How does rising atmospheric CO2 affect marine organisms?

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Fish Genes and Climate from Medieval to Modern Times
Olafsdottir, G.A., Westfall, K.M., Edvardsson, R. and Palsson, S. 2014. Historical DNA reveals the demographic history of Atlantic cod (Gadus morhua) in medieval and early modern Iceland. Proceedings of the Royal Society B 281: 10.1098/rspb.2013.2976.

The authors begin by noting that Atlantic cod vertebrae have accumulated at historical fishing sites in the North Atlantic since the beginning of commercial fishing (Perdikaris, 1998; Barrett et al., 2004); and they say this has occurred in Iceland since the time of its settlement (Amundsen et al., 2005; Edvardsson, 2010). In addition, they report that estimates of species population size based on genetic modelling has improved rapidly in recent years (Hedgecock, 1994; Luikart et al., 2010), to the point, in fact, that serial coalescent framework (Rodrigo and Felsenstein, 1999) has been successfully applied to the study of historical terrestrial and aquatic animal population fluctuations (Chan et al., 2006; Campos et al., 2010; Alter et al., 2012).

What was done
Using Atlantic cod (Gadus morhua) vertebrae that they obtained from historical fishing sites in Western Iceland, Olafsdottir et al. examined the species' history of medieval-to-present genetic variation and demography.

What was learned
The four Icelandic scientists report that their findings are "consistent with an expanding population during the warm medieval period, large historical effective population size (NE), a marked bottleneck event at 1400-1500 and a decrease in NE in early modern times." In fact, they say their historical population size estimates "are extreme compared with modern-day values," but they note that historical documents cite "vast numbers of cod in the North Atlantic at the height of the European fisheries expansion to Iceland and Newfoundland (Cell, 1969; Porsteinsson, 1976)." And they also note in this regard that "previous research on Atlantic cod growth using otoliths from archaeological excavations in Norway showed disruptions of growth patterns in the early sixteenth century, best explained by a significant drop in sea temperatures (Geffen et al., 2011)."

What it means
With such a huge difference between the Atlantic cod numbers of the Medieval Warm Period (MWP) and those of the Current Warm Period (CWP), it would appear that the MWP was significantly warmer than the CWP has been to date.

Alter, S.E., Newsome, S.D. and Palumbi, S.R. 2012. Pre-whaling genetic diversity and population ecology in Eastern Pacific gray whales: insights from ancient DNA and stable isotopes. PLOS ONE 7: e35039.

Amundsen, C., Perdikaris, S., McGovern, T.H., Krivogorskaya, Y., Brown, M., Smiarowski, K., Storm, S., Modugno, S., Frik, M. and Koczela, M. 2005. Fishing booths and fishing strategies in medieval Iceland: an Archaeofauna from the Akurvik, North-West Iceland. Environmental Archaeology 10: 141-198.

Barrett, J.H., Locker, A.M. and Roberts, C.M. 2004. The origins of intensive marine fishing in medieval Europe: the English evidence. Proceedings of the Royal Society London B 271: 2417-2421.

Campos, P.F., Kristensen, T., Orlando, L., Sher, A., Kholodova, M., Therstrom, A.G., Hofreiter, M., Drucker, D., Kosintesv, P., Tikhonov, A., Baryshnikov, G.F., Willerslev, E. and Gilbert, M.T.P. 2010. Ancient DNA sequences point to a large loss of mitochondrial genetic diversity in the saiga antelope (Saiga tatarica) since the Pleistocene. Molecular Ecology 19: 4863-4875.

Cell, G.T. 1969. English Enterprise in Newfoundland 1577-1660. University of Toronto Press, Toronto, Canada.

Chan, Y.L., Anderson, C.N. and Hadly, E.A. 2006. Bayesian estimation of the timing and severity of a population bottleneck from ancient DNA. PLOS Genetics 2: e59.

Edvardsson, R. 2010. The Role of Marine Resources in the Medieval Economy of Vestfiroir, Iceland. PhD Thesis. City University of New York, New York, New York, USA.

Geffen, A.J., Hoie, H., Folkvord, A., Hufthammer, A.K., Andersson, C., Ninnemann, U. and Nedreaas, K. 2011. High-latitude climate variability and its effect on fisheries resources as revealed by fossil cod otoliths. ICES Journal of Marine Science 68: 1081-1089.

Hedgecock, D. 1994. Temporal and spatial genetic structure of marine animal populations n the California Current. California Cooperative Oceanic Fisheries Investigations Report 35: 73-81.

Luikart, G., Ryman, N., Tallmon, D.A., Schwartz, M.K. and Allendorf, F.W. 2010. Estimation of census and effective population sizes: the increasing usefulness of DNA-based approaches. Conservation Genetics 11: 355-373.

Perdikaris, S. 1998. The transition to a commercial economy: Lofoten fishing in the Middle ages, a preliminary report. Anthropozoologica 25: 505-510.

Porsteinsson, B. 1976. Tiu Porskastrid, 1415-1976. Sogufelagid, Reykjavik, Iceland.

Rodrigo, A.G. and Felsenstein, J. 1999. Coalescent approaches to HIV-1 population genetics. In: Crandall, K. (Ed.) Coalescent Approaches to HIV Population Genetics. Johns Hopkins University Press, Baltimore, Maryland, USA, pp. 233-272.

Reviewed 25 June 2014