Biology Reference
In-Depth Information
Fig. 17.6
Photosynthetic
performance and growth of
floating
Macrocystis pyrifera
maintained under different
temperature and light
conditions in outdoor
mesocosm experiments.
Figure modified after
Rothausler et al. (
2011c
)
studies in outdoor mesocosms confirmed that floating individuals of
M. pyrifera
lost
biomass at water temperatures
20
C. A rapid disintegration of the algal thalli was
observed at 24
C, where all algae sank after 5 days, even in treatments without
grazers (Rothausler et al.
2009
). Similarly, floating persistence of temperate
A. nodosum
and
F. vesiculosus
from the southwestern North Sea was reduced at
water temperatures
>
15
C due to high losses of biomass (Vandendriessche et al.
2007a
). At equatorial latitudes in the Atlantic, John (
1974
) documented floating
individuals of
A. nodosum
that were small (
>
0.5 m long) and not particularly
robust. Possibly, high water temperatures are responsible for the rapid demise of
floating algae in these oceanic regions. Besides temperature, also desiccation may
affect the physiological functioning and thus the disintegration of algae, but this
effect probably depends on the degree of buoyancy of each algal species (Thiel
et al. unpublished).
Suboptimal water temperatures can also affect the reproductive activity of floating
algae (Macaya et al.
2005
;Roth
<
ausler et al.
2009
)(Fig.
17.7
). Along the Chilean
Pacific coast, in situ sampling and mesocosm experiments with floating
M. pyrifera
confirmed the absence of reproductive tissues (sporophylls) at low latitudes, while at
higher latitudes many rafts had fertile sporophylls (Macaya et al.
2005
). The authors
inferred that unfavorable sea surface conditions, such as water temperatures
€
20
C,
at low latitudes are responsible for the observed pattern. Overall, results imply that
low water temperatures (and possibly also winter conditions) favor the persistence
and reproductive success of temperate species at the sea surface, which consequently
have higher potential for long-distance dispersal.
Contrary to meropelagic rafts, the tropical holopelagic
S. natans
and
S. fluitans
in the Sargasso Sea have growth optima and thus an optimal persistence at
>
