Variation in coral photosynthesis, respiration and growth characteristics in contrasting light microhabitats: an analogue to plants in forest gaps and understoreys?

Abstract

Summary 1.The often complex architecture of coral reefs forms a diversity of light microhabitats. Analogous to patterns in forest plants, light variation may drive strategies for efficient light utilization and metabolism in corals. 2. We investigated the spatial distribution of light regimes in a spur-and-groove reef environment and examine the photophysiology of the coral Montipora monasteriata (Forskål 1775), a species with a wide habitat distribution. Specifically, we examined the variation in tissue and skeletal thickness, and photosynthetic and metabolic responses among contrasting light microhabitats. 3. Daily irradiances reaching corals in caves and under overhangs were 1-5 and 30-40% of those in open habitats at similar depth (3-5 m), respectively. Daily rates of net photosynthesis of corals in cave habitats approximated zero, suggesting more than two orders of magnitude variation in scope for growth across habitats. 4. Three mechanisms of photoadaptation or acclimation were observed in cave and overhang habitats: (1) a 20-50% thinner tissue layer and 40-60% thinner skeletal plates, maximizing light interception per unit mass; (2) a two-to threefold higher photosynthetic efficiency per unit biomass; and (3) low rates of dark respiration. 5.Specimens from open and cave habitats displayed a high capacity to acclimate to downshifts or upshifts in irradiance, respectively. However, specimens in caves displayed limited acclimation to further irradiance reduction, indicating that these live near their irradiance limit. 6. Analogous to patterns for some plant species in forest gaps, the morphological plasticity and physiological flexibility of M. monasteriata enable it to occupy light habitats that vary by more than two orders of magnitude.

Deep in shadows, deep in time: the oldest mesophotic coral ecosystems from the Devonian of the Holy Cross Mountains (Poland)

“…Light capture, however, is a purely physical process, and relevant adaptations are most probably not related to the systematic position of the groups of corals investigated. Such analogies can even be relevant across kingdoms (Anthony and Hoegh-Guldberg 2003). Models inferred from Recent scleractinians probably also work for other calcifying, photosynthetic organisms.…”

“…A species can display bulbous or massive morphology in shallow waters, but in deeper water the same species becomes flattened, as in the case of the Caribbean Montastraea cavernosa (Baker et al 2016). Under a low light regime corals tend to grow toward the expanding surface rather than by expanding volume (Anthony and Hoegh-Guldberg 2003), and production of a platy skeleton is energetically more efficient . In general, shade-dwelling corals have flat morphologies and small sizes of coralla, mostly 20-60 cm (Dinesen 1983).…”

“…In general, shade-dwelling corals have flat morphologies and small sizes of coralla, mostly 20-60 cm (Dinesen 1983). MCEs are dominated by platy or encrusting corals, and such a morphology is broadly considered as photoadaptive growth (e.g., Macintyre 1976, 1982;Rosen et al 2002;Anthony and Hoegh-Guldberg 2003;Kahng et al 2010Kahng et al , 2012Kahng et al , 2014. Platy morphologies in scleractinians were possibly widespread in Meso-and Cainozoic reefs (Rosen et al 2002), and are indicative of photosymbiosis in fossil record (e.g., Insalaco 1996;Rosen et al 2002;Santodomingo et al 2015).…”

Ocean acidification causes bleaching and productivity loss in coral reef builders

“…Net productivity was estimated from daytime assays of maximum net rates of photosynthesis (PNetMax, 10 a.m.-3 p.m.) under controlled artificial lighting (200 W metal-halide lamp, AquaMedic, Germany) simulating daytime environmental irradiances of Ϸ1000 mol photons m Ϫ2 s Ϫ1 in situ and nighttime assays of dark respiration (Rdark, 8 p.m.-2 a.m.). Photosynthesis and respiration measurements were conducted using four sealed, recirculating respirometry chambers with flow regimes simulating natural conditions (44), each chamber connected to a high-precision optical oxygen sensor (optode) and logging system (Oxy-4, Presens, Germany). Oxygen fluxes of all specimens were normalized to tissue surface area determined from geometric analyses of digital photographs (Image Tools, The University of Texas Health Science Centre).…”

Modelling coral calcification accounting for the impacts of coral bleaching and ocean acidification

“…the amount of solar radiation incident to the Earth's surface (kW m −2 day −1 ; see equation in the Appendix). Photosynthesis-irradiance (P − I ) curves for corals have been extensively studied, and how their parameters change with local light environment has been well established (Anthony and Hoegh-Guldberg, 2003a;Chalker et al, 1983;Dubinsky et al, 1984;Mass et al, 2007;Porter et al, 1984). These studies show that there is a strong decrease in the saturation intensity as ambient light levels decrease, which corresponds to an increase in the efficiency of photosynthesis.…”