Paul S. Lavery

The Central Role of Dispersal in the Maintenance and Persistence of Seagrass Populations

Global seagrass losses parallel significant declines observed in corals and mangroves over the past 50 years. These combined declines have resulted in accelerated global losses to ecosystem services in coastal waters. Seagrass meadows can be extensive (hundreds of square kilometers) and long-lived (thousands of years), with the meadows persisting predominantly through vegetative (clonal) growth. They also invest a large amount of energy in sexual reproduction. In this article, we explore the role that sexual reproduction, pollen, and seed dispersal play in maintaining species distributions, genetic diversity, and connectivity among seagrass populations. We also address the relationship between long-distance dispersal, genetic connectivity, and the maintenance of genetic diversity that may enhance resilience to stresses associated with seagrass loss. Our reevaluation of seagrass dispersal and recruitment has altered our perception of the importance of long-distance dispersal and has revealed extensive dispersal at scales much larger than was previously thought possible.

Differences in recreationally targeted fishes between protected and fished areas of a coral reef marine park

Many comparisons have been made between sanctuary (no-fishing) and fished areas, where fishing pressure is exerted by artisanal or commercial fishers, but few have examined the effect of recreational fishing on fish assemblages in coral reef habitats. In this study, we compared assemblages of targeted fish from coral reef habitats in sanctuary (no-fishing) and recreationally fished zones of a marine protected area (MPA). Surface visual census (SVC) transects were conducted two times, at three regions, to compare the composition of predatory fish assemblages and the abundance, biomass, and size of the most commonly targeted fish. Baited remote underwater video (BRUV) was used to make relative counts of fish between zones. We also measured benthic cover and rugosity, which may influence fish assemblages. Analysis of similarity (ANOSIM) revealed significant differences in the composition of fish families/genera targeted by fishers (Lethrinidae, Lutjanidae, Haemulidae, Serranidae, and the genus Choerodon of the family Labridae) in terms of biomass (P<0.01) and abundance (P<0.05). The most consistent trends were recorded for biomass and this was supported by clustering of replicates in nonmetric multidimensional scaling (nMDS) ordinations. Similarity percentages (SIMPER) analysis indicated that the family Lethrinidae accounted for 73% (as abundance), and up to 69% (as biomass), of the dissimilarity between zones. Three-factor ANOVA highlighted significantly greater biomass, size, and abundance of legal-sized lethrinids (the most targeted family in the region) in sanctuary zones, but no differences in other families/genera. Results of BRUV supported SVC with greater relative counts of lethrinids (P<0.01) in sanctuaries, but no significant differences for other families. Cover of Acropora coral and hard substrate differed between zones at some regions but differences were inconsistent. There were no significant differences in algal cover or rugosity between zones. Given the inconsistency in benthic cover, the similarity of rugosity between zones, the consistently greater biomass of lethrinids in sanctuaries, and the abundance of large lethrinids in sanctuaries, the cessation of fishing in sanctuary zones appears responsible for observed differences in the populations of these fish. These results demonstrate that recreational

Variability in the carbon storage of seagrass habitats and its implications for global estimates of blue carbon ecosystem service.

The recent focus on carbon trading has intensified interest in ‘Blue Carbon’–carbon sequestered by coastal vegetated ecosystems, particularly seagrasses. Most information on seagrass carbon storage is derived from studies of a single species, Posidonia oceanica, from the Mediterranean Sea. We surveyed 17 Australian seagrass habitats to assess the variability in their sedimentary organic carbon (Corg) stocks. The habitats encompassed 10 species, in mono-specific or mixed meadows, depositional to exposed habitats and temperate to tropical habitats. There was an 18-fold difference in the Corg stock (1.09–20.14 mg Corg cm−3 for a temperate Posidonia sinuosa and a temperate, estuarine P. australis meadow, respectively). Integrated over the top 25 cm of sediment, this equated to an areal stock of 262–4833 g Corg m−2. For some species, there was an effect of water depth on the Corg stocks, with greater stocks in deeper sites; no differences were found among sub-tidal and inter-tidal habitats. The estimated carbon storage in Australian seagrass ecosystems, taking into account inter-habitat variability, was 155 Mt. At a 2014–15 fixed carbon price of A

Epiphytes of seagrasses

25.40 t−1 and an estimated market price of

Mechanisms and ecological role of carbon transfer within coastal seascapes

35 t−1 in 2020, the Corg stock in the top 25 cm of seagrass habitats has a potential value of

Influence of Ecklonia radiata kelp canopy on structure of macro-algal assemblages in Marmion Lagoon, Western Australia

AUD 3.9–5.4 bill. The estimates of annual Corg accumulation by Australian seagrasses ranged from 0.093 to 6.15 Mt, with a most probable estimate of 0.93 Mt y−1 (10.1 t. km−2 y−1). These estimates, while large, were one-third of those that would be calculated if inter-habitat variability in carbon stocks were not taken into account. We conclude that there is an urgent need for more information on the variability in seagrass carbon stock and accumulation rates, and the factors driving this variability, in order to improve global estimates of seagrass Blue Carbon storage.

Influence of water depth on the carbon sequestration capacity of seagrasses

In all aquatic environments, available surfaces are rapidly colonized by a variety of organisms. If these organisms grow on plants they are called epiphytes. Seagrasses provide an excellent substratum for epiphytic organisms and these organisms are an integral component of seagrass ecosystems. The ecology and physiology of seagrass epiphytes have been reviewed previously (Harlin, 1980; Borowitzka and Lethbridge, 1989) and this chapter focuses primarily on new developments in our understanding of seagrass epiphyte biology and ecology that have occurred since then.

Linking Land and Sea: Different Pathways for Marine Subsidies

Worldwide, coastal systems provide some of the most productive habitats, which potentially influence a range of marine and terrestrial ecosystems through the transfer of nutrients and energy. Several reviews have examined aspects of connectivity within coastal seascapes, but the scope of those reviews has been limited to single systems or single vectors. We use the transfer of carbon to examine the processes of connectivity through multiple vectors in multiple ecosystems using four coastal seascapes as case studies. We discuss and compare the main vectors of carbon connecting different ecosystems, and then the natural and human‐induced factors that influence the magnitude of effect for those vectors on recipient systems. Vectors of carbon transfer can be grouped into two main categories: detrital particulate organic carbon (POC) and its associated dissolved organic and inorganic carbon (DOC/DIC) that are transported passively; and mobile consumers that transport carbon actively. High proportions of net primary production can be exported over meters to hundreds of kilometers from seagrass beds, algal reefs and mangroves as POC, with its export dependent on wind‐generated currents in the first two of these systems and tidal currents for the last. By contrast, saltmarshes export large quantities of DOC through tidal movement, while land run‐off plays a critical role in the transport of terrestrial POC and DOC into temperate fjords. Nekton actively transfers carbon across ecosystem boundaries through foraging movements, ontogenetic migrations, or ‘trophic relays’, into and out of seagrass beds, mangroves or saltmarshes. The magnitude of these vectors is influenced by: the hydrodynamics and geomorphology of the region; the characteristics of the carbon vector, such as their particle size and buoyancy; and for nekton, the extent and frequency of migrations between ecosystems. Through a risk‐assessment process, we have identified the most significant human disturbances that affect the integrity of connectivity among ecosystems. Loss of habitat, net primary production (NPP) and overfishing pose the greatest risks to carbon transfer in temperate saltmarsh and tropical estuaries, particularly through their effects on nekton abundance and movement. In comparison, habitat/NPP loss and climate change are likely to be the major risks to carbon transfer in temperate fjords and temperate open coasts through alteration in the amount of POC and/or DOC/DIC being transported. While we have highlighted the importance of these vectors in coastal seascapes, there is limited quantitative data on the effects of these vectors on recipient systems. It is only through quantifying those subsidies that we can effectively incorporate complex interactions into the management of the marine environment and its resources.

Effects of multiple disturbances in seagrass meadows: shading decreases resilience to grazing

A recent study of the influence of a wave exposure gradient on macroalgal assemblages associated with kelp stands in Marmion Lagoon, Western Australia found macroalgal communities had high spatial heterogeneity. Much of this heterogeneity was between replicate quadrats within sites and exposure level. The cause of such spatial heterogeneity is investigated further. Ninety 0.25 m2 quadrats were sampled from 9 sites (10 quadrats from each site) during the Australian autumn (April-May) 1996. The sites were nested in groups of 3 across a gradient in wave exposure. The quadrats were also grouped by density of adult Ecklonia radiata thalli, which is the local canopy forming kelp. Three categories were used: 4 kelp thalli m−2. Eighty two species were observed, but only 19 species occurred in >10% of quadrats and a further 13 species in 5–10% of quadrats. This suggests that species were patchily distributed among quadrats. This patchy distribution was found to be greatest in quadrats with Ecklonia radiata densities 4. The major taxa contributing to this patchy distribution were the brown algae Lobophora variegata, Sargassum spinuligerum and Sargassum spp. juveniles, and the red algae Amphiroa anceps, Chauviniella coriifolia, Dictymenia sonderi, Heterodoxia denticulata, Jeannerettia pedicellata, Pterocladia lucida and Rhodymenia sonderi. Many of these species only occurred or were most abundant in areas of low kelp density. The results demonstrate that assemblage structure at local scales, between replicate quadrats, was influenced by density of the kelp canopy just as much as gradients in exposure to ocean swells between reef lines. Many species were influenced both by kelp density and exposure to swells.

Ecological significance of seagrasses: assessment for management of environmental impact in Western Australia

The actual estimates of carbon stocks beneath seagrass meadows worldwide are derived from few data, resulting in a tendency to generalize global carbon stocks from a very limited number of seagrass habitats. We surveyed Posidonia oceanica and Posidonia sinuosa meadows along depth-induced gradients of light availability to assess the variability in their sedimentary organic carbon (Corg) stocks and accretion rates. This study showed a fourfold decrease in Corg stocks from 2–4 m to 6–8 m depth P. sinuosa meadows (averaging 7.0 and 1.8 kg m−2, respectively; top meter of sediment) and a fourteenfold to sixteenfold decrease from shallow (2 m) to deep (32 m) P. oceanica meadows (200 and 19 kg m−2 average, respectively; top 2.7 m of sediment). The average Corg accretion rates in shallow P. sinuosa meadows were higher (10.5 g m−2 yr−1) than in deeper meadows (2.1 g m−2 yr−1). The reduction of sedimentary Corg stocks and accretion rates along depth-related gradients of light reduction suggests that irradiance, controlling plant productivity, meadow density, and sediment accretion rates, is a key environmental factor affecting Corg storage potential of seagrasses. The results obtained highlighted the exceptional carbon storage capacity of P. oceanica meadows at Balearic Islands (Spain), containing the highest areal Corg stocks of all seagrasses (estimated in up to 691–770 kg m−2 in 8–13 m thick deposits). Seagrass communities are experiencing worldwide decline, and reduced irradiance (following e.g., eutrophication or sediment regime alterations) will lead to photoacclimation responses (i.e., reduced plant productivity and shoot density), which may impact the carbon sequestration capacity of seagrasses.