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.
Exploration of biomass of mesopelagic fishes
This brief summarizes the paper “Mesopelagic fish biomass in the southern California current system” by Davison et al., which was published in the journal Deep-Sea Research II: Topical Studies in Oceanography.
What is the mesopelagic zone?
The mesopelagic zone is an aquatic layer of the ocean that runs from approximately 200 m to 1000 m below the surface. It is bordered above by the photic epipelagic layer and below by the aphotic bathypelagic layer. This means that the mesopelagic zone serves as a transition region between sections of the ocean illuminated by sunlight where plants can grow and sections that sunlight does not reach. Mesopelagic fishes are important marine life inhabiting this zone.
Why is the biomass of mesopelagic fishes relevant?
Because of this layer’s location between the explored and relatively unexplored regions of the ocean, mesopelagic organisms provide a link between deep sea marine life and the surface that is more familiar to humans. Many mesopelagic fishes take part in diel vertical migration, a feeding pattern in which organisms migrate vertically at night in order to feed on plankton in the productive epipelagic layer. These species play an essential role in the movement of organic matter between the surface and deeper parts of the ocean, significantly affecting open-ocean food web interactions. Mesopelagic fishes are the most abundant vertebrates on Earth, and diel vertical migration is the largest migration of animals on the planet.
In scientific literature, the influence of mesopelagic consumers of zooplankton and their role in carbon transport is often overlooked, plausibly due to a lack of knowledge about the biomass of mesopelagic organisms. Biomass is a measurement of the weight of organisms in a given area, measured in metric tons (one metric ton equals 1,000 kilograms).
How did we go about surveying mesopelagic biomass?
We surveyed mesopelagic fish populations in the Pacific Ocean off the coast of Southern California. Our data spans three years and was obtained through a combination of trawl net and sound (sonar) surveys so as to provide the most accurate result possible. In a trawl survey, large nets are used to capture organisms; the number of organisms caught is then used to make an estimate of biomass in an area. Trawl surveys tend to underestimate the biomass of mesopelagic fishes because many organisms are capable of avoiding the nets or simply pass through the mesh. We combined trawl surveys with acoustic survey methods (in which an estimation of abundance is made by using sound waves) to obtain a more accurate result.
What were our results?
The biomass of mesopelagic fishes varied depending on the area studied and the season, but results clearly support the idea that the influence of mesopelagic fishes on marine ecosystems has historically been hugely underestimated. In this region, a biomass of 25-37 g/m2 was estimated. Because most of these fishes weigh less than 1 g, there are more than 50 mesopelagic fishes for every square meter of ocean surface.
Both trawl and sonar estimates of biomass are biased by a variety of factors including community composition and the physical attributes of organisms (i.e., size, agility, fragility, and uncertain acoustic reflectance). However, the use of multiple measurement methods simultaneously can provide insight that improves the overall results.
Changes in commercial fisheries yield predicts fisheries collapses
This brief summarizes “Rising catch variability preceded historical fisheries collapses in Alaska” by Litzow et al. published in the journal Ecological Applications.
What is an ecological regime shift?
An ecological regime shift is a sudden reorganization of an environment caused by complex interactions of changing ecological dynamics. The recent intensification of human-induced environmental stressors has lead to an increase in worldwide chance of these kinds of large-scale transformations. Naturally, it is of extreme importance to those in the field of ecosystem management to be able to predict how environments will change in order to stay as up-to-date as possible on the current state of the ecosystem and thus produce the most effective programs.
What is the relationship between fisheries and ecological regime shifts?
Decreases in the catch yield of commercial fisheries often occur simultaneously with ecological regime shifts, making the fishing industry a well-documented avenue for the study of ecological indicators of large-scale environmental changes. In this study, we used records from crustacean fisheries in the Bering Sea and the Gulf of Alaska beginning in the 1970s and continuing through the 1990s, a period of time during which these industries saw several major collapses.
What were the results?
Our original theoretical approach to this study also cited changes in catch skewness as a potential indicator of impending fishery collapse. Our statistical analysis, however, could not support this prediction; further investigation into this area will be necessary before any kind of meaning can be determined.
Which type of management approach do our results support?
According to these results, it would be possible for creators of fisheries legislation to base their program designs on a single ecological indicator of oncoming environmental regime shifts: increased spatial variability.
In terms of individual trends, only 4 of the 12 fisheries showed significant changes in variability; therefore, it is preferable to analyze data across multiple fisheries in order to accurately predict collapses. Moreover, there are many ecosystem models that do not show significant changes among ecological indicators before a regime shift. For the most part, empirical evidence of these indicators’ accuracy has had to take place in a simulated lab setting, and thus the efficacy of environmental indicators as a prediction of ecological regime shifts is relatively unknown.
Wind intensification in upwelling ecosystems
This brief summarizes the paper “Climate change and wind Intensification in coastal upwelling ecosystems” by Sydeman et al., which was published in Science Magazine.
What is upwelling and how do wind patterns relate to it?
Upwelling refers to the process by which equator-ward, alongshore wind currents over ocean regions drive nutrient-drained water away from the shoreline, replacing it with cold, nutrient-rich water from the bottom of the ocean. This helps to maintain ecosystem productivity and thus overall health.
What is the importance of eastern boundary upwelling systems?
Eastern boundary current systems (EBCSs) are areas in the ocean along the eastern margins of ocean basins. In these regions, wind-driven currents and coastal formations (i.e. headlands) create a prime environment for upwelling, leading to extraordinary productivity and range of species. The California (California, Oregon, and Washington), Humboldt (Peru and Chile), Benguela (South Africa and Namibia), and Canary (northern Africa to Spain) regions comprise the world’s EBCSs, and thus are the focus of this study’s analysis. These essential upwelling systems are among the most heavily impacted in the world; mankind is exhausting fish populations, changing food web dynamics, and altering habitats to the detriment of naturally stable cycles. The scientific framework for an all-encompassing approach to ecosystem management is still in the process of being developed. Ecosystem-based management will be enhanced by understanding changes to upwelling since it is fundamental to the health and productivity of these ecosystems.
What did Andrew Bakun propose in 1990? How is this paper related to Bakun’s hypothesis?
In 1990, Andrew Bakun proposed that the increase in greenhouse gases provoked by humans would lead to intensification of upwelling in the world’s EBCSs. He proposed that a strengthening of upwelling-favorable winds in key regions would cause this intensification. Since there is significant debate within the scientific community as to whether current wind patterns corroborate his hypothesis, scientists at the Farallon Institute and their collaborators created a combined analysis of 22 different studies, published between 1990 and 2012, that tested Bakun’s theory in order to get a more accurate view of global upwelling patterns.
What were our results and what do they mean for ecosystem productivity?
The results of the combined analysis find that the existing body of research generally supports Bakun’s hypothesis, with evidence of wind intensification in the California, Humboldt, and Benguela systems. We also found that at greater latitudes, the degree of wind intensification was more pronounced, which is in line with warming patterns observed with the onset of climate change. While it may sound as if wind intensification could benefit ecosystems due increased upwelling, large changes in wind patterns could, in fact, harm ecosystems by throwing off the balance of organism interactions and by changing ocean chemistry. The complex nature of natural systems, though, makes it extremely difficult to predict the ecological effects of wind intensification in these ecosystems.