Transcript PPT
Zooplankton processes Puget Sound Oceanography Jan. 28, 2011 Plankton – “that which is made to wander or drift” organisms that float or weakly swim through water Phytoplankton – organisms that use sunlight to fix carbon Zooplankton – the animal portion of the plankton; herbivorous, carnivorous, or mixed Autotrophs – fix their own energy from inorganic substances (producers). Heterotrophs – depend on energy fixed by others (consumers) Mixotrophs – do both Holoplankton – are planktonic through their whole life cycle Meroplankton – are planktonic only during part (usually larval) stage of their lives Herbivores Carnivores Omnivores Characteristics of estuaries: • Highly advective • Strong gradients • Fronts / mixing • Very productive • Benthic / pelagic coupling • High abundances of organisms • Terrestrial influences • Human influences Zooplankton need: • food • to avoid predators • find good growth habitat • find mates • ‘life cycle closure’ Special challenges for estuarine species: • tolerating / responding to strong gradients •overcoming advection • predator density • contaminants / pollution • altered food webs Species are zonated along gradients of salinity: Species composition (meso-zooplankton): Freshwater Moderate diversity: Cladocerans (e.g., Daphnia) Freshwater molluscs Typically 5-7 species of copepods Freshwater jellyfish (rare) Truly estuarine a few species of calanoid copepods, usually 1-2 dominant Meroplankton (bivalves, barnacles, crabs) jellyfish Oceanic high diversity of copepods (>30 spp) amphipods euphausiids jellyfish meroplankton (echinoderms, bivalves, barnacles, crabs) Zonation of species distributions along salinity gradients: Cumulative salinity distribution of common zooplankton in San Francisco Bay E. affinis = Eurytemora (a copepod) Kimmerer (2004) Salinity gradients (species patterns set by tolerance) - diversity lowest in brackish water (5-10‰) Why?? Species richness in estuaries follows a long established pattern along the salinity gradient described by Remane (1934) Acartia tonsa is only found in estuaries and nearshore environments. H0: they cannot feed effectively on very low phytoplankton concentrations. (Feeding) Species gradients also set by behavior: (Food) Paffenhoffer et al, 1988 Microzooplankton: rapid reproduction and growth. Highly dependent on food and temperature. At maximum, doubling rates in hours! Jellyfish: annual life cycle, growth to 0.7 d-1 Crustaceans Copepods ~ 1 month to complete Egg Nauplius (6 stages) Adult Copepodites (5 stages) Generalized seasonal cycles of phytoplankton and zooplankton biomass: Late, single bloom J F M A M J J A S O N D Early, bi-modal bloom J F M Phytoplankton Zooplankton A M J J A S O N D Difference of ~1 month between Main Basin and Dabob Bay phytoplankton blooms and copepod reproduction Dabob vs. Main Basin Zooplankton Dabob vs. Main Basin Phytoplankton productivity Percent composition Calanus marshallae 1st appearance of young life stages (purple) Calanus pacificus Zooplankton diel vertical migration (DVM): Who migrates? Crab larvae Shrimp Large copepods Euphausiids Some Jellyfish Some Amphipods Chaetognaths Pteropods Magnitude of Diel Vertical Migration by Life Stage Life History Stage 0 25 50 Average nighttime depth Depth (m) 75 100 125 Range of migration 150 175 200 Average daytime depth Vertical migration in 2-layer circulation River end Ocean end Some may migrate on tidal cycle for transport: Fernandes et al. 2002 http://northweb.hpl.umces.edu/videos_animations/Oyster_Larvae_Animations.htm North et al, MEPS 2008 Copepod abundance #/m3 Gelatinous predator predation on zooplankton in Chesapeake Bay Ctenophore abundance #/m3 Inverse relationship between calanoid copepod and Mnemiopsis leidyi densities at two stations in Chesapeake Bay. Optical Plankton Counter (OPC) OPC mounted on a ScanFish