Response of herbivore functional groups to multiple disturbances in Moorea, French Polynesia

Xueying (Shirley) Han, R Schmitt, S Holbrook,

A Brooks, T Adam

University of California, Santa Barbara

xhan@lifesci.ucsb.edu

7 August 2013

ESA

Response of herbivore functional groups to

multiple disturbances in Moorea, French Polynesia

BackgroundDisturbances

Ocean acidification Disease outbreaks Large stormsGlobal warming

HerbivoresHerbivorous fishes and sea urchinsControls macroalgaeCrucial to coral reef systems

Moorea, French Polynesia

2008-2009

Acanthaster planci:Crown-of-thorns starfish

(COTS) outbreak

February 2010

Cyclone Oli

Consequences

Decrease in fore reef coral cover from ~40% to ~3%Decline in corallivores and coral dwellersIncrease in herbivores

Adam et al. (in prep)

Study Site: MooreaHabitats (3): fringing, backreef, and fore reef

Sites (6): LTER1-6

Total: 18 sites

Annual fish surveys: 2006-2012

BrowsersDetritivoresExcavatorsFarmersGrazer/detritivoresScrapers

Herbivore Functional Groups

Browser—consumes standing macroalgae(e.g. Naso lituratus)

Herbivore Functional Groups

Browser—consumes standing macroalgae(e.g. Naso lituratus)

Detritivore—consumes detritus(e.g. Ctenochaetus striatus)

Herbivore Functional Groups

Browser—consumes standing macroalgae(e.g. Naso lituratus)

Detritivore—consumes detritus(e.g. Ctenochaetus striatus)

Excavator—consumes epilithic algal turf and removes large amounts of the calcium carbonate substrata(e.g. Chlorurus sordidus)

Herbivore Functional Groups

Farmer—site-attached, territorial species that maintain algal farms(e.g. Stegastes nigricans)

Herbivore Functional Groups

Farmer—site-attached, territorial species that maintain algal farms(e.g. Stegastes nigricans)

Grazer/detritivore—feeds on epilithic algal turf without scraping/excavating the substratum(e.g. Acanthurus nigrofuscus)

Herbivore Functional Groups

Farmer—site-attached, territorial species that maintain algal farms(e.g. Stegastes nigricans)

Grazer/detritivore—feeds on epilithic algal turf without scraping/excavating the substratum(e.g. Acanthurus nigrofuscus)

Scraper—consume epilithic algal turf and small portions of the reef substratum(e.g. Scarus psittacus)

Questions

1. How did functional groups respond on an island-wide scale?

2. Are there differences in the functional community assemblage among the three habitats?1. Did these habitats respond similarly

to the disturbance?

3. Are responses related to the initial biomass of a species?

Island-wide response of functional groups

Functional group

Scraper

Excavator

DetritivoreGrazer/detritivore

Browser

Farmer

Magnitude of change

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Functional groups responded differently in both direction and magnitude.

Island-wide response of functional groups

Pre-disturbance biomass (g/m2)

0 2 4 6

Post-disturbance biom

ass (g/m2 )

0

1

2

3

4

5

6

7

ScraperExcavator

Detritivore

BrowserFarmer

Grazer/detritivore

Functional group response is not related to pre-disturbance biomass.

Functional community assemblages among habitats

1. Habitats have different functional assemblages.2. Despite difference, the response among habitats was the same

—increased scrapers.

Are responses related to the initial biomass of a species?

Forereef

Species

Ctenochaetus striatus

Acanthurus nigrofuscus

Centropyge flavissima

Chlorurus sordidus

Zebrasoma scopas

Naso lituratusCtenochaetus flavicauda

Centropyge bispinosa

Acanthurus nigricans

Centropyge loricula

Stegastes fasciolatus

Acanthurus pyroferus

Scarus oviceps

Scarus psittacus

Ctenochaetus binotatus

Centropyge heraldi

Naso unicornis

Naso annulatus

Acanthurus nigricauda

Acanthurus olivaceus

Scarus forsteni

Zebrasoma veliferum

Scarus altipinnis

Cha

nge

in Bio

ma

ss

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

**

**

* *

*

*

Response is not related to a species’ pre-disturbance biomass.

BrowserDetritivoreExcavatorFarmerGrazer/detritivoreScraper

Summary1. How did functional groups respond on an island-

wide scale?

Herbivore functional groups responded differentlyDirection and magnitude of response was not related to the pre-disturbance biomass of a functional group

Summary1. How did functional groups respond on an island-

wide scale?

Herbivore functional groups responded differentlyDirection and magnitude of response was not related to the pre-disturbance biomass of a functional group

2. Are there differences in the functional community assemblage among the three habitats?1. Did these habitats respond similarly to the

disturbance?Characteristically different functional assemblages among habitatsAll habitats moved towards a community with increased scrapers

Summary1. How did functional groups respond on an island-

wide scale?

Herbivore functional groups responded differentlyDirection and magnitude of response was not related to the pre-disturbance biomass of a functional group

2. Are there differences in the functional community assemblage among the three habitats?1. Did these habitats respond similarly to the

disturbance?Characteristically different functional assemblages among habitatsAll habitats moved towards a community with increased scrapers3. Are responses related to the initial biomass of a species?Differences in post-disturbance response are not related to the initial biomass of a species

Thank you!

Questions?xhan@lifesci.ucsb.edu

@xueyinghan

Outline Background/introduction Recent dynamics in Moorea, French Polynesia Study site Herbivore functional groups Research questions

How did functional groups respond on an island-wide scale?

Are there differences in the functional community assemblage among the three habitats?

Did these habitats respond similarly to the disturbance?

Are responses related to the initial biomass of a species?