DOI: 10.5061/dryad.7m0cfxpxj
title: Quantitative biogeography: Decreasing and more variable dynamics of keystone and foundation species in an iconic meta-ecosystem

description: Ecosystem stability has intrigued ecologists for decades, and the
 realization that the global climate was changing sharpened and focused
 this interest. Determination of climate change effects on community
 stability, however, requires long-term studies of structure and underlying
 dynamics, including bottom-up and top-down effects in natural ecosystems.
 Although relevant datasets were rare in the early years of community
 ecology, such information has increased in recent decades. In a rocky
 intertidal system, we investigated the changes in ecological subsidies
 (nutrients, phytoplankton, prey colonization), several performance metrics
 of the dominant space occupier (mussels) and its primary predator (sea
 stars), and rate of predation by sea stars on mussels in relation to
 climatic oscillations, temperature, and disease. We focused on
 spatio-temporal changes in the mean and variability of these metrics. The
 research protocol involved annually repeated multiyear (~1999–2018),
 multisite (13 sites nested within 5 regions along ~260 km of the Oregon
 coast) observations, measurements, and experiments. We analyzed
 associations between environmental variables and ecological performance of
 key elements of the sea-star-mussel-dominated mid-intertidal system. We
 found that upwelling declined in some regions, but became more variable
 across all study regions. Air and water temperatures oscillated, but their
 mean and variation increased through time, with peak values coinciding
 with the 2014–16 combined El Niño and Marine Heat Wave. Ecological
 subsidies generally declined during the study period, and bottom-up
 processes increased in variability. Excepting growth rate, mussel (Mytilus
 californianus) performance (condition index, reproductive output)
 generally decreased and became more variable. Primarily due to a sea star
 wasting epidemic, reproductive output of the top predator Pisaster
 ochraceus decreased and became more variable, and predation rate on
 mussels also dropped abruptly. Analyses indicated that the primary drivers
 of these changes were temperature-related environmental factors. Since
 declining means and increasing variability of ecological performances are
 thought to typify destabilizing ecosystems, and environmental trends are
 toward ever more stressful conditions, the outlook for this iconic
 ecosystem is discouraging. Immediate and rapid action to mitigate and
 ultimately reverse climate change likely is the only option available to
 prevent an irreversible shift in the future of this, and most other
 ecosystems.
description: Climate measures (NPGO, ENSO, PDO) and upwelling (CUTI) indices
 were downloaded from websites given in the paper. Temperature data were
 collected in situ with dataloggers. Mussel and barnacle colonization,
 mussel growth/reproduction/condition index, nutrients, chlorophyll-a, sea
 star reproduction rate and sea star predation rate data were collected as
 noted in the paper using observations and experiments. Processing of all
 samples is described in the paper, as is data analysis.
description: All are Microsoft Excel files.