Kelp Bed / Forest Ecology

I. What are kelp beds or forests? Kelp Bed / Forest Ecology I.
What are kelp beds and forests? II.
Distribution Stands of large brown algae in the order Laminariales (i.e., kelps) that provide food and shelter for a diverse array of marine plants and animals. III.
Morphology IV.
Kelp life cycle V.
Biological characteristics of kelp forests VI.
Abiotic Influences VII.
Effects of kelp on biotic conditions VIII.
Biotic interactions IX.
Kelp harvesting Kelp Forest vs. Kelp Bed I. What are kelp beds/forests? -- terms often used interchangeably, but technically: 27 genera of kelps form kelp beds or forests •
kelp forest = large brown algae that form floating surface canopies Macrocystis •
kelp bed = large brown algae that do not form a surface canopy kelp bed kelp forest Pelagophycus Pterygophora II. Distribution •
worldwide in temperate seas (cold & nutrient rich) – larger forests in water <20˚ C •
generally shallower than 15-40 m II. Distribution North and South American west coasts: •
kelp forests are dominated by two genera of canopy-forming kelps: –
Nereocystis (bull kelp) in north –
Macrocystis (giant kelp) in north & south Macrocystis Nereocystis 1 II. Distribution •
on the North American east coast, Asian east coast, and in Europe, kelp beds are dominated by Laminaria III. Kelp Morphology •
holdfast - rootlike attachment to substrate •
stipe – long stem •
blades - “leaves” II. Distribution •
in South Africa, Australia, and New Zealand, kelp beds are dominated by Ecklonia spores IV. Kelp Life Cycle Alternation of generations, haploid and diploid: gametes •
diploid sporophytes produce haploid spores fertilization •
pneumatocysts - gas-filled floats •
haploid gametophytes (male & female) produce haploid gametes that fuse to form a diploid sporophyte V. Biological Characteristics of Kelp Forests •
High productivity -
Macrocystis can grow up to 50 cm per day & reaches 60 m long V. Biological Characteristics of Kelp Forests: Productivity Comparisons between terrestrial forests and giant kelp forests FOREST TYPE NET PRODUCTION PRODUCER MASS (dry kg / m2 / yr) (dry kg / m2) (dry kg / m2) •
High diversity LITTER MASS Tropical rain forest 2.2 45 0.2 Tropical deciduous forest 1.6 35 0.5 Temperate evergreen forest 1.3 35 3.0 Temperate deciduous forest 1.2 30 2.0 Boreal forest 0.8 20 4.0 Giant kelp forest 2.2 0.35 0.015 2 V. Biological Characteristics of Kelp Forests: Kelp as food: •
kelps are ~ 3-10x more productive than shallow-water phytoplankton & about 50x more productive than oceanic phytoplankton Percentage of Kelp-Derived Carbon in Kelp Forest Consumers (from Duggins et al. 1989, Alaskan kelp forests, Alaria & Laminaria) 13C to 12C ratios Note: more recent research indicates these estimates are too high because of problems with the original methods (Miller and Page 2012) •
but few animals directly eat the living fronds of kelps •
as kelp disintegrates, chunks, particles, and organic molecules feed suspension feeders and deposit feeders Suspension Feeders mussel (Mytilus edulis) soft coral (Alcyonaria sp). barnacle (Balanus nubilus) sea anemone (Metridium senile) rock jingle (Pododesmus cepio) mysid (Proneomysis sp.) % kelp carbon 25 - 40 40 - 70 75 - 85 15 - 40 40 - 55 45 - 60 Detritivores amphipod (Anonyx sp.) crab (Dermaturus mandtii) 70 - 95 20 - 35 Predators rock greenling (Hexagrammos lagocephalus) ) sea star (Leptasterias spp.) cormorant (Phalacorcorax peligicus) And kelp forests/beds Export their Production to other habitats: e.g.,Kelp Wrack 40 - 65 30 - 55 35 - 70 V. Biological Characteristics of Kelp Forests: Diversity High Diversity of Primary Producers – not just kelps V. Biological Characteristics of Kelp Forests: Diversity High Diversity of Consumers Causes of High Diversity •
high structural diversity (3-dimensional structure; like coral reefs and tropical rain forests) – places to hide from predators – unique foraging locations •
high productivity 3 Microhabitats & associated species in a typical California kelp forest: A. Canopy assemblage Canopy assemblage: isopods, tubeworms, bryozoans, fishes Membranipora membranacea,
filter feeding colonies; eaten by several species of nudibranch and a few fishes a common bryozoan B. Planktonic assemblage Idotea sp., a common isopod C. Holdfast assemblage D. Horizontal substrate assemblage E. Vertical wall assemblage Canopy assemblage: fishes Holdfast assemblage: sea urchins, crustaceans, worms, brittle stars, snails kelp bass giant kelpfish kelp perch señorita brittlestars in holdfast blue rockfish Horizontal substrate assemblage: urchins, sea stars, algae, and bottom fish Vertical wall assemblage: coralline algae, anemones, cup corals, sponges, mollusks in crevices blackeye goby sculpin 4 VI. Abiotic factors that influence kelp forests VI. Abiotic factors that influence kelp forests •
Light •
Temperature LIGHT •
Nutrients •
Water Motion •
Hard Substrate availability of light limits depths of kelps: •
need > 1% of surface irradiance •
can grow deeper in clearer water VI. Abiotic factors that influence kelp forests Water Motion: VI. Abiotic factors that influence kelp forests Substrate type: •
big waves rip out kelp forests •
kelps generally require a hard substrate to attach to (rocks) •
some species better able to deal with high water motion than others: •
cannot settle and grow on sand or other soft substrates - e.g., Nereocystis can handle larger waves (water motion) than Macrocystis VI. Abiotic factors that influence kelp forests Temperature & Nutrients: Effects of El Niño Temperature & Nutrients: •
correlated: high temperature  low nutrients •
nitrate thought to be key limiting nutrient El Niño conditions: low temperature high nutrients •
warm surface waters •
depress thermocline •
keep nutrients away from kelp Kelp growth declines & then kelps die high temperature low nutrients from Dayton et al. 1999 5 Variation in abiotic conditions often drives kelp abundance Seasonal variation •
example: Macrocystis in Southern California -
highest abundance & recruitment during winter/spring (cold water, high nutrients) •
Seasonal variation (predictable) •
Interannual variation (unpredictable) -
lowest abundance late summer/fall (warm water, low nutrients) Dayton et al. 1992 Interannual variation Interannual variation •
example: Macrocystis in Southern California (Dayton et al. 1992) -
highest abundance during cold water periods (La Niña) -
lowest abundance during warm water periods (El Niño) 1948 Pt. Loma Kelp Forest: 1940’s - 1970’s 1959 1965 1970 VII. Effects of kelp beds on abiotic conditions VIII. Biological factors that influence kelp forests COMPETITION GRAZING PREDATION •
kelp forests alter the local hydrodynamic regime — slow down currents — allow sediments to settle out — planktivores “filter” edible particles (e.g., plankton) 6 Competition: Trophic Interactions X •
intense competition for light - occurs among kelps & understory algae - in southern CA, Macrocystis is the dominant competitor because of fast growth •
competition for space - competition for attachment spots on hard substrate - occurs among algae and also between algae and invertebrates Alternate Stable States? Ecosystem changes kelp forests and urchin barrens X X Factors that influence sea urchin populations in southern California •
other predators on sea urchins in California - lobster - California sheephead IX. Kelp Harvesting •
kelp is a main source of algin and other emulsifiers and thickeners - foods - cosmetics - paints - pharmecueticals •
sporadic recruitment of sea urchins in California •
$40 million a year industry in California in the mid 1980’s •
urchin disease -
known to greatly reduce urchin numbers over relatively wide areas •
started in early 1900’s to make potash for gunpowder in World War I -
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 7 IX. Kelp Harvesting •
boats with cutters about six feet deep take all surface growth and the top 4 feet of the stipes •
kelp beds were leased to private groups •
in California, Kelco (until 2005) •
between 100,000 and 170,000 wet tons were harvested from California waters each year Summary Kelp forests are… •
highly productive •
highly diverse •
highly dynamic - due to strong biotic & abiotic influences •
no longer harvested in CA 8