Tuesday, July 24, 2012

Week 8: Graphs

Ok!  At this point, I've collected data on the attachment of almost 600 spores. That's what nonstop data collection for 2 weeks straight gets you. That's a lot of data points!  I finally got to plotting this data to share here.  This data is super-fresh, like 2 hours since I generated it.

The main species I've been using is Pterosiphonia bipinnata, (which I initially misidentified as a Polysiphonia). Here's what it looks like under a microscope:

It has these cute little tiers of cells that give it a banding pattern.  The spores are made on the inside of the tube of cells, kind of like a jelly-filled long-john donut.  You can see the packet of spores as lines of darkly colored dots.  These packets break into 4 individual spores once released.

Ok, and now to the main story of spore attachment.  I'm plotting the shear stress (or how strongly spores have attached) on the x-axis, with the time that the spores had been settling on the y-axis.  Since what I see is spores that are around at one shear and then gone at the next, I know that the attachment strength of the spores lies in between the forces of when I last saw it to when it was gone.  So I decided to plot the data as a bar, showing the range of where the spore's attachment strength must be, for how long they have settled.

This data is actually really cool!  It confirms the work of my thesis that spores attach really quickly and strongly.  How do I know this?  Well, notice that most of the points group on the left side of the graph, at really low attachment strengths where they are barely attached, or on the right side of the graph, where spores are really strongly attached.  I rarely catch spores at intermediate attachment strengths, meaning spores really just have one of two states: 1) unattached and waiting for a wave to knock them to a better location, and 2) fully attached, unable to be shaken by the strongest waves.  For Pterosiphonia bipinnata (as well as the species in my thesis), it may take several hours for them to "decide" to switch from state 1) to 2), but when they decide to do it, the switch happens faster than we can usually catch in our shear flume (on the order of minutes).

Oddly enough, Pterosiphonia bipinnata takes quite a while to make the decision to attach.  It is rarely attached in anything less than 12 hours, and even after 24 hours most but not all spores have moved to the right side of the graph (indicated by the darker color of the lines at 24 hours).  

At some point, I had accidentally tested a different species, and hadn't noticed till afterwards, when I had an outlier where spores were fully attached in 10 hours in just a few tests.  Going back to them, I found I actually had tested Polysiphonia hendryi. Here's the few data I collected for it:

And last, I ran a few pH tests.  So the big question: how will Pterosiphonia's spores fare in a future, acidic ocean?  The answer: not well.  In 24 hours of attachment, 73% of the spores had attached in the normal waters, but only 35% managed to attach in the acidic water.  It's interesting that as far as I could tell, when the spores did attach, they were just as strong, but seem to be taking longer to make that decision to attach.  I don't have enough trials yet to be fully confident in this story (I still got a few more days here!), but the trend so far is quite strong and I hope it'll hold up to more data.

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