This post is written by guest blogger Dr Zoë Doubleday, who is a Post-doctoral Fellow in the Marine Biology Program at The University of Adelaide. She has a particular interest in the utilisation of hard calcified tissues found in aquatic organisms as tools for answering critical questions in aquatic ecology. What interests me about Zoe’s work is how you can apply the techniques below to understanding past environmental conditions in the ocean and what that can tell us about the future…..
When you look at a tree stump what do you see? That’s right, rings, rings radiating out from the center to the edge; rings that represent the growth history of the tree. Aquatic species also have rings laid down like this, year after year, decade after decade, in all kinds of body parts. Fish and squid ear bones, shark vertebrae, coral skeletons, marine mammal teeth, bivalve and gastropod shells, cuttlefish bones. . .and the list goes on. The beauty of hard calcified tissues is that many form growth rings with a precise periodicity (e.g. daily or annual), providing a time-calibrated archive of biological and environmental information. To extract information from these natural chronometers we can analyse their chemical composition (such as trace elements and isotopes) and examine their growth ring
The otolith (ear bone) of a Murray Cod showing annual growth rings. Photo: Zoe Doubleday
patterns (such as number and width) in relation to the temporal context of ring formation. From here we can examine both the biological history (e.g. age, growth, diet, and movement) and environmental history (e.g. temperature and salinity) of an individual from birth to death. This type of data can additionally tell us two important things: how the environment is changing and what biological impact that environmental change is having.
Another valuable attribute of calcified tissues is that they can hang around long after the organism has died. This allows us to compare information derived from modern-day samples with information derived from historical (e.g. 19th and 20th Century), archeological and even paleontological samples. Such comparisons are very powerful and can provide a rare and crucial insight into past biological baselines and what aquatic environments may have been like, say, prior to industrial-scale fishing or European colonization. This in turn can help us make a more realistic assessment of how much humans have impacted, and are impacting, the environment and about what environmental changes might happen in the future.
In the Marine Biology Program, we have a number of biochronologists working away on a range
Red Gurnard Perch (deep-water marine fish) ear bone with growth ring measurements. Photo: Gretchen Grammer
of calcified tissues collected from freshwater to oceanic environments. From here we are linking chemical and growth pattern data to various climatic and oceanographic variables, tracking movement patterns of individuals over large spatial and temporal scales, and seeing how biological indices, such as growth rate, age, and diet are changing. However, there is still much to discover and uncover in calcified tissues and, in my opinion, is a mu ch underutilized resource of historical data, particularly in Australia. As we continue to dig up long forgotten sample archives, find novel body parts with chronological properties, and work with constantly evolving analytical technology, who knows what we will find next…