International Journal of Marine Science 2016, Vol.6, No.27, 1-22
20
coastal waters of Ghana usually linked with upwelling periods as documented by Koranteng, 1995; Minta, 2003
and Djagoua et al., 2011. None of the ocean acidification indicators and parameters was found to relate with
abundance of
Sardinella larvae
from the CCA biplot (Figure 15), however, it is inconclusive to say that ocean
acidification does not impact
Sardinella larvae
, and thus requires further investigation in the future.
Decapod larvae, mainly of families Peneaidae and Portunidae were however found to relate well with carbonate
ion concentration, pH and the Revelle factor from the CCA biplot (Figure 15). Species of these families which
include
Peneaus notialis
and
Callinectes sapidus
identified in the artisanal fishery can therefore be said to
susceptible to ocean acidification, and could thus be a factor to low abundances of adult
Peneaus notialis
and
Calinectes sapidus
species observed in the artisanal fishery (Table 5). The result is in support of the report from
Vezina and Hoegh-Guldberg, 2008 and Doney et al., 2009 which anticipates that larvae of calcifying organisms
are highly susceptible to ocean acidification.
5 Conclusions
This study has shown that ocean acidification is possibly occurring in Ghanaian waters, as evidenced by
decreasing pH, decreasing carbonate ion concentration, decreasing calcite and aragonite saturation states,
decreasing total alkalinity and increasing Revelle factor. Secondly, evidence has been provided that ocean
acidification has possible impacts on the abundance and diversity of fish species landed by the artisanal and
semi-industrial fisheries in Ghana. Finally, although it is not clear whether ocean acidification parameters are
impacting on abundance and diversity of adult species of crustaceans, there is evidence that this could occur with
their larvae.
In the light of observed ocean acidification and its impacts, it is recommended that efforts should be sustained to
gather long term data on ocean acidification and fish diversity in Ghanaian coastal waters. The effort should
include instituting an ocean acidification observance programme to effectively monitor changes in seawater
carbonate chemistry and ocean acidification parameters. These datasets could be used to develop a bioclimatic
model to further predict future impacts of ocean acidification on fish diversity in Ghana and for the Guinea
Current Large Marine Ecosystem. It would be useful to undertake tissue analyses of fish species to ascertain the
uptake of carbon by fish species found to be impacted by ocean acidification. Finally, further studies on impacts of
ocean acidification on ichthyoplankton should be undertaken to inform the dynamics of abundance of fish stocks.
Acknowledgements
We are grateful to the International Atomic Energy Agency for funding this project, under the Co-ordinated Research Project (CRP)
number K41012 and Contract number 17539. We also thank Messrs. J. Akomeah, E. Klubi, M. Boateng and K. Enyan, all of the
Department of Marine and Fisheries Sciences, University of Ghana, for their assistance on the field and in the laboratory.
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