Pelican Briefs are designed for general audiences (managers, policy-makers, and informed members of the public). The name refers to the iconic California brown pelican, a once-endangered species in the California Current marine ecosystem which has recovered from chemical contamination of its primary food sources. In each brief, a synopsis of a recent research paper from Farallon Institute scientists is presented. The mission of Pelican Brief is to facilitate communication between scientists and general audiences and in doing so provide a bridge to decision-makers and other interested parties.
Global effects of climate change
This brief summarizes “Global imprint of climate change on marine life,” a paper by Poloczanska et al. published in the journal Nature Climate Change.
How is global climate change directly affecting the oceans?
The ocean has absorbed over 80% of the heat added to the earth’s system due to climate change, but water temperatures are changing three times slower than terrestrial air temperatures. Significant changes in temperature patterns, however, show the effects of climate change on marine ecosystems. Some effects of increasing temperatures are changes in marine species distributions as well as their timing of reproduction. Additionally, CO2 uptake is leading to ocean acidification. This causes a decrease in calcification, meaning that certain species are having difficulty forming shells. All in all, the evidence reveals that marine organisms are at least equally likely to respond to climate change as terrestrial species.
How is this study unique?
Most studies generally focus on limited species, regions, or biological responses; in this study, we provide a comprehensive study of the effects of global climate change on marine ecosystems. In order to do so, we synthesized information from 208 studies, creating a data set of 1,735 marine biological responses to anthropogenic climate change. This study includes responses consistent with and contradictory to the predictions of climate change consequences, as well as some studies in which no change was observed.
On a global scale, how did the responses line up with the expectations?
We examined distribution, phenology, abundance, community change, calcification and demography of marine species, taking into account studies from every one of the world’s oceans. We found that 81-83% of the biological responses were consistent with the expectations of global climate change. These results speak to the magnitude of the effects of climate change and its importance in marine ecosystems.
Supporting evidence may include biases, but we attempted to mitigate any possible problems by considering groups of data spanning 30 years or more and discounting changes attributed to factors other than climate change. Furthermore, 24% of the species in our data showed no response, which could be due to sub-par data collection techniques and analysis, complex drivers of change, or evolutionary adaptation.
A roadmap for the future
This brief summarizes the paper “Seabirds and climate change: roadmap for the future” by Sydeman et al., which was published in the journal Marine Ecology Progress Series in 2012.
What are some of the predicted effects of global climate change?
Scientists predict significant global temperature increases due to rising greenhouse gas concentrations. Much of this heat will continue to be absorbed by the oceans, exacerbating other anticipated physical changes such as decreased sea ice mass and rising sea levels. These environmental changes are likely to have a notable impact on the dynamics of both marine and terrestrial ecosystems. Consequently, it is necessary for scientists to provide policymakers with substantial research on the effects of climate change.
What role do seabirds play in the study of the effects of climate change on the natural world?
Seabirds are unique in that they live at the barrier between the ocean and the atmosphere and rely on both terrestrial and marine habitats for survival. Because of this, seabird species are both good indicators and constant casualties of global climate change. Seabirds rely primarily on micronekton (small fish and squids) and mesozooplankton (krill and copepods) for food; these small species are highly susceptible to climactic variation, so seabird productivity also reflects climate change through effects of food availability.
What was the goal of our analysis?
We prepared a literature review for a a variety of studies to lay out past, present, and possible future developments of the effects of climate change on seabird populations. We used studies from both the northern and southern hemispheres that focused on a host of factors, including timing of breeding and migration, habitat choice, range, demographic traits, food habits, and community structure. We analyzed results from these papers in order to identify patterns and explore possible inconsistencies, thus providing a comprehensive view of how climate change is affecting seabirds.
What did we conclude?
It is clear that seabirds are responding to climate change on a global scale and thus can be of use to us in demonstrating the potential future effects of this phenomenon. However, the methods by which scientists study these species could be adjusted in order to provide a more comprehensive view, linking climate, oceanographic conditions, food resources, and seabird responses. Integrated ecosystem science is the future of accurately predicting changes in seabird populations.
Although many of the studies included in this analysis are highly credible and respected in the scientific world, not all of them have the duration to eliminate the chance that the variation is due to expected decadal variability rather than human-caused climate change. To address this issue, we recommend that data continue to be collected on developments in the seabird sphere so that scientists can make statistically significant inferences.
Changes in krill distribution
This brief summarizes “Advection and starvation cause krill (Euphausia pacifica) decreases in 2005 Northern California coastal populations: Implications from a model study” by Dorman et al., which was published in the journal Geophysical Research Letters.
Why are krill studied so often?
Krill play a key role in marine food webs; they consume large phytoplankton and are consumed by a host of upper-level species including marine mammals and commercially important fishes such as salmon. Even if a marine organism does not directly depend on krill for sustenance, few species will go through their entire life cycle without having been within two trophic links of krill at some point. The high connectivity of krill within the marine food web means that krill availability strongly impacts the productivity and survival of upper-level species.
What did we do?
During 2005, krill availability in the northern California Current region was anomalously low. In order to investigate the cause (or causes) of this decrease, we modeled data from that year and compared it to winter/spring of 2001, which was considered to be a time of “normal” abundance. These models laid out the krill distribution for this time period and indicated how it differed from previous years.
What factors could have incited the 2005 decrease in krill availability?
During wintertime, there is often a northward current off the California coast, but the 2005 current was unusually strong and persisted for an abnormal amount of time. These differences in the alongshore currents caused krill particles to move poleward. In addition, these anomalous currents also affected upwelling along the California and Oregon coast; upwelling was delayed and reduced in comparison to “normal” years, which led to low chlorophyll a levels. Without a sufficient concentration of this essential nutrient, the productivity of this region decreased significantly.
We did not attempt to investigate the interannual variation in predation that could have impacted our results. However, species lower on the food chain are generally considered to be most directly affected by “bottom-up,” or physical, processes rather than “top-down” effects such as predation, so it is logical to conclude that krill population biology was most likely not significantly affected by differences in predation between 2001 and 2005.
Spatial organization of krill and their predators
This brief summarizes a paper by Santora et al. entitled “Spatial organization of krill and seabirds in the central California Current,” which was published in the ICES Journal of Marine Science.
What was our goal with this study?
In the past, many studies examined habitat selection and the relationship between krill distribution and organisms that depend on krill for nourishment, such as seabirds and whales. However, many of these studies covered only a brief period of time (a single season or only a few years). We aimed to outline the spatial distribution of krill in the California Current system over a five year period, thus increasing the reliability of our results. We then associated the krill distributions with seabird distributions, attempting to reinforce the hypothesis that krill and seabird distributions vary together from year to year.
What were our methods?
First, we narrowed our focus down to two species of seabirds, the Cassin’s auklet and the sooty shearwater, both of which depend heavily on krill for survival. We chose these species because although they both are greatly affected by krill abundance, each has its own unique life cycle timing (phenology) and method of feeding. We analyzed krill data from acoustic surveys (where vessels use sonar to detect the location and abundance of organisms in the water) and net samples, and we used visual surveys of seabirds to determine the spatial distribution of the species involved.
What did we conclude?
We found that in recent years, there has been considerable variation in the spatial distribution and amount of krill in the California region. Despite these fluctuations, the relationship between krill and seabird species remained steady. In general, we confirmed the hypothesis that the spatial distributions of seabirds and of krill change concurrently.
Why is this important?
A wide range of species in this region directly or indirectly depend on krill as a food source, therefore a clear understanding of the spatial distribution and abundance of krill is a solid foundation upon which policy makers can create effective ecosystem-based plans. Our results can be used to make educated decisions based on the durability of species in the California Current, including species important to commercial and recreational fisheries. It would be useful to take krill distribution into consideration when assessing the potential future health of sought-after fish species as well as areas of the ocean ecosystem most worth protecting.