Cumulative Effects of Nutrient Enrichment and Elevated Temperature Compromise the Early Life History Stages of the Coral Acropora tenuis

PLoS One. 2016 Aug 30;11(8):e0161616. doi: 10.1371/journal.pone.0161616. eCollection 2016.

Abstract

Inshore coral reefs are experiencing the combined pressures of excess nutrient availability associated with coastal activities and warming seawater temperatures. Both pressures are known to have detrimental effects on the early life history stages of hard corals, but studies of their combined effects on early demographic stages are lacking. We conducted a series of experiments to test the combined effects of nutrient enrichment (three levels) and elevated seawater temperature (up to five levels) on early life history stages of the inshore coral Acropora tenuis, a common species in the Indo-Pacific and Red Sea. Gamete fertilization, larval survivorship and larval settlement were all significantly reduced as temperature increased, but only fertilization was further affected by simultaneous nutrient enrichment. Combined high temperatures and nutrient enrichment affected fertilization in an additive manner, whereas embryo abnormalities increased synergistically. Higher than normal temperatures (32°C) increased coral juvenile growth rates 1.6-fold, but mortality also increased by 50%. The co-occurrence of nutrient enrichment with high temperatures reduced juvenile mortality to 36%, ameliorating temperature stress (antagonistic interaction). Overall, the types of effect (additive vs synergistic or antagonistic) and their magnitude varied among life stages. Gamete and embryo stages were more affected by temperature stress and, in some cases, also by nutrient enrichment than juveniles. The data suggest that coastal runoff events might exacerbate the impacts of warming temperatures on fertilization if these events co-occur during corals spawning. The cumulative impacts of simultaneous exposure to nutrient enrichment and elevated temperatures over all early life history stages increases the likelihood for failure of larval supply and recruitment for this coral species. Our results suggest that improving the water quality of river discharges into coastal areas might help to enhance the thermal tolerances of early life history stages in this common coral species.

MeSH terms

  • Animals
  • Anthozoa / growth & development*
  • Coral Reefs
  • Hot Temperature
  • Life Cycle Stages
  • Water Quality

Grants and funding

This study was funded by the Australian Institute of Marine Science the Australian Government’s National Environmental Research Program and the Australian Government’s National Environmental Science Programme. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Adriana Humanes also expresses gratitude for financial support from AIMS@JCU and to the Australian Research Council for support through AusAID.