Pepper Creek, or Pepper’s Creek, depending on who you’re talking to — developers along the headwaters (which originate somewhere west of Dagsboro) have latched onto this charming appellation.
Several pending residential projects carry the surname — the Village on Pepper Creek, the Woodlands of Pepper’s Creek and the Highlands on Pepper’s Creek, to name a few.
Apparently, Pepper Creek’s turning into quite the place to settle down — as long as you’re not a fish.
While things aren’t so bad that the fish are actually dying off, scientists from the University of Delaware’s College of Marine Studies (CMS) have determined that two dominant species in Pepper Creek — weakfish and summer flounder — are experiencing “sub-lethal” effects from hypoxia.
Literally “low oxygen,” hypoxia is more likely to affect humans in the high mountain passes. But as CMS’s Timothy Targett explained, low dissolved oxygen (DO) in Pepper Creek is having a marked impact on the growth rates of the two local species.
Targett’s colleague, Damian Brady, detailed how the fish are responding, physically — that is, how effectively they are managing to swim out of affected areas when DO levels start dropping.
They detailed their findings at a recent Center for the Inland Bays Scientific and Technical Advisory Committee meeting, at the CMS in Lewes on Jan. 13.
Both men referred to “diel-cycling” — that is, the cycle through low DO, particularly in the hours before dawn, followed by the slow return to decent DO levels, sometimes not until early afternoon.
Brady said he’d reviewed data from the past 10 years, and nowhere else in the United States had been able to find diel-cycling as severe as what CMS had observed in Delaware’s Inland Bays. (He did add the caveat, though, that low-cost data collection technologies were a recent development.)
“We’re seeing an increased frequency and severity of DO events, worldwide,” Targett pointed out — and the Atlantic seaboard was far from exempt. He noted “chronic hypoxia” in Delaware’s coastal bays (and the Chesapeake).
According to Targett, diel-cycling is natural, to the extent that aquatic plant life stops photosynthesizing oxygen at sundown and then starts burning oxygen to produce energy (respiration). However, as frequently noted, excess nutrient levels in the local waterways tend to make diel-cycling a more dramatic affair.
This is because the nutrients act as fertilizer (which is often exactly where the nutrients came from), encouraging rampant algae growth. When the algae start dying off, its chemical decomposition burns up most, and sometimes all, of the available DO.
Both Targett and Brady also cited poor exchange, or flushing, in their areas of study (the westernmost “fingers” of the Indian River and Rehoboth bays).
According to Targett, 2 milligrams of oxygen per liter of water is basically the level below which aquatic organisms start to feel the pain. “At those levels, they either avoid the low-DO areas, or it starts to affect their growth rates,” he said.
He focused in particular on the period of June through August, when there are a lot of fish in the creeks, temperatures and food demand are high, and DO levels are low (especially at night).
He’d established baseline responses to low DO in the laboratory, and settled on a solid way to measure immediate responses. (This was actually one of the most important aspects of Targett’s study – his use of RNA-to-DNA ratios as a metric for evaluating growth rates on a very short time scale.)
And he’d established that, yes, low DO levels did have a substantial impact on growth rates. However, Targett said he’d been surprised to find a far more dramatic impact in the field. “The growth rates for both species were less than what we’d predicted,” he said.
In both cases, he said, the lower growth rates were linked to reduced appetite, but that alone didn’t explain the difference between lab and field testing. He introduced Brady with the suggestion that reduced swimming speed probably compounded the situation, as the fish became increasingly sluggish predators.
As Brady explained, the two fish species respond differently — weakfish tend to flee from low DO early on, summer flounder tend to slow down and conserve energy until things turn critical.
Once DO levels dropp below 2.8 milligram per liter, he said the fish start getting disoriented and are less likely to escape the area. He noted a “piston” effect, where fish come to feed during the day and leave the creeks for the waters of the open bay when DO levels drop at night.
“Avoidance is extremely effective, but at what cost?” Brady asked. To at least some extent, the time spent escaping low DO levels is time that could have been spent feeding, he noted.
Brady said he used to dread going out in Pepper Creek to collect weakfish, because he always knew it would be a burdensome task. But there are far fewer fish in the creek these days, he said.
Again noting the recent development of low-cost data collection technologies, he said it was difficult to say whether the dramatic diel-cycling was characteristic, or a relatively new development.
The next Center for the Inland Bays Scientific and Technical Advisory Committee meeting is scheduled for March 31, at the CMS in Lewes.
Committee members reminded local scientists, environmentalists and educators of the pending 2007 fiscal-year Center for the Inland Bays grant cycle (deadline for submission, March 10).
The center is soliciting proposals “which support the implementation of the Inland Bays Comprehensive Conservation and Management Plan (CCMP).”
Possible recipients — projects or applied research targeting nutrient reduction and improvements to water quality or habitat in Delaware’s Inland Bays, or monitoring and assessment programs ($62,000 total, no more than $20,000 per project) habitat creation or enhancement ($9,000 total, no more than $2,000 per project), or education and outreach activities ($9,000 total, no more than $2,500 per project).
For more information, or to view the CCMP in PDF format, visit the Web site at www.inlandbays.org.