Ocean Acidification Impacts on Fisheries: Implications of Ocean Acidification for Shellfish

Ocean Acidification Impacts on Fisheries: Implications of Ocean Acidification for Shellfish


Hey everyone. This is Hauke Kite Powell. I’m
with the Marine Policy Center at the Woods Hole Oceanographic Institution and
we work at the Marine Policy Center on marine resource management issues
broadly including fisheries and aquaculture and marine environmental
topics including ocean acidification. I want to amplify on some of the things
that Jon and Barbel have said focusing in particular on shellfish because as
Jon mentioned they are among the most vulnerable and likely to be affected. The
reason of course is as Barbel pointed out the fact that lower pH in the ocean
makes it more difficult for calcifying organisms to build their shells and
skeletons and it particular it affects their survival in early life stages and
this is a problem not just for ecological integrity of the systems but
for human beings too who rely on these species for income and for nutrition in
many parts of the world. Calcifying shellfish like oysters make
different forms of calcium carbonates to build their shell and oysters for
example build their shells out of a form of calcium carbonate called aragonite
early on in their life and then later switched to making calcite and it
turns out that this is a problem for juvenile early life stage shellfish
because the aragonite form of calcium carbonate is less stable and more
vulnerable to dissolution in low pH environments and this is one of the
reasons why larvae and early life stage forms of shellfish are particularly
susceptible to these kinds of ocean chemistry changes.
Jon mentioned the concept of coastal acidification and this is important when
thinking about shellfish because most shellfish farming and harvesting takes
place in nearshore coastal waters and in those waters the chemistry of seawater
is much more dynamic than it is typically in the open ocean and the
reason for that is that biological activity in particular marine plant life
is heavily concentrated in the coastal ocean and plants during the day will
absorb CO2 from the seawater in the process of photosynthesizing and when they
do that they decrease the concentration of CO2 in the seawater and thereby raise
the pH. At night when the photosynthesis shuts down but other kinds of biological
respiration continue CO2 in the coastal waters rises notably and the pH declines
and so coastal waters generally have a much more variable pH regime than open
ocean waters. That variability is amplified in places where people put a
lot of additional nutrients into coastal waters because that amplifies plant
growth, in extreme cases leads to algal blooms and things like that and that in
turn amplifies the cycling of high and low pH conditions over daily and
seasonal time scales and so the coastal acidification story is more complicated
than that in the open ocean and this is relevant particularly to coastal
shellfish operations of course. There are also as both Jon and Barbel
mentioned, regional variations in these conditions. For example the Gulf of Maine
waters in New England are particularly acidic naturally already and this is an
issue not just in the near shore shellfish communities but also for
species like sea scallops which are wild and on the seabed naturally in
conditions often that are already close to the limit of what calcifying
organisms like sea scallops can tolerate and so in some of these
locations small additional changes in ocean pH could have dramatic effects in
the coming decades on the viability of those biological stocks. This is a
summary of results from lab experiments on the effect of lower pH conditions on
variety of marine species. A paper by Gledhill and colleagues and similar to
some of the results that Jon presented. Again if the calcifying organisms, the
mollusks in particular, that show the most clear pattern of negative effects.
For other species the effects are less severe or unclear but an important point
also is that people notice differences in subpopulations in the way they
respond to lower pH conditions and that may have to do with the fact that the
coastal pH regime is so dynamic and different subpopulations may adapt and
evolve in different ways in response to that.
If you look globally at sea food production, very rough numbers, you can
see that shellfish in aggregate account for about a quarter or so of the annual
value of sea food production around the world and this is just here a quick
note to illustrate the scale of the potential vulnerability of seafood
supply over the course of the coming century if conditions really become
significantly inhospitable to these animals in large parts of the
global ocean. People are looking at global models as Jon said of ocean pH
change from the present conditions to what’s likely to persist at the end of
the century and for shellfish and other marine organisms what probably matters
is the time roughly speaking where the ocean chemistry conditions
leave the envelope that these species been used to living in for the recent
historical past and the time at which that’s projected to happen in the models
varies from location to location around the globe but you can do this analysis
and see where things will change outside of the envelope that local populations
of marine organisms have been used to so to speak and you can see that these
changes will happen in most parts of the world over the course of the coming
century some places sooner and others. I want to just quickly mention two other
assessments that you may find interesting. There was a study published
recently by Sarah Cooley and colleagues on the likely effect of acidifying sea
conditions on the US scallop fishery and that includes not just the
biogeochemical analysis and the scallop biological submodel but also
a model of the fishery, the socio-economic component, that attempts
to model how the fishery would likely respond to these changes that are coming.
It includes estimates of how the scallop growth and survival will be affected by
future ocean conditions. There’s still some uncertainty about this but people
are doing a lot of experimental work now to help nail this down and what the
model, modeling efforts concluded is that certainly by roughly the middle of this
coming century we should expect to see under the RCP 8.5 emission scenario that
Jon described before, a significant effect on scallop biomass and on the
revenue of the scallop fishery from ocean acidification changes.
One other study to mention quickly is one by Ekstrom and colleagues that tries
to look at the vulnerability and the millions of fishing
communities around the United States in response to these kinds of effects and
so how well a fishing community can respond to or adapt to these sorts of
changes depends not just on the biogeochemistry and the biology of the
local fish and shellfish stocks but also the capacity of that community
technologically, economically, and socially to adapt to the to the changes
that are coming and what they find is a high degree of variability not just in
the biogeochemical and physical effect from ocean acidification but also in the
ability of, likely ability of fishing communities impacted by this to adapt
and respond. And finally you can look at that on the
global scale too. There are big differences in the extent to which
countries around the world rely on mollusk harvest for protein or for
economic value and if you combine that sort of information with the likely rate
at which conditions will change in the coastal waters of those countries and
the economic and technical wherewithal of the fishing populations there to
adapt to this, you can assess the vulnerability of different countries to
these impact in the future. So what can we do about this? I want to
just highlight 4 possible things that could be done. The first one and probably
a most general one is we should try hard to limit coastal acidification by
reducing the nutrient loading that makes eutrophication and other negative
effects happen in coastal waters and that amplifies the cycles of low pH and
low oxygen conditions in coastal waters. Those kinds of steps to limit
nutrient inputs to coastal waters can go a long way to making it easier for
shellfish species and others there to withstand the changes in broader ocean
chemistry. A second possibility particularly around shellfish farms is
to influence local water chemistry to buffer it, effectively raising the pH
around shellfish farms and one way to do that is to grow large quantities of
marine plants in the vicinity of the shellfish farms. Again these plants
absorb carbon dioxide during photosynthesis and effectively raise the
pH in the water around them so people are beginning to experiment with that,
Another possibility is to move shellfish hatcheries and farms away from the
nearshore waters where the effects are often most traumatic and low pH
conditions cause the biggest problems. Some of this has already happened in the
Pacific Northwest where some shellfish growers have moved their hatcheries out
of Puget Sound to Hawaii. And a fourth possibility is to select in
shellfish farming for populations that prove to be more resilient to low pH
and other stresses. So to summarize I think it’s pretty
clear now that ocean acidification is a significant potential threat to many
marine organisms particularly calcifying organisms including mollusks and corals.
The effects are often species and location specific so it’s difficult to
generalize about the specific things that are likely to happen. You need to
think as Jon emphasized about not just pH but multiple stressors that will
accompany climate change and we need to keep in mind the differences between
open ocean conditions and the much more highly variable coastal acidification
scenarios. The economic values globally that are potentially at risk from
effects of ocean acidification on shellfish are significant, and there are
a range of adaptation and mitigation measures that ought to be studied to see
how we can respond to this because even if the world gets serious about carbon
emissions we will be living with ocean acidification effects for the next
century at least and with that I’m going to hand it back to Cassy.

local_offerevent_note October 10, 2019

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