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Marine heatwaves cause widespread environmental, biological, and socio-economic impacts, placing them at the forefront of 21st-century management challenges. However, heatwaves vary in intensity and evolution, and a paucity of information on how this variability impacts marine species limits our ability to proactively manage for these extreme events. Here, we model the effects of four recent heatwaves (2014, 2015, 2019, 2020) in the Northeastern Pacific on the distributions of 14 top predator species of ecological, cultural, and commercial importance. Predicted responses were highly variable across species and heatwaves, ranging from near total loss of habitat to a two-fold increase. Heatwaves rapidly altered political bio-geographies, with up to 10% of predicted habitat across all species shifting jurisdictions during individual heatwaves. The variability in predicted responses across species and heatwaves portends the need for novel management solutions that can rapidly respond to extreme climate events. As proof-of-concept, we developed an operational dynamic ocean management tool that predicts predator distributions and responses to extreme conditions in near real-time. This study examines the effect of four marine heatwaves in the Northeast Pacific on the distributions of 14 top predators, revealing a wide-array of predator responses both among and within heatwaves. Predator responses were highly predictable, demonstrating capacity for early warning systems of heatwave impacts, similar to weather forecasts.

An apparent mismatch between periods of high reproduction (spring) and high copepodite abundance (autumn) has been observed for the copepod Calamus pacificus in Dabob Bay, Washington, U.S.A. This persistent pattern leads to a lost generation of progeny that are produced in spring but do not recruit to the juvenile and adult populations, and this is likely due to a combination of factors including advective losses, predation mortality, and nonviability of progeny. Here we test the hypothesis that observed detrimental effects of diatoms on the viability of copepod embryonic and naupliar stages (the diatom effect) are the primary reason for the observed patterns of reproduction and abundance. Furthermore, we test how assumptions about egg production rate and naupliar viability can affect calculations of copepod recruitment. To test these hypotheses, we developed a numerical model to quantitatively explore how certain parameters may have affected the population of C. pacificus population in Dabob Bay. Predation mortality was the most significant contributor to population losses, while advective losses and naupliar viability were of lesser importance, and the model results were more sensitive to parameterization of naupliar viability than egg production rate. Although brief instances of low naupliar viability caused a 25-30% reduction in cumulative stage I copepodite abundance over time when compared with the assumption of persistent high naupliar viability, the lost generation of C. pacificus in Dabob Bay is likely due to predation mortality, not the diatom effect.

We tested a hypothesis we termed ‘foray foraging’, which states that zooplankton make repeated short-term and short-distance migrations between food-rich surface layers and deeper layers throughout the night. Ultimately, the reason for the behavior is to balance the necessity of feeding with the predation risk in surface waters. We tested the hypothesis on 2 species of marine copepods, Calanus pacificus and Metridia pacifica, in Dabob Bay, Washington, USA. Zooplankton nets and traps were used to collect females of both species from specific layers and while migrating up into and down out of the surface mixed layer to determine turnover rates in the surface layer. Gut contents of individuals were measured to determine if feeding history varied between individuals caught migrating upward and downward or in different layers. Turnover rates of the surface layer were highly variable, ranging from near zero to over 1000%, and were higher in summer and autumn than in spring for both species. Gut contents were consistently higher in animals migrating downward than in those migrating upward, but overall gut contents were higher in spring than in summer or autumn. These results suggest that foray behavior varies in magnitude seasonally and occurs throughout the year for both species but is most pronounced for M. pacifica. These findings suggest that vertical migration behaviors occurring in periods shorter than diel scales may affect zooplankton population dynamics through feeding and predation and likely impact the flux of energy and material into and out of the surface mixed layer.

Evidence has shown that thin, horizontally extending phytoplankton layers may be comprised of smaller high-concentration aggregations of phytoplankton, rather than a homogeneous high-concentration sheet. A 2-D (horizontal and vertical dimensions) individual-based model of copepod foraging was developed, in order to examine whether the foraging success of a copepod would be significantly affected by phytoplankton patchiness. The foraging rules for the simulated copepods were to decrease speed and increase turning angle when high food concentrations are encountered. The underlying distributions of phytoplankton used in the model were, for the patchy layer scenario, representations of raw 2-D field fluorescence obtained using the Optical Serial Section Tomography (OSST) device, and for the homogeneous layer scenario, distributions created by simulated vertical sampling of the OSST distributions with a CTD/Fluorometer. In both the patchy and homogeneous layer scenarios, the copepods always had higher net foraging efficiency than randomly behaving controls, suggesting that the simple behavioral rules adopted are advantageous for copepod-like organisms. Foraging efficiency was significantly greater for the patchy layer scenarios than for the homogeneous layer scenarios when patches were small (i.e. one step length in width) and intense (i.e. near ingestion-saturating concentrations). Ingestion was up to 30% higher in the most patchy case versus its paired homogeneous case, suggesting that the existence of patchiness is critical to copepod survival, and that sampling scales should not exceed the step length of a copepod.

The swimming behavior of Acartia clausi within small aquaria containing phytoplankton was videotaped, along with unfed controls. From these videos, aspects such as swimming speed, distance traveled, and 2D (horizontal, X, and vertical, Z) headings were then measured from over 75000 X Z positional data in order to quantify their swimming functional response. There was generally no significant difference in swimming behavior between different food levels, although there was a large difference between feeding and unfed controls. Because feeding bouts moved the copepods a short distance at a slow speed, net vertical displacement decreased as feeding-bout frequency increased. Non-feeding individuals showed longer periods of sinking, interspersed with longer-distance, high-speed jumps, which displaced them farther distances than filter-feeding copepods over the same time interval. For both fed and unfed control copepods, a 1D unbiased random walk was adequate to describe their displacement over these very short time periods (10 s). This behavior is consistent with an area-restricted search foraging strategy. The net vertical displacements predicted by combining the experimental data with a 1D random walk model suggest that A. clausi would be retained within even small 10 cm phytoplankton patches long enough to fill their gut. However, copepods outside of phytoplankton patches must rely on other means to find patches of food greater than 50 cm apart. Potentially, knowledge of a copepod's swimming functional response could enable predictions about the typical spatial and temporal patchiness of its food in situ.[PUBLICATION ABSTRACT]

Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) on Georges Bank are subjected to a high degree of variability in temperature, turbulence, and prey densities, depending on when they are spawned and where they are advected. We have developed an individual-based model that includes the effect of varying prey density, turbulence, and temperature. Temperature effects were included by using a Q 10 -type adjustment to the standard metabolic rate as well as a second temperature-dependent term added to the overall ingestion ability of our model fish, a function of the swimming speed, capture efficiency, and \"liveliness\" of a fish. Three cases were analyzed: (i) constant food and temperature conditions, (ii) variable temperature cycles, and (iii) variable temperature cycles plus turbulence. We found that prey density, turbulence, and temperature ranges typical of the peak spawning season are variable enough to be limiting to larval growth. The timing and location of spawning are crucial to the survival of the larvae. Increasing the average temperature cycle by 1°C, as might occur due to climatological change or interannual variability, increased growth for larvae that were not growing well previously. The increased temperature failed to increase larval growth in areas where larvae were already growing at rates close to their maximum.

The California Current System (CCS) is a dynamic and highly productive region dominated by a large southward surface flow that extends from near the U.S.–Canadian border, south to the southern tip of the Baja Peninsula, and offshore to several hundred kilometers. The physics of the system are controlled primarily by atmospheric forcing, which causes direct response of the ocean. In turn, the resulting physical features of the ocean drive ecosystem responses. Hence the CCS is thought of as a “bottom up”–driven ecosystem. Although highly variable, the major feature of the atmospheric forcing is a somewhat reliable spring and

The California Current System (CCS) is one of the world’s four eastern boundary upwelling systems, which are among the most productive ecosystems in the ocean. Prevailing northwesterly winds at the California coast drive a southward-flowing current that moves cold water to lower latitudes. These winds also drive surface water offshore, causing upwelling of colder, nutrient-rich subsurface water to replace it. This seasonal abundance of nutrients results in phytoplankton blooms at the base of a food web that supports an abundance of animal species from zooplankton to small fish (e.g., anchovy and sardines) up to large predators such as tuna, sharks,

Many species of copepods form dense aggregations, known as swarms. In the laboratory, we experimentally induced 5 different species of copepod to swarm in response to a point source of light. To map out the (x, y z, t) positions of swarm members, 2 right-angle views of the 3-dimensional swarm were videotaped. Since images of individual copepods appear indistinguishable on the paired 2-dimensional projections, an algorithm was developed which matched the temporal changes of the vertical (z) positions of all images from the 2-dimensional projections of the 3-dimensional copepod movement to produce (x, y, z, f) positions of each individual. With the temporal/spatial positional data of swarm members, we tested the hypothesis that the fluid disturbance surrounding individual moving copepods, rather than the exoskeleton, maintains minimum separation distance. As the density of the swarm increased, the average nearest-neighbor distance NND decreased, as did the mean minimum NND (MNND). For 3 of the 5 species, the MNND was significantly greater than that predicted from a random distribution, and was greater than twice the antennule or prosome length. While occasional physical contact may occur, resulting in escapes or attempted mating, it appears that most swarm members remain outside the field of self-generated fluid motion in the boundary layers surrounding their neighbors.