The carbon and nitrogen budget of Desmophyllum dianthus—a voracious cold-water coral thriving in an acidified Patagonian fjord

Abstract

In the North Patagonian fjord region, the cold-water coral (CWC) Desmophyllum dianthus occurs in high densities, in spite of low pH and aragonite saturation. If and how these conditions affect the energy demand of the corals is so far unknown. In a laboratory experiment, we investigated the carbon and nitrogen (C, N) budget of D. dianthus from Comau Fjord under three feeding scenarios: (1) live fjord zooplankton (100–2,300 µm), (2) live fjord zooplankton plus krill (>7 mm), and (3) four-day food deprivation. In closed incubations, C and N budgets were derived from the difference between C and N uptake during feeding and subsequent C and N loss through respiration, ammonium excretion, release of particulate organic carbon and nitrogen (POC, PON). Additional feeding with krill significantly increased coral respiration (35%), excretion (131%), and POC release (67%) compared to feeding on zooplankton only. Nevertheless, the higher C and N losses were overcompensated by the threefold higher C and N uptake, indicating a high assimilation and growth efficiency for the krill plus zooplankton diet. In contrast, short food deprivation caused a substantial reduction in respiration (59%), excretion (54%), release of POC (73%) and PON (87%) compared to feeding on zooplankton, suggesting a high potential to acclimatize to food scarcity (e.g., in winter). Notwithstanding, unfed corals ‘lost’ 2% of their tissue-C and 1.2% of their tissue-N per day in terms of metabolism and released particulate organic matter (likely mucus). To balance the C (N) losses, each D. dianthus polyp has to consume around 700 (400) zooplankters per day. The capture of a single, large krill individual, however, provides enough C and N to compensate daily C and N losses and grow tissue reserves, suggesting that krill plays an important nutritional role for the fjord corals. Efficient krill and zooplankton capture, as well as dietary and metabolic flexibility, may enable D. dianthus to thrive under adverse environmental conditions in its fjord habitat; however, it is not known how combined anthropogenic warming, acidification and eutrophication jeopardize the energy balance of this important habitat-building species.

Environmental stability and phenotypic plasticity benefit the cold-water coral Desmophyllum dianthus in an acidified fjord

“…3a , Supplementary Results, and Supplementary Fig. 6 ), possibly fuelled by higher food intake 83 , 84 (but also see Supplementary Discussion for temperature effects on respiration rates of deep corals). While the higher food availability appears to contradict the zooplankton data, it has to be taken into account that other factors (e.g.…”

“…A laboratory study by Maier et al 84 clearly indicates that prey size is important. With a diet of small fjord zooplankton, D. dianthus requires a minimum of 700 individuals per day to balance metabolic needs, while the addition of one euphausiid provides a positive scope for growth 84 . Euphausiids are known to form dense swarms in Chilean fjords 85 , 86 , but data from the immediate vicinity of the corals are missing.…”

“…Euphausiids are underrepresented in the study by Garcia-Herrera et al 48 as they are active swimmers capable of escaping plankton nets at low tow speeds. Mysids account for up to 70% of the zooplankton volume and abundance in deep waters of Comau Fjord in all seasons and may provide a reliable food source for deep corals throughout the year 48 with potentially similar energy gain as derived from euphausiids 84 , 87 . Thus, a difference in zooplankton composition may compensate for a large difference in zooplankton abundance between depths, and together with other drivers (high-frequency fluctuations, competition, behavioural adaptation), contribute to differences in energy gain.…”

Lipid biomarkers reveal trophic relationships and energetic trade‐offs in contrasting phenotypes of the cold‐water coral Desmophyllum dianthus in Comau Fjord, Chile

“…While most tropical corals are mixotrophic due to their symbiosis with Symbiodiniacea algae in shallow water, the deep-dwelling and higher latitude cold-water corals (CWCs) are exclusively heterotrophic. The availability of food (both in quantity and quality), however, affects an organism's physiological performance, like their metabolic rate and growth, as has been observed in CWCs (Larsson et al, 2013;Maier et al, 2021;Naumann et al, 2011).…”

“…However, combined changes in physico-chemical conditions and food availability (multiple stressors) have been shown to compromise performance in CWCs (Büscher et al, 2019;Hennige et al, 2015) and other foundation species (Ingels et al, 2012). Similar to other benthic suspension-feeding omnivores, CWCs gain their metabolic energy strictly from heterotrophic feeding on a variety of food particles ranging from microbes to phyto-and zooplankton (Duineveld et al, 2004;Höfer et al, 2018;Maier et al, 2019;Mueller et al, 2014;Rakka et al, 2021), where the zooplankton appears to provide a key energy source to sustain their metabolic needs (Maier et al, 2019(Maier et al, , 2020(Maier et al, , 2021Naumann et al, 2011). Thus, the relative availability of food along the in situ plankton size spectrum may be crucial to determine the coral adaptation capability to future environmental conditions.…”