Oceanography | Vol. 38, No. 3
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reproduction, photosynthetic efficiency, behavior, predator-prey
interaction, chemical signaling and sensing, epigenetics, and much
more. There have been a number of attempts, using meta-analyses,
to group responses by organism type (Kroeker et al., 2013; Alter
et al., 2024), trophic level, and/or geographic location (Busch and
McElhany, 2016; Hu et al., 2024). These results have been used to
discuss socioeconomic impacts, such as those on fisheries and
aquaculture (Barton et al., 2015; Narita and Rehdanz, 2017) as well
as on human health (Falkenberg et al., 2020).
Some of the varying responses to OA can be accounted for by
experiment duration (short-term experiments having more of an
acute effect than longer-term acclimation experiments; e.g., Form
and Riebesell, 2012) or by the method of acidification used (Hurd
et al., 2009). These inconsistencies led to the development of com-
munity best practice guides (Riebesell et al., 2011) designed to
promote more robust ongoing and future research that would be
repeatable and useful for meta-analysis. It also led to the OA-ICC
providing two online databases: a bibliographic database that can
be shared using Zotero or pCloud, and a database on the impacts
of ocean acidification on marine organisms.
Researchers also need to consider spatial variation in marine
ecosystems: how organisms have acclimated and adapted to their
environments, and what this means for their responses to future
change (e.g., Lewis et al., 2013; Vargas et al., 2022). Short-term,
local fluctuations can result in different responses for marine
organisms that are exposed to them compared to organisms
exposed to less variable environments (e.g., Mangan et al., 2019;
Lowder et al., 2022).
HOW GOAL 2 SUPPORTS mCDR RESEARCH
Understanding ecosystem responses is fundamental for evalu-
ating the ecological implications of mCDR techniques. Research
on OA provides insights into the vulnerabilities of various species
and habitats to changing carbonate chemistry, helping to predict
which life stages, species, or habitats to focus on first in mCDR
impact studies, or helping to generate risk analyses for species
responses (Bednaršek et al., 2025). For example, early life stages
are likely to be most sensitive, and both calcifying and photosyn-
thetic organisms have additional energetic requirements for main-
taining internal physiology against shifting carbonate chemistry
in surrounding seawater. Calcifying and photosynthetic organ-
isms may respond to mCDR conditions, especially at the point
source of the activity, because of their direct reliance on compo-
nents of the carbonate system. Understanding the dynamics of any
discharge plume and its dilution moving away from the source
will be important for determining the exposure, and therefore the
vulnerability, of organisms and ecosystems. Additionally, fluctu-
ating exposure to plumes could result in different responses than
continued exposure.
In the case of seaweed cultivation and nutrient fertilization, it
will be critical to understand how large-scale farming or nutrient
additions or removals might affect a variety of ecosystems, not
just the immediate ecosystem being manipulated. Large-scale cul-
tivation or nutrient addition could alter habitats and biodiversity,
shift nutrient availability (cause nutrient “robbing”), and alter the
deep-sea environment. The GOA-ON community is again useful
here as it is not solely focused on the surface ocean, but members
also study the interior and deep ocean and their ecosystems. Use
of the latest biological mapping methods combined with sensitiv-
ity analysis from the OA community could be transformative in
assessing potential habitat and ecosystem vulnerabilities to dif-
ferent mCDR interventions.
Clarity in the methods used to change the carbonate chemis-
try, as well as how impacts to organisms are measured, is vitally
important to make sure experiments and field studies are com-
parable. A highlight from the OA community has been the prin-
ciple that experiments should be reported clearly and conducted
according to published best practices, allowing results to be col-
lated for data transparency (OA-ICC, 2023) and metadata anal-
yses. The production of a guide to best practices for ocean alka-
linity enhancement (Oschlies et al., 2023), with input many
GOA-ON members, is a positive step toward creating a coor-
dinated research effort. While there is an understandable need
to focus on key marine organisms for experimental purposes,
understanding the consequences of any ecosystem-scale impacts
is more complex and ties into the need to co-develop modeling
and monitoring processes. Determining these complex inter-
actions exemplifies the need for a community approach to con-
sider impacts from multiple angles using multiple techniques.
Organisms are exposed to multiple stressors, and changes in
carbonate chemistry can act with other variables synergistically,
additively, or antagonistically (Secretariat of the Convention on
Biological Diversity, 2014). For mCDR research, key questions in
preparation for experimentation will be whether to test impacts
individually or in combination with other stressors, which can
be informed by the existing body of OA research, such as that
developed by the SCOR Changing Ocean Biological Systems
working group.
Finally, the biology working group of GOA-ON has devel-
oped a conceptual framework for the biological monitoring
needed to be able to attribute observed changes in the field to OA
(Widdicombe et al., 2023). In addition to the GOA-ON biologi-
cal working group, a number of other groups are looking at estab-
lishing biological indicators for OA (e.g., Bednaršek et al., 2019).
These activities are useful to consider for mCDR, in particular
for identifying potentially vulnerable species, which can then be
mapped to determine where they may be at risk of impact or ben-
efit from mCDR. For instance, for environmental MRV, consid-
ering specific biological indicators that are known to respond to
changes in carbonate chemistry could be useful for monitoring
impact at mCDR field trials (and if mCDR techniques are scaled).