Published in February, another paper titled “The impacts of climate change in coastal marine systems” in Ecology Letters describes a litany of other ways that climate change may shake the foundations of marine ecosystems - from acidification of the ocean to altering routes traveled by young, drifting in-vertebrates and fish. Many people are entirely unaware of these profound shifts identified by Christopher Harley, a zoologist at the University of British Columbia, and his co-authors.

The scientific message is that climate change will totally transform marine ecosystems in ways that today's management, conservation and policy paradigms don’t necessarily accommodate, and the biggest changes are yet to come.
What do these changes mean for ecosystem-based management in the Gulf of Maine?

The core philosophy of ecosystem-based management is to take a broader view of management decisions in order to understand the ecosystem context. If the ecosystem itself will be undergoing massive change, then management decisions must be made in this context, not in the context of today's or tomorrow's conditions. Fundamental ecosystem changes may affect management approaches on seemingly non-climate issues.

How fast will the sea rise?

The rising sea level usually gets the spotlight when people talk about impacts of climate change on the ocean and coast. Direct human implications of the rising sea level are coastal flooding, accelerated erosion, loss of coastal property and saltwater intrusion into aquifers. Although these threats to human life and property grab headlines, the ecological effects on animals, plants and habitats are no less important.

For example, one study estimates that 51 percent of tidal wetlands in Maine will disappear if the sea level rises 20 to 49 centimeters (8 to 19 inches) in the next century; 79 percent will disappear if the sea level rises 86 centimeters (34 inches). Because tidal marshes play a major role in supporting fisheries and marine ecosystems (see Science Insights, Gulf of Maine Times, summer 2005), the loss will be felt far beyond the narrow margin of the coast.

In the management and policy realm, the focus is usually on scenarios in which the sea-level rises one to three feet by 2100. Overpeck’s Science paper makes it clear that three feet is by no means the maximum possible increase in sea level. By 2100 the world’s climate may reach temperatures comparable to those of 130,000 to 127,000 years ago, when the sea level was four to six meters (13 to 20 feet) higher than today. Therefore, it’s possible that the sea level will rise faster than one meter, or three feet, per century.

Nobody knows precisely how quickly or how high it will rise, but for coastal management and conservation it’s worth looking beyond the standard 100-year scenarios to consider more disastrous and longer-term poss-ibilities. What might happen in the Gulf of Maine, and what are the prudent steps that ought to be taken now?

Warming water

Along with the sea-level rise, warmer water temperature is the best understood effect of climate change on the ocean. Already, for example, scien-tists have documented climate-related geographic shifts in North Sea fishes and kelp, barnacles, zooplankton and fish of the northeast Atlantic.

The Ecology Letters paper makes it plain that warmer water will have a range of effects beyond killing species outright or forcing them to shift where they live.

• Timing of life stages. Clams in Europe spawn earlier due to warmer water, putting them out of sync with the main food supply for young clams.
• Changes in ecological inter-actions. On the west coast, sea stars increased in warmer temperatures, suggesting they could wipe out mussel beds and species living among the mussels.
• Disease. Warmer water temp-eratures favor pathogens and enable them to inflict greater damage.
• Invasive species. In the Gulf of Maine, climate change and overfishing seem to enable invasive green algae, bryozoans, tunicates and red algae to replace kelp beds and urchin barrens.

Other ecosystem changes

Harley and his co-authors provide a comprehensive overview of lesser-known implications of climate change for marine ecosystems. Ultimately, these impacts - altered circulation patterns, elevated carbon dioxide, acidification of seawater and changes in ecosystem functions - could pack more ecologically and economically wallop than the sea-level rise and warmer water.

Changing Circulation

• Dispersal of young. Many shellfish, fish, and other ocean-dwelling creatures begin life as tiny larvae that drift with currents. Climate change could alter ocean currents and thus the movements of larvae, causing localized extinctions of adult populations and shifts in predator-prey dynamics.
• Migration and dispersal. American eels migrate from the Gulf of Maine to the middle of the North Atlantic to spawn. Will eels and other migratory species be disrupted by shifts in currents?
• Nutrients and temperature. A driving force behind the productivity and ecological character of the Gulf of Maine is its unique cir-culation, including cold, nutrient-rich currents entering from the North Atlantic. Will changes in currents alter nutrient supply in the Gulf of Maine?
• Species range limits. For some species, ocean currents apparently block the dispersal of young, setting invisible geographic boundaries. With climate change, these boundaries could move or disappear, causing species ranges to expand or contract independently of water temperature.

Carbon Dioxide and Acidification

• Increased CO2. Elevated CO2 concentrations in the ocean could spur the growth of sea grasses, enabling them to replace seaweeds in some places.
• Acidification of seawater. By impairing the growth of carbonate shells and body parts, acidification could reduce growth and survival of mussels, snails, sea urchins, and coralline algae.

Ecosystem-Level Effects

• Biodiversity. Changes in bio-diversity could alter productivity of ocean areas and resistance to invasive species.
• “Leverage” species. Leverage species are those that play a linchpin role in ecosystem function. The decline of one or a few leverage species in the Gulf of Maine could redefine the whole ecosystem.

Compounding the Problem

Climate change can magnify other human impacts.

• Precipitation and runoff. Taking steps now against sediments, nutrients, and other pollutants - for example, by creating riparian buffers and reducing fertilizer usage - could pay off handsomely if precipitation and runoff into the ocean increase with climate change.
• Pollution. Because UV radiation has been shown to make polycyclic aromatic hydrocarbons (PAHs) even more deadly to crabs, reducing contaminants may be an important way to fight the negative effects of stronger UV on marine species.
• Shoreline armoring. Seawalls and other shoreline structures are notorious for interfering with natural ecological processes, and their effects will worsen as the sea level rises, causing loss of mudflats, beaches, and salt marshes
• Fishing. In combination, fishing and climate change could push some fish stocks to dangerously low levels.

The bad news is that climate change cannot be stopped. The good news is that strategically addressing other human impacts on the ocean and coast may help to mitigate climate change.

By reshaping the ocean ecosystem, the changing climate sets the context for management and conservation for centuries. It is the defining issue for all management and conservation initiatives in the Gulf of Maine region - all that seek an ecosystem-based approach.

Peter Taylor is a consultant working with the Gulf of Maine Science Translation Project.
Visit www.gulfofmaine.org/science_translation.

© 2006 The Gulf of Maine Times