Variable nutrient stoichiometry (carbon:nitrogen:phosphorus) across trophic levels determines community and ecosystem properties in an oligotrophic mangrove system

Abstract

Our study investigated the carbon:nitrogen:phosphorus (C:N:P) stoichiometry of mangrove island of the Mesoamerican Barrier Reef (Twin Cays, Belize). The C:N:P of abiotic and biotic components of this oligotrophic ecosystem was measured and served to build networks of nutrient flows for three distinct mangrove forest zones (tall seaward fringing forest, inland dwarf forests and a transitional zone). Between forest zones, the stoichiometry of primary producers, heterotrophs and abiotic components did not change significantly, but there was a significant difference in C:N:P, and C, N, and P biomass, between the functional groups mangrove trees, other primary producers, heterotrophs, and abiotic components. C:N:P decreased with increasing trophic level. Nutrient recycling in the food webs was highest for P, and high transfer efficiencies between trophic levels of P and N also indicated an overall shortage of these nutrients when compared to C. Heterotrophs were sometimes, but not always, limited by the same nutrient as the primary producers. Mangrove trees and the primary tree consumers were P limited, whereas the invertebrates consuming leaf litter and detritus were N limited. Most compartments were limited by P or N (not by C), and the relative depletion rate of food sources was fastest for P. P transfers thus constituted a bottleneck of nutrient transfer on Twin Cays. This is the first comprehensive ecosystem study of nutrient transfers in a mangrove ecosystem, illustrating some mechanisms (e.g. recycling rates, transfer efficiencies) which oligotrophic systems use in order to build up biomass and food webs spanning various trophic levels.

Climate effects on fish body size–trophic position relationship depend on ecosystem type

“…Carbon-limited organisms in warmer climates, therefore, should prefer to ingest a food source with higher carbon-to-nutrient ratio, while in colder temperatures nutrients should assume the limiting role (Moody et al 2019). In warmer waters, the preference to forage on carbon-rich resources can manifest for both carnivorous and omnivorous fish, as prey carbon-to-nutrient ratios tend to increase at lower trophic levels (Gonzalez et al 2011, Scharler et al 2015. However, this foraging strategy should be even more represents the adjusted pattern of fish trophic position for the tropical climate as a deviation from the pattern observed for freshwater ecosystems across both climates.…”

Are global mangrove carbon stocks driven by rainfall?

“…Therefore, increasing rainfall driven by climate change [ Huang et al , ; Wentz et al , ] may potentially increase belowground carbon stocks as indicated in our predictive model (Figure ). However, there are other potentially important factors that may regulate organic matter diagenesis, such as nutrient availability [ Lovelock et al , ; Scharler et al , ], species diversity, and sea level rise [ Lovelock et al , ].…”

“…Carbon sequestration in mangroves may be influenced by climatic factors (e.g., temperature, rainfall, and evapotranspiration), coastal oceanographic process (e.g., tidal amplitude, currents, and geomorphology) [ Alongi , ; Breithaupt et al , ], and nutrient availability [ Lovelock et al , ; Scharler et al , ]. Even though many of these parameters have been proposed as influencing ecosystem soil stocks, predictions of mangrove's capacity to store carbon have been largely based on an assumed relationship between carbon pools and climatic gradients [ Hutchison et al , ; Jardine and Siikamäki , ; Rovai et al , ; Saenger and Snedaker , ].…”

Anthropogenic global shifts in biospheric N and P concentrations and ratios and their impacts on biodiversity, ecosystem productivity, food security, and human health

“…Changes in N and/or P availability and associated shifts in N:P ratios drive changes in species competition and dominance in communities of terrestrial plants (Sardans, Rodà, & Penuelas, ; Zhang, Liu, et al, ), animals (Jochum et al, ), microbes (Delgado‐Baquerizo et al, ; Fanin, Fromin, Biatois, & Hättenschwiler, ; Ren et al, ; Shao et al, ; Zechmeister‐Bolstenstren et al, ), and plankton (Elser, Andersen, et al, ; Elser, Kyle, et al, ; Grosse, Burson, Stomp, Huisman, & Boschker, ; He, Li, Wei, & Tan, ; Moorthi et al, ; Plum, Husener, & Hillebrand, ). Changes in media (water or soil) N:P ratios affect the structure of terrestrial (Fanin et al, ; Scharler et al, ; Zechmeister‐Bolstenstren et al, ) and aquatic (Sitters, Atkinson, Guelzow, Kelly, & Sullivan, ) food webs, but associated impacts on community diversity are unclear. For example, some studies have reported increases in N:P ratios due to N deposition or land‐use change associated with reduced diversity of microbes (Zhang, Chen, & Ruan, ), plants (DeMalach, ; Güsewell, Bailey, Roem, & Bedford, ), and animals (Vogels, Verbek, Lamers, & Siepel, ; Wei et al, ), but other studies have found increases in microbial (Aanderud et al, ; Ren et al, ; ) and plant (Laliberté et al, ; Pekin, Boer, Wittkuhn, Macfarlane, & Grieson, ; Wassen et al, ; Yang et al, ) diversity.…”