Climate change is affecting nearly every aspect of our marine ecosystems, from thce very water itself to every type of biodiversity; this will continue and magnify over the coming decades and centuries. Historically, marine wildlife has been degraded by overharvesting, bycatch, habitat destruction, pollution and invasive species. Climate change impacts have been underway in our seas for decades, but only recently have they been noticed. The dramatic changes underway due to climate change act in tandem with all the other pressures, and some exacerbate each other. Here we present the top issues in relation to climate change and marine ecosystems.

1) Increasing Sea Temperature:       
-Decreasing Ice at the Poles: In September of 2005 the Arctic sea ice extent (area covered) was the least ever recorded by satellites. The Met Office in the UK predicts that by the 2080s, there may be no summer sea ice at all, under the high emissions scenario.
-Huge range shifts have been documented in temperate regions and are associated with a halving of critical plankton biomass in some areas. Extinctions are also predicted.
-Bleaching coral in the tropics: The 1997/98 ENSO bleaching event certainly got everyone’s attention in the tropical reef community. However, since then bleaching is becoming more common place and reefs continue to suffer as a result. In 2005, waters in the Caribbean were hotter for longer than ever before measured by regional monitoring systems. This resulted in dramatic bleaching throughout the region, from Colombia to the Florida Keys. Only this year’s record breaking hurricane activity limited additional bleaching. This bleaching also led to outbreaks of coral disease.

2) Decreasing Marine pH – the other CO2 problem:
Half the world’s industrial CO2 has already dissolved into the oceans and in the past few years the huge buffering capacity of the oceans has been outstripped; consequently, the ocean have become more acidic as CO2 turns into carbonic acid in sea water. By 2050, it is predicted that the seas will be more acidic than at any time in the last 25 million years. This has dramatic implications. Acidic conditions make it more difficult for organisms to form their protective calcium based shells. Particularly vulnerable species include corals and plankton, which form the basis of the world’s entire marine ecosystems. All gill breathing animals may also be affected by increased CO2. Warmer and less productive seas will be less able to absorb CO2, so exacerbating climate change further.

3) Shifting Currents:         
Dramatic current changes are linked to climate change, including the thermohaline circulation, or global conveyer belt, which is already thought to be slowing down. There are countless other marine currents which are sensitive to global warming. Such currents run upwelling patterns that exchange nutrients and oxygen and are critical to biodiversity and marine productivity. In the past year several upwelling locations have shutdown as waters warm.

4) Methane Hydrates:
Methane crystals in the marine and coastal environment pose a potentially huge additional contribution to climate change. Methane is 20 times more potent as a greenhouse gas than CO2 and huge reserves exist within our seas and coasts. Releases from marine and coastal reserves could cause abrupt climate changes. Some release of methane from melting coastal permafrost is thought to be underway already.

5) Rising Sea Level:
This means that coastlines change as water levels rise, inundating regions, and in some areas, whole nations and millions of people’s homes and livelihoods will be lost. Elsewhere, changing effects from storm surges and introducing, in some cases, pollutants from coastal industry and waste sites.  Habitats and species will face additional challenges. For example, marine turtles will lose more, already limited, nesting beaches. This also means that more of the world is marine, resulting in limited marine conservation funds being stretched further.