Human Impact on Marine Ecosystem

Narasimha Moger, Kishor K.T., Rajeish Moger, Harshavardhan Joshi, Milind Katare, Chandrashekar B. H., Mahesh V., Pradeepkumar N.

KVAFSU, College of Fisheries, Mangalore, Karnataka, India

Corresponding auther: Narasimha Moger

Humans have used and had an impact on marine ecosystems throughout history. As human populations and their economic activity increased the impact intensified, but our awareness of the long-term, pervasive effects on marine life is relatively recent and very incomplete. This chapter introduces some of the ethical and utilitarian values which underlie our relationship with marine ecosystems and gives a brief overview of historic evidence concerning past states of marine ecosystems and intensification of human impacts. It describes impacts of fishing and other human pressures on the demography and biomass of exploited species and on loss of vulnerable species and habitats. Fishing and climate interact to cause observed change to ecosystems, including their trophic structure, with consequences for resilience and productivity. Emerging conclusions about human impacts, future human stewardship and utilization of marine ecosystems are presented.

Human activity over the centuries has depleted 90% of marine species, eliminated 65% of seagrass and wetland habitat, degraded water quality 10-1,000 fold, and accelerated species invasions in 12 major estuaries and coastal seas around the world, according to a study published in Science Magazine on Friday, June 23d, and supported in part by the Lenfest Ocean Program. However, in areas where conservation efforts have been implemented in the 20th century, signs of recovery are apparent.

Entitled "Depletion, Degradation, and Recovery Potential of Estuaries and Coastal Seas," the study is the most comprehensive quantitative assessment of the state of estuaries and coastal ecosystems ever conducted. Initiated by the National Center for Ecological Analysis and Synthesis and co-authored by ten international experts, it shows that human impact on estuaries and coastal waters dates back to ancient times (e.g. Roman Empire in the Adriatic Sea). However, damage to marine ecosystems has accelerated over the past 150-300 years as populations have grown, demands for resources have increased, luxury markets have developed, and industrialization has expanded.

"Throughout history, estuaries and coastal seas have played a critical role in human development as a source of ocean life, habitat for most of our commercial fish catch, a resource for our economy, and a buffer against natural disasters," a marine biologist at Dalhousie University in Halifax, Canada and lead author of the study. "Yet, these once rich and diverse areas are a forgotten resource. Compared to other ocean ecosystems such as coral reefs, they have received little attention in the press and are not on the national policy agenda. Sadly, we have simply accepted their slow degradation."

Most mammals, birds and reptiles in estuaries were depleted by 1900 and declined further by 1950 as the demand for food, oil, and luxury items (such as furs, feathers and ivory) grew. Among fish, the highly desirable and easily accessible salmon and sturgeon were depleted first, followed by tuna and sharks, cod and halibut, and herring and sardines. Oysters were the first invertebrate resource to degrade because of their value and accessibility as well as destructive harvesting methods.

The primary cause of estuarine damage is human exploitation, which is responsible for 95% of species depletions and 96% of extinctions, often in combination with habitat destruction. In the coming years, however, invasive species and climate change may play a larger role in stressing estuarine resources.

According to the study, the fastest path to recovery has been through mitigating the cumulative impacts of human activity. Seventy-eight percent of recoveries have happened by reducing at least two human activities, including resource exploitation, habitat destruction, and pollution .

Despite severe degradation in these 12 very different estuarine and coastal water environments, there is good news. "Only 7% of species went regionally extinct, and some are rebounding (birds and seals in particular). Clearly, recovery is achievable. As we expand our conservation efforts, we will see more evidence of healthier, abundant marine ecosystems." said Roger Bradbury, a resource management scientist at Australian National University.

In developed countries, trends suggest that estuaries may have passed the low point and are on the path to recovery, according to the study. In developing countries, however, population growth, which puts pressure on coastal areas, may further increase degradation.

"The 2004 Asian Tsunami and 2005 Hurricane Katrina helped us recognize how important healthy estuaries are in our lives," stated Jeremy Jackson, a paleontologist at Scripps Institution of Oceanography. "Thanks to this study, we can now see much more clearly what coastal ecosystems looked like before humans interfered with them, which has given us a historical baseline and a vision for how to regenerate diverse, resilient ecosystems that can thrive in the centuries to come."

The study quantifies the magnitude and causes of ecological change in 12 estuaries and coastal seas in Europe, North America, and Australia from the onset of human settlement to the present day. They are Massachusetts Bay, Delaware Bay, Chesapeake Bay, Pamlico Sound, Galveston Bay, Francisco Bay, Western Baltic Sea, Wadden Sea, Northern Adriatic Sea, Southern Gulf of St. Lawrence, Outer Bay of Fundy, and Moreton Bay. The researchers combined palaeontological, archaeological, historical, and ecological records to trace changes in important species, habitats, water quality parameters and species invasions.

Commercial fishing boat

Throughout human existence we have relied on the oceans for food, as a waste dump, for recreation, for economic opportunities and so on. However, it's not only our activities in the marine environment that affect life in the sea it's also the things we do on land.

With more than half the world's population now living within 100 kilometres of the coast, it's not surprising that our activities are taking their toll. Human impacts have increased along with our rapid population growth, substantial developments in technology and significant changes in land use. Over-fishing, pollution and introduced species are affecting life in the seas and New Zealand is no exception!

Fisheries

Humans living near the coast have probably always used the ocean as a source of food. However, with advances in fishing equipment, larger ships and new tracking technologies, many fish stocks around the world have reduced significantly. Fish stocks on continental shelf areas are now widely considered to be fully or over exploited. Aside from reducing fish stocks, unsustainable fishing practices can have other negative impacts on the marine environment. For example, some fishing techniques such as dredging and trawling can cause widespread damage to marine habitats and organisms living on the sea floor. These techniques also often capture non-target species (known as bycatch) that are then discarded.

In New Zealand, fisheries are managed by a quota system that sets catch limits for commercially important species and aims at sustainable management of our fish stocks. The Royal Forest and Bird Protection Society (NZ) publishes the Best Fish Guide to try and encourage us to make more sustainable choices when purchasing seafood. The list evaluates fish stocks and bycatch levels and the fishing methods used.

Pollution

Phytoplankton bloom — Our oceans have long been used as an intentional dumping ground for all sorts of waste including sewage, industrial run-off and chemicals. In more recent times, policy changes in many countries have reflected the view that the ocean does not have an infinite capacity to absorb our waste. However, marine pollution remains a major problem and threatens life in the sea at all levels.

Some marine pollution may be accidental, for example, oil spills caused by tanker accidents. Some may be indirect, when pollutants from our communities flow out to sea via stormwater drains and rivers. Some effects may not be immediately obvious, for example, bioaccumulation, the process where levels of toxic chemicals in organisms increase as they eat each other at each successive trophic level in the food web.

All marine pollution has the potential to seriously damage marine habitats and life in the sea. Scientists are concerned that marine pollution places extra stress on organisms that are already threatened or endangered.

Eutrophicationss

Eutrophication is the result of a particular type of marine pollution. It is caused by the release of excess nutrients into coastal areas via streams and rivers. These nutrients come from fertilisers used in intensive farming practices on land. Additional nutrients in the sea can lead to excessive phytoplankton growth that results in "blooms". When these large numbers of organisms die, the sharp increase in decomposition of the dead organisms by oxygen-using bacteria depletes oxygen levels. In some cases, this can result in the death by oxygen starvation of large numbers of other organisms such as fish.

Introduced species

Since the arrival of humans in New Zealand, introduced species in our terrestrial ecosystems have contributed to a significant loss of biodiversity. Introduced species also present a threat to our marine environment. It is not always easy to monitor or prevent the introduction of unwanted marine organisms, and visiting ships may introduce them accidentally on their hulls, in ballast water or on equipment.

Not all introduced species will spread or even survive, but once established, they may be difficult or impossible to remove. For example, the Japanese seaweed, Wakame Undaria pinnatifida, which probably arrived in 1987, is now widespread. Scientists are still monitoring its impact on our native marine organisms.

Biosecurity New Zealand provides information about the prevention of marine pests and maintains a list of high-risk organisms.

NATURE OF SCIENCE

Scientific research sometimes uncovers environmental problems that are linked to human lifestyles. This research shows that the way we live needs to be balanced with environmental needs, which sometimes puts scientists in a difficult position in defending their work.

Ocean acidification

There is evidence to suggest that human activities have caused the amount of carbon dioxide in our atmosphere to rise dramatically. This impacts on the marine environment as the world's oceans currently absorb as much as one-third of all CO2 emissions in our atmosphere. This absorption of CO2 causes the pH to decrease, resulting in the seawater becoming more acidic.

Scientists have long understood that an increase in carbon dioxide in the atmosphere will result in higher levels of dissolved CO2 in seawater. However, a relatively recent discovery is that even small changes in water pH can have big impacts on marine biology. Ocean acidification is a worldwide issue, but as CO2 is more soluble in colder water, it is of particular concern in New Zealand's temperate oceans.

It is difficult to predict the overall impact on the marine ecosystem but many scientists fear that ocean acidification has the potential to decrease marine biodiversity on a very large scale.