Trophic Interactions between Anadromous Juvenile Alewife (Alosa pseudoharengus) and Cyanobacterial Populations in a Shallow Mesotrophic Pond ()
ABSTRACT
Alosa pseudoharengus is an anadromous fish that migrates from marine to
freshwaters to spawn. The early larval and juvenile forms are known to be
planktivorous, where heavy feeding upon their preferred food source of large
crustacean zooplankton often results in changes to composition and size
structure within this trophic guild which in turn can result in shifts within
the trophic spectrum and a classic trophic cascade. In this study of Lower Mill
Pond, Brewster MA, we evaluated the feeding strategy of juvenile Alosa to determine whether juvenile alewife switches to feeding largely on cyanobacteria and
whether cyanotoxins microcystin (MC) and β-methlyamino-L-alanine (BMAA)
bioaccumulate in their muscle tissue. Within 15 - 30 days
of their estimated spawning date, overexploitation of crustacean zooplankton
resulted in a shift from planktivory to benthic detritivory for the majority of
their life history, although this did not reduce their condition based on
weight-length relationships (Log Wwt. = -5.503 + (3.101 × Log
Length). Mean MC (0.003 μg·g-1 dwt) and BMAA (4.49 μg·g-1 dwt) concentrations in the muscle tissue of out-migrating juveniles were
presumably derived from benthic subsidies, exporting freshwater cyanotoxins and
creating a potential transfer to consumer of 0.0012 μg MC and 1.85 μg BMAA.
Biodilution of MC and biomagnification of BMAA were observed. Depletion of the
crustacean biomass by >95% resulted in an increase in the rotifer biomass,
where Log crustacean (μg·L-1 dwt) = - 5.642 - (7.976 × Log rotifer (μg·L-1 dwt), and an
increase in the amount of potentially edible <50 μm cyanobacterial biomass
(r(8) = - 0.676, p = 0.046). A secondary
cascade appears to have been maintained via invertebrate planktivory by Chaoborus spp.; however for a period of time edible cyanobacteria growth exceeded grazing
pressure, resulting in a bloom of edible cyanobacteria. Continued grazing
resulted in a shift to larger, inedible cyanobacterial communities where late
season (October) surface accumulations were observed. The mass occurrence of
juvenile Alosa pseudoharengus appears to be coupled to the
sequential increases of cyanobacterial biomass via its influence on the trophic
spectrum. Overall, the rotifer biomass (μg·L-1) was positively
correlated with MC (pg·mL-1) (r(8) = 0.577, p = 0.104), and negatively correlated with BMAA (μg·L-1)
(r(8) = - 0.388, p = 0.373) in the edible cyanobacterial fraction of the water column, although
neither of these were significant.
Share and Cite:
Leland, N. , Landon, R. and Haney, J. (2020) Trophic Interactions between Anadromous Juvenile Alewife (
Alosa pseudoharengus) and Cyanobacterial Populations in a Shallow Mesotrophic Pond.
Natural Resources,
11, 394-419. doi:
10.4236/nr.2020.119023.