‘Tis the Season for
Red and Green By Dr. Joe Richardson
As we move into December, thoughts, music and scenes of the Christmas
season start to surround us. Tybee Island always goes all out with decorations
and lights throughout the city. Red and green are the traditional colors for
this time of year, helping to brighten the shorter days and longer nights.
And in their own way, even the jetty rocks at Tybee’s North and South
Beach get into the decorating spirit of the season. One of the things that
I look forward to most about the arrival of winter conditions at Tybee is
the yearly appearance of green and red seaweeds growing on the intertidal
surfaces of our jetties. Part of the reason is that I enjoy seeing the colors, but
I have to admit that a big part of my anticipation is because I like seaweeds!
And winter time is when they are most abundant around here.
The most obvious are the green seaweeds. On our jetties, these green
ones include a few species of tubular, stringy-looking Enteromorpha (sorry,
Enteromorpha doesn’t really have a common name, but it means “intestine
like”). Mixed in with them are some flat, blade-like Ulva or Sea Lettuce.
Both of these can also be found starting to become more abundant in the
marshes and on floating docks.
The deep brownish-red seaweed on the jetty is a small, thin, flat blade
alga named Porphyra, but it is also known as Nori (the seaweed that is used
to wrap sushi rolls). Down here, our Porphyra individuals are small, only 2-3
26 TYBEE BEACHCOMBER | DEC 2017
inches; but up north I’ve seen thin flat blades of Porphyra more than a foot
long and wide. It is a cold-water seaweed, so it grows much more abundant
and much larger up there, and we are at the very southern edge of its range
on the east coast.
Although you would assume that it is the cold water temperature that
stimulates these seasonal seaweeds to grow during the winter, there
are actually other environmental factors involved. With the red seaweed
Porphyra, it turns out that it is the shorter day length and longer night/dark
period that stimulates its growth, rather than cold temperature.
For the green seaweeds, I think it has to do with some biological factors.
Both of these green seaweeds are capable of growing here year round, and
both can be found year round if you look hard enough. So it doesn’t appear
that temperature or day length stimulate or inhibit growth. I’m sure that the
intense sunlight and hot temperature on the jetty rocks during the summer
could limit thick growth somewhat. But my hypothesis is that grazing
animals, especially fish, eat the green seaweeds and keep them cropped
down during the summer when those fish are abundant around the rocks at
high tide. And it is when the water cools and the grazers leave that the green
seaweeds can flourish for a few months.
So for a variety of reasons, ‘tis the season that our jetties get decorated
with the Christmas colors. During your beach walks at the north and south
end of Tybee, enjoy the colors while they last.
Dr. Joe Richardson is a retired marine science professor with 35+ years of
research and teaching experience along GA and the southeastern coast and
Bahamas. Besides research, he conducts Tybee Beach Ecology Trips year
round (www.TybeeBeachEcology.com) and frequently posts pictures of what
they are finding on his Tybee Beach Ecology Trips Facebook page.
Beach Walks
with Dr. Joe