Paul H York

James Cook University | JCU · Centre for Tropical and Freshwater Research (TropWATER)

Nutrient enrichment of coastal waters is widely recognized as a major driver of seagrass decline. Under conditions where seagrasses are nutrient-limited, however, moderately elevated nutrient loads can enhance seagrass biomass and increase above- and below- ground consumers that support higher order predators. To improve understanding of bottom-up...

Understanding how multiple environmental stressors interact to affect seagrass health (measured as morphological and physiological responses) is important for responding to global declines in seagrass populations. We investigated the interactive effects of temperature stress (24, 27, 30 and 32°C) and shading stress (75, 50, 25 and 0% shade treatmen...

The dispersal of propagules (seeds, fruit, or viable plant fragments) is critical to the distribution, structure, and resilience of seagrass populations in the Great Barrier Reef World Heritage Area (GBRWHA). Biophysical models are used to predict the dispersal of seagrass propagules by combining the simulation of movement (such as the motion of wa...

Background and aims Long distance dispersal (LDD) contributes to the replenishment and recovery of tropical seagrass habitats exposed to disturbance, such as cyclones and infrastructure development. However, our current knowledge regarding the physical attributes of seagrass fragments that influence LDD predominantly stems from temperate species an...

Vegetated coastal ecosystems, in particular mangroves, tidal marshes and seagrasses are highly efficient at sequestering and storing carbon, making them valuable assets for climate change mitigation and adaptation. The state of Queensland, in northeastern Australia, contains almost half of the total area of these blue carbon ecosystems in the count...

Seed size can have an impact on angiosperm reproductive fitness. Ecological theory predicts plants that will produce larger seeds in stressful environments to increase the chances of seedling survival and numerous small seeds in favourable conditions to increase the number of recruits. We measured seed morphology of the seagrass Heterozostera nigri...

Angiosperms have co-evolved with animals over thousands of years leading to an array of mutualistic relationships. Passage of plant seeds through animal intestines leads to an important mutualism providing the animal with food and the plant with seed dispersal and enhanced germination. This phenomenon is well studied in terrestrial angiosperms, but...

Megaherbivore grazing (e.g. by turtles, and sirenians) plays a major and well-documented role in structuring seagrass meadows around the world; however, we know little about local-scale (intra- and inter-meadow) variability in megaherbivore grazing. This is surprising given that megaherbivores are highly selective eaters who may feed by targeting c...

Australia’s Great Barrier Reef (GBR) catchments include some of the world’s most intact coastal wetlands comprising diverse mangrove, seagrass and tidal marsh ecosystems. Although these ecosystems are highly efficient at storing carbon in marine sediments, their soil organic carbon (SOC) stocks and the potential changes resulting from climate impac...

Grazing by all members of an herbivore community can act to structure the ecosystems they feed on. The outcome of this grazing pressure on the plant community also depends on the interaction between different herbivore groups that are present. We carried out a three-month multi-level field exclusion experiment to understand how different groups of...

Wetland ecosystems are critical to the regulation of the global carbon cycle, and there is a high demand for data to improve carbon sequestration and emission models and predictions. Decomposition of plant litter is an important component of ecosystem carbon cycling, yet a lack of knowledge on decay rates in wetlands is an impediment to predicting...

Macroherbivory is an important process in seagrass meadows worldwide; however, the impact of macroherbivores on seagrasses in the Great Barrier Reef (GBR) has received little attention. We used exclusion cages and seagrass tethering assays to understand how the intensity of macroherbivory varies over space and time in the seagrass meadows around Gr...

Seagrass ecosystems have suffered significant declines globally and focus is shifting to restoration efforts. A key component to successful restoration is an understanding of the genetic factors potentially influencing restoration success. This includes understanding levels of connectivity between restoration locations and neighbouring seagrass pop...

The Great Barrier Reef (GBR) contains extensive seagrass meadows with abundant and diverse herbivore populations. Typically, meadows in the region are multi-species and dominated by fast growing opportunistic sea-grass species. However, we know little about how herbivores modify these types of seagrass meadows by grazing. We conducted the first meg...

The global distribution of primary production and consumption by humans (fisheries) is well-documented, but we have no map linking the central ecological process of consumption within food webs to temperature and other ecological drivers. Using standardized assays that span 105° of latitude on four continents, we show that rates of bait consumption...

Consumer communities play an important role in maintaining ecosystem structure and function. In seagrass systems, algal regulation by mesograzers provides a critical maintenance function which promotes seagrass productivity. Consumer communities also represent a key link in trophic energy transfer and buffer negative effects to seagrasses associate...

Seagrass meadows are an important habitat for a variety of animals, including ecologically and socioeconomically important species. Seagrass meadows are recognised as providing species with nursery grounds, and as a migratory pathway to adjacent habitats. Despite their recognised importance, little is known about the species assemblages that occupy...

Seagrass meadows are considered important natural carbon sinks due to their capacity to store organic carbon (Corg) in sediments. However, the spatial heterogeneity of carbon storage in seagrass sediments needs to be better understood to improve accuracy of Blue Carbon assessments, particularly when strong gradients are present. We performed an int...

All fishery food webs are ultimately underpinned by organic matter produced by algae and plants, some of it supplied by primary producers at the fringes of fish habitats. This is no different in tropical and subtropical estuaries where secondary production by crustaceans and finfish may depend on coastal wetlands (e.g. mangroves, seagrass, saltmars...

Structural habitat complexity is a fundamental attribute influencing ecological food webs. Simplification of complex habitats occurs due to both natural and anthropogenic pressures that can alter productivity of food webs. Relationships between food web structure and habitat complexity may be influenced by multiple mechanisms, and untangling these...

Shallow-water seagrasses capture and store globally significant quantities of organic carbon (OC), often referred to as 'Blue Carbon'; however, data are lacking on the importance of deep-water (greater than 15 m) seagrasses as Blue Carbon sinks. We compared OC stocks from deep-, mid-and shallow-water seagrasses at Lizard Island within the Great Bar...

Seagrasses are a relatively small group of marine angiosperms that have successfully colonised the oceans and includes monecious, dioecious and hermaphroditic species. They display a range of mating systems, dispersal mechanisms and recruitment strategies that have allowed them to adapt and survive within the marine environment. This includes a gen...

Seagrass habitats support diverse animal assemblages and while there has been considerable progress in the study of these fauna over the last few decades, large knowledge gaps remain. There are biases in our knowledge of taxonomic and functional information that favour the temperate regions over the tropics, some seagrass genera over others, shallo...

Coastal development is contributing to ongoing declines of ecosystems globally. Consequently, understanding the risks posed to these systems, and how they respond to successive disturbances, is paramount for their improved management. We study the cumulative impacts of maintenance dredging on seagrass ecosystems as a canonical example. Maintenance...

Seagrass meadows support key ecosystem services, via provision of food directly for herbivores, and indirectly to their predators. The importance of herbivores in seagrass meadows has been well-documented, but the links between food webs and ecosystem services in seagrass meadows have not previously been made explicit. Herbivores interact with ecos...

Seagrasses are hugely valuable to human life, but the global extent of seagrass meadows remains unclear. As evidence of their value, a United Nations program exists (http://data.unep-wcmc.org/datasets/7) to try and assess their distribution and there has been a call from 122 scientists across 28 countries for more work to manage, protect and monito...

Aim: Long-distance dispersal (LDD) events occur rarely but play a fundamental role in shaping species biogeography. Lying at the heart of island biogeography theory, LDD relies on unusual events to facilitate colonization of new habitats and range expansion. Despite the importance of LDD, it is inherently difficult to quantify due to the rarity of...

Better mitigation of anthropogenic stressors on marine ecosystems is urgently needed to address increasing biodiversity losses worldwide. We explore opportunities for stressor mitigation using whole-of-systems modelling of ecological resilience, accounting for complex interactions between stressors, their timing and duration, background environment...

Terrestrial plants use an array of animals as vectors for dispersal, however little is known of biotic dispersal of marine angiosperms such as seagrasses. Our study in the Great Barrier Reef confirms for the first time that dugongs (Dugong dugon) and green sea turtles (Chelonia mydas) assist seagrass dispersal. We demonstrate that these marine mega...

Seagrass species form important marine and estuarine habitats providing valuable ecosystem services and functions. Coastal zones that are increasingly impacted by anthropogenic development have experienced substantial declines in seagrass abundance around the world. Australia, which has some of the world’s largest seagrass meadows and is home to ov...

In a series of experiments, seeds from a temperate seagrass species, Zostera nigricaulis collected in Port Phillip Bay, Victoria, Australia were exposed to a range of salinities (20 PSU pulse/no pulse, 25 PSU, 30 PSU, 35 PSU), temperatures (13 °C, 17 °C, 22 °C), burial depths (0 cm, 1 cm, 2 cm) and site specific sediment characteristics (fine, medi...

Current evidence suggests that there is a positive relationship between biodiversity and ecosystem functioning, but few studies have addressed tropical ecosystems where the highest levels of biodiversity occur. We develop two hypotheses for the implications of generalizing from temperate studies to tropical ecosystems, and discuss the need for more...

This project was initiated by the Gold Coast Waterways Authority (GCWA). The GCWA has created a Scientific Advisory Committee, which is in part responsible for the GCWA Scientific Research and Management Strategy and the accompanying Scientific Research and Management Program (SRMP). This project is part of that program and is intended to enhance u...

The emerging field of blue carbon science is seeking cost-effective ways to estimate the organic carbon content of soils that are bound by coastal vegetated ecosystems. Organic carbon (Corg) content in terrestrial soils and marine sediments has been correlated with mud content (i.e., silt and clay, particle sizes < 63 µm), however, empirical tests...

Seagrasses are ecosystem engineers that offer important habitat for a large number of species and provide a range of ecosystem services. Many seagrass ecosystems are dominated by a single species, with research showing that genotypic diversity at fine spatial scales plays an important role in maintaining a range of ecosystem functions. However, for...

Recovery from disturbance is a key element of ecosystem persistence, and recovery can be influenced by large scale regional differences and smaller local scale variations in environmental conditions. Seagrass beds are an important yet threatened nearshore habitat and recover from disturbance by regrowth, vegetative extension, and dispersive propagu...

Seagrasses are ecosystem engineers that offer important habitat for a large number of species and provide a range of ecosystem services. Many seagrass ecosystems are dominated by a single species; with research showing that genotypic diversity at fine spatial scales plays an important role in maintaining a range of ecosystem functions. However, for...

Seagrass meadows are threatened by coastal development and global change. In the face of these pressures, molecular techniques such as reverse transcription quantitative real-time PCR (RT-qPCR) have great potential to improve management of these ecosystems by allowing early detection of chronic stress. In RT-qPCR, the expression levels of target ge...

Seagrass ecosystems, considered among the most efficient carbon sinks worldwide, encompass a wide variety of spatial configurations in the coastal landscape. Here we evaluated the influence of the spatial configuration of seagrass meadows at small scales (metres) on carbon storage in seagrass sediments. We intensively sampled carbon stocks and othe...

Global seagrass research efforts have focused on shallow coastal and estuarine seagrass populations where alarming declines have been recorded. Comparatively little is known about the dynamics of deep-water seagrasses despite evidence that they form extensive meadows in some parts of the world. Deep-water seagrasses are subject to similar anthropog...

SUMMARY POINTS Background 1. North Queensland Bulk Ports commissioned an ambient marine water quality monitoring program for the region surrounding the Ports of Mackay and Hay Point. The primary objective of this program has been to develop a long term understanding of the marine water quality characteristics for the region. 2. This program has inc...

Seagrass in Port Phillip Bay is dominated by the eelgrass, Zostera nigricaulis, which occurs around the margin of the bay from the shallow subtidal zone to depths of up to 8 metres. Zostera provides crucial ecosystem services such as stabilising sediments and improving water quality, reducing coastal erosion, and increasing biological productivity...

Resilience of seagrass meadows relies on the ability of seagrass to successfully recolonise denuded areas or disperse to new areas. While seed germination and rhizome extension have been explored as modes of recovery and expansion, the contribution of seagrass viviparous propagules to meadow population dynamics has received little attention. Here,...

Seagrass meadows are among the most efficient and long-term carbon sinks on earth, but disturbances could threaten this capacity, so understanding the impacts of disturbance on carbon stored within seagrass meadows—‘blue carbon’—is of prime importance. To date, there have been no published studies on the impacts of seagrass loss on ‘blue carbon’ st...

Resilience is the ability of an ecosystem to recover from disturbance without loss of essential function. Seagrass ecosystems are key marine and estuarine habitats that are under threat from a variety of natural and anthropogenic disturbances. The ability of these ecosystems to recovery from disturbance will to a large extent depend on the internsi...

Seagrasses are marine angiosperms with a worldwide distribution that form conspicuous beds in nearshore habitats. Despite being universally recognised as a foundation species that performs a number of important ecosystems functions (incl. sediment stabilisation, facilitation of biodiversity, nutrient cycling and carbon sequestration), global seagra...

Simple ecological models that predict trophic responses to bottom-up forcing are valuable tools for ecosystem managers. Traditionally, theoretical ecologists have used resource-dependent functional responses to explain the modification of food chains exposed to bottom-up perturbations. These models predict alternating positive, negative and zero re...

Patterns of spatial variation of molluscan communities associated with coralline algal turfs were evaluated over 1,000 km of the coast of Argentinean Patagonia. A hierarchically-nested experimental design was used to determine the relative importance of molluscan assemblage variation at three different spatial scales (shores, sites and cores). Hypo...

The importance to food-webs of trophic cul-de-sacs, species that channel energy flow away from higher trophic levels, is seldom considered outside of the pelagic systems in which they were first identified. On intertidal mudflats, inputs of detritus from saltmarshes, macroalgae or microphytobenthos are generally regarded as a major structuring forc...

Classical resource- and the less studied ratio-dependent models of predator-prey relationships provide divergent predictions as to the sustained ecological effects of bottom-up forcing. While resource-dependent models, which consider only instantaneous prey density in modelling predator responses, predict community responses that are dependent on t...

Seagrass beds in estuaries are important habitats and nursery grounds for a great variety of fishes, including many economically important species. The introduction of the invasive green alga Caulerpa taxifolia could potentially threaten the seagrasses of south-eastern Australia. This study examined the implications of the spread of C. taxifolia on...