35 Climate change Trends and Impact on Marine Organisms

As a result of the burning of fossil fuels coupled with habitat destruction including deforestation and clearing of mangrove and saltmarsh which releases stored carbon, carbon dioxide concentrations have increased at an increased rate, leading to anthropogenic climate change. Carbon dioxide concentrations are higher than have been seen previously in history and are increasing at an alarming rate (Figure 1; Figure 2). Impacts of climate change on the marine environment include: ocean acidification impacting calcium carbonate structure organisms and internal organs; behavioural changes; decreased oxygen concentrations; reducing habitat forming species; altered food web dynamics; range shifts of organism often poleward or deeper to previously cooler climates; changes in growth and reproduction of organisms; increased severity of disease outbreaks; coral bleaching and other impacts of marine heat waves (Hoegh-Guldberg and Bruno, 2010; Assan et al., 2020). Temperatures have increased by approximately 1 degrees Celsius since industrialisation began.

Images and data (Trends in CO₂, CH₄, N₂O, SF₆) provided by NOAA Global Monitoring Laboratory, Boulder, Colorado, USA (https://gml.noaa.gov), measures are for mean carbon dioxide measured at Mauna Loa Observatory, Hawaii. Content is in the public domain.

Global temperature change over time

Open the link, and check out Global Climate Change – Climate Spiral (1880 – 2022), then watch the video below to see how global temperatures have changed over time.

Climate change impact on marine organisms

Climate change is anticipated to affect organisms including their individualism, the scope and structure of their populations, the species construction of communities, and the structure as well as the functioning of ecosystems. Effects include poleward or high-altitude shifts in the distribution of ectothermic animals (Spies et al., 2020). All aquatic ecosystems, comprising of freshwater bodies, coastal estuarine habitats as well as marine ecosystems are influenced by climate change (Beck, 2018; Hewitt et al., 2016). According to previous studies, relatively small changes in temperature modifies the metabolism and physiology of aquatic animals, such as fish, resulting in difficulties in growth, fecundity, feeding behaviour, distribution, migration as well as abundance (Mir et al., 2019; Nagelkerken & Munday, 2016; Portner et al., 2017; Rael et al., 2020). However, the impacts of climate change have been revised and shortened for freshwater and marine ecosystems (Hewitt et al., 2016; Rosenzweig et al., 2007).

‘Bleached Coral Reefs at Byron Bay, Australia’ by Oscar Trisley used under a Pexels License

Climate change has led to the adjustments in the distribution of invertebrates, vertebrates, and also plant species, in terms of the timing of their cyclic activities and their physiological responses in both aquatic and terrestrial environs (Beaugrand & Kirby, 2018; Gilg et al., 2017; Root et al., 2003; Rosenzweig et al., 2007; Sunday et al., 2015), these include marine zooplankton and fish (Beaugrand & Kirby, 2018; Spies et al., 2020). According to literature and recent analyses, threats are imminent and predictions are being made on climate warming in the next decades (Smith et al., 2007). Esia-Donkoh (2017) specified that an increase in temperature of 2˚C to 3˚C above pre-industrial levels is expected to place predictably 30% of plants and animal species at high risk of extinction, while key changes in the structure and function of marine and extra aquatic ecosystems are foreseen, and in current eras, these changes are taking place and if precautions are not put in place they will intensify, triggering more species to go extinct.

Recent models have projected a 0.2˚C increase in the mean worldwide temperature per decade in the next 2 decades and 1.8˚C – 4˚C increase by the year 2100. According to Poloczanska et al. (2016), aquatic ecosystems are prone to the effects of climate change globally. This is because, the vast majority (>95%) of aquatic species are ectotherms, in other words, poikilothermic. Poikilotherms body temperature changes with that of the environment which, results in the adjustments of the rates of all physiological and biochemical reactions and steadiness of biological molecules (Bonachea, 2019; Heuer et al., 2019).

Examples of effects of climate change on marine organisms include:

• Species Distribution and Abundance of Marine Organisms
• Change on Growth and Reproduction of Marine Organisms
• Disease Outbreak on Marine Organisms

(Assan et al., 2020)