The neritic habitat includes the waters and biological communities living in the water column over the continental shelf. The neritic habitat is characterized by CMECS as including the nearshore and offshore marine subsystems, and includes the surface, upper water column, pycnocline, and lower water column layers. Neritic habitat also occurs beyond the planning area, westward to deeper oceanic habitats that start at the continental shelf break at approximately the 200 m depth contour. The waters of the neritic habitat are in constant motion. The California Current System, seasonal upwelling and downwelling, El Niño/La Niña events and changes in the Pacific Decadal Oscillation are all examples of physical events that move the waters in this habitat over varying time scales. The water is replaced many times over during an average human lifetime. The setting for the CMECS biotic component of this habitat is planktonic biota and the plankton varies with the water mass. The ecology of the neritic habitat is affected by processes taking place at scales varying from global to local. The dynamics of the neritic habitat affect all of the other habitats described later in this section.
Many physical and chemical environmental factors affect neritic ecology. These factors include but are not limited to solar light and radiation influence, salinity, temperature, layer position, physical mixing, hydrostatic pressure, biogeochemical composition, atmospheric exposure and influence, surface and under water currents, swells, waves, and water mass movements. Many of these factors can change by location and time of year. The neritic habitat encompasses many water column habitats that shift, expand, and contract over time and space in both predictable and stochastic patterns.
Coastal upwelling is perhaps the most defining feature of Oregon’s neritic habitat with its alternating upwelling-relaxation events. Upwelling is a water column hydroform, described by CMECS as an upwardly-directed current caused by divergence of water masses. In spring and summer months, strong northerly winds push surface and upper water layers westward towards the deep ocean. This movement causes deep, cold, oxygen-poor but nutrient-rich waters to rise to the surface near the coast replacing the water that was driven offshore. These nutrients, brought to the upper layers of the water column help propagate and sustain the rich biota of Oregon’s coastal waters. The relaxation events, when the northerly winds briefly cease or reverse, allow the upper water layer to move back towards shore bringing its rich biotic content with supplies of food, larvae, and juvenile organisms. In fall and winter months when winds blow predominantly from the south, the surface and upper water layers move shoreward and downward in a process called downwelling. Downwelling is an important part of the annual seasonal cycle that forces oxygen rich waters from the upper layers downward in the water column. Surface water temperatures provide a good indication of these seasonal wind forcing differences that bring the cold, nutrient-rich waters to the surface in the summer (Figure 6.6a) and the warmer waters from offshore to the coast in the winter Figure 6.6b).
Large-scale changes in water masses, temperatures and currents result in changes in plankton species composition and abundance, which impact the survival and distribution of organisms within coastal and oceanic ecosystems. These large scale oceanic events, such as El Niño/La Niña and the Pacific Decadal Oscillation, occur at multi-year or decadal time scales. Recently, scientists have made strides in understanding how El Niño/La Niña events and the warm and cool regimes of the Pacific Decadal Oscillation influence Oregon’s coastal and marine water ecosystem.
Another water column component that affects Oregon’s neritic habitats is river plumes. CMECS does not characterize the marine waters affected by these plumes as estuarine because they are not meaningfully enclosed by landforms. Riverine waters entering the ocean often carry high concentrations of nutrients, create gradients in salinity, cause physical mixing, and create areas of high turbidity. Large river plumes, such as that from the Columbia River, may serve as a microhabitat within neritic habitats and can potentially act as biogeographic barriers between marine areas to the north and south. The Columbia River plume stretches hundreds of miles offshore and shifts predictably over the course of each year. In the summer the plume spreads south and offshore from the river’s mouth, while during the winter the plume is found to the north of the river mouth and is usually directly adjacent to the coast. This plume has important ecological effects, not only to neritic habitats, but to nearshore and offshore habitats as well. The oceanographic fronts created by the Columbia River plume in the marine systems generate productive conditions that attract many species of invertebrates, fish, seabirds, and marine mammals.
Neritic habitats support two basic types of marine organisms: plankton and nekton. Planktonic organisms live in the water column and are incapable of swimming against currents, instead drifting with them. Plankton are often categorized as either phytoplankton or zooplankton. Phytoplankton are microscopic photosynthesizing organisms (e.g., diatoms), and are the primary producers that form the base of the marine food web. Huge surges in phytoplankton populations, known as “blooms,” are commonly associated with upwelling events. Zooplankton are heterotrophic organisms that range in size from microscopic single-celled organisms to enormous jellyfish a meter or more in diameter. Some plankton, called holoplankton, like many diatoms, copepods, krill and jellyfish spend their entire lives as drifters in the water column. Many species like sea urchins, mussels, crabs, some snails and many fishes have planktonic stages as eggs or larva, called meroplankton, before either settling to the bottom or growing large enough to be nekton. The CMECS biotic component uses these planktonic classes and subclasses to describe the open water neritic zone. They can be further refined by taxonomic groups and communities that are dominant in any given area of interest. Dramatic changes in plankton communities occur in Oregon waters with water masses changes. For example warm water species are brought in to nearshore water with El Niño events.
In contrast, nektonic marine organisms are capable of swimming against currents and include animals such as adult crustaceans, mollusks, and vertebrates. Highly migratory and schooling species are typical of nekton in neritic habitats. Many species of invertebrates, fish, birds, and marine mammals travel and forage exclusively or occasionally within this habitat.
Many nearshore Strategy, Watch List and commonly associated species utilize the open water neritic habitat during their life history (Table 6.3, Appendix E and F). Many forage fishes such as northern anchovy, Pacific herring, topsmelt, surfsmelt, Pacific sandlance and longfin smelt feed in this open water neritic habitat. Juvenile rockfish are found in the water column. Breeding birds such as tufted puffin and common murre are central place foragers that feed on the forage fish and other species while nesting. In all, 59 of the 73 nearshore Strategy Species depend on this habitat for some phase of life. This is also the habitat that supports primary production by phytoplankton and secondary production by zooplankton, which is at the base of the food web for the nearshore ecosystem. Ocean currents transport and disperse larvae and juveniles of many invertebrate and fish species throughout the region.
Human uses of the neritic habitat include commercial and recreational fishing, nonconsumptive recreational pursuits such as boating or whale watching, scientific research, commercial maritime transportation, and military operations. Development of renewable energy sources from both wind and waves is an emerging use of the neritic habitat.