Abundance,survival, and annual rate of change of Cuvier's beaked whales (Ziphius cavirostris) on a Navy sonar range

Bayesian mark-recapture estimates of survival, abundance, and trend are reported for Cuvier's beaked whales (Ziphius cavirostris) using a Navy training range off southern California. The deep-diving beaked whale family is exceptionally vulnerable to mid-frequency active sonar (MFAS), which has been implicated in mass strandings and altered foraging behavior. Extremely low sighting probabilities impede studies of population-level impacts of MFAS on beaked whales. The San Nicolas Basin hosts a Navy training range subject to frequent MFAS use and attracts high densities of Z. cavirostris. An 11-year (2007–2018) photo-identification program leveraged automated acoustic detection and location capabilities on the range's 1,800-km² hydrophone array to enhance capture probability. Estimated population parameters for Z. cavirostris using the range included mean (90% credibility intervals) apparent annual survival of 0.950 (0.899–0.986), annual number of individuals as 121 (71–219), and annual rate of change of −0.8% (−5.6%–4.1%). Simulations show the probability of detecting abundance changes is currently low, but can be greatly improved through continued monitoring and increased effort. Complementary data collection on habitat use and demographic rates in San Nicolas and surrounding basins is also essential to relating direct effects of MFAS use to changes in vital rates and broader population outcomes.     

Organisation of the soil seed bank in mixed chaparral

Seed densities, estimated from germinations under glasshouse conditions, were determined for fire-treated and control soils sampled from north and south facing stands of mixedAdenostoma fasciculatum-Ceanothus greggii chaparral that last burned 10, 17, 36, 62 and 86 years before 1987. A total of 53 species was recorded. Total germinable seed density was not influenced by aspect nor by an experimental fire treatment, however, densities varied significantly, but not predictably, over the time since fire sequence. Species diversity was significantly lower in the 86 year old stand, but neither diversity or richness was influenced by the fire treatment. Soils from north facing slopes supported a higher species diversity overall, and seed densities of six species were significantly higher on north than on south slopes.We identify two functional groups in the seed bank on the basis of the direct effects of fire on seed densities: a fire-dependent group, comprising 6 species and about 21% of the total seed bank, in which germinable densities increased after the fire treatment, and a fire-independent group, made up of 11 species and almost two-thirds of the seed bank. The fire-independent group is further separated into two: a shrub-centred sub-group (Crassula erecta, Filago californica, Pterostegia drymarioides, Streptanthus heterophyllus andCryptantha intermedia) maintained larger seed banks in older stands and was associated with shrub cover; and an opportunistic sub-group (Camissonia hirtella, Gnaphalium chilense, Mimulus pilosus andSenecio vulgaris) tended to have larger seed banks in younger stands and was associated with canopy gaps.Overall, the soil seed assemblage from this mixed chaparral does not appear to be tightly coupled to fire-generated opportunities for recruitment. The reason for this is that the fire-dependent group represents only 6 species. In addition, among the fire-independent species, the shrub-centred group of 5 annuals made up almost 40% of total soil seed density. This group shows ecological and taxonomic affinities with desert annuals.     

Charles Stacy French: A tribute

Charles Stacy French, one of the great men of photosynthesis research, died on 13 October 1995. He received his PhD at Harvard University where he associated with William Arnold, Caryl Haskins, later president of the Carnegie Institution of Washington, and Pei-Sung Tang. He did early work on the photosynthesis of photosynthetic bacteria with Robert Emerson and later with Otto Warburg. French worked for three years with James Franck in Chicago. His associates there included Hans Gaffron, Robert Livingston, Warren Butler and Roderick Clayton. After spending three years at the University of Minnesota he became the director of the Department of Plant Biology of the Carnegie Institution of Washington and remained there until he retired in 1973. French's research career at the Carnegie Institution was marked by the development of novel and ingenious pieces of equipment such as the French pressure cell used to prepare chloroplast particles to measure partial reactions of photosynthesis. He developed the first recording fluorescence spectrophotometer and demonstrated efficient energy transfer between certain photosynthetically-active pigments, a spectrophotometer that measured the first derivative of absorbance, as well as a novel analog computer to show that complex absorption curves in living plants are produced by a number of distinct forms of chlorophyll occurring in vivo. French used the Blinks rate-measuring oxygen electrode to measure action spectra of oxygen evolution by photosynthesis automatically. He and Jack Myers did some of the pioneering work on the Emerson effect showing the necessary cooperation of two photosystems in photosynthesis. French used the Carnegie Institution's fellowship program to bring large numbers of scientists from around the world to his laboratory. When Stacy French died in 1995, the field of photosynthesis lost one of its great and early pioneers.This is CIW/DPB publication No. 1314.     

Mass distribution in the fronds of macrocystis pyrifera from New Zealand and California

The mass distribution along the fronds of Macrocystis is examined for plants collected from California and New Zealand. Analysis of fronds classified according to length and condition yields polynomial curves for cumulative mass as a function of distance above the holdfast. Models for this functional relationship are discussed. Similarities and differences between the deep-water California plant and the shallow-water New Zealand plant are highlighted.     

Exotic plant invasions in an endemic‐rich habitat: The spread of an introduced Australian grass,Agrostis avenacea J. F. Gmel., in California vernal pools

Abstract The present abundance and historical spread of an exotic grass, Agrostis avenacea, is documented for California, USA, and for the vernal pools of San Diego County in particular. Agrostis avenacea is native to Australia where it is a common grass of ephemeral and fluctuating wetlands. California vernal pools, by reason of their extreme variability and high endemism, have been thought to be relatively resistant to invasion. The recent expansion of A. avenacea in San Diego County demonstrates, however, that the alleged resistance is probably a function of a relatively small pool of invaders and a low probability of targeted dispersal. Although A. avenacea is now abundant in pools with little current disturbance, human disturbance appears to have been a major factor that facilitated its initial establishment. This specific instance adds to the mounting evidence that there are probably few, if any, habitats immune to invasion.     

Spatial Variability in Decomposition Rates in a Desert Scrub of Northwestern Mexico

The decomposition of leaf litter for five dominant plant species of a desert scrub in Baja California Sur, Mexico was investigated. We designed a factorial decomposition experiment using decomposition bags and the collected leaf-litter from Prosopis articulata, Jatropha cinerea, J. cuneata, Cyrtocarpa edulis, and Fouquieria diguetti. Factors, such as radiation exposure, rainfall, and the size of litter-consuming organisms were considered. The rates of litter decomposition were calculated for these plant species and the environmental conditions by using single exponential models. The initial concentration of nutrients (C, N, P, K, and Ca) and crude-fiber content of the leaf litter were determined. Our results show that the environmental heterogeneity generated by different conditions of radiation exposure and short-term rainfall patterns are the most relevant factors affecting decomposition processes in this Sonoran desert community. A species-specific pattern was observed in decay rates and mass-loss patterns. Decomposition rates varied from 0.0027 to 0.0201 depending on the species and exposure to different ecological conditions. The decay rates were higher under bare-soil conditions and during a wet year than under the shade provided by the canopy of nurse trees and during a dry year. The leaf litter of J. cuneata reincorporated to the soil more rapidly than that of P. articulata and C. edulis. Termites were the more important macroarthropods associated with litter decomposition, and their harvest distribution was independent of the resources distribution. The ecological significance of these results is discussed considering the extreme climatic conditions prevailing in this region.     

A marine protected area network does not confer community structure resilience to a marine heatwave across coastal ecosystems

Marine protected areas (MPAs) have gained attention as a conservation tool for enhancing ecosystem resilience to climate change. However, empirical evidence explicitly linking MPAs to enhanced ecological resilience is limited and mixed. To better understand whether MPAs can buffer climate impacts, we tested the resistance and recovery of marine communities to the 2014–2016 Northeast Pacific heatwave in the largest scientifically designed MPA network in the world off the coast of California, United States. The network consists of 124 MPAs (48 no-take state marine reserves, and 76 partial-take or special regulation conservation areas) implemented at different times, with full implementation completed in 2012. We compared fish, benthic invertebrate, and macroalgal community structure inside and outside of 13 no-take MPAs across rocky intertidal, kelp forest, shallow reef, and deep reef nearshore habitats in California's Central Coast region from 2007 to 2020. We also explored whether MPA features, including age, size, depth, proportion rock, historic fishing pressure, habitat diversity and richness, connectivity, and fish biomass response ratios (proxy for ecological performance), conferred climate resilience for kelp forest and rocky intertidal habitats spanning 28 MPAs across the full network. Ecological communities dramatically shifted due to the marine heatwave across all four nearshore habitats, and MPAs did not facilitate habitat-wide resistance or recovery. Only in protected rocky intertidal habitats did community structure significantly resist marine heatwave impacts. Community shifts were associated with a pronounced decline in the relative proportion of cold water species and an increase in warm water species. MPA features did not explain resistance or recovery to the marine heatwave. Collectively, our findings suggest that MPAs have limited ability to mitigate the impacts of marine heatwaves on community structure. Given that mechanisms of resilience to climate perturbations are complex, there is a clear need to expand assessments of ecosystem-wide consequences resulting from acute climate-driven perturbations, and the potential role of regulatory protection in mitigating community structure changes.