Mass coral spawning: A natural large‐scale nutrient addition experiment

Abstract

A mass coral spawning event on the Heron Island reef flat in 2005 provided a unique opportunity to examine the response of a coral reef ecosystem to a large episodic nutrient addition. A post-major spawning phytoplankton bloom resulted in only a small drawdown of dissolved inorganic phosphorus (DIP minimum 5 0.37 mmol L 21 ), compared with almost complete removal of dissolved inorganic nitrogen (DIN) (minimum NO, suggesting that pelagic primary production is potentially N limited on the timescale of this study. DIN, DIP, dissolved organic nitrogen (DON), and dissolved organic phosphorus were used in the production of biomass, and mass balance calculations highlighted the importance of organic forms of N and P for benthic and pelagic production in tropical coral reef environments characterized by low inorganic N and P. The input of N and P via the deposition of coral spawn and associated phytodetritus resulted in large changes to N cycling in the sediments, but only small changes to P cycling, because of the buffering capacity provided by the large pool of bioavailable P. It is most likely that this large pool of bioavailable P in the sediments drives potential N limitation of benthic coral reef communities. For example, there was sufficient bioavailable P stored in the top 10 cm of the sediment column to sustain the prespawning rates of benthic production for over 200 d. Most of the change in benthic N cycling occurred via DON and N 2 pathways, driven by changes in the quantity and quality of organic matter deposited and decomposed post-major spawning. The heterotrophic and autotrophic microbial communities within the coral reef sands were able to rapidly (6 to 7 d) process the large episodic load of N and P provided by coral mass spawning.

The short-term combined effects of temperature and organic matter enrichment on permeable coral reef carbonate sediment metabolism and dissolution

“…These results agree with prior work, where increased concentrations of OM were quickly aerobically degraded by bacteria within minutes to hours (Ferrier-Pages et al, 2000) and enhanced GPP more than R Eyre et al, 2008). While some of this OM was likely degraded in the water column, previous experiments (e.g.…”

“…Wild et al, 2004a;24 h) or coral spawn and phytodetritus (e.g. Eyre et al, 2008; 1 week), on coral reef sediment metabolism have shown a short-term increase in GPP / R, contrasting the results provided from short-term temperature studies on coral reef sediments, where GPP / R decreased (Trnovsky et al, 2016;24 h). Experimental additions of coral mucus from Acropora spp.…”

Coral sand O2 uptake and pelagic–benthic coupling in a subtropical fringing reef, Aqaba, Red Sea

“…sediments can rapidly pick up organic matter that is then degraded over a longer time period), despite their function as biocatalytical filter systems (Wild et al 2004a(Wild et al ,c, 2008. This is supported by Eyre et al (2008), who demonstrated the buffer function of reef sediments for phosphorus. After a sedimentation event, organic matter may be adsorbed by the relatively large surface area of the porous carbonate grains , loading the porous matrix with degradable material like a sponge soaking up water.…”

Functional significance of dinitrogen fixation in sustaining coral productivity under oligotrophic conditions

“…Despite the observed seasonal variability in Symbiodinium population density, all corals maintained high gross productivity and organic matter release throughout the year, indicating high metabolic plasticity to seasonal variation in environmental conditions. For tropical coral reefs, it is widely accepted that N is the most limiting nutrient to coral primary productivity [19]. Phosphorus (P) may also be limiting to coral metabolism [47], particularly in the case of an imbalanced nutrient supply with excess inorganic N (e.g.…”

“…Additionally, corals have evolved strategies to exploit any source of inorganic N [18], enabling them to survive in oligotrophic tropical waters where N is the most limiting nutrient to primary productivity [19,20]. However, the abundance of symbiotic Symbiodinium within the coral host is limited by N concentrations [4,21].…”