Ch 21: Subtidal Hard Substrata Ecosystems

Coastal Subtidal

the region extending from the intertidal zone to the edge of the continental sehlf at~ 200 m

Infralittoral Zone

the shallowest subtidal zone extending to ~5m depth and dominated by macroalgae

Circalittoral Zone

the deeper of the subtidal zones that is dominated by invertebrate sessile epifauna and is characterised by:

• high biodiversity

• two-dimensionality (biota grows on substratum)

• lack of protection

• dominance of clonal organisms

Major Sources of Disturbance for Benthic Communities

1. temperature and associated heat stress

2. mechanical damage

3. hydrodynamics (Direct and indirect)

Key Biotic Variables in Benthic Communities

• Primary Consumers

• Competition

• Recruitment

• Predation & trophic cascades

Where are Kelp Forests Dominant?

dominate rocky substrates in cool, nutrient rich temperate waters. Typically subpolar lattitudes.

Lattitudes of Kelp Forests

medium and high latitudes at 20-40 m depth

Lifespan of Kelp Forests

longevity of up to 25 years, but some annual

Function of Macrophytes in Kelp Forests

• Provide protective role for coastlines, reducing waver energy and thus coastal erosion

• Enhance benthic recruitment by trapping sediments

• reduce light penitration

• feeding and nursery habitat for other species

Canopy Forests

formed by largest kelp that produce floating canopies which dominate the west coasts of North and South America

Stipitated Forests

Kelp fronds grow above the seafloor aided by rigid stem-like stipes that support the fronds. Maximum length 10m, average 5.

Prostrate Kelp / Kelp Beds

smaller kelps, whose fronds blanked the seafloor. Refer to smaller habitats than those of forests

Overgrazing

where herbivores graze kelp excessivley

Kelp Barrens

biological deserts formed in reginos of normally high kelp abundance caused by overgrazing by sea urhcins

Sea Urchins’ Interactions with Kelp Forests

• hide from predators between cracks in rocks where kelp occur; kelp consumed by urchins

• became abundant and to feed directly on kelp blades, forming compact patches as a predator defense →urchin barrens

Theories on Urchin Proliferation

1. Some factor “represses” their predators

2. environmental factors improve urchin population dynamics

3. environmental conditions favor intensive recruitment, eventually reducing kelp

Main Regions of Kelp Forests

• leaf (holdfasts) surfaces

• water between algal blades

• substratum beneath the kelp

Global Distribution of Coral Reefs

occupy tropical waters with water temperatures > 18 degrees

Reef Crest/ Reef Edge

the outer portion of the reef with the stongest wave action

Reef Upper Slop

reef zone that occurs at 10-15m characterized by greater diversity and larger forms

Drop Off Region

a zone of coral reefs at 20-20m that hosts gorgonians and pelagic fish

Coral Rubble

coral fragments formed by wave action

Branching Corals

a reef building coral that branch and several secondary branchces, sometimes brush like

Columnar Corals

a reef building coral that has a single column without branches

Global or Massive Coral

a reef building coral that are globular structures with convulsions sometimes like human brains

Encrusting Corals

a reef building coral that form thin layer over bottom of ocean

Tabular or Plate Corals

a reef building coral that form flat, fan-shaped horizontal structure

Foliose Corals

a reef building coral that resemble lettuce leaves

Solitary Mushroom Corals

a reef building coral that resembles bars of soap

Sciaphilous

referring to the shade tolerant organisms such as some corals (lower slope)

Fringing Reefs

reefs over which waves break, running parallel and adjacent to the shore, where reef flats or small lagoons separate the reef from the coast

Barrier Reefs

compact structures parallel to the coastline, located at a specific distance from the mainland that result in the formation of a large lagoon between the reef and the mainland

Atolls

isolated circular reef structures surrounded by deep water

Platforms

flattened structures that rise above the seafloor at shallow depths

Darwin’s Subsidence Theory

as plates move, volcanic cones form on the seafloor, sometimes forming islands that subside over time → forming coral atolls

Glacial Control Hypothesis

changes in sea level, caused by alteration between glacial and interglacial periods form coral atolls

Karst Theory

integrates concepts of subsidence and sea level variation to explain coral atoll formation

Mesenteric Filaments

folds of the gastrovascular cavity at the base of the polyp of corals, which they can evert as weapons of defense or prey capture

Ectoderm

outer tissue of corals that comes into contact with the external environment and helps to protect them

Calcification

the mineralization of calcium carbonate crystals on cell walls or within cells

Methods of Coral Reproduction

• Asexually

• Sexually

Asexual Reproduction in Corals

• fission (intra-tentacular)

• budding (extra tentaclular)

Sexual Reproduction in Corals

• broadcast spawning released through mouth

• fertilized eggs become meroplanktonic larvae called planulae

  • if hermaphroditic are able to produce both male or female gametes

  • if gonochoric only able to release eggs or sperm

Zooxanthellae

symbiotic algae that occur within the tissues of hard corals → give corals their color

Coral Response to too little light or too much light

Environmental Stress → zooxanthellae expelled → coral bleaches → coral dies

Coral Feeding

• polyps take up organic nutrients that are released by zooxanthellae

• prey at night and nematocysts to capture plankton

• also mixotrophic → part of diet from predation, other from symbiotic algae

Nematocytes

stinging cells of coral

mixotrophy

part of diet from predation/organic particles and part from symbionic algae

Factors Limiting Coral Reef Growth

• light intensity and wavelenght

• temperature tolarances of 18-32 C

• salinity

• sedimentation

• hydrodynamics

Coral Reef Diversity is ____ than Coral Diversity

much greater

In Coral Reefs Scarce Nutrients ______

limit growth of phytoplanktonic primary producers

How is High Biomass and Productivity of Reefs

• continuous influx of nutrients with currents

• efficient recycling of nutrients within polyps

• rapid recycling of nutrients and bacterial N fixation in the external environment

Main Strategies Coral Reefs Employ for Competition of Living Space

• rapid growth

• aggression towards species occupying adjacent space

• release of toxic substances

Function of Mangroves in Association with Coral

• prevnets errosion

• nursery

• production of nutrients

Function of Seagrass in Association with Coral

• sediment stabilization

• nursery

• production of nutrients

Rhodolith Beds

slow growing red algae that form complex beds between lower intertidal and lower photic zone and is a key habitat. Threatened by climate change, harvesting, trawling, dredging, excess nutrients

Simple Echo Sounder Surveys

echo sounders, including the relativley inexpensive depth sounders on many boats, bounce high or low frequency sound waves off the seafloor to provide largely one-dimensional representations of seabed topography but little information on substrate or biota

→ used to sample Coralligenous Habitats

Advaced Acoutstic Methods

sidescan sonar, uses sound rather than light but can produce a reasonably accurate topographic seafloor map. By emmiting sound pulses towards the seafloor at an oblique angle, sound reflects back in different ways depending on the nature of the substrate. Multibeam takes this approach a step further by emmiting sounds at multiple wavelenghts, therefore producing considerably more information about seafloor composition

→ used to sample Coralligenous Habitats

Conventional Aerial Photography

on clear days with favorable sea conditions, aerial photographs provide good and rapid mapping of shallow benthic biocenosis. Under these conditions, researchers can piece together aerial photographs to produce precise maps that support effective monitoring of temporal changes in shallow biocensis, even if photo-interpretation limits fine-scale resolution of some features

→ used to sample Coralligenous Habitats

Airborne Remote Sensing, ARS

in shallow, clear waters remote sensors and/or analog digital cameras carried on airplanes can produce color images with spatial resolution of a few meters

→ used to sample Coralligenous Habitats

Geographic Information System, GIS

the expansion of human pressures on natural systems requires advanced spatial tools to aid conservation efforts. Biological and mathematical disciplines alone cannot assemble and compare spatial changes over time. The development of this has revolutionized conservation effors because it allows researchers to integrate and map the types of data decribed above. Integrates theoretical approached from geogrpahy and ecology into a powerful spatial database with statistical functions

→ used to sample Coralligenous Habitats

Marine Caves

a cavity with burrows, branches, and large chambers, totally or partially flooded

Environmental Conditions in Marine Caves (HINT: resemble deep sea)

• absence of light

• limited food resources

• reduced hydrodynamics

• stable temperature over time

Effect of Reduced Hydrodynamics on Cave Sponges

• reduced size

• increased diameter of exhalent channels to reduce friction

• cylindrical shape with a single exhalent apical chimny-like opening, used to remove wastewater

Types of Biotic Zones in Marine Caves (in descending order)

• shady phytal

• cave entrance

• cave anterior

• cave central (rich biodiversity)

• posterior (total darkness)

• empty quarter (absence of fauna)

another big table on slide 50 on Subtital Hard Substrata ecosystems