Ocean acidification: climate change at the sour end

A few weeks ago, I overheard a 58 year old man telling a 12 year old boy that the most dire of scientists' warnings concerning global warming over the past 30 years had failed to materialise - and that what the boy needed to learn was to be able to separate facts from propaganda.

Although it is no doubt next to impossible to be able to change such entrenched mindsets as those of this particular baby boomer, there is still extremely limited public understanding of the insidious changes currently taking place in our oceans. In addition to the rise in both sea temperature and sea level (approaching a centimetre every two-to-three years) a rapid increase in ocean acidity is now on course to profoundly disrupt marine life.

With the USA pulling out of the Paris Agreement, will the rest of world manage to pull together in order to prevent another tipping point? After all, increasing ocean acidification isn't something us non-marine scientists can directly observe. One key point that is immediately obvious is that it isn't a localised issue: as a third of atmospheric carbon dioxide is absorbed into the oceans, all the planet's seas will be affected. The decrease of 0.1pH unit in the past few centuries equates to an astonishing 26-29% increase in acidity. What's more, this change is predicted to have doubled by the end of this century. Clearly, the effect on marine life is set to be substantial.

So what is being done to assess the probable issues? Various projects around the world are using mesocosms - transparent cylinders up to ten metres long - to understand the effects of current and predicted near-future acidity levels on marine life. Coral bleaching is possibly the one condition people will have heard of (although there appear to be an astonishing number of people who think that coral is a plant rather than invertebrate animal) but sea temperature changes are as much a cause as increased acidity. Apart from causing stress to some marine organisms, leading to such conditions as lowered immune systems and so the spread of disease, acidification reduces the material available for shell and carapace formation, especially for juveniles and nauplii.

The problem isn't so much the change itself as the rate of change, which is far faster than normal geophysical processes. Indeed, one report states that over the past 20 million years, changes in oceanic acidification have been barely one percent of the current rate. Obviously, there is minimal chance of the non-directed mechanism of natural selection keeping pace with adaptations to the new conditions.

While many organisms will suffer, some such as jellyfish and toxic algae may benefit, with the latter leading to the poisoning of key fishing industry species. This in turn could lead to toxins entering the human food chain, on top of the economic issues from the decline in fish and shellfish stocks. Indeed, the US Pacific coast aquaculture industry is already experiencing a reduction in the shellfish populations. This will be in addition to the pollution of fresh waterways already explored in a post last year.

Of the various experiments aiming to understand the impact of the rapid increase, the largest project is the pan-European Biological Impacts of Ocean Acidification (BIOACID) scheme. Giant mesocosms sunk in a Swedish fjord have been sealed with local ocean water (and associated organisms) and half of them modified with the projected pH level.

Similar but small projects are underway in New Zealand and the Canary Islands, with preservation of edible stocks a key priority. Another problem with a decline in shellfish species destined for human consumption would be the loss of the raw material for chitosan, which may prove to be an ecologically-friendly replacement for plastic packaging.

Clearly, there could be numerous - and some as yet unknown - knock-on effects from the ocean acidification. Unlike the rise in atmospheric temperature, it is much more difficult to see the results of this fundamental change and for the public to understand the consequences. Yet again, the life forms affected are far from the cute poster species usually paraded to jump-start the public's environmental consciousness. Unfortunately, these may prove to be far more critical to the future of humanity and the wider world than say, giant pandas or Amur leopards. It's time for some serious sci-comm to spread the warning message!

Our feline friends - not so miaowvellous after all?

I've published a few posts concerning citizen science, from the active participation in conservation-orientated projects here in New Zealand to the more passive involvement in distributed computing projects that I briefly mentioned back in 2012.

A type of public involvement in scientific research half way between these examples has been developed to utilise the human ability to match up patterns, a skill which artificial intelligence is only just beginning to replicate. One early implementation of this was the Galaxy Zoo crowdsourced project, in which volunteers examining photographs taken by robotic, Earth-based telescopes to classify galaxies. Since 2009, the Zooniverse online portal has utilised more than one million volunteers to examine data on behalf of over fifty projects, many of which are within STEM disciplines.

Although initially often used for astronomy or astrophysics programmes, crowd sourcing platforms have latterly found an important role in conservation and biodiversity research. An example is the Smithsonian Institute-sponsored eMammal, which specialises in the examination of camera trap footage to identify the locations of animal species on a scale that could not obtained by other means.

In line with the outcome of the perhaps too ambitious Predator-free 2050 programme, one project that may require the assistance of the Zooniverse volunteers is analysis of feral cat DNA from New Zealand's Auckland Island. The DNA, derived partially from fecal matter (nice), is to discover what the cats on the island are eating. Although this research aims to discover the best way to remove invasive species from Auckland Island (cats are known to predate on native seabird species) there now appears to be another issue caused by cats living near coastlines.

Over the past fifteen years a body of evidence from around the world has shown that cats are directly responsible for the deaths of marine mammals. This might sound rather unlikely, but the microbial culprit, Toxoplasma gondii, is only found in the digestive system of cats. Both feral and domestic cats that catch and eat infected rodents or birds can acquire the parasite and pass it by their fecal matter into the wider environment via fresh water run-off or sewage outfalls. Eventually, it enters the marine food chain, reaching the apex in the former of cetaceans and pinnipeds among others.

Species such as sea otters, seals, and dolphins have been killed by toxoplasmosis, according to autopsies of specimens washed up on seashores as far apart as New Zealand and the USA. Increasing temperatures (thanks again, man-made climate change) and greater rainfall can spread toxoplasmosis even further. In addition to direct contamination from fecal matter, cat owners who flush cat litter down the toilet can also start the highly resilient microbes on a journey via sewer networks to the ocean. Among the New Zealand species proven to have been killed by infection are the critically endangered Maui dolphin and locally vulnerable Hector’s dolphin, so there is definitely a need for some prompt action.

It isn't just a case of the top marine predators eating infected fish or squid: sea mammals could swallow oocysts (basically, the protozoan equivalent of a fertilised egg) directly from water. Only now that Maui dolphins are falling victim to the parasite is the story of this deadly microbe becoming better known. Not incidentally, our species can also become ill with toxoplasmosis due to exposure to cat feces, with serious consequences for babies born to infected mothers and to people with compromised immune systems. In addition to the other potential dangers from the likes of Salmonella, Listeria and E. coli, the recent fad for 'raw' (i.e. unpasteurised) milk could lead to a far higher rate of toxoplasmosis in humans.

What can be done? Well, cat owners could stop flushing kitty litter down their toilets for a start. Is it a case that there are just too many cats in the world? Some recent reports claim that Homo sapiens and their domesticated species constitute 96% of the global mammal biomass. As for cat numbers, an estimate last year suggested that there are six hundred million pet cats and the same number of feral individuals worldwide.

Is this just too many? I admit that I'm fairly biased as it is: a few cat owners I know here in Auckland have pets that regularly kill skinks and it's only luck that these are invasive rainbow skinks rather than rare native species. When it comes to the likes of the last 55 Maui dolphins falling prey to a disease spread by an extremely common domesticated species, I'd rather be over-zealous than over-cautious in developing a solution. As far as I can see, the best control methods would be a vast reduction in cat numbers or the development of an innoculation for our feline friends that can kill the parasite. Somehow I doubt either course of action is likely, which means a far from purrfect method would be to educate cat owners as to how to minimise the spread of Toxoplasma gondii. So if you are a cat owner, or know of one, I guess this could be your time to shine...