What happens beneath the surface: Carmel Bay’s circulation and the transport of baby fish

A guest blog by Anna Lowe

           

The calm waters that serve as the backdrop for one of the most photographed greens in the world at Pebble Beach (left) belie the constantly moving currents in Carmel Bay that control where kelp rockfish (above) call home. Photo credits: B Sanders and A Lowe. 

The calm waters that serve as the backdrop for one of the most photographed greens in the world at Pebble Beach (left) belie the constantly moving currents in Carmel Bay that control where kelp rockfish (above) call home. Photo credits: B Sanders and A Lowe. 

Pebble Beach golf course was ranked #14 on the list of Top 100 Golf Courses Worldwide. Is this golf course really better than thousands of other courses in the area and around the world? Perhaps, but most golfers would likely attribute the breathtaking ocean views as the true reason to visit this course. It is quite a view. You can pause and watch a wave roll in and crash into the rocks, but how does the water move beneath the surface?

Let’s start with a unique feature of Carmel Bay – the canyon. Carmel Canyon is one of the steepest submarine canyons off the California coast, and it connects to the Monterey Submarine Canyon system offshore. As a visual reference, the Grand Canyon would fit inside the Monterey Submarine Canyon, and the Carmel Canyon is steeper than both canyons, but not as large. The head of Carmel Canyon is located just off Monastery beach (swim about two pool lengths) and you will be hovering over water about 100 ft deep. This canyon is quite a dramatic feature for such a small bay and influences the water circulation.  

An aerial view of Carmel Bay (above) and the model view of water currents at 65 feet depth (right). The clockwise motion in Southern Carmel Bay are highlighted by the arrows, which show velocity, and colors, which shows speed. Photo credit: Kip Evans

An aerial view of Carmel Bay (above) and the model view of water currents at 65 feet depth (right). The clockwise motion in Southern Carmel Bay are highlighted by the arrows, which show velocity, and colors, which shows speed. Photo credit: Kip Evans

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The circulation during summer months generally flows clockwise in Carmel Bay. Water enters the northern part of the bay and flows out the southern region. Interestingly, the inflow is weaker because it is spread out over a larger region and the outflow is concentrated into a smaller, subsurface jet of strong northwestward flow out of the bay near Point Lobos. The tidal circulation has a strong influence in southern Carmel Bay due to the submarine canyon and results in a strong, concentrated, outward flow. Often, we think of tides as a symmetric process because we can watch the tide go in and out at the beach. But off the beach, the flow does not always “turn around” and reverse, instead it may change directions and develop an alternate flow pattern, which is the case in southern Carmel Bay. Therefore, the tides have a large influence on the circulation and account for about a third of the energy in Carmel Bay.

Many fish and invertebrates (like anemones) are found deep in the canyon whereas other species prefer to reside in shallower depths. You may notice kelp floating at the surface in regions – these areas are shallower (less than 90-ft) and house many fish, sea stars, abalone, and other underwater creatures. Within and around Carmel Bay, there are four marine protected areas. The density of marine protected areas in this area highlights the importance of these healthy ecosystems lying beneath the surface.

After being moved by the ocean’s currents, baby kelp rockfish settle in the kelp forest canopy where they continue to grow. Photo credit: Paul Mattern.

After being moved by the ocean’s currents, baby kelp rockfish settle in the kelp forest canopy where they continue to grow. Photo credit: Paul Mattern.

Kelp rockfish are very common in this area. Fun fish fact: a female kelp rockfish releases thousands of baby fish into the water each spring. These baby fish are so small (1-2 mm) they are unable to swim and are moved by the water for about 1-2 months until they can swim. If the circulation transports a baby fish far offshore, it is unlikely to survive, whereas baby fish transported close to the coast are more likely to find kelp forest habitat and survive. Once a juvenile kelp rockfish settles, it moves very little during its adult life (some adults will stay near the same rock!). Therefore, the ocean’s circulation plays a major role in fish population distribution along the coast. My research uses a model to simulate the ocean’s circulation off the central coast and within Carmel Bay. Then, I seed the model with particles representing baby kelp rockfish to track where they go. Most baby fish released in Carmel Bay go southward along the coast, but some move northward and settle nearby in southern Monterey Bay. Interestingly, there is a strong, subsurface current transporting some of these larvae northward around the Monterey Peninsula.

Carmel Bay supports a vibrant underwater ecosystem off the central California coast. Next time you find yourself golfing at Pebble Beach, sightseeing on 17-mile drive, picnicking at Monastery Beach, or hiking at Point Lobos, I hope you remember this brief description of the bay’s circulation and the transport of baby fish that is happening beneath the surface of your incredible ocean view.

Anna Lowe is a PhD candidate in Ocean Sciences at UCSC.