Sorting Out Seaweeds: Which Species Native, Which Are Not
By Rebecca Zeiber, NH Sea Grant
October 24, 2007
Sherlock Holmes would have had a difficult time distinguishing between the
various species of red seaweed (genus Porphyra) found in New England. Although
this puzzle is far from “elementary,” using DNA from the plants
has helped researchers like Art Mathieson and Chris Neefus come closer to determining
which plant is which.
Mathieson and Neefus, both UNH research professors of plant biology, along
with several graduate students, have welcomed playing the part of scientific
sleuths for part of a N.H. Sea Grant-funded project investigating this topic.
There has been recent concern among researchers over whether or not many of
the Porphyra species found in New England are originally from the region or
if they are instead Japanese cultivars, plant varieties propagated for specific
traits. This concern stems from the potential of non-native species to utilize
the habitat and resources necessary for the survival of native plants.
When researchers realized that distinguishing among the various species was
too difficult to do by sight, they turned to more powerful genetic analysis
tools to help out.
“There’s a lot more genetic variation in Porphyra than people
originally understood, there’s more cryptic variability,” Mathieson
explains. “There has been difficulty knowing what is the native plant
and what is introduced, so we had to apply molecular techniques in addition
to traditional taxonomic techniques. A lot of Porphyra plants look alike but
are extremely diverse genetically.”
DNA sequencing of the species requires being able to compare present-day samples
collected throughout the coastal regions of New England with species collected
from the region in the past. This enables researchers to determine if new species
have begun colonizing the region or if samples from the past were simply misidentified.
It is possible that a species considered to be a newcomer to the area has actually
been here for quite a long time, Mathieson said.
This research requires going back to historical collections of seaweeds held
in herbariums where samples are kept from 200 years ago in some cases, rehydrating
the samples, and then doing genetic analyses on a small piece of the old seaweed.
“It’s fascinating to be able to use samples from herbarium collections
that are really old and make them have meaning, that’s really interesting,” Mathieson
Once analyses are conducted on both the old and new samples, the genetics
can be compared to see if a Japanese cultivar has been introduced recently
and is spreading or if it was here hundreds of years ago without scientists
knowing it. However, it can be extremely difficult to determine how a species
came to be in a particular region.
Mathieson and Neefus explain that one potential method of introducing non-native
Porphyra is accidental aquaculture release, specifically when the spores of
Porphyra grow on shellfish and the host organisms are subsequently relocated.
Transportation via boat traffic is another potential method, where the species
may have hitched a ride in the hulls of ships moving from port to port. In
addition, the introduction could have come from the nori industry that has
tried to raise certain Porphyra cultivars off the coast of Maine and along
Long Island Sound.
Future research will include trying to determine the geographic distribution
of the various red seaweed species along the New England coast and sorting
out the pieces of the genetic puzzle.
“It’s a can of worms in terms of finding out the right names of
the species and when they were introduced to a region, and then determining
the potential effects they could have on native species,” Mathieson says. “There’s
a lot of detective work that goes on.”