Marine ecosystem in the context of "Fishing"

The salinity of water bodies varies widely, being lower near the surface and the mouths of large rivers and higher in the depths of the ocean; however, the relative proportions of dissolved salts vary little across the oceans. The most abundant solid dissolved in seawater is sodium chloride. The water also contains salts of magnesium, calcium, potassium, and mercury, among other elements, some in minute concentrations. A wide variety of organisms, including bacteria, protists, algae, plants, fungi, and animals live in various marine habitats and ecosystems throughout the seas. These range vertically from the sunlit surface and shoreline to the great depths and pressures of the cold, dark abyssal zone, and in latitude from the cold waters under polar ice caps to the warm waters of coral reefs in tropical regions. Many of the major groups of organisms evolved in the sea and life may have started there.

Aquatic plants, also referred to as hydrophytes, are vascular plants and non-vascular plants that have adapted to live in aquatic environments (saltwater or freshwater). In lakes, rivers and wetlands, aquatic vegetations provide cover for aquatic animals such as fish, amphibians and aquatic insects, create substrate for benthic invertebrates, produce oxygen via photosynthesis, and serve as food for some herbivorous wildlife. Familiar examples of aquatic plants include waterlily, lotus, duckweeds, mosquito fern, floating heart, water milfoils, mare's tail, water lettuce, water hyacinth, and algae.

Aquatic plants require special adaptations for prolonged inundation in water, and for floating at the water surface. The most common adaptation is the presence of lightweight internal packing cells, aerenchyma, but floating leaves and finely dissected leaves are also common. Aquatic plants only thrive in water or in soil that is frequently saturated, and are therefore a common component of swamps and marshlands.

Human activities affect marine life and marine habitats through overfishing, habitat loss, the introduction of invasive species, ocean pollution, ocean acidification and ocean warming. These impact marine ecosystems and food webs and may result in consequences as yet unrecognised for the biodiversity and continuation of marine life forms.

The ocean can be described as the world's largest ecosystem and it is home for many species of marine life. Different activities carried out and caused by human beings such as global warming, ocean acidification, and pollution affect marine life and its habitats. For the past 50 years, more than 90 percent of global warming resulting from human activity has been absorbed into the ocean. This results in the rise of ocean temperatures and ocean acidification which is harmful to many fish species and causes damage to habitats such as coral. With coral producing materials such as carbonate rock and calcareous sediment, this creates a unique and valuable ecosystem not only providing food/homes for marine creatures but also having many benefits for humans too. Ocean acidification caused by rising levels of carbon dioxide leads to coral bleaching where the rates of calcification is lowered affecting coral growth. Additionally, another issue caused by humans which impacts marine life is marine plastic pollution, which poses a threat to marine life. According to the IPCC (2019), since 1950 "many marine species across various groups have undergone shifts in geographical range and seasonal activities in response to ocean warming, sea ice change and biogeochemical changes, such as oxygen loss, to their habitats."

The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification. The majority of Earth's atmosphere (78%) is atmospheric nitrogen, making it the largest source of nitrogen. However, atmospheric nitrogen has limited availability for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems.

The nitrogen cycle is of particular interest to ecologists because nitrogen availability can affect the rate of key ecosystem processes, including primary production and decomposition. Human activities such as fossil fuel combustion, use of artificial nitrogen fertilizers, and release of nitrogen in wastewater have dramatically altered the global nitrogen cycle. Human modification of the global nitrogen cycle can negatively affect the natural environment system and also human health.

An aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems. Freshwater ecosystems may be lentic (slow moving water, including pools, ponds, and lakes); lotic (faster moving water, for example streams and rivers); and wetlands (areas where the soil is saturated or inundated for at least part of the time).

Overfishing is the removal of aquatic animals — primarily fish — from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stocks), resulting in the species becoming increasingly underpopulated in that area. Excessive fishing practices can occur in water bodies of any sizes, from ponds, wetlands, rivers, lakes to seas and oceans, and can result in resource depletion, reduced biological growth rates and low biomass levels. Sustained overfishing, especially industrial-scale commercial fishing, can lead to critical depensation, where the fish population is no longer able to sustain itself, resulting in extirpation or even extinction of species. Some forms of overfishing, such as the overfishing of sharks, has led to the upset of entire marine ecosystems. Types of overfishing include growth overfishing, recruitment overfishing, and ecosystem overfishing. Overfishing not only causes negative impacts on biodiversity and ecosystem functioning, but also reduces fish production, which subsequently leads to negative social and economic consequences.

The ability of a fishery to recover from overfishing depends on whether its overall carrying capacity and the variety of ecological conditions are suitable for the recovery. Dramatic changes in species composition can result in an ecosystem shift, where other equilibrium energy flows involve species compositions different from those that had been present before the depletion of the original fish stock. For example, once trout have been overfished, carp might exploit the change in competitive equilibria and take over in a way that makes it impossible for the trout to re-establish a breeding population.

Wilderness or wildlands (usually in the plural) are Earth's natural environments that have not been significantly modified by human activity, or any nonurbanized land not under extensive agricultural cultivation. The term has traditionally referred to terrestrial environments, though growing attention is being placed on marine wilderness. Recent maps of wilderness suggest it covers roughly one-quarter of Earth's terrestrial surface, but is being rapidly degraded by human activity. Even less wilderness remains in the ocean, with only 13.2% free from intense human activity.

Some governments establish protection for wilderness areas by law to not only preserve what already exists, but also to promote and advance a natural expression and development. These can be set up in preserves, conservation preserves, national forests, national parks and even in urban areas along rivers, gulches or otherwise undeveloped areas. Often these areas are considered important for the survival of certain species, biodiversity, ecological studies, conservation, solitude and recreation. They may also preserve historic genetic traits and provide habitat for wild flora and fauna that may be difficult to recreate in zoos, arboretums or laboratories.

Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations. The first seabirds evolved in the Cretaceous period, while modern seabird families emerged in the Paleogene.

Seabirds generally live longer, breed later and have fewer young than other birds, but they invest a great deal of time in their young. Most species nest in colonies, varying in size from a few dozen birds to millions. Many species are famous for undertaking long annual migrations, crossing the equator or circumnavigating the Earth in some cases. They feed both at the ocean's surface and below it, and even on each other. Seabirds can be highly pelagic, coastal, or in some cases spend a part of the year away from the sea entirely.