Case Study Coral Reef Microcosm

The Caribbean coral reef ecosystem model shown in Figure 5 received natural sunlight from one side, south-facing at 37.5° N latitude; the metabolic unit had six

Experimental coral reef microcosm (5.0 m2; 1680 l)

Experimental coral reef microcosm (5.0 m2; 1680 l)

(0.757 m2; 400 l) Refugium unit

Figure 5 Diagram of coral reef microcosm with its refugium.

(0.757 m2; 400 l) Refugium unit

Figure 5 Diagram of coral reef microcosm with its refugium.

Microcosm vs. St. Croix

Microcosm vs. St. Croix

0600 1000 1400 1800 2200 0200 0600 0800 1200 1600 2000 2400 0400

Time

0600 1000 1400 1800 2200 0200 0600 0800 1200 1600 2000 2400 0400

Time

Figure 6 Comparison of mean daily oxygen concentration in the coral reef microcosm in comparison with that over the wild analog reef (1-year means).

160WVHF flourescent lamps (to match tropical intensity), step-cycled to bring mid-day peak intensity to approximately 800uEm"2s" and total incoming light to 220 Langleys/day (Figure 6). The ATS, lighted at night, had three 100 W metal halide lamps. The discussion presented represents data accumulated throughout the 9th year of 10 years of operation.

The physical and chemical components of the microcosm were measured in the metabolic unit and closely match those of the St. Croix analog (Table 1). The pH of the microcosm ranges from 7.96 ± 0.01 (n = 62) in the morning to 8.29 ± 0.10 (n = 39) in the late afternoon. Because of linked interacting photosynthesis and calcification in the ecosystem, calcium concentrations and alkalinity continually fall during the day and are stable or rise slightly at night. Calcium was added each morning as a solution of aragonite dissolved in HCl at approximately 24 000mgl"\ To keep microcosm concentrations above 420 mgl"1, after a full day of calcification, the mean concentration of calcium in the system was maintained at 491 ± 6mgl"\ Bicarbonate, was added as either NaHCO 3 or KHCO3 dissolved in distilled water. The mean alkalinity was 2.88 meql"1 (n = 59), in order to maintain levels above 2.40 meq l"1. Water quality (nutrients, oxygen, and pH) of the system was controlled by algal turf scrubbing.

The mean oxygen concentration of the microcosm as shown in Figure 6 is very close to that of the analog St. Croix reef. Net primary productivity (NPP) and respiration (R) were calculated based on the rate of oxygen increase and decrease, respectively, across the point of saturation (6.5 mg1" O2), to avoid atmospheric fluxes. This gave a mean gross primary productivity (GPP) of 14.2 ± 1.0 gO2 m"2 d"1, as compared to the mean GPP for the analog fore-reef at 15.7gO2m"2d"1. The difference between the microcosm and reefs in situ can be accounted for by the difference in spatial heterogeneity; topographic relief on the St. Croix fore-reef typically ranges from 1 to 2 m, while in the microcosm only 10-30 cm is possible.

In Figure 7, GPP versus R for the microcosm and its analog are plotted, showing that both are well within the

Table 1 Comparison of physical/chemical parameters between coral reef microcosm and the wild analog reef

Microcosm

St. Croix Reefs (fore-reef)a

Temperature (°C) (am-pm)

26.5 ± 0.03 (n = 365)-27.4 ± 0.02 (n --

= 362)

24.0-28.5

Salinities (ppt)

35.8 ± 0.02 (n = 365)

35.5b

pH (am-pm)

7.96 ± 0.01 (n = 62)-8.29 ± 0.02 (n =

39)

8.05-8.35c

Oxygen concentration (mgl-1) (am-pm)

5.7±0.1 (n = 14)-8.7±0.2 (n = 11)

5.8-8.5

GPP (g O2m-2d-1); (mmol O2m-2d-1)

14.2 ± 1.0 (n = 4); 444 ± 3 (n = 4)

15.7; 491

Daytime NPP (g O2m-2day-1); (mmol O2m-2d-1)

7.3 ± 0.3 (n = 4); 228 ± 9 (n = 4)

8.9; 278

Respiration (g O2m-2h-1); (mmol O2m-2h-1)

0.49 ± 0.04 (n = 4); 15.3 ± 1.3 (n = 4)

0.67; 20.9

N - NO2 + NO3 (mmol)

0.56 ± 0.07 (n = 6)

0.28

Calcium (mgr1); (mmoll-1)

491 ±6 (n = 33); 12.3 ±0.2 (n = 33)

417.2d; 10.4

Alkalinity (meq l-1)

2.88 ± 0.04 (n = 59)

2.47b

Light® (Langleys d-1)

220

430 (surface); 220 (5 m deep in fore-reef)

aThe St. Croix data is from Adey and Steneck (1985).

bTropical Atlantic means from Millero and Sohn (1992); no data available for St. Croix. cValues from Enewetak and Moorea (Odum and Odum, 1955; Gattuso et al., 1997). dTropical Atlantic means from Sverdrup et al. (1942); no data available for St. Croix.

eThe light levels of the system were measured with a pyranograph. All of the physical and chemical components of the microcosm are compared to the fore-reef of St. Croix since light levels are equivalent (Kirk, 1983; Adey and Steneck, 1985).

For references, see Small A and Adey W (2001) Reef corals, zooxanthellae and free-living algae: A microcosm study that demonstrates synergy between calcification and primary production. Ecological Engineering 16: 443-457.

aThe St. Croix data is from Adey and Steneck (1985).

bTropical Atlantic means from Millero and Sohn (1992); no data available for St. Croix. cValues from Enewetak and Moorea (Odum and Odum, 1955; Gattuso et al., 1997). dTropical Atlantic means from Sverdrup et al. (1942); no data available for St. Croix.

eThe light levels of the system were measured with a pyranograph. All of the physical and chemical components of the microcosm are compared to the fore-reef of St. Croix since light levels are equivalent (Kirk, 1983; Adey and Steneck, 1985).

For references, see Small A and Adey W (2001) Reef corals, zooxanthellae and free-living algae: A microcosm study that demonstrates synergy between calcification and primary production. Ecological Engineering 16: 443-457.

Microcosm

CL CL O

Respiration (mol C m 2 yr 1)

Figure 7 GPP as a function of respiration in the coral reef microcosm and its wild analog reef in comparison with selected worldwide reefs.

Respiration (mol C m 2 yr 1)

Figure 7 GPP as a function of respiration in the coral reef microcosm and its wild analog reef in comparison with selected worldwide reefs.

range of typical wild reefs. Even though primary productivity of the microcosm is very close to the wild analog, the fact that respiration is somewhat lower probably relates to the proportionally lower spatial heterogeneity in the microcosm.

Whole ecosystem calcification in the coral reef model, at 4.0 ± 0.2 kg CaCO3 m~ yr _ , is related to its primary components (stony coral 17.6%, Halimeda 7.4%, Tridacna 9.0%, algal turf, coralline and foraminifera 29.4%, and miscellaneous invertebrates 36%). Through analysis of the microcosm's daily carbonate system, it is demonstrated that bicarbonate ion (Figure 8), not carbonate ion, is the principal component of total alkalinity reduction in the water column.

This coral reef microcosm contained 534 identified species within 27 phyla (Table 2), with an estimated 30%

95 93 91 89

Microcosm

95 93 91 89

Figure 8 Mean daytime carbonate cycle in coral reef microcosm calculated by namograph from pH and total alkalinity data.

H 81

79 77 75

Time pH

Figure 8 Mean daytime carbonate cycle in coral reef microcosm calculated by namograph from pH and total alkalinity data.

unaccounted for due to lack of taxonomic specialists. Because of the length of time that this model system was closed to biotic interchange, virtually all of the biotic composition of the system (over 95%) had to be maintained by reproduction. Based on standard species/area relationships (S = kAz, where S = species richness and A = area), the predicted pan tropic coral reefbiodiversity calculated from the model biodiversity (at three million species) exceeds that of recent estimates for wild coral reefs.

Table 2 Families of organisms, with numbers of species and genera found in the Coral reef microcosm after 10 years of operation, 7 years in closure

Plants, algae, and cyanobacteria Division Cyanophota Chroococcaceae 6/5 Pleurocapsaceae 4/2 UID Family 4/4 Oscillatoriaceae 8/6 Rivulariaceae 4/1 Scytonemataceae 1/1 Phylum Rhodophyta Goniotrichaceae 2/2 Acrochaetiaceae 2/2 Gelidiaceae 1/1 Wurdemanniaceae 1/1 Peysonneliaceae 3/1 Corallinaceae 11/8 Hypneaceae 1/1 Rhodymeniaceae 3/2 Champiaceae 1/1 Ceramiaceae 3/3 Delesseriaceae 1/1 Rhodomelaceae 7/6 Phylum Chromophycota Cryptomonadaceae 2/2 Hemidiscaceae 1/1 Diatomaceae 6/4 Naviculaceae 9/4 Cymbellaceae 3/1 Entomoneidaceae 1/1 Nitzchiaceae 6/4 Epithemiaceae 3/1 Mastogloiaceae 1/1 Achnanthaceae 9/3 Gymnodiniaceae 6/4or5 Gonyaulacaceae 1/1 Prorocentraceae 2/1 Zooxanthellaceae 1/1 Ectocarpaceae 2/2 Phylum Chlorophycota Ulvaceae 1/1 Cladophoraceae 4/2 Valoniaceae 2/2 Derbesiaceae 3/1 Caulerpaceae 3/1 Codiaceae 6/2 Colochaetaceae 1/1 Phylum Magnoliophyta Hydrocharitaceae 1/1 Kingdom Protista Phylum Percolozoa Vahlkampfiidae 2/1 UID Family 2/2 Stephanopogonidae 2/1

Phylum Euglenozoa UID Family 4/3 Bondonidae 7/1 Phylum Choanozoa Codosigidae 2/2 Salpingoecidae 1/1 Phylum Rhizopoda Acanthamoebidae 1/1 Hartmannellidae 1/1 Hyalodiscidae 1/1 Mayorellidae 2/2 Reticulosidae 2/2 Saccamoebidae 1/1 Thecamoebidae 1/1 Trichosphaeridae 1/1 Vampyrellidae 1/1 Allogromiidae 1/1 Ammodiscidae 1/1 Astrorhizidae 1/1 Ataxophragmiidae 1/1 Bolivinitidae 3/1 Cibicidiidae 1/1 Cymbaloporidae 1/1 Discorbidae 5/2 Homotremidae 1/1 Peneroplidae 1/1 Miliolidae 10/2 Planorbulinidae 2/2 Siphonidae 1/1 Soritidae 4/4 Textulariidae 1/1 Phylum Ciliophora Kentrophoridae 1/1 Blepharismidae 2/2 Condylostomatidae 1/1 Folliculinidae 4/3 Peritromidae 2/1 Protocruziidae 2/1 Aspidiscidae 7/1 Chaetospiridae 1/1 Discocephalidae 1/1 Euplotidae 11/3 Keronidae 7/2 Oxytrichidae 1/1 Psilotrichidae 1/1 Ptycocyclidae 2/1 Spirofilidae 1/1 Strombidiidae 1/1 Uronychiidae 2/1 Urostylidae 4/2 Cinetochilidae 1/1 Cyclidiidae 3/1 Pleuronematidae 3/1 Uronematidae 1/1

(Continued)

Table 2 (Continued)

Vaginicolidae 1/1 Vorticellidae 2/1 Parameciidae 1/1 Colepidae 2/1 Metacystidae 3/2 Prorodontidae 1/1 Amphileptidae 3/3 Enchelyidae 1/1 Lacrymariidae 4/1 Phylum Heliozoa

Actinophyridae 2/1 Phylum Placozoa

Family UID 5 Phylum Porifera Plakinidae 2/1 Geodiidae 5/2 Pachastrellidae 1/1 Tetillidae 1/1 Suberitidae 1/1 Spirastrellidae 2/2 Clionidae 4/2 Tethyidae 2/1 Chonrdrosiidae 1/1 Axinellidae 1/1 Agelasidae 1/1 Haliclonidae 4/1 Oceanapiidae 1/1 Mycalidae 1/1 Dexmoxyidae 1/1 Halichondridae 2/1 Clathrinidae 1/1 Leucettidae 1/1 UIDFamily 2/? Eumetazoa Phylum Cnidaria UID Family 3/? Eudendridae 1/1 Olindiiae 1/1 Plexauridae 1/1 Anthothelidae 1/1 Briareidae 1/1 Alcyoniidae 2/2 Actiniidae 3/2 Aiptasiidae 1/1 Stichodactylidae 1/1 Actinodiscidae 4/3 Corallimorphidae 3/2 Acroporidae 2/2 Caryophylliidae 1/1 Faviidae 3/2 Mussidae 1/1 Poritidae 3/1

Zoanthidae 3/2 Cerianthidae 1/1 Phylum Platyhelminthes UID Family 1/1 Anaperidae 3/2 Nemertodermatidae 1/1 Kalyptorychidae 1/1 Phylum Nemertea UID Family 2/2 Micruridae 1/1 Lineidae 1/1 Phylum Gastrotricha Chaetonotidae 3/1 Phylum Rotifera UID Family 2/? Phylum Tardigrada Batillipedidae 1/1 Phylum Nemata

Draconematidae 3/1 Phylum Mollusca Acanthochitonidae 1/1 Fissurellidae 2/2 Acmaeidae 1/1 Trochidae 1/1 Turbinidae 1/1 Phasianellidae 1/1 Neritidae 1/1 Rissoidae 1/1 Rissoellidae 1/1 Vitrinellidae 1/1 Vermetidae 1/1 Phyramidellidae 1/1 Fasciolariidae 2/2 Olividae 1/1 Marginellidae 1/1 Mitridae 1/1 Bullidae 1/1 UID Family 4/? Mytilidae 2/1 Arcidae 2/1 Glycymerididae 1/1 Isognomonidae 1/1 Limidae 1/1 Pectinidae 1/1 Chamidae 1/1 Lucinidae 2/2 Carditidae 1/1 Tridacnidae 2/1 Tellinidae 1/1 Phylum Annelida Syllidae 3/2 Amphinomidae 1/1 Eunicidae 3/1 Lumbrineridae 1/1

(Continued)

Table 2 (Continued)

Dorvilleidae 1/1 Orbiniidae 1/1 Spionidae 1/1 Chaetopteridae 1/1 Paraonidae 1/1 Cirratulidae 4/3 Ctenodrilidae 4/3 Capitellidae 3/3 Muldanidae 1/1 Oweniidae 1/1 Terebellidae 2/1 Sabellidae 14/4 Serpulidae 6/6 Spirorbidae 2/2 Dinophilidae 1/1 Phylum Sipuncula Golfingiidae 1/1 Phascolosomatidae 3/2 Phascolionidae 1/1 Aspidosiphonidae 3/2 Phylum Arthropoda Halacaridae 1/1 UID Family 2/? Cyprididae 2/2 Bairdiiaae 1/1 Paradoxostomatidae 1/1 Pseudocyclopidae 1/1 Ridgewayiidae 2/1 Ambunguipedidae 1/1 Argestidae 1/1 Diosaccidae 1/1 Harpacticidae 1/1 Louriniidae 1/1 Thalestridae 1/1 Tisbidae 1/1 Mysidae 1/1 Apseudidae 2/1 Paratanaidae 1/1 Tanaidae 1/1 Paranthuridae 1/1 Sphaeromatidae 1/1 Stenetriidae 1/1 Juniridae 1/1 Lysianassidae 1/1 Gammaridae 4/4 Leucothoidae 1/1 Anamixidae 1/1 Corophiidae 1/1 Amphithoidae 2/2 Alpheidae 2/2 Hippolytidae 2/1

Nephropidae 1/1 Diogenidae 1/1 Xanthidae 2/?

Phylum Echinodermata Ophiocomidae 1/1 Ophiactidae 1/1 Cidaroidae 1/1 Toxopneustidae 1/1 Holothuriidae 1/1 Chirotidae 1/1

Phylum Chordata Ascidiacea UID Fam..1/1 Grammidae 1/1 Chaetodontidae 1/1 Pomacentridae 5/4 Acanthuridae 1/1

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