Imagine you wanted to know how to pack for a trip to Barcelona this weekend, but the only information you had about the weather came from an air temperature sensor tucked inside a plastic shade and perched at the top of a pole 3,000 feet tall. Plus, you were only given one average temperature reading for each day. You'd probably make some grave errors in judgement when you picked out what clothes to take.
Marine ecologist Brian Helmuth did things a little differently when he wanted to understand how four species of intertidal mussels experience climate. Mussels are ectotherms that live along the seashore in places that are covered by water when the tide is high but exposed to the air and sun when the tide is low. Being an ectotherm, mussels depend on external sources for body temperature regulation such as sunlight or wind. Therefore, the tide plays an important role on the temperatures they experience. You can see one of his study species in the photograph on the right. Notice that while mussels are sedentary, meaning they don't move or behaviorally thermoregulate (like the beetle in the example above), the conditions they're experiencing keep changing with the tides—and beyond. For instance, if they get splashed by a wave during a low tide, mussel body temperatures can rapidly drop temporarily.
These "robomussels" were attached to rocks within existing mussel beds, surrounded by living mussels. Robomussels were also placed in multiple locations within sites, to capture the variable thermal conditions mussels experience as a result of differences in substrates, shading, and submersion. All this thermal variability would have been missed if Helmuth only looked at air temperatures collected by a nearby weather station. Spot the robomussel in the mussel bed (Image Credit: Alison Smith).
Researchers in the Buckley lab, where this website comes from, wanted to use Helmuth's robomussel data to ask questions about how intertidal mussels experience environmental extremes and variability. Luckily, he had been kind and smart enough to share it all freely, which is something scientists are starting to do more and more. You can look at it yourself right here. The following figures were made by Lauren Buckley, Anthony Cannistra, and Aji John using Helmuth's data.
The interactive figures below allow you to plot the maximum daily temperatures recorded by robomussels at several different study sites during the summer season. On the x-axis, you'll see the day of the year (e.g. 200 means July 19) and on the y-axis, the maximum daily temperature in celsius. The different colors within each plot reflect data collected by robomussels that were placed in different subsites (mussel beds) with different tidal heights, and therefore exposed for more or less of the day. It's useful to look at maximum daily temperatures because looking at daily averages smooths out differences both within and across sites. Maximum temperatures can also tell us about extreme conditions faced by these mussel populations, and help forecast future extremes. Extreme climatic conditions are likely the most relevant factor in determining whether an organism will face physiological stress and how it will fare through climate change.
We will start by learning more about mussels, particularly those found in Puget Sound so we can understand their role in the environment closer to home.
Similar to geoducks, oysters, and clams, mussels belong to a class of organisms known as bivalves. Bivalves are filter feeders, meaning they eat by drawing the surrounding water in through a siphon and consuming the phytoplankton (microscopic plants) and decomposing material they remove from the water. Bivalves serve as important water filterers cleaning up the water around them. This can also sometimes mean that they can be dangerous to eat because they can contain high levels of bacteria and toxins from filtering the water.
Bivalves create important habitats for other organisms. Their shells form many small cracks and crevices. Many species along the shore and more shallow waters can hide in these crevices and use them as shelter from predators.
Bivalves are also “grown” by many different farmers who sell these mussels, clams, oysters, and geoducks for money. This is a profitable industry in Washington state and is an important part of the local economy, especially in rural areas.
This graph shows the number of native oysters that were caught annually from the mid-19th century to the mid-20th century.
Warming temperatures decrease the ability of bivalves to reproduce effectively, and they increase the amount of food bivalves have to eat. In addition, when water warms, it holds less oxygen. Bivalves do not do well in low-oxygen environments. Another challenge caused by climate warming is ocean acidification, which makes it more difficult for bivalve larvae to survive and grow to be mature adults. Ocean acidification also damages the adult shells.
In this final visualization, you can explore mean monthly maxima of daily temperatures. These are averages, for each month of the year, of the highest daily temperatures recorded in that month across all the years when robomussels were recording. You'll see a simplified heat map called a quilt plot, in which colors stand in for numerical values—with higher temperatures represented by hotter colors. The months of the year are arrayed from left to right, and latitudes increase from bottom to top.
Hopefully, exploring the robomussel data has made it clear how important it is to measure environmental conditions at the right spatial and temporal scale for the particular organism you are interested in. It would be impossible to understand how intertidal mussels experience their current climate, let alone how they might respond to climatic changes, without a clear understanding of how much their environments vary across space (even within one site!) and time, as well as by considering extremes of climate and not just averages.