Editorial: Deep Pelagic Ecosystem Dynamics in a Highly Impacted Water Column: The Gulf of Mexico After Deepwater Horizon

The intermediate-sized midwater fauna (fishes, shrimps, and cephalopods; “micronekton” collectively) are dominant components of the pelagic ocean, which is by far the largest ecosystem type on Earth by several metrics (volume, organismal numbers, biomass, and productivity). Deep-pelagic micronekton, those animals residing in the water column below 200 m depth during the day, are the direct link between plankton and oceanic top predators, and through the linked processes of feeding and daily vertical migration facilitate one of Earth\u27s most important ecosystem services to humans, carbon sequestration. Despite increasing recognition of this importance, a disconnect exists between stewardship and human impact; only a miniscule fraction of the deep-pelagic ocean has been studied in detail, while anthropogenic threats to that system are increasing rapidly. Perhaps nowhere on Earth is that dichotomy more demonstrable than the Gulf of Mexico (Gulf hereafter), a complex, high-diversity ecosystem under intense human usage and subjected to arguably the worst marine pollution event in human history. Assessment of the impacts of the Deepwater Horizon disaster to the deep-pelagic biota was impeded from the start by the lack of pre-event information, both in terms of baselines (faunal composition, abundance, and distribution) and in terms of understanding natural variability, against which impacts of anthropogenic disturbance could be detected and quantified. In this Research Topic, we present a description of three interlinked research programs (ONSAP, DEEPEND, and DEEPEND|RESTORE, described below) that began in 2010 and continue as of this writing. These programs were designed to investigate key aspects of the Gulf pelagic ecosystem, including its faunal structure, biophysical drivers of that structure, organismal and community ecology, natural variability, and potential resilience to disturbance. The contributed papers are grouped below by major themes, indicated in the conceptual model (Figure 1) of DEEPEND (Deep Pelagic Nekton Dynamics; www.deependconsortium.org), the largest of the three aforementioned research programs

The 48-inch lidar aerosol measurements taken at the Langley Research Center

This report presents lidar data taken between July 1991 and December 1992 using a ground-based 48-inch lidar instrument at the Langley Research Center in Hampton, Virginia. Seventy lidar profiles (approximately one per week) were obtained during this period, which began less than 1 month after the eruption of the Mount Pinatubo volcano in the Philippines. Plots of backscattering ratio as a function of altitude are presented for each data set along with tables containing numerical values of the backscattering ratio and backscattering coefficient versus altitude. The enhanced aerosol backscattering seen in the profiles highlights the influence of the Mount Pinatubo eruption on the stratospheric aerosol loading over Hampton. The long-term record of the profiles gives a picture of the evolution of the aerosol cloud, which reached maximum loading approximately 8 months after the eruption and then started to decrease gradually. NASA RP-1209 discusses 48-inch lidar aerosol measurements taken at the Langley Research Center from May 1974 to December 1987

Feeding behavior of the ctenophore Thalassocalyce inconstans : revision of anatomy of the order Thalassocalycida

© 2009 The Authors. This article is distributed under the terms of the Creative Commons Attribution Noncommercial License. The definitive version was published in Marine Biology 156 (2009): 1049-1056, doi:10.1007/s00227-009-1149-6.Behavioral observations using a remotely operated vehicle (ROV) in the Gulf of California in March, 2003, provided insights into the vertical distribution, feeding and anatomy of the rare and delicate ctenophore Thalassocalyce inconstans. Additional archived ROV video records from the Monterey Bay Aquarium Research Institute of 288 sightings of T. inconstans and 2,437 individual observations of euphausiids in the Gulf of California and Monterey Canyon between 1989 and 2005 were examined to determine ctenophore and euphausiid prey depth distributions with respect to temperature and dissolved oxygen concentration [dO]. In the Gulf of California most ctenophores (96.9%) were above 350 m, the top of the oxygen minimum layer. In Monterey Canyon the ctenophores were more widely distributed throughout the water column, including the hypoxic zone, to depths as great as 3,500 m. Computer-aided behavioral analysis of two video records of the capture of euphausiids by T. inconstans showed that the ctenophore contracted its bell almost instantly (0.5 s), transforming its flattened, hemispherical resting shape into a closed bi-lobed globe in which seawater and prey were engulfed. Euphausiids entrapped within the globe displayed a previously undescribed escape response for krill (‘probing behavior’), in which they hovered and gently probed the inner surfaces of the globe with antennae without stimulating further contraction by the ctenophore. Such rapid bell contraction could be effected only by a peripheral sphincter muscle even though the presence of circumferential ring musculature was unknown for the Phylum Ctenophora. Thereafter, several live T. inconstans were collected by hand off Barbados and microscopic observations confirmed that assumption.Supported by the David and Lucile Packard Foundation and NOAA Grant #NA06OAR4600091

Long-Term Effects of the Cleaner Fish Labroides dimidiatus on Coral Reef Fish Communities

Cleaning behaviour is deemed a mutualism, however the benefit of cleaning interactions to client individuals is unknown. Furthermore, mechanisms that may shift fish community structure in the presence of cleaning organisms are unclear. Here we show that on patch reefs (61–285 m2) which had all cleaner wrasse Labroides dimidiatus (Labridae) experimentally removed (1–5 adults reef−1) and which were then maintained cleaner-fish free over 8.5 years, individuals of two site-attached (resident) client damselfishes (Pomacentridae) were smaller compared to those on control reefs. Furthermore, resident fishes were 37% less abundant and 23% less species rich per reef, compared to control reefs. Such changes in site-attached fish may reflect lower fish growth rates and/or survivorship. Additionally, juveniles of visitors (fish likely to move between reefs) were 65% less abundant on removal reefs suggesting cleaners may also affect recruitment. This may, in part, explain the 23% lower abundance and 33% lower species richness of visitor fishes, and 66% lower abundance of visitor herbivores (Acanthuridae) on removal reefs that we also observed. This is the first study to demonstrate a benefit of cleaning behaviour to client individuals, in the form of increased size, and to elucidate potential mechanisms leading to community-wide effects on the fish population. Many of the fish groups affected may also indirectly affect other reef organisms, thus further impacting the reef community. The large-scale effect of the presence of the relatively small and uncommon fish, Labroides dimidiadus, on other fishes is unparalleled on coral reefs

Lidar and Balloon-Borne Cascade Impactor Measurements of Aerosols: A Case Study

Aerosol size distributions, elemental components, complex refractive indices, extinction profiles and extinctionto- backscatter ratios have been measured and inferred from balloon-borne cascade impactor and lidar observations made during a cooperative joint experiment conducted during the period 4-10 April, 1980 in Tucson, AZ. Size distributions obtained from quartz crystal microbalance (QCM) cascade impactor measurements at different heights (1 to 1000 m) and times over a period of several days were fairly similar in form, being clearly bimodal in their mass distributions with the coarse particle mode being dominant. Electron microscope and energy dispersive X-ray analyses of particles deposited on the QCM stages over the particle radii range ~0.5-4.0 µm revealed that the particle samples were elementally dominated by both sulfur and crustal type (Al, Ca, Mg and Si) elements. Complex refractive index estimates for a wavelength of 649 nm were obtained by comparing the lidar inferred aerosol extinction-to-backscatter ratios with theoretically computed values calculated for the impactor-derived size distributions. The real part of the index was estimated to be 1.45 for most cases, while the estimates for the imaginary part ranged between 0.000 and 0.01. Aerosol extinction coefficients calculated for the impactor-derived size distributions were found to be somewhat smaller but in fair agreement with the extincti

Distribution of net-collected planktonic cnidarians along the northern Mid-Atlantic Ridge and their associations with the main water masses

Planktonic cnidarians and ctenophores were sampled with a multiple opening-closing net (Multinet) as well as a non-quantitative plankton net along the northern Mid-Atlantic Ridge (MAR) between Iceland and the Azores. Sixty-four species or genera of planktonic cnidarians (38 siphonophora, 21 hydromedusae, 5 scyphomedusae) and one genus of ctenophore were collected. Of these, Leuckartiara adnata and Clausophyes laetmata were new records for the area. Multinet samples collected from depths of 0-100, 100-500, 500-1000, 1000-1500 and 1500-2500 m at 11 stations were compared. Multivariate analysis of the data indicated that species composition and abundance along the ridge varied with the dominant water masses, with changes in the cnidarian zooplankton assemblage observed with regard to geographic location as well as depth. The surface waters of the two northernmost stations characterized by modified North Atlantic Water (MNAW) as well as the three southernmost stations characterized by North Atlantic Central Water (NACW) exhibited relatively high abundances (3284-13,915 individuals . 1000 m(-3)) in the upper 100 m. No such peak was evident at the middle stations characterized by Subarctic Intermediate Water (SAIW), where the abundances in the upper three depth strata were consistently lower (57-863 individuals . 1000 m(-3)). Across the study area, the lowest abundances were found in the 1500-2500 m stratum (0-56 ind. . 1000 m(-3)) The main divergence in the species composition and abundance of planktonic cnidarians was observed at the Subpolar Front (SPF), which marked the boundary for the distribution of many species. The divergence at the SPF was strongest in the upper 500 m but observable down to 1500 m. Profoundly different epipelagic species assemblages were observed in SAIW and NACW on opposite sides of the SPF, with the distribution of several species of calycophoran siphonophores confined to the southern NACW. At mid-water depths, the species composition north of the SPF was possibly influenced by Labrador Sea Water (LSW). The highest diversity of planktonic cnidarians was observed in the surface waters south of the SPF and in the 100-1000 m range north of the SPF. (c) 2007 Elsevier Ltd. All rights reserved

48-Inch Lidar Aerosol Measurements Taken at the Langley Research Center July 1991 to December 1992

This report summarizes measurements obtained using the ground-based 48-inch lidar system at the Langley Research Center in Hampton, Virginia, from July 1991 through December 1992. The data set extends the long-term ground-based lidar measurements of mid-latitude stratospheric and upper tropospheric aerosols at Langley to a database that includes 19 years of data. NASA RP-1209 reports measurements obtained from May 1974 through December 1987. The present report covers a shorter, but very important period, since the stratospheric aerosol loading was greatly enhanced by the eruption of Mount Pinatubo in June 1991. iii Summar

Vertical distribution and relative abundance of gelatinous zooplankton, in situ observations near the Mid-Atlantic Ridge

Fourteen dives were conducted with the ROVs Aglantha and Bathysaurus to depths of 2335 m along the Mid-Atlantic Ridge (42 degrees 52'-53 degrees 17'N). The most frequently observed gelatinous fauna in order of overall abundance included medusae, ctenophores, siphonophores, appendicularians, and tunicates. All of these animals, except the tunicates, occurred throughout the water column. Their relative abundances differed with depth and location. Identification to species was limited to easily recognized fauna because relatively few gelatinous animals were collected. Each group of gelatinous zooplankton tended to be most numerous in a region just south of the Charlie-Gibbs Fracture Zone. Medusae (mainly Aeginura grimaldii) were the most frequently encountered animals (LIP to 25 individuals per 100 m(3)). Oil a vertical scale their abundance peaked from 550 to 800 m and these maxima were consistently within the SAIW and NACWe. In the NACW their densities were notably lower (up 2 individuals per 100 m(3)) and the majority of the population was deeper, ranging from 800 to 1050 m. Ctenophores (mainly Bathocyroe fosteri) were most prominent (as many as 27 individuals per 100 m(3)) in a zone from 300 to 600 m in the NACWe. Appendicularians (primarily oikopleurids) had a broader vertical distribution in all water masses, mainly from 450 to 1000 m. Up to 12 houses per 100 m(3) were noted in the NACWe, and these estimates are considered to be very conservative. Sorties near the sea floor (as deep as 2100 m) indicated these detritivores were a prominent component (up to 5 houses per 100 m(3)) of the epibenthic macrozooplankton. Siphonophores (mostly calycophorans) reached densities of about 14 colonies per 100 m(3) in the NACWe and occurred mainly from 300 to 600 m, at most locations. Tunicates (salps and doliolids) were patchy in their distribution and infrequently observed. Salps were numerous (up to 3 solitary individuals per 100 m(3)) at only one location (sta. 50) near the surface. Deep-living doliolids (up to 1 individual per 100 m(3)) appeared from 400 to 500 m at this site and occasionally within the same depth range at most of the other stations. (c) 2007 Elsevier Ltd. All rights reserved

Zooplankton distribution in four western Norwegian fjords

A multi-instrumental array constructed in the Laboratoire d'Ecologie du Plancton Marin in Villefranche sur mer, France, named the Underwater Video Profiler (WP), was used to investigate the vertical distribution of zooplankton in four western Norwegian fjords in the summer 1996. Six distinct zoological groups were monitored. The fauna included: (a) small crustaceans (mainly copepods), (b) ctenophores (mainly lobates), (c) siphonophores (mainly physonects), (d) a scyphomedusa Periphylla periphylla, (e) chaetognaths and (f) appendicularians. The use of the non-disturbing video technique demonstrated that the distribution of large zooplankton is heterogeneous vertically and geographically. Furthermore, the abundance of non-migrating filter feeders in the deep basins of the fjords indicates that there is enough food (living and non-living particulate organic matter) to support their dietary needs. This adaptation may be considered as a strategy for survival in fjords. Specifically, living in dark, deep water reduces visual predation and population loss encountered in the upper layer due to advective processes. (C) 2000 Academic Press