Knowledge sharing about deep-sea ecosystems to inform conservation and research decisions

The Marianas Trench Marine National Monument (MNM) currently extends policy-based protection to deep-sea ecosystems contained within it, but managers require better understanding of the current knowledge and knowledge gaps about these ecosystems to guide decision-making. To address this need, we present a case study of the Marianas Trench MNM using in-depth interviews to determine scientists’ (1) current understanding of anthropogenic drivers of change and system vulnerability in deep-sea ecosystems; and (2) perceptions of the least understood deep-sea ecosystems and processes in the Marianas Trench MNM, and which of these, if any, should be research priorities to fill knowledge gaps about these systems and the impacts from anthropogenic drivers of change. Interview respondents shared similar views on the current knowledge of deep-sea ecosystems and potential anthropogenic drivers of change in the Marianas Trench MNM. Respondents also identified trench and deep pelagic (bathyal, abyssal, and hadal zones) ecosystems as the least understood, and highlighted climate change, litter and waste, mining and fishing, and interactions between these drivers of change as critical knowledge gaps. To fill key knowledge gaps and inform conservation decision-making, respondents identified the need for monitoring networks and time-series data. Our approach demonstrates how in-depth interviews can be used to elicit knowledge to inform decision-making in data-limited situations

Multidisciplinary Observing in the World Ocean’s Oxygen Minimum Zone Regions: From Climate to Fish — The VOICE Initiative

Multidisciplinary ocean observing activities provide critical ocean information to satisfy ever-changing socioeconomic needs and require coordinated implementation. The upper oxycline (transition between high and low oxygen waters) is fundamentally important for the ecosystem structure and can be a useful proxy for multiple observing objectives connected to eastern boundary systems (EBSs) that neighbor oxygen minimum zones (OMZs). The variability of the oxycline and its impact on the ecosystem (VOICE) initiative demonstrates how societal benefits drive the need for integration and optimization of biological, biogeochemical, and physical components of regional ocean observing related to EBS. In liaison with the Global Ocean Oxygen Network, VOICE creates a roadmap toward observation-model syntheses for a comprehensive understanding of selected oxycline-dependent objectives. Local to global effects, such as habitat compression or deoxygenation trends, prompt for comprehensive observing of the oxycline on various space and time scales, and for an increased awareness of its impact on ecosystem services. Building on the Framework for Ocean Observing (FOO), we present a first readiness level assessment for ocean observing of the oxycline in EBS. This was to determine current ocean observing design and future needs in EBS regions (e.g., the California Current System, the Equatorial Eastern Pacific off Ecuador, the Peru–Chile Current system, the Northern Benguela off Namibia, etc.) building on the FOO strategy. We choose regional champions to assess the ocean observing design elements proposed in the FOO, namely, requirement processes, coordination of observational elements, and data management and information products and the related best practices. The readiness level for the FOO elements was derived for each EBS through a similar and very general ad hoc questionnaire. Despite some weaknesses in the questionnaire design and its completion, an assessment was achievable. We found that fisheries and ecosystem management are a societal requirement for all regions, but maturity levels of observational elements and data management and information products differ substantially. Identification of relevant stakeholders, developing strategies for readiness level improvements, and building and sustaining infrastructure capacity to implement these strategies are fundamental milestones for the VOICE initiative over the next 2–5 years and beyond

Influence of ocean deoxygenation on demersal fish communities: Lessons from upwelling margins and oxygen minimum zones

As oceans warm due to anthropogenic climate change, the global ocean oxygen inventory decreases in a process known as ocean deoxygenation. Since oxygen is fundamental for aerobic life, ocean deoxygenation can impact marine organisms across multiple levels of biological organization. This research used the steep gradients in oxygen characteristic of upwelling margins with oxygen minimum zones (OMZs), as a natural experiment to study how hypoxia affects the composition, diversity, trophic structure and dynamics of demersal fish communities. Despite the severely hypoxic conditions ([O2] < 22 μmol kg-1), demersal fish are shown to be present in OMZ systems around the world; several species exhibit remarkable hypoxia tolerance in the Gulf of California ([O2] < 2 μmol kg-1). Demersal fish diversity is sensitive to hypoxia, and diversity shows a non-linear response to low oxygen conditions, decreasing rapidly below a region-specific oxygen threshold. Density patterns are less predictable in relation to oxygen levels. Paired video and environmental samples, taken using an autonomous nanolander, show that seafloor communities on the upper margin (100-400 m) in the Southern California Bight (SCB) experience substantial natural oxygen variability at daily and weekly timescales, but communities do not respond to low-oxygen events at these timescales. Feeding relationships are also altered by hypoxia. At the upper OMZ boundary in the SCB a transition occurs from primarily pelagic-feeding to benthic-feeding fishes, which contrasts with the pattern on non-upwelling margins. The expansion of low-oxygen conditions in the E. Pacific may lead to a shift in community composition as intolerant species are excluded and hypoxia-tolerant species become competitive, an overall decrease in diversity, a reduction in bentho-pelagic coupling, and a lengthening of the food chain as demersal fish shift to utilizing benthic resources. Considering the natural variation of oxygen conditions across different timescales is important as existing modes of variability determine exposure histories of animals and likely influence sensitivity of communities to deoxygenation. Despite major ecological consequences of ocean deoxygenation, an analysis of Nationally Determined Contributions submitted under the Paris Agreement indicate that oxygen loss remains an under acknowledged topic by policy-makers in the international climate community

Evolution of space dependent growth in the teleost Astyanax mexicanus.

The relationship between growth rate and environmental space is an unresolved issue in teleosts. While it is known from aquaculture studies that stocking density has a negative relationship to growth, the underlying mechanisms have not been elucidated, primarily because the growth rate of populations rather than individual fish were the subject of all previous studies. Here we investigate this problem in the teleost Astyanax mexicanus, which consists of a sighted surface-dwelling form (surface fish) and several blind cave-dwelling (cavefish) forms. Surface fish and cavefish are distinguished by living in spatially contrasting environments and therefore are excellent models to study the effects of environmental size on growth. Multiple controlled growth experiments with individual fish raised in confined or unconfined spaces showed that environmental size has a major impact on growth rate in surface fish, a trait we have termed space dependent growth (SDG). In contrast, SDG has regressed to different degrees in the Pachón and Tinaja populations of cavefish. Mating experiments between surface and Pachón cavefish show that SDG is inherited as a dominant trait and is controlled by multiple genetic factors. Despite its regression in blind cavefish, SDG is not affected when sighted surface fish are raised in darkness, indicating that vision is not required to perceive and react to environmental space. Analysis of plasma cortisol levels showed that an elevation above basal levels occurred soon after surface fish were exposed to confined space. This initial cortisol peak was absent in Pachón cavefish, suggesting that the effects of confined space on growth may be mediated partly through a stress response. We conclude that Astyanax reacts to confined spaces by exhibiting SDG, which has a genetic component and shows evolutionary regression during adaptation of cavefish to confined environments

Differences between fish raised in small or large volumes of water under static conditions.

<p>Pairs of fish originally of the same initial weight and length were raised in 5 or 10 ml (left panels) or 40 ml (right panels) volumes in either light or darkness for 18–32 days. A, B. Surface fish raised in light. C, D. Pachón cavefish raised in light. E, F. Tinaja cavefish raised in light. G, H. Surface fish raised in darkness. I, J. F1 hybrids raised in light. Magnifications are the same in frames A and B, C and D, E and F, G and H, and I and J.</p

Effects of confined space on growth rate in <i>Astyanax mexicanus</i> surface fish (SF), Pachón cavefish (CF), Tinaja cavefish (CF), and F1 and F2 hybrids.

a<p>Games-Howell post-hoc tests were used to analyze the data when Levene’s test was significant (p<0.05) and Tukey’s post hoc tests were used when Levene’s test was not significant (p>0.05).</p