240
J. Tarazona and W. Arntz
Although upwelling may increase during El Nifio events, primary production in the euphotic zone decreases by about 50% ( 1.03-1.68 g
C m- 2 d- 1 ) because the deeper pycnocline moves nutrient-rich waters out of
upwelling reach (Chavez et al. 1989). During the 1982-1983 El Nifio event,
most autochthonous phytoplankton species of the Peru Coastal Current
disappeared and were replaced by equatorial and oceanic warm water
species. The replacement of native species and reduction of phytoplankton
density negatively affected higher food web levels, in particular zooplankton grazers and pelagic fish. Furthermore, zooplankton and pelagic fish
species suffered mortality due to the inflow of warm water and/or were
replaced mainly by tropical predators, such as chaetognaths, salps, jellyfish, and siphonophores. The reduction of local holoplankton and meroplankton was accompanied by an increase of tropical holoplanktonic organisms and the range of tropical meroplankton distribution extended 10°
further south (Tarazona et al. 1985).
Several warm water invertebrates immigrated from tropical areas, such
as shrimps (mostly Xiphopenaeus riveti and Penaeus califormiensis),
swimming crabs (Euphylax robustus, Euphylax dovii, Portunus acuminatus, Callinectes arcuatus, Arenaeus mexicanus), spiny lobster (Panulirus
gracilis), stalked barnacle (Pollicipes elegans), and mollusks (i.e., Pteria
sterna, Atrina maura, Malea ringens; Arntz and Tarazona 1990; Paredes et
al. 1998). The high temperatures and the increased swell during the
1982-1983 El Nifio event together with warm water predatory swimming
crabs from tropical areas caused mass mortality of key species like the
mussel Semimytilus algosus and brown algae (Macrocystis pyrifera, Lessonia spp.) along Peruvian rocky shores (Tarazona et al. 1988). The subsequent decrease in density, biomass, and species numbers opened new
space in the intertidal zone that was colonized by green algae (e. g., Ulva
lactuca), followed by a red algal stage until the community stabilized with
brown algal dominance and the return of invertebrates. On sandy beaches,
reduced latitudinal distribution (7°) and mass mortality of the dominant
surf clam Mesodesma donacium induced drastically lower density and
biomass of the community. Mussel beds (Aulacomya ater) died and detached from the substrate and commercially important bivalves (Semele
spp., Gari sol ida, Tagelus dombeii) and decapods (Cancer setosus, Platyxanthus orbignyi) suffered almost complete mortality. In contrast, the
gastropod Thais chocolata and the octopus Octopus mimus benefited from
El Nifio conditions and landings of the warm water-tolerant scallop (Argopecten purpuratus) increased by 60- to 100-fold. Soft bottoms at the seafloor are favored by a pronounced increase in dissolved oxygen concentrations during El Nifio events, leading to increased species richness and
densities (Fig. 16.2).
J. Tarazona and W. Arntz
Although upwelling may increase during El Nifio events, primary production in the euphotic zone decreases by about 50% ( 1.03-1.68 g
C m- 2 d- 1 ) because the deeper pycnocline moves nutrient-rich waters out of
upwelling reach (Chavez et al. 1989). During the 1982-1983 El Nifio event,
most autochthonous phytoplankton species of the Peru Coastal Current
disappeared and were replaced by equatorial and oceanic warm water
species. The replacement of native species and reduction of phytoplankton
density negatively affected higher food web levels, in particular zooplankton grazers and pelagic fish. Furthermore, zooplankton and pelagic fish
species suffered mortality due to the inflow of warm water and/or were
replaced mainly by tropical predators, such as chaetognaths, salps, jellyfish, and siphonophores. The reduction of local holoplankton and meroplankton was accompanied by an increase of tropical holoplanktonic organisms and the range of tropical meroplankton distribution extended 10°
further south (Tarazona et al. 1985).
Several warm water invertebrates immigrated from tropical areas, such
as shrimps (mostly Xiphopenaeus riveti and Penaeus califormiensis),
swimming crabs (Euphylax robustus, Euphylax dovii, Portunus acuminatus, Callinectes arcuatus, Arenaeus mexicanus), spiny lobster (Panulirus
gracilis), stalked barnacle (Pollicipes elegans), and mollusks (i.e., Pteria
sterna, Atrina maura, Malea ringens; Arntz and Tarazona 1990; Paredes et
al. 1998). The high temperatures and the increased swell during the
1982-1983 El Nifio event together with warm water predatory swimming
crabs from tropical areas caused mass mortality of key species like the
mussel Semimytilus algosus and brown algae (Macrocystis pyrifera, Lessonia spp.) along Peruvian rocky shores (Tarazona et al. 1988). The subsequent decrease in density, biomass, and species numbers opened new
space in the intertidal zone that was colonized by green algae (e. g., Ulva
lactuca), followed by a red algal stage until the community stabilized with
brown algal dominance and the return of invertebrates. On sandy beaches,
reduced latitudinal distribution (7°) and mass mortality of the dominant
surf clam Mesodesma donacium induced drastically lower density and
biomass of the community. Mussel beds (Aulacomya ater) died and detached from the substrate and commercially important bivalves (Semele
spp., Gari sol ida, Tagelus dombeii) and decapods (Cancer setosus, Platyxanthus orbignyi) suffered almost complete mortality. In contrast, the
gastropod Thais chocolata and the octopus Octopus mimus benefited from
El Nifio conditions and landings of the warm water-tolerant scallop (Argopecten purpuratus) increased by 60- to 100-fold. Soft bottoms at the seafloor are favored by a pronounced increase in dissolved oxygen concentrations during El Nifio events, leading to increased species richness and
densities (Fig. 16.2).