SCIENCE UNDER THE SEA Aquanauts explore an ecosystem on the brink CHAPTER 13 MARINE ECOSYSTEMS

What is ocean acidification and why is it a threat to ocean ecosystems?

Ocean ecosystems cover about 70% of Earth’s surface, and house a greater variety of flora and fauna than all land masses combined. WHAT ARE OCEAN ECOSYSTEMS?

WHAT KEY FACTORS SHAPE OCEAN ECOSYSTEMS?

Ocean ecosystems are influenced by: depth of the water column proximity to the shore Sunlight supplies both heat and energy for photosynthesis, and since 80% of sunlight is absorbed in the top 10 meters, the upper layers of the ocean are more productive. The closer to land and rivers that empty into the ocean, the more nutrient-rich the area, and thus more productive.

WHAT ARE THE DIFFERENT TYPES OF OCEAN ECOSYSTEMS?

Which zone of the ocean absorbs the greatest amount of sunlight? A. hadal zone B. mesopelagic C. bathypelagic D. epipelagic Question

____________ are areas where saltwater mixes with freshwater and creates a distinct habitat. A. wetlands B. estuaries C. gyres D. ocean currents

WHY DO OCEAN ECOSYSTEMS MATTER?

Temperature moderation OCEANS PROVIDE ECOSYSTEM SERVICES Nutrient cycling Support for commercial fisheries Storm protection for coastal areas Recreational opportunities Source of medicines

Coral reefs are among the most biodiverse of all ocean ecosystems.

WHAT IS A CORAL REEF? Do Meow WHY ARE CORALS CONSIDERED THE ULTIMATE KEYSTONE SPECIES?

Coral reefs are ocean ecosystems that are found in shallow, nutrient-poor water in tropical regions. WHAT IS A CORAL REEF?

WHY ARE CORALS CONSIDERED THE ULTIMATE KEYSTONE SPECIES? Corals are extremely important to their ecological community as they provide the primary structure for the reef community.

The mutualistic relationship with photosynthetic zooxanthellae enable corals to live in nutrient-poor marine waters.

Scientists estimate that 25% of all ocean species spend at least some portion of their life in a coral reef. This outsized role in marine ecology makes understanding coral reefs critical to understanding what is going on in the ocean.

WHAT IS GOING WRONG IN CORAL REEFS AND OTHER OCEAN ECOSYSTEMS?

Human activities that are threatening ocean life: overfishing – 90% of top trophic-level fish have been eliminated impacts of fishing techniques– bottom trawling damages sea beds; dynamite damages coral reefs killing of non-target species FISHING PRESSURES

nutrients pathogens toxins oil spills Human activities that are threatening ocean life: litter and plastic waste sediments POLLUTION

80% of global ocean harbors host invasive species invasive species may kill native species or outcompete them when foraging Human activities that are threatening ocean life: 80% of native species in a coral reef may disappear if a lionfish is introduced INVASIVE SPECIES

WHAT ARE THE BIGGEST THREATS TO THE HEALTH OF OCEANS? Be specific Do Meow

These same threats are exacerbated in coral reefs. 75% of the world’s coral reefs are threatened by human activity. Due their proximity to coasts, reefs are particularly threatened by activities on land.

But…probably the most significant threat to oceans is fossil fuel combustion.

The ocean and atmosphere come into direct contact over 75% of Earth’s surface, and they are constantly exchanging gases over that interface —including CO2. Winds mix CO2 into the top few hundred feet of water, and as years pass, currents pull it ever deeper into the ocean.

From the analysis of nearly 80,000 water samples, scientists estimate some 30% of all the CO 2 released by humans in the last two centuries has been absorbed by the world’s oceans.

This is good news for terrestrial ecosystems but bad news for ocean ecosystems. WHY? Because it acidifies the ocean.

WHAT IS AN ACID? HOW MUCH ARE THE OCEANS ACIDIFYING?

WHAT ARE THE CONSEQUENCES OF OCEAN ACIDIFICATION?

Today the oceans are 30% more acidic than in By 2100 the oceans could be 150% more acidic than in 1800.

Ocean acidification corresponds to increase in atmospheric CO2

Species of plankton more tolerant of nutrient declines gain an advantage Such a change in species composition can alter the food chains and decrease primary production in the oceans. Declines in availability of key nutrients like nitrogen and iron have been documented to occur in tandem with declines in pH. Plankton biomass may have already decreased by as much as 40% since 1950.

POSITIVE FEEDBACKNEGATIVE FEEDBACK Less plankton means less primary production, thus less CO 2 capture and storage Less nitrogen fixing means less N 2 O (another greenhouse gas) produced As nutrients decline it could set off an unpredictable chain of events –

Increases in carbonic acid both eat away at existing calcium-based materials and interfere with their production.

This affects marine calcifiers from snails to corals to plankton – they grow more slowly and their bodies dissolve in the acidified ocean water.

CAN MARINE SPECIES AND ECOSYSTEMS ADAPT TO THESE CHANGES (caused by ocean acidification)? PERHAPS …

Acidification of oceans may also reduce the water’s ability to absorb low- frequency sounds, which would make at least some regions of the ocean much noisier and thereby disrupt whales, dolphins, and fish.

But ocean acidification is not the only threat to marine ecosystems resulting from fossil fuel combustion.

Global warming from the increased greenhouse gases in the atmosphere is also associated with rising ocean temperatures, which can increase thermal stress, thus increasing coral bleaching. rising sea levels, which may decrease sunlight penetration, thus reducing photosynthesis.

Coral bleaching may be an adaptive response –coral take up different species of zooks better suited to the changed conditions. So the effect of stress on a reef system is influenced by past events—some reefs may be acclimated or adapted to thermal stress or lower pH.

Coral only survive for short periods without zooks, and will die if not recolonized. Multiple stresses or a stress that persists may push a coral beyond its ability to survive or adapt.

HOW DO WE PROTECT MARINE ECOSYSTEMS?

“We can’t reverse the tide at this point. But if we act quickly, we can at least slow it down ” - Marc Slattery