Open Ocean: MBNMS

The vast majority of the Monterey Bay National Marine Sanctuary consists of open waters – three-dimensional habitats not associated with the seafloor. These waters are divided by depth into three zones: the epi-, meso- and bathypelagic zones. The epipelagic zone, which includes the upper 200 meters (650 feet) of the water column, is the focus of this section.

The epipelagic zone receives sunlight, which drives photosynthesis in microscopic floating plants called phytoplankton. Phytoplankton form the base of the complex and diverse open-ocean food web.

Upwelling in the spring and summer fuels blooms of phytoplankton, which in turn feed zooplankton and some planktivorous fishes such as anchovies and sardines. Zooplankton (such as larvae, copepods, krill and jellies) are eaten by a wide variety of large, highly mobile animals, including squid, fishes, sea turtles, seabirds and mammals.

Coastal upwelling occurs within about 45 to 50 kilometers (28 to 31 miles) of shore, but alongshore upwelling does not occur uniformly throughout the sanctuary’s coastal waters. There are two upwelling centers in the sanctuary: one near Point Año Nuevo and one south of Point Sur.

Plumes of upwelled water are carried south of these promontories, where they can be retained and recirculated in upwelling shadows; or they move offshore as filaments of high-productivity waters. (Upwelling shadows are warm-water patches that occur in nearshore regions where upwelling is absent and the warm, buoyant surface water is retained inshore of upwelled water.)

Retention zones in upwelling shadows concentrate primary production, which makes these areas attractive to higher trophic level animals. For example, the upwelling shadow within northern Monterey Bay is a foraging “hot spot” for a number of large pelagic organisms, including leatherback turtles, Sooty Shearwaters and harbor porpoise.

The waters around Point Año Nuevo are foraging hot spots for a number of marine mammal and seabird species that use the island for breeding and resting. An increase in white shark abundance in this region during the fall coincides with the peak occurrence of northern elephant seal pups (one to three years of age) – the preferred prey of adult white sharks – on the island.

El Niño events affect the composition and structure of open-ocean communities off central California. Some of the changes appear to be related to reduced upwelling-associated primary production and a subsequent reduction in the biomass of zooplankton and forage fishes.

Decreased food supply during these events contributes to mortality and decreased reproductive success of local predatory fish, seabird and marine mammal populations. In addition, changes in current patterns and increased water temperature are related to immigration of warm-water pelagic species and emigration of cold-water species.

Southern species with elevated abundance in the sanctuary during El Niño events include skipjack tuna, striped marlin, Pacific mackerel, jack mackerel, kelp bass, Pacific barracuda and bluefin tuna. Surprisingly, El Niño events also tend to draw more whales to the sanctuary, possibly because food availability is reduced dramatically offshore.

Commercial, recreational and other human interests play an important role in the open ocean, since many economically valuable resources, such as squid, anchovy, sardine, mackerel, salmon and tunas that demand fair to high market value, are sustained by and caught in this ecosystem. Interestingly, these same resources attract marine organisms, such as white sharks, whales, seals and seabirds; and in some cases conflicts develop between human use and resource protection.

Many human activities, such as commercial vessel traffic, motorized personal watercraft, whale watching and aircraft overflights, have the potential to harm or disturb the natural behavior of open-ocean animals. Monitoring the distribution, behavior and movement patterns of these animals relative to human activities will help to identify those activities that may need to be regulated to ensure healthy populations in sanctuary waters.

Phytoplankton blooms, including harmful algal blooms, have increased in frequency and distribution worldwide since at least 1980. The frequency of blooms may be increasing with nutrient enrichment from agricultural and urban storm runoff and sewage effluent. Although the sanctuary is relatively pristine, there is growing evidence for the role of coastal runoff – due to urbanization, land-use practices and sewage discharge – in stimulating phytoplankton, including potentially harmful organisms.

Monitoring

The open ocean is one of the largest components of the sanctuary, yet it is one of the least understood. The large spatial and long temporal scales at which important processes operate make the system difficult to study; and rough conditions can make research challenging. Furthermore, many open-water organisms are very difficult to study either due to their large size and high mobility (often swimming from one region to another) or their small size and fragility.

Monitoring Harmful Algal Blooms (HABs)
HABs in the sanctuary are usually associated with toxin-producing algae. In May 1998, ongoing monitoring in Monterey Bay detected a bloom of the diatom Pseudo-nitzschia australis, which produces domoic acid, a neurotoxin that was subsequently found in high levels in anchovy, sardines and California sea lions in central California. More than 400 California sea lions died, and many others along the central California coast displayed signs of neurological dysfunction during May and June 1998. Domoic acid has also been implicated in 62 percent of dead, stranded southern sea otters.

Monitoring also tracks dinoflagellates that cause paralytic shellfish poisoning; dinoflagellates that cause diarrhetic shellfish poisoning; dinoflagellates thought to be responsible for the production of yessotoxin (a newly identified problem in California); and Cochlodinium fulvescens, a species first detected in Monterey Bay in July 2004. Dense blooms of C. fulvescens produce a foul-smelling slime and have been associated with fish kills and other damage off Canada, Mexico and Central America. Ongoing monitoring tracks the seasonal abundance and distribution of harmful algal species, trying to identify the conditions under which blooms occur.

Monitoring the Open Water Community over the Monterey Submarine Canyon
Many open-water organisms (e.g., ctenophores, siphonophores, jellies, salps, larvaceans) are fragile and cannot be investigated accurately with conventional sampling methods. The Monterey Bay Aquarium Research Institute’s (MBARI) ROVs, with their sophisticated cameras, samplers and sensors, have afforded investigators the opportunity to spend thousands of hours monitoring and describing open-water organisms. Researchers have found that the discarded mucus houses of larvaceans living in the upper water column sink rapidly and provide a significant amount of organic matter to deep-sea detritivores.

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
The Center for Integrated Marine Technologies’ (CIMT) has created a coastal ocean observing and forecasting system for the Monterey Bay region that strives to link the distribution and abundance of zooplankton and large pelagic animals (e.g., sea turtles, seabirds, mammals) to physical oceanographic processes and nutrient availability. In 2005, CIMT instruments recorded a lack of springtime northwest winds and upwelling. This lack of upwelling appeared to be the cause of low zooplankton densities, decreased blue whale sightings and increased numbers of malnourished seabirds.