KELP FORESTS What Charles Darwin said I know few things more surprising than to see this plant growing and flourishing amidst those breakers of the western ocean, which no mass of rock, let it be ever so hard, can long resist. Charles Darwin, 1 June 1834, Tierra del Fuego, Chile Kelp Lecture 1. Descriptive ecology 2. Distribution 3. Morphology 4. Productivity 5. Life history and reproduction 6. Abiotic factors that influence kelp distribution and growth 7. Biological factors that regulate kelp populations 8. Kelp Forest communities Laminaria Pterygophora Kelps worldwide Nereocystis Ecklonia 1
Kelp (Brown Algae) Brown Algae (Phaeophyta) 1 species, almost all marine Includes Sargassum, Padina, kelps Most common in cold, temperate seas Two pigments for photosynthesis: 1) Chlorophyll a (like all plants) 2) Fucoxanthin (brown color) Giant kelp (Macrocystis pyrifera) Occur on rocky bottoms (2 m to 3 m) Competitive dominant alga Northern limit set by hydrodynamic forces Southern limit set by poor substrate & temperature/nutrients conditions Kelp: Division Phaeophyta (Brown Algae) Parts of a kelp Gas-filled pneumatocysts Rootlike holdfast to attach to substrate Long hollow stem or stipe Leaflike blades Complex life cycle Kelp Lecture 1. Descriptive ecology 2. Distribution 3. Morphology 4. Productivity 5. Life history and reproduction 6. Abiotic factors that influence kelp distribution and growth 7. Biological factors that regulate kelp populations 8. Kelp Forest communities 2
Kelp forests - Where do they occur? Worldwide Kelp (Laminariales) Distribution They grow in cold nutrient rich waters Laminaria Macrocystis and Nereocystis Macrocystis and Lessonia Ecklonia and Macrocystis From: Steneck et al. 2 Macrocystis, Ecklonia and Laminaria II. DISTRIBUTION 1. kelp forests are found in shallow rocky habitats along temperate coasts throughout the world 2. the area of the world s oceans covered by kelp forests is comparable to that covered by coral reefs. Unlike corals, however, kelp thrives in cool nutrient rich water 3. this explains why the most extensive kelp forests are found on western continental margins, which are areas where extensive upwelling occurs. 3
Giant kelp s range Santa Cruz ~145 km Apical Meristem N Asunción Pacific Ocean 3. MORPHOLOGY Canopy 1. simple plants consisting of a holdfast, stipe of variable length, vegetative blades, and reproductive blades called sporophylls that produce spores. The primary function of the holdfast is to anchor plant. Thus it differs from a root in that it is not specially adapted to absorb nutrients. Very little in the way of tissue specialization in kelps, or in algae in general. All parts of the plant serve in nutrient absorption and photosynthesis. Sporophylls Stipe Blade 2. most photosynthesis occurs in the upper portions of the plant. A plant that extends throughout the water column it has a need to transport some of food derived from photosynthesis to support growth of lower portions. It does this using specialized cells in the stipe that form a primitive conductive tissue that is unique among the kelps Sporophyll Sorus Holdfast 4
4. PRODUCTIVITY 1. among the fastest growing plants in the world in either marine or terrestrial habitats. maximum elongation rates in the giant kelp Macrocystis pyrifera are on the order of 12-18 inches per day 2. kelp forests are among the most productive communities in the world. Estimates of productivity comparable to tropical rain forests. 3. Interestingly, the biomass of the primary producers is two orders of magnitude less in the kelp forest. which really points to the high productivity of kelp relative to land plants FOREST TYPE ANNUAL NET PRODUCTION (dry kg / m 2 / yr) PRODUCER BIOMASS (dry kg / m 2 ) LITTER MASS (dry kg / m 2 ) Tropical rain forest 2.2 45.2 Tropical seasonal forest 1.6 35.5 Temperate evergreen forest Temperate deciduous forest Boreal forest 1.3 35 3. 1.2 3 2..8 4. Giant kelp forest 2.2.35.15 Two sources of productivity Macrophyte production - bathed in nutrients - second fastest growing plant on earth - constant production / loss of blades (leaves) - fed on directly by grazing snails and crustaceans - blades litter reef to create detritus food chain 4. PRODUCTIVITY 4. Only about 5-1 % of the primary production is consumed by grazers in either terrestrial or kelp forests. 5. In terrestrial forests most of the biomass accumates on the ground and persists as litter on the forest floor. 6. There is an order of magnitude less litter on the floor of a kelp forest compared to terrestrial forests Plankton influx - phytoplankton, holoplankton, meroplankton - great abundance and diversity of planktivores 5
4. PRODUCTIVITY 7. Another reason for the small accumulation of kelp litter is that kelps continually sluff organic material which ultimately enters the nearshore food web. 8. As kelp senesces it releases particulate and dissolved organic matter which provides a significant source of carbon for secondary consumers. 9. Interesting study that used stable carbon isotope analyses in the Aleutian Islands to confirm the important trophic role of kelp derived carbon in nearshore marine communities. Kelp forests vs terrestrial forests Percentage of Kelp-Derived Carbon in Kelp Forest Consumers Suspension Feeders % kelp carbon Mussel (Mytius edulis) 25-4 Soft coral (Alcyonaria. sp.) 4-7 Barnacle (Balanus nubilus) 75 85 Sea anemone (Metridium senile) 15-4 Rock jingle (Pododesmus cepio) 4-55 Mysid (Proneomysis sp.) 45-6 Detritivores Amphipod (Anonyx sp.) 7-95 Crab (Dermaturus mandtii) - 35 Predators Similarities and differences to terrestrial forests Both forest types: Recruitment and growth depends upon canopy breaks for available light Structure similar - different canopy levels, varied understory Form foundation for large diversity of animals and plants Both are primary producers, get their energy from the sun Kelp forests have shorter life spans, shorter heights Kelp forests are faster growing, shorter-lived: Few kelp sp. last more than 25 years Terr. forest trees can live for thousands of years Kelp forests are more diverse in terms of number of animal phyla, less in terms of animal species? Terrestrial forests are habitat for roughly 3 phyla Kelp forests are habitat for 1 or more phyla Rock greenling (Hexagrammos lagocephalus) 4 65 Sea star (Leptasterias spp.) 3-55 Cormorant (Phalacorcorax peligicus) 35-7 6
5. LIFE HISTORY AND REPRODUCTION 1. alternation of generations between a macroscopic spore producing stage = sporophyte, and a microscopic gamete producing stage = gametophyte Juvenile sporophyte Adult sporophyte Macroscopic growth recruitment Microscopic growth Embryonic sporophyte syngamy Gametophytes m f settlement release Zoospores 7
5. LIFE HISTORY AND REPRODUCTION 2. kelps are very fecund - A given plant can produce over 1 trillion spores during its relatively short lifetime, which for some species like the giant kelp is at most a couple years. 3. fertilization occurs after spores have dispersed and settled, which is very different from marine animals. This means that spores need to settle at relatively high densities in order to insure successful fertilization. The chance of this happening declines with dispersal distance due to the rapid dilution of spores following their release from the parent plant. The ecological consequence of this life history feature is that it constrains the distances over which spores can effectively colonize. rsing at least distance X Percent dispe 1% 8% 6% 4% % Carpinteria - June Carpinteria - Jan/Feb Naples - June Naples - Jan/Feb %.1.1.1.1 1 1 1 Distance (km) 1% 8% 6% 4% % % Figure 9 atch distances less than X Percent of inter-pa Spore Dispersal 1 Percent Occurrence (cumulative) 8 6 And this leads to???? 4 1 1 1 1 Maximum Spore dispersal (log m) 8
Percent Occurrence 1 9 8 7 6 5 4 3 1 Selfing In Kelps. Time Density (#*m 2 ) High (>.15 ) Medium (.5-.15) Low (<.5) 1 3 4 5 6 7 8 9 1 Self-fertilization rates n kelpbed Percent self-fertilization in Selfing rates should increase with age of kelp bed 1 9 8 7 6 5 4 3 1.25. Age of Kelp Bed.15.1 Plant Density (# per sq meter).5. Fitness consequences Consequences of limited dispersal Self Fertilization Costs Fitness component Proportional difference between selfed (1% treatment) and outcrossed (5% treatment) individuals 1) Zygote production.61.61 Accumulated fitness of selfed individuals relative to out-crossed individual (proportion) Kelp forests come and go 2) Survival to adulthood 3) Development of reproductive structures 1.1.62.24.15 4) Fecundity.11.165 9
Generalized Life History of a Macrocystis Population Kelpbed senescence through self-fertilization? 6. ABIOTIC FACTORS THAT INFLUENCE KELP DISTRIBUTION & GROWTH Density ercent self-fertilization Pe Age of Kelp Bed 1 9 8 7 6 5 4 3 1.25..15.1.5. Plant Density (# per sq meter) Fitness consequences 1) Nutrients- plants obviously need nutrients to grow and reproduce. Concentrations of nitrogen and phosphorus vary spatially and temporally in coastal waters. In California, nutrient concentrations generally greater in the north than in the south. They typically peak in the spring when most upwelling occurs and are at a low in the fall. Nutrient concentrations can vary greatly from year to year owing to oceanographic events such as El Nino during which time they tend be in very short supply. Time 5. LIFE HISTORY AND REPRODUCTION 5 4 3 central California N = 5879 4. abiotic factors such as nutrients, temperature and light on growth and reproduction greatly affect life history stages. The production of gametes in the microscopic stage only occurs under certain conditions of light nutrients and temperature. 5. This is particually important t when you think about the habitat t that kelp plants recruit to. They start life as a microscopic cell on the bottom not at the surface. It turns out that in most cases the lower depth limit of kelp is determined by the amount of light reaching small stages on the bottom. It has been estimated that the depth that this occurs is where light is reduced to» 1% of that at the waters surface. te (μg / L) Nitrat 1 5 4 3 1 5 4 3 1 southern California N = 9119 Temperature ( C) Baja California N = 4137 5 7 9 11 13 15 17 19 21 23 25 Nutrient-limited 1
6. ABIOTIC FACTORS THAT INFLUENCE KELP DISTRIBUTION & GROWTH 2) Temperature- primarily cool water plants. The effects of temperature are difficult to assess in nature because in many temperate areas where kelp grows temperature covaries inversely with nutrient concentration. In southern California kelp growth is extremely seasonal: greatest in spring when temperatures typically are low and nutrients are high and lowest in the late summer and fall when sea water temperatures are high and nutrient concentrations are low. Such seasonal variation can disappear during prolonged periods of high temperature and low nutrients such as that that occurs during El Niños. Under these conditions growth and reproduction remains low year round and in the most severe cases results in death 6. ABIOTIC FACTORS THAT INFLUENCE KELP DISTRIBUTION & GROWTH 3. Light essential for growth and reproduction Provides energy for photosynthesis Influenced by depth, water clarity, season, latitude, vegetation shading Most severe in early life history stages and transitions (spore, gametophyte, fertilization, sporophyte) Kelpbeds in Southern California Figure 2 1% 9% Fraction of Pat tches Occupied (%) 8% 7% 6% 5% 4% 3% % 1% % 197 1975 198 1985 199 1995 Year 11
6. ABIOTIC FACTORS THAT INFLUENCE KELP DISTRIBUTION & GROWTH 4. Water Motion: The concentration of nutrients is not the only thing that affects nutrient absorption in kelp. For example, in calm conditions growth can be limited by nutrients even in relatively nutrient rich waters. This is because nutrients can become locally depleted d near the surface of plant tissues in still water. Water motion prevents this from happening by maintaining a constant flux of nutrients across the tissues of the plant. Too much water motion, however, is not good. it can dislodge plants from the bottom, then they end up on the beach or get transported offshore where they die. 1982-83 El Niño There is a tradeoff in being large. Light vs Drag While light may set the lower depth limit for kelp, water motion is believed to be important in determining the upper limit for many species. High water motion associated with storms is extremely important source of disturbance in kelp communities and can have a profound effect on the spatial and temporal dynamics of kelp populations. Severe storms such as the ones that occurred during the 1982-83 El Niño can completely destroy entire populations of kelp. Fraction of Pat tches Occupied (%) 1% 9% 8% 7% 6% 5% 4% 3% % 1% % Kelpbeds in Southern California 197 1975 198 1985 199 1995 Year Figure 2 12
6. ABIOTIC FACTORS THAT INFLUENCE KELP DISTRIBUTION & GROWTH Hard substrate- usually a solid substrate to anchor. Some controversy about the nature of rock that is best Based on artificial reef experiments Colonized by kelp then overgrown by Muricea WHY???? BIOLOGICAL FACTORS THAT REGULATE KELP POPULATIONS Dispersal Kelp populations are very dynamic and frequently undergo local extinctions and recolonizations. Dispersal is a key element to the recolonization process. Historically spore dispersal in kelps has been thought to be limited to within a few meters of the parent plant. Such limited dispersal, however, cannot account for the rapid and widespread recolonization of kelps that is frequently observed. Dispersal Pt. Conception Range of soft bottomed kelp 1. Spore dispersal in kelps may not be limited to a few meters. 2. We have measured spore dispersal over distances as large as several kilometers. Large storms Turbulent flow 3. Storms also cause massive release of spores 4. Together release and dispersal during storms leads to long distance dispersal What else?? 13
Competition 1. Competition between different vegetation layers can be important in structuring kelp populations. Most the work that has been done has focused on adults inhibiting juveniles. In general the recruitment of nearly all algae is suppressed underneath dense kelp canopies. Light reduction to 1% 2. Hormonal trickery 3. Layering - Given this high level of shading it is not surprising that there is strong competition for light among the different vegetation layers. 4. There has also been much work done on the effects of intraspecific competition. In general, kelps tend to grow larger, live longer, and produce more spores in lower density stands, though there are some exceptions to this pattern. San Clemente Artificial Reef (SCAR) Experimental Design Two types of material quarry rock boulders recycled concrete rubble Three bottom coverages low (~4%) medium (~6%) high (~8%) Stratified block design 7 replicate blocks of 6 reef designs Module size = 4 m x 4 m Duration five years ( 4) SM and B represent the natural reefs at San Mateo and Barn, which are used as reference sites. 14
Hard Substrate Performance Standard - At least 9% of the initial area of hard substrate must remain available for attachment of reef biota. Percent cover of understory algae on the artificial and natural reefs B SM Low Med High Cover) Understory algae (% 1 Rock 8 6 4 1 2 3 4 1 8 6 4 Concrete 1 2 3 4 Density of adult giant kelp on the different reef designs Percent cover of sessile invertebrates on the artificial and natural reefs 1 m -2 ) Adult density (No. 1 B SM Low Med High Performance standard 6 6 Rock 4 1 2 3 4 4 Concrete 1 2 3 4 r) Invertebrates (% cover 1 1 8 6 4 B SM Low Med High Rock 1 2 3 4 1 1 8 6 4 Concrete 1 2 3 4 15
Adult density (No. 1 m -2 ) 6 Macrocystis Rock 4 1 2 3 4 SCAR Reference Reefs Competition for light Control of grazers (predation, disease, storms, recruitment) 1. The single most effective predator on sea urchins are sea otters which once ranged from the Kuril Islands in Japan through the Aleutian Is and down the coast of North America to Baja California. Otters eat 25 % of their body weight per day and can effectively eliminate local populations of sea urchins and other shellfish. Understory alg gae (% Cover) Invertebrates (% cover) 1 Rock 8 6 4 1 2 3 4 1 Rock 1 8 6 4 1 2 3 4 2. Islands with sea otters had low densities of urchins and densely vegetated kelp beds. In contrast, islands without sea otters are basically unvegetated barren areas with have high densities of urchins and no macro algae. Thus sea otters have been given this keystone status. The paradigm is that where there are otters you get kelp beds where there is no otters you get sea urchin barren grounds. This paradigm seems to apply generally in Alaska. Grazing 1. Clearly the number one enemy of kelp are sea urchins. They are the single most important grazer in kelp communities worldwide. They can form large feeding fronts and eat everything in sight (including fiberglass transect tapes), essentially leaving behind a barren ground devoid of macro algae. Sea urchins graze on kelp 2. Urchins don t always display an active grazing behavior. They are typically sit and wait herbivores much like abalone that catch detached pieces of fkelp as they drift by. Questions: What causes their change in behavior passive sit and wait to active grazing?? How long are barrens maintained?. What controls urchins?? 16
Sea otters control urchin populations by eating them NORTH PACIFIC/ALASKA Sea otters, sea cows, sea urchins and humans Kelp forest changes History of fishing in N. Pacific Colonization 3, years ago, boats used off Japan coast for past 25, years Stellar s sea cow hunted to extinction (35 feet long, several tons) 17
History of fishing in Alaska Humans in Alaska for 9-1, years. Indigenous tribes began to hunt otters ~ 25 years ago. Otter hunting intensified with European arrival in 17s. Ecosystem changed to urchin dominated. Otters and urchins Sea urchins and kelp, but no sea otters, but very large predatory fish! NORTH ATLANTIC 18
Cod fishery intense for centuries CALIFORNIA CA kelp forests considered most diverse in world Exploited for past 12-13, yrs Shell middens from aboriginal people show decrease in animal size with hunting Fishing technology decreases cod pop. by 193s Urchins rise again Animals begin to disappear from kelp forests Otters functionally gone by early 18s Kelp forest ecosystem persisted for next 15 years Probably because other predators, like fish, compensated by increasing in numbers and eating urchins 19
White sea bass landings other predators on sea urchins in California, which include lobster and fish predators such as the sheephead wrasse CA kelp begins to change CA kelp forest so diverse, other predators keep urchins in check even with few otters Continues to persevere for another 15 years Now in trouble - not so diverse other predators on sea urchins in California, which include lobster and fish predators such as the sheephead wrasse sporadic recruitment of sea urchins disease, which has been known to greatly reduce urchin numbers over relatively wide areas. In California these outbreaks of disease are generally associated with periods of warm water. Expansion of kelp beds have been documented following massive urchin die offs. storms - which not only destroy kelp, but also can drastically reduce populations of sea urchins. Perhaps the best example of this comes from a study done at Naples Reef off Santa Barbara by Al Ebeling
Kelp conservation status Climate change (global temp. increase), human pop. growth, coastal development, oil spills, overfishing impacts, non-native sp. invasions all predicted to increase over next 25 years Kelp forest ecosystems Habitat structure - surface canopy Currently, in some areas fisheries for urchins coincide with fisheries for urchin predators a delicate balance - subcanopy - turf Kelp Forest Communities Giant kelp communities Juvenile finfish Invertebrates Understory algae Adult finfish Invertebrates Marine mammals 21
"The numbers of living creatures of all Orders whose existence intimately depends on kelp is wonderful I can only compare these great aquatic forests with the terrestrial ones in the intertropical regions." Kelp forest zonation "Yet if in any country a forest was destroyed, I do not believe nearly so many species of animals would perish as would here from the destruction of kelp." Charles Darwin (186) The Voyage of the Beagle Kelp Forest Ecosystems Primary producers ca. 9 spp. macroalgae Grazers ca. 4 spp. fish, gastropods, echinoderms, crustaceans Planktivores ca. 21 spp. fish, porifera, bivalves, bryozoans, tunicates, crustaceans Predators ca. 145 spp. fish, gastropods, echinoderms, crustaceans Detritivores ca. 15 spp. echinoderms, (single Channel Is. kelp forest, species > 2 cm) Biodiversity 22
Kelp conservation status Climate change (global temp. increase), human pop. growth, coastal development, oil spills, overfishing impacts, non-native sp. invasions all predicted to increase over next 25 years Currently, in some areas fisheries for urchins coincide with fisheries for urchin predators a delicate balance 23