An overall synthesis of biology and non-equilibrium thermodynamics remains a challenge at the interface between the physical and life sciences. Herein, theorems from finite-time and control thermodynamics are applied to biological processes to indicate which biological strategies will succeed over different time scales. In general, living systems maximize power at the expense of efficiency during the early stages of their development while proceeding at slower rates to maximize efficiency over longer time scales. The exact combination of yield and power depends upon the constraints on the system, the degrees of freedom in question, and the time scales of the processes. It is emphasized that biological processes are not driven by entropy production but, rather, by informed exergy flow. The entropy production is the generalized friction that is minimized insofar as the constraints allow. Theorems concerning thermodynamic path length and entropy production show that there is a direct tradeoff between the efficiency of a process and the process rate. To quantify this tradeoff, the concepts of compensated heat and waste heat are introduced. Compensated heat is the exergy dissipated, which is necessary for a process to satisfy constraints. Conversely, waste heat is exergy that is dissipated as heat, but does not provide a compensatory increase in rate or other improvement. We hypothesize that it is waste heat that is minimized through natural selection. This can be seen in the strategies employed at several temporal and spatial scales, including organismal development, ecological succession, and long-term evolution. Better understanding the roles of compensated heat and waste heat in biological processes will provide novel insight into the underlying thermodynamic mechanisms involved in metabolism, ecology, and evolution.
On coral reefs, microorganisms are essential for recycling nutrients to primary producers through the remineralization of benthic-derived organic matter. Diel investigations of reef processes are required to holistically understand the functional roles of microbial players in these ecosystems. Here we report a metagenomic analysis characterizing microbial communities in the water column overlying 16 remote forereef sites over a diel cycle. Our results show that microbial community composition is more dissimilar between day and night samples collected from the same site than between day or night samples collected across geographically distant reefs. Diel community differentiation is largely driven by the flux of Psychrobacter sp., which is two-orders of magnitude more abundant during the day. Nighttime communities are enriched with species of Roseobacter , Halomonas , and Alteromonas encoding a greater variety of pathways for carbohydrate catabolism, further illustrating temporal patterns of energetic provisioning between different marine microbes. Dynamic diel fluctuations of microbial populations could also support the efficient trophic transfer of energy posited in coral reef food webs.
The natural beauty of coral reefs attracts millions of tourists worldwide resulting in substantial revenues for the adjoining economies. Although their visual appearance is a pivotal factor attracting humans to coral reefs current monitoring protocols exclusively target biogeochemical parameters, neglecting changes in their aesthetic appearance. Here we introduce a standardized computational approach to assess coral reef environments based on 109 visual features designed to evaluate the aesthetic appearance of art. The main feature groups include color intensity and diversity of the image, relative size, color, and distribution of discernable objects within the image, and texture. Specific coral reef aesthetic values combining all 109 features were calibrated against an established biogeochemical assessment (NCEAS) using machine learning algorithms. These values were generated for ∼2,100 random photographic images collected from 9 coral reef locations exposed to varying levels of anthropogenic influence across 2 ocean systems. Aesthetic values proved accurate predictors of the NCEAS scores (root mean square error < 5 for N ≥ 3) and significantly correlated to microbial abundance at each site. This shows that mathematical approaches designed to assess the aesthetic appearance of photographic images can be used as an inexpensive monitoring tool for coral reef ecosystems. It further suggests that human perception of aesthetics is not purely subjective but influenced by inherent reactions towards measurable visual cues. By quantifying aesthetic features of coral reef systems this method provides a cost efficient monitoring tool that targets one of the most important socioeconomic values of coral reefs directly tied to revenue for its local population.
16Primary production due to photosynthesis results in daytime oxygen production across marine and 17 freshwater ecosystems. However, a prevalent, globally-occurring nighttime spike in dissolved oxygen 18 (DO) challenges our traditional assumption that oxygen production is limited to daylight hours, 19 particularly in tropical coral reefs. When considered in the context of ecosystem oxygen budget estimates, 20 these nocturnal spikes in DO could account for up to 24 percent of the daytime oxygen production. Here 21 we show, 1) the widespread nature of this phenomenon, 2) the reproducibility across tropical marine 22 ecosystems, 3) the lack of a consistent abiotic mechanism across all datasets we examined, and 4) the 23 observation of nighttime DO spikes in vitro from incubations of coral reef benthic samples. Our study 24suggests that in addition to physical forcing, biological processes may be responsible for the production 25 of oxygen at night, a finding that demands additional research. 26
16Primary production due to photosynthesis results in daytime oxygen production across marine and 17 freshwater ecosystems. However, a prevalent, globally-occurring nighttime spike in dissolved oxygen 18 (DO) challenges our traditional assumption that oxygen production is limited to daylight hours, 19 particularly in tropical coral reefs. When considered in the context of ecosystem oxygen budget estimates, 20 these nocturnal spikes in DO could account for up to 24 percent of the daytime oxygen production. Here 21 we show, 1) the widespread nature of this phenomenon, 2) the reproducibility across tropical marine 22 ecosystems, 3) the lack of a consistent abiotic mechanism across all datasets we examined, and 4) the 23 observation of nighttime DO spikes in vitro from incubations of coral reef benthic samples. Our study 24suggests that in addition to physical forcing, biological processes may be responsible for the production 25 of oxygen at night, a finding that demands additional research. 26
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