Ocean acidification

A shrinking problem

Acid seas mean smaller, more vulnerable oysters

IN THE clear blue coastal waters of California lives a much cherished mollusc. The Olympia oyster, sought for its rich taste, brings millions of dollars into the local economy. But these oysters are proving useful in other ways too. They have drawn the interest of scientists who want to study how species react to a change that is happening in the oceans.

The change in question is acidification. When carbon dioxide dissolves in water, it makes that water acidic. And as CO2 levels rise in the atmosphere they rise in the oceans too. This could be a problem for creatures like oysters that have shells made of calcium carbonate, a chemical which tends to dissolve in acid.

Recent years have seen reports of the thinning of marine organisms’ shells, but the consequences are unknown. A group of biologists led by Eric Sanford of the University of California, Davis, set out to put that right. As they report in the Proceedings of the Royal Society, they looked in the laboratory at how CO2-enriched seawater affects the growth of Olympia oysters, and how that, in turn, affects the molluscs’ attractiveness to predators—specifically carnivorous snails called Atlantic oyster drills, which, as their name suggests, really belong on America’s east coast but which have invaded the Pacific, too.

Dr Sanford and his colleagues raised the larvae of wild-caught oysters in tanks of filtered seawater for 20 days, and raised oyster drills from eggs in a similar way. Both predator and prey were therefore still juveniles (the oysters’ shells had an area of less than a square millimetre).

Some of the tanks the researchers used were filled with normal seawater while others contained seawater with twice the usual amount of CO2 dissolved in it. The acidity of the world’s oceans is expected to double by 2100, so the second set of tanks contained an approximation of what the sea will be like at the end of the century.

Acidity did indeed affect the oysters’ growth, but not in the way the researchers expected. Both groups’ shells were equally thick, but animals raised in acid water were 30-40% smaller than their confrères.

Even though the acid-raised oysters were smaller, when the snails were given a choice they ate almost 50% more of them than of snails raised in normal water. Why, is not clear. Perhaps their shells, though just as thick, were weaker. Acid-raised snails, though, were just as successfully predatory as the others. Dr Sanford thinks that is because the rasping part of an Atlantic oyster drill’s tongue is made not of calcium carbonate but of chitin—a sugar-based polymer unaffected by mild acids.

Natural ecosystems are, of course, much more complicated than a two-species laboratory experiment. But if Dr Sanford’s results are reflected in the real world as its seas become more acidic, then that is bad news for gourmets—and for all the other animals that like to wait until oysters are a reasonable size before they eat them.

From the print edition: Science and technology

Article analysis.

Article taken into consideration comes from the famous weekly "The Economist", a specialized magazine treating a variety of themes, ranging from the local and the global economy, to any kind of art, recently developed technologies and the latest scientific discoveries. Knowing the origin of the product, the reader expects the discussion of an unusual topic, but especially the use of a specific language.

The article title is preceded by the field of interest of the subject, always present in the online version of this weekly. The two terms constituting the loop allow the one who is viewing the page to immediately understand that we will talk about an environmental issue ("Ocean"), more particularly a problem related to acidification of water ("acidification" which refers to the increase of acidity of ocean water). The actual title of the article, made ​​more visible due to different formatting, attracts the attention of the casual reader as it does not specify anything about the subject dealt: the phrase "A shrinking problem" could refer to anything in science suggested by the eyelet. By the time the reader knows only that it will speak about a problem with the oceans and the increased acidity in their waters, so it is aware only of the central theme of the product. This lack of specific lead to the creation of expectations in the mind of the intelligent reader; he might wonder if it will discuss the problems caused by the acidity on marine organisms or on man-made structures, which impact would the acidity bring in the two fields and whether there were conducted some studies on the subject. The first question is answered directly in the subtitle: the central topic, the influence of the acidity of the water on marine organisms, especially oysters, is soon made ​​known to the reader.

The article consists of an argumentative text type nonlinear: even before the introduction is in fact a picture portraying the protagonist of the research reported below, which allows any person visits the page of the website to understand what the article sets out immediately, without even the need to go and read the caption.

Under the picture comes the article divided in eight sections, each with its own specific function:

- The first serves as an introduction: the field of interest will be the study of the consequences that changes in the ocean have on organisms through the consideration of Olympia oysters;

- The second introduces the point of the increase in acidity, providing a scientific explanation of what is meant by acidity, and the problematic character that this has on the oysters;

- The third shows the existence of a study directed by Eric Sanford of the University of California, about the impact on oysters and what they entail in the context of their relationship with predators, snails called Atlantic oyster drills;

- The fourth clarifies the presence of an experiment conducted with animals of both species of young age;

- The fifth exposes the methods of animal growth (one part in normal water and one part in water with double acidity);

- The sixth and seventh paragraphs illustrate the consequences of the abnormal growth condition reported, respectively, on oysters and snails;

- The last section presents the conclusion drawn by the journalist after consideration of the results of the experiment.

In light of the considerations just mentioned, it is possible to say that the article follows a basic structure composed of three sequences:

- The first includeing the first three paragraphs and comprising the introduction to the general of the problem treated;

- The second going from the third to the seventh paragraph and describing all the details about the experiment;

- The third consists only of the last paragraph and attributable to the conclusion expressing the deductions made ​​by the author based on what detected by the experiments and his personal opinion.

Regarding the syntax, the item is made ​​up of short periods each showing different information about the topic but not directly connected to the previous or next to it through connectors: each period is a separate but the issues discussed are closely related. As regards vocabulary, the writing uses a basic vocabulary understandable by anyone, but it also brings specific data derived from scientific studies, they too exposed in a very simple way.

As every article in "The Economist" the article concludes with an ironic statement by the journalist, who puts in his reflection a joke about the fact that the increase in acidity in the waters of the oceans is not detrimental to the organizations in those waters are forced to live, but to other animals and food lovers that usually expected that oysters have reached a certain extent before eating them.