Biodiversity and ecosystem processes are intertwined in a tangled web with complex feedback loops. Changes in one aspect of biodiversity, loss of a top predator for example, will affect some aspect of the food web, which can then lead to changes in other biodiversity and ecosystem processes. Figure 16.5 summarizes the idea that human impacts interact to change biodiversity in
many ways. Changes in the distribution and abundance of taxa alter the food web, at least temporarily disturbing it from its previous state. These alterations in the food web can have repercussions on the microbial loop and nutrient pools in the open ocean, which ultimately result in changes to ecosystem processes. This is not meant as a substitute for a careful analysis of the specific effects of impact A on ecosystem process B, but rather a reminder that the impacts are likely to be many-fold, diffuse and not always predictable.
Human impacts on open-ocean biodiversity are as diverse in nature and scale as any on land (Table 16.2). Recent reviews include those by GESAMP (1990) and Norse (1993). Despite the large distances that connect most human activities to the open ocean, much of our impact is land-based (GESAMP 1990).
Table 16.2 A list of potential anthropogenic impacts on coastal and oceanic ecosystems. Coastal systems are limited to the continental shelf; epipelagic systems occur above a depth of 200 m, and the mesopelagic below 200 m. Ranking of impact: ***. expected serious impact; **„ expected moderate impact; *, expected mild impact. Indirect effects resu.lt from cascading impacts from other ocean systems
Coastal benthic and pelagic
Land based activities Air pollution Change in atmospheric gases (e.g. CO?, acid rain) Increased UV radiation Global warming
Land pollution Siltation
"Accidental" waste disposal (e.g. flotsam) Waste disposal
Ocean-based activities Additions Introductions
"Accidental" waste disposal (e.g. oil spills') Waste disposal
Subtractions Resource extraction (harvesting and mining)
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