Publications

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Book Chapter
Angel, MV, Checkley Jr. DM, Heany SI.  1985.  Chapter One: Plankton migrations. Introduction. Contributions in marine science volume 27 supplement. ( Rankin M, Wohlschlag DE, Eds.).:43-44., Port Aransas, TX: Port Aransas Marine Laboratory, University of Texas Marine Science Institute Abstract
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Checkley, DM, Asch RG, Rykaczewski RR.  2017.  Climate, anchovy, and sardine. Annual Review of Marine Sciences, Vol 9. 9:469-493., Palo Alto: Annual Reviews   10.1146/annurev-marine-122414-033819   Abstract

Anchovy and sardine populated productive ocean regions over hundreds of thousands of years under a naturally varying climate, and are now subject to climate change of equal or greater magnitude occurring over decades to centuries. We hypothesize that anchovy and sardine populations are limited in size by the supply of nitrogen from outside their habitats originating from upwelling, mixing, and rivers. Projections of the responses of anchovy and sardine to climate change rely on a range of model types and consideration of the effects of climate on lower trophic levels, the effects of fishing on higher trophic levels, and the traits of these two types of fish. Distribution, phenology, nutrient supply, plankton composition and production, habitat compression, fishing, and acclimation and adaptation may be affected by ocean warming, acidification, deoxygenation, and altered hydrology. Observations of populations and evaluation of model skill are essential to resolve the effects of climate change on these fish.

Checkley Jr., DM, Ayon P, Baumgartner TR, Bernal M, Coetzee JC, Emmett R, Guevara R, Hutchings L, Ibaibariaga L, Nakata H, Oozeki Y, Planque B, Schweigert J, Stratoudakis Y, Van der Lingen CD.  2009.  Habitats. Climate change and small pelagic fish. ( Checkley Jr. DM, Alheit J, Oozeki Y, Roy C, Eds.).:12-44., Cambridge, UK; New York: Cambridge University Press Abstract
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Checkley Jr., DM, Bakun A, Barange M, Castro LR, Freon P, Guevara R, Herrick Jr. SF, McCall AD, Ommer R, Oozeki Y, Roy C, Shannon L, Van der Lingen CD.  2009.  Synthesis and perspective. Climate change and small pelagic fish. ( Checkley Jr. DM, Alheit J, Oozeki Y, Roy C, Eds.).:344-351., Cambridge, UK; New York: Cambridge University Press Abstract
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Conference Paper
Iwamoto, I, Trivedi MM, Checkley Jr. DM.  1998.  Real-time detection and classification of objects in flowing water. Machine vision systems for inspection and metrology VII : 4-5 November, 1998, Boston, Massachusetts . 3521( Batchelor BG, Miller JWV, Solomon S, Eds.).:214-220., Bellingham, Wash.: SPIE (International Society for Optical Engineering) Abstract
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Journal Article
Petrik, CM, Jackson GA, Checkley JDM.  2013.  Aggregates and their distributions determined from LOPC observations made using an autonomous profiling float. Deep Sea Research Part I: Oceanographic Research Papers.   10.1016/j.dsr.2012.12.009   AbstractWebsite

The vertical flux of particles in the ocean drives the movement of organic carbon to the deep ocean. We have been studying the distribution and flux of these particles using the SOLOPC, a profiling Lagrangian (SOLO) float with a Laser Optical Particle Counter (LOPC). We have been able to distinguish between aggregate-like and zooplankton-like particles with diameters > 2 mm but needed a way to separate the smaller particles into aggregates and zooplankton. Observations included a lognormal-shaped fraction in the normalized volume distribution similar to that observed in results for simulations of particles in the euphotic zone. By fitting a lognormal distribution to the volume spectrum of particles with diameters ≤ 2 mm , we have been successful at making a separation of marine snow material from other, presumably living, particles. The particle volumes derived using the separations are positively correlated with fluorescence, particulate organic carbon, and the volume of larger particles classified as aggregate-like, which supports the conclusion that these particles are truly aggregates, in some cases derived from phytoplankton. The residual volumes (total less the above fit) are highly correlated with the volumes of large, zooplankton-like particles. Downward velocities of the aggregate fraction calculated from time series of particle profiles are consistent with previous estimates of particle settling rates ( 20 – 70 m d − 1 ) . We now have a tool to estimate aggregate distributions, properties, and vertical fluxes in the euphotic zone, including when and where they change.

Song, H, Miller AJ, McClatchie S, Weber ED, Nieto KM, Checkley DM.  2012.  Application of a data-assimilation model to variability of Pacific sardine spawning and survivor habitats with ENSO in the California Current System. Journal of Geophysical Research-Oceans. 117   10.1029/2011jc007302   AbstractWebsite

The Pacific sardine (Sardinops sagax) showed significant differences in spawning habitat area, spawning habitat quality and availability of survivor habitat as the Pacific Ocean went through the La Nina state in April 2002 to a weak El Nino in April 2003. During another El Nino/Southern Oscillation transition period in 2006-2007 when the El Nino state retreated and the La Nina returned, a similar pattern in spawning habitat quality was seen. The coupling between the atmospheric forcing, the physical ocean states and the properties of the sardine egg spawning are investigated using dynamically consistent data-assimilation fits of the available physical oceanographic observations during these months. Fits were executed using the Regional Ocean Modeling System four-dimensional variational assimilation platform along with adjoint model runs using a passive tracer to deduce source waters for the areas of interest. Analysis using the data-assimilation model runs reveals that unusually strong equatorward wind-forcing drives offshore transport during the La Nina conditions, which extends the spawning habitat for sardine further offshore. A statistical model of sardine spawning habitat shows better habitat quality during the El Nino conditions, which is associated with higher egg densities and corresponded to higher daily egg production. Concentration of eggs is also increased by convergence of water. The results of the source waters analysis using the adjoint data assimilation model support the idea that offshore transport extends the spawning habitat, and show that higher levels of nutrient are brought into the spawning habitat with high concentration of sardine eggs.

Checkley, DM, Davis RE, Herman AW, Jackson GA, Beanlands B, Regier LA.  2008.  Assessing plankton and other particles in situ with the SOLOPC. Limnology and Oceanography. 53:2123-2136.   10.4319/lo.2008.53.5_part_2.2123   AbstractWebsite

We combined a Sounding Oceanographic Lagrangian Observer float with a Laser Optical Plankton Counter (LOPC) and a fluorometer to make an autonomous biological profiler, the SOLOPC. The instrument senses plankton and other particles over a size range of 100 mm to 1 cm in profiles to 300 m in depth and sends data ashore via satellite. Objects sensed by the LOPC include aggregates and zooplankton, the larger of which can be distinguished from one another by their transparency. We hypothesized that the diel production of particles and their loss by sinking and grazing are reflected in the change of the particle distribution. We present data from four deployments of the SOLOPC off California. Particle volume was maximal at the base of the surface mixed layer and correlated with chlorophyll a fluorescence. In a 3-d deployment in 2005, particle volume was greatest in the early evening and smallest in the morning, and average particle size increased with depth. Eigenvector analysis of the particle volume distribution as a function of diameter for each of the deployments yielded size peaks characteristic of planktonic crustaceans. Ship-based measurements showed that the abundance of opaque particles of 1.1-1.7 mm equivalent spherical diameter was positively correlated with copepods of this size and simultaneously collected in nets. This relationship was used with SOLOPC data to estimate the distribution of large copepods, which were most abundant beneath the depth of maximal particle flux, estimated from particle size and published sinking rates. Our data are consistent with a model with diel production of particles and their loss by sinking and grazing.

Van der Lingen, CD, Checkley D, Barange M, Hutchings L, Osgood K.  1998.  Assessing the abundance and distribution of eggs of sardine, Sardinops sagax, and round herring, Etrumeus whiteheadi, on the western Agulhas Bank, South Africa, using a continuous, underway fish egg sampler. Fisheries Oceanography. 7:35-47. AbstractWebsite

A continuous, underway fish egg sampler (CUFES) was employed to assess the abundance and distribution of eggs of both sardine, Sardinops sagax, and round herring, Etrumeus whiteheadi, on the Western Agulhas Bank, South Africa, during September 1996. Samples were collected while underway along six inshore/offshore transects, and at stations along the transects. Volumetric estimates of egg density (eggs m(-3)) from on-station CUFES samples were highly correlated with both volumetric and areal (eggs m(-2)) estimates of egg density from samples collected from CalVET net hauls at these stations, demonstrating the validity of this novel sampling technique. Sardine and round herring eggs were encountered in a band running parallel to the coast and extending from 10 to 33 nautical miles offshore to the shelf edge, and highest egg densities were associated with strong north-west-flowing currents in the region of the shelf edge. Collecting samples while underway increased the precision of the estimate of mean egg density for sardine eggs but not for round herring eggs. The use of CUFES in obtaining a fine-scale resolution of sardine egg distribution, and as a tool for stock assessment, are discussed.

Davison, PC, Checkley DM, Koslow JA, Barlow J.  2013.  Carbon export mediated by mesopelagic fishes in the northeast Pacific Ocean. Progress in Oceanography. 116:14-30.   10.1016/j.pocean.2013.05.013   AbstractWebsite

The role of fishes in the global carbon cycle is poorly known and often neglected. We show that the biomass of mesopelagic fishes off the continental USA west to longitude 141 degrees W is positively related to annual net primary productivity, and averages 17 g m(-2). We estimate the export of carbon out of the epipelagic ocean mediated by mesopelagic fishes ("fish-mediated export"; FME) with individual-based metabolic modeling using the catch from 77 mesopelagic trawls distributed over the study area. FME was 15-17% (22-24 mg C m(-2) d(-1)) of the total carbon exported in the study area (144 mg C m(-2) d(-1)), as estimated from satellite data. FME varies spatially in both magnitude and relative importance. Although the magnitude of FME increases with increasing total export, the ratio of FME to total export decreases. FME exceeds 40% of the total carbon export in the oligotrophic North Pacific Subtropical Gyre, but forms <10% of the total export in the most productive waters of the California Current. Because the daytime residence depth of these fishes is below the depths where most remineralization of sinking particles occurs, FME is approximately equal to the passive transport at a depth of 400 m. The active transport of carbon by mesopelagic fishes and zooplankton is similar in magnitude to the gap between estimates of carbon export obtained with sediment traps and by other methods. FME should be considered in models of the global carbon cycle. (C) 2013 Elsevier Ltd. All rights reserved.

Jones, WA, Checkley DM.  2017.  Classification of otoliths of fishes common in the Santa Barbara Basin based on morphology and chemical composition. Canadian Journal of Fisheries and Aquatic Sciences. 74:1195-1207.   10.1139/cjfas-2015-0566   AbstractWebsite

Morphological and chemical features of fish otoliths are used to distinguish between populations and stocks. We hypothesized that these features can also be used to distinguish between fishes of different taxonomic groups common in and near the Santa Barbara Basin, including mesopelagic, pelagic, and demersal fish. Sagittal otoliths obtained from 905 fish representing six taxonomic groups were imaged, and 12 geometric and 59 elliptic Fourier morphometric features were extracted. A subset of 143 otoliths was also analyzed for Li, Na, Mg, K, Mn, Sr, and Ba. We used chemical composition in addition to morphology because the latter may be altered between otolith formation and analysis. Two sets of classifiers were made: one using only morphometric features and one using both morphometric and element features. Random forest analysis was generally superior to discriminant function analysis. Highest classification success, evaluated using cross-validation and otoliths of masked identity, was achieved with multiple feature types. The ten strongest discriminatory features of all available feature types were used in the final classification models. Our method is applicable to the classification of otoliths recovered from guts, feces, middens, and sediments as well to classify other biological objects.

Politikos, DV, Curchitser EN, Rose KA, Checkley DM, Fiechter J.  2018.  Climate variability and sardine recruitment in the California Current: A mechanistic analysis of an ecosystem model. Fisheries Oceanography. 27:602-622.   10.1111/fog.12381   AbstractWebsite

Recruitment varies substantially in small pelagic fish populations. Understanding of the mechanisms linking environment to recruitment is essential for the effective management of fisheries resources. In this study, we used a fully coupled end-to-end ecosystem model to study the effect of climate variability on sardine recruitment in the California Current System during 1965-2006. Ocean variability was represented by ROMS hydrodynamic and NEMURO biogeochemical models, and sardine population dynamics was simulated through a full life cycle individual-based model. Model analysis was designed to elucidate how changes in abiotic and biotic conditions may impact the spawning habitats, early life stage survival, and ultimately recruitment of sardine. Our findings revealed the importance of spatial processes to shape early life stages dynamics. Shifts in spawning habitats were dictated by the spatial variations in temperature and the behavioral movement of adults. Additionally, the spatial match of eggs with warmer temperatures and larvae with their prey influenced their survival. The northward shifts in spawning locations and the accomplishment of good recruitment in warmer years agreed with existing knowledge. Egg production and survival during egg and yolk-sac larval stages were key factors to drive the long-term variations in recruitment. Finally, our analysis provided a quantitative assessment of climate impact on year-to-year variation in sardine recruitment by integrating multiple hypotheses.

Lindegren, M, Checkley DM, Rouyer T, MacCall AD, Stenseth NC.  2013.  Climate, fishing, and fluctuations of sardine and anchovy in the California Current. Proceedings of the National Academy of Sciences.   10.1073/pnas.1305733110   AbstractWebsite

Since the days of Elton, population cycles have challenged ecologists and resource managers. Although the underlying mechanisms remain debated, theory holds that both density-dependent and density-independent processes shape the dynamics. One striking example is the large-scale fluctuations of sardine and anchovy observed across the major upwelling areas of the world. Despite a long history of research, the causes of these fluctuations remain unresolved and heavily debated, with significant implications for fisheries management. We here model the underlying causes of these fluctuations, using the California Current Ecosystem as a case study, and show that the dynamics, accurately reproduced since A.D. 1661 onward, are explained by interacting density-dependent processes (i.e., through species-specific life-history traits) and climate forcing. Furthermore, we demonstrate how fishing modifies the dynamics and show that the sardine collapse of the 1950s was largely unavoidable given poor recruitment conditions. Our approach provides unique insight into the origin of sardine–anchovy fluctuations and a knowledge base for sustainable fisheries management in the California Current Ecosystem and beyond.

Lindegren, M, Checkley DM, Koslow JA, Goericke R, Ohman MD.  2018.  Climate-mediated changes in marine ecosystem regulation during El Nino. Global Change Biology. 24:796-809.   10.1111/gcb.13993   AbstractWebsite

The degree to which ecosystems are regulated through bottom-up, top-down, or direct physical processes represents a long-standing issue in ecology, with important consequences for resource management and conservation. In marine ecosystems, the role of bottom-up and top-down forcing has been shown to vary over spatio-temporal scales, often linked to highly variable and heterogeneously distributed environmental conditions. Ecosystem dynamics in the Northeast Pacific have been suggested to be predominately bottom-up regulated. However, it remains unknown to what extent top-down regulation occurs, or whether the relative importance of bottom-up and top-down forcing may shift in response to climate change. In this study, we investigate the effects and relative importance of bottom-up, top-down, and physical forcing during changing climate conditions on ecosystem regulation in the Southern California Current System (SCCS) using a generalized food web model. This statistical approach is based on nonlinear threshold models and a long-term data set (similar to 60years) covering multiple trophic levels from phytoplankton to predatory fish. We found bottom-up control to be the primary mode of ecosystem regulation. However, our results also demonstrate an alternative mode of regulation represented by interacting bottom-up and top-down forcing, analogous to wasp-waist dynamics, but occurring across multiple trophic levels and only during periods of reduced bottom-up forcing (i.e., weak upwelling, low nutrient concentrations, and primary production). The shifts in ecosystem regulation are caused by changes in ocean-atmosphere forcing and triggered by highly variable climate conditions associated with El Nino. Furthermore, we show that biota respond differently to major El Nino events during positive or negative phases of the Pacific Decadal Oscillation (PDO), as well as highlight potential concerns for marine and fisheries management by demonstrating increased sensitivity of pelagic fish to exploitation during El Nino.

Bird, JL, Eppler DT, Checkley DM.  1986.  Comparisons of herring otoliths using Fourier series shape analysis. Canadian Journal of Fisheries and Aquatic Sciences. 43:1228-1234.   10.1139/f86-152   AbstractWebsite

Numeric analysis of otolith morphology provides vital information to commercial fisheries concerning the age distribution, racial origin, and, to some extent, the environmental history of fish stocks. Conventional methods used to retrieve these data, though proven to be effective, are time consuming, susceptible to ambiguous interpretations, and only semiquantitative. Fourier shape descriptors, when used to analyze outlines of otolith silhouettes, represent a rapid, objective, semiautomated means of obtaining much of this information. Analysis of Fourier shape information derived from otoliths of juvenile and adult Alaskan herring and adult Northwest Atlantic herring show that otolith shape reflects differences in fish age and fish race. The shape of otoliths of juvenile fish are significantly different from those of adult fish. Few shape differences can be found, though, between otoliths from adult fish of different age within the same stock. Distinct differences exist between Atlantic and Alaskan adult otolith shapes. For some stocks, minor shape differences occur between left and right otoliths. Differences in otolith shape arising from sexual dimorphism are not apparent.

Osgood, KE, Checkley Jr. DM.  1996.  Concentration of Calanus pacificus in the Santa Barbara Basin. EOS Trans. AGU. 76:36. Abstract
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Checkley, DM, Ortner PB, Settle LR, Cummings SR.  1997.  A continuous, underway fish egg sampler. Fisheries Oceanography. 6:58-73.   10.1046/j.1365-2419.1997.00030.x   AbstractWebsite

We describe a method to sample the highly contagious distribution of pelagic fish eggs. CUFES, the continuous, underway fish egg sampler, consists of a submersible pump, concentrator, electronics and sample collector. This system operates continuously and under nearly all sea conditions, providing a real-time estimate of the volumetric abundance of pelagic fish eggs at pump depth, usually 3 m. CUFES-derived estimates of volumetric abundance agree well with those from nets towed at pump depth and with areal abundance estimated from vertically integrated plankton tows. CUFES has been used successfully to sample the eggs of menhaden, pinfish, sardine, and anchovy off the coasts of the eastern and western United States and South Africa. Two large patches of eggs of the Atlantic menhaden were sampled off North Carolina in winter 1993-94, had a linear scale of 5-10 km, and were found in waters between the Gulf Stream and mid-shelf front. Spawning location may he related to bathymetry. CUFES is now being used to estimate spawner biomass by the daily egg production method. An optical plankton counter provided accurate estimates of the number of Atlantic menhaden eggs sample by CUFES.

Checkley, DM, Dotson RC, Griffith DA.  2000.  Continuous, underway sampling of eggs of Pacific sardine (Sardinops sagax) and northern anchovy (Engraulis mordax) in spring 1996 and 1997 off southern and central California. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 47:1139-1155. AbstractWebsite

Eggs of the northern anchovy and Pacific sardine were sampled at 3 m depth using the Continuous, Underway Fish Egg Sampler (CUFES) during two cruises off southern and central California in March and April 1996 and 1997. Simultaneous measurements were made of seawater temperature and salinity. Real-time AVHRR satellite images of sea surface temperature were processed onshore and transmitted to the ship at sea. Sardine and anchovy eggs were identified and counted live, at sea, and again ashore, preserved. A total of 2129 CUFES samples were collected during 41 d at sea and contained 62,409 sardine and 15,123 anchovy eggs. Sardine eggs were widespread and abundant in both cruises (mean concentrations: 5.2 and 5.1 eggs m(-3)) at and shoreward of the eastern boundary of the California Current. Anchovy eggs were found primarily inshore in the Southern California Eight and were less abundant (0.4 and 1.0 eggs m(-3), respectively, for the two cruises). Temperature-salinity plots indicated distinct separation of the spawning habitat of these two species and consistency in habitat between cruises in successive years. The distributions of sardine eggs and euphausiids collected by CUFES were complementary in space and time. (C) 2000 Elsevier Science Ltd. All rights reserved.

Rose, KA, Fiechter J, Curchitser EN, Hedstrom K, Bernal M, Creekmore S, Haynie A, Ito S, Lluch-Cota S, Megrey BA, Edwards CA, Checkley D, Koslow T, McClatchie S, Werner F, MacCall A, Agostini V.  2015.  Demonstration of a fully-coupled end-to-end model for small pelagic fish using sardine and anchovy in the California Current. Progress in Oceanography. 138:348-380.   10.1016/j.pocean.2015.01.012   AbstractWebsite

We describe and document an end-to-end model of anchovy and sardine population dynamics in the California Current as a proof of principle that such coupled models can be developed and implemented. The end-to-end model is 3-dimensional, time-varying, and multispecies, and consists of four coupled sub-models: hydrodynamics, Eulerian nutrient-phytoplankton-zooplankton (NPZ), an individual-based full life cycle anchovy and sardine submodel, and an agent-based fishing fleet submodel. A predator roughly mimicking albacore was included as individuals that consumed anchovy and sardine. All submodels were coded within the ROMS open-source community model, and used the same resolution spatial grid and were all solved simultaneously to allow for possible feedbacks among the submodels. We used a super-individual approach and solved the coupled models on a distributed memory parallel computer, both of which created challenging but resolvable bookkeeping challenges. The anchovy and sardine growth, mortality, reproduction, and movement, and the fishing fleet submodel, were each calibrated using simplified grids before being inserted into the full end-to-end model. An historical simulation of 1959-2008 was performed, and the latter 45 years analyzed. Sea surface height (SSH) and sea surface temperature (SST) for the historical simulation showed strong horizontal gradients and multi-year scale temporal oscillations related to various climate indices (PDO, NPGO), and both showed responses to ENSO variability. Simulated total phytoplankton was lower during strong El Nino events and higher for the strong 1999 La Nina event. The three zooplankton groups generally corresponded to the spatial and temporal variation in simulated total phytoplankton. Simulated biomasses of anchovy and sardine were within the historical range of observed biomasses but predicted biomasses showed much less inter-annual variation. Anomalies of annual biomasses of anchovy and sardine showed a switch in the mid-1990s from anchovy to sardine dominance. Simulated averaged weights- and lengths-at-age did not vary much across decades, and movement patterns showed anchovy located close to the coast while sardine were more dispersed and farther offshore. Albacore predation on anchovy and sardine was concentrated near the coast in two pockets near the Monterey Bay area and equatorward of Cape Mendocino. Predation mortality from fishing boats was concentrated where sardine age-1 and older individuals were located close to one of the five ports. We demonstrated that it is feasible to perform multi-decadal simulations of a fully-coupled end-to-end model, and that this can be done for a model that follows individual fish and boats on the same 3-dimensional grid as the hydrodynamics. Our focus here was on proof of principle and our results showed that we solved the major technical, bookkeeping, and computational issues. We discuss the next steps to increase computational speed and to include important biological differences between anchovy and sardine. In a companion paper (Fiechter et al., 2015), we further analyze the historical simulation in the context of the various hypotheses that have been proposed to explain the sardine and anchovy cycles. (C) 2015 Elsevier Ltd. All rights reserved.

Checkley, DM, Uye S, Dagg MJ, Mullin MM, Omori M, Onbe T, Zhu MY.  1992.  Diel variation of the zooplankton and its environment at neritic stations in the Inland Sea of Japan and the north-west Gulf of Mexico. Journal of Plankton Research. 14:1-40.   10.1093/plankt/14.1.1   AbstractWebsite

Diel variations in the zooplankton and its environment were investigated at two, contrasting neritic stations. The first (BG-1), in the Inland Sea of Japan, was mixed and eutrophic, while the second (GM-1), in the north-west Gulf of Mexico, was stratified and oligotrophic. Intensive studies were conducted at each station in late summer for 2-3 days. Dissolved nutrients and the particulate matter were evenly distributed in time and space at BG-1, but were variable, and often maximal at depth in a nepheloid layer, at GM-1. For each station, approximately 20 categories of zooplankton were enumerated in samples collected with a plankton pump and retained on approximately 100-mu-m mesh filters, In general, the zooplankton at BG-1 exhibited little diel variation in abundance and distribution. By contrast, most types of zooplankton at GM-1 performed diel vertical migrations, though primarily within the lower half of the water column between the thermocline and nepheloid layer. Significantly, similar taxa and stages did not always behave similarly in these two, differing environments, nor did the zooplankton at GM-1 tend to aggregate at the depths of maximal particle abundance or primary productivity. We suggest that studies of diel variation of the distribution and abundance of the zooplankton often require more intense sampling, in time and space, in environments which are stratified rather than mixed.

Dagg, MJ, Jackson GA, Checkley DM.  2014.  The distribution and vertical flux of fecal pellets from large zooplankton in Monterey bay and coastal California. Deep-Sea Research Part I-Oceanographic Research Papers. 94:72-86.   10.1016/j.dsr.2014.09.001   AbstractWebsite

We sampled zooplankton and fecal pellets in the upper 200 m of Monterey Bay and nearby coastal regions in California, USA. On several occasions, we observed high concentrations of large pellets that appeared to be produced during night-time by dielly migrating euphausiids. High concentrations of pellets were found in near-surface waters only when euphausiids co-occurred with high concentrations of large (> 10 mu m) phytoplankton. Peak concentrations of pellets at mid-depth (100 or 150 m) during the day were consistent with the calculated sinking speeds of pellets produced near the surface at night. At these high flux locations (HI group), pellet concentrations declined below mid-depth. In contrast, at locations where the phytoplankton assemblage was dominated by small phytoplankton cells (< 10 mu m), pellet production and flux were low (LO group) whether or not euphausiid populations were high. Protozooplankton concentrations did not affect this pattern. We concluded that the day and night differences in pellet concentration and flux in the HI profiles were mostly due to sinking of dielly-pulsed inputs in the surface layer, and that small zooplankton (Oithona, Oncaea), heterotrophic dinoflagellates, and bacterial activity probably caused some pellet degradation or consumption below 100 m. We estimated that consumption of sinking pellets by large copepods was insignificant. High fluxes of pellets were episodic because they required both high concentrations of large phytoplankton and large stocks of euphausiids. Under these conditions, flux events overwhelmed retention mechanisms, resulting in large exports of organic matter from the upper 200 m. (C) 2014 The Authors. Published by Elsevier Ltd.

Hoss, DE, Checkley Jr. DM, Settle LR.  1989.  Diurnal buoyancy changes in larval Atlantic menhaden (Brevoortia tyrannus). Journal du Conseil International pour l'Exploration de la Mer. 191:105-111. Abstract
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Asch, RG, Checkley Jr DM.  2013.  Dynamic height: A key variable for identifying the spawning habitat of small pelagic fishes. Deep Sea Research Part I: Oceanographic Research Papers. 71:79-91.   10.1016/j.dsr.2012.08.006   AbstractWebsite

Small pelagic fishes off southern California exhibit interannual variations in the regions they occupy. An enhanced understanding of these fluctuations could improve fisheries management and predictions of fish's responses to climate change. We investigated dynamic height as a variable for identifying the spawning habitat of northern anchovy (Engraulis mordax), Pacific sardine (Sardinops sagax), and jack mackerel (Trachurus symmetricus). During cruises between 1998 and 2004, dynamic height was calculated from temperature and salinity profiles, while fish egg concentration was measured with obliquely towed bongo nets and the Continuous, Underway Fish Egg Sampler. Dynamic height ranged between 68 and 108 cm, with values increasing offshore. The greatest probability of encountering anchovy, sardine, and jack mackerel eggs occurred at dynamic heights of 79–83 cm, 84–89 cm, and 89–99 cm, respectively. Four mechanisms were proposed to explain how dynamic height affects egg distribution: (1) dynamic height is a proxy for upper water column temperature and salinity, which are known to influence spawning habitat. (2) Low dynamic heights are indicative of coastal upwelling, which increases primary and secondary productivity. (3) Egg concentration is greater at dynamic heights coincident with geostrophic currents that transport larvae to favorable habitats. (4) Eddies delineated by dynamic height contours retain eggs in productive habitats. To evaluate these mechanisms, a generalized linear model was constructed using dynamic height, temperature, salinity, chlorophyll, zooplankton volume, geostrophic currents, and eddies as independent variables. Dynamic height explained more variance than any other variable in models of sardine and anchovy spawning habitat. Together temperature, salinity, and chlorophyll accounted for 80–95% of the dynamic height effect, emphasizing the importance of the first two mechanisms. However, dynamic height remained statistically significant in the models of anchovy and jack mackerel spawning habitat after considering the effects of all other variables. Dynamic height shows promise as an ecological indicator of spawning habitat, because it integrates the effects of multiple oceanic variables, can be remotely sensed, and is predicted by ocean circulation models.

Checkley, DM.  1980.  The egg production of a marine panktonic copepod in relation to its food supply - Laboratory studies. Limnology and Oceanography. 25:430-446. AbstractWebsite

Egg production by Paracalanus parvus, a particle-grazingcopepod, was investigated in relation to its food supply. The concentration of available food (P) and the rates of ingestion (I) and egg production (B) were measured simultaneously at intervals of 6 h to 2 d for periods of 2-10 d. Concentration, chemical composition (carbon and nitrogen), and species of phytoplankton were experimental variables.Egg production was related to the food ingested during the previous day. For one food type, I and B were rectilinear functions of P. The average maximum rates of ingestion and egg production were 1.1 µg N ∙ female^-1 ∙ d^-1 and 53 eggs ∙ female^-1 ∙d^-1, equivalent to specific rates of 1.5 and 0.37 d^-1. B was proportional to I below a critical ingestion rate, Ic, and independent of I above Ic. For I < Ic, the gross efficiency of egg production (B ∙ I^-1) in terms of nitrogen was 0.37 while in terms of carbon it was a hyperbolic function of the ratio of C:N in the food, ranging between 0.41 (C:Nfood= 4.0) and 0.15 (C:Nfood= 11). For I >Ic, B ∙ I^-1 declined in terms of both carbon and nitrogen.These results, together with the ratio of C:N in particulate matteri n the sea off southern California, suggest that nitrogen (hence protein) potentially limits egg production by adult female Paracalanus and that ingested carbon is used inefficiently.