How to track the environment with fish

Clockwise from right – Juvenile Murray cod after calcein marking; Juvenile silver perch during the experiment; An adult golden perch. Credit: Zoe Doubleday

Clockwise from right – Juvenile Murray cod after calcein marking; Juvenile silver perch during the experiment; An adult golden perch. Credit: Zoe Doubleday

Following up on an earlier post about how hard body parts can be used to reconstruct environmental signatures, Dr Zoe Doubleday and her team have identified the relative contribution of water (that the fish are swimming in) and diet to otolith (fish ear bones) chemistry in freshwater fish. Now I know that this isn’t strictly a study about oceans, but the techniques and findings of this paper are extremely useful if you want to do this in the ocean as well! See her report below.

Otolith chemistry is used extensively around the world to address key questions relating to fish ecology and fisheries management, particularly in marine systems. Nevertheless, there is limited research on the relative contribution of water and food to elements within otoliths.
Using a controlled lab experiment, researchers at the University of Adelaide sought to address this gap by explicitly testing the relative contribution of water and food in three iconic Australian freshwater fish species — silver perch, golden perch and Murray cod.  Water was found to be the key, but not sole, contributor to otolith chemistry in all fish species. This research will improve interpretation of otolith chemistry data in freshwater fish and will help to build a more accurate picture of their movements and the environments they inhabit.
Read journal article here: http://bit.ly/12pHsLr

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Atmospheric CO2 reaches 400 ppm

In May 2013 the National Oceanic and Atmospheric Administration in the USA reported that the atmospheric concentration of CO2 at one of their recording stations topped 400 ppm for the first time. The media surrounding this event seems to have been very much based around the event itself with little comment on what it may mean. I find this moderately disappointing because we can be moderately confident of one thing  – increased CO2 in the atmosphere means that more will dissolve into the ocean, which means an increase in ocean acidification (this is classical chemistry!).

Despite the recent efforts of some of the worlds best scientists, both here in Australia and overseas, we still have an incomplete picture of the likely biological and ecological effects of this ocean acidification. However, we can be fairly certain of two things:

1. Ocean acidification will have negative impacts on organisms which form calcareous structures like the shells of molluscs (see pictures below) and the skeletons of corals; and

2. We are becoming increasingly aware that the increase in CO2 as a resource will cause changes to systems that are dominated by primary producers like seagrass and algae (e.g. kelp), mostly for the worse (for a starting point you could look at my webpage, but contact me for more information if you want!).

Unfortunately, as we enter a time of uncertainty for science funding in Australia, we may not develop a complete understanding of the system-wide effects of ocean acidification until it’s too late.

The growing edge of a juvenile abalone under high atmospheric CO2 (ultra-high magnification). Photo: Owen Burnell

The growing edge of a juvenile abalone under high atmospheric CO2 (ultra-high magnification). Photo: Owen Burnell

The growing edge of a juvenile abalone under normal atmospheric CO2 (ultra-high magnification)

The growing edge of a juvenile abalone under normal atmospheric CO2 (ultra-high magnification)

Aquatic body parts reveal all

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…..

Zoe

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

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

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…

Vertebra of Port Jackson Shark. Photo: Chris Izzo

Vertebra of Port Jackson Shark. Photo: Chris Izzo