Mesozooplankton assemblage in the gulf of cádiz estuaries: Taxonomic and trait-based approaches.

In this study, two different approaches based on taxonomic assemblages and on copepod functional groups were used to investigate the mesozooplankton assemblage structure and its relationship with environmental variables in the main estuaries of the Gulf of Cádiz (Guadalquivir, Guadiana and Tinto-Odiel) during the dry-warm season. In general, the mesozooplankton assemblages were dominated by copepods, especially the calanoid Acartia tonsa, which reached its highest abundance in the inner zones while the adjacent coastal zones were characterized by a mixture of copepods and cladocerans, especially Penilia avirostris. Regarding the trait-based approach, three copepod functional groups were identified, principally sorted by their feeding strategy. Group 1 (composed of omnivorous copepods displaying a mixed feeding strategy and broadcast-spawners) was found mainly in the inner areas, while Groups 2 (omnivorous cyclopoids, sac-spawners that feed via active ambush) and 3 (herbivores-omnivores employing a filter feeding strategy and mostly broadcast-spawners) were predominant in the adjacent coastal zones. The relative abundance of copepod functional groups suggested that Group 1 could be considered the most important contributor to secondary production in the estuarine systems of the Gulf of Cádiz. In relation to environmental factors, salinity was the most influential variable on mesozooplankton assemblages in both approaches. Our results suggest that the studied estuaries, although taxonomically different, have mesozooplankton assemblages that perform similar ecological functions. Both methods provide valuable and complementary information about mesozooplankton assemblage dynamics in the main estuaries of the Gulf of Cádiz.

Large deep-sea zooplankton biomass mirrors primary production in the global ocean.

The biological pump transports organic carbon produced by photosynthesis to the meso- and bathypelagic zones, the latter removing carbon from exchanging with the atmosphere over centennial time scales. Organisms living in both zones are supported by a passive flux of particles, and carbon transported to the deep-sea through vertical zooplankton migrations. Here we report globally-coherent positive relationships between zooplankton biomass in the epi-, meso-, and bathypelagic layers and average net primary production (NPP). We do so based on a global assessment of available deep-sea zooplankton biomass data and large-scale estimates of average NPP. The relationships obtained imply that increased NPP leads to enhanced transference of organic carbon to the deep ocean. Estimated remineralization from respiration rates by deep-sea zooplankton requires a minimum supply of 0.44 Pg C y-1 transported into the bathypelagic ocean, comparable to the passive carbon sequestration. We suggest that the global coupling between NPP and bathypelagic zooplankton biomass must be also supported by an active transport mechanism associated to vertical zooplankton migration.

Larval development of the symbiotic pea crab Pinnaxodes chilensis (H. Milne Edwards, 1837) (Decapoda, Brachyura, Pinnotheridae) reared in laboratory.

The complete larval development of Pinnaxodes chilensis (including four zoeal stages and a megalopa stage) is described and illustrated in detail for the first time. The descriptions are based on laboratory-reared larvae obtained from ovigerous females found inside specimens of the sea urchin Loxechinus albus collected in the coast of Valparaíso, Chile. In order to allow the correct differentiation of specimens from plankton samples, the larval stages of P. chilensis are compared with those from other Pinnotheridae species, whose larval development is known for the Chilean continental waters (Calyptraeotheres politus). The morphological characters described for P. chilensis larvae, as well as the comparison with the remaining larval development descriptions available for the genus Pinnaxodes, are used to discuss the heterogeneity within this genus.

Ubiquitous healthy diatoms in the deep sea confirm deep carbon injection by the biological pump.

The role of the ocean as a sink for CO2 is partially dependent on the downward transport of phytoplankton cells packaged within fast-sinking particles. However, whether such fast-sinking mechanisms deliver fresh organic carbon down to the deep bathypelagic sea and whether this mechanism is prevalent across the ocean requires confirmation. Here we report the ubiquitous presence of healthy photosynthetic cells, dominated by diatoms, down to 4,000 m in the deep dark ocean. Decay experiments with surface phytoplankton suggested that the large proportion (18%) of healthy photosynthetic cells observed, on average, in the dark ocean, requires transport times from a few days to a few weeks, corresponding to sinking rates (124-732 m d(-1)) comparable to those of fast-sinking aggregates and faecal pellets. These results confirm the expectation that fast-sinking mechanisms inject fresh organic carbon into the deep sea and that this is a prevalent process operating across the global oligotrophic ocean.

Large mesopelagic fishes biomass and trophic efficiency in the open ocean.

With a current estimate of ~1,000 million tons, mesopelagic fishes likely dominate the world total fishes biomass. However, recent acoustic observations show that mesopelagic fishes biomass could be significantly larger than the current estimate. Here we combine modelling and a sensitivity analysis of the acoustic observations from the Malaspina 2010 Circumnavigation Expedition to show that the previous estimate needs to be revised to at least one order of magnitude higher. We show that there is a close relationship between the open ocean fishes biomass and primary production, and that the energy transfer efficiency from phytoplankton to mesopelagic fishes in the open ocean is higher than what is typically assumed. Our results indicate that the role of mesopelagic fishes in oceanic ecosystems and global ocean biogeochemical cycles needs to be revised as they may be respiring ~10% of the primary production in deep waters.