Thesis Defense By Bennett Bugbee – May 8th

"EFFECTS OF DENSITY ON MORPHOMETRICS AND REPRODUCTIVE PHYSIOLOGY IN THE BULL KELP (NEREOCYSTIS LUETKEANA), AN ANNUAL FOUNDATION SPECIES"

A Thesis Defense by Bennett Bugbee

MLML Phycology

Live-Stream | May 8th, 2025 at 9:00 am PDT

Bennett holding a crowned bull kelp from the Albion soral bank tank at the MLML shore lab.

Abstract

The bull kelp, Nereocystis luetkeana, is the predominant canopy forming kelp along much of the northeastern Pacific. However, it remains largely understudied due to the dynamic nature of its niche coupled with its annual life history. For populations to persist, reproductive sporophytes must release substantial spores to facilitate successful sexual fertilization among male and female gametophytes that will develop into the next cohort of sporophytes. High densities of spores increases the likelihood of completing the alternation of generation life cycle characteristic of kelp genera. Yet those high densities of spores have the potential to result in a high density of sporophytes, competing for light to reach the surface canopy. It is currently unknown how density-dependence will alter the morphological development and reproductive investment of Nereocystis, thereby affecting population persistence. To address this, I investigated how density affects the morphology and reproductive traits of Nereocystis across its life history. Laboratory studies were conducted to test the effects of density on gametogenesis, gametophyte growth, female egg production, and sporophyte production. Additional studies were conducted on juvenile whole sporophytes and crowned sporophytes (i.e., modified to retain a small portion of the pneumatocyst) in land-based tumble culture to assess the effects of density on survivorship, stipe growth, pneumatocyst growth, blade growth, blade development (number), and reproductive investment (soral number, blades bearing sori, and soral size). Low spore density treatments resulted in significantly larger female gametophytes. Intermediate spore densities yielded higher eggs per female, yet there were no significant differences across density treatments. Sporophyte density was significantly greater at higher spore densities. Juvenile sporophytes grown in tumble culture showed no significant difference in survivorship as a function of sporophyte density. High densities delayed sporophyte development compared to sporophytes grown in low density treatments, which were characterized by long stipes and numerous blades. Density-dependent effects on crowned sporophytes were similar to juvenile sporophytes with low densities promoting increased growth and development, while high densities inhibited normal development. At 4 weeks, sporophytes shifted from allocating resources from growth to reproduction. Soral (i.e., reproductive tissue) size and soral number exhibited a significant negative density-dependent relationship. At the individual scale, low density treatments displayed significantly greater reproductive investment. However, scaling reproduction to the population resulted in intermediate densities having the highest cumulative reproductive potential. Given its life history and need for sustained annual reproductive success to fuel population replenishment, these results suggest that Nereocystis may have a higher threshold for negative density-dependent interactions compared to other perennial kelps.

 

Bio

Bennett earned his B.S. in Biology from Pacific Lutheran University in 2018. While at PLU, when not competing on the men’s soccer team, he developed his passion for marine environment and got SCUBA certified. After joining the Phycology lab at MLML, he quickly began spending a lot of time in the water, helping fellow students collect data, developing ideas for his thesis, and working on bull kelp restoration projects in Mendocino and Sonoma counties. Much of his research focused on bull kelp morphometrics and physiology, both in the lab and in the field. Outside of his research, he served as Open House co-chair, brew club organizer, and a Phycological Society of America Student and Early Career Researcher committee member. He can often be found in the tidepools around the Monterey Peninsula or running around with his dog Scuba. After graduation, Bennett will continue at MLML as a technician on the bull kelp restoration efforts in Mendocino, along with working at Monterey Bay Seaweeds.

Seminar – The effects of environmental change on the importance of non-consumptive predator effects in the rocky intertidal zone

Dr. Paul Bourdeau  | California State Polytechnic University, Humboldt
Presenting: "The effects of environmental change on the importance of non-consumptive predator effects in the rocky intertidal zone"
Hosted by the Invertebrate Ecology Lab

MLML Seminar | May 7th, 2025 at 4pm (PDT)

Watch the Live Stream here or here

The effects of environmental change on the importance of non-consumptive predator effects in the rocky intertidal zone
Prior to the 1990s, most ecological theory viewed predator–prey interactions from the simple perspective of predators consuming their prey. In recent decades, ecologists have amassed evidence showing that prey respond to the threat of predation by changing their behaviors, morphologies, and life histories. These non-consumptive effects (NCEs) of predators may act in concert with the direct consumption of prey to influence prey abundance and community dynamics. Yet, we have only scratched the surface of this active and fascinating field. Despite all the excellent research in this area, some significant questions remain unanswered, including: “How important are NCEs relative to consumptive effects in predator– prey interactions?”; “How are properties of predators used by prey to encode threat?”; and “How does the environment affect predator detection and subsequent NCEs”?. My students and I have used experimental approaches in the lab and field to assess the potential for strong NCEs in the rocky intertidal zone and what factors or environments produce strong versus weak NCEs.

Dr. Paul Bourdeau

Dr. Paul Bourdeau is an Associate Professor of Marine Biology and Ecology at Cal Poly Humboldt, where he also serves as the Graduate Coordinator for the Department of Biological Sciences and the interim director of the Telonicher Marine Laboratory. A native of southeastern Massachusetts, Dr. Bourdeau earned his BS in Biology and MS in Marine Biology from the University of Massachusetts Dartmouth, followed by a PhD in Ecology and Evolution from Stony Brook University. He conducted postdoctoral research at Michigan State University before joining Humboldt in 2014. Dr. Bourdeau’s lab’s research focuses on how marine organisms respond to environmental changes, particularly those induced by human activities, such as the introduction of non-native species and climate change.

Thesis Defense by Dylan Sarish – May 1st

"The Influence of Maternal Size/Age Effects On the Physiological Responses of Adult Female Gopher Rockfish (Sebastes carnatus) to Ocean Acidification and Hypoxia"

A Thesis Defense by Dylan Sarish

MLML Ichthyology

Live-Stream | May 1st, 2025 at 4:00 pm PDT

Abstract

Climate change is rapidly reshaping the chemistry of the ocean. Fishes living in California coastal waters experience ocean acidification, elevated pCO2, and hypoxia (OAH) in response to upwelling of deep water, and this process may increase in frequency and intensity with climate change. Nearshore rockfish may be particularly threatened by increasingly frequent OAH conditions due to their long lifespans and late maturation. Maternal effects, whereby larval condition is influenced by non-genetic components of the maternal phenotype (e.g. size, age) or environment, is one process that may allow rockfish to rapidly adapt to climate change. To understand the physiological effects of OAH on pregnant rockfish during gestation, adult female gopher rockfish, Sebastes carnatus, were collected and exposed to four different combined OAH stress treatments, from fertilization to parturition. A second group was exposed to two combined OAH stress treatments. Routine metabolic rate (RMR), maximum metabolic rate (MMR), blood chemistry, including hematocrit (Hct), hemoglobin (tHb), pCO2, HCO3-, ions (Na+, K+, Cl-), and metabolites, were measured to assess physiological responses to OAH stress. Ovarian oxygen levels were measured to examine the potential capacity of females to buffer their developing broods against changing ocean chemistry. Fish exposed to higher OAH stress displayed elevated Hct and tHb, higher blood pCO2 and HCO3-, and decreased MMR, indicating they attempted to compensate for low pH and hypoxia exposure. Only partial compensation was achieved as blood pH was not always maintained near ambient levels. Fish showed signs of buffering their ovaries against hypoxia under OAH exposure. Lastly, pregnancy altered Hct and MMR under OAH exposure and size/age did not have a consistent effect on maternal physiology. By evaluating the responses of maternal physiology to OAH stress, which directly impact larval physiology, we can better understand how climate change affects, fecundity, larval condition, and survival which will influence the management of nearshore fisheries in an ever-changing climate.

Bio

Dylan earned her B.S. in Marine Biology with a minor in Environmental Science from UC San Diego in 2019. While at UCSD, when not practicing as a member of the varsity fencing team, she volunteered for Dr. Andrew Nosal, where she helped with the tagging of sevengill sharks in La Jolla cove, and was in charge of the care and feeding of a tank of juvenile horn sharks in the Scripps Institute of Oceanography’s experimental aquarium. She was also a member of the Coral Ecology Lab under Dr. Stuart Sandin, where she contributed to the 100 Island Challenge. After graduating, Dylan spent some time working for the California Department of Fish and Wildlife, where she contributed to the California Recreational Fisheries Survey (CRFS) as a sampler, assisting with the mission to collect fishery-dependent data on California’s marine recreational fisheries and to accurately estimate catch, effort, and stock.

Dylan joined the Ichthyology lab in Fall of 2022, and examined the effects of ocean acidification and hypoxia on the reproductive success of female gopher rockfish. In her spare time, Dylan enjoys being around animals, baking, and traveling

Thesis Defense by Keenan Guillas – May 1st

"DRIVERS OF RHYTHMIC CONTRACTIONS IN THE TEMPERATE DEMOSPONGES TETHYA CALIFORNIANA AND HYMENIACIDON PERLEVIS"

A Thesis Defense by Keenan C. Guillas

MLML Invertebrate Ecology

Live-Stream | May 1st, 2025 at 2:00 pm PDT

 

Keenan aboard the R/V John H. Martin.

Abstract

Sponges (Phylum Porifera) are suspension feeders whose water filtration is important to benthic ecosystems because of their conversion of large amounts of dissolved carbon and nitrogen into particulate waste available for detritivores. Sponges filter water by drawing it through a complex aquiferous system of canals and pores. Rhythmic contractions of tissue, which temporarily constrict canals and reduce body size, can diminish filtration rates and therefore affect ecosystem services; however, the physiological function of rhythmic contractions is not completely understood. I recorded long-term time-lapses of the demosponges Tethya californiana and Hymeniacidon perlevis to determine the endogenous and environmental factors that influence rhythmic contractions. I found that contractions occurred simultaneously in the osculum, ostia, and whole body in T. californiana. In H. perlevis, contractions originated and spread between many different oscula, with no evidence of cohesive whole-body behaviour. In T. californiana, duration of rhythmic contractions were significantly correlated with body size, oceanographic season, and dissolved oxygen. Both species reduced contraction frequency and increased total time expanded in seawater enriched with Rhodomonas sp. microalgae. This thesis provides support for rhythmic contractions in sponges as products of both endogenous and environmental factors, improving our understanding of the complexity of behaviours in early-diverging aneural metazoans.

 

Bio

Keenan earned his BSc in 2018 from the University of Alberta, where he worked with Dr. Sally Leys investigating the ecology of glass sponge reefs in Hecate Strait, British Columbia. At MLML his research focused on drivers of rhythmic contraction behaviours in the marine demosponges Tethya californiana and Hymeniacidon perlevis. He used time-lapse photography and microscopy to improve our understanding of sponge coordination, behaviour, and resilience. He was also student body vice president and an active member of the MLML community. He is now a research technician in the Marine Structural Biology unit at Okinawa Institute of Science and Technology in Japan. He is also a coffee enthusiast and a fiction writer.