Global warming is a reality. Temperatures are rising and the consequences for the marine environment are being eagerly researched. While it is known that thermal stress affects respiration in some marine life, little is known about how it affects marine invertebrate mitochondria. Doris Abele and her colleagues have examined respiration in a mud clam that comes from an intertidal region where extreme temperature variations are normal. They found that the number of potentially damaging oxygen chemicals doubled in clams that were kept in warmer water than they normally experience(p. 1831).
Abele and her colleagues in Germany and Argentina are interested in the limits of marine animals and how warming affects their geographical distribution. `Intertidal animals are supposed to be extremely tolerant of all sorts of environmental conditions,' explains Abele. In contrast polar animals have very narrow limits. To answer their questions the researchers compare related species that come from different habitats, like the mud clams that are found in both polar and intertidal areas.
Warming seawater causes two problems for marine animals. Firstly, the temperature of marine water determines the body temperature of marine animals. When the water is warmed they quickly approach a critical temperature where their function becomes impaired. Secondly, as seawater is warmed it loses oxygen. The oxygen supply to the animals' tissues decreases and they switch to anaerobic pathways. But these can only be used for a limited amount of time before damage occurs.
So how did Abele come to be exploring the details of mitochondria? `I started out doing radical research in intertidal species,' she explains. Here`radical' refers to reactive chemicals, and respiration produces examples of these. But the cell has defensive mechanisms against such damaging radicals.`Radicals are converted into non-radical hydrogen peroxide that is then released from mitochondria,' explains Abele. Unfortunately hydrogen peroxide is toxic and more stable than the radicals and can also damage the cell.
The increased numbers of radicals that Abele found in the mud clams is a cause for concern, particularly as the limited environment of polar animals means they are more susceptible to respiratory stress. But Abele is also working on polar mud clams, and has found that the rate at which oxygen radicals are produced is very similar in both these and intertidal animals. There is still much to find out.
Abele and her colleagues now intend to concentrate more closely on oxygen radical production in intact cells of both intertidal and polar species. They also want to use more sophisticated methods to measure the role of oxygen radicals in temperature tolerance. This is a challenge considering the scale they are thinking about — Abele would like to `try to really measure the oxygen content in the tissues'. Age has also caught their interest —intertidal mud clams have only half the lifespan of Antarctic mud clams. The intertidal clams have higher metabolic rates because of the higher temperatures, so they consume more oxygen and produce more radicals. As Abele says, `radicals destroy your cells and make them age.' Who knows where the next anti-wrinkle cream could come from!