Seasonal cycles of zooplankton from San Francisco Bay

Abstract

The two estuarine systems composing San Francisco Bay have distinct zooplankton communities and seasonal population dynamics. In the South Bay, a shallow lagoon-type estuary, the copepods Acartia spp. and Oithona davisae dominate. As in estuaries along the northeast coast of the U.S., there is a seasonal succession involving the replacement of a cold-season Acartia species (A. clausi s.l.) by a warm-season species (A. californiensis), presumably resulting from the differential production and hatching of dormant eggs. Oithona davisae is most abundant during the fall. Copepods of northern San Francisco Bay, a partiallymixed estuary of the Sacramento-San Joaquin Rivers, organize into discrete populations according to salinity distribution: Sinocalanus doerrii (a recently introduced species) at the riverine boundary, Eurytemora affinis in the oligohaline mixing zone, Acartia spp. in polyhaline waters (18-30%0)' and neritic species (e.g., Paracalanus parvus) at the seaward boundary. Sinocalanus doerrii and E. affinis are present year-round. Acartia clausi s.l. is present almost year-round in the northern reach, and A. californiensis occurs only briefly there in summer-fall. The difference in succession of Acartia species between the two regions of San Francisco Bay may reflect differences in the seasonal temperature cycle (the South Bay warms earlier), and the perennial transport of A. clausi s.l. into the northern reach from the seaward boundary by nontidal advection.Large numbers (> 1 0 6 m-3 ) of net microzooplankton (>64 Jlm), including the rotifer Synchaeta sp. and three species of tintinnid ciliates, occur in the South Bay and in the seaward northern reach where salinity exceeds about 5-10%0' Maximum densities of these microzooplankton are associated with high concentrations of chlorophyll. Meroplankton (of gastropods, bivalves, barnacles, and polychaetes) constitute a large fraction of zooplankton biomass in the South Bay during winter-spring and in the northern reach during summer-fall.Seasonal cycles of zooplankton abundance appear to be constant among years (1978)(1979)(1980)(1981) and are similar in the deep (> 10m) channels and lateral shoals «3 m). The seasonal zooplankton community dynamics are discussed in relation to: (1) river discharge which alters salinity distribution and residence time of plankton; (2) temperature which induces production and hatching of dormant copepod eggs; (3) coastal hydrography which brings neritic copepods of different zoogeographic affinities into the bay; and (4) seasonal cycles of phytoplankton.

Zooplankton spatial and diurnal variations in the Changjiang River estuary before operation of the Three Gorges Dam

“…Although there is little evidence that river inputs of terrestrial carbon make a direct contribution to coastal food webs, such exported nutrients may stimulate in situ production in estuaries and thus enhance the survivorship and growth of fish and crustaceans in these systems (Loneragan et al, 1999). Moreover, river discharge into estuaries is characterized by variability under natural conditions, influencing plankton community composition and dynamics in the receiving waters (Haertel et al, 1967;Hodgkin et al, 1971;Ambler et al, 1985;Mallin et al, 1993). It is believed that reductions in the freshwater influx into estuaries will have a dramatic effect on ecosystem function, including zooplankton productivity, with subsequent shifts in energy flow patterns (Whitfield et al, 1988).…”

Changes in production and respiration during a spring phytoplankton bloom in San Francisco Bay, California, USA:implications for net ecosystem metabolism

“…In contrast, plankton respiration in Chesapeake Bay exhibited a very tight coupling with no lags between production and respiration, suggesting the importance of labile sources of organic matter (Sampou & Kemp 1994). In South San Francisco Bay, the spring bloom is a period of greatly enhanced bacterial production (Hollibaugh & Wong 1996), as well as microzooplankton abundance, and recruitment of copepods and benthic invertebrates such as spionid polychaetes (Ambler et al 1985). These heterotrophs all contribute to the consumption of organic matter.…”

The impact of trophic interactions on rates of nitrogen regeneration and grazing in Chesapeake Bay

“…Ambler et al 1985). In August in Chesapeake Bay, densities of A. tonsa copepodites (including adults) can easily surpass 1 O-20 animals liter-l (Roman et al 1993).…”