Showing 1 - 10 of 18 Items

Date: 2024-01-01

Creator: Renske Kerkhofs

Access: Open access

American lobsters (Homarus americanus) produce humming sounds by vibrating their carapace. These sounds have a fundamental frequency on the order of 100 Hz, with multiple higher harmonics. Though I found no relationship between lobster carapace length and hum frequency, I observed sounds similarly structured to hums but with frequencies an order of magnitude higher, suggesting that lobsters may use a wider range of sounds than previously thought. Using laser vibrometry, I was able to pick up high frequencies of carapace vibration that were similar to those I observed on sound recordings. Lobsters seem to hum most readily when approached from above, but many studies have found it difficult to reliably find soniferous lobsters. To find a way to reliably evoke sound production in American lobsters without contributing to the sound environment, lobsters were exposed to overhead abstract visual stimuli on a screen, after which their behavioral reactions were recorded, as well as any sound production in response to the stimulus. Lobsters responded to the screen stimulus with the same types of behaviors with which they responded to general overhead physical stimuli. This study demonstrates that American lobsters may produce high-pitched sounds and that abstract visual cues can be used as a silent tool to elicit lobster behaviors, but not sound production.

• Embargo End Date: 2029-05-16

Date: 2024-01-01

Creator: Nicholas Takaki Tienhui Yoong

Access: Embargoed

• Embargo End Date: 2027-05-16

Date: 2024-01-01

Creator: Everett Horch

Access: Embargoed

Date: 2024-01-01

Creator: Andre Eden

Access: Open access

During every second of a human’s life, the cardiovascular system is modulated by factors both intrinsic and extrinsic to the physiology of the heart. We can uncover new insights regarding the nature of our system through investigations of similar systems in other model species. One example materializes itself in the form of the American Lobster (Homarus americanus) whose single-chambered heart finds resemblance to the function and anatomy to that of humans. The lobster heart is powered by the cardiac ganglion (CG), a group of neurons that drive contractions of surrounding heart muscles, known as the myocardium. Both the CG and myocardium work in a feedback loop, with both intrinsic (afterload and preload) and extrinsic (temperature and neuropeptides) factors affecting cardiac output (CO) or the overall ability of the heart to carry out its primary function of nutrient distribution. In this paper, we examine how the addition of these factors into in vitro whole heart preparations affect CO and other associated variables. From experimentation, we conclude that the neuropeptide SGRNFLRFamide (SGRN) increases the heartbeat frequency and the active force exerted by the heart. We also conclude that increases in temperature decrease CO as higher temperatures decrease heartbeat frequency and the active force exerted by the heart. Lastly, we conclude that the effect of preload and afterload combined produce more robust effects on the CO and active force of the heart, potentially painting a better picture of what may happen in vivo.

Date: 2024-01-01

Creator: Jared Lynch

Access: Open access

The mitochondrial genome has historically been relegated to a neutral genetic marker, but new evidence suggests mitochondrial DNA to be a target for adaptation to environmental stress. The invasive European green crab (Carcinus maenas) exemplifies this in the Gulf of Maine’s hybrid zone, where interbreeding populations exhibit thermal tolerances influenced by mitochondrial genotype. To better understand the mechanism behind this phenomenon, the effect of mitochondrial genotype on mitochondrial activity was tested by measuring mtDNA copy number (mtCN) and the activity of complex I, II, and IV of the electron transport system via high-resolution respirometry. Mitochondria isolated from frozen heart tissue were measured at three temperature points—5°C, 25°C, and 37°C—to represent thermal stresses and a control. It was predicted that cold-adapted haplogroups would exhibit both higher mtCN and increased activity for each complex, either across all temperatures or exclusively at 5°C compared to a warm-adapted haplogroup. Initial comparisons of mitochondria from fresh and frozen tissue at 25°C found lower activity for complex II and IV in frozen extracts, but they continued to be used for convenience. No differences were observed across haplogroups for mtCN or high-resolution respirometry, suggesting that mitochondrial activity does not underlie differences in thermal tolerance. However, temperature greatly influenced activity measurements with complex II and IV exhibiting the highest rates at 37°C while complex I exhibited optimal activity at 25°C. This study represents the first of its kind for C. maenas, providing a foundation for future experiments to continue exploring mitochondria in the context of adaptive evolution.

• Embargo End Date: 2026-05-18

Date: 2023-01-01

Creator: Bridget Marjorie Patterson

Access: Embargoed

Date: 2023-01-01

Creator: Charlie Francis O'Brien

Access: Open access

Harpswell Sound (HS) is an inlet in northeastern Casco Bay that exerts control on Gulf of Maine ecosystem health, yet its complex phytoplankton community dynamics have not been characterized with sufficiently detailed analyses. In this research, high-resolution automated microscopy and current velocity observations were used to test the seasonality, ecological succession, bloom origin location, and potential toxicity of populations in HS between 2020 and 2022. Winter months could exhibit slow accumulation of diatom biovolume. Cold, salty surface water has net outflow in winter as nutrients from depth are replenished during net upwelling conditions, and populations could be exported from the inlet at the surface. Extreme current velocity variability in spring due to the Kennebec River plume in HS destabilizes spatially uniform populations. Warm, low-salinity surface water with net inflow in summer (net downwelling which retains populations at the head of the sound) corresponds with temporally separate dinoflagellate and diatom blooms. Large, multi-peaked spring and fall diatom blooms are recurrent, contrasting small, short-lived blooms in summer. A successional pattern from diatoms to dinoflagellates is confirmed for summer but refuted for other seasons. The hypothesis that diatom succession during all blooms in HS is characterized by large centric cells preceding small cells or pennate cells was explored but no clear pattern in decreasing cell size was observed. Observed tidal effects on biovolume concentration could mask that blooms develop at coherent times but spatially separated. A diverse community of toxic phytoplankton, including dinoflagellates and Pseudonitzschia, are observed throughout the year.

Date: 2023-01-01

Creator: Gretchen Clauss

Access: Open access

As the Gulf of Maine warms and lobsters move north to colder waters, Maine’s working water front has begun to diversify. There is a thriving new ecosystem of aquaculturists looking to keep Maine’s waterfront traditions alive in a lasting, sustainable way. One of the most popular aquaculture industries is oyster farming. With an increasing number of oyster farms developing in Midcoast Maine each year, we seek to develop a decision support tool to aid farmers in seed management. Oyster farmers can choose weather or not to use an upweller on their farm, and our goal is to provide guidance on this choice, as well as on upweller management. We begin by culminating and synthesizing data from previous literature and oyster farmers. We then use this data to first build a basic analytical model of a cohort of oysters based on an exponential growth model. We expand this model to include biological differences among oysters as well as management practices. Finally, we walk through a case study, illustrating how our tool could be used to make seed management decisions on an individual farm scale.

• Embargo End Date: 2026-05-18

Date: 2023-01-01

Creator: Deva K Holliman

Access: Embargoed

Date: 2021-01-01

Creator: Hannah L. Randazzo

Access: Open access

Anthropogenic CO2 is changing the pCO2, temperature, and carbonate chemistry of seawater. These processes are termed ocean acidification (OA) and ocean warming. Previous studies suggest two opposing hypotheses for the way in which marine climate stress will influence echinoderm calcification, metabolic efficiency, and reproduction: either an additive or synergistic effect. Sea stars have a regenerative capacity, which may be particularly affected while rebuilding calcium carbonate arm structures, leading to changes in arm growth and calcification. In this study, Asterias forbesi were exposed to ocean water of either ambient, high temperature, high pCO2, or high temperature and high pCO2 for 60 days, and the regeneration length of the amputated arm was measured weekly. Ocean acidification conditions (pCO2 ~1180 μatm) had a negative impact on regenerated arm length, and an increase in temperature of +4°C above ambient conditions (Fall, Southern Gulf of Maine) had a positive effect on regenerated arm length, but the additive effects of these two factors resulted in smaller regenerated arms compared to ambient conditions. Sea stars regenerating under high pCO2 exhibited a lower proportion of calcified mass, which could be the result of a more energetically demanding calcification process associated with marine climate stress. These results indicate that A. forbesi calcification is sensitive to increasing pCO2, and that climate change will have an overall net negative effect on sea star arm regeneration. Such effects could translate into lower predation rates by a key consumer in the temperate rocky intertidal of North America.