectively when given the same hypo-osmotic treatment. Fucoid embryos
also encountered hypo-osmotic stress after a period of desiccation followed by reimmersion
to seawater. Bursting was highest among embryos from the low shore (F.
serratus) with survival increasing respectively in F. vesiculosus and then F. spiralis.
Adaptive Mechanisms: To examine mechanisms, we looked at volume control during
mild stress exposure the high shore alga, F. spiralis, exerted considerable control over
its internal volume preventing rhizoid apex swelling. However, when re-immersed in
natural (32‰ S) seawater, F. spiralis expressed ion loss as a function of drastic rhizoid
shrinking. The mid shore species, F. vesiculosus, demonstrated negligible fluctuations
to its internal volume both during exposure and following re-immersion to seawater, no
significant swelling or shrinking. The low shore species, F. serratus, possessed little
internal volumetric control, swelling considerably during exposure and once reimmersed
returned to a volume comparable prior to exposure. Burst characterisation
indicated that the mid shore species, F. vesiculosus, possesses a high internal pressure
despite not swelling prior to bursting, suggesting that cell walls may be reinforced in a
thickening process. Assessing the sub-lethal effects following various exposure
regimes, higher shore species (F. spiralis and F. vesiculosus) exhibited a negative
response in terms of length/width growth compared to low shore species (F. serratus).
Field studies: Manipulative field sampling showed survival to be highest among higher
shore species, F. spiralis and F. vesiculosus, and lowest survival recorded among low
shore species, F. serratus at all shore levels. Wild embryos of all three Fucus species
could be identified on the basis of their autofluorescence properties. Descriptive field
sampling indicated a significant export of low shore species’ (F. serratus) propagules
to higher shore levels; similarly higher shore species’ (F. spiralis and F. vesiculosus)
propagules were also being supplied to lower shore levels. Higher shore species exhibit
41 st S.I.B.M. CONGRESS Rapallo (GE), 7-11 June 2010
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