Biogenic acidification reduces sea urchin gonad growth and increases susceptibility of aquaculture to ocean acidification

Decreasing oceanic pH (ocean acidification) has emphasised the influence of carbonate chemistry on growth of calcifying marine organisms. However, calcifiers can also change carbonate chemistry of surrounding seawater through respiration and calcification, a potential limitation for aquaculture. This study examined how seawater exchange rate and stocking density of the sea urchin Tripneustes gratilla that were reproductively mature affected carbonate system parameters of their culture water, which in turn influenced growth, gonad production and gonad condition. Growth, relative spine length, gonad production and consumption rates were reduced by up to 67% by increased density (9 to 43 individuals.m-2) and reduced exchange rates (3.0 to 0.3, but survival and food conversion efficiency were unaffected. Analysis of the influence of seawater parameters indicated that reduced pH and calcite saturation state (ΩCa) were the primary factors limiting gonad production and growth. Uptake of bicarbonate and release of respiratory CO2 by T. gratilla changed the carbonate chemistry of surrounding water. Importantly total alkalinity (AT) was reduced, likely due to calcification by the urchins. Low AT limits the capacity of culture water to buffer against acidification. Direct management to counter biogenic acidification will be required to maintain productivity and reproductive output of marine calcifiers, especially as the ocean carbonate system is altered by climate driven ocean acidification.

Ocean Acidification

The oceans are big – 70% of the Earth surface. Scientists often thought they were just too big for humans to really affect them very much. But then they discovered that carbon dioxide emissions were changing the chemistry of the oceans, making them more acidic. The rate of change may be faster than at any other time in the last 300 million years. Corals and shellfish are already affected.


Ocean acidification expressed as global mean surface ocean hydrogen ion concentration from a suite of models (CMIP5) based on observations of atmospheric CO2 until 2005 and thereafter RCP8.5.
SOURCE: James Orr, LSCE/IPSL, France; Bopp et al. 2013 and IPCC Fifth Assessment Report, Working Group 1, Chapter 6 (Ciais et al. 2013).

Marine Fish Capture

For many decades marine fish capture increased dramatically with an average growth rate greater than population growth. It has levelled off in the last decade, but this is largely because fish stocks are depleted. The industry is shifting to aquaculture.


Global marine fishes capture production (the sum of coastal, demersal and pelagic marine fish species only), i.e., it does not include mammals, molluscs, crustaceans, plants etc. There are no FAO data available prior to 1950.
SOURCE: Data is from the FAO Fisheries and Aquaculture Department online database (FAO-FIGIS 2013).

Shrimp Aquaculture

Aquaculture is an indicator of how coasts are changing. Mangroves and other natural protective sea barriers are being replaced with vast stretches of aquaculture. Around 89% of world aquaculture is in Asia, and this is dominated by China.


Global aquaculture shrimp production (the sum of 25 cultured shrimp species) as a proxy for coastal zone modification.
SOURCE: Data is from the FAO Fisheries and Aquaculture Department online database FishstatJ (FAO 2013).

Nitrogen To Coastal Zone

It is estimated that industrial fertilizers are responsible for one third of the global population. However, in many places, farmers use more fertilizer than they need. It runs off the land into waterways and coastal zones causing vast dead zones. Fertilizers are essential to feed the world population, but to feed seven billion they need to be managed carefully to avoid unintentional consequences.


Model-calculated human-induced perturbation flux of nitrogen into the coastal margin (riverine flux, sewage and atmospheric deposition).
SOURCE: Mackenzie et al., 2002.

Tropical Forest Loss

The rainforests are precious ecosystems essential to the functioning of our planet. They harbor a rich diversity of life, they drive weather systems and they absorb carbon dioxide. There is a real risk rainforests like the Amazon may cross tipping points leading to widespread collapse of the rainforest environment and a move to more savannah-like conditions.


Loss of tropical forests (tropical evergreen forest and tropical deciduous forest, which also includes the area under woody parts of savannas and woodlands) compared with 1700.
SOURCE: Julia Pongratz, Carnegie Institution of Washington, Stanford, US; Pongratz et al. 2008. AD 1700 to 1992 is based on reconstructions of land use and land cover (Pongratz et al. 2008). Beyond 1992 is based on the IMAGE land use model.

Domesticated Land

Humanity uses an area the size of South America to grow crops and an area the size of Africa for livestock. There are now very few truly wild areas left. Even unmanaged woodlands or verges are within a mosaic of managed land. Better agricultural technologies and less easily available fertile land means this curve is beginning to bend in a more positive direction.BIO_Domesticated_Land

Increase in agricultural land area, including cropland and pasture as a percentage of total land area.
SOURCE: Julia Pongratz, Carnegie Institution of Washington, Stanford, US; Pongratz et al. 2008. AD 1700 to 1992 is based on reconstructions of land use and land cover (Pongratz et al., 2008). Beyond 1992 is based on the IMAGE land-use model.

Terrestrial Biosphere Degradation

Thousands of species of animal, plant and microorganism are either extinct or dying out. Entire ecosystems are being destroyed. Some scientists say Earth is approaching mass extinction rates. In the past this has often been caused by a massive external event like the asteroid impact that wiped out the dinosaurs. This time, one species is responsible: humans.


Percentage loss of terrestrial mean species abundance relative to abundance in undisturbed ecosystems as an approximation for degradation of the terrestrial biosphere.

Source :1.