Post #16 - Emily's research on coral larvae

I think it's time I explain what Emily is up to here in a bit more detail.  I have briefly described her dissertation research earlier, but just to recap, she is looking at what effects ocean acidification (due to increased CO2 in the atmosphere from burning fossil fuels) and temperature have on the larvae of a Pacific coral whose common name is "cauliflower coral" and whose Latin name is Pocillopora damicornis.   There is a picture of  a "P-dam" colony in Post #12.  Interestingly, this species of coral is a brooder as opposed to a broadcast spawner, so that it releases fully formed larvae instead of gametes.  Each month for about 7-10 days after the new moon, P-dam colonies release larvae during the hours of darkness.

Since P-dam lives in shallow water, it can be collected by wading (see Post #3)  or snorkeling. Below, Emily is using a small chisel and a hammer to break free selected colonies.  I hold open a plastic bag into which Emily carefully places a coral colony.  I then swim it back to the boat which is anchored nearby and place it in a mesh bag suspended in the water to minimize how much the coral gets jostled.

When eight colonies are collected, we gently lift the plastic bags into the boat and place them into a sea water-filled cooler.  Back at the lab, Emily has made an impressive array of buckets for her coral colonies.

One colony is placed in each bucket.  There is a slow trickle of filtered sea water delivered to each bucket, with excess water flowing out the hose on the side. 

Since the larvae float when released, they are swept out of the bucket and down the hose, right into Emily's larval trap.  Each morning before the sun is up, Emily is down collecting her larvae.  At the beginning and end of a larval-release-cycle, she may have just a few dozen to deal with, but in the middle she may have thousands!   She takes the larvae into the aquarium room where they are counted and if there are enough, allocated into different groups.  

This is what the larvae look like in her beaker.

The larvae are cigar-shaped and only about one mm long.  They are brownish in color because they have the same symbiotic algae inside of them that the adult colonies do.

To test the effects of ocean acidification and temperature on the larvae, some are placed in home-made incubation containers with holes cut in the sides that are covered with a fine mesh.  These containers are floated in aquaria that have different conditions of temperature and CO2 levels.  

The tape label at the lower left tells us that this tank has ambient CO2 levels and an ambient temperature.

Some larvae are taken into the lab where they are digitally photographed under a microscope so that the size their size can be easily measured.

This is one of Emily's pictures of a P-dam larva:

  

When the larvae are abundant, each morning Emily is dealing with both the new larvae produced overnight and the larvae that have been incubating in the aquaria since the previous morning.  This is Emily's third (and probably last) visit to Moorea; in previous field seasons she has looked at other aspects of the larval physiology, but this year's experiments are designed to determine if the energy reserves in the larvae are impacted by ocean acidification or increases in water temperature.  Prior to analysis, the larvae are put in microcentrifuge tubes and placed in the -80 degree Centigrade freezer.

Each good day produces dozens of tubes, and each tube may involve one or more hours to process later!

The success of her experiments hinges on so many things going right.  One of the key elements involves monitoring the water chemistry in the aquaria to make sure the pH levels are where they should be.   This monitoring takes hours and hours every day.  How this is done will be described soon.....