• Energy Research
• 14. Life underwater close
• AU close
• Netherlands Research Portal close

Patterns of movement of marine species can reflect strategies of reproduction and dispersal, species’ interactions, trophodynamics, and susceptibility to change, and thus critically inform how we manage populations and ecosystems. On coral reefs, the density and diversity of metazoan taxa is greatest in dead coral and rubble, which is suggested to fuel food webs from the bottom-up. Yet, biomass and secondary productivity in rubble is predominantly available in some of the smallest individuals, limiting how accessible this energy is to higher trophic levels. We address the bioavailability of motile coral reef cryptofauna based on small-scale patterns of emigration in rubble. We deployed modified RUbble Biodiversity Samplers (RUBS) and emergence traps in a shallow rubble patch at Heron Island, Great Barrier Reef, to detect community-level differences in the directional influx of motile cryptofauna under five habitat accessibility regimes. The mean density (0.13–4.5 ind.cm-3) and biomass (0.14–5.2 mg.cm-3) of cryptofauna were high and varied depending on microhabitat accessibility. Emergent zooplankton represented a distinct community (dominated by the Appendicularia and Calanoida) with the lowest density and biomass, indicating constraints on nocturnal resource availability. Mean cryptofauna density and biomass were greatest when interstitial access within rubble was blocked, driven by the rapid proliferation of small harpacticoid copepods from the rubble surface, leading to trophic simplification. Individuals with high biomass (e.g., decapods, gobies, and echinoderms) were greatest when interstitial access within rubble was unrestricted. Treatments with a closed rubble surface did not differ from those completely open, suggesting that top-down predation does not diminish rubble-derived resources. Our results show that conspecific cues and species’ interactions (e.g., competition and predation) within rubble are most critical in shaping ecological outcomes within the cryptobiome. These findings have implications for prey accessibility through trophic and community size structuring in rubble, which may become increasingly relevant as benthic reef complexity shifts in the Anthropocene. We address the bioavailability of coral reef cryptofauna in rubble based on small-scale patterns of emigration. We adapted the accessibility of Rubble Biodiversity Samplers (RUBS), models used to standardise biodiversity sampling in rubble (Wolfe and Mumby 2020), to explore the local movement patterns of rubble-dwelling fauna, with inference to predation processes within and beyond the cryptobenthos. Five treatments were developed to detect community-level differences in the directional influx of motile cryptofauna under various habitat accessibility regimes. Four of these treatments were developed by modifying accessibility into RUBS (https://www.thingiverse.com/thing:4176644/files) to understand limitations on the directional influx and movement of cryptofauna within coral rubble patches using four treatments; (1) open (completely accessible), (2) interstitial access (top closed), (3) surficial access (sides and bottom closed), and (4) raised (above rubble substratum). The fifth treatment involved a series of emergence plankton traps, designed to target demersal cryptofauna that vertically migrate from within the rubble benthos at night, given emergent zooplankton biomass and diversity are greatest at night. Fieldwork was conducted over several weeks (11th September to 5th October 2021) in a shallow (~3–5 m depth) reef slope site on the southern margin of Heron Island (-23˚26.845’ S, 151˚54.732’ E), Great Barrier Reef, Australia (Fig. 1). All collections were conducted under the Great Barrier Reef Marine Park Authority permit G20/44613.1.

Poleward range extensions by warm-adapted sea urchins are switching temperate marine ecosystems from kelp-dominated to barren-dominated systems that favour the establishment of range-extending tropical fishes. Yet, such tropicalization may be buffered by ocean acidification, which reduces urchin grazing performance and the urchin barrens that tropical range-extending fishes prefer. Using ecosystems experiencing natural warming and acidification, we show that ocean acidification could buffer warming-facilitated tropicalization by reducing urchin populations (by 87%) and inhibiting the formation of barrens. This buffering effect of CO2 enrichment was observed at natural CO2 vents that are associated with a shift from a barren-dominated to a turf-dominated state, which we found is less favourable to tropical fishes. Together, these observations suggest that ocean acidification may buffer the tropicalization effect of ocean warming against urchin barren formation via multiple processes (fewer urchins and barrens) and consequently slow the increasing rate of tropicalization of temperate fish communities. In order to allow full comparability with other ocean acidification data sets, the R package seacarb (Gattuso et al, 2021) was used to compute a complete and consistent set of carbonate system variables, as described by Nisumaa et al. (2010). In this dataset the original values were archived in addition with the recalculated parameters (see related PI). The date of carbonate chemistry calculation by seacarb is 2021-07-26.

The impacts of increasing natural climate disasters are threatening food security in the Asia-Pacific region. Rice is Asia’s most important staple food. Climate variability and change directly impact rice production, through changes in rainfall, temperature and CO2 concentrations. The key for sustainable rice crop is water management. Adaptation can occur through shifts of cropping to higher latitudes and can profit from river systems (via irrigation) so far not considered. New opportunities arise to produce more than one crop per year in cooler areas. Asian wheat production in 2005 represents about 43 % of the global total. Changes in agronomic practices, such as earlier plant dates and cultivar substitution will be required. Fisheries play a crucial role in providing food security with the contribution of fish to dietary animal protein being very high in the region – up to 90 % in small island developing states (SIDS). With the warming of the Pacific and Indian Oceans and increased acidification, marine ecosystems are presently under stress. Despite these trends, maintaining or enhancing food production from the sea is critical. However, future sustainability must be maintained whilst also securing biodiversity conservation. Improved fisheries management to address the existing non-climate threats remains paramount in the Indian and Pacific Oceans with sustainable management regimes being established. Climate-related impacts are expected to increase in magnitude over the coming decades, thus preliminary adaptation to climate change is valuable.

This study examined the potential use of macroalgae epiphytic on mangrove aerial roots as indicators of estuarine contamination. The distribution and abundance of macroalgae was investigated in four estuaries in the vicinity of Sydney, Australia, and compared to water and sediment metal concentrations, nutrient concentrations and physicochemical parameters over four seasonal surveys. Macroalgal diversity and distribution appeared to be highly influenced by the ambient contaminant concentrations, while biomass appeared to be linked with nutrient concentrations. The distribution of the Rhodophyta species, Catenella nipae Zanardini significantly decreased as metal concentrations increased among the estuaries during all seasonal surveys. This species showed strong potential for use as a bioindicator of estuarine contamination.

The Abrolhos Bank (eastern Brazil) encompasses the largest and richest coral reefs of the South Atlantic. Coral reef benthic assemblages of the region were monitored from 2003 to 2008. Two habitats (pinnacles' tops and walls) were sampled per site with 3-10 sites sampled within different reef areas. Different methodologies were applied in two distinct sampling periods: 2003-2005 and 2006-2008. Spatial coverage and taxonomic resolution were lower in the former than in the latter period. Benthic assemblages differed markedly in the smallest spatial scale, with greater differences recorded between habitats. Management regimes and biomass of fish functional groups (roving and territorial herbivores) had minor influences on benthic assemblages. These results suggest that local environmental factors such as light, depth and substrate inclination exert a stronger influence on the structure of benthic assemblages than protection from fishing. Reef walls of unprotected coastal reefs showed highest coral cover values, with a major contribution of Montastraea cavernosa (a sediment resistant species that may benefit from low light levels). An overall negative relationship between fleshy macroalgae and slow-growing reef-building organisms (i.e. scleractinians and crustose calcareous algae) was recorded, suggesting competition between these organisms. The opposite trend (i.e. positive relationships) was recorded for turf algae and the two reef-building organisms, suggesting beneficial interactions and/or co-occurrence mediated by unexplored factors. Turf algae cover increased across the region between 2006 and 2008, while scleractinian cover showed no change. The need of a continued and standardized monitoring program, aimed at understanding drivers of change in community patterns, as well as to subsidize sound adaptive conservation and management measures, is highlighted.

A theoretical basis for Ecosystem-based Fisheries Management (EBFM) was derived for pelagic fish by applying marine ecology theory of analytical relationships of predator-prey biological production transfers between trophic levels to FAO guidelines for an ecosystem approach to fisheries. The aim is to describe a simple method for data-limited fisheries to estimate ecosystem-based FMSY and how EBFM modellers could mimic the way natural fish communities function for maintaining ecological processes of biological production, biomass and ecosystem stability. Ecosystem stability (ES) FMSY were estimated by proportion of biological production allocated to predators, giving ESFMSY of 0.23 for small pelagic and 0.27 for pelagic finfish, prioritising ecosystem over economics. To maintain both stability and biomass (SB) a full pelagic EBFM SBFMSY of about 0.08 was obtained for both small pelagic and pelagic finfish, having mostly ecosystem considerations. As the FMSY are single-species averages of catchable species targeted in a specific trophic level, multispecies fishing mortalities were proportioned by the biological production of each species in the trophic level. This way catches for each species are consistent with the average ecosystem FMSY for a trophic level. The theoretical estimates gave similar results to other fisheries for sustainable fish catches that maintain the fishery ecosystem processes. They were also tested using six tropical Ecopath Models and showed the effects of imposing commercial fishing mortalities on predominantly EBFM conditions. The ecosystem stability ESFMSY is suggested to be investigated for sustainable fish catches and the full EBFM SBFMSY for protected areas or recovery of heavily depleted stocks.

Coral reefs are vulnerable to the impacts of global climate change (e.g rising sea temperature) as well as to numerous local disturbances (e.g overfishing). In combination, these impacts are known to degrade coral reefs, compromising critical ecosystem functions and leading to the potential loss of biodiversity and associated ecosystem services. Management aims to minimise these negative effects but is challenged by substantial uncertainty about the relative contribution and interactions among the various types of stressors on coral reefs. One of the most widely applied management tools on coral reefs are Marine Protected Areas (MPAs). MPAs restrict certain or all types of human activities within their boundaries and are aimed at rebuilding degraded habitats, maintaining ecosystem functions, and protecting healthy reefs to ensure the continued provision of ecosystem services. However, using MPAs effectively requires an understanding of their optimal placement to ensure the conservation of biodiversity and ecological functions in support of local communities and stakeholders. My thesis addresses this topic by developing a novel marine spatial planning approach that integrates reef ecosystem services explicitly into the decision-making process.The first chapter of my thesis is a general introduction that provides an overview of current scientific knowledge about the vulnerability of coral reefs and how these ecosystems are likely to respond to various impacts from global and local stressors. Chapter 2 is focused on investigating the response of coral communities to global and local disturbances more explicitly by using an ecological model to examine the impacts of sea surface temperature, local thermal stress, cyclone, fishing pressure, nutrient enrichment and crown of thorns starfish (CoTS) outbreaks on reefs under alternative climate scenarios by examining applied to Indonesian coral reefs. We used three greenhouse gas emissions (Representative concentration pathway - RCP8.5, RCP4.5, and RCP2.6) for the scenarios of climate change. Reefs are likely to experience further declines in coral cover under all alternative scenarios of climate change and local thermal regimes, but with varied rates of decline in different geographic locations. Management benefits were greater under the more pessimistic greenhouse gas emission scenario RCP8.5 and management of two local stressors with complementary ecological targets (i.e., coral recruitment and adult mortality) provided greater benefits than utilizing tools with similar modes of action. For example, combining approaches that targeted CoTS and either fishing or nutrients, that affect adult mortality and recruitment (respectively), had far greater efficacy than targeting the duality of fishing and nutrients, which both influence recruitment only. The results provide new insight into the importance of applying management tools that address different ecological processes.In Chapter 3, I establish a generally applicable MPA design approach to reconcile multiple reef ecosystem services under explicit consideration of local community needs. Using Selayar Island, South Sulawesi (Indonesia) as a case study, I found that the design of MPAs to address all three ecosystem services – biodiversity, fisheries productivity, and coastal protection – proved challenging. Relatively few reefs exhibit high values of all three services and optimization software is needed to seek network locations that achieve reasonable trade-offs between services. Local fishers valued fisheries benefits over biodiversity and coastal protection. Finding MPA networks that deliver fishers’ preferences was particularly difficult if attempting to include the highest levels of fisheries benefit. Compromising on the magnitude of fishery benefits provided much greater flexibility in the choice of MPA networks that delivered moderately high benefits across all services. Moreover, it becomes more challenging to find good solutions as the target level of MPA coverage increases from 10% to 30%, implying that fewer good solutions occur.In Chapter 4, I examine the extent to which governance factors and management processes, such as involvement of the local community in conservation planning and prior experience with MPAs, influence the perceived benefits of MPAs for fisheries. I incorporate governance factors and preferred MPA distribution based on interviews of local fisher communities. The results reveal that the better engagement of the community into the MPA planning process and governance of MPAs lead to a more positive perception of MPA benefits by fishers. Yet fishers’ perceptions of MPAs were more nuanced. Generally, the perceptions were less positive (1) in fishers that fish more frequently, and (2) fishers operating larger boats that include pelagic fishing (cf. fishers using small-scale artisanal methods). It is hypothesized that pelagic fishers are less invested in the benefits of MPAs and that fishers operating more frequently might be less likely to notice modest changes in productivity should it occur.I also asked whether fishers with a more positive perception of MPA benefits would be more likely to locate future MPAs closer to their fishing grounds. However, this simple hypothesis was not supported. Fishers in Selayar recommend a minimum average distance of ~5 km of MPAs from fishing grounds while people involved in MPA planning tended to suggest distances about 8 km farther from fishing grounds. The absence of a simple relationship between fisher perceptions and the separation of MPA-fishing grounds implies that other – unmeasured – factors are responsible. In general, our findings emphasize the importance of incorporating governance processes and social factors into MPA designation.In Chapter 5, I review my conclusions and consider their broader implications and needs for further work. Prioritising multiple reefs for multiple ecosystem services is challenging and therefore the use of optimisation software is necessary to find suites of MPAs that can meet such diverse objectives. A willingness to compromise on the absolute magnitude of fisheries benefits – the ecosystem service of the greatest value to the community – led to far greater flexibility in finding MPA solutions. Overall, tackling more complex sets of objectives is feasible but requires the use of standard optimisation software to select reasonable solutions. Yet management implementation, such as MPA design, requires good governance and an increasing reliance on sophisticated tools has the potential to undermine the transparency and inclusivity of the implementation process. Future studies will need to consider the communication of tools usage as well as the development of frameworks to apply the tools effectively.

While the physical dimensions of climate change are now routinely assessed through multimodel intercomparisons, projected impacts on the global ocean ecosystem generally rely on individual models with a specific set of assumptions. To address these single-model limitations, we present standardized ensemble projections from six global marine ecosystem models forced with two Earth system models and four emission scenarios with and without fishing. We derive average biomass trends and associated uncertainties across the marine food web. Without fishing, mean global animal biomass decreased by 5% (±4% SD) under low emissions and 17% (±11% SD) under high emissions by 2100, with an average 5% decline for every 1 °C of warming. Projected biomass declines were primarily driven by increasing temperature and decreasing primary production, and were more pronounced at higher trophic levels, a process known as trophic amplification. Fishing did not substantially alter the effects of climate change. Considerable regional variation featured strong biomass increases at high latitudes and decreases at middle to low latitudes, with good model agreement on the direction of change but variable magnitude. Uncertainties due to variations in marine ecosystem and Earth system models were similar. Ensemble projections performed well compared with empirical data, emphasizing the benefits of multimodel inference to project future outcomes. Our results indicate that global ocean animal biomass consistently declines with climate change, and that these impacts are amplified at higher trophic levels. Next steps for model development include dynamic scenarios of fishing, cumulative human impacts, and the effects of management measures on future ocean biomass trends.