Short-term Changes to the Coral Reef Fish Community Structure Following the Regional Coral Bleaching Event of René F.

Transcription

1 Short-term Changes to the Coral Reef Fish Community Structure Following the Regional Coral Bleaching Event of 2005 By René F. Esteves Amador

2 Outline Introduction Key shapers of spatial variability Short-term fluctuations of fish assemblages at individual reef stations Time series of spatial variability patterns of oceanic and neritic reef stations

3 Introduction Factors shaping fish communities The role of disturbance Temporal variability

4 Part 1. Objectives Examine patterns of fish community structure before the 2005 coral bleaching event Evaluate the roles of distance from shore, rugosity, live coral, algae and depth as shapers of fish community structure

5 Materials and Methods Study Sites "W D esecheo!. D 20 D 10 Miam i!( Havana!( Tropic o Atlantic O cean D 30 Kingston!( Port-au-Prince!( San Juan!( M 10 Caribbean Sea M 20!. M ayaguez M "N "N Kilom eters "W G 10!. Guanica DE 20 Ponce!. CDM 10 Caja de Muerto!.

6 Sampling Design Sets of five 10 m long permanent transects were marked on areas of optimal coral growth at constant depth Belt-transects for diurnal fish surveys were conducted along 1.5 m to both sides of each 10 m long transect centerline, and within 3 m from the reef substratum Percent cover by benthic categories was assessed by the continuous intercept chain-link method

7 Data Analysis Transformation One-way ANOVAS Double standardization Bray-Curtis MDS ANOSIM SIMPER CCA

8 Results and Discussion Mean fish abundance ranged between Ind/30m² at and 84.6 Ind/30m² at,,, >,,, No significant differences of species richness between reef stations were found

9 Overall, an assemblage of 16 species represented 90.4 % of the total fish abundance

10 Results and Discussion The top four numerically dominant species Coryphopterus personatus 35% Chromis cyanea 12.5% Thalassoma bifasciatum 9.7% Stegastes partitus 6.1%

11 Transform: Log(X+1) Standardise Variables by Maximum Standardise Samples by Total Resemblance: S17 Bray Curtis similarity 2D Stress: 0.21 Reef Similarity 40 Non-metric, multidimensional scaling (MDS) plot of Bray-Curtis similarities based on the rank order abundances of reef fishes from sets of five replicate belt-transects surveyed at nine reef stations encompassing a m depth gradient of the west and south coast of Puerto Rico.

12 Oceanic vs Neritic Chromis cyanea Acanthurus coeruleus Coryphoterus lipernes Halichoeres maculipinna Mychrospathodon chrysurus Holocanthus tricolor Grama loreto Epinephelus fulva Canthigaster rostrata Stegastes leucostictus Coryphopterus personatus Scarus iserti Myripristis jacobus Chaetodon capistratus Sparisoma viride Haemulon flavolineatum Amblychirrinos pinos

13 Functional Groups Zooplanktivores Diurnal/pelagic Nocturnal/demersal Herbivores Scrapers Non-scrapers Omnivores General Carnivores

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15 Diurnal/pelagic Zooplanktivores 2D Stress: 0.21 Diurnal/Pelagic Zooplanktivores Trophic link between the open ocean and coral reef communities

16 Nocturnal/demersal Zooplanktivores 2D Stress: 0.21 Nocturnal/Demersal Zooplanktivores Both smaller and nocturnal zooplanktivorous fishes hide under reef crevices during the day and come out at night to prey on resident zooplankters which avoid currents that could remove them from their home ground (Hobson and Chess, 1978, 1986)

17 Herbivores 2D Stress: 0.21 Scaridae Vertical distribution of herbivorous fishes has been shown to be associated with active photosynthesis, which is inversely related to depth due to light attenuation (Steneck, 1988)

18 Herbivores 2D Stress: 0.21 Non Scarid Herbivovres Unlike scarids, which indiscriminately scrape the reef substrate to feed, others herbivores such as the acanthurids are morphologically specialized to selectively graze on food with higher nutritional value, even before it settles on the bottom

19 General Carnivores 2D Stress: 0.21 Haemulidae Several species commonly settle at adjacent seagrass and mangrove ecosystems before moving to the reef D Stress: 0.21 Hypoplectrus Available settlement habitats at Desecheo are limited to coral reefs and a rocky shoreline

20 Omnivores Stegastes partitus peaked at low rugosity reef stations where there was an absence of other congeners. S. partitus mortality was lower on piles of Porites porites coral rubble, where availability of small size crevices was highest (Nemeth, 1996) The larger more aggressive S. leucostictus and S. planifrons has been shown to out-compete smaller species, such as S. partitus for available shelter (Robertson, 1996)

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22 Canonical Correspondence Analysis 3-dimensional plot showing affinity between reef station fish assemblages and measured environmental variables Algae CD Rugosity Distance % Coral Depth

23 Conclusions Two main patterns of fish community structure variability emerged from the data m 1) Stations sharing the insular shelf were different from those at Desecheo 2) Stations at 10 m were different from those at 30 at both neritic and oceanic sites

24 Conclusions Higher abundances of diurnal/pelagic zooplanktivores characterized fish communities at Desecheo, whereas neritic stations presented a more conspicuous herbivorous fish assemblage dominated by parrotfishes (Scaridae)

25 Conclusions It is proposed that higher abundances of diurnal/pelagic zooplankton feeders at Desecheo were influenced by higher zooplankton availability brought by open ocean currents and higher zooplanktivore feeding efficiency enhanced by clear water

26 Conclusions Fish settlement habitats at Desecheo are limited to coral reefs and rocky shoreline, which could explain why several fish species commonly found on mangrove, and seagrass habitats as juveniles, such as scarids and haemulids are either rare or missing at Desecheo

27 Conclusion Differences of fish community structure associated with depth were driven by herbivores, which were more abundant at shallower stations, suggesting that light penetration plays an important factor regulating the distribution of algal foods supporting herbivorous reef fish assemblages

28 Conclusions Rugosity, mostly resulting from coral buildup was an important shaper of fish communities as it significantly influenced abundance of numerically dominant small nocturnal/demersal zooplanktivores.

29 Conclusions Live coral per se explained the smallest portion of the variation of fish assemblages between surveyed reefs among the environmental variables examined

30 Part 2. Objectives Examine the response of fish communities at individual reefs to the loss of live coral cover resulting from the regional bleaching event of

31 Results and Discussion As a result of the coral bleaching event reef stations,,, DER20,, CD and exhibited declines of over 50 % in total live coral cover. Largely driven by mortality of Boulder Star Coral, Orbicella annularis (complex) Benthic algae, cyanobacteria and abiotic categories. Rugosity remained stable

32 % Live Coral Cover 60 Reef Stations CD DER Monitoring trends of % live coral cover from surveyed reef stations

33 Abundance (ind/m 2 ) Richness (spp/transect) Fish Abundance and Species Richness at Monitoring Years 0

34 Conclusions Inter annual variations of fish community structure were seemingly independent of changes in benthic community

35 Conclusions The variable response of fish species expected to directly suffer or benefit from the immediate loss of coral and subsequent increase in benthic algae suggest that at present these populations are regulated by density independent processes

36 Conclusions The lack of persistent changes of fish community structure at monitored reef stations (except ) may be influenced by resiliency of these populations resulting from exposure to previous coral bleaching events

37 Conclusions Although it is possibly too early to asses the impact of the Lionfish (Pterois volitans) upon the resident fish community structure at monitored reefs, no evident changes have been noted since it s arrival in 2010

38 Part 3. Objectives Examine the spatial variability patterns of fish community structure between reefs located on the south and western insular shelves of Puerto Rico, and oceanic island reef systems after the 2005 coral bleaching event

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40 Results and Discussion A total of 75,348 individual fish distributed into 179 species were identified from 415 censuses between The average number of species per transect per reef site was 21.9 per monitoring year Species that accounted for the greatest overall total proportion of individuals were C personatus (25.8%), C cyanea (14.5%), C parrae (8.5%), T bifasciatum (8.1%) and S partitus (8%)

41 Transform: Log(X+1) Standardise Variables by Maximum Standardise Samples by Total Resemblance: S17 Bray Curtis similarity 3D Stress: 0.2 Site M CDM G D MO DER Non-metric, multidimensional scaling (MDS) plot of Bray-Curtis similarities based on the rank order abundances of reef fishes from sets of five replicate belt-transects surveyed between 1999 and 2011 at twelve reef stations encompassing a m depth gradient of the west and south coast of Puerto Rico.

42 Results and Discussion One-way Analysis of Similarities (ANOSIM) confirmed the temporal patterns of significant differences of fish community structure between oceanic and neritic stations (Global R = 0.397; p < 0.01), as well as between 10 m and 30 m depths (Global R = 0.326; p < 0.01) Transform: Log(X+1) Standardise Variables by Maximum Standardise Samples by Total Resemblance: S17 Bray Curtis similarity 3D Stress: 0.2 N vs O N O Transform: Log(X+1) Standardise Variables by Maximum Standardise Samples by Total Resemblance: S17 Bray Curtis similarity 3D Stress: 0.2 Depth

43 Conclusions The combined processes governing fish assemblages at the oceanic islands of Mona and Desecheo override differences in habitat variables such as rugosity, depth, % live coral cover and % benthic algal cover

44 Conclusions Marked losses of live coral cover associated to the regional coral bleaching event of 2005 may be below a threshold potentially regulating phase shifts of reef fish community structure, and/or there is also a time threshold required for coral structural loss that has not been surpassed

45 Conclusions Processes shaping fish assemblages become less probabilistic as spatial scale increase

46 Questions?