Blast from the past

This blog is going to focus on the latest research into how previous climate events changed the ecology of oceans, and how this knowledge could help predict what will happen in modern oceans in the near future.

Harnik et al. (2012) believe the past is key to understanding the present and future ecological state of the Earth's oceans. By looking at how organisms change and adapted in previous periods of climate change, we may be able to identify patterns that can be applied to modern ocean ecology. While extinctions in the ocean are less well known that the extinctions of say, megafauna on land, there is evidence of such occurences in fossil records. Today, the changes in ocean temperature and chemistry caused by global warming are amplifying the problems we were already having in the ocean such as over-exploitation and habitat degradation. There are already regional declines in the abundance of some at risk groups such as corals and tuna. Therefore the myth that ocean extinctions do not occur needs to be addressed so we can discover what species may be at risk.

Below is figure 2 from the paper, which compares extinction rates between fossil, historical and modern species. The median of fossil extinction rates is shown by the dot in a, and the interquartile range represented by the line. Historical extinction rates are divided between global and local in b, and modern extinction risk of assessed species is show in c, with red showing endangered and yellow showing vulnerable with a line to show the upper and lower limits of the estimate. One issue with  the modern species assessment is that very few marine animals have been classified, therefore some taxon are missing an entire estimate for this factor.

Figure 2 from Harnik et al.

This figure would appear to show that there have been significant periods of marine faunal extinction in the past and that we are currently in such a period now. Discrepancies in the data limit how useful it is for predicting the outcomes for different groups of species, for example fossil extinction rates for invertebrates are well known because invertebrate fossils are well preserved due to containing biomineralised elements, however there is no current risk assessment for some of these groups which could be crucial because they are typically near the base of the foodweb and therefore represent a key diet constituent for larger organisms.

Table one in the paper shows that there are more current threats to extinction that there have ever been before, with acidification, anoxia, warming, habitat loss, over-exploitation and pollution affecting species' chances of survival. There is significant uncertainty over how all the threats together may increase and interact to the detriment of the species. One thing we are certain of though is that the stresses will interact with one another to bring about extinctions, and so further study is required here.

The paper finds that data from all 3 time spans will need to be integrated to produce a prediction of future extinction risk. The future risk of extinction of producers and primary consumers such as plants and invertebrate species could be found using projections from the strong fossil record. It is also thought that resilience to extinction may be related to genetics, and therefore past vulnerability of species could help give predictions of current and future risk. In the past, warming, anoxia, and acidification have driven extinctions, therefore the fossil record can also be used to find how certain species respond to climatic and environmental change. The fossil record indicates that at a times of large-scale environmental change, small geographical range was the greatest risk factor for extinction, suggesting that a similar relationship may occur in present and future climate change. Historical and fossil data could also provide observed data which can be compared with the outputs of model moderns to assess their reliability in predicting species extinctions, especially since the models have not been proven to work for adaptive marine ecosystems.

Overall, I feel that this paper provides clear, logical suggestions for how different historical records and present day assessments can be combined to predict future extinction risk for marine species. I like that it only considers marine species, because in doing so it recognises that this unique ecosystem requires its own specifically tailored models and predictions. However I do feel that the paper is fairly generalised, and seems to deal fairly briefly with the seemingly important fact that there are huge differences between taxon of the extent of fossil and historical records and modern assessment, especially seeing as this is crucial for applying information from ancient extinctions to the modern.