Title: THE INFLUENCE OF UPWELLING ON THE TROPHIC STATUS OF CORALS FROM THE SHALLOW AND DEEP SLOPE IN THE CENTRAL MALDIVES

Abstract: Upwelling stimulates primary productivity, which is known to support megafauna but the influence of upwelling on coral is understudied. Nutrient availability and light are important for coral symbiosis with increasing depth. Here we use natural abundance stable isotopes to examine the assimilation of carbon (d13C) and nitrogen (d15N) by the coral host and algal symbiont. We investigate how depth, reef exposure and atoll position affects the trophic status of three corals. The central Maldives is a unique location to study the influence of upwelling on coral reefs due to its bathymetry and monsoonal climate. Temperature records reveal cold-water influxes extend to the deep (30 m) slope, but not shallow (10 m). Depth and genus significantly affected both isotope compositions. d13C values significantly differed among coral, with a spectrum of heterotrophy to autotrophy for Pocillopora and Pachyseris, respectively. Depth significantly affected coral trophic status, particularly Galaxea, which relied more on heterotrophy at 30 m. Differential d13C may also indicate diverse fractionation patterns in the symbiont, which we investigate next. d15N suggest that deep-water nitrate is a primary nitrogen source for these corals. Moreover, the interaction of i) coral, depth, and atoll position, ii) coral and reef exposure, and iii) reef exposure and atoll position had a significant effect on both isotope values of host and symbiont. Our results provide insight into factors influencing coral trophic status, which is important to consider for coral fitness especially during thermal stress.

Authors: Radice VZ, Hoegh-Guldberg O, Fry B, Dove SG

Presentation: Oral

Session: 10

Date: 06/20/16

Time: 14:45

Location: 317 A/B

Back