Ecology's workshop: research and mentorship in the heart of Monterey Bay
At the edge of the trails that meander through gathered tourists, restaurants, and scattered remnants of tin and steel, lies the heart of the Monterey Bay. Expansive tidal rocks and fine-sand beaches define the boundary between land and sea. Turquoise water beats with life. Pelicans dive for bait balls of anchovies. Sea otters rest in the comfort of a protected kelp canopy that surges in the cold, nutrient-filled water. It is here nature hosts an extraordinary workshop in ecology.
Ecological communities are not simply collections of species, but the product of relationships between species that can vary across space and time. Funded by the Future Leaders in Coastal Science (FLCS) Award, Ph.D. student Josh Smith and two UCSC undergraduate students (Sabrina Garcia; Torrey Gorra) are studying the relationships between species in kelp forest communities. Lessons in science, research, and mentorship are the modules of their workshop.
Module 1: The Science
In kelp forests along the Northeast Pacific Ocean, populations of voracious sea urchin grazers are controlled by predators such as sea otters and sea stars. However, when sea urchin populations are uncontrolled, they scour temperate reefs of key species of algae (e.g., giant kelp) that provide essential habitat for many economically and ecologically important marine species, thereby shifting the state of kelp forests to "barrens" (Figure 2). Barrens are an accepted measure of ecosystem health and considered to represent a collapsed kelp forest state. At low densities, urchins are well fed and contain high energy content through gonad production (Figure 4). Conversely, urchins at high densities (i.e., those in barrens) are often starved, which may deter foraging sea otters. In turn, highly dense urchin populations remain uncontrolled and can have devastating impacts on temperate kelp forest communities.
Figure 2.Left: kelp forest at Lovers Point, June 2012; Middle: sea urchin foraging front; Right: sea urchin barren at Lovers Point, July 2016.
Like a heartbeat, the pulse of the Monterey Bay is changing. In 2013, sea star wasting disease decimated local populations of important sea star predators that prey on sea urchins. Increased outbreaks in the number of sea urchins (i.e., urchin barrens) around Monterey have already been observed, with a corresponding decline in kelp abundance. As such, the current absence of sea stars in the kelp forest presents a unique and timely opportunity to explore how urchin populations will expand or retract relative to other predators, such as sea otters, or environmental perturbations.
Module 2: The Research
To investigate the ability of sea otters to control urchin populations based on urchin quality, the team is conducting a series of underwater visual surveys in the heart of Monterey. Purple sea urchin condition (i.e., gonad mass relative to urchin size), sea urchin size-structure, distribution, abundance and habitat structure (substrate type, rugosity, algal cover) are examined to determine how these attributes influence the ability of sea otters to control sea urchin populations. The team suspects that if high densities of sea urchins in barrens (low algal cover) are malnourished and in poor condition (low gonad volume), then sea otters may preferentially feed on sea urchins of higher condition outside of barrens. If this is true, then sea otters will not feed on the high numbers of urchins in barrens and consequently not bring the outbreak of sea urchins under control. Therefore, surveys have been initiated to determine the relative condition (gonad biomass to urchin volume) of sea urchins inside barrens, along sea urchin fronts at the edge of barrens, and outside barrens. These surveys will be paired with otter real time sea otter foraging surveys to determine if sea otters prefer urchins inside or outside of barrens.
Effective workshops require strategic planning and detailed facilitation. Indeed, the pursuit of the hypotheses outlined above requires thorough field and lab experiments. In summer 2017, a total of 25 underwater sites were surveyed at locations where otters appeared to preferentially target urchins, based on concurrent foraging observations by an otter tracking team at the Monterey Bay Aquarium. An additional 80 reference sites were surveyed to characterize the distribution of sea urchin barrens, forested locations, and sea urchin foraging fronts around the study region. At each site, sea urchins were counted and measured. Data on the habitat structure and algae availability (i.e., urchin food resources) were also recorded.Â A subsample of urchins were collected from each site and brought to the lab for gonad and stomach dissections to determine how these factors contribute to sea urchin condition and ultimately scale-up to influence patterns of sea otter foraging.
Module 3: Mentorship
The two undergraduate students conducting summer research with Josh Smith will integrate this research with their academic curriculum by developing senior theses. Senior theses are not required at UCSC, but highly recommended for those interested in graduate school or research careers. Indeed, the benefits of undergraduate student research are well documented and have been linked to academic performance and post-graduate research careers. Oâ€™Donell et al. (2015) stated, "The opportunity to deeply engage [undergraduates] with role models, be they professors, graduate students, or more advanced peers, allows students to identify similarities in their backgrounds, demystify the path their mentors took to their positions, and, ultimately, view themselves in those roles."
Torrey Gorra is studying how factors such as depth, urchin-diet, and density influence where red and purple sea urchins are found, and if the size of their populations vary inside and outside and barrens. Specifically, her research compares population densities of red and purple sea urchins across depth strata. Torrey is extracting data on algae diversity from photo quadrats (Figure 3) and from urchin stomach contents in the lab (Figure 5), to determine how these factors influence urchin quality and their distribution.
Sabrina Garcia is studying the feeding structures of urchins inside and outside of barrens. She is focusing on how urchins may change the structure of their feeding apparatus (i.e., lantern) in response to changes in their food availability. Measurements of both sea urchin size and lantern structure are obtained during dissection. Data on food availability are extracted from field photo quadrats, and sea urchin diet composition of algae from lab dissections. These factors will be used to determine how environmental attributes contribute to lantern structure and urchin foraging behavior.
Untangling species interactions
Beneath the surface, the kelp sways to the rhythm of Monterey's heartbeat, where complex interactions between predators and their prey form the pulse of ecological communities. From urchin barrens to kelp forests, the research outlined above presents only a glimpse of nature's cadence, but nonetheless deepens understanding of the mechanisms that regulate the relationships between predators and their prey. Continued exploration into the processes that shape the structure of kelp forest communities will shed light on the overall health of the ecosystem.