What Impact Does Upwelling Have On The Productivity Of Fisheries?

Coastal upwelling is a process where surface waters are pushed offshore by wind, resulting in the upward movement of deep, colder water. This process supports the growth of seaweed and plankton, which provide food for marine ecosystems and fisheries. Coastal upwelling is responsible for thriving marine ecosystems and fisheries that are disproportionately productive. High-resolution climate models under a high emission scenario show an anticipated advancement and extension of coastal upwelling, supporting a highly productive marine ecosystem off the West Coast.

Newly developed indices quantify the intensity of upwelling and its delivery of nutrients to the ocean. The study underscores the role of freshwater influx in regulating coastal upwelling and upper ocean stratification controlling the regional. In the tropical Angolan upwelling system (tAUS), the seasonal productivity maximum is due to the combined effect of coastal trapped waves (CTWs) and elevated tidal mixing on the water.

Coastal upwelling is the best known type of upwelling and closely related to human activities as it supports some of the most productive fisheries in the world. Upwelling of nutrient-rich, subsurface water sustains high productivity in the ocean’s eastern boundary currents. These ecosystems support a rate of fish harvest nearly 100 times the global mean and account for >20 of the world’s marine fish catch.

In some ways, upwelling can be a mixed blessing to coastal ecosystems. It can infuse coastal waters with critical nutrients that fuel dramatic productivity, but it can also rob coastal ecosystems of offspring required to replenish these resources. Upwelling can lead to a decrease in fisheries production in most regions, but in upwelling zones, where subsurface layers are present, it brings water to the surface enriched with nutrients important for primary productivity (algal growth).

What impact does downwelling have on biological productivity?

Upwelling and downwelling play a crucial role in influencing sea-surface temperature and biological productivity. Upwelling waters, which may originate below the pycnocline, are colder than the surface waters they replace, and are rich in dissolved nutrients required for phytoplankton growth. This transport of nutrients into the surface waters, where sunlight is present, results in rapid growth of phytoplankton populations. The world’s most productive fisheries are located in areas of coastal upwelling, which bring cold, nutrient-rich waters to the surface, resulting in about half of the world’s total fish catch.

On the other hand, coastal downwelling thickens the surface layer of warm, nutrient-deficient water, reducing biological productivity and transporting heat, dissolved materials, and surface waters rich in dissolved oxygen to greater depths. This occurs along the west coast of Alaska in the eastern boundary region of the Gulf of Alaska gyre.

Alternate upwelling of nutrient poor and nutrient rich waters off the coast of Ecuador and Peru are associated with El Niño and La Niña episodes in the tropical Pacific. During El Niño, the pycnocline is so deep that upwelled waters come from the nutrient poor waters above the pycnocline. In extreme cases, nutrient-deficient waters coupled with over-fishing cause fisheries to collapse, causing severe, extended economic impacts.

Coastal upwelling and downwelling also influence weather and climate. Upwelling lowers sea surface temperatures and increases the frequency of summer fogs, while cold surface waters chill the overlying humid marine air, inhibiting the formation of tropical cyclones.

What is caused by upwelling?

Coastal upwelling is a process where strong winds push surface waters offshore, causing water from ocean depths to rise to the surface. This process is closely linked to the climate and economy of California, contributing to its foggy weather, robust fisheries, and delicious wine. Upwelling intensity along the west coast of North America varies due to environmental and oceanographic conditions, with northern California experiencing the most intense upwelling. The California Current, encapsulating Bodega Bay, is one of four major upwelling-driven ecosystems globally, offering unique research opportunities.

Coastal upwelling is important because bottom water, which is colder due to lack of sunlight, more nutrient-rich due to decomposition of settling organic matter, and more acidic and less oxygenated, is pushed offshore and replaced by surface water. This nutrient-rich water fuels an ecosystem driven by high primary production when exposed to sunlight.

How can upwelling impact net primary production?

Upwelling and vertical mixing are processes that promote primary productivity by bringing nutrients from deep depths into well-lit surface waters. Upwelling-influenced areas are some of the most productive in the global ocean. ScienceDirect uses cookies and all rights are reserved for text and data mining, AI training, and similar technologies. Open access content is licensed under Creative Commons terms.

How does upwelling and downwelling affect marine life?

Upwelling and downwelling are ocean movements that affect surface and deep currents, ensuring the ocean’s circulation, oxygen delivery, heat distribution, and nutrient supply. Upwelling involves cold, deep water moving to the surface mixed layer, while downwelling involves surface water moving to deeper depths. Downwelling occurs when surface waters converge, pushing water downwards, leading to low productivity in regions with depleted nutrients due to insufficient nutrient supply from below the surface.

How does upwelling affect productivity?

Upwelling is defined as the phenomenon whereby colder, nutrient-rich waters rise to the surface, where they fertilize the surrounding waters, leading to high biological productivity and the formation of ideal fishing grounds.

What is upwelling in aquaculture?

Ghana’s coastal shores in the Gulf of Guinea are prone to upwelling, a rare phenomenon where cold water and nutrients from the deep ocean are displaced to the surface of the coastlines. This leads to increased biological activities of phytoplankton and zooplankton, which are nutrient-rich and serve as food for fish along the coast. From June to September, upwelling occurs, causing fish growth and increased numbers of fish along the coast. Traditionally, it is taboo for fishermen to go to sea during these months, as the myth suggests that sea gods are fishing themselves.

However, elders have used this fear to det
er fishermen from fishing during these periods, aiming to restore fish stocks to levels that can produce maximum sustainable yield. In 2021, the Ministry of Fisheries and Aquaculture Development declared these months a fishing Closed Season, targeting both industrial and artisanal fishers. The compliance rate was 100% for industrial trawlers and inshore fleet, with 90% for artisanal and semi-industrial fishers.

The major upwelling season of fish falls within July and September, with a minor upwelling season from December to February representing the period with greater spawning activity for both small pelagic and demersal species.

How does upwelling affect phytoplankton productivity?

Upwelling has diverse ecological effects, with two significant impacts. Firstly, it brings cold, nutrient-rich waters to the surface, encouraging seaweed growth and supporting phytoplankton blooms. These blooms provide energy for large animal populations, including fish, marine mammals, and seabirds. Coastal upwelling ecosystems, like the U. S. west coast, are highly productive and support significant fisheries. Despite accounting for only one percent of the ocean surface, they contribute around 50% of the world’s fisheries landings.

Secondly, upwelling affects animal movement. Most marine fish and invertebrates produce microscopic larvae that drift in the water as they develop. Upwelling that moves surface water offshore can potentially move drifting larvae long distances away from their natural habitat, reducing their chances of survival. Upwelling can infuse coastal waters with critical nutrients, but it can also rob coastal ecosystems of offspring needed to replenish populations.

What happens if there is increased upwelling?

Researchers are exploring the ecological impact of increased upwelling on the ocean. While upwelling can initially increase the abundance of organisms in the ocean due to nutrient-rich deep waters, excessive upwelling can lead to adverse effects, such as hyperdrive and a dead zone. Climate-induced changes in the ocean can also alter the spatial gradient of upwelling, making conditions at different latitudes more similar, potentially affecting biodiversity. This research is ongoing to understand the potential consequences of increased upwelling.

What does upwelling allow algae to do?

In central and northern California, blooms of phytoplankton are often triggered by natural shifts in ocean currents and wind circulation. Coastal upwelling occurs when strong winds cause surface waters to move away from the shoreline, allowing colder, nutrient-rich deeper water to rise. This allows algae to grow and support the coastal food web. However, algae can grow to excessive numbers after upwelling ends, leading to surface waters warming and stratifying, trapping phytoplankton near the surface.

Other regional bloom events may be linked to overfeeding, where excess nutrients from farms and lawns build up and stimulate excessive algae growth. The majority of phytoplankton species are harmless and serve as the food web’s base, with only a few dozen harmful species producing toxins that can kill fish, shellfish, mammals, birds, and humans.

Why is net primary productivity high in upwelling ecosystems?

The most productive waters globally are found in regions of upwelling, where nutrient-rich coastal waters bring nutrients to the surface, allowing phytoplankton to reproduce rapidly and grazing zooplankton to multiply, providing abundant food for nekton. These regions are home to some of the world’s richest fisheries, such as the temperate waters off Peru and California. However, if upwelling fails, the effects on animals and fisheries can be disastrous.

The intensity and location of upwelling are influenced by changes in atmospheric circulation, such as El Niño conditions. Plankton production cycles vary at different latitudes due to seasonal patterns of light and temperature. In extreme conditions, plankton populations crash during winter and bloom in summer. In tropical waters, sunlight and temperature variation is slight, and planktonic assemblages do not undergo large fluctuations in abundance. However, rapid cycles of reproduction and high rates of grazing and predation result in a low-standing crop.

Plankton abundance peaks in temperate regions in spring, with seasonal winter storms mixing the water column, facilitating phytoplankton growth. Peak zooplankton production generally lags behind phytoplankton, while consumption by zooplankton and phagotrophic protists reduces phytoplankton abundance. Secondary peaks in abundance occur in autumn.

Local conditions, such as heavy rainfall in coastal regions, can also influence plankton abundance. Changes in production may depend on the season, proximity to fresh water, upwelling timing and location, currents, and reproduction patterns.

How does upwelling affect coral reefs?

Coral calcification in both gulfs was significantly lower during the upwelling season than during the non-upwelling season, which was expected for the GoP. Coral reefs provide essential ecosystem services to coastal communities, including fisheries, tourism, and protection from storms. These services rely on the ability of stony corals to accumulate calcium-carbonate skeletons and produce a complex, three-dimensional framework.

However, the accumulation of reef framework is reduced by erosion by biological and physical agents, and abiotic dissolution. Bioerosion is a persistent driver of reef-framework removal, with various organisms contributing to this process.

Net accretion occurs when calcification exceeds erosion, while net erosion drives a loss of reef-framework habitat over time. The capacity of reefs to break waves and protect coastlines depends on their ability to keep up with sea-level rise through net accretion. Identifying which reefs will grow fast enough to keep up with current and future sea-level rise and which will likely drown is essential for identifying the regions and human populations most vulnerable to climate change. Most reefs in the Caribbean region are currently in a net-erosional or net-neutral state due to decreasing coral cover from coral bleaching and disease outbreaks.