Evaluation of Impacts

ERDC TN-DOER-E19

March 2005

Non-burrowing substrate organisms, SAV, shell reefs (oysters). This may not be most

sensitive (with the exception of some kelp), but loss or impairment (growth, reproduction)

would require long recovery time (long-lived, difficult to establish stable population).

Eggs and larvae of pelagic fish if near bottom. Many pelagic fish have eggs or early life

stages that settle to the bottom and may be affected by bedded sediment.

Avoidance or failure of spawning by adults due to sudden presence of sediments. This

response has the potential to be deleterious to a population, but unless the species has a very

high site affinity or disturbance is very widespread, it will be difficult to assess whether

adults successfully spawn elsewhere. May be amenable to modeling.

Metamorphosis of benthic life stages of fish. Little is known of the effects of sediment on

this process, but it has the potential to affect a critical life stage.

Juvenile fish. Both pelagic and benthic fish are likely to be vulnerable to predation and/or

restriction of food supply if they avoid areas due to sedimentation.

Sessile benthic invertebrates. The most sensitive would include non-burrowing filter feeders

(apart from shell reefs above) followed by interface feeders.

Benthic fish. Benthic fish can have high affinity to specific substrate types but are also

capable of relocating during the assimilation of the bedded sediments. Relocation may

subject fish to increased predation or loss of foraging area.

Burrowing benthic invertebrates. Relatively high overburden stress would be required to

affect burrowing invertebrates, but this may scale with the size of the organism.

Pelagic fish. Pelagic fish are least likely to be sensitive to bedded sediments, but may react

to effects on food resources.

Evaluation of Impacts

Appropriate laboratory time scales for measuring impact of sedimentation on

fish/shellfish/SAV. Laboratory time scales should reflect assumptions of field effects; duration

of event, 3-5 days; assessment of impacts:

Adhesion of eggs (e.g., herring) in the presence of varying concentrations of sediments.

Fertilization success of eggs in presence of sediments.

Developmental success and hatching (days to weeks).

Larval behavior and feeding: minutes to hours.

Development of kelp: hours to days.

Long-term effects on adults: SAV growth and physiology-hours to weeks.

Appropriate laboratory volume scales for measuring impact of sedimentation on

fish/shellfish/SAV. This will depend on scale of organism and mass or volume of bedded layer.

Based on species and life stages of concern, benthic fish eggs and larvae are a high priority and

may be most tractable based on scale. Eggs and embryos can be on the milliliter scale (see

Chapman and Fletcher (2002)), whereas larvae and juveniles may require many liters to even

mesocosm scales. Complexity of scaling effects becomes more difficult as the size of the

organism increases.

Appropriate in-situ time scales for measuring impact of sedimentation on

fish/shellfish/SAV. Short-term measurements are most likely to capture direct effects of

sedimentation events, and should extend from hours to 3-5 days. Longer-term measurements are