Biology Reference
In-Depth Information
physiology. Currently, only one pilot study has been conducted on the calcifying
red alga
Corallina sessilis
indicating some synergistic effects of UV- and low
pH-exposure on growth, photosynthetic oxygen evolution, and calcification (Gao
and Zheng
2010
). Revealing synergisms of both environmental factors on a wider
range of marine organisms will be an important research direction, which needs to
come up in the very near future.
20.5 UV Effects on Different Life History Stages and
Implications for Reproduction and Recruitment
In recent years, UV research on seaweeds focused particularly on the potential
impacts of climate change, ozone depletion, and UVB exposure on the microscopic
reproductive stage. It has been shown for a number of the ecologically most
important species of kelp (order Laminariales and related) that the sensitivity
toward UVB radiation is highly dependent on the respective life history stage
under investigation (Dring et al.
1996
; Wiencke et al.
2006
; Roleda et al.
2007
;
M
uller et al.
2008
). Generally, the unicellular zoospores of kelps have been
identified as the developmental stage most vulnerable toward UVB exposure
(Wiencke et al.
2000
). This is amongst others based on the small sizes of spores
and thus large surface-to-volume ratios, which facilitate the penetration of harmful
radiation into the cell and thus the damage to cellular components. Another
explanation for the high UVB susceptibility of spores is provided by the level of
ploidy. With respect to zoospores and gametes being haploid stages, UVB-
mediated damage to the DNA bears even more severe consequences, as single
copy genes might be damaged without a potential substitute by a second allele, as e.
g., in the diploid sporophytes (Roleda et al.
2008
). Evidently, the impact of UVB
exposure on the reproductive success of seaweeds is determined by the most UVB
susceptible stage in the life history of a species. There is common sense that if there
will be an adverse impact of UVB radiation on seaweed communities it will be
mediated by a disruption of the developmental cycle due to pronounced damage to
the haploid, unicellular life history stages (zoospores and gametes), which will
ultimately preclude reproduction and recruitment (Roleda et al.
2007
;M
€
uller et al.
€
2008
,
2009
; Steinhoff et al.
2011b
).
Via its significance to the reproductive microstages, impacts of solar UV radia-
tion on the cellular level are closely related to effects on a community level as it
may result in, e.g., impaired release of zoospores (Makarov and Voskoboinikov
2001
) and recruitment (Wiencke et al.
2000
,
2006
; Roleda et al.
2007
). At present,
only a small number of publications describe UVR effects on cellular ultrastructure
of seaweed spores (Steinhoff et al.
2008
). UV effects observed on the ultrastructural
level include wrinkled thylakoid membranes, dilatations of the thylakoid lumen,
and disrupted mitochondria with plastoglobuli formation as well as changes of the
nucleoplasm structure (Poppe et al.
2002
,
2003
; Holzinger et al.
2004
; Holzinger
and L
utz
2006
; Steinhoff et al.
2008
; see also Karsten et al.
2009
).
€
