Seasons in the Sea - A month-by-month guide to Central California sea life

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Sea star: Image credit-Alaska Dept. of Fish and Game

Rocky intertidal areas

in January and February

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Storms bring death and opportunity

During a winter storm, a large log or other debris broke off a piece of this tubeworm colony, revealing its internal structure. The storm also damaged colonies of goose-neck barnacles (upper left) (Source: Kim Fulton-Bennett)

Like the kelp beds, the rocky tide pools are pretty stripped down in January and February. There is usually be plenty of bare rock exposed, both above and below the high tide line. The upper rocky areas may be bare because algae or animals have been removed by storm waves. The lower rocky areas are bare because storm waves have stripped away the sand that covers these rocks most of the year. All of this bare, exposed rock provides a once-a year opportunity for some algae and animals.

By January or February, after several months of winter storms, most of the soft, frilly red algae have either died out or been torn completely off the rocks. The remaining algae are the hardiest of the hardy--those that are particularly good at surviving cold, rain, and pounding storm surf. By late winter, you will see many places where these algae have been ripped off the rock or scraped of by the pounding of logs and other floating debris.

On intertidal rocks covered by dense algal turf, gaps in the algal cover will often be recolonized by the same species that existed previously at the site, or by algae that live next to the cleared area. Even when a rock appears to be barren, microscopic remnants of the original algae often remain remained, and may be capable of regrowing. In addition, the neighboring algae release spores in winter that settle on nearby cleared areas. However, this process can take up to several years. In the mean time, weedy algae may colonize the space, just as fast growing plants spring up in a forest meadow after a large tree has fallen.

Mussel beds are torn up by waves and debris

Not only algae, but many attached animals are torn off the rocks by winter waves. On the outer portions of rock ledges, beds of California mussels (Mytilis californianus) are often conspicuous in winter because the algae that covered them have died back. However there may be large gaps in the mussel beds where redwood logs have been dragged over the rocks by winter storm surf during high tides.

Where they remain intact, the mussel beds provide much-needed refuge for smaller animals and algae. You can often see short tufts of green or brown algae peeking out between the mussel shells, able to grow to the height of the mussels themselves, but no taller.

Perennial brown algae are pruned back but survive

Most of the intertidal algae you will see in January and February are perennial species that survive even after being severely "pruned" by winter waves. Though tattered and worn, these one- to three-inch-high tufts will survive just about anything.

One notable example is the leathery red alga in the genus Mastocarpus, which somehow manages to colonize tiny cracks and toe-holds in upper intertidal rocks, where even barnacles and limpets fear to tread in winter. In January and February, Mastocarpus may only be few inches high in January or February, but will grow to its full height of perhaps six or eight inches in summer.

After the green algae (described below), Mastocarpus is one of the first colonizers of newly exposed bare rocks, growing to visible size within a couple of months after the rock has been cleared by winter storms.

Endocladia muricata (maroon-colored algae at base of slope) and other algae growing in the shelter of a rock ledge. (Source: (c) Kim Fulton-Bennett)

Another amazingly durable red algae is Endocladia muricata, sometimes called "nail-brush algae" because of it's tough, bristly appearance. In some areas you can find more Endocladia in winter than in summer, as it rapidly recolonizes areas that have been scraped down to bare rock. As one of the few algae that is reliably present in early spring, Endocladia provides shelter for young intertidal animals, such as lined shore crabs, which begin to settle into the tidepools in early spring (and are discussed in greater detail in March).

A little lower down on the rocks, you may see tattered remnants of other perennial brown algae--rockweeds in the genus Silvetia and Fucus. Some rockweeds, such as Silvetia compressa release spores primarily in winter and spring, when sand levels are low and more bare rock surfaces are available for colonization.

Feather-boa kelp (Egregia menziesii) is a very hardy perennial brown alga that survives in areas of strong wave energy and sand scour. (Source: Kim Fulton-Bennett)

In the middle and lower intertidal areas, the most visible alga in February is Egregia menziesii, the feather boa kelp. Exposed to some of the most violent wave action, even this durable kelp is pruned by winter storms, leaving short segments only a foot or two in length (compared to their summer length of up to 20 feet). These shorter remnants are even more resistant to wave damage than the full-grown blades.

The feather-boa's holdfast itself is even more durable than the rest of the alga. It is shaped like a low, rounded volcano, with stipes emerging from a protected "crater" in the middle, which protects the stipes from being scraped off by the bulldozer action of storm-driven logs and other debris.

Like the feather boa kelp, the tips of the surf grass blades sometime break off under severe conditions. This reduces drag on the plant, making it less likely that he rhizomes will be pulled off of the rock, while still keeping some leaf area for photosynthesis.

Another brown algae that survives in abbreviated form during January or February, especially along exposed coastal areas, is Laminaria sinclairii. By this time of year, the graceful, inch-wide blades of this kelp have been tattered or torn off entirely, leaving the stick-like stems or "stipes" sticking up through the water surface at low tide.

Like many algae, Laminaria have amazing powers or regeneration. Their spatula-like blades may start to grow back after just a week or two of calmer weather. Even if all of its blades are totally removed, the Laminaria holdfast will survive to send out new blades. The new Laminaria blades will grow rapidly once the storm season is over, reaching full length by late spring or early summer.

Coralline red algae grow lush in winter

Still lower down in the intertidal, other hardy, low-growing organisms become obvious in January or February, when most of the overlying algae has been removed. Although they are present all year, the colorful pink crusts and branches of coralline red algae are more visible at this time of year, growing underneath the Laminaria and along the edges of tide pools. Coralline red algae may even put on a growth spurt in winter, perhaps because they can obtain more sunlight without being shaded by the blades of larger algae.

Corraline red algae are extremely tough, with hard skeletons of calcium carbonate (like the bones in our bodies). They also have a neat trick that helps them survive winter storms--if their holdfast is ripped off a rock and then deposited on another hard surface for a few days, it can reattach and keep growing.

Limpets, chitons, and tubeworms colonize cleared areas

Owl limpet tucked into the edge of a clump of mussels. Note the parallel lines in the thin algal turf, which are caused by the owl limpet's file-like radula. (Source: Kim Fulton-Bennett)

An owl limpet's domain. This area may have originally been scraped barren by wave action, but the owl limpet keeps it free of both algae and animals by persistent grazing. (Source: (c) Kim Fulton-Bennett)

Large gaps in the otherwise continuous beds of mussels and algal turf provide mute evidence of the massive logs that grind across horizontal rock surfaces like bulldozers and crash against vertical rock surfaces like battering rams during storms. However, such gaps provide opportunities for other algae and animals that are able to grow and expand during winter's turbulence.

Grazing animals, such as limpets and chitons, migrate onto cleared areas to feed on diatoms and microscopic algae that settle on the newly bared rock. Owl limpets (Lottia gigantea), in particular, may be able to keep such areas from being colonized by larger algae, barnacles, and mussels by scraping off any algal spores or larvae that may try to settle on the rock surface. Where the bedrock is relatively soft and erodible, however, even barnacles and limpets have a hard time holding on.

Another type of colonizing animal expands in winter to take advantage of the decline in brown algae. On the sides of rocky ledges, just below the mussel beds, you can often see large, bulbous, sand-colored colonies of Phragmatopoma tubeworms. Where mussels and algae have been torn out by winter storms, tubeworm colonies may grow to cover the exposed areas of bare rock.

This large tubeworm colony has expanded during the winter months, almost engulfing the algae that peaks out of the few remaining gaps in the colony (Source: Kim Fulton-Bennett)

During January or February you may tufts of algae sticking out between the tubeworms after being surrounded by the tubeworm colonies. Come summer, however, these same algae will have grown out and their blades will be long enough to practically cover the tubeworm colonies. (During summer the sweeping action of the blades of algae limits the growth of the tubeworms at high tide, but at low tide the blanket of algae helps keep the tubeworm colonies moist and out of the hot summer sun).

Sand moves offshore, exposing bare rocks

One of the first things you will notice about tidepool areas in January and February is how little (if any) sand there is in small pocket beaches and around the tidepools. In some areas, the sand may be six to eight feet lower than in summer, especially after severe storms or when large swells arrive in late winter, after earlier storms have already removed much of the sand.

Storm waves typically strip sand from the uppermost portions of the beach and deposit it offshore--the larger the waves, the farther offshore the sand may be carried. Once offshore, this sand may be carried down coast (in a southerly direction), or it may settle in low areas, such as channels between submerged rock reefs or kelp beds.

In concert with littoral currents (moving parallel to shore) and rip currents (moving out from shore) large storm waves may deposit sand offshore of what are normally sandy bays or coves, such as those at Natural Bridges or Mitchell's Cove along West Cliff Drive in Santa Cruz. Sometimes this allows later waves to break farther out from shore, in areas that would normally be deep water.

Diatoms and green algae colonize bare rocks

Almost immediately after intertidal rocks are exposed by dropping sand levels, they begin to be colonized, first by marine bacteria, then by diatoms, then by green algae. The bacteria and diatoms form a coating on the rocks that is invisible to the human eye, but provides a perfect grazing ground for limpets and chitons. Unless the area is heavily sand scoured or grazed, the diatom films will soon be overgrown by green algae.

Note: Rocks colonized by diatom films and sea lettuce are extremely slippery and are one of the major hazards to watch for when exploring the winter-time tidepools.

Sea lettuce thrives in winter

After the marine bacteria and diatom films, green algae are the next colonizers of bare rock. Green algae do particularly well on rocks that exposed by dropping sand levels (especially where frequent sand scour discourages grazing limpets) Within two to three weeks after being exposed, many bare rocks will acquire a slight green tint as they are colonized by fast-growing green algae in the genus Ulva. With their thin, translucent green blades, these algae are collectively known as sea lettuce.

Within a month or two, if the intertidal rock is not buried, scoured by sand, or cleared by grazers, sea lettuce may expand to cover almost all of the newly bared rock. However, this ephemeral algae will die off when sand returns to the beaches during calmer periods.

Ulva can tolerate both brackish and fresh water, so they are often found in high tidal pools where runoff of fresh water makes it hard for other intertidal algae to survive. (Source: Kim Fulton-Bennett)

Unlike most marine algae, Sea lettuce will grow in brackish water. Thus, you can often find sea lettuce growing where freshwater streams, springs, or storm drains flow across intertidal rock ledges. Such runoff is often rich in plant nutrients from agricultural and home fertilizers. Patches of sea lettuce are particularly extensive in January and February, when fresh water runoff is at its yearly maximum.

Although sea lettuce is fragile compared with many types of marine algae, it grows so high on intertidal rocks that it is only reached during the highest tides. In such challenging areas there is also less competition from other algae than in lower intertidal areas.

Some algae and animals benefit from sand scour

Polysiphonia thrives in winter

On flat rocky platforms, a red alga called Polysiphonia actually benefits from the removal of sand in the winter months. This alga grows particularly well along the exposed coast northwest of Santa Cruz.

Polysiphonia thrives only where its holdfast is buried under two to four inches of sand throughout most of the year. Like surf-grass roots, Polysiphonia holdfasts retain sediment and provide habitat for many small animals such as worms and crustaceans.

Later in the spring and fall, when the sand fills in and covers the rock flats to depths of more than about four inches, Polysiphonia dies back. As soon as the sand moves away again, Polysiphonia will grow back quickly. In fact, new Polysiphonia sprouts can colonize former growing areas in only six weeks--even faster than other winter colonizers such as Mastocarpus (which take about twice as long).

On the wide, flat rock platforms, surf grass usually survives the worst of the winter, though it often becomes tattered and brown as the winter progresses. The root-like rhizomes of the surf grass help hold sand in place that would otherwise be carried offshore by winter waves.

Periwinkles dominate sand-scoured areas

Among the sand-scoured Polysiphonia beds, the dominant grazers are the tiny snails known as periwinkles (Littorina keenae). Although present all year, by winter time, these little snails are just about the only grazing animal left in sand-scour areas. Perhaps their small size allows them to shelter from the winter storms among Polysiphonia's blades or holdfasts.

Anemones survive abuse and burial

These colonial anemones do just fine being half buried in sand. (Source: Kim Fulton-Bennett)

A final hardy survivor of winter storms and a champion at living among shifting sands are the anemones in the genus Anthopleura. Some of these greenish anemones form dense colonies consisting of hundreds or thousands of clones, each about an inch or less across. Another, larger species grows much larger (up to 10 inches across) and does not form colonies, though several individuals may share prime areas such as the edges of rock ledges or surge channels.

Both the solitary and colonial Anthopleura anemones are champions at surviving on solid rock surfaces that are periodically buried and then exposed by shifting sands. Some colonies of anemones are only exposed when sand levels drop during the winter time. The rest of the year, they somehow survive being buried under as much as six feet of sand for up to three months at a time.

These solitary anemones have survived sand scour, but are in danger of being engulfed by colonial tubeworms. (Source: Kim Fulton-Bennett)

Because they do not move around much, anemones must wait for prey to be swept into their tentacles by the action of the waves. Anemones find plenty to eat during winter--the same winter storms waves that tear animals off intertidal rocks often deliver these animals into the gullets of waiting anemones.

Despite their soft bodies, colonial anemones are amazingly persistent in the face of abuse, whether by waves or humans. One marine biologist tried to remove a small Anthopleura colony from an intertidal rock ledge to see what animals would recolonize the area. He tried hand scrapers, scouring pads, and even a blow-torch, but was not able to remove all of the anemone tissue from the rock, and the colony kept growing back. Presumably the anemones were regrowing from tiny bits of mashed tissue, or perhaps their young were very good at colonizing smashed and scraped members of their own species.

A few tidepool animals spawn in early spring (many more will spawn later in spring)

There are several possible advantages for intertidal animals that give birth in January or February. For one thing, the prevailing currents at this time of year tend to flow toward shore. This means that the tiny drifting larvae released by many intertidal animals will stay close to home. Once upwelling starts (in March or April), the prevailing currents tend to carry such drifting larvae away from shore.

Another possible advantage is that certain types of food are more available in the winter time. For example, the thin algal films that form on newly cleared rocks provide the perfect food for some young grazing animals such as limpets and chitons. Similarly, the debris stirred up by winter storms provides food for some types of scavengers and filter feeders.

A third advantage of spawning early is that young animals will find plenty of vacant space on intertidal rocks. Such space will be at a premium later in spring, as algae grows out and many other animals begin to spawn and recolonize any bare rock surfaces.

Acorn barnacles spawn

Acorn barnacles (about 1/6 inch wide) (Source: Kim Fulton-Bennett)

Acorn barnacles in the genus Cthamalus are a classic example of intertidal animals that spawn before upwelling begins. Many barnacles begin to release larvae as early as January or February. This "early crop" of barnacle larvae will float around the open ocean for a month or so, but will return and settle down in intertidal areas before all the vacant rock spaces have been taken up by algae or other animals that colonize these areas en masse later in spring.

The down-side of spawning early is that some young barnacles will end up settling on bare rocks that will be covered with sand later in summer. This can be deadly for the young barnacles because they won't be able to eat or breathe. But inevitably some early settlers survive, and live long enough to send out their own young, to try again. Many more barnacles spawn in March and April.

Some chitons spawn

Some intertidal animals minimize the chance of being carried too far from home by having larvae that settle back to the tidepools after only a few days. Several species of chitons (Ischnochiton interstinctus, Ischnochiton regularis, and Lepidozona mertensii) spawn in February. Their young spend just a week or two drifting as larvae before settling down.

Rough limpets spawn

Many limpets spawn in the winter time, presumably so that their young will find plenty of bare space and lots of young algae to eat when they settle on intertidal rocks. Rough limpets (Collisella scabra) are actually one of the later limpets to spawn, releasing young from January through March.

Unlike the young of many limpets, those of rough limpets spend months and months drifting around the ocean, and don't settle back down on intertidal rocks until summer or fall. Thus, these larvae are released at the last part of the storm season, but settle out during the calmest part of the year. Presumably this allows the larvae to colonize far and wide along the coast.

Rough limpets live on relatively horizontal rock surfaces in the upper intertidal zone. This makes them easy to find, both for humans and for predators such as oystercatchers and other animals. Perhaps having their young being spread far and wide allows these limpets to find areas that are less picked over by predators.

Mussel worms spawn

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Growing up to 8 inches long, mussel worms are formidable predators of the tidepools. (Source: Lynette Schimming)

One of the most spectacular (but seldom seen) events of spring is the spawning of mussel worms (Nereis vexillosa). These large, feisty worms begin spawning in January or February and may continue to spawn once a month throughout the spring. But the largest spawning events typically occur early in the year.

For most of the year, these six- to ten-inch-long many-legged wrigglers live in mucus tubes they secrete beneath the mussels, or in kelp holdfasts. They prowl around under the mussels eating just about anything they can find, from algae, bryozoans, and sponges to small shrimp and crabs. However, they don't seem to tolerate others of their own species. As one marine biologist put it, mussel worms are "very aggressive... extending an impressive set of jaws and biting and snapping at each other" (they will also bite humans who try to pull them out of the mussel beds).

Each spring, however, the year's crop of mussel worms reaches sexual maturity and prepares for the one and only mating experience of their lives. And it is quite an experience.

At midnight on the appointed night, each worm goes through a werewolf-like transformation. It's rear end turns into what biologists call an epitoke--basically a swimming sex machine. The worm's gonads expand dramatically, causing the back half of the worm to swell up like a balloon, while its digestive tract virtually disappears. The worm's rear legs turn into swimming paddles. It's eyes bulge out (“...the better to see you with, my dear...").

When the transformation is complete, The worm's body splits in half and the epitoke swims off, leaving the rest of the body behind to die. Typically all of the mussel worms in a particular area make this transformation at the simultaneously (imagine everyone in your town becoming a werewolf at the same time), typically within a few hours of midnight, around high tide.

Like zombies in a B-grade horror movie, the mussel worm epitokes all swim upward toward the water surface. The resulting orgy has inspired many a marine biology writer.

Here let me quote one of the best of these writers, Ed Rickets (the real-life "Doc" of Steinbeck's Cannery Row). "When moon and tide are favorable” the male epitoke “flinging caution to the winds... swims rapidly and violently through the water, shedding sperm as he goes... the females follow within a short time, releasing their eggs.” This mating process is truly a "bodice ripper" in the literal sense--the bodies of female worms literally rupture, ripping wide open to release eggs. Inevitably, both the males and females die shortly after mating.

As if this wasn't enough melodrama for any movie, the mating frenzy is followed by a feeding frenzy, as fish and birds attack the weakened and dying epitokes. In fact, these events provide a welcome source of food at a time of year when Central Coast waters are not very productive over all.

This may seem like a Romeo and Juliet tragedy, but there is something of a happy least for the species as a whole. The fertilized mussel-worm eggs sink toward the bottom, largely uneaten because the predators are so busy eating their parents. The eggs hatch three or four days later. The mussel-worm larvae spend a little over a week drifting around, before settling back down into a new mussel bed, to begin the process anew.

Tiny white sea stars give birth

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Leptasterias pusilla is a small but very beautiful sea star. (Source: Lovell and Libby Langstroth / Creative commons)

If you're out exploring the tidepools at night in January (an occupation for the truly dedicated naturalist), look very carefully in the bottom of some of the sand-filled pools. In addition to seeing Ulva, coralline algae, and turban snails, you may see a tiny white, five-armed sea star--Leptasterias pusilla. When full grown, this diminutive predator is only an inch and a half across. It lives only in Central Coast tidepools between Monterey Bay to Halfmoon Bay, where it hunts small limpets and snails.

If you pick up one of these stars and look at its underside with a hand lens, you see may find that it is carrying dozens of tiny white eggs. Female Leptasterias carry 40 to 100 of these tiny white eggs during the winter months. In February or March, these eggs will hatch, releasing tiny little sea stars that will trundle off across the tidepool, looking for newly settled barnacles or periwinkles on which to feed.

If you find a small, white sea star with six arms instead of five, it is Leptasterias hexactis, which also carries eggs during the winter months. Females of this species brood 50 to 1500 eggs for about six weeks. During this time, the female cannot eat, since she carries her eggs directly in front of her mouth. When not carrying eggs, this sea star typically lives in mussel beds and feeds on larger prey than its five-armed relative, including sea cucumbers, snails, limpets, chitons, small mussels, and barnacles.

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