Zooplankton vertical distribution in waters of the Mallorca shelf: autumn and summer

The zooplankton vertical distribution (VD) has been studied in two areas of the Mallorca shelf during December 2009 and July 2010. Five and eight, depth levels were sampled at day/night by using BIONESS an MOCNESS multinet. 17 zooplankton groups were found, where copepods were the most abundant (70%), being responsible of the whole zooplankton VD pattern. Copepod high diversity was found in both months (4.3 bits and 3.3bits) and more than 88 species identified. The highest diversity was found in deeper waters (90-120 m) in the afternoon than during day time (0-90m) in December but in July, always found at deeper layer (100-150 m), suggesting that epipelagic and mesopelagic copepods co-occurred, and diel changes induced the increased diversity. Clausocalanus arcuicornis (13%), Nannocalanus minor (10%) and Pleuromamma (P. gracilis and P. abdominalis, 8% and 6%) were the most abundant. However others such as Acartia clausi and Clausocalanus furcatus appeared in December and Centropages typicus, Euchaeta acuta and Lucicutia flavicornis in July. In relation to water conditions the VD exhibited different patterns with a higher difference in autumn between the two sites than in summer when the zooplankton was concentrated around the FMD. Species like N. minor, A. clausi, as well as all Clausocalanus and Oithona did not show clear vertical movements; but others showed weak, intermediate or strong migration, such as Lucicutia, Euchaeta and Pleuromamma which exhibited clear nocturnal VD. The importance of these species in the active carbon transfer is discussed in this oligotrophic area of the central western Mediterranean

Trying to resolve the taxonomic confusion of Paracalanus parvus species complex (Copepoda, Calanoida) in the Mediterranean and Black Seas through a combined analysis of morphology, molecular taxonomy and DNA metabarcoding

Paracalanus parvus is reported as the most abundant representative of the genus and one of the main components of the coastal zooplankton in the Mediterranean and Black Seas. However, the subtle taxonomic differences between P. parvus and the congeneric species P. indicus and P. quasimodo, in combination with the ample morphological variation found in Mediterranean specimens, render problematic the correct identification. A recent molecular study by Cornils and Held (2014) provided evidence of cryptic speciation in the P. parvus complex and indicated that P. parvus s.s. does not have global distribution, but may be restricted to the northeastern Atlantic. In order to clarify the taxonomic status and distribution of this species complex in the Mediterranean and Black Seas, a study was conducted on Paracalanus specimens collected from different locations across the aforementioned marine basins and sequenced for portion of the COI mitochondrial gene. An accurate taxonomic analysis was also carried out to correlate morphological characteristics with the molecular species' assignation. The phylogenetic analysis of the specimens together with the publicly available sequences of P. parvus complex revealed the presence of four molecular operational taxonomic units (MOTUs) in the Mediterranean, which differed in abundance and geographic distribution. The combination of morphological and molecular data revealed great inconsistencies between morphospecies and MOTUs. Moreover, several bulk zooplankton samples were analyzed through DNA metabarcoding in the frame of the “MetaCopepod” project to provide more extensive information on the spatiotemporal distribution and abundance of the target specie

Diel vertical migration of copepods in the tropical and subtropical Atlantic Ocean

The vertical distribution of the zooplankton community was analyzed from the surface to 800 m depth in the tropical-subtropical Atlantic Ocean in a transect of 12 stations during day and nighttime from Brazilian waters (10°S) to the Canary Islands (27°N). A depth stratified opening-closing 1 m2 mouth MOCNESS was used and 8 layers analyzed. Besides this net, the epipelagic layer (0–200 m) was sampled for microzooplankton (53 µm Calvet net) and mesozooplankton (200 µm WP2 net) communities. An increasing gradient of mesozooplankton abundance was observed from the oligotrophic waters off Brazil to the oceanic upwelling off Northwest Africa. Copepods were always the most abundant group (86 %) and 241 species identified, although only 60 were >1 %. Smaller species predominated and Oncaea was the dominant group (18 %) followed by Clausocalanus (14 %) with C. furcatus dominating. Paracalanus and Oithona were also quite abundant (12 and 9 % respectively). Small copepods such as C. furcatus and Euchaeta marina predominated in the oligotrophic waters while Calanus helgolandicus, Calanoides carinatus, Temora stylifera, Paracalanus parvus, and Pleuromamma robusta dominated in the upwelling area. In the epipelagic layer large copepods (e.g., Rhincalanus, Pleuromamma, Euchirella, and Metridia) were numerous during nighttime and in the mesopelagic zone during day were quantitatively less abundant. The vertical distribution of the dominant copepods (>1 %) showed multiple diel patterns but at least five were distinguished and their dominant taxa defined: (1) Species living in the twilight zone with slight up and down motion. (2) Species dominating the epipelagic layers with weak vertical movements. (3) Strong migrants living in the mesopelagic zone during day and moving upward towards the surface or (4) migrating to the subsurface layer at nighttime, and (5) those organisms characterizing the oceanic upwelling where the calanoids predominated (e.g., C. helgolandicus and C. carinatus). Our findings highlight the complexity in the diel vertical migration patterns of copepods in the tropical-subtropical Atlantic Ocean and the relevant role of the deep-sea copepods and their diel vertical migration. These results could be used as baseline information for low latitudes of the Atlantic Ocean in future studies of the biological carbon pump.This work was supported by project “Migrants and Active Flux of In the Atlantic Ocean” (MAFIA, CTM 2012-39587-C04-2), project “Disentangling Seasonality and Active Flux In the Ocean (DESAFÍO, PID2020-118118RB-100) from the Spain Ministry of Science and Innovation, and by the European Union (Horizon 2020 Research and Innovation Programme) through projects SUMMER (Grant Agreement 817806) and TRIATLAS (Grant Agreement 817578).Peer reviewe

Zooplankton composition changes during a submarine post-eruptive process in waters of El Hierro (Canary Islands, Atlantic Ocean)

In order to know the impact on the zooplanktonic ecosystem of the eruptive submarine processes, three surveys were carried out (March and October 2013 and March 2014) around the Hierro Island (World Biosphere Reserve, 2000), 15 months after the volcanic eruption (1.8 Km from the nearest coast and 275 m from the sea bottom). As a consequence of this phenomenon three main stress factors were found: increasing temperature, acidification and water deoxygenating with the highest implication of Fe enrichment. During this period the composition and diversity of main zooplankton species were analyzed in relation to the environment, observing high similarity (>85%) in the entire area, where the largest variability was due to the different seasons analyzed. In spring 2014 was however, double the abundance of the other months in relation to the cool water. The copepods were the dominant group (77%) with a high diversity and 126 spp identified. Oncaea and Oithona were the most abundant organisms, followed by the small Clausocalanus and Paracalanus group. They together with small species of Calanoids (N. minor, M. tenuicornis, M. clausi, C. vanus, L. flavicornis, C. styliremis and A. danae) and their juveniles contributed 70% of the whole copepod community. Therefore, it can be highlighted that the faunistic enrichment and the singularity of the Hierro island in the most western site of the Canary Islands, as well as the necessity of monitoring the protected area that can be considered as a “hot spot” for studies of natural changes in the Atlantic Ocea

Zooplankton vertical distribution across the tropical Atlantic Ocean

Vertical distribution of main zooplankton species involved in active flux in the tropical Atlantic Ocean was studied in a transet from Brazil to the Canary Islands. The survey was carried out during April, 2015 using an opening-closing MOCNESS 9 nets from 800 m depth to the surface in 12 stations. We also analyzed the epipelagic strata (0-200 m) using micro (Calvet 53 µm ) and mesozooplankton (WP2, 200 µm ) nets.According to the decreasing temperature and stratification along the transect, a gradient of increasing mesozooplankton abundance was observed in the epipelagic zone, being maximun in the oceanic upwelling area off Mauritania. Copepods were the most abundant group (82%) with more than 155 species identified, being the smaller size always predominant. Clausocalanus were the most abundant one (18%) with C. furcatus dominating. They were followed by small Oncaea species (17%), Paracalanus (14%) and Oithona (9%) in the whole water column analyzed. Large copepods (Calanoids, Euchaeta, Pleuromamma, etc...) although important in biomass in the epipelagic strata during the night and in mesopelagic during day, were quantitatively less important (<20%). The most dominant copepod species and their vertical distribution are analyzed in relation to the different oceanographic zone