Future of the Marine Life: a study with multiple storylines

Climate Change has been influencing the past and present biodiversity variations extensively. Marine species distributions are known to be directly related to environmental factors. Insights from observational studies as well as theory revealed that marine species respond to an increase in ocean temperatures by altering their depth and latitudinal range. However, these changes could result in the disruption of marine biodiversity and ecosystems which can lead to invasions and local extinctions. A review of the recent literature on quantitative analysis of the Climate Change on distributional variations on marine communities proceeded to reveal that the majority of the reviewed papers focus on the regional changes in specific regions including; North Atlantic, Northeast Pacific, and the Mediterranean.

While local impacts of climate change on marine biodiversity has been studied extensively in various regions, the global patterns have never been under the microscope of science until recently. A study conducted by William et al (2009) has investigated the global patterns of marine biodiversity changes lead by three different Climate Change scenarios.

3 Scenarios:

The study carried out, included three climate scenarios of greenhouse gas emissions with climate projections related to each level, generated by the Geophysical Fluid Dynamics Laboratory of the U.S. National Oceanic and Atmospheric Administration.

1st scenario was the “720 ppm stabilization experiment” which was based on a world with rapid economic growth as well as the rapid introduction of new and efficient technologies and a low population increase. The scenario assumes a moderate use of available resources will continue to take place balanced with the use of appropriate technologies. In the 2nd scenario, named the “550 ppm stabilization experiment”, predictions were based on a world with low population growth. The use of cleaner energy and less stress on natural resources was the focus of the scenario which would result in a significant decrease in carbon dioxide levels in the atmosphere compared to present values. The “Committed Climate Change Experiment” is the low- range scenario of the study, where it is assumed that the climate change forcing agents ie. Greenhouse gas emissions would be stabilized by the end of 20th-century levels through the 100-year duration of this experiment.

How to Project?

Species turnover is known to be able to affect community structures, biodiversity and ecosystem functions of a habitat. The average frequency of species invasion and local extinctions were calculated in 30 x 30 m cells for 20 year period between 2040 and 2060 concerning the average calculations from the time range of 2001-2005. The regions impacted by climate change were identified for 2050. Through the study, 1066 species samples were used and distribution change of these species was projected using a dynamic bioclimate envelope model for each climate scenario.

What’s in store?

The study concluded that global species turnover patterns were generally dominated by species invasion as a result of range shifts of species. While the species invasions are predicted to be concentrated in high latitude regions including Arctic and Southern Ocean, local extinctions were observed to be at peak in tropical waters. Biodiversity in high latitudes is known to be highly sensitive to climate change as, overall, polar species are up to 4 times more sensitive to temperature changes compared to tropical species. Model projections revealed that an increase in temperature can lead to narrowing of polar species latitudinal boundaries resulting in local extinctions. Besides, an expansion of low latitude species range with the increasing high latitude temperatures is observed to result in intense invasions in polar regions.

Figure 1: "Predicted distribution of biodiversity impact due to the warming-induced range shifts. Biodiversity impact is expressed in terms of (a) invasion intensities; (b) local extinction intensity and (c) species turnover for the 1066 species of fish and invertebrates in 2050 relative to the mean of 2001-2005 (high-range climate change scenario). Intensity is expressed as proportional to the initial species richness in each 30` x 30` cell."

83% of the species showed a positive poleward shift for high-range climate change projections for the 20 years between 2040 and 2060. The range of poleward shift was observed to be lower for low-range climate change projections which concluded a percentage of 79 for species with a positive poleward shift. The global average rate of range-shift under the climate change scenarios was projected to be 45-59 km per decade.

Polar range expansion of species being dependent on suitable habitat availability within the region can lead to range contraction which would further affect biodiversity. In semi-enclosed seas where the dispersal of species was constrained by land, including the Mediterranean Sea and the Red Sea, high local extinction rates were observed. Furthermore, sea surface and bottom temperatures were predicted to rise at a faster rate compared to open seas leading to more local extinctions.

Is it representative?

Through the study, several assumptions and approximations were made including the uncertainties associated with current distribution maps. Furthermore, anthropogenic effects on marine populations were not captured within the project as the effects of ocean chemistry changes which are predicted to have negative impacts on marine habitats and biodiversity.

The scenarios of the study were generated based on a coupled atmosphere and ocean model, where projections based on different models may lead to variability in results.

What does it all mean?

The study is one of the first quantitative projections of global marine biodiversity alterations concerning climate change. The study brings the potential scale of the problem into the stark focus of policymakers as well as the general public. While the study achieves to form a representative projection of the possible changes in biodiversity, the magnitude of projections could be uncertain as a result of the complexity of processes involved.

To conclude, climate change is known to be a threat to the environment and biodiversity. Numerous studies conducted on marine biodiversity have shown us localized disasters that are bound to happen if we didn’t force change. This study is one of the many studies that are acting as “wake-up” calls for humanity to try and save the living.

Notes from the blogger:

This post was inspired by the study "Projecting global marine biodiversity impacts under climate change scenarios" conducted by William et al. (2009). The study could be accessed via this link.

Scientific term definitions are available.