A Review of Zooplankton Communities in the Massachusetts Bay/Cape Cod Bay System

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A Review of Zooplankton Communities in the
Massachusetts Bay/Cape Cod Bay System

• Jefferson T. Turner
• UMass Dartmouth
• OMSAP Meeting
• October 21, 2003

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• Concern that the MWRA effluent discharge might
  adversely change the zooplankton community in
  Massachusetts Bay
• Several attempts to develop a Contingency Plan
  zooplankton threshold
• In 2000 OMSAP recommended Since the
  Massachusetts and Cape Cod Bays system flows like
  a conveyor belt from north to south, MWRA
  should develop a method for analyzing the current
  data spatially and temporally to contrast
  differences between the northern boundary
  stations and Cape Cod Bay. (OMSAP 2000).

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Zooplankton Threshold Study Objectives

• Review relevant literature for evidence of
  specific responses that could be used to
  postulate a zooplankton threshold
• Explore the conveyor belt hypothesis of north
  to south transport of zooplankton communities
• Review available data to examine the effects of
  local and regional environmental factors on
  zooplankton communities in Mass Bay
• Determine whether an appropriate zooplankton
  threshold can be developed

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MWRA Zooplankton Monitoring Stations
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Review of the Literature - Summary

• Zooplankton taxa in the area MWRA monitors are
  typical of the Gulf of Maine and New England
  coastal waters in terms of taxonomic composition,
  seasonal cycles and life history.
• Genetic studies by Bucklin indicate that Calanus
  finmarchicus and Pseudocalanus spp. are part of a
  genetically homogeneous population from the Gulf
  of St. Lawrence through the Gulf of Maine to
  Georges Bank. This is not the case with Acartia
  tonsa.

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conveyor belt hypothesis

• Can advection of zooplankton population at the
  northern boundary through the nearfield with
  subsequent transport southward, ultimately lead
  to changes in zooplankton in Cape Cod Bay?
• Suggestion was that the timing of peaks in
  important zooplankton species could be
  sequential, with taxa peaking first at the
  northern boundary, later in the nearfield and
  southern Massachusetts Bay, and ultimately
  reaching Cape Cod Bay

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Conveyor belt hypothesis not supported by the
MWRA data

• pulses of zooplankton not evident in north to
  south data within the bays rather pulses often
  occur simultaneously or bays leads boundary
• Peak C. finmarchicus abundances often coincident
  or occur earlier at the southern stations than
  northern.
• No consistent north-south sequence in peak
  abundances for O. similis, Paracalanus parvus,
  Pseudocalanus spp., Paracalanus/Pseudocalanus
  copepodites, and Centropages typicus.

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PCA analysis found two major influences on
zooplankton community structure

• Seasonal/Temperature gradient in communities.
  Temperature is positively loaded on Factor 1,
  DO is negatively loaded. Cold-water taxa which
  are abundant relatively early in the year, such
  as cirripede larvae have negative or weak
  loadings on factor 1, taxa abundant in warm
  summer waters (e.g. Oithona similis, Osim) have
  positive loadings.
• Estuarine/offshore gradient in community
  structure. Taxa abundant in somewhat turbid,
  low salinity, Harbor waters like Acartia
  hudsonica (Ahuds) have positive loading on Factor
  2. Taxa more abundant in higher salinity, clearer
  offshore waters like Oithona similis and
  Paracalanus parvus (Ppar) have negative Factor 2
  loadings.

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Long-term measurements Sorting out species
responses

• Hemispheric scale processes may be influencing
  the response and abundance
• (Turner et al. May 2003 International Zooplankton
  Production Symposium, Spain)

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Findings

• The zooplankton community in Mass Bay is
  dominated by species which have widespread
  distributions in the Gulf of Maine and some of
  which are found throughout the East coast of the
  US
• Zooplankton abundance tends to follow a
  predictable temporal pattern, with peak abundance
  in mid-summer and lower levels in spring and fall
  
• Blooms tend to co-occur throughout system
  regional differences not strongly evident
• The conveyor belt concept not evident in the
  zooplankton data as treated by cluster analysis
  and PCA
• The beginning of discharge at the MWRA outfall in
  September 2000 had no clear effect on zooplankton
  abundance or community structure

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Conclusions

• Unable to define a meaningful simple numerical
  threshold for zooplankton community data at this
  time.
• MWRA will continue to evaluate and interpret the
  zooplankton community in its interpretive
  synthesis reports.