Harold P. Batchelder

Life histories of large, grazing copepods in a subarctic ocean gyre: Neocalanus plumchrus, Neocalanus cristatus, and Eucalanus bungii in the Northeast Pacific

Life histories for the dominant, larger copepods of the subartic Pacific have been constructed by sampling from weatherships patrolling Ocean Station P (50°N, 145°W) during 1980 and 1981. Neocalanus plumchrus reproduced at depths below 250 m from July through February. Copepodite stages were present in surface layers from October through August with a large peak in numbers and biomass in spring. Fifth copepodites prepared for diapuse in 38 days during spring and descended to depths below 250 m. They commenced immediately to mature, and the females reproduced without renewed feeding. This schedule contrasts with that of the population in the Strait of Georgia, which remains in diapause from July to January and matures exclusively in January and February. There appears to be a difference between the coastal and oceanic habitats in preparing the diapausing individuals for maturation. Maturation of the diapausing stock of N. plumchrus maintained constant adult populations, averaging 714 males m−2 from June through October and 1,434 females m−2 from August through January. This constancy, together with the exponential pattern of decline in the diapause stock from September through February, suggests that density of adults may regulate maturation of fifth copepodites. Offspring of individuals delaying maturation and, thus, reproduction would benefit from the resulting moderation of intraspecific competition, probably that among copepodites. Reproduction of Neocalanus cristatus also occurred below 250 m, and, while spawning was continuous through the year, there was a substantial peak in November. That resulted in a peak of abundance for early copepodite stages in mid-winter, and a peak for the fifth copepodite stage in June. Stocking of the population of fifth copepodites in diapause below 250 m occurred from July through October. Some fifth copepodites were present in surface layers through the entire summer, and some younger copepodites persisted through the summer in progressively declining abundance just below the mixed layer. In autumn 1980 resurgence of early copepodite populations was rapid, occurring during the course of a prolonged October storm. The storm may have improved the habitat either by cooling the mixed layer or by resupplying nutrients to the euphotic zone. Eucalanus bungii reproduced in the mixed layer in early May and in early July. The first event was a spawning by females that had previously spawned in 1979 and then had returned to diapause. The second, heavier spawning (more females, more eggs per female) was by newly matured females from stocks that had overwintered as fifth copepodites. Nauplii peaked sharply in abundance on 19 July, one week after the peak in spawning. First and second copepodites peaked on 1 August, and all had advanced to the third copepodite stage by September. The diapause stock was established by September, principally between 250 and 500 m, and consisted of copepodite stages from third to sixth. Duration of the E. bungii life cycle appears to be typically two years. New nauplii develop as far as the third or fourth copepodite stage during their first summer, then enter diapause. The second summer they advance to the fifth copepodite stage and reenter diapause. Fifth copepodites mature in their third summer at two years of age. The males remain at depth and mate without subsequent feeding. Females migrate at night to the mixed layer where spawning occurs. About 20% of females that had already spawned in 1980 reentered diapause. They would reproduce again in their fourth summer at three years of age. All aspects of the life cycle suggest low mortality rates for copepodite stages, particularly at depth in the habitat occupied during diapuse. There can be no premium on rapid reproduction for E. bungii in the subartic Pacific, and there must even be benefit from spreading reproduction between years. This iteroparity may amount to a “bet-hedging” tactic, the young from a given mother having more than one chance to find sustaining conditions. It also produces gene flow between the year classes of the biennial life cycle.

Individual-based models of copepod populations in coastal upwelling regions : implications of physiologically and environmentally influenced diel vertical migration on demographic success and nearshore retention

We link a two-dimension coastal upwelling circulation hydrodynamic-ecosystem (NPZ) model with an individual-based model (IBM) for an intermediate sized (ca. 2.5 mm) copepod capable of diel vertical migration (DVM) at larger sizes. The NPZ model is that of Franks, Wroblewski and Flierl (1986), with the zooplankton state variable parameterized for macrozooplankton. IBM simulations are done with different scenarios for behavioral responses; the interaction of the organisms with the circulation is evaluated by examining growth/development, reproduction, survival and distribution. Since ocean productivity in coastal upwelling systems is greatest nearshore, zooplankton production is favored by nearshore retention. Model results, using an idealized, intermittently wind-forced, upwelling circulation, indicate that non-migrating copepods are flushed from the nearshore system in offshore zonal surface flow; highest population abundances occur offshore, in a region of relatively low food resources. Conversely, migrating copepods interact with the stratified zonal flow within the upwelling system and are retained nearshore when the amplitude of the DVM is sufficient to place the individuals in near-bottom onshore flow during the day. Environmental features, like deep-extending food resources, and physiological controls, like satiation or body size, that permit copepods to remain deeper, or spend more time away from the surface, favor nearshore retention. Diel vertical migration is one mechanism, which may permit animals to exploit favorable habitats located nearshore in upwelling systems.

Seasonal abundance, vertical distribution, and life history of Metridia pacifica (Copepoda: Calanoida) in the oceanic subarctic Pacific

Abstract Abundances of the life stages of Metridia pacifica were followed at Ocean Station P in the eastern subarctic Pacific from February 1980 to March 1981. All stages were present throughout most of the year, but spawning was most concentrated during late winter, summer, and autumn. Three cohorts appeared to be completed during the study period. Each cohort proceeded through development from early nauplii to adults at the same rate. This was probably achieved, in spite of substantially warmer sea surface temperatures during summer, because the third copepodite and older life stages (except adult males) migrate vertically during the day from the surface layer occupied at night to depths below 250 m, where water temperature does not vary seasonally. The recommencement of reproduction in February and March, following a hiatus in female reproduction from November to January, initiates a cohort and provides an impetus for a cycling of the population age structure. Cyclic variation of the female reproductive condition, whereby few females are reproducing during late May to June and in August, may reinforce the synchrony by restricting egg laying to short intervals.

The stability of an NPZ model subject to realistic levels of vertical mixing

The linear stability of a vertically-distributed, Nutrient-Phytoplankton-Zooplankton (NPZ) ocean ecosystem model is analyzed to understand how vertical mixing influences biological dynamics. In the absence of vertical diffusion, the model generally exhibits both stable fixed point and limit cycle behavior, depending on the depth and choice of parameters. Diffusion couples the dynamics of nearby levels and can induce stable profiles as well as oscillatory dynamical trajectories that become vertically phase-locked for large mixing levels. Calculations of the Lyapunov exponent reveal that vertical diffusion can drive this model into a chaotic state, though this occurs only for levels of diffusion well below those found in nature. The dynamics of the model, assuming macrozooplankton are the dominant grazers in the ecosystem, are compared to those in which microzooplankton dominate, with a faster grazing rate and poor assimilation efficiency. While the coupled physical-macrozooplanton system has a stable profile, the coupled microzooplankton profile remains unstable, even at large mixing levels. Fluctuations occur on time scales varying between a few days and a few months, depending on the parameters and magnitude of diffusion.

Abundance and distribution of ichthyoplankton in the upwelling zone off Oregon during anomalous El Niño conditions

The abundance and distribution patterns of nearshore ichthyoplankton were investigated during a year of anomalously high sea temperatures off Oregon. Samples collected from 2 to 18 km offshore from April through September of 1983 showed increased occurrences and higher abundances of taxa usually found at distances offshore of 37 km in other years. The dominant species collected, comprising more than half of the total larval fish abundance, was the northern anchovy (Engraulis mordax). Larval anchovy have rarely been collected inshore in previous studies. Many of the dominant taxa normally found inshore, especially osmerids, were present in reduced numbers in 1983. Changes in the hydrographic conditions associated with onshore surface drift and reduced summer upwelling during the 1983 El Nino could explain the distributional patterns observed. The warm inshore waters apparently provided a substantial spatial and temporal expansion of the spawning habitat for E. mordax.

Life history and population dynamics of Metridia pacifica: Results from simulation modelling

Abstract A numerical population dynamics model (POPCYCLE) has been developed that predicts numbers and phenology of the copepod Metridia pacifica Brodsky, and which was used to investigate the functional response parameters of this copepod. To accomplish these modelling goals, we developed an ‘individual vector model’. This mode of modelling is powerful, in that physiological functions are represented at the individual level (the level at which they operate), and flexible, in that extensions and applications are straightforward to implement since the fundamental unit within the model is the individual. Inter-individual variation in physiology is easily represented and the results of such variation are explicit in the model output. Equations describing growth, mortality, and reproduction are formulated and used to describe the development of individuals and to generate a population dynamics history for year-long model runs. Growth is described using an energetics-based, input-output model. Mortality is implemented as a constant daily probability of predation. Reproductive parameters of clutch size, clutch frequency, and total number of clutches are chosen to provide lifetime egg production similar to those previously reported for other calanoid copepods. In formulating the model, it was assumed that growth of M. pacifica in the subarctic Pacific was food-limited, and that temperature was unimportant. Seasonal abundance and life history data for M. pacifica from Station P in the subarctic Pacific were used to evaluate the validity of the model. The timing of life processes, such as the time for development from egg to egg, was considered the important criterion for judging the suitability of the model and chosen functional response parameters. A criterion of secondary importance was stage densities in the model similar to those observed in the field. ‘Reasonable’ parameter sets provided growth rates which allowed completion of development in a generation time of approximately 100 days; the generation time observed in the field.

Population characteristics of the Intertidal Green Sea Anemone, Anthopleura xanthogrammica, on the Oregon coast

Field population censuses using a photographic quadrat method were used to describe the density and size structure of intertidal populations of the green sea anemone, Anthopleura xanthogrammica, on different types of rocky intertidal habitats on the Oregon coast. Anemone populations in marked plots were monitored for individual motility, growth, mortality and recruitment. Experiments were performed to evaluate anemone population responses to simulated harvesting. Rocky intertidal locations with dense populations of the green anemone are not abundant along the Oregon coast. No detectable fluctuations in anemone population density or size-frequency distribution were found during the 2-year study. Adult anemones showed little movement in either disturbed or undisturbed populations. No natural mortality or recruitment was found in study plots at any Oregon coastal location between July 1977 and May 1979. Removal of adult anemones from rock surfaces did not promote recruitment from the plankton onto the newly available surface, nor did individuals adjacent to depopulated plots rapidly immigrate into the cleared areas. Individual growth is inferred to be very slow in intertidal populations. Field studies indicate that A. xanthogrammica is a long-lived, slow growing species with limited, low or erratic recruitment and highly stable intertidal adult populations. This study indicates that harvest of A. xanthogrammica will probably not be possible on a continuing basis.

Modeling Larval Connectivity of Coral Reef Organisms in the Kenya-Tanzania Region

Most coral reef organisms have a bipartite life-cycle; they are site attached to reefs as adults but have pelagic larval stages that allow them to disperse to other reefs. Connectivity among coral reef patches is critical to the survival of local populations of reef organisms, and requires movement across gaps that are not suitable habitat for recruitment. Knowledge of population connectivity among individual reef habitats within a broader geographic region of coral reefs has been identified as key to developing efficient spatial management strategies to protect marine ecosystems. The study of larval connectivity of marine organisms is a complex multidisciplinary challenge that is difficult to address by direct observation alone. An approach that couples ocean circulation models with individual based models (IBMs) of larvae with different degrees of life-history complexity has been previously used to assess connectivity patterns in several coral reef regions (e.g., the Great Barrier Reef (GBR) and the Caribbean). We applied the IBM particle tracking approach to the Kenya-Tanzania region, which exhibits strong seasonality in the alongshore currents due to the influence of the monsoon. A 3-dimensional (3D) ocean circulation model with 2 km horizontal resolution was coupled to IBMs that track virtual larvae released from each of 661 reef habitats, associated with 15 distinct regions. Given that reefs provide homes to numerous species, each with distinctive, and in aggregate very diverse life-histories, several life-history scenarios were modeled to examine the variety of dispersal and connectivity patterns possible. We characterize virtual larvae of Acropora corals and Acanthurus surgeonfish, two coral reef inhabitants with greatly differing pelagic life-histories, to examine the effects of short (50 days) pelagic larval durations (PLD), differences in swimming abilities (implemented as reef perception distances), and active depth keeping in reef connectivity. Acropora virtual larvae were modeled as 3D passive particles with a precompetency period of 4 days, a total PLD of 12 days and a perception distance of 10 m. Acanthurus virtual larvae were characterized by 50 days precompetency period, a total PLD of 72 days and a perception distance of 4 km. Acanthurus virtual larvae were modeled in

Characterizing the circulation off the Kenyan‐Tanzanian coast using an ocean model

The Kenyan-Tanzanian coastal region in the western Indian Ocean faces several environmental challenges including coral reef conservation, fisheries management, coastal erosion, and nearshore pollution. The region lacks hydrodynamic records and oceanographic studies at adequate spatial and temporal scales to provide information relevant to the local environmental issues. We have developed a 4 km horizontal resolution ocean circulation model of the region: the Kenyan-Tanzanian Coastal Model (KTCM) that provides coastal circulation and hydrography with higher resolution than previous models and observational studies of this region. Comparisons to temperature profiles, satellite-derived sea surface temperature and sea surface height anomaly fields, indicate that the model reproduces the main features of the regional circulation, while greatly increasing the details of the nearshore circulation. We describe the seasonal ocean circulation and hydrography of the Kenyan-Tanzanian coastal region based on a climatology of 8 years (2000–2007) of the KTCM simulations. The regional monsoon seasonality produces two distinct coastal circulation regimes: (1) during December–March, there are relatively sluggish shelf flows and (2) during April–November, there are strong northward transports. Simulations from the model will be useful for examining dispersal of pollutants and spatial connectivity of coral reef species.

Forecasting Northeastern Pacific Ecosystem Responses to La Niña

A decade of coastal ecosystem studies in the northeastern Pacific Ocean (NEP) have been carried out by the U.S. Global Ocean Ecosystems Dynamics (GLOBEC) program. Our understanding of how these ecosystems respond to climate forcing was assessed by way of a forecasting exercise conducted during the annual GLOBEC-NEP scientific investigator meeting held 24–25 September 2007 in Seattle, Wash. The forecasting exercise used a real-life situation as a means of identifying the strengths and gaps in the understanding of climate/ocean physics/ecosystems interactions. The nature of the exercise was not divulged ahead of time, in part to encourage interactions among participants, and also to simulate conditions under which such requests are made by the media or by local regulatory agencies and policy makers.