Macroalgal blooms on southeast Florida coral reefs: I. Nutrient stoichiometry of the invasive green alga Codium isthmocladum in the wider Caribbean indicates nutrient enrichment

Invasive blooms of the siphonaceous green algae Codium spp. have been considered a symptom of coastal eutrophication but, to date, only limited biochemical evidence supports a linkage to land-based nutrient pollution. Beginning in the summer of 1990, spectacular blooms of unattached Codium isthmocladum developed on deep coral reef habitats in southern Palm Beach County and northern Broward County, and in subsequent years, attached populations formed on reefs in northern Palm Beach County.To better understand the nutrition of these HABs, we collected C. isthmocladum and other reef macroalgae from various locations in southeast Florida as well as the wider Caribbean region for tissue C:N:P analysis in order to gauge variability in the type and degree of N- and/or P-limited growth. Widespread nutrient enrichment in floridian C. isthmocladum populations was evidenced by significantly higher tissue P (0.06% versus 0.04% of dry weight) and lower C:N (12 versus 19), C:P (425 versus 980), and N:P (35 versus 50) ratios compared to more nutrient-depleted Caribbean populations. To determine nutrient availability on southeast Florida's reefs, we sampled near-bottom waters at a variety of locations for DIN (NH₄⁺ + NO₃⁻ + NO₂⁻) and SRP analysis. In general, concentrations of NH₄⁺, NO₃⁻and SRP were all high on southeast Florida's reefs compared to values reported for Caribbean coral reefs. Although summertime upwelling provides episodic NO₃⁻ and SRP enrichment to reefs in southeast Florida, these transient nutrient pulses have not historically supported C. isthmocladum blooms.We suggest that the widespread P enrichment of C. isthmocladum tissue and water column DIN:SRP ratios <16:1 in southeast Florida drive this system toward N limitation where low level NH₄⁺ enrichment becomes of paramount importance. Hence, the recent C. isthmocladum blooms appear to be supported by increasing land-based nutrient pollution, particularly, sewage that is enriched in NH₄⁺ and SRP at a low N:P ratio (<10:1) critical to sustaining balanced growth during bloom formation.     

Anthropogenic nutrient enrichment of seagrass and coral reef communities in the Lower Florida Keys: discrimination of local versus regional nitrogen sources

Land-based nutrient pollution represents a significant human threat to coral reefs globally. We examined this phenomenon in shallow seagrass and coral reef communities between the Content Keys (southern Florida Bay) and Looe Key (south of Big Pine Key) in the Lower Florida Keys by quantifying the role of physical forcing (rainfall, wind, tides) and water management on mainland South Florida to nutrient enrichment and blooms of phytoplankton, macroalgae, and seagrass epiphytes. Initial studies (Phase I) in 1996 involved daily water quality sampling (prior to, during, and following physical forcing events) at three stations (AJ, an inshore area directly impacted by sewage discharges; PR, a nearshore patch reef located inshore of Hawk Channel; and LK, an offshore bank reef at Looe Key) to assess the spatial and temporal patterns in advection of land-based nutrients to the offshore reefs. Concentrations of dissolved inorganic nitrogen (DIN=NH₄⁺+NO₃⁻+NO₂⁻), soluble reactive phosphorus (SRP), and chlorophyll a increased at PR and LK following a wind event (∼15 knots, northeast) in mid-February. The highest DIN (mostly NH₄⁺) and SRP concentrations of the entire study occurred at the inshore AJ during an extreme low tide in March. Following the onset of the wet season in May, mean NH₄⁺ and chlorophyll a concentrations increased significantly to maximum seasonal values at PR and LK during summer; relatively low concentrations of NO₃⁻ and a low f-ratio (NO₃⁻/NH₄⁺+NO₃⁻) at all stations during summer do not support the hypothesis that the seasonal phytoplankton blooms resulted from upwelling of NO₃⁻. A bloom of the seagrass epiphyte Cladosiphon occidentalis (phaeophyta) followed the onset of the rainy season and increased NH₄⁺ concentrations at LK, resulting in very high epiphyte:blade ratios (∼3:1) on Thalassia testudinum. Biomass of macroalgae increased at all three stations from relatively low values (<50 g dry wt m⁻²) in winter and early spring to higher values (∼100-300 g dry wt m⁻²) typical of eutrophic seagrass meadows and coral reefs following the onset of the rainy season. The mean δ¹⁵N value of Laurencia intricata (rhodophyta) during 1996 at AJ (+4.7‰) was within the range reported for macroalgae growing on sewage nitrogen; lower values at the more offshore PR (+3.1‰) and LK (+2.9‰) were at the low end of the sewage range, indicating an offshore dilution of the sewage signal during the 1996 study. However, transient increases in δ¹⁵N of Cladophora catanata (chlorophtyta) from ~+2% to +5% at LK concurrent with elevated NH₄⁺ concentrations following rain and/or wind events in May and July suggest episodic advection of sewage nitrogen to the offshore LK station. The Phase II study involved sampling of macroalgae for δ¹⁵N along a gradient from the Content Keys through Big Pine Key and offshore to LK in the summer wet season of 2000 and again in the drought of spring 2001. During the July 2000 sampling, macroalgae in nearshore waters around Big Pine Key had elevated δ¹⁵N values (~+4‰) characteristic of sewage enrichment; lower values (~+2‰) at LK were similar to values reported for macroalgae in upstream waters of western Florida Bay influenced by nitrogen-rich Everglades runoff. That pattern contrasted with the drought sampling in March 2001, when δ¹⁵N values of macroalgae were elevated (+6‰) to levels characteristic of sewage enrichment over a broad spatial scale from the Content Keys to LK. These results suggest that regional-scale agricultural runoff from the mainland Everglades watersheds as well as local sewage discharges from the Florida Keys are both significant nitrogen sources supporting eutrophication and algal blooms in seagrass and coral reef communities in the Lower Florida Keys. Hydrological and physical forcing mechanisms, including rainfall, water management on the South Florida mainland, wind, and tides, regulate the relative importance and variability of these anthropogenic nitrogen inputs over gradients extending to the offshore waters of the Florida Reef Tract.     

Nutritional resources as positional information for morphogenesis in the stony coral Stylophora pistillata

We are interested in deciphering the mechanisms for morphogenesis in the Red Sea scleractinian coral Stylophora pistillata with the help of mathematical models. Previous mathematical models for coral morphogenesis assume that skeletal growth is proportional to the amount of locally available energetic resources like diffusible nutrients and photosynthetic products. We introduce a new model which includes factors like dissolved nutrients and photosynthates, but these resources do not serve as building blocks for growth but rather provide some kind of positional information for coral morphogenesis. Depending on this positional information side branches are generated, splittings of branches take place and branch growth direction is determined. The model results are supported by quantitative comparisons with experimental data obtained from young coral colonies.     

Copper enrichment reduces thermal tolerance of the highly resistant Red Sea coral Stylophora pistillata

Coral Reefs - Corals in the Gulf of Aqaba (GoA) in the northern Red Sea show high thermal tolerance. The GoA has therefore been suggested as a coral reef refuge from climate change. However, as a...     

Bioaccumulation of zinc in the scleractinian coral Stylophora pistillata

The uptake kinetics of zinc (Zn), an essential nutrient for both photosynthesis and calcification, in the tissue of S. pistillata showed that the transport of Zn is composed of a linear component (diffusion) at high concentrations and an active carrier-mediated component at low concentrations. The carrier affinity (K _m=28 pmol l⁻¹) was very low, indicating a good adaptation of the corals to low levels of Zn in seawater. Zn accumulation in the skeleton was linear; its level was dependent on the length of the incubation as well as on the external concentration of dissolved Zn. There was also a light-stimulation of Zn uptake, suggesting that zooxanthellae, through photosynthesis, are involved in this process. An enrichment of the incubation medium with 10 nM Zn significantly increased the photosynthetic efficiency of S. pistillata. This result suggests that corals living in oligotrophic waters might be limited in essential metals, such as zinc.     

Evidence of low molecular weight components in the organic matrix of the reef building coral, Stylophora pistillata

Biominerals contain both inorganic and organic components. Organic components are collectively termed the organic matrix, and this matrix has been reported to play a crucial role in mineralization. Several matrix proteins have been characterized in vertebrates, but only a few in invertebrates, primarily in Molluscs and Echinoderms. Methods classically used to extract organic matrix proteins eliminate potential low molecular weight matrix components, since cut-offs ranging from 3.5 to 10 kDa are used to desalt matrix extracts. Consequently, the presence of such components remains unknown and these are never subjected to further analyses. In the present study, we have used microcolonies from the Scleractinian coral Stylophora pistillata to study newly synthesized matrix components by labelling them with 14C-labelled amino acids. Radioactive matrix components were investigated by a method in which both total organic matrix and fractions of matrix below and above 5 kDa were analyzed. Using this method and SDS-PAGE analyses, we were able to detect the presence of low molecular mass matrix components (<3.5 kDa), but no free amino acids in the skeletal organic matrix. Since more than 98% of the 14C-labelled amino acids were incorporated into low molecular weight molecules, these probably form the bulk of newly synthesized organic matrix components. Our results suggest that these low molecular weight components may be peptides, which can be involved in the regulation of coral skeleton mineralization.     

The relative importance of nutrient enrichment and herbivory on macroalgal communities near Norman's Pond Cay, Exumas Cays, Bahamas: a “natural” enrichment experiment

The simultaneous effects of grazing and nutrient enrichment on macroalgal communities were experimentally investigated using plastic mesh enclosure/exclosure cages along a natural nutrient (DIN, SRP) gradient from the discharge of a tidal mangrove creek on the west side of Norman's Pond Cay, Exumas Cays, Bahamas. Nutrient enrichment was the only factor affecting total biomass of macroalgae whereas selective herbivory moderated species composition. Biomass ranged from >2 kg dry weight m⁻² at the DIN-enriched Waterfall to <600 g dry weight m⁻² in the DIN-limited Algal Halo. Grazing by the queen conch Strombus gigas and the sea hare Aplysia dactylomela significantly reduced biomass of the epiphyte Laurencia intricata, but not its host Digenea simplex at the DIN-enriched Waterfall. These two rhodophytes dominated the macroalgal community at the DIN-enriched Waterfall and inner Algal Halo, whereas the chlorophytes Microdictyon marinum and Cladophora catenata dominated the relatively DIN-depleted outer Algal Halo. Higher grazing rates by S. gigas, A. dactylomela, and juvenile parrotfish and surgeonfish at the DIN-enriched Waterfall compared to the more oligotrophic Algal Halo suggested selective grazing on higher quality (nitrogen) diets by these herbivores. A pronounced increase in the carbon/nitrogen (C:N) ratios of D. simplex and L. intricata from the Waterfall to the Algal Halo indicated increased DIN-limitation of growth in the more offshore, lower DIN macroalgal communities. In contrast, only modest increases in C:N ratios of M. marinum and C. catenata between the Waterfall and Algal Halo suggested that these species are better adapted to growth in reef environments with lower levels of DIN enrichment. Low coral cover (<2%) co-occurred with high macroalgal cover (>35%) at DIN-enriched reef sites around Norman's Pond Cay (Waterfall, Patch Reef, North Perry Reef) compared to relatively high coral cover (10-20%) and low macroalgal cover (<20%) at the lower DIN reef sites (Rainbow Reef, Lang's Reef). These results support ecological theory that bottom-up control via nutrient enrichment is a primary factor regulating overall biomass and taxonomic assemblages of macroalgae on coral reefs, whereas grazing is more important in controlling relative species composition via dietary preferences.     

Response of a scleractinian coral, Stylophora pistillata, to iron and nitrate enrichment

The purpose of this study was to determine whether the addition of iron alone or in combination with nitrate affects growth and photosynthesis of the scleractinian coral, Stylophora pistillata, and its symbiotic dinoflagellates. For this purpose, we used three series of two tanks for a 3-week enrichment with iron (Fe), nitrate (N) and nitrate+iron (NFe). Two other tanks were kept as a control (C). Stock solutions of FeCl(3) and NaNO(3) were diluted to final concentrations of 6 nM Fe and 2 &mgr;M N and continuously pumped from batch tanks into the experimental tanks with a peristaltic pump. Results obtained showed that iron addition induced a significant increase in the areal density of zooxanthellae (ANOVA, p=0.0013; change from 6.3+/-0.7x10(5) in the control to 8.5+/-0.6x10(5) with iron). Maximal gross photosynthetic rates normalized per surface area also significantly increased following iron enrichment (ANOVA, p=0.02; change from 1.23+/-0.08 for the control colonies to 1.81+/-0.24 &mgr;mol O(2) cm(-2) h(-1) for the iron-enriched colonies). There was, however, no significant difference in the photosynthesis normalized on a per cell basis. Nitrate enrichment alone (2 &mgr;M) did not significantly change the zooxanthellae density or the rates of photosynthesis. Nutrient addition (both iron and nitrogen) increased the cell-specific density of the algae (CSD) compared to the control (G-test, p=0.3x10(-9)), with an increase in the number of doublets and triplets. CSD was equal to 1.70+/-0.04 in the Fe-enriched colonies, 1.54+/-0.12 in the N- and NFe-enriched colonies and 1.37+/-0.02 in the control. Growth rates measured after 3 weeks in colonies enriched with Fe, N and NFe were 23%, 34% and 40% lower than those obtained in control colonies (ANOVA, p=0.011).     

Ecological indicators of nutrient enrichment, freshwater wetlands, Midwestern United States (U.S.)

Vegetation and soil indicators of nutrient condition were evaluated in 30 wetlands, 10 each in 3 Nutrient Ecoregions (NE) (VI-Corn Belt and Northern Great Plains, VII-Mostly Glaciated Dairy Region, IX-Temperate Forested Plains and Hills) of the Midwestern United States (U.S.) to identify robust indicators for assessment of wetland nutrient enrichment and eutrophication. Nutrient condition was characterized by surface water inorganic N (NH₄-N, NO₃-N) and P (PO₄-P) concentrations measured seasonally for 1 year, plant available and total soil N and P, and aboveground biomass, leaf N and P and species composition of emergent vegetation measured at the end of the growing season. Aboveground biomass, nutrient uptake and species composition were positively related to surface water NH₄-N (N) but not to PO₄-P or NO₃-N. Aboveground biomass and biomass of aggressive species, Typha spp. plus Phalaris arundinacea, increased asymptotically with surface water N whereas leaf P, senesced leaf N and senesced leaf P increased linearly with N. And, species richness declined with surface water N. Soil total P was positively related to surface water PO₄-P but it was the only soil indicator related to wetland nutrient condition. Individual regressions for each NE generally were superior to a single regression for all NEs. In NE VI (Corn Belt), few indicators were related to surface water N because of the high degree of anthropogenic disturbance (85% of the landscape is cleared) as compared to NEs VII and IX (24–53% cleared). Of the indicators evaluated, stem height (r² = 0.42 for all NEs, r² = 0.56 for NE VII + IX) and percent biomass of aggressive species, Typha spp. plus Phalaris, (r² = 0.46 for all NEs, r² = 0.54 for NE VII + IX), were the best predictors of wetland nutrient enrichment. Vegetation-based indicators are a promising tool for assessment of wetland nutrient condition but they may not be effective in NEs where landscape disturbance is intense and widespread.     

Carbonic anhydrase inhibitors. Inhibition studies with anions and sulfonamides of a new cytosolic enzyme from the scleractinian coral Stylophora pistillata

The catalytic activity and the inhibition of a new coral carbonic anhydrase (CA, EC 4.2.1.1), from the scleractinian coral Stylophora pistillata, STPCA-2, has been investigated. STPCA-2 has high catalytic activity for the physiological reaction being less sensitive to anion and sulfonamide inhibitors compared to STPCA, a coral enzyme previously described. The best STPCA-2 anion inhibitors were sulfamide, sulfamic acid, phenylboronic acid, and phenylarsonic acid (K_Is of 5.7-67.2 μM) whereas the best sulfonamide inhibitors were acetazolamide and dichlorophenamide (K_Is of 74-79 nM). Because this discriminatory effect between these two coral CAs, sulfonamides may be useful to better understand the physiological role of STPCA and STPCA-2 in corals and biomineralization processes.     

Effect of temperature on the settlement choice and photophysiology of larvae from the reef coral Stylophora pistillata

To better understand the consequences of climate change for scleractinian corals, Stylophora pistillata was used to test the effects of temperature on the settlement and physiology of coral larvae. Freshly released larvae were exposed to temperatures of 23 degrees C, 25 degrees C (ambient), and 29 degrees C at light intensities of approximately 150 micromol photons m(-2) s(-1). The effects were assessed after 12 h as settlement to various substrata (including a choice between crustose coralline algae [CCA] and limestone) and as maximum quantum yield of PSII (F(v)/F(m)) in the larvae versus in their parents. Regardless of temperature, 50%-73% of the larvae metamorphosed onto the plastic of the incubation trays or in a few cases were drifting in the water, and 14% settled on limestone. However, elevated temperature (29 degrees C) reduced the percentage of larvae swimming by 81%, and increased the percentage choosing CCA nearly 7-fold, both relative to the outcomes at 23 degrees C. Because temperature did not affect settlement on limestone or plastic, increased settlement on CCA reflected temperature-mediated choices by larvae that otherwise would have remained swimming. Interestingly, F(v)/F(m) was unaffected by temperature, but it was 4% lower in the larvae than in the parents. These results are important because they show that temperature can affect the settlement of coral larvae and because they reveal photophysiological differences between life stages that might provide insights into the events associated with larval development.     

Effects of increased pCO2 on zinc uptake and calcification in the tropical coral Stylophora pistillata

Zinc (Zn) is an essential element for corals. We investigated the effects of ocean acidification on zinc incorporation, photosynthesis, and gross calcification in the scleractinian coral Stylophora pistillata. Colonies were maintained at normal pH_T (8.1) and at two low-pH conditions (7.8 and 7.5) for 5 weeks. Corals were exposed to ⁶⁵Zn dissolved in seawater to assess uptake rates. After 5 weeks, corals raised at pH_T (8.1) exhibited higher ⁶⁵Zn activity in the coral tissue and skeleton, compared with corals raised at a lower pH. Photosynthesis, photosynthetic efficiency, and gross calcification, measured by ⁴⁵Ca incorporation, were however unchanged even at the lowest pH.     

Photochemical response of the scleractinian coral Stylophora pistillata to some sunscreen ingredients

Coral Reefs - Ultraviolet (UV) filters and preservatives, which are common constituents of sunscreens and other cosmetics, are reported as a threat for coastal coral reef ecosystems; however, few...     

Macroalgal blooms on southeast Florida coral reefs: II. Cross-shelf discrimination of nitrogen sources indicates widespread assimilation of sewage nitrogen

Since 1990, coral reefs off southeast Florida have experienced an unprecedented succession of macroalgal blooms and invasions. To determine if anthropogenic land-based nitrogen (N) sources support these HABs, we collected macroalgal tissue for stable nitrogen isotope (δ¹⁵N) analysis at three spatially distinct depths ranging from the shallow subtidal to the shelf break (43 m) along seven transects from Jupiter to Deerfield Beach, Florida, USA. This sampling was initiated during a historically significant drought in the spring of 2001 when rainfall, stormwater runoff, and upwelling were at a minimum. The sampling was repeated in the summer wet season following significant stormwater runoff and during a strong upwelling event.Despite significant seasonal changes in N source availability, δ¹⁵N values did not vary between samplings. Collectively, δ¹⁵N values were significantly higher on inshore shallow reefs (+8.1‰) compared to mid (+6.1‰) and deep reefs (+6.7‰). Values were also elevated in the southern portion of the study area (e.g., Boca Raton, +8.5‰) where nearly 1.5 billion l/day of secondarily treated wastewater is discharged into the ocean via coastal outfalls. Codium isthmocladum, a macroalga that assimilates its nutrients entirely from the water column, was the dominant bloom species in the southern study area, where tissue δ¹⁵N values matched source values of nearby sewage outfalls. The northern study area was dominated by species of the genus Caulerpa, particularly the invasive Pacific native C. brachypus var. parvifolia, which are capable of accessing benthic nutrient sources (e.g., submarine groundwater discharge, SGD) by means of root-like rhizoids. The northern area does not have sewage outfalls but features a highly transmissive geologic zone where SGD may be enriched with septic tank leachate and effluent from municipal deep injection wells.Multiple lines of evidence supported the hypothesis that land-based sewage N was more important than upwelling as a N source to these HABs: (1) δ¹⁵N values were highest on shallow reefs and decreased with increasing depth, indicating land-based sources of enrichment; (2) elevated δ¹⁵N values occurred in these HABs during the dry season, prior to the onset of the summer upwelling; (3) elevated NH₄⁺ concentrations occur on these reefs during both upwelling and non-upwelling periods and are kinetically preferred by macroalgae compared to upwelled NO₃⁻. These findings provide a case study of a coupling between increasing anthropogenic activities and the development of macroalgal HABs, including invasive species that threaten economically important reef resources in southeast Florida.     

Molecular cloning and localization of a PMCA P-type calcium ATPase from the coral Stylophora pistillata

Plasma-membrane calcium pumps (PMCAs) are responsible for the expulsion of Ca(2+) from the cytosol of all eukaryotic cells and are one of the major transport systems involved in long-term regulation of resting intracellular Ca(2+) concentration. An important feature of stony corals, one of the major groups of calcifying animals, is the continuous export of large quantities of Ca(2+) for skeletogenesis. Here, we report the cloning and functional expression of the stpPMCA gene from the coral Stylophora pistillata, and whose features resemble those of the plasma-membrane Ca(2+)-ATPase family of mammalian cells. This is the first known example of a Ca(2+)-ATPase from the phylum Cnidaria, and thus, the most phylogenetically distant PMCA sequence in the animal kingdom described to date. We demonstrate that the localization of stpPMCA within calicoblastic cells is fully coherent with its role in calcification. We also show that the coral Ca(2+) pump is more closely related to vertebrate PMCAs than to Caenorhabditis elegans PMCAs. The cloning of evolutionarily conserved genes from cnidarian species repeatedly shows that these genes encode similar functional domains. Moreover, this high level of gene conservation further validates the use of cnidarian model systems for studying processes shared by Eumetazoans.     

Photo-acclimation of the hermatypic coral Stylophora pistillata while subjected to either starvation or food provisioning

This study investigated the photo-acclimation capacity of the coral Stylophora pistillata (Esper). Outer branches of coral colonies, taken from 2 m, were subjected to 90, 20, or 3% of incident surface photosynthetic active radiation (PAR(0)), or kept in total darkness. The corals were maintained either in filtered seawater (i.e., under starvation), or in seawater that had daily additions of zooplankton (rotifers). The experiments were maintained for 31 days. Zooxanthellae population densities and chlorophyll concentrations increased in S. pistillata fragments subjected to 20 and 3% PAR(0). The zooxanthellae densities decreased after 6 days in corals kept in total darkness, although chlorophyll concentrations remained higher. Corals that were fed and subjected to 90% PAR(0) showed lower degrading zooxanthellae frequencies, higher photosynthetic and respiration rates, and higher chlorophyll concentrations than corals in the same light regime under starvation. Complete acclimation to dim (20% PAR(0)) and low (3% PAR(0)) light was only apparent for corals fed with zooplankton. Changes in zooxanthellae population densities occurred through differential rates of zooxanthellae division and degradation.     

In vivo light-microscopic documentation for primary calcification processes in the hermatypic coral Stylophora pistillata

Skeletogenesis in the hermatypic coral Stylophora pistillata was studied by using the lateral skeleton preparative (LSP) assay, viz., a coral nubbin attached to a glass coverslip glued to the bottom of a Petri dish. Observations on tissue and skeletal growth were made by polarized microscopy and by using vital staining. The horizontal distal tissue edges developed thin transparent extensions of ectodermal and calicoblastic layers only. Four stages (I-IV) of skeletogenesis were observed at these edges, underneath the newly developed tissue. In stage I, a thin clear layer of coral tissue advanced 3–40 μm beyond the existing LSP peripheral zone, revealing no sign of spiculae deposition. At stage II, primary fusiform crystals (1 μm each) were deposited, forming a primary discontinuous skeletal front 5–30 μm away from the previously deposited skeleton. During stage III, needle-like crystals appeared, covering the primary fusiform crystals. Stage IV involved further lengthening of the needle-like crystals, a process that resulted in occlusion of the spaces between adjacent crystals. Calcification stages I-III developed within hours, whereas stage IV was completed in several days to weeks. Two basic skeletal structures, “scattered” and “laminar” skeletons, were formed, integrating the growth patterns of the needle-like crystals. High variation was recorded in the expression of the four calcification stages, either between different locations along a single LSP or between different preparations observed at the same diurnal time. All four skeletogenesis stages took place during both day and night periods, indicating that an intrinsic process controls S. pistillata calcification. This study was supported by the Israel Science Foundation (206/01 to J.E.), by the BARD, US-Israel Bi-National Agricultural Research and Development, by INCO-DEV project (REEFRES), and by CORALZOO, EC Collective Research project.     

Calcification and associated physiological parameters during a stress event in the scleractinian coral Stylophora pistillata

High calcification rates observed in reef coral organisms are due to the symbiotic relationship established between scleractinian corals and their photosynthetic dinoflagellates, commonly called zooxanthellae. Zooxanthellae are known to enhance calcification in the light, a process referred as "light-enhanced calcification". The disruption of the relationship between corals and their zooxanthellae leads to bleaching. Bleaching is one of the major causes of the present decline of coral reefs related to climate change and anthropogenic activities. In our aquaria, corals experienced a chemical pollution leading to bleaching and ending with the death of corals. During the time course of this bleaching event, we measured multiple parameters and could evidence four major consecutive steps: 1) at month 1 (January 2005), the stress affected primarily the photosystem II machinery of zooxanthellae resulting in an immediate decrease of photosystem II efficiency, 2) at month 2, the stress affected the photosynthetic production of O2 by zooxanthellae and the rate of light calcification, 3) at month 3, there was a decrease in both light and dark calcification rates, the appearance of the first oxidative damage in the zooxanthellae, the disruption of symbiosis, 4) and finally the death of corals at month 6.     

Community metabolism of a coral reef exposed to naturally varying dissolved inorganic nutrient loads

Daily community rates of calcification, photosynthesis and respiration were measured on a coral reef located in the Northern Red Sea, Gulf of Eilat, Israel between March 2000 and March 2002. This reef is exposed to seasonally varying levels of inorganic nutrient loading due to mixing and stratification of the adjacent open sea water column. Net production measurements were positively and linearly correlated with open sea nutrient levels, and the community photosynthesis to respiration ratio varied between 0.9 and 1.7 accordingly. Community calcification varied between 30 ± 20 and 60 ± 20 mmol C m⁻² day⁻¹ during summer and winter, respectively. Under increased nutrient loading the relation between community calcification and aragonite saturation state is suppressed by 30% on average. Both of these findings demonstrate the deleterious effects of nutrient loading on coral reefs.