The shallow tidal and freshwater coastal wetlands adjacent to the Great Barrier Reef lagoon provide a vital nursery and feeding complex that supports the life cycles of marine and freshwater fish, ...important native vegetation and vital bird habitat. Urban and agricultural development threaten these wetlands, with many of the coastal wetlands becoming lost or changed due to the construction of artificial barriers (e.g. bunds, roads, culverts and floodgates). Infestation by weeds has become a major issue within many of the wetlands modified (bunded) for ponded pasture growth last century. A range of expensive chemical and mechanical control methods have been used in an attempt to restore some of these coastal wetlands, with limited success. This study describes an alternative approach to those methods, investigating the impact of tidal reinstatement after bund removal on weed infestation, associated changes in water quality, and fish biodiversity, in the Boolgooroo lagoon region of the Mungalla wetlands, East of Ingham in North Queensland. High resolution remote sensing, electrofishing and in-water logging was used to track changes over time- 1 year before and 4 years after removal of an earth bund. With tides only penetrating the wetland a few times yearly, gross changes towards a more natural system occurred within a relatively short timeframe, leading to a major reduction in infestation of olive hymenachne, water hyacinth and salvina, reappearance of native vegetation, improvements in water quality, and a tripling of fish diversity. Weed abundance and water quality does appear to oscillate however, dependent on summer rainfall, as changes in hydraulic pressure stops or allows tidal ingress (fresh/saline cycling). With an estimated 30% of coastal wetlands bunded in the Great Barrier Reef region, a passive remediation method such as reintroduction of tidal flow by removal of an earth bund or levee could provide a more cost effective and sustainable means of controlling freshwater weeds and improving coastal water quality into the future.
The global urgency to halt and reverse mangrove loss has led to the implementation of numerous initiatives to protect and restore mangroves and recover critical ecological functions and services. ...Restoration success is assessed by estimating mangrove survival, while diversity, vegetation structure, and soil characteristics are often overlooked with no long‐term monitoring. Here, we investigated long‐term changes in vegetation and soil characteristics of Avicennia germinans‐dominated stands planted along Guyana's coast between 5 and 11 years old. A chronosequence approach was used to examine changes in vegetation and soil parameters in restored mangrove stands of different ages compared to natural stands of the same ages. Tree height, diameter, and aboveground biomass were inconsistent between restored and natural mangrove stands. Redundancy analysis (RDA) revealed that the soil properties were the important factors influencing both the restored and natural mangrove communities. There were no clear trajectories between the vegetation and soil characteristics with age, possibly due to site‐specific and hydrodynamic environmental factors, such as tidal dynamics, riverine inputs, and climatic variations. While there were some equivalent vegetation and soil characteristics at the end of the first decade after restoration, the restored mangroves may require a longer timespan (approximately 25 years) than the period overserved in our study to be entirely identical to the natural mangroves. This case study from Guyana provides valuable insights into the ecological processes driving mangrove recovery dynamics, growth patterns, and restoration effectiveness and offers reliable data needed to inform future restoration projects.
The Reef 2050 Plan has identified a range of measures aimed at reducing end-of-catchment loads of sediment and nutrient and recognizes the role that freshwater wetlands may have in achieving this. ...However, quantitative information on the potential for tropical wetlands to filter agricultural runoff is scarce, so this paper describes a study that combines field data from a 10 ha wetland constructed on land previously used for sugar cane near Babinda, north Queensland with a water balance and denitrification model. During the 12-month monitoring period (from October 2017 to September 2018) we estimate that the nitrogen filtering capacity of the wetland was 52% (26% lost as gaseous denitrification from the water and soil, and 26% as sedimentation of particulate nitrogen, PN). The remaining nitrogen (48%) left in the drainage water and this emphasises the importance of the wetland hydrology in determining denitrification and filtering. The current estimates are highly variable, so we have also identified the key parameters that need to be measured in order to improve long-term wetland filtering capacity estimation. Babinda is in the Mulgrave-Russell catchment, where the Reef 2050 Water Quality Improvement Plan has set target reductions in DIN of 300 t and PN of 53 t by 2025. 10% of the DIN reduction target could be achieved from ~593 ha of wetland with the same mean denitrification properties as currently estimated for the Babinda wetland (i.e. 51 kg N ha−1 year−1). This amounts to 2.3% of the total sugarcane area in this catchment that, as wetland, would also remove 56% of the 2025 PN reduction target.
•Combined water balance and denitrification modelling of a tropical wetland•Estimation of total nitrogen filtering in a constructed wetland•Clear demonstration of the importance of hydrology in wetland filtering•Identification of key parameters affecting wetland filtering•Potential contribution of wetlands to Reef water quality improvement targets
Mangrove forests are important habitats for fish. However, their utilisation by fish, and the specific values they confer, are still not fully understood. This study describes how fish use mangrove ...forests in an Indo-Pacific mangrove-coral reef seascape. Sampling was conducted using underwater video cameras (UVCs) to describe spatial and temporal variations in fish assemblages across a small-scale (~ 2.5 km2) system, and over the tidal and lunar cycle. UVCs were deployed in the two main component habitats of mangrove forests: at the mangrove forest edge, and inside the forest (5 m from the forest edge), to establish patterns of utilisation of fish across the tidal and lunar cycle. Proximity to coral reefs had a strong influence on the mangrove fish community, as most fish recorded were reef-associated. Juveniles of 12 reef species were observed, including two species classified as vulnerable on the IUCN list, and one endemic species. Fish assemblages on the mangrove edge differed significantly from those inside the forest. Most fish utilised the forest edge, with few species making regular use of in-forest habitats, supporting the contention that most fish species remain on the edge and potentially retreat into the forest for opportunistic feeding, or when threatened by larger predators. Species-specific patterns of utilisation varied across the tidal and lunar cycle. Small differences in depth profiles and substrate across the small-scale system had a significant effect on fish assemblages, highlighting the importance of accounting for spatial heterogeneity in these factors. These data provide important information for managers to implement adequate conservation strategies that include broader interconnected habitat mosaics.
To test the model that eco-engineering plant boxes on seawalls sustain water temperatures within thermal tolerance to maximize tropical marine biodiversity, we conducted acute thermal effects (AET) ...experiments using intertidal gastropods (Nerita albicilla and Littoraria articulata). The AET50 (50th percentile) for N. albicilla (39.6 °C) was higher than L. articulata (32.8 °C). Loggers (Hobo) in boxes on a seawall positioned for full exposure to air temperature at mean sea level (<1.1 m) recorded temperature every 20 min during summer months. Temperature frequency distribution plots were generated for day and night, above and below 1.1 m (which is proximal to mean tide level for the region). Using the AET50, N. albicilla would need to thermoregulate for a lower percentage of time compared to L. articulata regardless of day and night. It is likely that designing eco-engineering improvements to include microclimate refugia are particularly relevant in tropical areas, where extreme environmental conditions mean that scale-specific actions are important components for climate adaptation.
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•Planter boxes mounted to seawalls attempt to provide new habitat for local species.•Water temperature acute thermal tolerance for two marine snails was determined.•Using water temperature data from plant boxes, snails need thermal refugia for many hours of the day.•Adding thermal refugia microhabitats to eco-engineering designs could increase biodiversity, particularly in tropical estuaries.
Installation of feral pig (Sus scrofa) exclusion fences to conserve and rehabilitate coastal floodplain habitat for fish production and water quality services remains untested. Twenty‐one floodplain ...and riverine wetlands in the Archer River catchment (north Queensland) were surveyed during postwet (June–August) and late‐dry season (November–December) in 2016, 2017, and 2018, using a fyke net soaked overnight (~14–15 hr) to test: (a) whether the fish assemblage are similar in wetlands with and without fences; and (b) whether specific environmental conditions influence fish composition between fenced and unfenced wetlands. A total of 6,353 fish representing twenty‐six species from 15 families were captured. There were no wetland differences in fish assemblages across seasons, years and for fenced and unfenced (PERMANOVA, Pseudo‐F < 0.589, p < .84). Interestingly, the late‐dry season fish were far smaller compared to postwet season fish: a strategy presumably in place to maximize rapid disposal following rain and floodplain connectivity. In each wetland, a calibrated Hydrolab was deployed (between 2 and4 days, with 20 min logging) in the epilimnion (0.2 m) and revealed distinct diel water quality cycling of temperature, dissolved oxygen and pH (conductivity represented freshwater wetlands), which was more obvious in the late‐dry season survey because of extreme summer conditions. Water quality varied among wetlands in terms of the daily amplitude and extent of daily photosynthesis recovery, which highlights the need to consider local conditions and that applying general assumptions around water quality conditions for these types of wetlands is problematic for managers. Though many fish access wetlands during wet season connection, the seasonal effect of reduced water level conditions seems more overimprovised when compared to whether fences are installed, as all wetlands supported few, juvenile, or no fish species because they had dried completely regardless of the presence of fences.
Fencing wetlands prevents pig access on tropical floodplains, which should be positive for fish. However, though many fish access (fenced and unfenced) wetlands during wet season connection, the seasonal effect of reduced water level conditions seems to be more overimprovised compared to whether fences are installed or not, as all wetlands supported few, or no fish species because they had dried completed regardless of whether fences were present or not.
Coastal Ecosystem Values, Threats, and Decline Coastal wetlands, such as seagrass beds, mangrove wetlands, salt marshes, macroalgal, and seaweed beds, shellfish reefs, tidal freshwater wetlands, and ...coral reefs, are remarkable features of tropical and temperate coastlines. ...these systems are subject to what may be called “a triple whammy” of increasing industrialization and urbanization, an increased loss of biological and physical resources (fish, water, energy, space), and a decreased resilience to the consequences of a warming climate and sea level rise (Elliott et al., 2016). Trans-Disciplinary Teams Looking forward into the next decade, coastal habitat restoration will truly require a trans-disciplinary approach with skills drawn from engineering, modeling, ecology, chemistry, hydrology, social sciences including economics, financial, and project planning, governance, and integrated land, and sea spatial planning and management. Coastal ecosystems are at least as complex as terrestrial ecosystems, although arguably more dynamic, with the added gravity of the “triple whammy”—future development expansion that further alters shoreline ecosystems, loss of biodiversity and environmental conditions (e.g., water quality), and changing climate which alters sea level in many complex ways.
Coastal freshwater and tidal wetland habitats are being transformed as a result of increasing demand for commercial, residential and tourism activities. The consequence is a habitat seascape complex, ...comprising a mosaic of natural and engineered coastal features. This study used the freely available mapping tool (Google Earth) to define the extent of coastal engineering structures in the Great Barrier Reef World Heritage Area (GBR; Australia), a marine ecosystem of global biodiversity and cultural significance. Continuing threats to the heritage estate concomitant with expanding urban and industrial developments has raised concerns directed at the future conservation and resilience of the reef ecosystems, along with maintaining expected human lifestyles and livelihoods it provides. The data here shows that break walls and pontoons/jetties dominate development, contributing to approximately 10% (equivalent) of the coastline linear length. Most (60%) development occurs along the coastline or within the first few kilometres upstream along estuaries. While conservation and protection of natural coastal habitats is still preferred for the objective of fisheries production and biodiversity, managers must consider seascape implication/benefits more broadly when approving new marine infrastructure rather than a case-by-case approach which further contributes to an ad hoc mosaic seascape of natural and engineered habitats. Not only within the GBR heritage estate, but more broadly, coastal managers need to regard wider seascape connectivity processes during the assessment of any new development. There is an urgent need for policy and planning instrument reform that is inclusive of accumulative impacts of urban and industrial development in this heritage estate. Opportunities to include eco-friendly (green engineering) solutions, in the repair and revitalisation of existing artificial structures, is necessary in any new proposed urban and industrial development and expansion.
•Plant boxes attached to seawalls create low tide rock pools.•Tilting boxes provides novel overhang microhabitats.•Shaded overhangs had highest benthic assemblage.•Net sediment accumulation averaged ...25 mm/yr.•Boxes will require desilting every 10 yrs.
Seawalls made from rock and concrete are engineered to defend coastlines and infrastructure from sea level rise, storm surge and shoreline erosion. However, while they provide a poor substitute for natural intertidal habitat, emerging designs addressing this biodiversity deficit have incorporated eco-engineering concepts with promising results. This study tested whether adding inexpensive household flower boxes (artificial rock pools) to a seawall in a tropical region would support benthic flora and fauna, and whether simple orientation of boxes improves benthic assemblage colonization. Boxes were positioned at mean tide height (1.1 m AHD) along a seawall in tropical Townsville, Australia. Nine boxes were deployed: three positioned vertically on the seawall, while three positioned at 45° facing towards the sea, and three positioned at 45° facing towards the land. Tilting the artificial rock pools at 45° compared overhang walls (simulating rocky shoreline ledge microhabitat) to vertical walls of artificial rock pools. After 12mths, boxes had accumulated (particularly inside on overhang walls compared to outside walls) a greater surface cover of algae and invertebrates. After the second year, box inside walls supported vastly different assemblages compared to outside box walls regardless of orientation, with the most diverse benthic assemblage found on overhang walls, giving support to the conclusion that artificial rock pools on seawalls support more biodiversity (of native species, with no non-indigenous species found) from tilting and creating overhangs. The turbid nature of this coastal region contributed to sediment accumulation at about 25 mm/yr, regardless of box orientation, which may pose maintenance problems (and cost) for managers, and if unchecked could negate any advantages offered by these engineered pool features.
Freshwater impounded wetlands are created by artificially restricting coastal wetlands connection to tides. The decrease in salinity and altered hydrology can significantly increase greenhouse gas ...(GHG) emissions, specifically methane (CH
4
). Restoration of freshwater impounded wetlands through tidal reintroduction can potentially reduce GHG emissions; however, studies in tropical regions are scare. This study investigates the potential for tidal restoration of impounded freshwater coastal wetlands by comparing their GHG emissions with tidally connected mangrove and saltmarshes in the Burdekin catchment in Queensland, Australia. We found that freshwater impounded wetlands had significantly higher CH
4
emissions (3,633 ± 812 μg CH
4
m
−2
hour
−1
) than mangroves (27 ± 8 μg CH
4
m
−2
hour
−1
) and saltmarsh (13 ± 8 μg CH
4
m
−2
hour
−1
). Soil redox, moisture, carbon, nitrogen, and bulk density were all significantly correlated to methane emissions. Conversely, freshwater impounded wetlands had significantly lower nitrous oxide (N
2
O) emissions (−0.72 ± 0.18 μg N
2
O m
−2
hour
−1
) than mangroves and saltmarsh (0.35 ± 0.29 and 1.32 ± 0.52 μg N
2
O m
−2
hour
−1
respectively). Nevertheless, when converting to CO
2
equivalents (CO
2‐eq
), freshwater impounded wetlands emitted 91 ± 20 g CO
2‐eq
m
−2
hour
−1
, compared to the much lower 0.8 ± 0.2 and 0.7 ± 0.2 g CO
2‐eq
m
−2
hour
−1
emission rates for mangroves and saltmarsh. In conclusion, restoration of freshwater impounded wetlands through tidal restoration is likely to result in reduced GHG emissions.
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