Monterey Bay intertidal zone

• Category: Marine and Oceanic Biomes.
• Geographic Location: North America.
• Summary: The intertidal region in the Monterey Bay region on the central coast of California owes its biodiversity to a mild climate, a ready mix of freshwater and seawater, and rich natural nutrients.

Consisting of rocky shorelines interspersed with sandy beaches along a semicircular bay and above a deep underwater canyon, the Monterey Bay intertidal zone biome hosts a vast array of organisms. Monterey Bay is an ecosystem built around the interface of the Pacific Ocean and the mouths of the Pajaro and Salinas Rivers. The Bay is ensconced in the rugged central coast of California at a point just south of the Santa Cruz Mountains and just north of the Santa Lucia Mountains, both segments of the coastal ranges in this location.

Over the course of the year, the average surface temperature range of the bay waters nearest the intertidal area is approximately 52 to 56 degrees F (11–13.5 degrees C).

The rocky shore and beach habitat, particularly in central California, is one of the most varied, most studied, and best understood biological regions of the world. Traditionally, such environments across the world are closely linked to the movements of ocean tides, in what is called the intertidal zone. In the intertidal zone, the most common organisms are small, and most are very resilient to the harsh environmental conditions. This occurs for a variety of reasons. First, the water supply marine organisms require to survive is intermittent. Second, the wave action around the shore can wash away and dislodge poorly suited or adapted organisms. Third, because of the intertidal zone’s high sun exposure, the daily temperature range can be extreme, from very hot to near freezing in frigid climates (with cold seas). Lastly, the salinity is much higher in the intertidal zone, because salt water trapped in rock pools evaporates, leaving behind salt deposits. These four factors make the intertidal zone an extreme environment for orgnanisms to live in.

Zonation of the Intertidal

According to the US National Oceanic and Atmospheric Administration (NOAA) classification levels, there are four general intertidal zones: the splash zone (Zone 1), the high intertidal (Zone 2), middle intertidal (Zone 3), and low intertidal zone(Zone 4).

Zone 1, the splash zone, also known as the supratidal or supralittoral zone, is the highest and the driest of these gradients, and can be found above the spring high-tide line. It tends to be exposed to the air most of the time, as it receives no more than the occasional ocean spray during high tides and is only actually covered by water during storms.

The splash zone has relatively few species. Mollusks such as limpet and periwinkle sea snails, crustaceans in the form of tiny barnacles, and algae survive in this hot, dry zone. In fact, the periwinkle snail (Littorina keenae, L. scutulata) is sometimes used as an indicator of this zone. Microscopic algae are common in winter months, when large waves produce consistent spray on the upper portions of the rocky shore.

Zone 2, the high intertidal zone, is exposed to air twice daily. It is here that the tide pools form during low tides. Tide pools are a harsh environment because the high temperature and repeated exposure drives evaporation, which in turn increases salinity, making it necessary for organisms living here to have an elevated tolerance both for high salinity and high temperatures.

The common Balanus glandula barnacle, along with several types of red algae (Endocladia muricata, Mastocarpus papillatus), are used as indicators of this zone, although these species are also found in other areas of the rocky shore. The other most common animal types in the intertidal are tube worms, wooly sculpin fish, lined shore crabs, and mussels. Giant green sea anemones and ochre sea star live in the deeper end of Zone 2.

Zone 3, the middle intertidal zone, features temperature fluctuations that are less extreme, due to briefer direct exposure to the sun. Therefore, salinity is only marginally higher than regular ocean levels. However, wave action is generally more extreme than the high intertidal and spray zones. This mid-intertidal zone is exposed to air once or twice a day for relatively brief periods. Many common organisms are found here; at wave-exposed sites, the mussel (Mytilus californianus) often dominates the available attachment substratum.

Zone 4, the low intertidal zone, is exposed only during the lowest tides. The presence of the Scouler’s surfgrass (Phyllospadix scouleri) and Torrey’s surfgrass (P. torreyi) are good indicators of the mean low-water tide level. This zone is where sponges and tunicates—anchored filter feeders sometimes called sea squirts—are most common. The sea lemons, a range of nudibranches or sea slugs; the toadfish; sculpin fish; reef surfperch (Micrometrus aurora); and monkey-faced eel (Cebidichthys violaceus) all thrive in this zone.

The aggregating anemone (Anthopleuraelegantissima) is a key link in the lower food web here, as it hosts zooxanthellae—much as corals do—thereby helping to buttress the algae population of the intertidal reaches of the bay.

In Monterey Bay, an additional type of intertidal environment exists in the estuarine area known as Elkhorn Slough, near the mouth of the Salinas River. This considerable-sized tidal salt marsh area—one of the largest on the west coast of North America—includes mud flats, sand bars, and swaths of eelgrass that all harbor the types of algae, snails, crustaceans, and small fish that make the site a haven for great numbers of resident and migratory birds across hundreds of species. Sea otters are among the most recognizable denizens of the Elkhorn.

Research and Conservation

Intertidal zones have received a large amount of scientific attention, for several reasons. Foremost among those reasons is the highly structured, or zoned, biological diversity present in such habitats. Furthermore, complex relationships among species here are readily studied because of the distinct boundaries between zones and inhabitants. Also, relatively large numbers of species can be present within the zones. For example, upper intertidal Endocladia algal colonies may contain as many as ninety-three different species of the algae within the colony, while some mussel beds have been shown to contain more than 300 associated taxa.

These factors are accentuated in the Monterey Bay Intertidal Zone biome, in part due to its considerable tidal range, typically as much as eight feet (2.4 meters). The upwelling of nutrient-rich water is another factor, along with the cool fog prevalent nearly every warm day around the bay, which helps prevent desiccation during low tides in otherwise dry summer months.

There are several very small nature preserves around the bay, all of which are benefited by the presence of the Monterey Bay National Marine Sanctuary (MBNMS), a major, federally-protected marine area that encompasses a shoreline length of 276 miles (444 kilometers) and covers nearly 6,100 square miles (15,800 square kilometers) of the ocean and bay. Supporting one of the world’s most diverse marine ecosystems, the MBNMS helps protect marine mammals, seabirds, fish, many invertebrates, kelp stands, and seagrass beds in this highly productive coastal environment.

The MBNMS rocky shores have historically been, and will continue to be, used to detect human impacts on a global scale. The effects of human-derived ecological impacts such as oil spills, disturbance from ship groundings, habitat destruction, and real estate development are some of the disturbances that have been studied here. By measuring levels of radioactive iodine–131 in the intertidal brown algae Fucus here, scientists were able to detect nuclear fallout from the 1986 Chernobyl nuclear power plant disaster in Russia.

Various researchers have detected increasing numbers of warmer-water species in Monterey Bay, and have concluded that the pattern is consistent with the anticipated trends of global warming. Continuing and improved monitoring efforts in this area will facilitate studies that impact global comprehension of both human-induced and natural changes and threats to intertidal ecosystems.

In the twenty-first century, global warming is impacting the Monterey Bay intertidal zone by causing rising sea temperatures, leading to shifts in species composition, a potential decline of kelp forests, an increased presence of warmer water species, and disruptions to the food web, with notable effects like the expansion of species typically found further south and potential impacts on key organisms like sea stars and abalone due to ocean acidification. Research and conservation efforts in the Monterey Bay intertidal zone focus on understanding and mitigating climate change impacts. Scientists use long-term data to monitor changes, which provides insights into ecosystem shifts. Marine protected areas are established to safeguard sensitive habitats and species, while conservation initiatives emphasize reducing greenhouse gas emissions to protect these vital ecosystems.

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