Is Climate Change Transforming Marine Ecosystems?

11/17/20222 min read

The surface of the ocean has been warmer in the past 30 years than it has been since 1880 (EPA 2021). As part of the process of climate change, marine ecosystems are experiencing significant population-level transformations.

Marine organisms are expected to interact differently with each other due to changes in their sources of nutrient and food and in the amount of light penetrating underwater (Hillebrand et al 2018).

For example, at higher temperatures, smaller cells have better nutrient absorption and growth rates compared to larger cells; this means that smaller microorganisms cope better than larger microorganisms (Hillebrand et al 2018). This means that the organisms that prey on microorganisms will receive reduced energy, and therefore transmit less energy above them in the food chain (Hillebrand et al 2018). The warmer the water, the more marine diversity is lost; for example, the reduction in cold water species and a rise in warm water species contributes to the “homogenisation of communities” (Hillebrand et al 2018).

A rise in ocean temperatures increases organisms’ metabolic rates while also reducing the solubility of oxygen in the ocean water, encouraging the growth of more sedentary organisms or those with lower metabolism. (Heneghan et al 2019). Surface warming also adds to stratification in the upper ocean, impeding the mixing of layers necessary for exchange of nutrients, thereby depriving phytoplankton nutrients from deep waters (Peng et al 2018). Trophic transfer efficiency between each level of the food chain is also negatively impacted by the decreased net primary production, heat-driven migration, and long-term damage from extreme weather events (Heneghan et al 2019).

Warming also encourages the proliferation of harmful algal blooms (EPA 2022) which produce toxins and deplete oxygen (EPA 2022).

As organisms react and adapt differently (if at all) to ocean warming, there is a disruption of the balance of interactions between species, between predator and prey, and across the ecosystem (Hillebrand et al 2018).

Impacts are differentiated between species because they adapt and respond to ocean warming in different ways.

Organisms adapt using three primary methods – “physiological acclimatization, selection from standing genetic variation (favouring genotypes with higher optimal temperature) or novel mutations” (Hillebrand et al 2018). The second mode, also known as phenotypic plasticity, is a long-term variation in behaviour and other characteristics (Hillebrand et al 2018). Organisms from temperate or coastal areas, who are able to withstand a wider temperature, range can employ phenotypic plasticity more effectively in comparison to tropical or polar organisms which have a smaller range of tolerance (Hillebrand et al 2018). Larger and more complex species take longer time to modify themselves genetically (Hillebrand et al 2018). species which are the most vulnerable to extinction also include “ecological specialists” and those with smaller populations and “longer generation cycles” as well as (Hillebrand et al 2018).

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