By: Kathryn Scafidi

Hello! My name is Kathryn, and I’m a graduate student in Dr. Mark Steele’s Fish Ecology Lab at California State University, Northridge. I am finishing up my first field season of my own research and starting my second year of grad school. I am studying the effects the invasive alga, Sargassum horneri, is having on the trophic dynamics of rocky reefs at Catalina Island.

I am specifically researching the potential indirect effects this alga is having on the local fishes. To do so, I am conducting what I think of as three stages of research. The first stage was fish foraging observations and benthic habitat characterization and algal coverage. Over the summer, I observed three species of fishes, rock wrasse, garibaldi, and sheephead, at six sites along the leeward side of Catalina. Each of these observations were done via SCUBA, where I followed an individual taking note of their number of bites and what alga the bites were associated with.

My benthic characterization involved running transects at each site and recording the habitat and algal species present. Coupling the foraging observations with the abundance of algae, I can see which algae fishes are preferring to forage among compared to how much is available.
I am currently working on my second stage of research, where I am collecting rock wrasse at each site to assess their growth, reproductive output, and gut contents. To do so, I collect them using a specialized pole spear, called a microspear. I then process them in lab, extracting their otoliths (which can be read like the rings of a tree to age), their gonads, and their gut contents. I am using the gut contents to see what small epifauna that are living on the algae, are the targeted prey for rock wrasse. I will then use this information for stage three.

Stage three involves collecting S. horneri so I can obtain the abundance of epifauna rock wrasse are eating living on the alga. I will then compare this to the abundance of epifauna on three of the native species of algae rock wrasse are frequently foraging among. Lastly, I will extract the anti-herbivory phenolic compounds from the invasive and the native algae to see if there is a heightened concentration which can deter epifauna.

So, what did all of this mean? I am essentially looking to see if S. horneri is providing a suitable habitat for epifauna, like the native algae, which alternatively provides a food source for fishes like rock wrasse, garibaldi, and sheephead. Given the rapid spread and growth of this invasive, it is important to assess the effects it is having on multiple trophic levels in order to assess the health of the reefs as the invasive persists.

All in all, the Wrigley Summer Fellowship has provided me with the opportunity to research a question I am passionate about and eager to find out the answer to. I have been able to network with other graduate students and meet researchers from all walks of life. And I can never complain when I get to dive some of the most beautiful dive spots around the island every day. It has truly been an educational and inspiring summer!

By: Pingping Qu

Hello everyone! My name is Pingping Qu and I am a fifth year Ph. D. candidate of Marine Environmental Biology. I am very honored to be a Sonosky Fellow this summer.
My research focuses on the responses of marine phytoplankton, namely, algae, to climate changes. In recent years, my interest is in the group of marine cyanobacteria, who have contributed to the global carbon cycling and food web since 3.5 billion years ago! In this group, “diazotrophs” (namely nitrogen fixers) are very important. They convert atmospheric nitrogen to organic nitrogen, and supply this nitrogen to other life forms including us! In other words, there would not exist plants, animals and humans on the planet today without them.

As we know, all ecosystems on this planet are facing huge challenges with climate changes. Among multiple changing variables, warming is an especially significant and influential one. Average surface seawater temperatures are predicted to increase by 3-5°C by the end of this century. To explore whether nitrogen fixers are able to survive in this future warming, we started a long-term evolution experiment on two of the most important diazotrophs, Trichodesmium and Crocosphaera (Figure 1).

Fig 1. Crocosphaera cells and Trichodesmium filaments

To test whether they acclimate (short term adjustments by the individual) or adapt (evolution over multiple generations) to different temperatures, we transferred them to three different temperatures (22°C, 28°C and 32°C) two years ago and maintained them under temperature selection for 2 years. The current optimal temperature is 28°C, while 22°C and 32°C are respectively lower or higher than the best temperature for the two nitrogen fixers. Specifically, 32°C can be viewed as the future warming condition for them.

The long-term temperature-selected cultures provide us with excellent opportunities to study both their short-term plasticity and long-term adaptation to temperatures. In this summer and the following fall semester, I am determining the “thermal curves” of Trichodesmium and Crocosphaera selected by three temperatures. Namely, I transfer the selected cultures to a wide temperature range covering the thermal limits of both strains and then observe whether they survive, grow or die at certain temperatures. With the help of our “secret weapon”, thermal block (Figure 2), I can set up a temperature range of 18°C to 36°C, provide the same incubation conditions for my cultures and achieve my goals.

Fig 2. Samples in a thermal block

In this study, my hypothesis is, 32°C selected cultures take advantage at high temperatures while 22°C selected ones perform better at low temperatures and 28°C selected ones are in the middle. My preliminary data have confirmed at least part of my hypothesis. If this pattern in the hypothesis can last a long time, it indicates the cells may have evolved in the past two years. If they can acclimate to different temperatures quickly, it means it is the plasticity, not the genetic difference that help cells survive at suboptimal temperatures.

Fig 3. Crocosphaera in a flask, and me

I worked in the lab for this whole summer with cultures, and collected both the physiological and molecular samples. The growth rates, nitrogen and carbon fixation rates, elemental ratios, cell size are measured. DNA and RNA samples are stored for the future analysis. I will fight on in the following semester! (Figure 3).