Chapter 18: Vulnerability of pelagic systems of the Great Barrier Reef to climate change

This review focuses on pelagic environments. The oceanography of the Great Barrier Reef (GBR) is dynamic and is the physical template to which organisms respond. Planktonic assemblages are the basis of pelagic food chains and they provide a rich supply of food for high trophic groups (eg fishes, birds and whales) as well as the larvae and adults of benthic assemblages (Figure 18.1). Changes in pelagic systems, therefore, cannot be viewed in isolation from other habitats (such as coral reefs). Plankton ranges from tiny viruses (less than 1 micron) and bacteria, to larger plant (phytoplankton) and animal plankton (zooplankton).This is Chapter 18 of Climate change and the Great Barrier Reef: a vulnerability assessment. The entire book can be found at http://hdl.handle.net/11017/13

High temporal resolution sampling reveals reef fish settlement is highly clustered

Coral reef fish larvae settle on reefs predominantly at night around the new-moon phase, after an early developmental period spent in the pelagic environment. Most sampling is conducted across whole nights, and any studies that have examined the frequency of arrival within nights have typically been limited to coarse sampling time scales of 1–5 h. Here, we present results for arrival numbers of fish caught between dusk and midnight from light traps sampled every 15 min at an Indonesian coral reef, providing the finest temporal resolution for this type of study to date. A spatial analysis by distance indices analysis, adapted to temporal data, revealed clustering of reef arrival times for many species, with an increase in catches immediately after dusk dropping off towards midnight. Importantly, the timing of clusters differed among species, indicating that different factors determine the timing of arrival among taxa. Our results support the hypothesis that larval behaviour influences the timing of arrival at a coral reef for different fish species

A function-based typology for Earth’s ecosystems

As the United Nations develops a post-2020 global biodiversity framework for the Convention on Biological Diversity, attention is focusing on how new goals and targets for ecosystem conservation might serve its vision of ‘living in harmony with nature’1,2. Advancing dual imperatives to conserve biodiversity and sustain ecosystem services requires reliable and resilient generalizations and predictions about ecosystem responses to environmental change and management3. Ecosystems vary in their biota4, service provision5 and relative exposure to risks6, yet there is no globally consistent classification of ecosystems that reflects functional responses to change and management. This hampers progress on developing conservation targets and sustainability goals. Here we present the International Union for Conservation of Nature (IUCN) Global Ecosystem Typology, a conceptually robust, scalable, spatially explicit approach for generalizations and predictions about functions, biota, risks and management remedies across the entire biosphere. The outcome of a major cross-disciplinary collaboration, this novel framework places all of Earth’s ecosystems into a unifying theoretical context to guide the transformation of ecosystem policy and management from global to local scales. This new information infrastructure will support knowledge transfer for ecosystem-specific management and restoration, globally standardized ecosystem risk assessments, natural capital accounting and progress on the post-2020 global biodiversity framework

Oceanography

The coral reefs that form the GBR are scattered over the continental shelf, which is shallow and fringed by the deep water of the Coral Sea (Fig. 4.1). Oceanography affects in many ways the organisms and the nature of contemporary geological processes. Seawater erodes and shapes reefs; it influences the transport of sediment and the deposition of material to the substratum. Organisms of all sizes are affected by oceanography. The storm generated seas of cyclones destroy reef structures, kill organisms and alter the nature of habitats. Changes in habitats can in turn affect organisms that typically 'respond' to different habitat types and the influence of oceanography on habitats call influence broad scale patterns of biogeography. The richness of inter-reefal and reef based flora and fauna are strongly influenced by nutrient input from rivers and upwelling over the shelf break. In the pelagic environment, plankton have limited control of their horizontal movements and, therefore, transport and dispersion will be influenced by currents

Biodiversity

Biodiversity generally refers to species richness (i.e. number of species), but other definitions are also common. It is critical that biodiversity is defined carefully as it is sometimes considered synonymous with genetic diversity, habitat diversity, structural diversity, the diversity of functional groups (e.g. trophic groups of life history stages) or even life history traits (e.g. feeding type, growth forms, reproductive strategy, longevity). Some definitions can be a proxy for species richness. For example, species representation and abundance are known to vary among habitats. Habitat richness, therefore, can be especially relevant where the taxonomy of organisms in the various habitats is poorly known and there are concerns to protect species richness. A critical component of the zoning plan of the GBR (the Representative Areas Program, see Chapter 12) was partly based on the protection of different habitats and used these as surrogates to conserve species diversity as the biota on the GBR is poorly known apart from the corals and fish. In this chapter we focus on patterns of species richness at different spatial and temporal scales. We also note that descriptions of biodiversity and an understanding of processes influencing biodiversity (e.g. the impact of human activities) are critical for ecosystem management

Movement, habitat utilization and behaviour of coral trout Plectropomus leopardus during and after the reproductive period on the southern Great Barrier Reef

Coral trout Plectropomus leopardus (mean total length = 498.9 +/- 19.7 mm, n = 10) were tagged and tracked with ultrasonic transmitters over 81 d at an intra-lagoonal location at One Tree Island, Great Barrier Reef, Australia (23.4979 degrees S, 152.0712 degrees E). Movement and habitat preferences were compared during the transition between the reproductive and post-reproductive period. Overall, mean movement was highest between 05: 00 and 10: 00 h, with the most movement during the crepuscular period and the least movement at night. There was no difference in nighttime movement during or after the reproductive period. Mean daily movement (14.48 +/- 0.26 km d(-1)) and fish depths (4.23 +/- 0.02 m) during the post-reproductive period were significantly greater than both movement (10.63 +/- 0.13 km d(-1)) and depths occupied (3.38 +/- 0.01 m) during the reproductive period, which was likely related to reallocation of bioenergetic resources to foraging related activities rather than spawning. Most fish movement was localized (within 0.04 km(2)), with some movements recorded outside of this area to a maximum distance of 0.6 km. Fish traversed sand and small scattered coral out-croppings to reach areas of continuous reef. The ranges of movement and habitat preferences described in this study are important for future research on habitat requirements and behavioural changes across the transition period between reproductive and post-reproductive states. Furthermore, this study provides additional information that may be used for focusing and delineating species-specific Marine Protected Area management plans

Variation in the population demographics of Scolopsis bilineatus in response to predators

Predatory fishes play critical roles in the trophodynamics of coral reefs, and the biomass of predatory fish can be a strong determinant of the structure of reef fish assemblages. In this study, we used variations in predator biomass between management zones on the Great Barrier Reef to examine how predators influence the biomass, mortality, condition, and reproductive potential of a common prey species Scolopsis bilineatus (bridled monocle bream; Nemipteridae). Despite no numerical differences in biomass or mortality, we found significant differences in a variety of demographic traits for S. bilineatus between multiple areas of high and low predator biomass. The size-at-age, condition, and reproductive potential of fish were reduced in marine reserves where predator biomass was high. The response of fish to predators was highly sex dependent; females suffered the greatest reductions in condition and reproductive potential. This study supports the notion that predators can play important roles in regulating prey dynamics and emphasises the importance of understanding top-down control by predators when considering fisheries management techniques and conservation strategies

Pelagic Cnidaria and Ctenophora

The jellyfishes are conspicuous, but poorly understood, members of the Great Barrier Reef (GBR) fauna. Much attention has been given over the past 50 years to two forms in particular, the so-called 'box jellyfishes' and 'Irukandjis', both of which are highly dangerous and are known to kill humans. However, the dangerous species comprise only a small fraction of the jellyfishes that make their home in the GBR region.\ud \ud Jellyfishes in general are among the most intriguing of animals, because they tantalise the child in all of us with their strange shapes, often bright colours, and sometimes flashing lights, and yet, even the milder stinging varieties seemingly represent the forbidden signal: DO NOT TOUCH! \ud \ud While appearing to be simple creatures consisting of no more than mucus and stinging cells, jellyfish have great potential to alter ecosystems through predation and uptake and excretion of nutrients. The medusa stage is the most obvious and often the most voracious part of the life cycle; however, the polyp stage represents the 'seed bank' of the species, making most jellyfish species incredibly difficult, if not impossible, to eradicate.\ud \ud Several well-studied cases exist of jellyfish species being introduced to exotic environments and causing great harm to the ecosystem in the process (e.g. Mnemiopsis in the Black Sea and Phyllorl1iza in the Gulf of Mexico). In other cases, serious impacts on the local biota have been caused by extreme concentrations of native species (e.g. blooms of Chrysaora in the Gulf of Alaska and Aurelia in California).\ud \ud Jellyfish can also be a food source for many species, such as fishes and turtles, and they are heavily fished in some parts of the world (e.g. China)

Vertical distribution patterns of ichthyoplankton in temperate waters of New Zealand

Multifactorial sampling designs were used to determine the vertical distribution of ichthyoplankton at multiple temporal and spatial scales in New Zealand. Hypotheses concerning the vertical distribution of fish larvae were tested in the following: depth strata, surface, near-surface, mid-depth and deep, and near the substratum. The consistency of abundance patterns was examined at three sites separated by 2-20 km over 2 months. We also tested for differences in shallow water columns of two depths (20 and 40 m) and both day and night. Although peak abundance of total larval fish was found at upper and lower strata, regardless of total depth of the water column, consistent taxa specific patterns of vertical distribution were also found. Some taxa were most abundant at the surface (e.g. mullids, hemiramphids, and kyphosids), whereas others were found at multiple depths below the surface and throughout the water column, regardless of site, time or depth of water column (e.g. carangids, engraulids, clupeids, scombrids, sparids and pleuronectids). Some taxa were most abundant in shallow water columns (e.g. mullids, tripterygiids and gobiids). Rank abundance by depth stratum for non-surface dwelling species varied among sites and times. Diel vertical movements were detected, some taxa (e.g. clupeids, scombrids and bothids) that were most abundant at the surface at night whereas for other taxa this pattern was more variable (e.g. carangids). We conclude that diel depth-related patterns in shallow water columns will influence interactions among taxa and the importance of different transport mechanisms for larval transport