Coastal regions are the world’s most densely populated areas, directly supporting some of the most biodiverse habitats, as well as trillions of dollars’ worth of ecosystem goods and services. As the interface between terrestrial and marine habitats, these areas are subject to numerous stressors, which when co-occurring with one another, can have interacting effects that pose a direct risk to coastal ecosystems, the rich aquatic life their harbor, and the services they provide to people. To effectively allocate resources towards and proactively manage against these threats, we must first understand their spatiotemporal patterns and how stressors impact our coastal ecosystems. My dissertation aims to uncover global patterns of risks to coastal ecosystem health across coral reefs, seagrass meadows, and kelp forests, three critical coastal ecosystems that have been in decline for decades. My studies answer questions about the past and current state of thermal and water quality stress along global coasts, uneven exposure to stressors across protected area statuses, potential economic losses in fish catch landings in impaired ecosystems, and the changing prevalence of diseases across the world's two largest coral reefs, the Great Barrier Reef and the Mesoamerican Reef. Insights from these analyses can help inform management decisions for the preservation of our coastal ecosystems towards the future. In the first data chapter, I analyzed global mean monthly trends using remotely sensed sea surface temperature (SST) and chlorophyll-a data over the 25-year period from 1998-2022 as proxies for global thermal stress and local water quality stress on coral reefs, seagrass meadows, and kelp forests. I found that in all three marine coastal ecosystems over 50% of their respective global habitat areas have undergone increases in both thermal and water quality stress over the study period. Next, comparing protected and not protected areas, there was no difference in thermal stress trends as all ecosystems, regardless of protection status, as they all experienced increases. By contrast, trends in water quality stress trends were heterogeneous across habitats and between protection status, indicating that our current matrix of protected areas are differentially experiencing water quality stress and that protected area positive gains are potentially being undermined or erased by poor water quality. Finally, by establishing associations between fish taxa and coastal ecosystems, I found that landed fish catch associated with coral reefs, seagrass meadows, and kelp forests to be valued at $33.9 billion year-1, with one-third of that value experiencing an increase in both thermal and water quality stress. With this information, there is a detailed inventory of regions by their levels of thermal and water quality stress. Debate continues as to whether we should invest our resources, including protected areas, in the most affected regions to try to limit their further decline, or prioritize pristine areas as they may have a higher likelihood of conservation success. In the second data chapter, I assess risk to coastal ecosystems by using decadal datasets from two largest coral reef systems in the world. Intensifying climate and anthropogenic pressures have been identified as a causal agent in the development of coral diseases, with exposure to these stressors being implicated as a causal agent of disease development. Disturbances in host, pathogen, environment, or all, can lead to periodic disease outbreaks that can decimate coral populations and cause shifts in coral community assemblages. I analyzed over 1.1 million corals in the Great Barrier Reef (GBR) from 2004-2016 and over 54,000 corals in the Mesoamerican Reef (MAR) from 2005-2018 to evaluate spatiotemporal patterns of coral disease. Contrary to the expected results, disease prevalence dropped by 87.1% in the GBR and 49.3% in the MAR. Investigating further, I found health prevalence decreased in the GBR from 96.1% to 83.6% and increased in the MAR from 73.5% to 81.4%. Coral density in the GBR plummeted from 21.15 to 8.45 corals per m² in just thirteen years, while the MAR's coral density did not change. Average community composition shifted significantly in the GBR, and community composition dispersion shrunk. Significant interactions were found between coral disease and accumulated thermal and water quality stressors, indicating their synergistic effect. Collectively, these results demonstrate the cryptic nature of disease patterns. While disease prevalence can increase or decrease in coral reefs systems, the causes of those fluctuations needs to be further investigated to explore the root cause of the changes and their relationship to disease. These studies highlight the dynamic nature of coastal ecosystem health, and the need for long-term monitoring, both across spatial scales and across sampling methodologies, to gain insights into the risks our coastal ecosystems face. Studies have shown that the recovery of marine populations is possible if major pressures, like climate change, were mitigated. While this is an ambitious proposition, it shows the strength and resiliency of these ecosystems when supported with favorable conditions and highlights the need for swift, actionable, and optimistic action.

Climate change and expanding human populations are converging threats that impact marine ecosystems, leading to global declines in critical habitat and biodiversity. Targeted and innovative management solutions that can reconcile the objectives of supporting human livelihoods alongside those of environmental sustainability are urgently needed. My research highlights important management considerations for the conservation and restoration of two foundation marine ecosystems that dominate global temperate coastal regions, seagrass meadows and canopy-forming kelp forests. Urban greening offers a strategic opportunity to reinforce the security and safety of food from the sea. Seagrass ecosystems can reduce human bacterial pathogens from terrestrial sources, however it remains unknown whether this health benefit is conferred to associated food fish. Marine bivalves are bioindicators of bacterial contamination and constitute over half of global seafood production. Following a three month deployment across 20 coastal urban locations in the greater Seattle Metropolitan Area, I found in Chapter 1 that bivalves deployed and subsequently retrieved from locations with seagrass present had a 65% reduction in the abundance of bacterial species with known human pathogenicity when compared to locations without seagrass. My global models estimate that 1.1 billion people currently reside in over one-third (662 of 1,860) of urban agglomerations (populations over 300,000 people) and 19 megacities (populations over 10 million people) within 50 km of seagrass ecosystems, which I forecast to rise 15% by 2030. Given increasing reliance on food from the sea to meet supply and nutritional needs, these results highlight the global opportunity to support ambitious human health and biodiversity sustainability targets. Canopy-forming kelps are foundation species that support biodiversity and provide ecosystem services valued at over USD$500 billion per year. Giant kelp forests are facing unprecedented loss due to climate-driven ecological stressors necessitating innovative restoration strategies. I produced a video for Chapter 2 to illustrate a protocol and tools for restoring canopy-forming giant kelp forests. I include field-based tissue collection and laboratory-based methods of sporulating, inoculating, rearing, maintaining, and monitoring substrates seeded with early life stages using the ‘green gravel’ technique. The protocol simplifies and centralizes existing practices in this field of restoration to facilitate conservation objectives for underwater kelp forests by researchers, managers and stakeholders. Climate change and anthropogenic disturbances are currently outpacing the adaptive capacity of natural kelp populations, challenging traditional conservation aims of restoration to historic states. Thus, conservation frameworks have expanded to include anticipatory management that proactively consider resilience and adaptive capacity. I conducted a >2-month long-term trial in Chapter 3 to assess the effect of rearing temperatures (12°C, 16°C, 20°C, and 24°C) on early microstages of a canopy-forming giant kelp species from potentially locally adapted Santa Cruz and San Diego populations of origin in constant thermal conditions, followed by a simulated deployment for restoration at 16°C and a realistic marine heatwave of 22°C. Samples reared in cooler 12 and 16°C temperatures performed best in constant thermal conditions. However, these samples were significantly impacted by a simulated heatwave. Despite poor performance in constant thermal conditions, samples reared at 20°C were able to recover from reproductive dormancy given a simulated deployment for restoration at 16°C, and performed best after a 22°C simulated heatwave. There was no kelp survival in the 24°C rearing temperature, and thus this treatment was terminated. These findings suggest that rearing M. pyrifera at warmer temperatures may confer an advantage when deployed into warming oceans with increasing frequency and magnitude of marine heatwaves, and provides an avenue forward for marine managers looking to future-proof restoration efforts. Critical marine habitats such as seagrass and kelp ecosystems continue to deteriorate at unprecedented rates, calling upon management solutions that pro-actively and simultaneously consider human populations and future environmental decisions.