Kelp forests are one of the planet's three most productive subtidal benthic habitats (grass beds and coral reefs are the other two)

Despite obvious differences, all three communities share several important ecological features:

High levels of benthic productivity

Structural complexity (generated by the primary producers)

Arising from these first two features: all support high levels of biological diversity

Diverse and productive intertidal habitats include rocky coastlines, estuaries/tideflats, and salt marshes.

Kelp forests, rocky intertidal regions, estuaries/tideflats, and salt marshes can all be found in temperate regions characterized by seasonal weather patterns, colder waters, and higher nutrient levels.

90% of marine animals are benthic... given this relationship between diversity and this association with the bottom, a focus on temperate marine coastal communities is warranted.

These nearshore communities are dominated by a few species of fast growing brown seaweed [though found worldwide, they are dominant ecological features only in colder (<20°C) waters].

Primary producers

Kelp

Because kelps are attached to the bottom, yet require sunlight, kelp forests occur only in shallow (5 - 20 m) regions

They are common in zones of upwelling where nutrients are not limiting, and high growth (up to 60 cm/day) is possible for species such as Macrocystis under ideal conditions. They may be up to 45 m in length!

Other important species of kelp include: Nereocystis along our coast, and the shorter Laminaria along the northeast coast of the United States.

Most kelps have complex life cycles that include spores and vegetative reproduction... thus, there is potential for dispersal by a variety of methods.

The presence of kelp generates zones of light availability

Many other species of seaweed (often adapted to low light levels) live beneath the kelp canopy

Food webs in kelp communities are structured by both "top down" and "bottom up" factors

Primary consumers

Together, these algae provide food for many grazing invertebrates (mollusks, arthropods, and echinoderms... also, previously, the Stellar's sea cow along the north Pacific rim.

Urchins are particularly important, because their scouring of the benthos can eliminate recently settled organisms.

Population booms of urchins can eliminate kelp forests, creating urchin barrens

Particles of decomposing kelp are also important for suspension feeders, such as mussels.

Secondary consumers

Carnivorous species such as sea stars, snails, lobsters, fish, and the sea otter prey on various invertebrates.

Otters can be a "keystone" species, and population fluctuations resulting from hunting and conservation efforts have obvious effects on kelp forest diversity.

Kelp forests are also influences by physical disturbance: big storms and el Nino events both diminish local kelp density, but may also promote dispersal

Together, predation, grazing pressure, disturbance, and competition for light all influence patterns of kelp forest community structure and diversity.

Several temperate tideland habitats are of interest to marine biologists, including: the rocky intertidal, estuaries, and Spartina salt marshes.

While kelp forests are iconic, Rocky intertidal regions are perhaps the best studied of the temperate coastal habitats

Intertidal habitats offer opportunities to examine physical and biological interactions

Intertidal habitats are characterized by periodic (predictable) exposure to air during low tide.

Marine animals within these habitats must cope with desiccation, heat stress, and exposure to terrestrial predators

As mentioned in past lectures, strategies include: "Clamming up", evaporative cooling (increases the risk of desiccation) and moving to cracks or tide pools

Strategies for coping with wave stress/shock (abrasion, pressure changes, drag) include flexibility, low profiles, hard shells, and strong muscles or hold fasts for attachment

Because of the constant and predictable fluctuation in exposure to water along a vertical gradient, zonation is common in all tideland habitats

Zonation is often organized by:

Physical limitations/tolerances at upper ranges of distribution

Larval preferences (cracks and crustose coraline red algae often induce settlement)

Competition for space: overgrowing and undercutting

Predation: Immersion times often limit the effectiveness of predators

 

Upper Intertidal

Organisms face the most extreme degrees of exposure to dessication and terrestrial predators.

Algae can survive, even in splash zones... but it is generally sparse

Herbivores such as limpits and gastropod snails may graze in these regions. Most have adaptations to prevent dessication... some small barnacles (filter feeders) may be found in the lower parts of this zone.

Middle Intertidal

Dessication becomes less of an issue, while exposure to wave energy becomes more important.  Biotic interactions (competition and predation) become structuring agents in the community.

Filter feeders are common (anemones, mussels, barnacles) and competition for space can be limiting

Tidepools may permit continuous submersion, but salinity and temperatures may change dramatically during low tides.

Lower Intertidal

This region is often dominated by algae. Most animals are mobile and simply move with the tide to remain submerged.

Some important lessons from intertidal studies:

Keystone predation

Complex food webs are well studied in intertidal regions

Indirect interactions within intertidal food webs can influence distribution and abundance

Cthamalus have an inducible morphological defense against predation by Acanthina

 

Estuaries and tide flats

These large expanses of relatively loose sediment are characterized by extensive flats and a network of drainage channels.

Because of their flat topography, estuaries are relatively ephemeral habitats (geologically), strongly influenced by relatively small changes in sea level.

In the short-term, they represent extremely rich, productive habitats: combining high levels of nutrient input with shallow, relatively protected marine habitats.

A gradient of salinity occurs in most estuaries: this gradient shifts with the tides.

Some species (e.g. crustaceans) have adapted to low salinities (10-15 o/oo) while others (e.g., many echinoderms) have not.

A critical salinity range of 3-8 o/oo limits exchange between fresh and marine spp. Salty enough to inhibit purely freshwater spp, but too dilute for marine adapted spp.

With time to adjust (acclimate), some spp (e.g. salmon) can make the transition from salt to fresh or vice versa.

Lots of work on physiology to understand how these tolerances change.

Large estuaries can be important nursery area, retaining larvae while they develop. Some species show larval adaptations to remain within estuaries (e.g. staying close to the bottom during outgoing tides)

Many estuary residents are adapted to life on soft bottoms rather than hard substrate

Estuary habitats are extremely important coastal wet lands

They are threatened by development, pollution, and agricultural practices that divert water flow.

Spartina/salt marshes

Spartina grasses are salt tolerant species that bind sediment with their rhizomes (like roots).

Rhizomes allow uptake of nutrients and vegetative reproduction.

The presence of grasses builds substrate... and where they have been introduced, their spread threatens native spp.

Spartina salt marshes show distinct patterns of zonation that reflect levels of competition and physiological tolerances