Is the tetrasporophyte of Asparagopsis armata (Bonnemaisoniales) limited by inorganic carbon in integrated aquaculture?¹

Abstract

Seaweeds cultivated in traditional land-based tank systems usually grow under carbon-limited conditions and consequently have low production rates, if no costly artificial source of inorganic carbon is supplied. In integrated aquaculture, the fish effluents provide an extra source of dissolved inorganic carbon (DIC) to seaweeds due to fish respiration. To evaluate if the tetrasporophyte of Asparagopsis armata (Harv.) F. Schmitz (the Falkenbergia stage) is carbon limited when cultivated with effluents of a fish (Sparus aurata) farm in southern Portugal, we characterized the DIC forms in the water, assessed the species photosynthetic response to the different DIC concentrations and pH values, and inferred for the presence of a carbonic anhydrase (CA)-mediated mechanism. Results showed that A. armata relies mainly on CO 2 to meet photosynthetic needs. Nevertheless, from pH 7.5 upward, the CO 2 supply to RUBISCO seems to derive also from the external dehydration of HCO 3 -mediated by CA. The contribution of this mechanism was essential for A. armata to attain fully saturated O 2 -evolution rates at the natural seawater DIC concentration (2-2.2 mM) and pH values ($8.0). We revealed in this study that seaweeds cultivated in fish-farm effluents benefit not only from a rich source of ammonia but also from an important and free source of DIC for their photosynthesis. If supplied at relatively high turnover rates ($100 vol AE d )1 ), fish-farm effluents provide enough carbon to maximize the photosynthesis and growth even for species with low affinity for HCO 3 -, avoiding the artificial and costly supply of inorganic carbon to seaweed cultures.

A direct comparison of the performance of the seaweed biofilters, Asparagopsis armata and Ulva rigida

“…armata in this system needs at least three to four effluent exchanges per hour to maintain daily saturating levels of CO 2 for photosynthesis and biomass production (Mata et al 2007). U. rigida on the other hand, after depleting the CO 2 , still has the ability to use HCO 3 − from the DIC pool (Beer 1994).…”

“…In flow-through integrated aquaculture systems, it is crucial to use relatively high effluent renewal rates to supply the algae cultures with non-limiting nitrogen and carbon levels. This allows attaining the best performance by species depending almost exclusively on CO 2 from the dissolved inorganic carbon (DIC) pool for their photosynthesis, such as A. armata (Mata et al 2007).…”

Effects of nutrient supply on photosynthesis and pigmentation in Ulva lactuca (Chlorophyta): responses to short-term stress

“…N supply influences the protein and pigment contents, and the C uptake rate in many types of seaweeds, including the genus Ulva (Gómez-Pinchetti et al 1998). Seaweeds under HNS from fishpond effluents benefit not only from a rich source of ammonia but also from an important and free source of dissolved inorganic C (DIC) coming from fish respiration that becomes available for algal photosynthesis (Mata et al 2007 of Ulva may also be related to high DOC excretion, which Gordillo et al (2003) reported in Ulva that was subjected to increased CO 2. Organic C release has been suggested as an effective mechanism of maintaining the C and N balance in algae in response to low CO 2 levels, although it was an inefficient response to N limitation (Gordillo et al 2003).…”

Effects of hydrogen peroxide on the content of major volatile halogenated compounds in the red alga Asparagopsis taxiformis (Bonnemaisoniaceae)

“…Tanks stocked with Asparagopsis were supplied with fish farm effluents and the optimal cultivation conditions were established (Mata et al , 2007. The production rates obtained were the highest reported so far for land-based cultivated algae in the scientific literature (Mata et al 2010).…”