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1. Large-scale impacts of sea star wasting disease (SSWD) on intertidal sea stars and implications for recovery

   https://doi.org/https://www.doi.org/10.1371/journal.pone.0192870  

   C. Melissa Miner1*, Jennifer L. ( March 2018 , PloS one)

   Disease outbreaks can have substantial impacts on wild populations, but the often patchy or anecdotal evidence of these impacts impedes our ability to understand outbreak dynamics. Recently however, a severe disease outbreak occurred in a group of very well-studied organisms±sea stars along the west coast of North America. We analyzed nearly two decades of data from a coordinated monitoring effort at 88 sites ranging from southern British Columbia to San Diego, California along with 2 sites near Sitka, Alaska to better understand the effects of sea star wasting disease (SSWD) on the keystone intertidal predator, Pisaster ochraceus. Quantitative surveys revealed unprecedented declines of P. ochraceus in 2014 and 2015 across nearly the entire geographic range of the species. The intensity of the impact of SSWD was not uniform across the affected area, with proportionally greater population declines in the southern regions relative to the north. The degree of population decline was unrelated to pre-outbreak P. ochraceus density, although these factors have been linked in other well-documented disease events. While elevated seawater temperatures were not broadly linked to the initial emergence of SSWD, anomalously high seawater temperatures in 2014 and 2015 might have exacerbated the disease's impact. Both before and after the onset of the SSWD outbreak, we documented higher recruitment of P. ochraceus in the north than in the south, and while some juveniles are surviving (as evidenced by transition of recruitment pulses to larger size classes), post-SSWD survivorship is lower than during pre-SSWD periods. In hindsight, our data suggest that the SSWD event defied prediction based on two factors found to be important in other marine disease events, sea water temperature and population density, and illustrate the importance of surveillance of natural populations as one element of an integrated approach to marine disease ecology. Low levels of SSWD-symptomatic sea stars are still present throughout the impacted range, thus the outlook for population recovery is uncertain. 

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2. Testing ecological release as a compensating mechanism for mass mortality in a keystone predator

   https://doi.org/10.3354/meps13227  

   Sullivan-Stack, J ; Menge, BA ( March 2020 , Marine Ecology Progress Series)

   Top predator decline has been ubiquitous across systems over the past decades and centuries, and predicting changes in resultant community dynamics is a major challenge for ecologists and managers. Ecological release predicts that loss of a limiting factor, such as a dominant competitor or predator, can release a species from control, thus allowing increases in its size, density, and/or distribution. The 2014 sea star wasting syndrome (SSWS) outbreak decimated populations of the keystone predator Pisaster ochraceus along the Oregon coast, USA. This event provided an opportunity to test the predictions of ecological release across a broad spatial scale and determine the role of competitive dynamics in top predator recovery. We hypothesized that after P. ochraceus loss, populations of the subordinate sea star Leptasterias sp. would grow larger, more abundant, and move downshore. We based these predictions on prior research in Washington State showing that Leptasterias sp. competed with P. ochraceus for food. Further, we predicted that ecological release of Leptasterias sp. could provide a bottleneck to P. ochraceus recovery. Using field surveys, we found no clear change in density or distribution in Leptasterias sp. populations post-SSWS, and decreases in body size. In a field experiment, we found no evidence of competition between similar-sized Leptasterias sp. and P. ochraceus . Thus, the mechanisms underlying our predictions were not in effect along the Oregon coast, which we attribute to differences in habitat overlap and food availability between the 2 regions. Our results suggest that response to the loss of a dominant competitor can be unpredictable even when based in theory and previous research. 

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3. Long‐term population dynamics of dreissenid mussels ( Dreissena polymorpha and D. rostriformis ): a cross‐system analysis

   https://doi.org/10.1002/ecs2.2701  

   Strayer, David L. ; Adamovich, Boris V. ; Adrian, Rita ; Aldridge, David C. ; Balogh, Csilla ; Burlakova, Lyubov E. ; Fried‐Petersen, Hannah B. ; G.‐Tóth, László ; Hetherington, Amy L. ; Jones, Thomas S. ; et al ( April 2019 , Ecosphere)

   Dreissenid mussels (including the zebra musselDreissena polymorphaand the quagga musselD. rostriformis) are among the world's most notorious invasive species, with large and widespread ecological and economic effects. However, their long‐term population dynamics are poorly known, even though these dynamics are critical to determining impacts and effective management. We gathered and analyzed 67 long‐term (>10 yr) data sets on dreissenid populations from lakes and rivers across Europe and North America. We addressed five questions: (1) How doDreissenapopulations change through time? (2) Specifically, doDreissenapopulations decline substantially after an initial outbreak phase? (3) Do different measures of population performance (biomass or density of settled animals, veliger density, recruitment of young) follow the same patterns through time? (4) How do the numbers or biomass of zebra mussels or of both species combined change after the quagga mussel arrives? (5) How does body size change over time? We also considered whether current data on long‐term dynamics ofDreissenapopulations are adequate for science and management. IndividualDreissenapopulations showed a wide range of temporal dynamics, but we could detect only two general patterns that applied across many populations: (1) Populations of both species increased rapidly in the first 1–2 yr after appearance, and (2) quagga mussels appeared later than zebra mussels and usually quickly caused large declines in zebra mussel populations. We found little evidence that combinedDreissenapopulations declined over the long term. Different measures of population performance were not congruent; the temporal dynamics of one life stage or population attribute cannot generally be accurately inferred from the dynamics of another. We found no consistent patterns in the long‐term dynamics of body size. The long‐term dynamics ofDreissenapopulations probably are driven by the ecological characteristics (e.g., predation, nutrient inputs, water temperature) and their temporal changes at individual sites rather than following a generalized time course that applies across many sites. Existing long‐term data sets on dreissenid populations, although clearly valuable, are inadequate to meet research and management needs. Data sets could be improved by standardizing sampling designs and methods, routinely collecting more variables, and increasing support.

    

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4. Rocky Mountain forests are poised to recover following bark beetle outbreaks but with altered composition

   https://doi.org/10.1111/1365-2745.13999  

   Rodman, Kyle C. ; Andrus, Robert A. ; Carlson, Amanda R. ; Carter, Trevor A. ; Chapman, Teresa B. ; Coop, Jonathan D. ; Fornwalt, Paula J. ; Gill, Nathan S. ; Harvey, Brian J. ; Hoffman, Ashley E. ; et al ( December 2022 , Journal of Ecology)

   1. Amplified by warming temperatures and drought, recent outbreaks of native bark beetles (Curculionidae: Scolytinae) have caused extensive tree mortality throughout Europe and North America. Despite their ubiquitous nature and important effects on ecosystems, forest recovery following such disturbances is poorly understood, particularly across regions with varying abiotic conditions and outbreak effects. 2. To better understand post-outbreak recovery across a topographically complex region, we synthesized data from 16 field studies spanning subalpine forests in the Southern Rocky Mountains, USA. From 1997 to 2019, these forests were heavily affected by outbreaks of three native bark beetle species (Dendroctonus ponderosae, Dendroctonus rufipennis and Dryocoetes confusus). We compared pre- and post-outbreak forest conditions and developed region-wide predictive maps of post-outbreak (1) live basal areas, (2) juvenile densities and (3) height growth rates for the most abundant tree species – aspen (Populus tremuloides), Engelmann spruce (Picea engelmannii), lodgepole pine (Pinus contorta) and subalpine fir (Abies lasiocarpa). 3. Beetle-caused tree mortality reduced the average diameter of live trees by 28.4% (5.6 cm), and species dominance was altered on 27.8% of field plots with shifts away from pine and spruce. However, most plots (82.1%) were likely to recover towards pre-outbreak tree densities without additional regeneration. Region-wide maps indicated that fir and aspen, non-host species for bark beetle species with the most severe effects (i.e. Dendroctonus spp.), will benefit from outbreaks through increased compositional dominance. After accounting for individual size, height growth for all conifer species was more rapid in sites with low winter precipitation, high winter temperatures and severe outbreaks. 4. Synthesis. In subalpine forests of the US Rocky Mountains, recent bark beetle outbreaks have reduced tree size and altered species composition. While eventual recovery of the pre-outbreak forest structure is likely in most places, changes in species composition may persist for decades. Still, forest communities following bark beetle outbreaks are widely variable due to differences in pre-outbreak conditions, outbreak severity and abiotic gradients. This regional variability has critical implications for ecosystem services and susceptibility to future disturbances. 

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5. Climate and fishing drive regime shifts in consumer‐mediated nutrient cycling in kelp forests

   https://doi.org/10.1111/gcb.14706  

   Peters, Joseph R. ; Reed, Daniel C. ; Burkepile, Deron E. ( June 2019 , Global Change Biology)

   Globally, anthropogenic pressures are reducing the abundances of marine species and altering ecosystems through modification of trophic interactions. Yet, consumer declines also disrupt important bottom‐up processes, like nutrient recycling, which are critical for ecosystem functioning. Consumer‐mediated nutrient dynamics (CND) is now considered a major biogeochemical component of most ecosystems, but lacking long‐term studies, it is difficult to predict how CND will respond to accelerating disturbances in the wake of global change. To aid such predictions, we coupled empirical ammonium excretion rates with an 18‐year time series of the standing biomass of common benthic macroinvertebrates in southern California kelp forests. This time series of excretion rates encompassed an extended period of extreme ocean warming, disease outbreaks, and the abolishment of fishing at two of our study sites, allowing us to assess kelp forest CND across a wide range of environmental conditions. At their peak, reef invertebrates supplied an average of 18.3 ± 3.0 µmol NH₄⁺ m⁻² hr⁻¹to kelp forests when sea stars were regionally abundant, but dropped to 3.5 ± 1.0 µmol NH₄⁺ m⁻² hr⁻¹following their mass mortality due to disease during a prolonged period of extreme warming. However, a coincident increase in the abundance of the California spiny lobster,Palinurus interupptus(Randall, 1840), likely in response to both reduced fishing and a warmer ocean, compensated for much of the recycled ammonium lost to sea star mortality. Both lobsters and sea stars are widely recognized as key predators that can profoundly influence community structure in benthic marine systems. Our study is the first to demonstrate their importance in nutrient cycling, thus expanding their roles in the ecosystem. Climate change is increasing the frequency and severity of warming events, and rising human populations are intensifying fishing pressure in coastal ecosystems worldwide. Our study documents how these projected global changes can drive regime shifts in CND and fundamentally alter a critical ecosystem function.

    

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