High reproduction, but low biomass: mortality estimates of the copepod Acartia tonsa in a hyper-eutrophic estuary

• Production, abundance and mortality of the copepod Acartia tonsa were studied for a period of 9 d in a hyper-eutrophic estuary, Mariager Fjord, Denmark. The estuary is characterised by oxygen-depleted and often sulphidic bottom water, and a relatively sparse mesozooplankton community with low species diversity. During the study, an intense phytoplankton bloom consisting mainly of the diatom Skeletonema costatum developed with chlorophyll a concentrations reaching 46 mu g l(-1). Egg production rate (EPR) in A. tonsa ranged from 30 to 65 eggs female(-1) d(-1), and egg hatching success was > 90 %, yet the abundance of copepods remained low (1 to 3 nauplii l(-1), 0.3 to 1.5 copepodites l(-1)). Calculated daily copepod mortality ranged from 18 % for nauplii, 16 % for Copepodite Stage C 1, up to 70 % for C2 and C3, then declining for older stages. The vertical distribution of copepodites in relation to the depth range of mussel beds suggests strong predation by suspension-feeding Mytilus edulis at depths of 5 to 10 m. Moreover, anoxia and the presence of sulphide in deep water, which prevented hatching of A. tonsa eggs and decreased the survivorship of older life stages sinking below 20 m depth, further contributed to the low copepod abundance.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Farmaceutiska vetenskaper (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Pharmaceutical Sciences (hsv//eng)

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Nyckelord

acartia tonsa

anoxia

egg production

mortality

mytilus edulis

mussel mytilus-edulis

pelagic food-web

egg-production

vertical-distribution

calanoid copepods

hatching success

mariager-fjord

resting eggs

baltic sea

high ph

Terrestrial, freshwater and marine ecology

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)