Geoscience Reference
In-Depth Information
CHAPTER 7
Effects of ocean acidii cation
on benthic processes, organisms,
and ecosystems
Andreas J. Andersson, Fred T. Mackenzie, and Jean-Pierre Gattuso
7.1 Introduction
2007 ), and upwelling ( Feely et al . 2008 ; Manzello
et al . 2008) that may provide important clues to the
impacts of ocean acidii cation on benthic processes,
organisms, and ecosystems.
The objective of this chapter is to provide an over-
view of the potential consequences of ocean acidii -
cation on marine benthic organisms, communities,
and ecosystems, and the major biogeochemical
processes governing the cycling of carbon in the
marine benthic environment, including primary
production, respiration, calcii cation, and CaCO 3
dissolution.
The benthic environment refers to the region dei ned
by the interface between a body of water and the
bottom substrate, including the upper part of the
sediments, regardless of the depth and geographi-
cal location. Hence, benthic environments, their
organisms, and their ecosystems are highly variable
as they encompass the full depth range of the oceans
with associated changes in physical and chemical
properties as well as differences linked to latitudi-
nal and geographical variation. The effects of ocean
acidii cation on the full range of different benthic
organisms and ecosystems are poorly known and
difi cult to ascertain. Nevertheless, by integrating
our current knowledge on the effects of ocean acidi-
i cation on major benthic biogeochemical processes,
individual benthic organisms, and observed char-
acteristics of benthic environments as a function of
seawater carbonate chemistry, it is possible to draw
conclusions regarding the response of benthic
organisms and ecosystems to a world of increas-
ingly higher atmospheric CO 2 levels. The fact that
there are large-scale geographical and spatial differ-
ences in seawater carbonate system chemistry (see
Chapter 3), owing to both natural and anthropo-
genic processes, provides a powerful means to eval-
uate the effect of ocean acidii cation on marine
benthic systems. In addition, there are local and
regional environments that experience high-CO 2
and low-pH conditions owing to special circum-
stances such as, for example, volcanic vents (Hall-
Spencer et al . 2008 ; Martin et al . 2008 ; Rodolfo-Metalpa
et al . 2010 ), seasonal stratii cation (Andersson et al .
7.2 The effect of ocean acidii cation
on major biogeochemical processes
7.2.1
Photosynthesis and primary production
The depth of the euphotic zone, i.e. the depth of
water exposed to sufi cient sunlight to support pho-
tosynthesis, varies depending on a range of factors
affecting the clarity of seawater, including river
input and run-off to the coastal ocean, upwelling,
mixing, and planktonic production. Benthic pri-
mary producers include micro- and macroalgae and
seagrasses (Gattuso et al . 2006 ). Some organisms,
such as corals and foraminifera, can host within
their tissues symbiotic algae that contribute to ben-
thic primary production in certain environments.
Photosynthesis reduces CO 2 using energy cap-
tured from the sun in order to produce organic
material in the form of sugars. Most, but not all,
autotrophs produce oxygen as a by-product of the
process of photosynthesis. Because dissolved CO 2
122
 
 
 
 
Search WWH ::




Custom Search