Benthic Assessments One benthic ecologists concerns and suggestions

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Benthic AssessmentsOne benthic ecologists
concerns and suggestions

• Fred Nichols
• USGS, retired

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IntroductionWhere I am coming from

• As a marine invertebrate ecologist, I want to
  know why species live where they do. That is,
  what determines their distribution and abundance
  in space and time?
• With respect to evaluating human influences on
  invertebrates, it is important to first define
  natural variability, in both species and their
  environment.
• It is against the background of natural
  variability that the effects of human stressors
  should be measured.

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Evolution of indices/assessments(Nichols
version)

• Long history of evaluating the relative abundance
  of tolerant vs. sensitive species.
• The concept of trophic indices applied to
  continental shelves, e.g., organic enrichment off
  Los Angeles
• Index of Biological Integrity applied to
  freshwater systems, contrasting impacted with
  pristine streams or watersheds (James Karr)
• EPA EMAP expanded a condition index concept to
  estuaries

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IntroductionWhat we have learned about estuaries

• Distribution and abundance are determined by many
  factors such as dispersal of larvae, substrate
  type, food availability, predation, and physical
  stressors.
• Abundances of individual species fluctuate widely
  over time.
• Most species, particularly estuarine species, are
  durable they tolerate a varying environment.
• We continue to be surprised by the very large
  ecosystem changes that periodically occur (e.g.,
  in the benthos, plankton and fish communities).

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IntroductionWhat we have learned (2)

• Most estuarine and coastal environments are
  somewhat contaminated.
• At heavily contaminated sites, the effects are
  usually obvious - few species survive.
• We are steadily making progress in understanding
  how individual species respond to contamination.
• Distinguishing clearly between the effects of
  natural factors and the effects of low to
  moderate contamination on community composition
  in estuaries has been exceedingly difficult,
  despite decades of good effort.

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Role of Benthic AssessmentsEMAP, IBI, etc.

• It is indeed important to take geographically
  comprehensive approaches in evaluating the
  condition of estuarine/coastal benthic habitats,
  e.g., the Triad approach
• Define community composition
• Assess contaminant distributions
• Carry out bioassays
• Such studies provide objective means of
  describing contaminant distributions and
  distinguishing those sites that seem to be most
  affected by contaminants.

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My Primary Concerns

• A. Interpreting contaminant effects on
  communities from limited sampling in physically
  dynamic environments.
• B. Tracking the status of environmental condition
  over time, i.e., trends.

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Contaminant effects in dynamic environmentsInflue
nce of salinity (1)

• Benthic community structure in river-dominated
  estuaries is in large part determined by physical
  processes, of which salinity is a key indicator.
• Physically dynamic estuaries like San Francisco
  Bay exhibit large and often sudden changes in
  salinity.
• Species distributions and abundances can change
  dramatically in response to the changing
  conditions.

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Contaminant effects in dynamic environmentsInflue
nce of salinity (2)

• EMAP-type studies, typically based infrequent
  sampling, assume that the relationship between
  community composition and salinity is defined at
  the time of sampling.
• Salinity measured at the time of sampling does
  not necessarily define the conditions under which
  community composition was established.
• The benthic community in the upper reaches of the
  Bay can be markedly influenced by water
  transport/salinity conditions months before the
  time of sampling.
• The physical regime at the time of recruitment is
  probably a much more meaningful influence on
  community structure than physical conditions at
  the time that one collects adults.

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Contaminant effects in dynamic environmentsInflue
nce of salinity (3)

• Infrequent sampling means that important events
  (storm, drought, flood, arrival of new predator,
  etc.) that determine species distributions/abundan
  ces are missed.
• One should have an understanding of antecedent
  physical conditions when interpreting community
  composition at any moment in time.
• The combination of a fluctuating environment and
  infrequent sampling makes the interpretation of
  non-lethal human effects on community composition
  very challenging.

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B. Tracking environmental condition

• Tracking environmental condition, including
  contaminant effects, over time is critical to
  evaluating water quality management and policy
  decisions (adaptive management).
• Geographically comprehensive but temporally
  limited sampling, combined with natural
  variability and few reference site options, can
  preclude meaningful biological community trends
  analysis
• The goal should be to develop strategies that
  provide resource managers and decision makers
  with defensible trends information
• The challenge is to identify trends in human
  impacts (e.g., with the Triad approach) in
  shallow, physically dynamic estuaries where the
  time scales of important natural change in the
  community are typically shorter or longer than
  most sampling frequencies.

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Conclusions and Recommendations (1)

• Distinguishing human-induced effects on estuarine
  benthic community structure, other than at highly
  impacted sites, is a major and, I think, largely
  unmet challenge.
• To measure the effectiveness of actions taken to
  improve conditions in estuarine systems, the next
  generation of studies should focus on
  investigations designed specifically to evaluate
  trends, i.e., to measure both the short- and
  long-term patterns of variability and change in
  these systems.
• Such studies should incorporate measures of
  natural perturbations of the environment in the
  analysis of the effects of contaminants on
  community structure

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Conclusions and Recommendations (2)

• Making substantial progress in evaluating the
  effects of contaminants on the Bays ecosystem
  will require
• deciding what tractable questions can be answered
  with future assessment studies, and
• establishing permanent, frequently sampled sites
  in the areas of most concern.
• Because of the scope of the challenge, the
  greatest focus should perhaps be on those areas
  of San Francisco Bay that are known to be heavily
  contaminated, with the goal of
• Distinguishing between natural and human induced
  impacts
• Tracking impacts over time to establish long-term
  trends.

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Conclusions and Recommendations (3)

• We should urge more coordination among studies of
  the benthos, plankton and fish communities
  because they are so closely interconnected in a
  single food web. Each of these communities is
  critical to an understanding of overall
  conditions and trends in the estuary.
• We need to pay attention to what the individual
  species themselves, by their distribution and
  abundance patterns over time, are telling us
  about what is going on in the environment.