Announcements

• Midterm exam (1 hour) next week, here in ILC. Bring your field trip data and calculator, too (for after exam) Sign up next week for date for presentations

• Extra Credit Opportunities (12 points each) ASDB (5 volunteers) - contact Erin Keller• Catalina Boy’s School (1 volunteer, next week, male,

30 min drive with Lee, name and ssn needed - contact Doug or Lee)

• 2 people for October 28th, Friday, 12-2:30, Koffler 511

Marine Community Ecology

• How do marine animals get to the reef?(reproduction and dispersal)

• How and where do they land on the reef?

• What determines who wins in competition for space on rocks?

• What can rocky intertidal community tell us about species diversity in general? (intermediate disturbance hypothesis)

Marine Invertebrates - How do they reproduce and disperse?

•Eggs and sperm•Internal or external fertilization•Planktonic larvae*•Metamorphosis on the reef into adult

*Definition: larvae = a pre-adult form, often free-floating in marine invertebrates

Tadpole larvae of adulttunicate (Botryllus) above

Life cycle

http://life.bio.sunysb.edu/marinebio/shallowsubtidal.htmlR.K. Grosberg

Actinula larvaeof a hydroid

Phylum CnidariaClass HydroideaTubularia

http://raven.zoology.washington.edu/embryos/

http://www.mbl.edu/marine_org/marine_org.php?func=reveal&myID=BX10002

Veliger larvae of a snail

Phylum MolluscaClass GastropodaCalliostoma

http://raven.zoology.washington.edu/embryos/

http://www.marlin.ac.uk/species/Calliostomazizyphinum.htm

Setigerlarvae of a polychaeteworm(note gut)

Phylum AnnelidaClass PolychaetaSerpula

http://raven.zoology.washington.edu/embryos/

http://www.marlin.ac.uk/baski/image_viewer.asp?images=Server&topic=Species

http://www.marlin.ac.uk/baski/image_viewer.asp?images=Server&topic=Species

Setiger larvaeof a polychaeteWorm

Phylum AnnelidaClass PolychaetaSabellaria

http://raven.zoology.washington.edu/embryos/

http://www.mba.ac.uk/PMF/PMF_Sp_Sabalv.htm

Tailbud embryoof a tunicate

Phylum ChordataCorella

http://raven.zoology.washington.edu/embryos/

http://life.bio.sunysb.edu/marinebio/shallowsubtidal.html

Pilidium larvae of a ribbon worm

Phylum Nemertea, Micrura

http://raven.zoology.washington.edu/embryos/

http://www.nwmarinelife.com/htmlswimmers/m_verrilli.html

Veliger larvaeof a scallop

Phylum MolluscaClass BivalviaChlamys

http://raven.zoology.washington.edu/embryos/

http://www.seaotter.com/marine/research/chlamys/rubida/html/pacscallop.jpg.html

Pluteuslarvaeof a brittlestar

PhylumEchinodermataClass StelleroideaSubclass OphiuroideaOphiopholis

http://raven.zoology.washington.edu/embryos/ (above)

http://www.afsc.noaa.gov/kodiak/photo/misophiur.htm (right)

Actinotroch larvaeof a phoronid worm

Phylum PhoronidaPhoronis“horseshoe worms”

http://raven.zoology.washington.edu/embryos/ http://www.ucmp.berkeley.edu/brachiopoda/phoronida.html

Larvae

Summary of invertebrate reproduction and larvae

Most marine invertebrates have planktonic larvae

They feed and drift passively in the water untilthey settle out on the reef and metamorphoseinto the adult form.

Larvae use chemical and physical cues to tell themwhere to settle and metamorphose (key decision!)

The adults produce gametes, that develop into larvae,that are released into the water.

Some larvae travel 100s of miles, some a few feet.

What happens after the larvae find a good spot?

Sessile marine organisms compete fiercely for space

Definitions:Sessile = attached permanently or semi permanently

(eg, sponge, tunicate, bryozoan, coral, algae)Clone = a group of genetically identical individuals living in a

colonyReef = marine habitat of hard substrate (rock, coral, worm…)Intertidal = area covered and uncovered by the tides each daySubtidal = area below the intertidal

Competition for space on rocks in the intertidal

Space is ultimate limiting resource

Soup of larvae and food landing on the reef always

Sessile, clonal species fight for space on rocks

Two general ways to compete:

Be a good fighter (chemical warfare, overgrowth, fusion - beat ‘em or join ‘em)

Have abundant and frequent settlement of larvae(swamp out competitors, be the first one there)

Botryllus schlosseri(tunicate)

Fusion occursbetween close relatives

Instead of fighting withyour relatives, you fusewith them.

Benefits: larger coloniescompete better, reproduceearlier.

Costs:Reduces offspring of yourgenotype, but genespassed on in relatives.

R. Grosberg, UC Davis

Tadpole larvae of adulttunicate (Botryllus) above

Life cycle

http://life.bio.sunysb.edu/marinebio/shallowsubtidal.htmlR.K. Grosberg

Three colonies of tunicates - overgrowth in direction of arrows.Two are fused on left, one colony on right. What do you predictabout degree of relatedness between the three colonies?

http://life.bio.sunysb.edu/marinebio/shallowsubtidal.html

Two colonies on the left are probably closely related genetically,And both more distantly related to the colony on right.

http://life.bio.sunysb.edu/marinebio/shallowsubtidal.html

http://life.bio.sunysb.edu/marinebio/shallowsubtidal.htmlWhat is it? How many clones?

http://life.bio.sunysb.edu/marinebio/shallowsubtidal.html

Fusion of multiple colonies (clones) of bryozoans.Those more closely related are more fused.

http://life.bio.sunysb.edu/marinebio/shallowsubtidal.html

Another bryozoan species: Symmetry suggests one clone, but it is actually two clones! Black dots are original settlers.

Algae also compete for space on the reef

Macroalgae (brown, green and red algae)

•Settle out from spores in the water•Adults require light for photosynthesis•Incorporate toxins and calcium carbonate to deter predators (snails, fish, etc)

Division: green algae (Chlorophyta)Require most light Example: Sea lettuce (Ulva)

Division: Red algae Rhodophyta)Can grow with least lightExample: Encrusting coralline algae

Division: brown algae (Phaeophyta)Need moderate lightExample: Zoned-fan algae (Padina)

What determines species diversity?

LOTS of theories… •Time (older communities more diverse)•Competition (agreeable climate and niche partitioning leads to many species)•Stability (unchanging habitat allows many species to exist)•Intermediate disturbance (most specieswhere there is intermediate disturbance)*

* We will focus on this one today.

Intermediate Disturbance Hypothesis: Background

Connell 1972 “Diversity in tropical rain forests and coralreefs”

• Disturbance (eg, tree falls, storms) creates patchinessand new space to be colonized

•Patchwork is created across the landscape with- early and late successional species

- inferior and superior competitors

This theory is considered a non-equilibrium view of how natural communities are structured because landscape is a

patchwork of different stages of succession.

Two studies we will focus on today:

Sousa, Wayne (1979) Disturbance in marine intertidal boulderfields: the non-equilibrium maintenance of species diversity.

Lubchenco, Jane (1978) Plant species diversity in a marineintertidal community: importance of herbivore food preferenceand algal competitive ability.

Both researchers:- marine intertidal, temperate communities (California, Maine)- interested in explaining patterns of species diversity.- multiyear studies

Ultimate question: Why are there so many species?

Sousa Study (California)Boulder fields - number of Newtons to move bouldersNumber of (algae) species beneath boulders over time

Lubchenco Study (Maine)She observed two types of tidepools:

- dominated by one species of algae (seaweed)- 10 or more species in one pool

She noticed that density of snails (Littorina) varied, too

Species diversity - how to measure?

Species diversity - how to measure?

1) Count number of species (simplest)

2) Use an Index (mathematical formula)that considers relative abundance of each species as well as total number of species

Example: Shannon-Weaver Index H’

Break and activity

Contrast the likely life history characteristicsof the most abundant species on bouldersthat roll over often versus those that move seldom.

For many years, ecologists have debatedwhat is meant by disturbance. What aspects ofdisturbance did Sousa look at in his study?

Why might some snails prefer some algaeover others?

Imagine what 300 snails per meter squaredlooks like. Is this a reasonable density forsnails in this habitat? Why is this an importantquestion?