‌‌Ocean acidification has been described as “the other CO2 problem”.  Like its better-known counterpart, climate change, it is caused by rising levels of carbon dioxide in the atmosphere.  Ocean acidification is already happening, yet we still know little about its impacts and implications.

Picture:  zooplankton at different stages.  A full-grown adult of the species studied, Acartia tonsa, is only 1 mm.

The team, based at the Centre for Sustainable Aquatic Research (CSAR) at Swansea University, and working with colleagues at Plymouth Marine Laboratory, studied a common species of zooplankton, the copepod Acartia tonsa.  These tiny creatures measure around 1 mm – the same size as the base of the letter “Z” in the name of the Queen on a 1p piece.

Watch BBC coverage of the research team at work

Previously, research by others, based largely on adult females, has suggested that copepods are not affected by ocean acidification. However, the Swansea team, looking at all stages of the life cycle – from eggs through to adulthood – reveal that this is not so. They examined how the creatures reacted to different levels of CO2 in seawater: from present-day levels to higher concentrations based on different projections for the future.

The researchers found:

•    Mortality rates increased across all ages in response to higher levels of CO2

•    Young zooplankton (known as nauplii) were the most vulnerable – they had a threefold increase in mortality when exposed to “near-future” levels of CO2

•    Fertility was also affected by rising CO2

•    Copepods “are not as resilient to the effects of ocean acidification (…)  as once perceived”

 Read the research paper

Picture: Gemma Cripps with Professor Kam Tang, both of Swansea University College of Science, studying zooplankton in Swansea Bay, aboard RV Noctiluca, the University’s research vessel‌

Gemma Cripps, PhD researcher at CSAR and lead author of the paper, said:

"Our results show how important it is to look at all stages of the life cycle.  Previous research, which has largely focused only on adult females, risked underestimating the effects of ocean acidification on zooplankton.

Zooplankton are the foundation of the whole food chain in the ocean, for example as a crucial food source for fish such as cod and herring.  Without zooplankton, life in the sea would not be as we know it.

Our research will help provide a better picture of how these tiny but vital creatures are responding to changes in our oceans."

‌Professor Kevin Flynn, head of CSAR, and one of the authors of the paper, said

“This research is part of a larger project on ocean acidification and commercial fisheries; led by CSAR Swansea and run jointly with Exeter and Strathclyde universities and with Plymouth Marine Laboratory.

At CSAR we explore facets of aquatic research ranging from algal biofuels, plankton ecology to fish behaviour, using techniques from molecular biology, genetics and fish nutrition through to mathematical modelling.”

Plankton facts:

•    Plankton comes from the Greek “planktos” meaning to wander or drift, referring to the fact that they are largely borne by ocean currents.

•    Plankton can be subdivided into animals - or zooplankton - plant-like phytoplankton, and the mixotrophs that combine (triffid-like) both plant and animal-like feeding.

•    Some zooplankton stay in that form for life – eg the copepods used in the research.  But some species (eg certain fish, crabs, shrimps) also go through a temporary stage of being zooplankton.

•    Some zooplankton are smaller than the diameter of a human hair; others, such as jellyfish, may exceed 1 metre in diameter.

Picture: The juvenile form (or nauplii) of Acartia clausi, a species of zooplankton.  It measures only 144 micrometers  (ie 0.14 mm).