Seasons at Fitzgerald Marine Reserve

Like all coastal habitats the coast of Central and Northern California is dominated by its proximity to the sea. The cold water we experience year round is due to the influence of the California Current. This wide, slow-moving current carries water southward from the cold northern Pacific and bathes the California coast is its cold grasp. In addition each year the coast cycles through a series of three seasons instead of the traditional four (spring, summer, fall, and winter) typically experienced on land.

The three coastal seasons are named for the primary oceanographic forces that dictate their conditions. Spring and summer along the coast are dominated by moderate to strong winds blowing out of the northwest. These winds cause the surface water to be blown offshore and it is replaced by cold bottom water that wells up to replace it. This phenomenon, called upwelling, brings nutrient rich bottom water to the surface, which along with the abundant sunshine of long spring days, allows the phytoplankton to bloom. The UPWELLING SEASON lasts from early spring well into summer and the productivity achieved during this period drives the rich coastal ecosystem we experience along our coastline.

As the northwest winds blow offshore they accumulate water vapor that has evaporated from the ocean’s surface; when these moisture-laden winds blows over the cold upwelled water near shore, the water vapor condenses resulting in that coastal staple, fog. As the inland areas warm in the late spring and summer, the warm air from the valleys rises creating low pressure that pulls the fog in through the Golden Gate.

In the fall the northwest winds die down and ocean is particularly calm. There is little upwelling and the surface waters warm. This season is referred to as the OCEANOGRAPHIC SEASON because nearshore oceanographic conditions dominate. During this season the coast typically experiences its warmest daytime temperatures and the Bay area basks in Indian Summer.

Following our nicest weather comes winter, sometimes with a vengeance. During this period, which typically lasts from November to March/April, we experience a series of major storms and nearly all our annual rainfall. These storms track across the Pacific from the west and southwest and the winds that accompany them blow against and weaken our southerly flowing California Current. The slowing of the California Current allows the pole-ward flowing undercurrent to be manifest on the surface inshore of the California Current. This seasonal surface current is called the Davidson Current and some oceanographers refer to our winter as the DAVIDSON CURRENT SEASON. As the Davidson Current flows from south to north, it brings warmer southern water with it. Often during El Nino years the Davidson Current is especially strong and we may see warm water pelagic species, like sea turtles and marlin, well out of their normal range.

UPWELLING SEASON at Fitzgerald Marine Reserve

How do these seasons affect us locally, especially at the Fitzgerald Marine Reserve? Over the next year we will be providing a series of seasonal previews of what to anticipate and look for at the Reserve as it moves through its annual cycle.

We’ll start with spring and summer, the Upwelling Season. As mentioned above, upwelling provides nutrient-rich water to well to the surface, fertilizing the phytoplankton and allowing it to take advantage of the increasing daylight of spring in a fantastic bloom of photosynthesis. The tremendous growth of phytoplankton is soon followed by corresponding growth of zooplankton and the nearshore marine food chain is anchored by this wealth of food.

The phytoplankton aren’t the only marine plants fertilized by upwelling. The marine algae and seagrasses likewise prosper and we witness a “greening” of the rocky intertidal zone at the Reserve. Look for annual algae like rockweeds, Fucus and Pelvetia, in the high intertidal zone and the bright Kelly green of sea lettuce, Ulva, that blossoms in profusion over rock and mussels. The perennial algae like feather-boa kelp, Egregia menziesii, sprout new stipes from their tough holdfasts left behind the previous winter. As spring wears on, bare rock becomes a premium in the middle and lower intertidal zones as the algae flesh out and cover the substrate.

The rich pasture of phytoplankton carried in by the tides is grazed by the many filter feeders in the Reserve like mussels and barnacles. The mussels store up energy for reproduction later in the spring. The barnacles replenish themselves after brooding their larvae all winter. The barnacle larvae are released into the plankton by their parents so they can also take advantage of the spring phytoplankton riches.

The abundance of algal growth gives herbivores like turban snails (Tegula spp.) and chitons bountiful pasture, and careful inspection of the larger algae will show the grazing marks of these mollusks. Also look for gangs of turbans chowing down on drifting kelp stipes that wave action has torn lose from the rocks and carried into the tide pools. Drifting algae also provide the sea urchins and red abalone with their main food.

These drifting algae are pulverized by wave action and contribute to a particulate food source, called detritus. Many small crustaceans, like amphipods and isopods, are dependent on this “detrital rain” for their food. Larger detrital pieces play a large role in the diet of scavengers like hermit crabs, Pagurus spp.

Those piles of blue “jellyfish” that have piled up along all our beaches in the last two weeks (April 1 – 21^st) are not jellyfish (medusa) at all, but instead are large (up to three inches long) floating polyps. This is the By-the-Wind Sailor, Velella Velella velella (Figure 1). Like many cnidarians (jellyfish, corals, sea anemones) Velella has a complex life cycle. It spends most of the winter in a sexual medusa form near the sea floor. In the spring larvae develop into small polyps that float to the surface. These polyps feed on fish eggs and zooplankton and grow into the animals we see on the beaches. Velella has a stiff exoskeleton made of chitin, which includes a gas-filled float and a transparent sail. The sail is mounted diagonally to the left or right of the long axis of the body, so that the animal tacks at an angle 45 degrees to the left or right of the true wind direction. Velella generally remain in offshore waters, however shifts in wind direction or currents can drive these animals onshore. When the wind pattern shifts to a northwesterly direction in early spring, and depending on its strength and persistence and the abundance of Velella offshore, windrows (narrow rows of deposited material that accumulates along the upper edge of the previous high tide) of beached by-the-wind sailors several inches deep can pile up on exposed sandy beaches and rocky shorelines. These animals create quite a stink for a short time, but quickly decompose, leaving behind only the thin, light blue, cellulose-like chitinous exoskeletons which can persist on the beach for months. These interesting animals are another harbinger of spring along the Pacific coast.

Spring is also the time many animals reproduce at the Reserve. Look for prominent aggregations of the angular unicorn snail, Acanthina spirata, under overhangs in the middle intertidal zone. These barnacle-feeding snails come together and mate in groups. The females remain behind to lay their fertilized eggs into unique egg capsules, which they attach to the rocks in clusters that look like kernels of corn.

Many crab species also answer spring's siren song and seek romance. The females of the shore crabs, Hemigrapsus nudusand Pachygrapsus crassipes, can be seen carrying large clusters of fertilized eggs attached to their abdomens, as can the larger red rock crab, Cancer antennarius.

Later in spring evidence of successful reproduction can also be seen all around the Reserve. Look for dense settlements of young barnacles on exposed rock faces. Also in high tide pools the newly settled young of the hairy hermit crab, Pagurus hirsutiusculus, can be seen scuttling about with their white-stripped legs protruding from periwinkle (Littornia spp.) shells.

Also look for newly born harbor seals. At the Reserve harbor seals regularly haul out near Nye’s Rock at low tide. They number from a few to over 20 animals. They are also seen on the edge of Seal Cove and at Frenchmen’s Reef near the Reserve’s southern boundary. Harbor seals occasionally give birth within the reserve’s boundaries; however, the nearest large breeding rookeries are at Ano Nuevo and inside San Francisco Bay. Harbor seal females give birth on land from May to July. The pups learn to swim fairly early, but initially are not strong enough swimmers to accompany their mother on feeding forays. The female will leave her pup unattended on a beach or rocky reef while she forages for food. This may lead to an unfortunate scenario of concerned humans "rescuing" a supposedly abandoned pup from the beach. Like most “found abandoned” wild young, they should be left alone, as the mother will almost always return to her young. Please remember to observe the harbor seal closure boundaries marked at the Reserve, these allow the marine mammals to be viewed and the seals to remain hauled out to rest. Get more information about harbor seals from the Marine Mammal Center.

FALL at Fitzgerald Marine Reserve

As mentioned above, this season is referred to as the Oceanographic Period. The prevailing Northwest winds die down and things warm up. The coastside experiences some of its nicest weather during this period as there is much less fog and glorious fall evenings.

The ocean also experiences some changes. With the reduction in wind, the strong upwelling is likewise reduced. This means the surface water nearshore remains in place and, with the increased sunshine, warms to its yearly high temperatures. The intertidal zone also takes on an autumnal look. The fleshy red and green algae of the middle and lower zones often show a bleached-out look. This is an indication that they have released their spores and completed their life cycles, and now have begun to die back. Soon large windrows of loose seaweed will pile up along the high tide line and slowly decompose.

During this season the Reserve usually plays host to large numbers of male California sea lions. Most of year these playful pinnipeds are seen locally at Pier 39 inside San Francisco Bay. However in the summer they leave the Bay and swim south for the annual reproductive season in the California Channel Islands. At the end of the season the female sea lions remain in southern California while the males return north. On this leisurely return journey it is not unusual for several hundred sea lions to congregate along the outer edge of the reserve and on Sail Rocks immediately to the south at Pillar Point. After a few days stay they continue their journey northward.

Sea lions are not the only marine animals moving during this period. Fall is the season for bird migration. There is an almost an endless parade of birds from the Arctic moving south, and of southern hemispheric birds moving north, all seeking to feed on small fish, planktonic organisms and invertebrates from the nutrient-rich waters along the Pacific coast. From their breeding areas in the South Pacific come thousands of Sooty Shearwaters, starting in mid-July. Perhaps you have seen long lines of thousands of these dark colored birds moving along our coast, flying just over the waves. In late fall they will return to their breeding grounds off of New Zealand. Brown Pelicans, Heermann’s Gulls and Elegant Terns regularly move into our waters when their breeding season in Mexican waters is complete. Elegant Terns and Brown Pelicans are plunge-divers, diving from the air and taking their prey underwater. Heermann’s Gulls often wait for the pelicans to surface seizing any bits of missed food. Watch for this smaller, smooth gray gull with a red bill.

Some of the seabirds arriving from the Arctic after the completion of their breeding season and enroute to their wintering areas are jaegers, two phalaropes, Arctic Terns, and Sabines Gull as well as our more common loons, grebes and sea ducks, which winter here. The Parasitic Jaeger can be seen from shore, harassing Elegant Terns until they drop their catch of fish. Adding to the array of birds in migration, there are the locally breeding alcids--Common Murres and Marbled Murrelets, plus Pelagic and Brandt’s Cormorants and Western Gulls.

Also returning to our shores after their short breeding season in the Arctic are the shorebirds. Sanderlings are the most conspicuous shorebirds along the beaches at the edge. With rapid running they follow the edge of a retreating wave, seize their prey (usually sand crabs) and retreat as the next wave advances. The number of shorebird species foraging along a rocky shore or sandy beach is less that the number of species feeding in an estuary or harbor. The beach sand is unstable while the invertebrates in the intertidal areas are usually well hidden by algal growth and are securely anchored to the rocks. Look for the resident “specialist” of the rocky shore habitat, the Black Oystercatcher, which uses its chisel-shaped. red bill to pry limpets and chitons from the rocks. To see probing shorebirds in action, walk along the muddy sand edge of outer Princeton Harbor during the fall and winter months.Watch the plump, short billed plovers pick their prey from the surface while longer-billed birds such as the Marbled Godwit probe deep into the muddy sand. You may see Black-bellied Plovers working over the flat reefs in the intertidal areas along with the Black Turnstones. The Turnstones actually do turn over pebbles and push aside fronds of seaweeds to find hidden invertebrates. A word of caution when identifying many of the birds that over winter at the Reserve--they are in non-breeding or basic plumage. Thus, the Black-bellied Plover does not have a black belly. That will happen next spring when it molts back into breeding plumage.

Land birds are also on the move. Many of the local birds that raised young during the summer return to warmer climates where insect food is more readily available. Their departure may not be noticed because other birds that nest in the Arctic or at higher elevations in the mountains are returning here to over winter and feast on the seeds and insects produced during the summer months. Look for a variety of sparrows, finches, nuthatches and others as well as increased numbers of hawks. Fall is the season of change. Enjoy the change of animal life that mirrors the seasonal changes in vegetation. Also, come December watch for the update on bird activity and winter changes in the Reserve.