Rising acid levels may make sea sediments more toxic
13 February 2013
recent report by Cefas scientists found that ocean
acidification, caused by climate change, could result in sediments
contaminated with metals becoming more toxic and harming the
animals that graze on that sediment.
The study looked at crustaceans that feed on the surface of
sediments from dredged ports and estuaries.
"The combined effect on these animals, of coping with adapting
to climate change as well as increased toxin levels, could prove to
be fatal," said Dave Sheahan, a senior Cefas researcher on the
Cefas already monitors
dredged sediments from industrialised estuaries for poisonous
metals. Such areas are regularly dredged to maintain harbour
entrances, and the excess material is tested for toxicity.
In the laboratory, burrowing crustaceans that normally graze on
the surface of sediment were placed in a tank with dredged material
from one of these sites. The creatures were then exposed to current
sea conditions as well as acid levels predicted for the next 50 and
100 years. The animals that survived ten days in these tanks were
then tested to see if they incurred DNA damage.
The animals experienced significant
DNA damage, which rose with acidification levels, suggesting that
when acidification is combined with metals in sediments it can be
The study also showed, however, that as the toxicity of ingested
metals rises, animals are sometimes able to adapt their behaviour
to cope with such changes.
Dr Silvana Birchenough, senior benthic ecologist and co-author
of the study, described how "initially you can see the distinct
burrows they made, but after treatment there was less activity:
some species just sat on top without moving much. This showed us
how some organisms may be able to move more or less to regulate for
these changes. So there could be a trade-off in behaviour."
The scientists may now find that certain species' are less
tolerant, or even some genotypes within species are better able to
tolerate changes. So, over time, species that cope less well may
face stiffer competition from groups of animals that are more
Cefas will continue to work in this area, focusing
on commercially important crustaceans like lobsters and crabs.
They will be assessed to see if those creatures are also
exposed to contaminated sediments.
Birchenough continued: "There's a commercial importance on where
we think the major exposure routes are. In our study we focused on
two aspects: whether contaminated sediments and changes in ocean
acidification will affect animals in the marine environment, and
whether the tests we do will help us to make a judgement about
sediments that we currently deem okay."
Currently, if toxicity in dredged sediments falls below a
predetermined threshold they are considered safe to deposit in the
sea. However, rising ocean acid levels may put more stress on
animals, on top of the metal toxicity, meaning that current
threshold values would need to be changed to make sure all marine
animals, including crustaceans, are protected.
- Laboratory tests on the amphipod, Corophium volutator,
were conducted to determine whether it would respond to the
combined effects of increasing CO2 levels and
- Amphipods were exposed to two test sediments - one with
relatively high metals concentrations and control sediment with
lower contamination - under conditions that mimic current and
projected ocean acidification conditions (390-1140 atm p
- The data demonstrated the clear potential for near-future
acidification to increase the susceptibility of benthic ecosystems
- Paper: Roberts, D A, Birchenough, S N R,
Lewis, C, Sanders, M B, Bolam, T and Sheahan, D (2013), Ocean
acidification increases the toxicity of contaminated
Global Change Biology, 19: 340-351.