10/24/2013. Functional diversity in coral reef herbivores: Impact upon ecosystem structure. Resilience. Grazing on coral reefs

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1 Number of species 1/24/213 Bio122 F13: Lecture 9 (1/24/13): Communities I. Communities (Ch 1) A. Defined B. Food webs II. Community structure A. Species diversity B. Measuring species diversity 1. Diversity indices 2. Rank abundance curves 3. Species accumulation curves C. Species composition III. Processes that shape community structure: Interactions A. Direct & Indirect effects 1. Types of indirect effects 2. Interaction strength 3. Dominant species 4. Ecosystem engineers. Keystone species IV. Community Succession(Ch 16) A. Succession & its drivers Community Structure Functional diversity in coral reef herbivores: Impact upon ecosystem structure Michelle Paddack Predators Herbivores Reef Builders? Resilience University of East Anglia, Norwich UK Simon Fraser University, BC Canada NCORE X Fishes Great Barrier Reef Caribbean Functional Group: Species that perform a similar role in ecosystem processes, irrespective of taxonomic affinities Grazing on coral reefs Macro-herbivores have high grazing rates 1 % of daily algal production Algal communities in lowbiomass, highly-productive states (algal turfs: filamentous, < 1 cm tall) Bellwood et al. Nature 24 Macroalgal biomass historically negligible 1

2 1/24/213 Functional Groups: Herbivores Scarids (Parrotfishes) 13 spp. Urchins (Diadema) Acanthurids (Surgeonfishes) 3 spp. Pomacentrids (Damselfishes) 6 spp. Kyphosids (Chubs) 1 sp. Are herbivorous fishes a single functional group? Acanthurus sp. Purcell & Bellwood 1993 Scarus spp. Sparisoma spp. Bellwood & Choat 199 Goals 1. Define herbivore functional sub-groups 2. Assign species to sub-groups 3. Determine whether correlations with benthic variables differ among sub-groups Methods: Defining & designating Caribbean herbivore functional sub-groups (23 fish species) Field observations: Feeding behavior Food preferences Laboratory observations: Randall 1967 Gut contents: type of algae Gut contents: sediment 2

3 1/24/213 Photo by R. Steneck Grazing rate variation among Caribbean herbivorous fishes bites minute Svir Saur Scroi Svet Abah 1. Define herbivore functional sub-groups Feeding strategies & ecosystem function Browser (Grazer) Scraper Excavator (Bioeroder) Gardener Diet Macroalgae Very little sediment in gut Epilithic algal turf & associated surface sediment/detritus High gut sediment content Epilithic and endolithic algae & sediment/detritus High gut sediment content Farmed epilithic algae & associated sediment/detritus Low gut sediment Disturbance to benthos Low - Crop algal fronds Moderate Partial clearing of surface High Remove substrate, visible scar High/Patchy modify algal community in territories Impact on coral Reduce shading, abrasion, overgrowth Facilitate growth & survival of CCA & corals Clear space for CCA & coral settlement Eat coral recruits No coral recruitment in territories Browsers: Kyphosus sectatrix Acanthurus coeruleus Sparisoma chrysopterum Sparisoma rubripinne Scarus coeruleus Sparisoma atomarium Sparisoma radians Crypototomus roseus Gardeners: Stegastes spp. Microspathadon chrysurus Scrapers: Scarus coelestinus Scarus guacamaia Scarus taeniopteris Scarus iserti Scarus aurofrenatum Acanthurus bahianus Acanthurus chirurgus Excavators: Scarus vetula Sparisoma viride 3. Examine sub-group correlations: Data Atlantic & Gulf Rapid Reef Assessment Fish Counts: 3 x 2 m belt transect Min. 1 per site All Scarids ( cm) All Acanthurids Microspathodon chrysurus Sized in cm bins Algal cover: (original methodology) 2 x 2 cm quadrat per transect Target algal-covered area % Cover Macroalgae Algal height (avg) # Coral Recruits ( 2cm) AGRRA Fore reef sites (13) 1 countries 3 9 m depth AGRRA data: Relative % Cover of Macroalgae Sub-country means Fore reef, 3 9 m Costa Rica removed (1 site) r 2 =.278 p = Total herbivore biomass (kg 1m -2 ) r 2 =.117 p = Browser biomass (kg 1m -2 ) r 2 =.24 p = Excavator biomass (kg 1m -2 ) r 2 =.6 p = Gardner biomass (kg 1m -2 ) Significant negative correlations for Excavators & Scrapers r 2 =.229 p = Scraper biomass (kg 1m -2 ) 3

4 Fish biomass (kg m -2 ) 1/24/213 Canopy height (mm) Macroalgal canopy height 7 6 r 2 =.181 p = Total herbivore biomass (kg 1m -2 ) Canopy height (mm) r 2 =.12 p = Scraper biomass (kg 1m -2 ) AGRRA data: Sub-country means Fore reef, 3 9 m Costa Rica removed (1 site) Significant negative correlation for All Herbivores, Excavators & Scrapers Canopy height (mm) 7 6 r 2 =.229 p = Excavator biomass (kg 1m -2 ) % coral cover % Live Coral Cover r 2 =.2 p = Total herbivore biomass (g 1 m -2 ) All herbivores: N/S relationship % coral cover Significant positive correlation for Excavators AGRRA data: Sub-country means Fore reef, 3 9 m r 2 =.27 p = Excavator biomass (g 1m ) % Functional group composition relative to total biomass Browser (8 spp.) Excavator (2 spp.) Scraper (7 spp.) Gardener (6 spp.) 38% < 1.1 (n=9) (n=8) (n=11) > 3 (n=7) Total herbivorous fish biomass (kg m -2 ) St Thomas 2 Photo: Jen Schull Findings: Few sites with high herbivore biomass in Caribbean Herbivorous fishes are functionally diverse; distinct sub-groups vary in impact on benthos Scrapers & excavators appear to have a particularly strong impact Only 2 excavator species in the Caribbean Excavators decline quickly on heavily fished reefs Low biodiversity -> vulnerability -> decreased resilience? To manage for resilience, need to identify & focus on important & vulnerable functional groups Food chain Trophic levels Trophē = feed 4

5 1/24/213 Rank Abundance Diagrams Rank Abundance Diagrams indicate differences in species richness & evenness Birds of Great Lakes Basin Species accumulation curve

6 1/24/213 Foundation species Important species Keystone species disproportionately large effect on its environment relative to its abundance Keystone Species Elephants Keystone species Oculina arbuscula Sea otter Ochre star (Pisaster) Community dynamics succession Disturbance Humans can change the flow of energy. Fishing down the food web. 6

7 1/24/213 Figure 16. A Theoretical Model of Succession Community Succession and Species Richness? 39 Study questions 1. Define community 2. Why is a community more than the sum of its parts? 3. Define guild. 4. What is the difference between a trophic web and an interaction web?. Compare direct from indirect interactions. 6. What is the difference between bottom-up and top-down control within a food web? 7. Describe a rank-abundance curve, noting what is plotted along each axis. How would the curves differ for communities with relatively higher vs. lower species Study questions 8. What 2 pieces of information are used in calculating species diversity (such as the Shannon index)? 9. What would cause a community with low species richness have a higher species diversity than another community with higher species richness? 1. Define: foundation species, ecosystem engineer, & keystone species. Provide an example of each. 11. Define succession. Provide an example of the steps of succession in a community, being clear as to what happens to allow each step to proceed into the next. 12. At what point in community succession is species richness the greatest? Why? richness and for higher vs. lower species evenness?

8 1/24/213 Study questions 13. What role does disturbance play in a community? 14. What is meant by space for time substitution of succession? 1. Define alternate stable states and give an example. 43 8