Konstantin Tkachenko Ph.D.Department of Natural and Geographic Sciences

Samara State Educational UniversitySamara, Russia

Location of study sites in Ihavandippolu atoll

CoordinatesLatitudinal extension:

7° 06’ – 6° 54’ N

Longitudinal extension:

72°47’ – 72°59’ E

SizeArea: 330 km2

Maximal dimension from W to E

is similar to that from N to S

and equal to 21 km

N

Material and methods

SamplingDepth: 3-7 m

Phototransect method

4×40 m photransects

20 photoquadrats per transect

Each photoquadrat = 0.4 sq. m

EstimationCPCe software

50 points per photoquadrat

Percent cover of:

1. Hard coral

2. Dead hard coral

3. Soft coral

4. Coralline algae

5. Macroalgae

6. Rock, rubble, sand

Census of herbivorous fish

Three major families of

herbivorous fish were counted:

Acanthuridae

Scaridae

Siganidae

4×10 min timed swim visual

estimations

Acanthuridae Scaridae

Siganidae

Distribution of major benthic and substrate categories on

study sites

Macroalgae cover < 0.5 % in all sites

Distribution of 12 dominant genera on study sites

Site 1

20.6

12.8

Distribution of specific coral groups with different susceptibilityto bleaching (% cover)

Susceptible Tolerant ResistantTypical reef on site 1

Site 2

Distribution of specific coral groups with different susceptibilityto bleaching (% cover)

Susceptible Tolerant Resistant

1 1.9

19.5

Typical reef on site 2

Site 3

5.7

0.2

22.3

Distribution of specific coral groups with different susceptibilityto bleaching (% cover)

Susceptible Tolerant Resistant

Typical reef on site 3

Site 4

18.5

1.2

20.5

Distribution of specific coral groups with different susceptibilityto bleaching (% cover)

Susceptible Tolerant Resistant

Typical reef on site 4

Site 5

11

2.1

8.9

Distribution of specific coral groups with different susceptibilityto bleaching (% cover)

Susceptible Tolerant Resistant

Typical reef on site 5

Site 6

14.6

2.1

16.5

Distribution of specific coral groups with different susceptibilityto bleaching (% cover)

Susceptible Tolerant Resistant

Typical reef on site 6

Site 7

28.3

0.8

10.3

Distribution of specific coral groups with different susceptibilityto bleaching (% cover)

Susceptible Tolerant Resistant

Typical reef on site 7

Site 8

15.3

4.76.8

Distribution of specific coral groups with different susceptibilityto bleaching (% cover)

Susceptible Tolerant Resistant

Typical reef on site 8

Site 9

38.1

0.1

13

Distribution of specific coral groups with different susceptibilityto bleaching (% cover)

Susceptible Tolerant Resistant

Typical reef on site 9

Site 10

18.5

0.1

2.8

Distribution of specific coral groups with different susceptibilityto bleaching (% cover)

Susceptible Tolerant Resistant

Typical reef on site 10

Site 11

Herbivorous fish

Abundant herbivore fish especially acanthurids prevent local coral reefs from phase shiftto algae-dominated communities

Effect of SW and NE monsoons and related hydrodynamic patterns on Ihavandippolu atoll

N

Status of coral communities in Ihavandippolu atoll

Stable coral community withhigh coral cover and dominance of susceptiblegenera

Plot is based on quantitative estimation of study sites and visual inspection of several reefs

Balanced coral community in terms of proportional abundance of susceptible and resistant + tolerant genera

Climax coral community with dominance of resistant genera and low total coral cover

Unstable coral community with low total coral cover and dominance of susceptible genera

Collapsed coral community with single occurrence of live corals

Conclusions

1. Inner reefs protected from the ocean swell and opened to the influence of internal waves generated by SW monsoon revealed the most healthy coral communities with relatively highest coral cover and proportion of susceptible genera

2. Reefs located in the center of atoll’s lagoon exhibited climax coral communities with low coral cover and diversity and dominance of resistant genera. Susceptible genera remain degraded after the first mass coral bleaching event in 1998.

3. Northern and eastern outer reefs most subjected to the influence of NE monsoon demonstrated unstable coral communities with low coral cover and high proportion of dead corals or totally degraded reef ecosystems

4. High abundance of herbivorous fish prevent microalgae blooms on local coral reefs

5. Increase of frequency of thermal anomalies may cause further decline of coral cover in Ihavandippolu atoll and strategic shift at most reefs to the dominance of coral genera that are more resistant to changing environment

Thank you for attention