Temporal and spatial analysis of the relationship between hypoxia, temperature, and benthic biodiversity in the St. Lawrence Estuary and Gulf

• Main Author: Steinhart, Rebecca
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2023
• Subjects: Newfoundland
• Online Access: https://research.library.mun.ca/16091/; https://research.library.mun.ca/16091/1/converted.pdf

This thesis explores temporal changes, and spatial patterns of marine benthic communities in Canada’s Lower St. Lawrence Estuary (LSLE) and Gulf of St. Lawrence (GSL) and finds benthic biodiversity consistent with responses to an altered environment. Dissolved oxygen in the LSLE has slowly and continuously declined for decades with no seasonal or episodic return to normal oxygen levels. Temporal analysis of sedimentary fauna from the region confirmed significant reductions in benthic species richness, evenness, and Shannon diversity between 1980 and 2005/6, but higher abundance in 2005/6 samples, a pattern seen in studies of succession following disturbance. These analyses identified multiple contributors to this shift beyond opportunistic species, including species displaying a range of tolerances for organic disturbance and minimal capacity to cope with hypoxia. Surprisingly, mean richness and Shannon diversity in the LSLE exceeded that in the GSL in locations of lowest oxygen concentration, noting no documentation of environmental shifts by 2005 in the GSL. Comparison of stations grouped by oxygen concentrations indicated a clear biological threshold in the LSLE by 2005 that excluded most omnivores and subsurface deposit feeders. Analysis of benthic communities in 2015 indicated significantly higher diversity and differences in assemblages between those near the southwest coast of Newfoundland and those at the intersection of the Laurentian and Esquiman Channels. Port au Port Bay stations supported the highest number of families tolerant of eutrophication and hypoxia. A shift to a higher proportion of surface deposit feeders and to organisms more tolerant of disturbance characterized stations in the Laurentian/Esquiman Channel in 2015 compared to nearby stations in 2006. These changes in benthos, combined with significant reductions in oxygen concentrations and rising temperatures in the eastern GSL suggest increasing risk of benthic community alteration in this region. Changes in LSLE and GSL benthos ...