Benthic responses to an Antarctic regime shift: food particle size and recruitment biology.

Polar ecosystems are bellwether indicators of climate change and offer insights into ecological resilience. In this study, we describe contrasting responses to an apparent regime shift of two very different benthic communities in McMurdo Sound, Antarctica. We compared species-specific patterns of benthic invertebrate abundance and size between the west (low productivity) and east (higher productivity) sides of McMurdo Sound across multiple decades (1960s-2010) to depths of 60 m. We present possible factors associated with the observed changes. A massive and unprecedented shift in sponge recruitment and growth on artificial substrata observed between the 1980s and 2010 contrasts with lack of dramatic sponge settlement and growth on natural substrata, emphasizing poorly understood sponge recruitment biology. We present observations of changes in populations of sponges, bryozoans, bivalves, and deposit-feeding invertebrates in the natural communities on both sides of the sound. Scientific data for Antarctic benthic ecosystems are scant, but we gather multiple lines of evidence to examine possible processes in regional-scale oceanography during the eight years in which the sea ice did not clear out of the southern portion of McMurdo Sound. We suggest that large icebergs blocked currents and advected plankton, allowed thicker multi-year ice, and reduced light to the benthos. This, in addition to a possible increase in iron released from rapidly melting glaciers, fundamentally shifted the quantity and quality of primary production in McMurdo Sound. A hypothesized shift from large to small food particles is consistent with increased recruitment and growth of sponges on artificial substrata, filter-feeding polychaetes, and some bryozoans, as well as reduced populations of bivalves and crinoids that favor large particles, and echinoderms Sterechinus neumayeri and Odontaster validus that predominantly feed on benthic diatoms and large phytoplankton mats that drape the seafloor after spring blooms. This response of different guilds of filter feeders to a hypothesized shift from large to small phytoplankton points to the enormous need for and potential value of holistic monitoring programs, particularly in pristine ecosystems, that could yield both fundamental ecological insights and knowledge that can be applied to critical conservation concerns as climate change continues.

A keystone ecologist: Robert Treat Paine, 1933-2016.

Robert T. Paine, who passed away on 13 June 2016, is among the most influential people in the history of ecology. Paine was an experimentalist, a theoretician, a practitioner, and proponent of the "ecology of place," and a deep believer in the importance of natural history to ecological understanding. His scientific legacy grew from the discovery of a link between top-down forcing and species diversity, a breakthrough that led to the ideas of both keystone species and trophic cascades, and to our early understanding of the mosaic nature of biological communities, causes of zonation across physical gradients, and the intermediate-disturbance hypothesis of species diversity. Paine's influence as a mentor was equally important to the growth of ecological thinking, natural resource conservation, and policy. He served ecology as an Ecological Society of America president, an editor of the Society's journals, a member of and contributor to the National Academy of Sciences and the National Research Council, and an in-demand advisor to various state and federal agencies. Paine's broad interests, enthusiasm, charisma, and humor deeply affected our lives and the lives of so many others.

Spatial patterns of fishing effort off San Diego: implications for zonal management and ecosystem function.

The essence of ecosystem-based management is managing human practices to conserve the ecosystem. Ecologists focus on understanding the ecosystem, but there are fundamental information gaps including patterns of human exploitation. In particular, the spatial distribution of fishing effort must be known at the scales needed for ecologically relevant management. Fishing is a primary impact on coastal ecosystems, yet catch distribution at scales relevant to habitats and processes are not well known for many fisheries. Here we utilized photographic time series, logbook records, and angler surveys to estimate the intensity and spatial pattern of commercial and recreational fishing. Effort was clearly aggregated for most types of fishing, the motivating factors for effort distribution varied among areas, and effort was coupled or uncoupled to habitat depending on the area and type of fishing. We estimated that approximately 60% and approximately 74% of private recreational and recreational charter vessel fishing effort, respectively, were concentrated into two small areas that also included approximately 78% of commercial sea urchin effort. Exploitation and effort were considerably greater in one kelp forest, which has important implications for patterns of kelp persistence, productivity, and ecosystem function. Areas subject to the greatest recreational fishing pressure appeared to have lower diversity. Our results indicate that fine-scale patterns of fishing effort and exploitation have profound consequences for ecosystem functioning and biodiversity. 'Ecosystem-based management of nearshore ecosystems depends on an understanding of the fine-scale patterns of exploitation.

First evidence of microbial wood degradation in the coastal waters of the Antarctic.

Wood submerged in saline and oxygenated marine waters worldwide is efficiently degraded by crustaceans and molluscs. Nevertheless, in the cold coastal waters of the Antarctic, these degraders seem to be absent and no evidence of other wood-degrading organisms has been reported so far. Here we examine long-term exposed anthropogenic wood material (Douglas Fir) collected at the seafloor close to McMurdo station, Antarctica. We used light and scanning electron microscopy and demonstrate that two types of specialized lignocellulolytic microbes-soft rot fungi and tunnelling bacteria-are active and degrade wood in this extreme environment. Fungal decay dominates and hyphae penetrate the outer 2-4 mm of the wood surface. Decay rates observed are about two orders of magnitude lower than normal. The fungi and bacteria, as well as their respective cavities and tunnels, are slightly smaller than normal, which might represent an adaptation to the extreme cold environment. Our results establish that there is ongoing wood degradation also in the Antarctic, albeit at a vastly reduced rate compared to warmer environments. Historical shipwrecks resting on the seafloor are most likely still in good condition, although surface details such as wood carvings, tool marks, and paint slowly disintegrate due to microbial decay.

Kelp forests at the end of the earth: 45 years later.

The kelp forests of southern South America are some of the least disturbed on the planet. The remoteness of this region has, until recently, spared it from many of the direct anthropogenic stressors that have negatively affected these ecosystems elsewhere. Re-surveys of 11 locations at the easternmost extent of Tierra del Fuego originally conducted in 1973 showed no significant differences in the densities of adult and juvenile Macrocystis pyrifera kelp or kelp holdfast diameter between the two survey periods. Additionally, sea urchin assemblage structure at the same sites were not significantly different between the two time periods, with the dominant species Loxechinus albus accounting for 66.3% of total sea urchin abundance in 2018 and 61.1% in 1973. Time series of Landsat imagery of the region from 1998 to 2018 showed no long-term trends in kelp canopy over the past 20 years. However, ~ 4-year oscillations in canopy fraction were observed and were strongly and negatively correlated with the NOAA Multivariate ENSO index and sea surface temperature. More extensive surveying in 2018 showed significant differences in benthic community structure between exposed and sheltered locations. Fish species endemic to the Magellanic Province accounted for 73% of all nearshore species observed and from 98-100% of the numerical abundance enumerated at sites. Fish assemblage structure varied significantly among locations and wave exposures. The recent creation of the Yaganes Marine Park is an important step in protecting this unique and biologically rich region; however, the nearshore waters of the region are currently not included in this protection. There is a general lack of information on changes in kelp forests over long time periods, making a global assessment difficult. A complete picture of how these ecosystems are responding to human pressures must also include remote locations and locations with little to no impact.

Forecasting the limits of resilience: integrating empirical research with theory.

Despite the increasing evidence of drastic and profound changes in many ecosystems, often referred to as regime shifts, we have little ability to understand the processes that provide insurance against such change (resilience). Modelling studies have suggested that increased variance may foreshadow a regime shift, but this requires long-term data and knowledge of the functional links between key processes. Field-based research and ground-truthing is an essential part of the heuristic that marries theoretical and empirical research, but experimental studies of resilience are lagging behind theory, management and policy requirements. Empirically, ecological resilience must be understood in terms of community dynamics and the potential for small shifts in environmental forcing to break the feedbacks that support resilience. Here, we integrate recent theory and empirical data to identify ways we might define and understand potential thresholds in the resilience of nature, and thus the potential for regime shifts, by focusing on the roles of strong and weak interactions, linkages in meta-communities, and positive feedbacks between these and environmental drivers. The challenge to theoretical and field ecologists is to make the shift from hindsight to a more predictive science that is able to assist in the implementation of ecosystem-based management.

Fishing from past to present: continuity and resilience of red abalone fisheries on the Channel Islands, California.

Archaeological data from coastal shell middens provide a window into the structure of ancient marine ecosystems and the nature of human impacts on fisheries that often span millennia. For decades Channel Island archaeologists have studied Middle Holocene shell middens visually dominated by large and often whole shells of the red abalone (Haliotis rufescens). Here we use modern ecological data, historical accounts, commercial red abalone catch records, and zooarchaeological data to examine long-term spatial and temporal variation in the productivity of red abalone fisheries on the Northern Channel Islands, California (USA). Historical patterns of abundance, in which red abalone densities increase from east to west through the islands, extend deep into the Holocene. The correlation of historical and archaeological data argue for long-term spatial continuity in productive red abalone fisheries and a resilience of abalone populations despite dramatic ecological changes and intensive human predation spanning more than 8000 years. Archaeological, historical, and ecological data suggest that California kelp forests and red abalone populations are structured by a complex combination of top-down and bottom-up controls.

Discriminating sources of PCB contamination in fish on the coastal shelf off San Diego, California (USA).

Management of coastal ecosystems necessitates the evaluation of pollutant loading based on adequate source discrimination. Monitoring of sediments and fish on the shelf off San Diego has shown that some areas on the shelf are contaminated with polychlorinated biphenyls (PCBs). Here, we present an analysis of PCB contamination in fish on the shelf off San Diego designed to discriminate possible sources. The analysis was complicated by the variability of species available for analysis across the shelf, variable affinities of PCBs among species, and non-detects in the data. We utilized survival regression analysis to account for these complications. We also examined spatial patterns of PCBs in bay and offshore sediments and reviewed more than 20 years of influent and effluent data for local wastewater treatment facilities. We conclude that most PCB contamination in shelf sediments and fish is due to the ongoing practice of dumping contaminated sediments dredged from San Diego Bay.

The effect of spatial and temporal heterogeneity on the design and analysis of empirical studies of scale-dependent systems.

Processes interacting across scales of space and time influence emergent patterns in ecological systems, but to obtain strong inference and empirical generalities, ecologists need to balance reality with the practicalities of design and analyses. This article discusses heterogeneity, scaling, and design analysis problems and offers potential solutions to improve empirically based research. In particular, we recommend bridging the dichotomy between correlative and manipulative studies by nesting manipulative studies within a correlative framework. We suggest that building on variation, by designing studies to detect variability, rather than fighting it often leads to an increase in generality. We also emphasize the importance of natural history information for determining likely scales of spatial and temporal heterogeneity and the probable occurrence of feedback loops, indirect effects, and interacting processes. Finally, we integrate these concepts and suggest planned iterations between multiscale studies to build up natural history information and test the strength of relationships across space and time. This offers a way forward in terms of heuristically developing models and determining ecological generalities.

Marine reserve design: optimal size, habitats, species affinities, diversity, and ocean microclimate.

The design of marine reserves is complex and fraught with uncertainty. However, protection of critical habitat is of paramount importance for reserve design. We present a case study as an example of a reserve design based on fine-scale habitats, the affinities of exploited species to these habitats, adult mobility, and the physical forcing affecting the dynamics of the habitats. These factors and their interaction are integrated in an algorithm that determines the optimal size and location of a marine reserve for a set of 20 exploited species within five different habitats inside a large kelp forest in southern California. The result is a reserve that encompasses approximately 42% of the kelp forest. Our approach differs fundamentally from many other marine reserve siting methods in which goals of area, diversity, or biomass are targeted a priori. Rather, our method was developed to determine how large a reserve must be within a specific area to protect a self-sustaining assemblage of exploited species. The algorithm is applicable across different ecosystems, spatial scales, and for any number of species. The result is a reserve in which habitat value is optimized for a predetermined set of exploited species against the area left open to exploitation. The importance of fine-scale habitat definitions for the exploited species off La Jolla is exemplified by the spatial pattern of habitats and the stability of these habitats within the kelp forest, both of which appear to be determined by ocean microclimate.

Rossella podagrosa Kirkpatrick, 1907-A valid species after all.

In this study we provide evidence that the species Rossella podagrosa Kirkpatrick, 1907, commonly considered a synonym of Rossella racovitzae Topsent, 1901, is truly a valid species. We show that it can be clearly distinguished from other species especially when taking into consideration the in situ habitus of the sponge in combination with the spicules. Furthermore we demonstrate the weaknesses in the so far published synonymy concept for the very complicated genus Rossella Carter, 1872. From this we conclude that the best strategy for further analysis of Rossella and establishment of acceptable synonymies will need to be based on detailed examination of the spicules, the holotypes, and in situ habitus. When possible it will be useful to analyze specimens from all Antarctic oceanographic regions.

Recruitment, growth and mortality of an Antarctic hexactinellid sponge, Anoxycalyx joubini.

Polar ecosystems are sensitive to climate forcing, and we often lack baselines to evaluate changes. Here we report a nearly 50-year study in which a sudden shift in the population dynamics of an ecologically important, structure-forming hexactinellid sponge, Anoxycalyx joubini was observed. This is the largest Antarctic sponge, with individuals growing over two meters tall. In order to investigate life history characteristics of Antarctic marine invertebrates, artificial substrata were deployed at a number of sites in the southern portion of the Ross Sea between 1967 and 1975. Over a 22-year period, no growth or settlement was recorded for A. joubini on these substrata; however, in 2004 and 2010, A. joubini was observed to have settled and grown to large sizes on some but not all artificial substrata. This single settlement and growth event correlates with a region-wide shift in phytoplankton productivity driven by the calving of a massive iceberg. We also report almost complete mortality of large sponges followed over 40 years. Given our warming global climate, similar system-wide changes are expected in the future.

What can ecology contribute to ecosystem-based management?

Modern fishing changes the ocean environment in many ways, including disturbing the sea floor, altering the food webs, and shifting many important ecosystem functions. Natural history, oceanographic, habitat, behavior, and ecological information must be integrated to implement meaningful ecosystem-based management. We discuss the urgent need to expand the concept of essential fish habitat to include important food-web relationships. The need for a broader perspective in terms of ecosystem function and the effects of interactive stressors is emphasized to maintain the vitality and resilience of valued ecosystems. Maintenance of multiple ecosystem functions is a key factor in the adaptive capacity of ecosystems to change. We argue that an ecological understanding of resilience embraces uncertainty and encourages multiple approaches to the management of humans such that ecosystem functions are maintained.

Ecological theory and continental margins: where shallow meets deep.

Continental margins, where land becomes ocean and plunges to the deep sea, provide valuable food and energy resources, and perform essential functions such as carbon burial and nutrient cycling. They exhibit remarkably high species and habitat diversity, but this is threatened by our increasing reliance on the resources that margins provide, and by warming, expanding hypoxia and acidification associated with climate change. Continental margin ecosystems, with environments, constituents and processes that differ from those in shallow water, demand a new focus, in which ecological theory and experimental methods are brought to bear on management and conservation practices. Concepts of disturbance, diversity-function relationships, top-down versus bottom-up control, facilitation and meta-dynamics offer a framework for studying fundamental processes and understanding future change.

The importance in fishery management of leaving the big ones.

Research by Berkeley et al. and by Bobko and Berkeley has recently demonstrated that older individuals of some fish species produce larvae that have substantially better survival potential than do larvae from younger fishes. These new findings augment established knowledge that larger individuals usually have exponentially greater fecundity. This is important because commercial fisheries and especially recreational fishing often target the larger fish. The protection of larger or older individuals is necessary for the sustainability of species currently exploited by humans.

The importance of the natural sciences to conservation: (an American Society of Naturalists symposium paper).

The last century has seen enormous environmental degradation: many populations are in drastic decline, and their ecosystems have been vastly altered. There is an urgent need to understand the causes of the decline, how the species interact with other components of the environment, and how ecosystem integrity is determined. A brief review of marine systems emphasizes the importance of natural sciences to understanding the systems and finding solutions. These environmental crises coincide with the virtual banishment of natural sciences in academe, which eliminate the opportunity for both young scientists and the general public to learn the fundamentals that help us predict population levels and the responses by complex systems to environmental variation. Science and management demands that complex systems be simplified, but the art of appropriate simplification depends on a basic understanding of the important natural history. It seems unlikely that meaningful conservation and restoration can be accomplished unless we recover the tradition of supporting research in and the teaching of natural history. We must reinstate natural science courses in all our academic institutions to insure that students experience nature first-hand and are instructed in the fundamentals of the natural sciences.

A general model for designing networks of marine reserves.

There is debate concerning the most effective conservation of marine biodiversity, especially regarding the appropriate location, size, and connectivity of marine reserves. We describe a means of establishing marine reserve networks by using optimization algorithms and multiple levels of information on biodiversity, ecological processes (spawning, recruitment, and larval connectivity), and socioeconomic factors in the Gulf of California. A network covering 40% of rocky reef habitat can fulfill many conservation goals while reducing social conflict. This quantitative approach provides a powerful tool for decision-makers tasked with siting marine reserves.