Showing 1 - 10 of 18 Items

• Embargo End Date: 2025-05-14

Date: 2020-01-01

Creator: Emma Victoria Bertke

Access: Embargoed

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.

Date: 2018-05-01

Creator: Madeline Schuldt

Access: Access restricted to the Bowdoin Community

• Embargo End Date: 2029-05-16

Date: 2024-01-01

Creator: Nicholas Takaki Tienhui Yoong

Access: Embargoed

Date: 2015-05-01

Creator: Courtney Michelle Payne

Access: Open access

With warming global temperatures and changes to large-scale ocean circulation patterns, warm water intrusion into Arctic fjords is increasingly affecting fragile polar ecosystems. This study investigated how warm Atlantic water intrusion and the tidewater glacial melting it causes impacted water mass formation and primary productivity in Kongsfjorden, Svalbard. Data were collected over a 2-week period during the height of the melt season in August near the Kronebreen/Kongsvegen glacier complex, the most rapidly retreating glacier in Spitsbergen. Since 1998, intruding waters have warmed between 4 and 5.5˚C, which has prevented sea ice formation and changed the characteristics of fjord bottom waters. Increased glacial melting in the last decade has changed the characteristics of surface waters in the fjord. Modeled light fields suggest that suspended sediment in this glacial meltwater has reduced the euphotic zone close to the ice face, preventing high primary production in both the consistent and intermittent sediment-laden meltwater plumes. However, measurements collected close to terrestrially terminating glaciers indicate that extremely high primary production can occur in conditions of low turbidity. The results of this study support a three-part model of the effects of warm-water intrusion on water mass formation and primary production, where changes in sea ice coverage and tidewater glacial dynamics affect the optical light field. This model allows for spatial predictions for the most likely impacts of warm water intrusion on primary production in Spitsbergen, and could be extrapolated out to explore potential phytoplankton response in other regions susceptible to warm-water intrusion.

• Embargo End Date: 2027-05-16

Date: 2024-01-01

Creator: Everett Horch

Access: Embargoed

Date: 2015-03-01

Creator: Aidan W. Short, David B. Carlon

Access: Open access

A new wave of green crabs Carcinus maenus is sweeping through the Gulf of Maine (GOM). While first reports of green crabs in the GOM date from the early 1900s, populations in southern GOM have exploded in the last five years. In the Casco Bay region, this unusually high abundance is associated with poor commercial shellfish landings and the decline of eel grass habitat (Zostera marina). To determine the mechanistic roles green crabs play in direct and indirect ecological interactions, it is important to understand diet breadth, and how feeding preferences change in response to ecological context. Since green crabs are omnivorous, traditional approaches to diet analysis via hard parts suffer from substantial bias. We are using DNA barcoding and next generation sequencing (NGS) to analyze green crab diets from a longitudinal sampling design in Casco Bay. In addition to a temporal dimension, our design includes two habitats: clam flats and eel grass beds. We have now sampled ~ 1000 crabs and have processed 460 individual stomachs from a range of sizes and both sexes. Here we will present: our sampling design, our NGS pipeline, and preliminary analysis from a lobster-specific (Homarus americanus) probe. Presenting author status: Undergraduate Preferred presentation type: Poster Preferred topics: 3. Biological invasions; 18. Molecular ecology Benthic Ecology Meeting, 2015 Quebec City, Canada Aidan Short was an undergraduate student at Bowdoin College when this research was conducted.

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.

Date: 2021-01-01

Creator: Grace Marie Hambelton

Access: Open access

Baroreceptors are stretch receptors located in the aorta of mammals; in response to increased afterload, they elicit a decrease in heart rate, creating a negative feedback loop that lowers blood pressure. Although lobsters (Homarus americanus) do not have baroreceptors like mammals, closely related land crabs have been shown to have baroreceptor-like responses. Heart contraction is also regulated by the Frank-Starling response, where increasing stretch or preload increases the contractile force of the heart. In addition to these types of biomechanical modulations, lobsters use a central pattern generator, the cardiac ganglion, to maintain synchronicity of the heartbeat. The heart is also controlled by the central nervous system via neuromodulators, such as myosuppressin, which has been shown to increase active force and decrease frequency in isolated lobster hearts. We performed experiments on a lobster heart with the main arteries still intact, and varied the preload by stretching anterior arteries, and the afterload by elevating the dorsal abdominal artery. We added myosuppressin to modulate the cardiac ganglion output and muscle contraction. We found that the baroreceptor-like response is most directly modulated by active force, whereas frequency could be a secondary control. Increasing preload does increase active force, but that does not correlate to a higher cardiac output, which shows that how hard the heart pumps is not what determines how effectively it is pumping. Additionally, we found that myosuppressin has a much stronger effect on frequency than active force, and so with myosuppressin, frequency becomes the main determinant of cardiac output.

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.