Standing Crop, Turnover, and Production Dynamics of Macrocystis pyrifera and Understory Species Hedophyllum nigripes and Neoagarum fimbriatum in High Latitude Giant Kelp Forests.

Production rates reported for canopy-forming kelps have highlighted the potential contributions of these foundational macroalgal species to carbon cycling and sequestration on a globally relevant scale. Yet, the production dynamics of many kelp species remain poorly resolved. For example, productivity estimates for the widely distributed giant kelp Macrocystis pyrifera are based on a few studies from the center of this species' range. To address this geospatial bias, we surveyed giant kelp beds in their high latitude fringe habitat in southeast Alaska to quantify foliar standing crop, growth and loss rates, and productivity of M. pyrifera and co-occurring understory kelps Hedophyllum nigripes and Neoagarum fimbriatum. We found that giant kelp beds at the poleward edge of their range produce ~150 g C · m-2 · year-1 from a standing biomass that turns over an estimated 2.1 times per year, substantially lower rates than have been observed at lower latitudes. Although the productivity of high latitude M. pyrifera dwarfs production by associated understory kelps in both winter and summer seasons, phenological differences in growth and relative carbon and nitrogen content among the three kelp species suggests their complementary value as nutritional resources to consumers. This work represents the highest latitude consideration of M. pyrifera forest production to date, providing a valuable quantification of kelp carbon cycling in this highly seasonal environment.

Ecological change in dynamic environments: Accounting for temporal environmental variability in studies of ocean change biology.

The environmental conditions in the ocean have long been considered relatively more stable through time compared to the conditions on land. Advances in sensing technologies, however, are increasingly revealing substantial fluctuations in abiotic factors over ecologically and evolutionarily relevant timescales in the ocean, leading to a growing recognition of the dynamism of the marine environment as well as new questions about how this dynamism may influence species' vulnerability to global environmental change. In some instances, the diurnal or seasonal variability in major environmental change drivers, such as temperature, pH and seawater carbonate chemistry, and dissolved oxygen, can exceed the changes expected with continued anthropogenic global change. While ocean global change biologists have begun to experimentally test how variability in environmental conditions mediates species' responses to changes in the mean, the extensive literature on species' adaptations to temporal variability in their environment and the implications of this variability for their evolutionary responses has not been well integrated into the field. Here, we review the physiological mechanisms underlying species' responses to changes in temperature, pCO2 /pH (and other carbonate parameters), and dissolved oxygen, and discuss what is known about behavioral, plastic, and evolutionary strategies for dealing with variable environments. In addition, we discuss how exposure to variability may influence species' responses to changes in the mean conditions and highlight key research needs for ocean global change biology.

Locomotion and behavior of Humboldt squid, Dosidicus gigas, in relation to natural hypoxia in the Gulf of California, Mexico.

We studied the locomotion and behavior of Dosidicus gigas using pop-up archival transmitting (PAT) tags to record environmental parameters (depth, temperature and light) and an animal-borne video package (AVP) to log these parameters plus acceleration along three axes and record forward-directed video under natural lighting. A basic cycle of locomotor behavior in D. gigas involves an active climb of a few meters followed by a passive (with respect to jetting) downward glide carried out in a fins-first direction. Temporal summation of such climb-and-glide events underlies a rich assortment of vertical movements that can reach vertical velocities of 3 m s(-1). In contrast to such rapid movements, D. gigas spends more than 80% of total time gliding at a vertical velocity of essentially zero (53% at 0±0.05 m s(-1)) or sinking very slowly (28% at -0.05 to -0.15 m s(-1)). The vertical distribution of squid was compared with physical features of the local water column (temperature, oxygen and light). Oxygen concentrations of ≤20 µmol kg(-1), characteristic of the midwater oxygen minimum zone (OMZ), can influence the daytime depth of squid, but this depends on location and season, and squid can 'decouple' from this environmental feature. Light is also an important factor in determining daytime depth, and temperature can limit nighttime depth. Vertical velocities were compared over specific depth ranges characterized by large differences in dissolved oxygen. Velocities were generally reduced under OMZ conditions, with faster jetting being most strongly affected. These data are discussed in terms of increased efficiency of climb-and-glide swimming and the potential for foraging at hypoxic depths.