A marine zooplankton community vertically structured by light across diel to interannual timescales

The predation risk of many aquatic taxa is dominated by visually searching predators, commonly a function of ambient light. Several studies propose that changes in visual predation will become a major climate-change impact on polar marine ecosystems. The High Arctic experiences extreme seasonality in the light environment, from 24 h light to 24 h darkness, and therefore provides a natural laboratory for studying light and predation risk over diel to seasonal timescales. Here, we show that zooplankton (observed using acoustics) in an Arctic fjord position themselves vertically in relation to light. A single isolume (depth-varying line of constant light intensity, the value of which is set at the lower limit of photobehaviour reponses of Calanus spp. and krill) forms a ceiling on zooplankton distribution. The vertical distribution is structured by light across timescales, from the deepening of zooplankton populations at midday as the sun rises in spring, to the depth to which zooplankton ascend to feed during diel vertical migration. These results suggest that zooplankton might already follow a foraging strategy that will keep visual predation risk roughly constant under changing light conditions, such as those caused by the reduction of sea ice, but likely with energetic costs such as lost feeding opportunities as a result of altered habitat use.

New and little-known families of Hemiptera Cicadomorpha from the Triassic of Central Asia—early analogs of treehoppers and planthoppers

One family, 12 monotypic genera, and 12 species of Triassic Cicadomorpha are described as new and two families, three genera, and three species are redescribed. All new taxa are from the Madygen Formation (Ladinian–Carnian) of Kyrgyzstan. Saaloscytinidae stat. nov. (Scytinopteroidea) includes Tingiopsis reticulata Becker-Migdisova, 1953 from Madygen and Saaloscytina Brauckmann et Schlueter, 1993 (= Chanarescytina Brauckmann, Martins-Neto et Gallego, 2006, syn. nov. = Chanarelytrina Martins-Neto et Gallego, 2006, syn. nov.) with one species from Germany and another from Argentina (Saaloscytina carmonae (Brauckmann, Martins-Neto et Gallego, 2006), comb. nov. = Chanarelytrina nana Martins-Neto et Gallego, 2006, syn. nov.). Maguviopseidae fam. nov. (Prosboloidea) comprises 2 subfamilies and 11 genera (all from Madygen): Sacvoyageinae subfam. nov. for Sacvoyagea ventrosa gen. et sp. nov. and Maguviopseinae subfam. nov. for Nonescyta mala gen. et sp. nov. and Nevicia imitans gen. et sp. nov. (Nonescytini trib. nov.), Maguviopsis kotchnevi Becker-Migdisova, 1953, Sitechka perforata gen. et sp. nov., Phyllotexta latens gen. et sp. nov., Cuanoma protracta gen. et sp. nov., Fasolinka beckermigdisovae gen. et sp. nov., Krendelia ansata gen. et sp. nov., Falcarta bella gen. et sp. nov., and Asiocula lima gen. et sp. nov. (Maguviopseini trib. nov.). Another family, Mesojabloniidae Storozhenko, 1992, is transferred from Grylloblattida to Hylicelloidea, and Fulgobole evansi gen. et sp. nov. and Scytachile emeljanovi gen. et sp. nov. are assigned to this family along with Mesojablonia kukalovae Storozhenko, 1992 (all three from Madygen). Homoplastic similarities of Saaloscytinidae and Maguviopseidae to Membracoidea and Mesojabloniidae to Fulgoroidea are discussed. The elaborate camouflage of these extinct hoppers and Dysmorphoptilidae is presumably due to increase of visual predation by small arboreal reptiles in the Triassic.

Vertical migration in adult Atlantic cod (Gadus morhua)

We investigate the trade-offs associated with vertical migration and swimming speed of Atlantic cod (Gadus morhua) using an adaptive individual-based model. Simulations with varying distribution and occurrence of prey, with and without swimbladder constraints, and visual predation were performed. Most simulations resulted in cod migrations between the bottom and pelagic zones. In simulations with high probability of encountering pelagic prey, the cod spent the daytime in the pelagic zone, moving to the bottom to feed only when no pelagic prey were encountered. At night the cod stayed in the pelagic zone to attain neutral buoyancy. In simulations with low occurrence of pelagic prey or high visual predation pressure, the cod remained at the bottom feeding on the consistently present benthic prey. If the pelagic prey occurred far above the sea floor or there were no benthic prey, the cod abandoned all bottom contact. The study thus predicts that the probability of encountering energy-rich pelagic prey is the key factor in driving vertical migration in adult cod. Buoyancy regulation is further shown to be an important constraint on vertical migration.