How do marine microbes affect fish?

Different environments harbour different micro-organisms. So how does this affect fish species?
10 December 2013

Interview with 

Molly McCargar, Columbia University




FijiChris - Working with Josh is Molly McCargar.  Now, Josh is looking at fish at the macroscopic level, what's swimming around and how many of them there are.  Molly is putting things both inside the fish and on the seabed under the microscope because she's interested in the micro ecology.  Hello, Molly.

Molly -   Hi.

Chris -   Tell us about your project.

Molly -   Well, so my project focuses on herbivores on the reefs and I'm looking at specific genus in the certain fish family.  They have this really interesting varied morphological adaptations to a degree, because fish don't possess all the right enzymes to digest plant matter.  So, they have all these different adaptations and I'm looking to see if these differences affect the microbial communities and their intestines.

Chris -   So, basically you're getting the gut contents of the fish that Josh has been studying in Fiji and analysing or asking what bacteria live inside these fish.

Molly -   Right.  So, the fish I'm looking at are all very closely related.  So normally, we would expect their microbes to be closely related as well.  But I'm looking at some that have different adaptations - morphological, chemical, and I'm seeing if these communities are different based on that.

Chris -   Why might this be important?

Molly -   So, these microbes are really important to reef health but we don't really know a lot about how they're dispersed.  They're not very mobile.  So, we're hypothesising that these animals play a role in it because of the specific adaptations that they have.  So, for instance, one of the species I'm looking at actually ingest sediment and keeps it in a sort of stomach-like structure.  And it uses the sediment to crush plant matter as it comes in. So, we're hypothesising that these fish will be interacting with their environment in such a way that their microbes will be spatially organised.

Chris -   Do you think you could use the array of different organisms that are in the fish and in the environment as a predictor of whether a reef is under threat, whether Josh needs to get involved in other words?

Molly -   Well, we're hoping to set up some indicators for that.  it would be a much longer study to really get it done to the science scale we would need to to say this is exactly where the microbes are going and this is exactly the area we need to protect.  But we are hoping it'll help us get a better idea of - if we see a certain amount of connectivity for some microbes in a certain area, and we notice maybe that reef is doing better than the others around them, we may be able to tell if there's some sort of correlation to the reef house.


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