Although species interactions are often assumed to be strongest at small spatial scales, they can interact with regional environmental factors to modify food web dynamics across biogeographic scales. The eastern oyster (
This content will become publicly available on December 21, 2023
- Award ID(s):
- 1832221
- NSF-PAR ID:
- 10424623
- Date Published:
- Journal Name:
- Frontiers in Marine Science
- Volume:
- 9
- ISSN:
- 2296-7745
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Crassostrea virginica ) is a widespread foundational species of both ecological and economic importance. The oyster and its associated assemblage of fish and macroinvertebrates is an ideal system to investigate how regional differences in environmental variables influence trophic interactions and food web structure. We quantified multiple environmental factors, oyster reef properties, associated species, and trophic guilds on intertidal oyster reefs within 10 estuaries along 900 km of the southeastern United States. Geographical gradients in fall water temperature and mean water depth likely influenced regional (i.e., the northern, central and southern sections of the SAB) variation in oyster reef food web structure. Variation in the biomass of mud crabs, an intermediate predator, was mostly (84.1%) explained by reefs within each site, and did not differ substantially among regions; however, regional variation in the biomass of top predators and of juvenile oysters also contributed to biogeographic variation in food web structure. In particular, region explained almost half (40.2%) of the variation in biomass of predators of blue crab, a top predator that was prevalent only in the central region where water depth was greater. Field experiments revealed that oyster mortality due to predation was greatest in the central region, suggesting spatial variation in the importance of trophic cascades. However, high oyster recruitment in the middle region probably compensates for this enhanced predation, potentially explaining why relatively less variation (17.9%) in oyster cluster biomass was explained by region. Region also explained over half of the variation in biomass of mud crab predators (55.2%), with the southern region containing almost an order of magnitude more biomass than the other two regions. In this region, higher water temperatures in the fall corresponded with higher biomass of fish that consume mud crabs and of fish that consume juvenile and forage fish, whereas biomas of their prey (mud crabs and juvenile and forage fish, respectively) was generally low in the southern region. Collectively, these results show how environmental gradients interact with trophic cascades to structure food webs associated with foundation species across biogeographic regions. -
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Abstract When prey alter behavioral or morphological traits to reduce predation risk, they often incur fitness costs through reduced growth and reproduction as well as increased mortality that are known as nonconsumptive effects (NCEs). Environmental context and trophic structure can individually alter the strength of NCEs, yet the interactive influence of these contexts in natural settings is less understood. At six sites across 1000 km of the Southeastern Atlantic Bight (SAB), we constructed oyster reefs with one, two, or three trophic levels and evaluated the traits of focal juvenile oysters exposed to predation risk cues. We monitored environmental variables (water flow velocity, microalgal resources, and oyster larval recruitment) that may have altered how oysters respond to risk, and we also assessed the cost of trait changes to oyster mortality and growth when they were protected from direct predatory loss. Regardless of trophic structure, we found that oyster shell strength and natural oyster recruitment peaked at the center of the region. This high recruitment negated the potential for NCEs by smothering and killing the focal oysters. Also independent of trophic structure, focal oysters grew the most at the northernmost site. In contrast to, and perhaps because of, these strong environmental effects, the oyster traits of condition index and larval recruitment were only suppressed by the trophic treatment with a full complement of risk cues from intermediate and top predators at just the southernmost site. But at this same site, statistically significant NCEs on oyster growth and mortality were not detected. More strikingly, our study demonstrated environmental gradients that differentially influence oysters throughout the SAB. In particular, the results of our trophic manipulation experiment across these gradients suggest that in the absence of predation, environmental differences among sites may overwhelm the influence of NCEs on prey traits and population dynamics.
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