If You Can’t Beat ‘Em, You Eat ‘Em!
By Micah Moen
Seaweed wreck is an important source of
nutrients to the coast. Braca seaweed that washes ashore and
connects a food web from the ocean to the land. But what happens if this tasty
seaweed is replaced by something else. Hi, i’m Ric DeSantiago from the Long Lab
here with McKenna and Wendy. We are investigating what happens when native
seaweed wreck is replaced by an invasive species. When seaweeds like this giant
kelp become dislodged, they’re carried to the shore by waves. Once on the shore,
they provide nutrients to the grazers who eat them. The nutrients then continue
through the food web as those grazers are eaten by predators like this bird. So
what happens when a foreign seaweed comes into the ecosystem? These are some
of the questions we are interested in here in Southern California, where the
invasive rockweed, Sargassum horneri, might be here to stay. This invasive rock
weed is often spotted growing alongside kelp and just like kelp it also washes
ashore. Since native seaweeds might not be able to beat it, we want to figure out
if native grazers will eat it and allow its nutrients to continue through the
food web. Back at headquarters, the crew and I are developing a method that
allows us to test this in the lab and in the field. In the lab we can set up experiments
called co-feeding assays that allow us to see if native grazers will eat the
invasive seaweeds. We’re using something called agar-based fake foods. First we
collect seaweeds and freeze them at negative 80 Celsius for five days. The
freezing process destroys the seaweeds reproductive parts to make sure that
when we use it in the field, it can’t spread. We then use a freeze dryer to dry
the seaweed. A freeze dryer removes all the moisture from the seaweed without
allowing it to break down. Once completely dry, we can grind it up into a
fine powder. Just a few more steps and voila: we have usable seaweed. With these
agar-based fake foods, we’re ready to experiment in the lab and in the field.
So here’s what we’ve seen so far. Most grazers completely avoid this invasive
rockweed. If you look at those dishes on the right side made from Sargassum rockweed, they never even touched it, but then we discover something pretty interesting.
Black abalone snails eat this invasive rockweed just fine.
So what does that mean? Does this invasive rockweed gonna continue to
provide nutrients to the food web through abalone? That’s difficult to say.
Black abalone are hard to find in the wild these days. These once plentiful
animals are considered a delicacy and people love to eat them. In fact, they
were harvested by the millions at some point. Many abalone that didn’t get
harvested suffered from withering foot syndrome, an infection that causes them
to wither away and die. Losing black abalone might mean we lose
a species that can actually eat this invasive rock weed and this might mean
it takes a lot longer for those nutrients from the seaweed to go under
the food web. Let’s let this be a lesson to us. When making conservation plans,
protecting biodiversity and understanding the whole food web might
be the key to minimizing the effects of an invasion, because if you can’t beat
them you eat them.