KELP FORESTS 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 1 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. 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. 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, 1 June 1834, Tierra del Fuego, Chile Laminaria Pterygophora Kelps worldwide Ecklonia Nereocystis 2 Kelp (Brown Algae) Brown Algae (Phaeophyta) • 1000 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) 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 3 Giant kelp (Macrocystis pyrifera) 1. In northern Hemisphere a) Occur on rocky bottoms (2 m to 30 m) b) Competitive dominant alga c) Northern limit set by hydrodynamic forces d) Southern limit set by poor substrate & temperature/nutrients conditions Kelp forests - Where do they occur? 4 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. Worldwide Kelp (Laminariales) Distribution They grow in cold nutrient rich waters From: Steneck et al. 2001 5 Distribution of Macrocystis and geographic features From: The biology and ecology of giant kelp forests. David R. Schiel & Michael S. Foster. 3. MORPHOLOGY Apical Meristem 6 3. MORPHOLOGY 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. 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 From: The biology and ecology of giant kelp forests. David R. Schiel & Michael S. Foster. Canopy Blade Sporophylls Stipe Sporophyll Sorus Holdfast 7 Two sources of productivity in a kelp forest 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 Plankton influx - phytoplankton, holoplankton, meroplankton - great abundance and diversity of planktivores 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 8 Comparisons between terrestrial forests and giant kelp forests FOREST TYPE ANNUAL NET PRODUCER LITTER PRODUCTION BIOMASS MASS (dry kg / m2 / yr) (dry kg / m2) (dry kg / m2) Tropical rain forest 2.2 45 0.2 Tropical seasonal forest 1.6 35 0.5 Temperate evergreen 1.3 35 3.0 forest Temperate deciduous 1.2 30 2.0 forest Boreal forest 0.8 20 4.0 Giant kelp forest 2.2 0.35 0.015 4. PRODUCTIVITY -continued 4. Only about 5-10 % of the primary production is consumed by grazers in either terrestrial or kelp forests. 5. In terrestrial forests most of the biomass accumulates 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 9 4. PRODUCTIVITY - continued 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. Percentage of Kelp-Derived Carbon in Kelp Forest Consumers Suspension Feeders % kelp carbon Mussel (Mytius edulis) 25 - 40 Soft coral (Alcyonaria. sp.) 40 - 70 Barnacle (Balanus nubilus) 75 – 85 Sea anemone (Metridium senile) 15 - 40 Rock jingle (Pododesmus cepio) 40 - 55 Mysid (Proneomysis sp.) 45 - 60 Detritivores Amphipod (Anonyx sp.) 70 - 95 Crab (Dermaturus mandtii) 20 - 35 Predators Rock greenling (Hexagrammos lagocephalus) 40 – 65 Sea star (Leptasterias spp.) 30 - 55 Cormorant (Phalacorcorax peligicus) 35 - 70 10 5. Life history and reproduction Nereocystis Macrocystis Sorus - Specialized zoospore producing tissue 4 2 1. Blade 1 2. Stipe Sorus 3. Holdfast 4. Pnuematocyst 3 21 From: The biology and ecology of giant kelp forests. David R. Schiel & Michael S. Foster. Life history and reproduction alternation of generations between a macroscopic spore producing stage = sporophyte, and a microscopic gamete producing stage = gametophyte Adult sporophyte Juvenile sporophyte growth Macroscopic recruitment growth Gametophytes release m syngamy f Embryonic Microscopic Zoospores sporophyte settlement 22 11 5. LIFE HISTORY AND REPRODUCTION – cont. 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 particularly important when you think about the habitat 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. 6. ABIOTIC FACTORS THAT INFLUENCE KELP DISTRIBUTION & GROWTH . • 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. 12 50 central California 40 N = 5879 30 20 10 0 50 40 southern California g / L) N = 9119 Nutrient-limited m 30 20 10 0 Nitrate ( Nitrate 50 40 Baja California 30 N = 4137 20 10 0 5 7 9 11 13 15 17 19 21 23 25 Temperature (°C) 6. ABIOTIC FACTORS THAT INFLUENCE KELP DISTRIBUTION & GROWTH . • Temperature – generally considered a cool water species – 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 13 Growth as a function of temperature and nitrate concentration From: The biology and ecology of giant kelp forests. David R. Schiel & Michael S. Foster. Figure 2 Kelpbeds in Southern California 100% 90% 80% 70% 60% 50% 40% 30% Fraction Fraction of Patches Occupied (%) 20% 10% 0% 1970 1975 1980 1985 1990 1995 2000 2015 Year 14 6. ABIOTIC FACTORS THAT INFLUENCE KELP DISTRIBUTION & GROWTH - continued 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) From: The biology and ecology of giant kelp forests. David R. Schiel & Michael S. Foster. 15 Growth as a function of irradiance and nutrient limitation Nutrients replete Nutrients limiting From: The biology and ecology of giant kelp forests. David R. Schiel & Michael S. Foster. 7. 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.