## 4 Discussion  
The results of this study indicate that the reintroduction of Common Carp had a significant impact on coastal wetlands due to changes to water quality and vegetation. Ten environmental variables were significantly different between the Excellent fish IBI group, OSM_Pre, and OSM_Post. Fish abundance and biomass were highest in OSM_Post, largely driven by a few tolerant invasive species, including Common Carp, but had the lowest diversity and richness, with four species making up 97% of the populations. After Common Carp recolonization, fish community health decreased, as determined by the fish IBI and by multivariate restoration trajectories. The distance between the Excellent group and OSM_Post was significantly larger than OSM_Pre, indicating a more tolerant, degraded system. Restoration monitoring indicated increasing fish community health until Common Carp gained access and the fish community became increasingly dissimilar to the Excellent group. This dissimilarity occurred rapidly within the first year, followed by a consistent dissimilarity over the next four years, demonstrating the potential impact of Common Carp on a newly restored wetland. There were significant differences between fish IBI in OSM_Pre and OSM_Post group averages, but they did have range overlap and a higher coefficient of variation. The impacts of Common Carp have been well documented [8; 10], but our research demonstrates the impacts they have on fish communities and wetland health immediately after restoration efforts if recolonization of Common Carp occurs. Despite restoration occurring at OSM only a few years previously, most environmental variables had significant negative relationships with Common Carp reintroduction. Two abiotic variables increased with the re-colonization of Common Carp: turbidity and TP, which may have contributed to the decreases in the vegetation variables. Turbidity increases caused by Common Carp have been documented to impact aquatic vegetation, decreasing reproductive and foraging habitat for native fish species and impairing biotic interactions,  
Figure 4: Comparing changes in fish community scores using multimetric and multivariate approaches. DRCWMP IBI is used for the multimetric score (grey solid line), and the Euclidean distance between OSM sampling events and the centroid of the Excellent group ellipse is used as a measure of fish community health for multivariate analysis (black dashed line). The vertical line represents the approximate time Common Carp regained access to Oshawa Second Marsh. such as visual foraging [6; 12; 13; 34; 35; 36]. Only three variables were not significantly different following Common Carp re-colonization. Water depth was not expected to change as restored bathymetry was not part of the restoration strategy, and WQI and conductivity values may not have changed due to a lack of a specific restoration strategy to mitigate these stressors. Given that the degree of hydrological connection between Farewell Creek and Oshawa Second Marsh did not change after the addition of carp, it is reasonable to assume an improvement would not be seen given that upstream inputs are the source of poor water quality and remained consistent over that time period. A higher richness is expected in healthier wetlands due to increased habitat quality, diversity, and cover, which is consistent with the results of our study [13; 37; 38]. Species richness at OSM was lower than the Excellent group but decreased further after the reintroduction of Common Carp (OSM_Post) and a decrease in habitat quality. Areas with high anthropogenic stressors have been documented to have homogenous fish communities, consistent with our findings [39]. Sensitive species were present in the Excellent group but not in either of the OSM groups.