Marine Microbes Matter in Kelp Forests
By Megan Morris, M.S. Candidate
You may not have microbes on your mind when you visit the beach, but bacteria are the most abundant organisms that you will encounter in the water.
In fact, there are ~1 million microbes in every mL of seawater!
Don’t let this scare you. Most microbes are safe and actually serve beneficial functions to marine ecosystems. But because microbes are so small, their roles in the ocean are often overlooked. In order to better understand the roles of microbes in coastal environments, I am studying the microbial communities offshore San Diego in Dr. Elizabeth Dinsdale’s
research lab at SDSU.
I am investigating microbial communities living on giant kelp, Macrocystis pyrifera
. Giant kelp is well-studied, but we know little about its associated microbes.
My research combines empirical ecology experiments with modern metagenomic methods, a technique that sequences genomic DNA fragments from many individuals. This process is similar to the sequencing methods used to study our own DNA.
In one experiment, I evaluated the effect of microbes on microscopic kelp juveniles (or propagules), which are very sensitive to their environment. Most kelp propagules don't survive long enough to grow into adults. In my experiment, I exposed kelp juveniles to different amounts of microbial cells. Some of the microbes came from a Catalina Island marine preserve, while other cells came from more polluted waters near Point Loma (offshore from San Diego Bay).
Megan prepares kelp reproductive blades for her experiment. The reproductive blades, called sporophylls, are responsible for releasing the microscopic propagules.
The growth and survival of kelp decreased when exposed to high amounts of microbial cells from Point Loma, and were more successful with a lower amount of microbes from Catalina Island. When I investigated the microbial DNA in the Point Loma water, I discovered a higher abundance of pathogenic bacteria, possibly influenced by runoff from the city. Catalina Island microbes had genes that could produce a compound attracting kelp juveniles to settle and grow.
These results indicate that microbes can either be beneficial or detrimental to kelp growth and survival.
To monitor the effects of microbes on kelp, Megan takes weekly pictures and measures the growth of kelp juveniles. Shown here are the stages called gametophytes which develop from zoospores. Pictured left, the gametophytes are more abundant and larger when exposed to fewer microbes. Pictured right, a higher number of microbes in seawater results in fewer, smaller gametophytes.
My research will improve our understanding of how microbes influence the life cycle of giant kelp, a key species to California’s marine environment.
Giant kelp supports a diversity of fishes, invertebrates and microbes along California’s coastline, and I hope that my research benefits the long-term conservation of this foundation species.
Members of the Dinsdale Lab and kelp forest ecologist, Dr. Matthew Edwards
, collect kelp blades and microbial samples from the Catalina Island kelp forest. (Photo credit Miranda Brett)
Why is being a biologist awesome?
Being a biologist is awesome because I find myself learning new knowledge and techniques every day. I also love the collaboration opportunities that come with being a scientist. At SDSU, I work with fellow ecology students and mentor exchange students who visit our lab from universities in Brazil.
Author: Megan Morris, M.S. Candidate, contact at email@example.com