Climate change, together with industrial and habitat-destructive fishing, pollution, and coastal urbanisation, has led to a sustained decrease in fish stocks over the last decades (Golden et al. 2016, Bayramoglu et al. 2019). With more than three billion people depending on marine biodiversity as a major source of food, understanding the consequences of human activity on the ocean is crucial for global food security (Sala et al. 2021).
This is particularly relevant for low- and middle-income countries, as their populations are heavily reliant on fish for nutrition. Across the globe, fish represents 17% of all animal proteins that are consumed. In low- and middle-income countries, this percentage reaches an average of 26%, with peaks of 50% or more in Southeast Asia and in small island developing states (Figure 1).
While a large body of evidence on climate change describes the socioeconomic consequences of atmospheric events inland, the impact of what is happening offshore has received little attention. Anthropogenic emissions of CO2 are transforming the ocean. Water acidity has been increasing since the Industrial Revolution – a phenomenon known as ocean acidification. In addition, global sea surface temperatures have risen, and the ocean’s oxygen content has dramatically decreased.
While all these factors are central for marine life, knowledge about the overall effect of climate change on fish stocks is still limited (Doney et al. 2020). Growing evidence, especially archaeological, points to a decrease in fish survival (see, for instance, Bottjer 2012, Hendry 2014, Nagelkerken et al. 2016).
Figure 1 Contribution of fish to animal protein supply
Notes: Select Demographic and Health Surveys countries are those selected in Armand and Kim Taveras (2021). Source: authors’ calculation using FAOSTAT database (FAO 2021).
New evidence shows impact of ocean acidification on developing countries
Coastal communities in developing countries have few nutritional alternatives. The consumption of macro- and micronutrients contained in fish is essential (FAO 2020). These can be especially vital during pregnancy because nutrient deficiencies can contribute to fetal growth restrictions – the main cause of neonatal deaths (Black et al. 2013).
Our recent study tests this hypothesis on a global scale by focusing on ocean acidification (Armand and Kim Taveras 2021). We study how in utero exposure to varying levels of ocean acidification in the closest waters influences early-childhood mortality and development in low- and middle-income countries. By homogenising information from the Demographic and Health Surveys, the study focuses on more than 1.5 million live births between 1972 and 2018 across 36 developing countries in Africa, Asia, and Latin America.
The ocean’s acidity significantly affects neonatal mortality – the probability that a child will die during their first month of life. An increase in 0.01 units in the ocean’s acidity while in utero increases neonatal deaths by approximately two deaths per 1,000 live births in communities living near the ocean’s shore. The size of this effect is nontrivial if we consider that a 0.01 change in acidity is equivalent to roughly one-sixth of the average increment in acidity experienced by sampled areas from 1972 to 2018, or just 3% of the predicted increase by the end of the 21st century by the Intergovernmental Panel on Climate Change (2013).
Rather than persisting over time, this effect gradually decreases beyond the first month of life. Among living children, those that experienced higher acidity in utero tend to have better anthropometrics and a lower probability of morbidity. However, no effect on contemporaneous nutrition indicators is recorded. These results suggest that ocean acidification leads to death harvesting among children, such that mortality is more prevalent among the weakest children.
Is maternal nutrition driving these results?
Increases in neonatal deaths in relation to acidification are mostly felt by communities where fish is an essential nutritional source. The largest effect is observed at the shore, while it vanishes as the distance from the ocean increases (Figure 2).
Figure 2 Impact of acidification on neonatal mortality by distance from the ocean’s shore
Dotted lines represent the confidence interval at 90%. Beyond that, confidence intervals are progressively shaded up to the 99% confidence interval. The colour intensity of the area is a function of the number of observations, with darker colours indicating larger number of observations. Source: Armand and Kim Taveras (2021).
If the mechanism behind this relationship is a reduction in fish availability, it follows that acidification would have a greater impact in places where commercial fishing has depleted fish stocks. In fact, for developing countries, marine capture from this activity is mainly feeding the international market and is rarely consumed where it is caught (Pauly and Zeller 2016). Using data about the number of hours industrial fishing vessels spend at specific locations allows us to identify areas characterised by higher versus lower pressure from commercial fishing.
The effect of acidification on neonatal mortality is indeed larger where commercial fishing is more intense, indicating a close relationship between the effect of climate change and over-exploitation of the ocean for commercial purposes (Figure 3). The same heterogeneity is not observed when we instead focus on the presence of vessels used for local fishing activities.
Figure 3 Effect of acidification on neonatal mortality, by intensity of industrial fishing
Notes: Intensity of industrial fishing is computed from the Global Fishing Watch (Kroodsma et al. 2018). Confidence intervals are built using a 90% confidence level. Source: Armand and Kim Taveras (2021).
Many models predict that ocean acidification will have dire consequences on the fishing industry and, thus, economies in the future. However, its impact on socioeconomic development is already present and measurable. While the United Nations (2019) underlines the priority for economic development to “conserve and sustainably use the oceans, seas and marine resources for sustainable development” (Sustainable Development Goal 14), the magnitude of these effects demands a much faster response among policymakers to protect the ocean and its resources from over-exploitation.
The ocean’s health and maternal malnutrition are closely related in the coastal areas of low- and middle-income countries. More importantly, communities in the poorest parts of the world lack the proper tools to mitigate the consequences of climate change. In fact, parental investments in child health do not adapt to a varying ocean acidification. Antenatal and delivery care are not affected, nor are breastfeeding practices (Armand and Kim Taveras 2021). Targeting nutritional support programmes to the most vulnerable communities, where acidification and overfishing are worst, could potentially reduce neonatal mortality.
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