Uncovering the Composition and Diversity of Pelagic Copepods in the Oligotrophic Blue Water of the South Pacific Subtropical Gyre

The subtropical gyres occupy approximately 40% of the surface of the Earth and are widely recognized as oligotrophic zones. Among them, the South Pacific subtropical gyre (SPSG) shows the lowest chlorophyll-a levels (0.02–0.04 μgL–1), the deepest nutricline (>200 m) and euphotic zone (∼160 m), and the lowest rates of nitrogen fixation. The zooplankton community is poorly known in the SPSG. We report a study focused on the composition and distribution of pelagic copepods within the gyre so as to uncover the diversity and habitat conditions of this special community. Therefore, during the austral spring of 2015, an oceanographic cruise was conducted across the eastern side of the SPSG. Physical and chemical variables were measured in the upper 1000 m, while zooplankton samples were collected by means of vertically stratified hauls using a multiple net sampler for five layers (0–800 m). Satellite data were also used to assess near-surface phytoplankton biomass (Chl-a) and physical-dynamics conditions during the cruise, and 121 species of copepods were identified, which belonged to five taxonomic orders, 24 families, and 50 genera. Calanoida and Cyclopoida were the most frequent orders, containing 57% and 38% of species, respectively, whereas Harpacticoida and Mormonilloida contained 2% of species each, and Siphonostomatoida contained 1% of species. The vertical distribution of copepods revealed an ecological zonation linked to a strongly stratified water column, such that three different vertical habitats were defined: shallow (0–200 m), intermediate (200–400 m), and deep (400–800 m). Both the abundance and diversity of copepods were greater in the shallow habitat and were strongly associated with water temperature, whereas copepods in the subsurface layers subsisted with relatively low oxygen waters (2–3 mL O2 L–1) and presumably originated at the Chilean upwelling zone, being transported offshore by mesoscale eddies. Furthermore, the analysis of species composition revealed a marked dominance of small-sized copepods, which may play a key role in nutrient recycling under an oligotrophic condition, as inferred from their mostly omnivorous feeding behavior. Our findings also suggested a potentially high endemism within the gyre, although basin-scale circulation and mesoscale eddies, traveling from the coastal upwelling zone and transporting plankton, can also influence the epipelagic fauna.

The crossover from microscopy to genes in marine diversity: from species to assemblages in marine pelagic copepods

An accurate identification of species and communities is a prerequisite for analysing and recording biodiversity and community shifts. In the context of marine biodiversity conservation and management, this review outlines past, present and forward-looking perspectives on identifying and recording planktonic diversity by illustrating the transition from traditional species identification based on morphological diagnostic characters to full molecular genetic identification of marine assemblages. In this process, the article presents the methodological advancements by discussing progress and critical aspects of the crossover from traditional to novel and future molecular genetic identifications and it outlines the advantages of integrative approaches using the strengths of both morphological and molecular techniques to identify species and assemblages. We demonstrate this process of identifying and recording marine biodiversity on pelagic copepods as model taxon. Copepods are known for their high taxonomic and ecological diversity and comprise a huge variety of behaviours, forms and life histories, making them a highly interesting and well-studied group in terms of biodiversity and ecosystem functioning. Furthermore, their short life cycles and rapid responses to changing environments make them good indicators and core research components for ecosystem health and status in the light of environmental change. This article is part of the theme issue ‘Integrative research perspectives on marine conservation’.

TASA DE PRODUCCIÓN DE HUEVOS DE COPÉPODOS DEL PACÍFICO CENTRAL MEXICANO

Se estimó la producción de huevos en aguas mexicanas del Pacífico tropical oriental mediante indicadores en copépodos pelágicos bajo condiciones de laboratorio. Los copépodos fueron recolectados durante abril de 2015, separados e incubados en tres estaciones oceanográficas frente a las costas de Guerrero, México. Solo Labidocera acutifrons, Subeucalanus pileatus y Centropages furcatus presentaron actividad reproductora. Los indicadores de producción secundaria fueron la tasa de producción de huevos (TPH), la relación masa-longitud y el factor de condición. La especie con mayor TPH y el valor más alto de factor de condición (K) fue L. acutifrons. En las tres especies se observó un crecimiento de tipo alométrico. Esta es la primera estimación de producción secundaria de zooplancton en el Pacífico Central de México, por lo que debe ampliarse a un mayor número de taxa y a una escala temporal-espacial estacional mayor. Copepod egg production rate in pelagic copepods in the Mexican Central Pacific Estimates of secondary production through indicators from pelagic copepods under laboratory conditions were carried out in Mexican waters of the eastern tropical Pacific. Copepods were collected during April 2015, separated and in three oceanographic stations off the coast of Guerrero, Mexico. Only Labidocera acutifrons, Subeucalanus pileatus and Centropages furcatus presented reproductive activity. Secondary production indicators were the rate of egg production (TPH), the mass-length relationship and condition factor. The species with the highest TPH and the highest value of condition factor (K) was Labidocera acutifrons. In all three species allometric growth was observed. This is the first estimate of secondary production for zooplankton in the Mexican Central Pacific. Thus it should be extended to a larger number of taxa and for a wider seasonal space-time scale