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Levesque Final Dissertation (5-06-19)

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Abstract

Natural resources are among the most valuable commodities on earth. Some natural resources (air, land, and water) are essential for human survival and many often constitute a large percentage of local, regional, and national economies, such as marine resources. Worldwide, marine resources have shaped culture, society, and local, regional, and global economies. Oceanic environmental conditions influence, shape, and control the geographical range, spatial distribution, abundance, and size composition of marine fauna. Thus, marine communities are vulnerable to major changes in the environmental conditions and disturbance (short and long-term), but the response and severity depends on various biological or ecological factors, such as resilience to stress or adaptation. Given the need to describe, understand, and interpret these processes, the broad purpose of this dissertation was to provide community-based marine resource information to fishery managers responsible for conserving, protecting, and restoring fish communities. More specifically, the goal was to examine several disturbances on the population dynamics and community structure of the marine community off the coast of New Jersey. The research in this dissertation developed valuable relative baselines for the nearshore environmental conditions, marine fauna populations, and the marine community in context of fast and slow-acting disturbance. Chapter One provides an overview, synopsis, and a historical perceptive on the importance of marine resources and highlights some of the issues related to short and long-term disturbances, such as hurricanes and climate variability. The first chapter summarizes how climate variability is affecting individual species and marine communities around the world. The background chapter justifies the dissertation, states the purpose and goals, and describes how the hypotheses were formulated; it also provides an organizational outline for the dissertation. Chapter two shows the abiotic conditions and marine community is changing with time. Mean surface water temperature increased significantly about 0.6°C per decade, mean salinity decreased about 1.3 psu per decade, and dissolved oxygen (DO) increased 0.09 mg/L per decade during 1988 through 2015. A total of 18.7 million individuals representing 216 species were collected during the 28-year period, and the estimated abundance and biomass of marine fauna decreased and increased over time, respectively. Subtropic-adapted species were the most abundant and coldwater-adapted were the least abundant water temperature preference group. The estimated abundance of coldwater-adapted species declined, warmwater-adapted species slightly increased, and subtropic-adapted species decreased with time. Chapter three demonstrates marine communities are vulnerable to changes in the environmental conditions associated with hurricane events, but the response and severity depends on various factors, such as ecological resilience. The results show the annual bottom salinity and surface DO varied significantly between pre- (1988−2012) and post- (2013−2015) Hurricane Sandy. The oceanographic and physicochemical conditions in January varied significantly between pre- and post-Sandy, and the interaction effect varied significantly among factors (year, month, and geographic sampling area), but the significance level depended on the sampling area. For instance, the abiotic conditions pre- and post-Sandy varied significantly in sampling area “19”, which was in the direct path of the storm. The marine community (abundance) in January also varied significantly between pre- and post-Sandy, but the magnitude of the significance level difference in the marine community depended on the sampling area. For example, the marine community pre- and post-Sandy varied significantly in sampling areas “16 and 20”; sampling area “20” was in the direct path of the storm. Overall, there was no significant change in the biomass, and the community structure was similar pre- and post-Sandy. Chapter four describes the biodiversity (alpha and beta diversity) in the nearshore marine community off New Jersey over the past 28 years. Estimated species richness increased substantially during the first few years of sampling, and reached asymptotic richness in about 13 years. Species richness estimates varied significantly over time, but in general the trend was similar and relatively stable. The lowest mean species richness (n = 121.3 species) was estimated using the mean Michaelis-Menten approach and the highest mean species richness (n = 156.3 species) was estimated using the mean Jackknife 2 approach. Alpha diversity and evenness estimates indicated the community was composed of a few species with high abundance. Fisher’s alpha diversity index best described the marine community, which ranged from 9.04 in 1988 to 15.95 in 1989 with an average of 11.76 (± 1.62 SD). Alpha diversity and evenness indices fluctuated from one year to the next, but remained stable over time. Beta diversity estimates also showed interannual variability, but similarity values were relatively stable over time; approximately 50 percent of the species were shared among samples. Analytical procedures could not detect an association between community stability and the environmental conditions suggesting the community is possibly shaped by other factors, such as inter- and intra-species associations. The findings propose the community is resilient despite the ongoing changes in the environmental and oceanic conditions. In the final chapter, Chapter five, the findings suggest the variability in the environmental and atmospheric conditions is shifting the marine community. The environmental, oceanic conditions, marine community, and coldwater-adapted community were significantly different among years and geographical sampling areas. The best environmental predictors of the marine community were primarily water temperature (surface and bottom), maximum depth, NAO, and surface salinity. The marine community was significantly different among years and sampling areas. A similarity profile routine test (SIMPROF) showed there was a statistically significant structure (pattern) in the marine community, and the main species representing the greatest similarity percentages were generally longfin squid (Loligo pealei; coldwater-adapted), windowpane flounder (Scophthalmus aquosus; coldwater-adapted), and little skate (Leucoraja erinacea; coldwater-adapted). The primary species contributing to the dissimilarity were Atlantic butterfish (Peprilus triacanthus; warmwater-adapted), longfin squid, scup (Stenotomus chrysops; warmwater-adapted), and bay anchovy (Anchoa mitchilli; subtropic-adapted). Longfin squid consistently contributed the most to within-group similarity and between-group dissimilarities. The coldwater, warmwater, and subtropic-adapted community was significantly different over time. Generally, longfin squid, little skate, and Atlantic herring (Clupea harengus) contributed to the difference in the coldwater-adapted community, and Atlantic butterfish, scup, and northern searobin (Prionotus carolinus) contributed to the difference in the warmwater-adapted community over time. The sequential order varied by time-series, but bay anchovy, rough scad (Trachurus lathami), and striped anchovy (Anchoa hepsetus) constituted between 59 and 73 percent of the dissimilarity in the subtropic-adapted community.
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