"Racing Tides" Audio Transcripts

Channel Islands Marine Ecologist Steve Whitaker on the Rockweed Decline

Whitaker:

I'm Steven Whitaker. I'm a marine ecologist at Channel Islands National Park. We have long term data throughout Channel Islands National Park, as well as the mainland of Southern California and Central California where rockweed is most common. Silvetia is found from San Francisco south down into Baja Mexico, north of the Mexican border, we have about 40 different sites where we monitor Silvetia.

For this project, We focus on the sites where we know the trends for Silvetia over time and we identified locations where we saw dramatic declines over time. Some cases, we've seen local extinction of the species at the site. So the way that we monitor is by way of fixed plots on the shoreline and we have them scattered throughout areas where the rockweed would occur and where it it it originally occurred.

And we go out every year and, and document those plots, we photograph them and score them to see how much cover of rockweed is in those plots. In some cases, we have seen that the rockweed has not only declined but it has actually disappeared throughout the entire monitoring site. Those are the types of places that we're interested in doing rockweed restoration.

Steve Whitaker on Transplanting Rockweed

Whitaker:

It's a very simple procedure really consists of identifying an individual plant and chipping that rock out of the substrate with taking special care to not affect the holdfast, ah which is the base of the plant that attaches to the rock. We try to keep that intact and then taking that individual and moving it to our recipient site and simply gluing it in place.

We've tested other methods that we were hopeful would have less impact on our donor population. So that's one, a big concern of ours is that, you know, we don't want to be pulling from these donor populations that we've identified these areas don't exist everywhere. You know, we don't want to impact those as much as possible. So we've looked at trying to outplant reproductive portion of the plant into the recipient site.

And so that consists of the upper part of the, the plant has the swollen tips on their branches and these are called receptacles and that's where the eggs and the sperm are housed. We've experimented with clipping those receptacles and putting them in a container and then bolting that down to the rock and, and seeing if maybe we could induce a reproduction in that way. But we, we didn't have any success with that yet. We've also been experimenting with cultivation in the lab to grow up individuals and then out plant those into the field. But what we've found is that there is extremely high mortality of the early life stages of rockweeds in general, particularly with Silvetia, they really need to attain a relatively large size. Those have much higher survival than individuals that are much smaller. That's why we've chosen to use the adults to do restoration work with.

Steve Whitaker on Rockweed Stressors

Whitaker:

A lot of the hypotheses that we have for these declines on Southern California mainland where I came from before I started working here. Things like visitor usage, trampling when you walk all over this stuff. What ends up happening? Studies have shown you end up clipping the tips of those branches off, which is where all the reproductive material was located that can have an impact on the population over a a long term.

You have a lot of people walking around can impact it. Other things like water pollution. We think that has a huge impact on, on the ability of these populations to persist; those types of things are not major stressors for the remote channel islands within Channel Islands National Park. And so that really made me question, what are the drivers for the trends particularly for the declines that we've been documenting with our long term data.

By and large no one really knows the cause of these declines. Now, we have hypotheses and climate change is one that certainly is high on the list of things that potentially are driving these trends. Specifically, our hypothesis is that the declines are occurring during periods of long exposure to air when the tide is out, coupled with things like offshore wind events.

And you know, locally, we we refer to those as Santa Ana events when you have these long periods of low tide and you have several days of repetitive stressful conditions caused by these dry hot winds. Those can have an impact on anything that is exposed to the air in the intertidal zone. And we, we see that all the time, you know, these species are evolved to live and endure stressful conditions. But what we think is that the Santa Anna events are becoming more frequent and more intense. When you have a very stressful event and that causes the stress for all these species. They then the tide comes in eventually, but they're stressed out the next day, the tide drops, you have another wind event and those things piled on top of each other. I think as w as it may be what's causing these, these gradual declines in some cases, they're very quick.