By: Griffin Srednick
Hello and welcome! My name is Griffin and I am a USC Wrigley Summer Fellow from California State University Northridge, where I am pursuing a Masters in Biology.
The author, Griffin Srednick
What I study can be summarized in two words: fish ecology. You may be thinking: there really aren’t many fish in Northridge, and you would be right! Which is what brings us fish ecologists out to the beautiful Santa Catalina Island. Catalina Island offers many unique attractions, experiences, and ecosystems. One of these that I am particularly passionate about is the kelp forest.
Kelp forests are incredibly important along the western coast of the US, as they provide valuable habitat for a diverse community of organisms. This habitat offers area to feed and hide from predators, and nursery space for many juvenile fishes and invertebrates. In addition, they provide habitat structure that spans the entire water column, even in depths of greater than 100 feet! These forests, formed by the foundation species giant kelp (Macrocystis pyrifera), can be highly dynamic in space and time. In other words, the density and size of the forest can change based on environmental conditions in certain locations or seasons. These changes can influence the associated community.
If you’ve been keeping up to date on recent oceanography, you may know that in 2014 and 2015 California experienced abnormally high sea surface temperature, due to a mild El Niño and a warm water phenomenon known as “the blob”. Kelp is not a fan. Kelp thrives in cold, nutrient rich waters that are “upwelled” from deep ocean canyons. However, kelp does not do as well under warmer conditions. This is certainly why you may have seen less kelp off coasts on the mainland and Catalina in the last year.
In addition to this, researchers have been documenting the spread of an alien algal species (disclaimer: not actually from Mars) known as Sargassum horneri. It is believed that Sargassum horneri was transported to southern California by ballast water exchange in container ships, and came to Catalina Island via smaller vessels. Since 2006, this S. horneri (also known as “devil weed”) has begun to occupy areas formerly dominated by giant kelp. So much so, that in some places, the rocky reef can resemble a 6’ high corn field of the invasive algae.
Sargassum horneri on a shallow rocky reef
Interestingly, S. horneri, provides physically different structure than giant kelp and other native algae, which we believe alters the distribution and behavior of associated fishes.
A) structure of a kelp forest versus B) the invasive S. horneri
Before I get into a bit of the nitty gritty, let me tell you a tale. Imagine you are taking a walk through the woods. As you move through the trees you suddenly come upon a bear. You run and the bear chases. Presumably, the density of the forest as well as the size of identity of the trees influence your ability to outrun the bear and its ability to catch you. This is what I study, but in the ocean.
The structure provided by algae (e.g., a giant kelp “plant”) is important to fish. So…do changes in this structure influence fishes? If so, does it change where we find them or how they behave? These are all questions that I aim to answer.
Young kelp bass navigate the Sargassum understory
In order to do so, I have been performing surveys of fishes, invertebrates, and algae at a number of sites along the west end of Santa Catalina Island. In addition to this, I collect algae from the field, quantify their size and see what type of invertebrates may be attached to them. In this way, I hope to better understand the relationship between fishes and algae.
The author surveying the fish community at a nearby reef
So what have we seen so far. Well, algae affects fish differently. No surprise here. Different fishes have different requirements: different types of foods, habitat, behavior, etc. In this way, algal identity and structure is important in providing resources. We have seen that while certain species are unaffected by changes in algae, others respond a great deal. The kelp bass (Paralabrax clathratus) and senorita (Oxyjulis californica) fishes, for example, are more abundant throughout the water column in the presence of kelp. However, blacksmith (Chromis punctipinnis) are more abundant in the absence of kelp and the presence of S. horneri. I believe that this is due to the fact that blacksmith are schooling fish that can perform schooling behaviors far easier in a structure-less environment (think back to the bear analogy). All in all, it is hard to say if or how this non-native species is affecting local fish ecology. The best we can say as of now is that “it depends”.
Three kelp forest fish species
I am honored and excited to be in my second summer at the USC Wrigley Institute for Environmental Studies. WIES provides the most ideal location to perform the SCUBA and experimental work required by a project of this nature, and offers some of the best sunset views in California. Throughout this summer I hope to continue the work explained above as well as a few interesting experiments that dive deeper (pun intended) into the relationships between fishes and algae. Stay tuned for these in the coming months and come visit us on the island soon! Hasta luego!
Griffin Srednick is a USC Wrigley 2016 Summer Fellow and a Master’s Candidate in Dr. Mark Steele’s Fish Ecology Lab at California State University Northridge