Consumer-driven nutrient recycling of freshwater decapods: Linking ecological theories and application in integrated multitrophic aquaculture

Abstract

The Metabolic Theory of Ecology (MTE) and the Ecological Stoichiometry Theory (EST) are central and complementary in the consumer-driven recycling conceptual basis. The understanding of physiological processes of organisms is essential to explore and predict nutrient recycling behavior, and to design integrated productive systems that efficiently use the nutrient inputs through an adjusted mass balance. We fed with fish-feed three species of decapods (prawn, anomuran, crab) from different families and with aquacultural potential to explore the animal-mediated nutrient dynamic and its applicability in productive systems. We tested whether body mass, body elemental content, and feeds predict N and P excretion rates and ratios within taxa. We also verified if body content scales allometrically with body mass within taxa. Finally, we compared the nutrient excretion rates and body elemental content among taxa. N excretion rates of prawns and anomurans were negatively related to body mass, emphasizing the importance of MTE. Feed interacted with body mass to explain P excretion of anomurans and N excretion of crabs. Body C:N content positively scaled with body mass in prawns and crabs. Among taxa, prawns mineralised more N and N:P, and less P, and exhibited higher N and C body content (and lower C:N) than the other decapods. Body P and N:P content were different among all species. Body content and body mass were the main factors that explained the differences among taxa and influence the role of crustaceans as nutrient recyclers. These features should be considered to select complementary species that efficiently use feed resources. Prawns need more protein in feed and might be integrated with fish of higher N-requirements, in contrast to crabs and anomurans. Our study contributed to the background of MTE and EST through empirical data obtained from decapods and it provided insightful information to achieve more efficient aquaculture integration systems.

Fig 1

Within taxa relationships between N excretion and body mass of Macrobrachium borellii (a) and Aegla uruguayana (b), between P excretion and body mass of Aegla uruguayana (c); between N excretion and body N content of Macrobrachium borellii (d). Macrobrachium borellii (black circle) (a, d), Aegla uruguayana (dark gray square) (b, c). The excretion rates values were expressed by hour, but the measures were taken at 30 minutes.

Fig 2

Linear regressions within taxa of body content of C:N as a function of invertebrate body mass of Macrobrachium borellii (a), Trichodactylus borellianus (b). Macrobrachium borellii (black circle) (a), Trichodactylus borellianus (light gray triangle) (b).

Fig 3

Box plots of excretion rates of N, P and N:P of each decapod species (a, b, c). The top, bottom, and line through the middle of the boxes correspond to the 75th, 25th, and 50th (median) percentile. The whiskers extended from the 10th percentile to the 90th percentile. Crosses indicate the median values. Different letters above bars indicate significant differences among taxa (p < 0.05). The excretion rates values were expressed by hour, but the measures were taken at 30 minutes.

Fig 4. Box plots of body content of N, P, C and N:P, C:N, C:P of each decapod species.

The top, bottom, and line through the middle of the boxes correspond to the 75th, 25th, and 50th (median) percentile, respectively. The whiskers extended from the 10th percentile to the 90th percentile. Crosses indicate the median values. Different letters above bars indicate significant differences among taxa (p < 0.05).

Fig 5. Principal component analysis with log10-transformed of nutrient excretion rates (N and P) and ratio (N:P), body elemental contents (body N, P, C and body N: P, C:N, C:P) and body mass.

Macrobrachium borellii (black circle), Aegla uruguayana (dark gray square), Trichodactylus borellianus (open triangle).