Abstract
In biological systems energy serves as the ultimate commodity, often determining species distributions, abundances, and interactions including the potential impact of invasive species on native communities. The Asian clam Potamocorbula amurensis invaded the San Francisco Estuary (SFE) in 1986 and is implicated in the decline of native fish species through resource competition. Using a combined laboratory/field study we examined how energy expenditure in this clam is influenced by salinity, temperature and food availability. Measures of metabolism were made at whole organism (metabolic rate) and biochemical (pyruvate kinase (PK) and citrate synthase (CS) enzyme activities) levels. We found in the field, over the course of a year, the ratio of PK to CS was typically 1.0 suggesting that aerobic and fermentative metabolism were roughly equivalent, except for particular periods characterized by low salinity, higher temperatures, and intermediate food availabilities. In a 30-day laboratory acclimation experiment, however, neither metabolic rate nor PK:CS ratio was consistently influenced by the same variables, though the potential for fermentative pathways did predominate. We conclude that in field collected animals, the addition of biochemical measures of energetic state provide little additional information to the previously measured whole organism metabolic rate. In addition, much of the variation in the laboratory remained unexplained and additional variables, including reproductive stage or body condition may influence laboratory-based results. Further study of adult clams must consider the role of organismal condition, especially reproductive state, in comparisons of laboratory experiments and field observations.
Highlights
Within biological communities energy serves as the ultimate commodity, determining broad patterns of distribution, abundance, persistence, and migration [1], [2]
The two enzymes were strongly correlated in mantle tissue (Figure 2) (Pearson correlation = 0.58, t58 = 5.47, p,0.001), though on two dates (DOY: 180 and 298) pyruvate kinase (PK) activity exceeded citrate synthase (CS) activity
If these two dates are removed the correlation between PK and CS is 0.87 illustrating that these points are considerably different from the others
Summary
Within biological communities energy serves as the ultimate commodity, determining broad patterns of distribution, abundance, persistence, and migration [1], [2]. Identifying how a species, especially an invasive species, will impact a native habitat, its potential to expand its range, and its persistence in a changing environment all require an understanding of how that species processes and exchanges energy with the environment [4], [5] (e.g., through feeding mode and intensity). A decline in abundance of three common estuarine copepod species coincided with the invasion of P. amurensis [10], probably through a combination of predation and competition for phytoplankton and microzooplankton resources. Concurrent declines in the abundance of higher trophic level pelagic taxa including delta smelt Hypomesus transpacificus [12], mysid shrimp Neomysis mercedis [13], longfin smelt Spirinchus thaleichthys [14], and striped bass Morone saxatilis [15] have occurred, all presumably due to food limitation
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