(1:00-1:15)
[22]: Clearance Rate Comparison Between Three Lineages of the Pacific Oyster
Lexi Hollister★§, Gillian Douglas, Griffin Sawyer§, Faith Hanshaw, Kristin Hardy, Kevin JohnsonDepartment of Biological Sciences, §Santa Rosa Creek Foundation Support, ★Speaker
The Pacific oyster (Crassostrea gigas) is a prominent global aquaculture species whose growth may be determined by feeding rate. A new population of Pacific oysters (Midori) from Southern Japan from the mouth of the Midori river, has been introduced into breeding programs to increase disease tolerance of the highly selected Miyagi population. Previous work has found differences in growth and survival of these lineages when reared on commercial farms in Tomales Bay and Morro Bay, CA. In this study, we compared the clearance rates across multiple trials of Midori and Miyagi lineages of the Pacific oyster as well as a Hybrid cross lineage of the two populations. For each trial, to measure clearance rate, oysters were acclimated in beakers for one day and then fed Reed Mariculture LPB Shellfish Diet and the cell density of each beaker was measured over time using spectrophotometry. Clearance rates were then calculated based on the number of algae cells consumed per minute per gram of dry oyster tissue. These data provide insights into differences in feeding efficiency between lineages and are used to better understand differences in growth and survival of the three lineages observed from on-farm trials. |
(1:15-1:30)
[23]: Short-term aquatic heat wave conditions alter estrogen signaling to impair oogenesis in the Amargosa Pupfish
Isabel Villafuerte★§, Sean LemaDepartment of Biological Sciences, §Santa Rosa Creek Foundation Support, ★Speaker
The increasing frequency and severity of aquatic heat wave events associated with climate change may pose a threat to fish reproduction. Extremely high temperatures have been shown to impair reproductive processes in many fish taxa, yet most studies to date have exposed fish either to a stable elevated thermal regime or to prolonged periods of elevated temperatures. These thermal regimes may not always represent the fluctuating temperature conditions that fish experience in their dynamic environments. Here, we examined how a simulated short-term aquatic heat wave impacted reproductive physiology in the eurythermal Amargosa Pupfish Cyprinodon nevadensis amargosae. Adult pupfish were acclimated in mixed sex groups to an ecologically relevant fluctuating temperature regime that cycled 11°C daily, from a morning low of 20-21°C to an afternoon high of 31-32°C. After 54 d of acclimation to these fluctuating thermal conditions, a subset of the fish was exposed to a simulated ‘heat wave’ for 6 d by elevating maximum and minimum daily temperatures by 6°C. Females exposed to the short-term heat wave had significantly reduced ovarian gonadosomatic index (GSI) values and lower blood plasma concentrations of 17?-estradiol (E2), a hormone that plays a key role in regulating egg development. Male pupfish, however, were not impacted by ‘heat wave’ conditions as shown by the invariable testicular GSI values. Overall, our data reveal that short-term exposure to elevated temperatures like those during a heat wave can alter the ovarian status and reproductive endocrinology of female pupfish. |
(1:30-1:45)
[24]: Development of apneustic breathing in northern elephant seal pups (Mirounga angustirostris)
Olivia Springer★§, Elise Fiskum, Molly Murphy, Heather Liwanag, Linnea PearsonDepartment of Biological Sciences, §Santa Rosa Creek Foundation Support, ★Speaker
The ability to perform prolonged apnea (breath hold) is a key adaptation in diving mammals. Pinnipeds (seals, sea lions, walruses) are known to practice apnea on land and while diving. The ability to extend breath hold duration tends to increase with ontogeny in pinnipeds, though previous research has reported opposite patterns during the dependent pup life stage for northern elephant seals (Mirounga angustirostris). We examined the development of apneustic breathing in northern elephant seals, a deep-diving species, throughout pups’ approximately 4-week nursing period and after they weaned from their mothers. We hypothesized that age would influence the development of apneustic breathing. Based on previous research, we predicted (1) that younger northern elephant seal pups would exhibit apnea more frequently and for longer durations compared to older dependent pups, and (2) that apnea length would increase again after weaning. To test this, we characterized respiratory patterns of northern elephant seal pups (n = 101) using weekly video footage of known-age pups resting on the beach from 1 week of age and through the weaning period. We quantified eupneic (i.e., normal) respiration rate (breaths/min), presence/absence of apneustic breathing, and apneustic interval (length of breath hold) for each recording. We found that many pups were able to perform apnea almost immediately after birth, and that apneustic length was significantly positively correlated with age. These results contrast with previous studies in this species, as older dependent pups in our study exhibited longer apneustic intervals compared to newborn pups. This indicates that apneustic development may increase throughout ontogeny for northern elephant seal pups, which aligns with patterns observed in other pinniped species. Additional research is needed to determine whether this pattern is true for other populations of northern elephant seals or for other deep-diving seal species. |
(1:45-2:00)
[25]: Harbor seal haulout behavior in and near Morro Bay
Claire Savage†★, Dr. Heather LiwanagDepartment of Biological Sciences, †Frost Support, ★Speaker
Harbor seals (Phoca vitulina) are coastal marine mammals that haul out close to areas of human activity, but they are notoriously reactive to human disturbance. Plans for a wind farm offshore of Morro Bay are likely to increase ship traffic and other human activity in the Morro Bay area. The goal of this project is to generate baseline data of harbor seal haulout patterns and abundance, prior to wind farm implementation. During the summer, we documented the location and timing of harbor seal haulout behavior in Morro Bay and surrounding areas to determine haulout patterns relative to abiotic factors. To do this, we conducted regular ground surveys using binoculars at Estero Bluffs, Morro Bay, and Los Osos, documenting harbor seal abundance through a half tide cycle. We then correlated harbor seal haulout behavior to tide level and direction, air temperature, and wind. These data indicated that harbor seal abundance was significantly influenced by different combinations of these factors at each site. During the academic year, we conducted standardized surveys each week at peak haulout conditions for each location, to generate baseline data for harbor seal abundance at each site. This information will ultimately help us understand the impacts of increased anthropogenic activity associated with the offshore wind farm on our local harbor seals. |
(2:00-2:15)
[26]: Leveraging long-term demographic data to detect and examine density dependence in North American songbirds
Jordan Langley†★, Clinton Francis†, Sarah Jennings†Department of Biological Sciences, †Frost Support, ★Speaker
Although density dependence is widely accepted amongst ecologists as a fundamental process that regulates the size of natural populations, it is challenging to detect within real world wildlife populations without sufficiently long time series, and thus, it is rarely examined in more than one species at a time. We leveraged multigenerational demographic data compiled by the Monitoring Avian Productivity and Survival (MAPS) Program to examine evidence of density dependence in bird populations across North America. We used over 60,000 bird capture records from 381 MAPS banding stations that have operated between 10 and 27 years to obtain a dataset for 56 bird species. For each species, we investigated the relationship between adult abundance and per-capita productivity, a measure of reproductive output, using hurdle log-normal models within a Bayesian framework with weakly informative priors. All 56 species exhibited a negative relationship between adult abundance and per-capita productivity; however, the population size reached before negative density dependent regulation was detected, as well as the intensity of the effect, varied considerably across species. We then implemented phylogenetically-informed Bayesian models to explore how four classes of ecological traits – life history, diet, morphometric, and sexual selection traits – explained variation in density-dependent population regulation across 56 species of North American birds. |
(2:15-2:30)
[27]: Beach Hopping or Beach Bound? The Pursuit of the Perfect Spot in Northern Elephant Seal Maternity
Mackenzie Davidson1★§, Allison Theobold2, Tim Bean1, Heather Liwanag11 Department of Biological Sciences, 2 Department of Statistics, §Santa Rosa Creek Foundation Support, ★Speaker
Polygynous breeding, in which a single male mates with multiple females , is the most common mating system among mammals and often results in variable levels of reproductive success for males. The monopolization of access to females restricts female choice, which is especially evident in the northern elephant seal (Mirounga angustirostris). Our study measured female beach choice , a decision made prior to breeding, to discern if females attempt to maximize reproductive success in this way. Over two breeding seasons (2023-2025), we marked and visually tracked 121 female northern elephant seals’ beach locations at the Piedras Blancas colony in San Simeon, CA. We combined seal observations with beach density to evaluate whether crowded beaches influenced beach choice and the likelihood of switching beaches. Using a logistical regression, we found that higher densities at the arrival beach significantly increased females’ chance of switching beaches (B = 1.57, SE = 0.81, z = 1.96, p = 0.05), while the density of the beach to which they switched was less significant (B = 1.29, SE = 0.72, z = 1.79, p = 0.07). The interaction between the first and second beach densities was highly significant and negative (B = -2.63, SE = 0.97, z = -2.70, p = 0.007), meaning that when both beach locations’ densities were high, seals were less likely to switch. We conclude that density is an important metric in determining female beach choice in northern elephant seals and is a conceivable way in which they can increase their reproductive success, an important parameter to understand in this protected species. |
(2:30-2:45)
[28]: Effects of Temperature and Oxygen Exposure on Survival and Physiology of Olympia Oysters
Buyanzaya BuyanUrt†★§, Lexi Hollister†, Kristin M. Hardy, Kevin M. JohnsonDepartment of Biological Sciences, †Frost Support, §Santa Rosa Creek Foundation Support, ★Speaker
Olympia oysters (Ostrea lurida) are the only oyster species native to the North American West Coast. As sessile invertebrates that inhabit estuaries along the Western coast, Olympia oysters are subject to frequent and intense environmental stressors, particularly marine heatwaves and hypoxia events. In this study, we evaluated how two different populations of Olympia oysters respond to elevated temperature and oxygen limitation stress. Our physiological evaluation of the stress resilience of O. lurida included an assessment of survival rates, enzyme indicators of metabolic shifts [PK:PEPCK activity], and oxidative stress response [total antioxidant activity]. We found that survival during combined elevated temperature and anoxia stress was much greater in the more southern Morro Bay oyster population (LT50 = 28.5d) as compared to those from Elkhorn Slough (LT50 = 18.5d). Furthermore, metabolic enzyme assays found that there was a significant effect of oyster population on the PK:PEPCK ratio and a marginally non-significant interactive effect of temperature and oxygen treatment. Finally, the total antioxidant activity assay revealed no significant effects of population, temperature, or oxygen; however, the meat weight of the oyster was a significant predictor of total antioxidant activity. Collectively, our results suggest that O. lurida populations display distinct physiological responses to combined temperature and oxygen stress. The drivers of these differences may not be inherently due to population differences, as individual meat weight was a major contributor to the differences in physiological responses and covaried with population. |