Kelp holdfast that has been torn loose by storm waves. (Source: Claire Fackler, NOAA)
January and February are probably the toughest time of the year for Central Coast kelp beds. Since November, winter storms have brought southeasterly winds and storms waves. Depending on how severe the winter storms have been, by January or February the kelp canopy (the part of the kelp you can see at the surface) may only show a few remnants, or may be gone entirely. Even kelp beds in protected areas are likely to have just a few spots of canopy, rather than extensive areas, as in summer.
Earlier winter storms remove the blades of giant kelp, leaving just the floats. This actually protects the kelp to some extent, by reducing its drag, while the remaining floats help keep the rest of the plant upright so that blades below the surface can continue to receive sunlight. Repeated periods of large storm waves tear off floats, break the kelp stipes (stalks), and occasionally pull entire kelp plants off of their rocky bases.
The condition of giant-kelp beds in January and February depends entirely on how many severe storms have hit the Central Coast during the previous months. During typical years, the kelp canopy (the part of the kelp visible at the surface) has been reduced to tattered remnants a few feet across. During mild winters, on the other hand, the kelp canopy may look “moth-eaten,” but patches five to fifteen feet may still be common, and new blades may continue growing in all winter.
During stormy years, you may see little or no kelp canopy (the part of the kelp that is visible at the surface) even at low tide. You may still see a “slick” at the sea surface, which indicates where kelp plants are growing below the surface, but have had their upper reaches “pruned” by winter storms. Even below the surface, the kelp plants may be reduced to bare stipes and a few floats, since many of the blades have been removed by wave turbulence. However, these remaining stipes and floats present very little resistance to wave action, and thus allow the plant as a whole to resist the waves.
Even though the kelp canopy may be decimated, battered kelp stipes and blades can still be found ten or twenty feet below surface. Similarly, most kelp “holdfasts” (the part of the plant that is attached to the seafloor) will survive. Between storms, if the ocean calms down and the sun comes out for a week or so, the surviving holdfasts will begin to send new stipes up toward the surface. During much of the winter, any new growth is usually limited by lack of sunlight (low sun angle) and wave damage during storms.
Many of the snails, crabs, bryozoans, and other small invertebrates that colonize the kelp canopy during summer leave the canopy during the winter months or are removed, along with the kelp itself, during winter storms. A few of these animals hide among the kelp holdfasts. Others head into deeper water.
California sea lion next to a raft of floating bull kelp. (Source: Jennifer Stock, NOAA)
If you're out in a boat in Central Coast waters during January or February, chances are you'll see an often overlooked source of both food and shelter--rafts of drift kelp. Formed from masses of interwoven kelp plants that have been uprooted by winter storm waves, such rafts may drift for weeks, and end up dozens of miles from shore. They often mark the locations of ocean “fronts”--the boundaries between different water masses. Such areas are hunting grounds for seabirds, marine mammals, and large fish.
Each kelp raft is a microcosm. A floating island. Rafts may shelter a variety of animals. Some of these, like kelp crabs or snails, lived on the kelp when it was growing near shore. Other kelp-raft residents include open-ocean fish, such as young rockfish, which find the drifting kelp a handy shelter from larger fish and seabirds. Both seabirds and large fish sometimes follow kelp rafts, picking off those smaller animals sheltering in the canopy.
Outside of Monterey Bay, in the more exposed portions of the Central Coast, the kelp beds are made up of bull kelp (Nereocystis luetkeana) rather than the more familiar giant kelp. Such bull-kelp beds are typically found on exposed, west-facing beaches, where they are exposed not only to southeasterly winds, but also to the full force of winter swells from the Gulf of Alaska that can be up to 20 feet high.
Unlike giant kelp, which has a thin, branching stipe (or stalk), bull kelp has a single long stipe that grows to 60 feet long and tapers like bull whip. At the upper end is a hollow float the size and shape of a small bowling ball. Leaf-like blades grow out of the top of the float like a “mohawk” haircut.
Bull kelp plants typically live only 12 to 18 months. By the end of their first year, the oldest plants are often heavily laden with hitchhiking red and green algae. These hitchhikers add drag and make these bull kelp more likely to be broken off by winter storm waves. Younger bull kelp plants simply shed their blades under storm conditions, which reduces the drag of the waves and reduces the chance that the entire plant will be yanked up off the seafloor.
In January and February, the seafloor underneath the kelp may be relatively barren. The deeper “surge channels” between kelp beds may be filled with sand that has been stripped from nearby beaches by winter storm waves, then deposited offshore.
By January, the leafy red algae that grow in abundance underneath the kelp canopy during summer have pretty much died back, been ripped out by storm surf, or been buried by shifting sand. Murky water and wave scour usually prevent new algae from growing up in sand channels during winter. However, on exposed rocky reefs, the ultra-hardy coralline red algae put on their year’s growth during the winter months, when the kelp canopy is thin and tattered, resulting in more light reaching the sea floor.
By the end of February, the kelp canopy is at its thinnest. Shafts of sunlight illuminate parts of the seafloor that do not get direct light at any other time of year (because they are shaded by the kelp canopy). In response to this sunlight (along with increasing day lengths and the nutrients from early upwelling events) some leafy red algae begin their annual spring growth spurt. These algae also benefit from the fact that relatively few grazing and encrusting animals are present.
In wave-protected areas such at Hopkins Marine Lab, microscopic young red algae on the seafloor may begin to sprout from spores in February. Many of these are annual species whose parents were buried by sand or torn out by storm waves during the previous winter.
In more exposed locations, such as Lighthouse Point, near Santa Cruz, sand scour keeps such "understory algae" from growing back until wave conditions settle down later in spring (more on this in the next chapter).
A school of blue rockfish swim around a kelp stipe. (Source: Chad King, NOAA/SIMON)
Just as some deep-sea rockfish release their young in January and February, so do several species of kelp-bed rockfish, including blue rockfish and black rockfish.
Blue rockfish (Sebastes mystinis) are one of the most common rockfish of Central Coast kelp beds, and typically give birth to live young in mid January. Blue rockfish mate in October, but the female blue rockfish stores the male's sperm inside her body until December. At that point the hundreds of thousands of eggs are fertilized and begin to develop.
The blue-rockfish larvae that are released as live young in January will drift and swim near the surface of the open ocean for the next four to five months. During this time, they will eat the drifting eggs and larvae of other animals. One of their main food items are young copepods, which hatch during several waves as the spring progresses.
By April or May, the blue rockfish larvae will have developed into juveniles (which look more or less like small adults). At this point they will return to the kelp beds, sometimes gathering in large schools.
Not all rockfish release young in winter. In addition to the many "winter-spawning rockfish," a second group of rockfish follows a later schedule, giving birth in late spring. The "spring spawners in the kelp beds include kelp rockfish, gopher rockfish, and black-and-yellow rockfish, all of which mate in late January or February. Gopher and black-and-yellow rockfish will release their young between March and May. Kelp rockfish wait even longer, and release their young in May or June.
If you compare the winter-spawning and spring-spawning rockfish, it's interesting to note that the transition months are similar, even if the life stages during those months are different:
- Oct-Nov: Mating
- Jan-Feb: Releasing larvae
- Apr-May: Young return to kelp beds
- Jan-Feb: Mating
- Apr-May: Releasing larvae
- Jul-Aug: Young return to kelp beds