Ecosystems of California: Kelp Forests

Ecosystems of California: Kelp Forests



I'm Erica Zabaleta and this is ecosystems of California the three-dimensional world of kelp forests is one that most people only view from the top the mirror of terrestrial forests was most people only view from the bottom in both cases there's a tremendous amount of vertical structural diversity presence with canopy sub canopy and understory species epiphytes living at all different levels of that structure and consumers specializing in the parts that occur at different points along that vertical spectrum kelp forests globally are found in areas with relatively cool nutrient-rich waters at least part of the time and they're especially prevalent in areas of strong upwelling like here on the California coast they require shallow rocky reefs and they can occur anywhere from very shallow waters all the way down to 40 meters in depth there are five canopy forming kelp species in kelp forests of North America four of them occur in California is a giant kelp bull kelp and its southern species and the feather boa kelp and of those four too are the main canopy producing species in most of California's kelp forests the bull kelp and the giant kelp kelp forests are incredibly productive ecosystems and that productivity is fueled by the kelp itself so anchored to the bottom or the benthos by a holdfast CalPERS spared from having to invest a lot into structural tissue to support their height because of the water holding them up so they can instead invest a lot into the growth of their blades these large surface area fin photosynthesizing surfaces that are up near the sunlight and produce lots and lots of energy that they can then translocate to depths where the sunlight may barely reach because they don't have to invest a lot in structural tissues kelp can grow on the order of a meter a day during the most productive times of year so in that way kelp forests subsidize not only a lot of consumers and productivity within kelp forests themselves but they also subsidize other more heterotrophic ecosystems including beaches like the one that I'm sitting on where kelp that washes up on the beach undergirds a community of consumers and the subsidization of fishery species that are favored offshore and that are produced in the kelp forests below the canopy other species of kelp like sea palms and laminaria form a sub canopy anywhere from about one to three meters above the bottom and then finally there are species of prostrate kelp that inhabit the benthos the very bottom and provide habitat for fish and invertebrates now the phenology of kelp the timing of its biomass and events over the course of the year is shaped by upwelling nutrient availability wave action temperature and day length among other things in California a typical life cycle for the kelp forest is one where adult kelp individuals are ripped out by winter storms and so its biomass declines and then in the summer as those storms subside day length is long temperatures are warm a lot of production can occur with the maximum biomass and productivity happening in late summer and early fall kelp forest ecosystems have a pretty interesting food web structure because they have two bases on the one hand the upwelling of nutrients and so on supports a lot of production by the kelp itself and so one base of primary production are the kelps and they support a variety of consumers including grazers on the kelp detritivores like a baloneys and certain kinds of sea stars and then fishes that are eating those animals but there's another entry point for primary production to the system because the other really important space inhabiting organisms and kelp forests aren't plants at all they're filter feeding invertebrates things like urchins that actually use phytoplankton out of the water column for their base of primary production so phytoplankton support a different pathway of production in the kelp forests whereby phytoplankton are consumed both by penc tuberous fishes like rock fishes and buy all of those bottom-dwelling filter feeding invertebrates and then those in turn move up the food web into carnivorous fishes and sea stars and finally apex predators which include things like the sunflower star sea otters and the Moray Eel as well as lots of non-resident predators that play a role such as sharks and harbor seals sea otters were hunted nearly to extinction earlier in California's history and their decline heavily affected kelp forest ecosystems sea otters feed heavily on invertebrates like sea urchins that are grazers on the kelp so without the sea otters those populations the sea urchins and other invertebrates really exploded with so many grazers the kelp individuals got eaten down or over grazed and what was left in the place of the kelp forests were low productivity relatively low diversity and structurally simple urgent Barrens and other benthic ecosystems so with the recovery of otters in recent decades kelp forests have come back and are much more widespread in California than they were in that period of otter decline and all of that demonstrates what an important role the otters play as a keystone species a species that impacts its ecosystem dynamics really out of proportion to its numbers in biomass you

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