Imagine travelling to a country where the temperature is 40°C. Sure, it would be nice at first. However, soon the high temperature would start fighting against your body. Like humans, crabs also experience a range of tolerance to temperature. This causes them to experience thermal stress, leading to behavioural and metabolic activity changes.
Since climate change has become a pressing issue, it is important to see how rising temperatures can affect the behaviour of these organisms. Earth’s average temperature has been exponentially rising and is projected to experience a 1.1°C to 5.4°C increase by the year 2100.
How does this affect organisms’ survival? Fluctuations in temperatures can cause sea levels to rise due to melting glaciers, ultimately altering the habitats of species. In particular, intertidal organisms, who live in both low and high tide lines, have evolved adaptations that help them cope with harsh and variable environments.
In my study, I investigated how the intertidal crab species, Hemigrapsus oregonensis, responds to changes in water temperatures by measuring its feeding rate. In order to determine what conditions they can tolerate, we must first consider the normal temperature in which they reside. Where do crabs like Hemigrapsus live? They prefer environments between 10°C to 11°C and often live underneath rocks where it is dark. Although they are omnivores, they mainly feed on green algae and sea lettuce such as Ulva. We know that crabs have claws which help them grasp food, but where does this food go afterwards? Crabs have outer and inner appendages which sort food so they can be chewed by the mandibles and eventually swallowed.
In my experiment, crabs were exposed to three temperatures treatments (11.5°C, 15°C and 20°C) for short and long periods of time before feeding on Ulva. Despite previous studies showing that metabolic activity increase with temperature until it reaches a saturation point, my study did not fully support this trend. While short-term acclimated crabs experienced the greatest feeding rate at 15°C, long-term acclimated crabs showed a decrease in feeding rate as temperature increased, contrary to my prediction. For both short and long temperature exposures, the feeding rate was lowest at 20°C. This indicates that this temperature may have been nearly outside their range of tolerance.
With temperature affecting the feeding rate of Hemigrapsus, it is vital to think of ways to prevent further behavioural changes. Along with human activities, greenhouse gases are being trapped in the Earth’s atmosphere, causing temperatures to rise and impact many species’ lifestyles. Seeing the impact that global warming has on humans, we must consider the preventative measures we can take to help the other species with whom we share our planet.
Watch this video to learn about how increasing temperatures are affecting the lifestyle of crab species.