Intraspecific variation in the thermal tolerance of microscopic giant kelp (Macrocystis pyrifera) sporophytes was tested using
a common garden experiment, where 49 unique family-lines were raised under four different water temperatures (12, 16,
20, and 24°C). The unique family-lines were taken from ongoing giant kelp gametophyte cultures held at IMAS, and represented
F1 offspring from seven 'selfed' individuals collected from 6 sites across ~250km in Tasmania, Australia, in addition to
a site-level cross from each of the sites, and a panmictic cross using the 42 pure family lines (i.e. 42 + 6 + 1 = 49).
There are preliminary data from the first run of the experiment. The experiment is currently being re-run to validate the
Intraspecific variation in thermal tolerance of microscopic sporophytes was tested using a common garden experiment, where
49 unique lines were raised under four different water temperatures (12, 16, 20, and 24°C). The common garden setup consisted
of four temperature-controlled seawater baths (100 x 100 x 10 cm, length x width x depth), each containing the 49 family
lines in individual 700 mL containers filled with seawater (containers were randomly positioned within each bath, and each
bath randomly allocated a water temperature). All the baths were situated within a temperature-controlled room at 12°C, and
the 16, 20, and 24°C seawater baths heated by aquarium heaters. All seawater used was 0.2μm filtered and UV sterilised,
but had no added nutrients; in order to simulate ambient levels of nutrients from Tasmania. Each testing container was sealed
except for a seawater inlet, a filtered air inlet, and an outlet. Aeration in each was achieved by constant gentle bubbling
from a common air source, whilst every container within an individual seawater bath was connected to a single 25 L temperature-controlled
header tank (i.e. one header tank per temperature treatment). Every ~48 hours the header tanks were opened, and each container
received ~500 mL of new seawater (with excess seawater overflowing from the outlet of each container).
The family lines were introduced to the individual containers as gametophytes seeded onto a single ~10m spool of AlgaeTwine
per container, and fertilised at the common temperature of 12°C, to remove any effect of temperature on fertilisation success.
At this initial stage, each water bath was illuminated with blue fluorescent lighting on a 12:12 light/dark cycle for 14
days, followed by an additional 14 days of illumination under blue and white light fluorescent lighting. Following development
to the very early sporophyte stage over this period, the temperature in each bath was adjusted to the experimental temperature
at a rate of ~2°C every 24 hours (thus the 24°C water bath took 6 days to reach the experimental temperature). At this point,
the experiment was considered to have begun.
Sporophytes were allowed to grow for ~15 weeks, until visible. A 10mm subsample of the twine was then taken from each container,
and all visible sporophytes were counted under a compound microscope at 20 x magnification.