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The Townsville region is on the dry tropical coast of north-eastern Queensland. Intertidal and shallow subtidal seagrasses predominate and tend to form multi-specific meadows that are arranged in mono-specific bands across a depth gradient. True reefal seagrasses are also rare in this region, but most fringing reefs associated with continental islands support moderately dense mixed species meadows. Area of seagrass in the region is estimated at 130 km2, of mostly moderate (11-49%) and light (1-10%) cover.

In the Townsville region, there are many seagrass meadows along Cape Cleveland, the Strand, Cape Pallarenda, and around Magnetic Island. The main seagrass species in shallow waters near Townsville are Halophila ovalis, Halodule uninervis, Zostera capricorni, and Cymodocea serrulata. Thalassia hemprichii can also be found on the reef flats of Magnetic Island. Halophila spinulosa that has been washed up from deeper waters can sometimes be found. Despite the variable inter-annual rainfall that occurs along this coastline, cyclones are a frequent feature(~15 cyclones/decade). In April 2000, intertidal seagrass meadows in the Townsville region were decimated by cyclone "Tessi" but are now virtually recovered.

Bushland Beach Shelly Beach Sandfly Creek Rowes Bay Magnetic Is: MI1, MI2

The distribution of seagrasses along this coastline is predominately influenced by seasonal (April-November) south-easterly trade winds. Seagrass meadows generally establish in places that offer protection from these winds, such as the large north opening bays and the lee ward sides of continental islands. The combination of seasonal terrestrial run-off, frequent cyclones, strong south-easterly trade winds and large tidal runs (in the south) creates significant coastal turbidity. Consequently seagrasses that inhabit this area are subjected to low light regimes, and high influxes of freshwater and sediment. To survive this regime seagrasses need to exhibit high vegetative growth rates and prolific seed banks. This has probably led to the predominance of opportunistic species, such as Halodule and Halophila within this region.

The greatest threat to seagrass throughout this region is agricultural land clearing (both grazing and cropping) and its inherent problems of soil erosion and associated loads of nutrients and pesticides.

Monitoring occurs at three or the four generalised seagrass habitats within the Townsville region: coastal, estuarine and reef.

Below is a conceptual diagram of coastal seagrass habitat in the Townsville region. Coastal habitats are generally on naturally dynamic intertidal sand flats and are subject to sand waves and erosion blowouts moving through the meadows. While episodic riverine delivery of freshwater nutrients and sediment is a medium time scale factor in structuring these coastal seagrass meadows, it is the wind induced turbidity of the costal zone that is likely to be a major short term driver. In these shallow coastal areas waves generated by the prevailing SE trade winds are greater than the depth of water, maintaining elevated levels of suspended sediments, limiting the amount of light availability for photosynthesis during the trade season. Intertidal seagrasses can survive this by photosynthesizing during periods of exposure, but must also be able to cope with desiccation. Another significant feature in this region is the influence of ground water.

Estuarine habitats within this region are in open estuaries/inlets and tend to be continuous with the coastal habitats. Both tidal and subtidal distributions are heavily influenced by their proximity to creeks and rivers. Delivery of freshwater and suspended solids, including clays, colloids, fine organic matter, is the major impact to all meadow types in this habitat. This influence extends beyond the estuarine zone during high flow events. Of the total sediment being delivered to the GBRWHA lagoon, the long term average discharge of sediment from this region represents 20%-40%. The major impact of terrestrial run-off on near-shore environments occurs during cyclones or heavy monsoonal rains and is only delivered during infrequent flooding events. Relatively low sediment discharge occurred over the intervening years. During flood events these habitats are subject to scouring, a combination of fast flow and course sediments. The habitats are productive nursery areas, particularly the southern parts of Cleveland and Bowling Green Bay as these are areas targeted by commercial and recreational fishers.

Reef habitats are mainly represented by fringing reefs on the many continental islands within this area. Most fringing reefs have seagrass meadows growing on their intertidal flats. Nutrient supply to these meadows is by terrestrial inputs via riverine discharge, re-suspension of sediments and groundwater supply. The meadows are typically composed of zones of seagrasses. Cymodocea serrulata and Thalassia hemprichii often occupy the lower intertidal/subtidal area, blending with Halodule uninervis (wide leaved) in the middle intertidal region. Halophila ovalis and Halodule uninervis (narrow leaved) inhabit the upper intertidal zone. Studies from overseas have often implicated phosphate as the nutrient most limiting to reefal seagrasses. Experimental studies on reef top seagrasses in this region however, have shown seagrasses to be nitrogen limited primarily with secondary phosphate limitation, once the plants have started to increase in biomass (Mellors 2003). In these fringing reef top environments fine sediments are easily resuspended by tidal and wind generated currents making light availability a driver of meadow structure.

 

Within seagrass canopy water temperatures

Within canopy temperature was monitored at coastal and reef-platform locations and generally follow a similar pattern. Mean temperatures were mostly within the 20 – 30°C range, with highest mean temperatures (>35°C) generally recorded from January to February. The highest sea temperature recorded across the region was 46.6°C at Shelley Beach between 3-4pm on 10th January 2008.

 

 

Marine Monitoring Program

The Marine Monitoring Program monitors the condition of water quality and the health of key marine ecosystems such as coral reefs and seagrass in the inshore Great Barrier Reef lagoon. The program forms part of the Reef Water Quality Protection Plan (Reef Plan) which is a joint commitment of the Australian and Queensland Governments. The Marine Monitoring Program is a key component in assessing long-term improvements in inshore water quality and marine ecosystem health that are expected to occur with the adoption of improved land management practices in the Reef catchments under Reef Plan.

Monitoring occurs at coastal and reef seagrass habitats in the Burdekin region. The Townsville coastal sites (Bushland Beach and Shelley Beach) are located on naturally dynamic intertidal sand flats dominated by Halodule uninervis. The declines in seagrass abundance and meadow extent since 2009 continued across the region in 2010/11. In February 2011, Tropical Cyclone Yasi (category 5) impacted the region further exacerbating declines until only a few isolated shoots remained in mid 2011. Seed banks also declined across the region in 2011 and reproductive effort was in a very poor state, raising concerns about the ability of reef seagrass meadows to recover from any major environmental disturbances.

Seagrass tissue nutrient concentrations and light monitoring in 2010/11 indicated decreasing light availability across the region since 2006 with nutrient loading from an increasing P pool. This resulted in reef habitat seagrass becoming replete (well supplied and balanced macronutrients for growth) and the coast becoming N-limited. The low light availability was possibly exacerbated by higher epiphyte abundance (increasing above GBR long-term average). Macroalgae abundance remained negligible and no herbicides were found above detectable limits in the sediments of the seagrass meadows in 2010/11.

Climate across the region in 2010/11 was cooler, wetter, cloudier, but not as windy, as the previous monitoring period. The increase in rainfall caused the Burdekin River to flow significantly higher than any other period in the last decade and above 100,000 ML day-1 for 5 consecutive months. The flood waters in high exposure of the seagrass monitoring sites to elevated TSS and Chlorophyll-a. Within seagrass canopy temperatures were cooler than the previous monitoring period and no extreme temperatures were recorded. Overall the status of seagrass condition in the region was rated as very poor.

To read the full technical report, CLICK HERE

For more information, visit GBRMPA

 

 

 

 

Bushland Beach

 

Monitoring: ongoing

Principal watchers: Seagrass-Watch HQ 

Occasional and past watchers: Jackie Stein, Sharon Taylor, Rose Zahrn, Gary Stein, Lux Foot, Sue Mulvany, Posa Skelton, Sandra Quintemeyer, Angelina, Peter Taylor, Belinda, Linda Davis, Jason Vains and Michelle.
Location: on the large intertidal sand bank in front of the Bushland Beach township, between the Bohle and Black Rivers
Site code: BB1

BB1 position: S19.18381 E146.68247 (heading 5 degrees)
Best tides: <0.6m (port Townsville, 59250)
Issues: Coastal development, land runoff
Comments: The Bushland Beach area is a sediment deposition zone, so the meadow must also cope with incursions of sediment carried by long shore drift. The meadows are frequented by dugongs and turtles as witnessed by feeding trails. These meadows are also visited regularly by recreational fishers. Sediments within this habitat are mud and sand that have been delivered to the coast during the episodic peak flows of the creeks and rivers (notably the Burdekin) in this area.

Status (January 2014):

  • seagrass cover appears to have recovered from the losses experienced between 2009 - 2012 and is currently similar to when sites were established in 2002
  • prior to 2009, abundance appears to follow a typical seasonal pattern (higher in late spring-summer than winter).
  • sites dominated by Halodule uninervis with some Halophila ovalis.
  • slight increases in composition of Halophila ovalis over previous 6 months may indicate some level of disturbance
  • macroalgae cover generally low and below GBR long-term average for coastal habitats (red line in figure below).
  • epiphytes were quite high in the later months of the year (up to 85%) and currently above GBR long-term average for coastal habitats (red line in figure below).
  • Halodule seed banks currently small relative to the peaks experienced in 2007

 

 

 

 

 

 

 

 

Shelley Beach

 

Monitoring: ongoing

Principal watchers: Seagrass-Watch HQ
Occasional and past watchers: Sue Mulvany, Steve McGuire, Dick Wickenden, Posa Skelton, Ann Ferguson, Dave Watson, David Reid, Des Wells, Deb Bass, Lyn McAndrew, Michelle Waycott, Mandy Young, Ray Matten, Sally Puet &, Barry Bendell
Location: Cape Pallarenda
Site code: SB1, SB2

SB1 position: S19.18626 E146.77102 (heading 35 degrees)
SB2 position: S19.18255 E146.76273 (heading 10 degrees)
Best tides: <0.7m (port Townsville, 59250)
Issues: Coastal development, land runoff.
Comments: The Shelley Beach area is a sediment deposition zone, so the meadow must also cope with incursions of sediment carried by long shore drift. The meadows are frequented by dugongs and turtles as witnessed by feeding trials and scars.  Sediments within this habitat are mud and sand that have been delivered to the coast during the episodic peak flows of the creeks and rivers (notably the Burdekin) in this area.

Status (January 2014):

  • seagrass cover appears to have recovered from the losses experienced between 2009 - 2012 and is currently similar to when sites were established in 2002
  • abundance appears to follow a typical seasonal pattern (higher in late spring-summer than winter).
  • both sites have remained dominated by Halodule uninervis with Halophila ovalis, Zostera capricorni has started to appear at SB2.
  • Canopy height showing a fairly typical seasonal pattern
  • Macroalgae appears to be generally higher over the summer months, and although more prevalent at SB2 than SB1, it is currently below the GBR long-term average for coastal habitats (red line in figure below).
  • Epiphyte abundance appears to reflect a similar seasonal pattern at both sites, and although slightly increased over last 12 months, remains below the GBR long-term average for coastal habitats (red line in figure below).
  • a large seed bank persists at SB2, and the relatively smaller seed bank at SB1 increased slightly over the last 12 months.

 


 

 

 

 

 

 

 

 

 

Magnetic Island

Magnetic Island, just offshore from Townsville, in Cleveland Bay is a 52 km² mountainous island which has effectively become a suburb of Townsville having well over 2000 permanent residents.

The name of the island came about because of the apparent "magnetic" effect it had on the ship's compass of Captain Cook as he passed the island when sailing up the east coast of Australia in 1770. People have since explored the island with magnets to verify the field that Cook experienced, but none have been discovered.

 

 

 

Picnic Bay (Magnetic Island)

Monitoring: ongoing

Principal watchers: Seagrass-Watch HQ
Occasional and past watchers: Rhonda Stevens, Karen Landt, Michelle Waycott, Hannah Laurie, Ainsley Calladine
Location: on the intertidal fringing reef flat in the north of Picnic Bay, adjacent to the wreck
Site code: MI1

MI1 position: S19.17898 E146.84126 (heading 154 degrees)
Best tides: <0.7m (port Townsville, 59250)
Issues: Coastal development, ground-water seepage, land runoff, boat and pedestrian traffic.
Comments: Picnic Bay is fringed by coral reefs on its seaward edge and has seagrass growing on its intertidal flat and subtidally, beyond the reef crest. The seagrass meadow at this location is multispecific with stands of Cymodocea serrulata with Thalassia hemprichii, Halophila ovalis (lower intertidal, subtidal), Halodule uninervis (wide) (middle intertidal) and Halophila ovalis/Halodule uninervis (narrow) occupying the upper intertidal region. Patches of Syringodium isoetifolium (shallow subtidal) and Zostera capricorni (intertidal) have also been observed within this meadow. Cymodocea rotundata has also been previously recorded from this meadow. Within the Seagrass-Watch site Halodule uninervis(narrow) /Halophila ovalis with Zostera capricorni almost encroaching on Transect 1. Hermit crabs, sesarmid crabs, Astropecten starfish are quite abundant within the site with the occasional dugong feeding trail.

Status (October 2013):

  • seagrass cover continued to recover from the losses experienced between 2009 - 2012, but still remains in a poor state
  • prior to 2009, abundance appeared to follow a typical seasonal pattern (higher in late spring-summer than winter).
  • sites dominated by Halodule uninervis with some Halophila ovalis.
  • macroalgae cover remained low and below GBR long-term average for reef habitats (red line in figure below).
  • epiphytes were similarly low, remaining below the GBR long-term average for reef habitats (red line in figure below).
  • A highly variable but small seed banks persists.


 

 

 

 

 

Cockle Bay (Magnetic Island)

Monitoring: ongoing

Principal watchers: Seagrass-Watch HQ
Occasional and past watchers: Dr. Don Kinsey, Babara Kinsey, University of the Third Age, Linda Davis, Sue Mulvaney, David Reid, Catherine Walsh, Elena Peirano, Michelle Waycott, Carla Wegscheidl, Ainsley Calladine

Location: on the fringing reef flat in the eastern corner of Cockle Bay, adjacent to the excavated boat harbour
Site code: MI2

MI2 position: S19.17686 E146.82895 (heading 205 degrees)
Best tides: <0.7m (port Townsville, 59250)
Issues: Coastal development, runoff from quarry and hobby farm activities.
Comments: Sea turtle feeding area. Large number of stingrays present. The seagrasses at Cockle bay form an extensive, multi-specific, fringing reef flat meadow. Species found within this meadow include Halophila ovalis, Halodule uninervis, (narrow and wide leaved morphologies) Cymodocea serrulata, Thalassia hemprichii and, recently, a patch of Syringodium isoetifolium has been observed.


Historical information on the species composition is known for this bay as it was the location of a ten year seagrass survey along two permanent transects conducted post being decimated by cyclone Althea in 1971. This historical survey documented the different recovery rates of the individual species, with some species re-colonising the area only to be out-competed by other species in subsequent years (Birch and Birch 1984). Birch and Birch’s (1984) study showed that after ten years of recovery this seagrass meadow was replaced by the coralline algae Halimeda opuntia. More recently Cyclone Tessi (2000) disturbed the seagrass meadow at Cockle Bay, although not to the same extent as Cyclone Althea. Seagrass-Watch monitoring has reported a shift from the site being predominantly a mixed Halophila ovalis/ Halodule uninervis/ Cymodocea serrulata meadow to a Halodule uninervis/Cymodocea serrulata/Halophila ovalis meadow. Continued monitoring will only tell us whether this meadow will develop into a coralline algae bed.

Status (October 2013):

  • seagrass cover continues to recover from the losses experienced between 2009 - 2012, but remains in a fair state
  • meadows dominated by colonising species (Halophila ovalis), but foundational species started to appear in 2013.
  • macroalgae at Cockle Bay is highly variable and predominately composed of Halimeda spp. Abundances generally above the GBR long-term average for reef habitats (red line in figure below).
  • Epiphyte cover at Cockle Bay is high and remains above the GBR long-term average for reef habitats (red line in figure below).
  • no seed bank is currently present

 

 

 

 

 

Rowes Bay

 

Monitoring: training/demonstration site

Principal watchers: Rowes Bay Junior Rangers- Belgian Gardens State School, Gayle Joyce, Brett Murphy & Seagrass-Watch HQ
Occasional & past watchers: Mundy CreekWatch, Catherine Walsh, Posa Skelton
Location: Rowes Bay, Townsville
Site code: RB1, RB2

RB1 position: S19.23976 E146.79315 (heading 30 degrees)
Best tides: <0.8m (port Townsville, 59250)
Issues: Downstream from estuarine creek, storm water and urban runoff, beach replenishment works.
Comments: The intertidal area of Rowes Bay includes several different marine habitats such as a mangrove forest, a rocky shoreline, a small muddy, coarser sandy and several rubbly reefal areas, one of which includes a tropical sponge garden on the seaward edge. Interspersed between and within all these habitats are seagrasses. Over the years this seagrass meadow has come and gone, clearly demonstrating the ephemeral nature of intertidal seagrass meadows. The Seagrass-Watch site is south-east of the estuarine creek and predominantly Halodule uninervis, interspersed with small amounts of Halophila ovalis. Macroalgae is also quite common within this site. This meadow is a highly disturbed site with regular pedestrian traffic, inputs of freshwater and associated sediment loads. Invertebrate diversity is high.

 


 

 

 

 

 

Sandfly Creek

 

Monitoring: suspended

Occasional and past watchers: Deb Bass, Steve McGuire, Dick Wickenden, Dez Wells, David Reid, Ann Ferguson, Jason Jeffery, Nicole Hudson, Sally Peut and Seagrass-Watch HQ
Location: Southern shore of Cleveland Bay
Site code: SC1, SC2

SC1 position: S19.29140 E146.86773 (heading 25 degrees)
SC2 position: S19.29497 E146.87082 (heading 35 degrees)
Best tides: <0.6m (port Townsville, 59250)
Issues: Sewage treatment outfall, land runoff, coastal development
Comments: Fishing grounds, dugong and turtle feeding grounds. Nursery area for mud and sand crabs.

Status (June 2004):

  • The sites have not been examined since 2004.
  • Insufficient data to describe long-term trends, but early data indicated that abundances showed typical seasonal pattern (higher in late spring-summer than winter).
  • Seagrass abundance at SC2 significantly decreased since mid-2002. Isolated patches of Zostera capricorni were in the vicinity.
  • SC1 has always had low seagrass abundance and appears to have remained similar.
  • Species composition appears unchanged over sampling period
  • Canopy height slightly lower although not significant as highly variable
  • Algae and epiphyte currently lower than expected, but not significant as highly variable. The seagrass and mangrove aerial roots were covered in filamentous algae in July 2004, but this seems to be widespread phenomena at this time of year.
  • Sediment appears similar, although at present possibly less muddy

 

 

 

 

 
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Phone: [+61][07] 40 350 100
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