Megan Murphy is presenting her crab research on Thursday, Dec. 19 as part of the Pratt Museum’s November/December “When Crab Was King” exhibit. Her research is also published in the science journal, “Estuaries and Coasts.”
By Megan Murphy
Special to the Tribune
Growing up in the land-locked state of Illinois, I first saw the ocean when I was 16. I would have been surprised to find that, a decade later, I’d be pursuing a degree in biological oceanography.
Having studied oceanography, I now more fully appreciate how our amazing “Blue Planet” functions. But the phenomenal roles the ocean plays are not what drew me to oceanography; it was my fascination with plankton.
Ask any person who has grown up in Homer and experienced a field trip with the Center for Alaskan Coastal Studies, the Kachemak Bay Research Reserve, or the Pratt Museum’s, “What Plankton Are,” and you’ll most likely get the straight scoop.
Plankton are plants or animals that drift (or weakly swim) in water. Most are observed with the help of a microscope. Here are a couple of factoids about plankton: 1. Plant or phyto plankton are responsible for 50-85 percent of the oxygen available in the earth’s atmosphere. 2. The early stages (or larvae) of most marine invertebrates begin their life as drifting plankton – such as crabs, barnacles, clams and more.
I first fell in love with plankton while out in a canoe at night in Puget Sound. Every dip of the paddle elicited an explosion of light within the water and a trail of magical pixie-dust-like radiance trailed behind the canoe’s path. I had encountered bioluminescence before, having grown up chasing fireflies, but this was my first observation within the water. I soon learned this was being produced by phytoplankton called dinoflagellates, and my intrigue with plankton was officially born.
It wasn’t until I moved to Homer that I got to live by the ocean. Working with the Kachemak Bay Research Reserve, I had the opportunity to learn more about plankton. One of the Reserve’s research interests is how marine invertebrate larvae are transported within and around Kachemak Bay. I grabbed hold of this research idea and brought it with me to graduate school through the University of Alaska Fairbanks School of Fisheries and Ocean Sciences.
In developing a specific research question to investigate, I settled on studying ocean transport as it applied to planktonic (or larval) crabs. In light of the king, Tanner, and Dungeness commercial crab fisheries all having previously closed in Kachemak Bay, I thought it would be important to investigate the first part of the crab lifecycle if we wanted to better understand the adult population dynamics. Ultimately, I wanted to help answer the question: Is Kachemak Bay the source of our crab populations, or are we dependent on an upstream source?
Undertaking this field study turned out to be fairly intense. It was a lesson in theoretical words on paper and how this translates to actual effort. From March to October in 2008 and 2009, I was one of 26 total volunteers who took weekly plankton tows and vertical profiles of temperature and salinity. This was done at three consistent points in the Bay, between the Homer Spit and McKeon Flats as I wanted to look at the exchange of plankton and water between the outer and inner Kachemak Bays. An occasional jelly would get caught in my plankton net, but mostly I was catching much smaller zooplankton – as the net holes were sized 500 microns (0.5 millimeters).
Collecting samples over the spring, summer and fall seasons provided a great deal of interesting information. The temperature and salinity measurements documented the dramatic changes in the water column, mostly driven by freshwater layers emerging in the top of the water column during the summer and fall. The summer and fall of 2009 had more freshwater exiting the inner Bay than in 2008, which could influence how and where marine invertebrate larvae were drifting — and thus settling.
The temperature and salinity profiles also supported the general circulation patterns that were documented in the late 1970s: Water enters the inner Bay on the south side, and exits on the north side. On the biology side of things, I observed seven crab species (including Dungeness and Tanner) over the March through October seasons and each species had a unique release period. Also, most crabs appeared to be released in Kachemak Bay, as I observed the entire larval development period over a few months. (If I had only observed larvae in their late development stage, this might mean they had traveled to Kachemak Bay from somewhere else).
Ultimately, I came away with the conclusion that Kachemak Bay adult crab are likely the main population source for new generations of crab in the Bay. Having had the opportunity to take a close, microscopic look at plankton, I have a much deeper appreciation for the intricate and overarching processes that are occurring all around us.
Next time you have the chance to peer down into the ocean, know that there is much more going on than meets the eye. While you’re at it, you can thank plankton for that breath of fresh air you’re breathing.
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