Multiple driving factors explain spatial and temporal variability in coral calcification rates on the Bermuda platform

Abstract

Experimental studies have shown that coral calcification rates are dependent on light, nutrients, food availability, temperature, and seawater aragonite saturation (X arag ), but the relative importance of each parameter in natural settings remains uncertain. In this study, we applied Calcein fluorescent dyes as time indicators within the skeleton of coral colonies (n = 3) of Porites astreoides and Diploria strigosa at three study sites distributed across the northern Bermuda coral reef platform. We evaluated the correlation between seasonal average growth rates based on coral density and extension rates with average temperature, light, and seawater X arag in an effort to decipher the relative importance of each parameter. The results show significant seasonal differences among coral calcification rates ranging from summer maximums of 243 ± 58 and 274 ± 57 mmol CaCO 3 m -2 d -1 to winter minimums of 135 ± 39 and 101 ± 34 mmol CaCO 3 m -2 d -1 for P. astreoides and D. strigosa, respectively. We also placed small coral colonies (n = 10) in transparent chambers and measured the instantaneous rate of calcification under light and dark treatments at the same study sites. The results showed that the skeletal growth of D. strigosa and P. astreoides, whether hourly or seasonal, was highly sensitive to X arag . We believe this high sensitivity, however, is misleading, due to covariance between light and X arag , with the former being the strongest driver of calcification variability. For the seasonal data, we assessed the impact that the observed seasonal differences in temperature (4.0°C), light (5.1 mol photons m -2 d -1 ), and X arag (0.16 units) would have on coral growth rates based on established relationships derived from laboratory studies and found that they could account for approximately 44, 52, and 5 %, respectively, of the observed seasonal change of 81 ± 14 mmol CaCO 3 m -2 d -1 . Using short-term light and dark incubations, we show how the covariance of light and X arag can lead to the false conclusion that calcification is more sensitive to X arag than it really is.

Herbivory facilitates growth of a key reef‐building Caribbean coral

“…In this study, we used Hobo data loggers to observe that mean light intensity incident at uncaged control plates on a particular day was slightly (4.7%) higher than within half cages, which in turn was (10.9%) greater than within full cages. However, coral calcification rates are relatively insensitive to such minor reductions in light intensity and consequently cage effects could only account for a small fraction of the differences in calcification between herbivore treatments (Venti, Andersson, & Langdon, ).…”

Species‐specific responses to climate change and community composition determine future calcification rates of Florida Keys reefs

“…Underscoring how reefs may vary in their responses to climate change, recent studies of reefs under elevated p CO 2 have documented stable states ranging from reduced growth (Manzello, ; Fabricius et al ., ) to tolerance (Shamberger et al ., , ) to phase shifts to macroalgae‐dominated systems (Enochs et al ., ). Furthermore, temperature often exerts a larger measurable influence on growth than Ω arag (Helmle et al ., ; Carricart‐Ganivet et al ., ; Venti et al ., ). This pattern is not surprising when the relative sensitivities of coral growth to temperature and Ω arag are compared to the annual variation of each parameter.…”

Aragonite saturation and pH variation in a fringing reef are strongly influenced by oceanic conditions

“…This seasonal variability is one of the largest ranges recorded in reefs worldwide. For example, the Saboga coral reef in the Gulf of Panama changed by at most 0.17 units between the wet and dry seasons (with and without upwelling, respectively; Manzello et al ), whereas a range of 0.16 units ΔΩ arag (0.3 units) between the wet and dry seasons (summer and winter) occurred in Bermuda (Bates et al ; Venti et al ). Differences as high as 0.54 units ΔΩ arag were observed between seasons (winter and summer in three offshore areas) in the Florida Reef Tract (Manzello et al ).…”

“…The latter is relevant to ocean acidification forecasts, which are based on measured oceanic data (Kleypas et al b ; Feely et al ; Dore et al ), and can be valid for fringing reefs under a direct oceanic influence, such as the Cabo Pulmo reef or the Galapagos Islands coral reefs, where large‐scale oceanographic variability controls the CO 2 system with little noticeable biological influence (Manzello et al ). In contrast, other reefs, such as barrier reefs, reef tracts, reef flats, and atolls, are subjected to a greater level of control over aragonite saturation and pH because of a high residence time and are capable of functioning as buffers to the seawater entering the reef through biological processes (Kleypas et al ; Manzello et al ; Shaw et al ; Venti et al ).…”