you're reading...


Whale skin samples track changes in ocean biogeochemistry

Article: Ruiz-Cooley RI, Koch PL, Fiedler PC, McCarthy MD (2014) Carbon and Nitrogen Isotopes from Top Predator Amino Acids Reveal Rapidly Shifting OceanBiochemistry in the Outer California Current. PLoS ONE 9(10): e110355. doi:10.1371/journal.pone.0110355



Scientists have devised alternative ways to study ocean food webs using stable isotope analysis – particularly for carbon and nitrogen. Isotopes represent variants of an element that differ only in the number of neutrons present, just slightly altering the mass of a molecule that incorporates the different isotopes. By following the changes in ratios of different isotopes (noted as δ), scientists can glean all sorts of information about food web interactions. Carbon and nitrogen isotope signals (δ13C and δ15N) ­are useful since they get altered in a relatively systematic way through each trophic level, giving scientists information as to the exact trophic level an organism occupies (Figure 1).


Figure 1. Isotopic composition of carbon and nitrogen (δ13C and δ15N, respectively) can track trophic interactions. Stable isotopes incorporated into specific amino acids (such as essential amino acids or source amino acids) in higher predators can preserve isotopic signals from earlier producers and be used to investigate changes in food sources.


Scientists can get even more information by looking at the isotopic signal in specific compounds, such as amino acids. Essential and source amino acids are compounds that certain animals are unable to synthesize themselves but are required for important protein synthesis and therefore must be obtained through food. Since these amino acids are directly incorporated into an animals’ biomass from their food, these amino acid isotopic signatures remain relatively unchanged, thus reflect the isotopic composition of their food source. In contrast, non-essential or trophic amino acids can have altered isotopic signatures which are more informative about things such as trophic level.

Dr. Rocio Ruiz-Cooley and colleagues from the University of California, Santa Cruz recently employed amino acid stable isotope analysis to study the changes occurring in the eastern portion of the California Current system. They used a long time series to characterize any changes that have occurred in the system over recent time.



Skin biopsy samples were collected from individual sperm whales. Seventeen samples were taken in total, either from live individuals off the California Coast system or from beached individuals from California up to Washington (Figure 2).

Fig 2.2

Figure 2. Skin biopsy samples were taken from 17 individual sperm whales from 1993-2005. Black circles are tissue samples used for bulk stable isotopes and red circles are samples used for amino acid stable isotope analysis.

            Tissues were analyzed for bulk isotopic composition by using an isotopic ratio mass spectrometer (IRMS), which is able to separate and quantify compounds based on different isotopic ratios. Four source amino acids (phenylalanine, glycine, lysine, and tyrosine) and five trophic amino acids (glutamic acid, alanine, isoleucine, leucine, and proline) were extracted from tissue samples and run through IRMS to determine the nitrogen isotopic composition of amino acids. Essential (phenylalanine, valine, and leucine) and non-essential (alanine, proline, aspartic acid, glutamic acid, and tyrosine) amino acids were extracted and run through the IRMS to determine the carbon isotopic composition of the amino acids. A sample from 1972 was also included in bulk and amino acid isotope analyses to potentially give an even longer study period to observe.



Dr. Ruiz-Cooley and colleagues found a consistent and statistically significant decline of both bulk and amino acid for δ15N and δ13C (Figure 3). From 1993 to 2005, δ15N decreased by 1.7 0/00. Including the sample from the 1972 tissue samples show a decrease of greater than 3 0/00 between 1972 and 2005. δ13C decreased by 1.1 0/00 between 1993 and 2005 and decreased by more than 4 0/00 from 1972 to 2005.


Figure 3. Bulk and amino acid specific δ15N (top) and δ13C show a significant decrease over the sampling period.

Scientists have observed changes in bulk δ15N and δ13C values in other systems in response to changes in system productivity. Large shifts in bulk δ15N can represent changes in system productivity, where increased primary production might allow higher trophic level organisms to shift down the food web (allowing them to use multiple trophic levels when conditions are good and food is plentiful). The opposite can also happen – decreases in primary productivity may force organisms to consume at higher trophic levels to sustain their baseline nutrient and energy requirements. However, the declines in bulk δ15N and δ13C observed by Dr. Ruiz-Cooley and colleagues was not a large enough shift to suggest a change in trophic level. Thus, something else must be occurring.

An alternative explanation for changing bulk δ15N and δ13C could be a system-wide shift in isotopic composition, from the phytoplankton up to whales. This is where amino acid stable isotope analysis comes into play. Source and essential amino acids (which track nitrogen and carbon isotopes, respectively) undergo little to no modification as they pass through the food web and remain more or less unaltered, even in very high trophic organisms such as whales. Dr. Ruiz-Cooley and colleagues observed a similar, parallel trend in their trophic and non-essential amino acids as in their source and essential amino acids. Thus, changes in bulk δ15N and δ13C observed in the whales can be explained by changes in the overall system baselines.



While not readily apparent, this decrease in bulk δ15N and δ13C indicate a changing system while the magnitude of decrease and parallel trends in lower trophic level proxies show that overall ecosystem structure is preserved. Dr. Ruiz-Cooley hypothesize that climate variability (such as Pacific Decadal Oscillation – Figure 4) or climate change effects may cause widespread changes in ocean biogeochemical cycling.

Fig 4.2

Figure 4. Time series of sea surface temperature in the California Current System (inset) showing the influence of Pacific Decadal Oscillation. The red line shows a regression line of sea surface temperature during the period of this study, showing a general cooling pattern which may cause changes in the system that might contrast with predicted climate change effects.

For example, warming may increase stratification and decrease nutrient exchange, which would then decrease the available nutrient for primary production. This might shift plankton communities to favor nitrogen fixers (like cyanobacterium) which can create their own nutrients from atmospheric nitrogen. This shift in biogeochemical process would shift the isotopic signal of the phytoplankton, and this signal change would continue throughout the rest of the food web. However, climate change and climate variability research shows conflicting or inconclusive results, making it hard to make guesses as to what is driving these changes, let alone develop a hypothesis to move forward.



No comments yet.

Post a Comment


  • by oceanbites 3 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 4 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 5 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 6 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 9 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 9 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 10 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 10 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 11 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 11 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 12 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 12 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 1 year ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com