Showing 1 - 5 of 5 Items

Date: 2022-01-01

Creator: Fiona G Ralph

Access: Open access

Species interactions are important to organisms and to the ecosystems they inhabit. These interactions, sometimes facilitations, can result in increased resiliency for both species. When facilitation occurs, organisms co-assist with physiological and environmental stressors. As anthropogenic impacts become more stressful for modern organisms, these interactions could offer a solution for many species. Ocean acidification has been shown to be detrimental to many calcifying organisms including oysters. More acidic conditions can slow the process of shell calcification, which can slow growth rates. This effect could directly impact the robust oyster farming business in Midcoast Maine. Because of its possible importance to oyster crops, we assessed the potential of Zostera marina, or eelgrass, to ameliorate the stresses of ocean acidification on farmed Eastern Oysters (Crassotrea virginica). Photosynthesizing organisms such as seagrasses have been shown to locally raise pH, which could create growth refugia for calcifying organisms. While eelgrass has the potential to enhance oyster growth rates, its meadows could also be influencing food availability. To better understand these dynamics, we grew C. virginica in two locations in Harpswell, ME. Crassostrea virginica were split into three habitats at each location: seagrass, fringe, and mudflat, and placed on surface or benthic arrays. We found that seagrass presence and depth interacted to increase shell growth rate. Similarly, Z. marina improved condition index of C. virginica. As ocean acidification worsens, oyster farmers might have to turn to mitigation strategies to ensure profit yield from their labors. Zostera marina could be the solution to their future problems.

Date: 2024-01-01

Creator: Mary Alta Rogalski, Elizabeth S Baker, Clara M Benadon

Access: Open access

Increasing application of road deicing agents (e.g., NaCl) has caused widespread salinization of freshwater environments. Chronic exposure to toxic NaCl levels can impact freshwater biota at genome to ecosystem scales, yet the degree of harm caused by road salt pollution is likely to vary among habitats and populations. The background ion chemistry of freshwater environments may strongly impact NaCl toxicity, with greater harm occurring in ion-poor, soft water conditions. In addition, populations exposed to salinization may evolve increased NaCl tolerance. Notably, if organisms are adapted to their natal lake water chemistry, toxicity responses may also vary among populations in a given test medium. We examined how this evolutionary and environmental context may interact in shaping NaCl toxicity with a pair of laboratory reciprocal transplant toxicity experiments, using natural populations of the water flea Daphnia ambigua from three lakes differing in ion availability. The lake water environment strongly influenced NaCl toxicity in both trials. NaCl greatly reduced reproduction and r in lake water from a low-ion/ calcium-poor environment compared with water from both a calcium-rich lake and an ion-rich coastal lake. Daphnia from this coastal lake were most robust to the effects of NaCl. A significant population x environment interaction shaped survival in both trials, suggesting that local adaptation to the test waters used contributed to toxicity responses. Our findings that the lake water environment, adaptation to that environment, and adaptation to a focal contaminant may shape toxicity demonstrate the importance of considering environmental and biological complexity in mitigating pollution impacts.

Date: 2020-01-01

Creator: Siena Brook Ballance

Access: Open access

Phytoplankton underpin marine trophic systems and biogeochemical cycles. Estuarine and coastal phytoplankton account for 40-50% of global ocean primary productivity and carbon flux making it critical to identify sources of variability. This project focuses on the Kennebec River and Harpswell Sound, a downstream, but hydrologically connected coastal estuary, as a case study of temperate river influence on estuarine nutrient regimes and phytoplankton communities. Phytoplankton pigments and nutrients were analyzed from water samples collected monthly at 8 main-stem rivers stations (2011-2013) and weekly in Harpswell Sound (2008-2017) during ice-free months. Spatial bedrock and land use impacts on river nutrients were investigated at sub-watershed scales using GIS. Spatial analysis reveals a 10-fold increase in measured phytoplankton biomass across the Kennebec River’s saltwater boundary, which demonstrates ocean-driven phytoplankton variability in the lower river. The biomass pattern is accompanied by a transition in phytoplankton community structure with respect to which groups co-occur (diatoms, chlorophytes, and cryptophytes) and which are unique (dinoflagellates in Harpswell). Upstream, the timing of each community depends on land-use proximity and seasonal discharge. In Harpswell Sound, the nutrient regime and phytoplankton community structure vary systematically: first diatoms strip silicate, then dinoflagellates utilize nitrate, followed by chlorophytes and cryptophytes that utilize available phosphate. These findings reveal, for the first time, patterns in phytoplankton communities and nutrient dynamics across the fresh to salt water interface. Ultimately the Kennebec River phytoplankton communities and nutrient regimes are distinct, and the river is only a source of silicate to Harpswell Sound.

Date: 2021-01-01

Creator: Eugen Florin Cotei

Access: Access restricted to the Bowdoin Community

Date: 2016-05-01

Creator: Sabine Y Berzins

Access: Open access

Eelgrass (Zostera marina) is a perennial seagrass that provides many vital ecosystem services including stabilizing sediments, maintaining water clarity, and providing complex habitat in the intertidal and shallow subtidal coastline. Historically, Maine supported dense eelgrass beds in shallow waters surrounding islands and along the coastal mainland. However, in 2012, high population densities of European green crabs (Carcinus maenas), which physically disturb and remove eelgrass as they forage, were correlated with widespread eelgrass declines. Over 55% of the area of eelgrass in Casco Bay was lost, mainly between 2012 and 2014. Eelgrass typically grows in low-oxygen sediments that produce a chemically reducing environment. Sulfate-reducing bacteria in these reduced sediments produce hydrogen sulfide, a toxin that can intrude into eelgrass tissues and impair the plants’ ability to photosynthesize. When eelgrass is not present, sulfide can build up in the pore-water. When eelgrass is present, it can oxygenate the sediments through its roots, thereby preventing the intrusion and buildup of toxic hydrogen sulfide. However, if the substrate is de-vegetated, oxygen levels drop as sedimentary organic matter is decomposed, and the accumulation of sulfides to harmful concentrations in the pore-water may make recolonization of eelgrass difficult or perhaps impossible even in the absence of green crabs. In an effort to monitor characteristics of Casco Bay eelgrass beds and determine spatially where eelgrass may be more likely to recover, four Casco Bay sites with varying degrees of vegetation loss were sampled in 2015 for pore-water sulfide concentration, sediment carbon and nitrogen content, and sediment grain size analysis. Measurements of sulfide concentrations showed correlations with the timing of eelgrass loss, such that vegetated sites had low pore-water sulfide concentrations and sites that had been de-vegetated for longer periods of time had high sulfide concentrations. Carbon and nitrogen content in the sediment was higher at de-vegetated sites, likely due to a higher percentage of finer sediments at those locations. Coarser sediments were more highly vegetated than finer sediments, perhaps displaying a preference of green crabs to forage in finer sediments. Catastrophic loss of eelgrass in Casco Bay has likely led to differences in sulfide levels, carbon and nitrogen content in the sediment, and grain size distribution, depending on degree of vegetation. Eelgrass restoration in Casco Bay will likely be limited by high pore-water sulfide concentrations.