Fig 1.
Map of the eastern tropical pacific coast of costa rica with the location of the study site, Matapalo Reef (10°32’21”N, 85°45’59”W), in the Gulf of Papagayo (small inset).
Mean sea surface temperatures (SST) on the right side indicate the oceanic hydrothermal setting during the major upwelling period (17 February 2014). The SST data were derived from daily global maps with a grid map resolution of 1 km (GHRSST, Level 4, G1SST) produced by the JPL Regional Ocean Modeling System group available from http://ourocean.jpl.nasa.gov/SST/. The data was visualized with the Ocean Data View software.
Table 1.
Monitored and calculated (pHVINDTA, fCO2, Ωarag) seawater parameters for carbon chemistry at the study site of Matapalo Reef, Costa Rica.
See also S2 Table and Fig 2A for comparison of pHManta and pHVINDTA.
Fig 2.
Graphs showing a) daytime means of seawater temperature, pHManta (total scale) and pHVINDTA (total scale), b) nutrient concentrations of nitrate, ammonia and phosphate, and c) bioerosion CaCO3 budget of the experimental coral substrate through time (with standard deviation, black bars). Temperature, pHManta and nutrient data modified after Stuhldreier et al. [23].
Fig 3.
Time-series BSE images of thin-sections from coral substrates throughout the experiment.
Shown are representative areas of thin-sections of coral substrates after a-c) one month, d-f) two months, g-i) three months, and j-l) four months of exposure. Encrusting species shown are c) crustose coralline red alga (CCA), d) lithophagine bivalve (genus Lithophaga/Leiosolenus), encrusting benthic foraminifer (Homotrema rubrum), e) encrusting bryozoan f) encrusting benthic foraminifer, g) lithophagine bivalve, h) encrusting benthic foraminifer, i) CCA, J) CCA (lower left) k) encrusting benthic foraminifer, and l) CCA. Note in k) darker thin bands indicate CaCO3 mineralogy change of the original coral skeleton (i.e. aragonite to calcite) due to microbioerosion. Also note the change in surface morphology and the increase in microbioerosion through time.
Fig 4.
Cross sections from modeled μCT scans of substrates per exposure period, which indicate the settlement succession of the bioeroder community and the internal change in morphology.
Shown are cross sections through the X-, Y- and Z-axis of coral substrates of a) control, and after b) one month, c) two months, d) three months, and e) four months of exposure. The hole in the middle part was pre-experimentally drilled to fix the substrates in the reef (cf. S1 Fig). Genera depicted in the μCT scan cross-sections are in c-e) serpulids (Ser), lithophagine bivalves (Biv), and balanids (Ba). Note the increase in abundance and size of lithophagine bivalves through time.
Fig 5.
Modeled μCT scans showing the surface morphological change and the settlement succession of bioeroders on the coral substrates.
Smaller quadrates at the bottom indicate the alteration of surface roughness per substrate and month. Shown are coral substrates of a) control, and after b) one month, c) two months, d) three months, and e) four months of exposure. Settled genera depicted are in b) serpulids and small CCA (lower left side), c) balanids and serpulids, d) balanids, serpulids and CCA (encrusting on right side, brownish color), and e) balanids and serpulids. Also see supplementary video files in S4–S8 Figs.
Table 2.
Coral substrates deployed on December 3rd 2013 at Matapalo Reef with date of collection, pre- and post-experimental weight, CaCO3 loss and indication, which individual substrates per exposure time are presented in Figures.
Fig 6.
SEM images of cast-embedded and partially etched cross sections of coral substrates with positive infills of microbioerosion traces on the skeletal surface.
Shown are coral substrates of a) control, and after b) one month, c) two months, d) three months, and e) four months of exposure. Most of the observed bioerosion traces were produced by euendolithic cyanobacteria complemented by some traces formed by chlorophyte algae and marine fungi. Note the increase in boring density over time and the increase in the depth of penetration into the skeletal structure.
Table 3.
Analysis of variance from the exponential loss rate of CaCO3 mg d-1.
Post-hoc Tukey HSD identified a significantly different rate of CaCO3 loss only in the final month of exposure, after the onset of upwelling (S1 Table). Note that statistical results base on low replication.
Fig 7.
Graphical concept of the role of bioerosion in ETP coral reef community transitions.
Short-term transitions between coral and algal dominance can occur due to changes in environmental boundary conditions. Coral growth may cease during ENSO events or during periods of intensive upwelling. Eutrophic conditions in the reef favor organotrophic settlers, in particular detritus and filter feeders, including many calcifying encrusting and bioeroding species. Enhanced activity of bioeroders, as an ecological response, supports the re-transition of the reef into an oligotrophic condition by the uptake of nutrients and buffering seawater carbon chemistry (carbonate sediment production and dissolution; influence seawater Ω, pH, AT, pCO2). Additionally, grazers and predators are attracted due to the increase in food or prey abundance. New substrate is formed by predation (reef fish, echinoderms, mollusks) and macrobioerosion, which allows coral dispersal (fragmentation) and formation of rhodolithic substrate serving as larvae settling grounds. The ecological effects benefit the growth of phototrophic calcifiers (i.e. corals, crustose coralline algae). Dashed lines indicate ecological responses to environmental processes (solid lines). Green lines indicate an effect on the reef community towards algal growth and blue lines indicate effects towards coral growth.