The pelagic, or open ocean, environment makes up the majority of the world’s ocean and is also the predominant habitat in the Greater Farallones National Marine Sanctuary. These waters are divided into two primary zones, based on their proximity to the continental shelf and the seafloor.
- The neritic zone overlies the continental shelf.
- The oceanic zone is the region of open water that overlies the shelf break and abyssal depths.
Generally, the oceanic zone is divided by depth into three regions: the epipelagic, mesopelagic and bathypelagic zones. The epipelagic zone includes the upper 200 meters (650 feet) of the water column. Areas deeper then 200 meters are covered in the Deep Sea section of this website.
Both the neritic and epipelagic zones receive high levels of light and are subjected to seasonal variations in temperature and salinity. Likewise, both zones support a diverse and complex food web of plankton, invertebrates, fishes and mammals.
The open ocean is a vast place. It is essentially bottomless and without sides – an endless column of water. As such, it requires special adaptations for survival: animals in this realm are either “drifters” or swift “swimmers”.
- Drifters include the larvae of many fishes and invertebrates as well as larger organisms like jellies, salps, krill and copepods.
- Rather than floating with the currents, swimmers – such as fishes, turtles, oceanic dolphins, migrating pinnipeds and whales – are capable of moving against currents and making prolonged migrations that may be unrelated to ocean currents.
In the open space of this habitat, structures in which to hide are few and far between. Where do you hide when there is just open water all around?
Some open-ocean creatures (such as many of the jellies and other gelatinous organisms) are transparent, or nearly so. By contrast, many fishes and marine mammals use counter-shading, well illustrated by the great white shark, Carcharodon carcharias. These animals are darker on top and lighter on the bottom. This allows them to blend in to the background: to an organism looking down on the shark, its dark upper body blends into the dark waters below; likewise, from underneath, the shark’s light underbelly blends into the waters lit from above.
The open-ocean habitat in the sanctuary is strongly influenced by the oceanographic patterns of the northern California coast. Strong upwelling events stimulate the productivity of organisms at all levels of the marine food web. Cool, nutrient-rich, upwelled waters support high primary productivity.
In terms of sheer number and diversity, invertebrates rule the sanctuary. These spineless creatures make up about 95 percent of all described animal species.
One of the most important components of the sanctuary’s food web is the euphausiid shrimp, or krill. These invertebrates are so critical to the functioning of the ecosystem that, in 2006, the U.S. federal government proposed a ban on commercial fishing for all krill species in the Greater Farallones and other West Coast federal waters.
However, in upwelling regions like the Greater Farallones, both copepods and krill can dominate the zooplankton.
Copepods are small crustaceans that are 1-2 mm (less than a tenth of an inch) long. They spend their entire lives as tiny zooplankton, drifting with ocean currents and serving as food for other invertebrates and fishes. Arguably the most important group of crustaceans, these one-eyed arthropods make up more than 70 percent of the zooplankton in the open ocean.
Much larger than their copepod cousins, krill are shrimp-like crustaceans that are approximately 1.25 to five centimeters (a half inch to two inches) in length. They are omnivores, feeding in particular on phytoplankton, copepods and even fish larvae; in turn, they are eaten by many predators, including salmon, seabirds and marine mammals.
In the Greater Farallones, the two most abundant species of krill are Thysanoessa spinifera and Euphausia pacifica. The former is the dominant krill species over the continental shelf, while the latter lives in deeper water at the edge of the shelf and over the continental slope. During the upwelling season, T. spinifera forms daytime swarms at the surface of up to 75,000 animals per cubic meter (about 112,500 animals per cubic yard).
The greatest protection for the offshore waters in the gulf was the designation of the sanctuary itself. Its size and the restrictions placed on its use provide additional oversight and protections to offshore waters.
Non-Point Source Pollution
The sanctuary’s offshore areas are at some risk from non-point source pollution, but the threat is generally considered to be less than for estuaries, due to the distance from the sources of pollutants and land-based runoff as well as the continuous circulation of the offshore waters.
Nevertheless, water quality in the offshore regions could be threatened or affected by large or continuous discharges from the shore, spills by vessels, illegal dumping activities or residual contaminants from past dumping activities. Further, the results of eight million people living in the Bay Area and the discharge of the San Francisco Bay Estuary (including agricultural wastes from the Central Valley and residual sediments and metals from historic mining) do periodically impact the sanctuary.
Oil and other discharges from sunken vessels as well as illegal discharges from oil tankers and cargo vessels have negatively impacted marine organisms within the sanctuary from time to time. The threat of an offshore spill is a constant presence in areas near well-used shipping lanes.
Even spills that happen near shore, such as the 2007 Cosco Busan incident, can pose a threat to offshore ecosystems, as winds and currents can spread the oil. Also, many offshore animals have wide ranging movements that may take them through oiled areas and transport the oil to offshore systems. In the event of an offshore oil spill, the effect to the open coast would mainly be determined by the wind and sea conditions, which could easily overcome protection efforts.
Debris that threatens sanctuary resources may come from the San Francisco Bay outflow and local watersheds that drain into the sanctuary or from across the Pacific Ocean. Plastic debris is a worldwide problem, due to its many potential sources, the longevity of plastic in the marine environment and the impacts plastics cause even as they degrade to smaller and smaller particles.
Plastic particles are often ingested by filter feeders and by marine organisms that live in the open water who mistake plastic for food. Plastic debris also entangles marine wildlife, such as sharks, sea birds, turtles and marine mammals.
Introduced species are often transported on commercial and recreational vessels as well as on research equipment, debris, dredging and drilling equipment, buoys and many other vectors. These organisms are of concern because they can out-compete native species for space and other resources, and often they have no natural predators in sanctuary waters.
Harmful Algal Blooms
A harmful algal bloom (HAB) is a rapid increase in algal species in a short amount of time that damages ecosystems. Harmful algal blooms are problematic because they can produce extremely potent toxins, which can cause injury or death to other organisms.
The open ocean is the largest, yet least understood, area of the sanctuary. Efforts are underway to increase our knowledge about this habitat, its ecosystems and the connections between it and other sanctuary environments. The following list includes some of the projects underway in the sanctuary. Please click on the Projects tab at the top of this page for more information.
Sanctuary Ecosystem Assessment Surveys (SEA Surveys)
SEA Surveys are designed to investigate the relationship among hydrographic conditions, physical features and the distribution and abundance of marine organisms in the Greater Farallones. These surveys include counts of marine turtles, birds and mammals along set transect lines.
One component of the Farallon SEA Surveys is to assess biological productivity (chlorophyll-a; phytoplankton species inventory; euphausiid abundance and distribution; distribution/abundance of jellyfish; assessment of drift algae). SEA’s plankton tows and HAB assessments will be used to sample for introduced species as well as native populations.
The Tagging of Pacific Pelagics (TOPP)
Since 2000, the TOPP research program has been using satellite tagging techniques to monitor the movements of large predators in the North Pacific basin and evaluate how these animals act and interact in their open-ocean habitats. TOPP has tagged 22 different species, including squid (Humboldt squid), fishes (albacore tuna, northern bluefin tuna, ocean sunfish, swordfish, yellowfin tuna), sharks (blue, great white, shortfin mako, salmon), sea turtles (leatherback, loggerhead), seabirds (Black-Footed Albatross, Laysan Albatross, Pink-Footed Shearwater, Sooty Shearwaters), pinnipeds (elephant seals, California sea lions) and whales (blue, fin, humpback, sperm). These data provide a better understanding of how large pelagic organisms move within and use sanctuary resources and highlight the location of foraging and reproductive hot spots and migratory corridors.
Wind to Whales
This project, through the Center for Integrated Marine Technologies (CIMT) at the University of California Santa Cruz, uses emerging technology to assess the processes underlying the dynamics of the coastal upwelling ecosystems along the California coast. The project includes study of primary production, nutrient flux, harmful algal blooms and the effects of these on the distribution, abundance and productivity of organisms at higher trophic levels, including squid, fishes, seabirds, sea turtles, pinnipeds and whales.
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