Publications

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Journal Article
Osgood, KE, Checkley DM.  1997.  Observations of a deep aggregation of Calanus pacificus in the Santa Barbara Basin. Limnology and Oceanography. 42:997-1001. AbstractWebsite

An optical plankton counter/CTD package was used with zooplankton net samples to map the distribution of fifth copepodid (C5) Calanus pacificus in the Santa Barbara Basin region during two autumn cruises. Diapausing C5 C. pacificus were aggregated in a layer just above the basin's oxygen-deficient bottom waters and below its sill depth. The maximal concentration measured was 6,900 ind. m(-3) from a net sample spanning a depth range double the thickness of the C5 layer Although the C5 concentration varied, the layer was found at all stations of sufficient bottom depth within the basin. During November 1994, C5 C. pacificus accounted for 95-97% of all zooplankton caught in net samples from the layer. Relatively low concentrations of deep-dwelling C5 C. pacificus were observed at nearby stations outside the basin. We hypothesize that C5 C. pacificus descend into the Santa Barbara Basin at diapause, are trapped, and accumulate in a region of relatively low predator abundance. The resultant aggregation is estimated to contain a significant fraction of the regional C. pacificus population and thus assumes an important role in its dynamics.

Gonzalez-Quiros, R, Checkley DM.  2006.  Occurrence of fragile particles inferred from optical plankton counters used in situ and to analyze net samples collected simultaneously. Journal of Geophysical Research-Oceans. 111   10.1029/2005jc003084   AbstractWebsite

[1] We hypothesized that the optical plankton counter (OPC) senses particles in situ that are not collected by nets and analyzed in the laboratory. An OPC was deployed in situ between 1998 and 2004 in the mouth of a bongo net with 505-mu m-mesh nets in the upper 210 m at stations in the California Current Region. Here we compare paired data sets from the OPC in situ and the OPC analysis in the laboratory of the simultaneously collected net samples for four seasons of 2 years. We restricted our analysis to particle sizes 1.26 - 6.35 mm equivalent spherical diameter (ESD), a size class shown from the lab OPC data to be retained efficiently by the net. On average, 4 (3) times more particles by number (volume) were sensed in situ by the OPC than sensed in net collections by the OPC in the lab. These values varied an order of magnitude among the eight cruises examined. Time of day, distance offshore, season, year, chlorophyll a concentration, and Brunt-Vaisala frequency each explained significant variation in these differences. The excess of particles sensed in situ over that measured in the net samples was due primarily to smaller particles in the 1.26 - 6.35 mm ESD range. We infer that the particles measured by the OPC in situ but not in the lab were fragile and thus not collected by the net. We hypothesize that these fragile particles are primarily aggregates and abandoned houses of larvaceans.

Shen, SG, Chen FY, Schoppik DE, Checkley DM.  2016.  Otolith size and the vestibulo-ocular reflex of larvae of white seabass Atractoscion nobilis at high pCO(2). Marine Ecology Progress Series. 553:173-183.   10.3354/meps11791   AbstractWebsite

We investigated vestibular function and otolith size (OS) in larvae of white seabass Atractoscion nobilis exposed to high partial pressure of CO2 (pCO(2)) The context for our study is the increasing concentration of CO2 in seawater that is causing ocean acidification (OA). The utricular otoliths are aragonitic structures in the inner ear of fish that act to detect orientation and acceleration. Stimulation of the utricular otoliths during head movement results in a behavioral response called the vestibulo-ocular reflex (VOR). The VOR is a compensatory eye rotation that serves to maintain a stable image during movement. VOR is characterized by gain (ratio of eye amplitude to head amplitude) and phase shift (temporal synchrony). We hypothesized that elevated pCO(2) would increase OS and affect the VOR. We found that the sagittae and lapilli of young larvae reared at 2500 mu atm pCO(2) (treatment) were 14 to 20% and 37 to 39% larger in area, respectively, than those of larvae reared at 400 mu atm pCO(2) (control). The mean gain of treatment larvae (0.39 +/- 0.05, n = 28) was not statistically different from that of control larvae (0.30 +/- 0.03, n = 20), although there was a tendency for treatment larvae to have a larger gain. Phase shift was unchanged. Our lack of detection of a significant effect of elevated pCO(2) on the VOR may be a result of the low turbulence conditions of the experiments, large natural variation in otolith size, calibration of the VOR or mechanism of acid-base regulation of white seabass larvae.