Spatial patterns of sub-tidal seagrasses and their tissue nutrients in the Torres Strait, northern Australia: Implications for management

The distribution and nutritional profiles of sub-tidal seagrasses from the Torres Strait were surveyed and mapped across an area of 31,000 km2. Benthic sediment composition, water depth, seagrass species type and nutrients were sampled at 168 points selected in a stratified representative pattern. Eleven species of seagrass were present at 56 (33.3%) of the sample points. Halophila spinulosa, Halophila ovalis, Cymodocea serrulata and Syringodium isoetifolium were the most common species and these were nutrient profiled. Sub-tidal seagrass distribution (and associated seagrass nutrient concentrations) was generally confined to northern-central and south-western regions of the survey area (<longitude 142.60), where mean water depth was relatively shallow (approximately 13 m below MSL) and where sediments were comprised primarily muddy sand to gravelly sand. Seagrass nitrogen and starch content, the most important nutrients for marine herbivores, were significantly correlated with species and with the plant component (above or below ground). For all seagrass species, the above-ground component (shoots and leaves) possessed greater nitrogen concentrations than the below-ground component (roots and rhizomes), which possessed greater starch concentrations. S. isoetifolium had the highest total nitrogen concentrations (1.40±0.05% DW). However, it also had higher fibre concentrations (38.2±0.68% DW) relative to the other four species. H. ovalis possessed the highest starch concentrations (2.76±0.12% DW) and highest digestibility (83.24±0.66% DW) as well as the lowest fibre (27.2±0.66% DW). The high relative abundance (found at 55% of the sites that had seagrass) and nutrient quality characteristics of H. ovalis make it an important source of energy to marine herbivores that forage sub-tidally in the Torres Strait. There were two regions in Torres Strait (north-central and south-western) where sub-tidal seagrass meadows were prevalent and of relatively higher nutritional value. This spatial and nutritional information can be used by local agencies to manage and to protect the ecological, economic and cultural values of the sub-tidal seagrass ecosystems and associated fisheries of the Torres Strait.

[1]  R. O'Neill,et al.  The value of the world's ecosystem services and natural capital , 1997, Nature.

[2]  J. P. Ross.  Biology of the Green Turtle, Chelonia mydas, on an Arabian Feeding Ground , 1985 .

[3]  Robert L. Folk,et al.  The Distinction between Grain Size and Mineral Composition in Sedimentary-Rock Nomenclature , 1954, The Journal of Geology.

[4]  G. Forbes.  The diet and feeding ecology of the green sea turtle (Chelonia mydas) in an algal-based coral reef community , 1996 .

[5]  W. R. Birch.  Some Chemical and Calorific Properties of Tropical Marine Angiosperms Compared with Those of Other Plants , 1975 .

[6]  A Preen,et al.  Impacts of dugong foraging on seagrass habitats: observational and experimental evidence for cultivation grazing , 1995 .

[7]  S. V. Wieren,et al.  Do large herbivores select a diet that maximizes short-term energy intake rate? , 1996 .

[8]  Kan Aketa,et al.  Carbon and nitrogen stable isotope ratios of the tissues and gut contents of a dugong from the temperate coast of Japan , 2004 .

[9]  I. Lawler,et al.  Near infrared spectroscopy as a rapid and inexpensive means of dietary analysis for a marine herbivore, dugong Dugong dugon , 2003 .

[10]  H. Kirkman,et al.  Baseline and Monitoring Methods for Seagrass Meadows , 1996 .

[11]  Anthony W. D. Larkum,et al.  Biology of seagrasses : a treatise on the biology of seagrasses with special reference to the Australian region , 1989 .

[12]  Lemnuel Aragones.  Dugongs and green turtles: grazers in the tropical seagrass ecosystem , 1996 .

[13]  A. Chirapart,et al.  Quality of the Seagrass Halophila ovalis on a Thai Intertidal Flat as Food for the Dugong , 2005 .

[14]  G. Heinsohn,et al.  FOODS AND FEEDING HABITS OF THE DUGONG, DUGONG DUGONG (ERXLEBEN), IN NORTHERN QUEENSLAND, AUSTRALIA , 1972 .

[15]  G. Smith,et al.  Mapping and characterisation of the inter-reefal benthic assemblages of the Torres Strait , 2008 .

[16]  William J. Foley,et al.  Dugong grazing and turtle cropping: grazing optimization in tropical seagrass systems? , 2006, Oecologia.

[17]  P. Harris.  Sediments, bedforms and bedload transport pathways on the continental shelf adjacent to Torres Strait, Australia—Papua New Guinea , 1988 .

[18]  Britta Schaffelke,et al.  Water quality in the Great Barrier Reef region: responses of mangrove, seagrass and macroalgal communities. , 2005, Marine pollution bulletin.

[19]  G. Hays,et al.  Behavioural plasticity in a large marine herbivore: contrasting patterns of depth utilisation between two green turtle (Chelonia mydas) populations , 2002 .

[20]  Onisimo Mutanga,et al.  Explaining grass‐nutrient patterns in a savanna rangeland of southern Africa , 2004 .

[21]  P. Harris,et al.  The nature of sediments forming the Torres Strait turbidity maximum , 1991 .

[22]  Helene Marsh,et al.  Seagrass as pasture for seacows: Landscape-level dugong habitat evaluation , 2007 .

[23]  C. Duarte,et al.  Patterns in leaf herbivory on seagrasses , 1998 .

[24]  Frederick T. Short,et al.  Natural and human-induced disturbance of seagrasses , 1996, Environmental Conservation.

[25]  D. Lindenmayer,et al.  Unsustainable harvest of dugongs in Torres Strait and Cape York (Australia) waters: two case studies using population viability analysis , 2004 .

[26]  C. Duarte.  The future of seagrass meadows , 2002, Environmental Conservation.

[27]  G. Hays,et al.  The diving behaviour of green turtles at Ascension Island , 2000, Animal Behaviour.

[28]  Carlos M. Duarte,et al.  Seagrass Biomass And Production: A Reassessment , 1999 .

[29]  B. Jupp,et al.  Distribution, abundance, and species composition of seagrasses at several sites in Oman , 1996 .

[30]  K. Pollock,et al.  Dugong distribution and abundance in Torres Strait , 2004 .

[31]  B. McCleary,et al.  Measurement of total starch in cereal products by amyloglucosidase-alpha-amylase method: collaborative study , 1997 .

[32]  David Hopley,et al.  The geomorphology of the Great Barrier Reef: Quaternary development of coral reefs , 1982 .

[33]  A. Mccomb,et al.  A Halodule-dominated community in a subtropical embayment: physical environment, productivity, biomass, and impact of dugong grazing , 2001 .

[34]  I. Lawler,et al.  The Sustainability of the Indigenous Dugong Fishery in Torres Strait, Australia / Papua New Guinea , 1997 .

[35]  S. Garnett,et al.  The Diet of the Green Turtle, Chelonia mydas (L.), in Torres Strait , 1985 .

[36]  C. Limpus,et al.  Diet selection by immature green turtles, Chelonia mydas, in subtropical Moreton Bay, south-east Queensland , 1999 .

[37]  A. Spain,et al.  Physiology of the dugong , 1978 .

[38]  J. Mellors.  Sediment and nutrient dynamics in coastal intertidal seagrass of north eastern tropical Australia , 2003 .

[39]  D. Tomasko,et al.  Seagrass in Australia : strategic review and development of an R & D plan , 1999 .

[40]  James Udy,et al.  Growth and physiological responses of three seagrass species to elevated sediment nutrients in Moreton Bay, Australia , 1997 .

[41]  E. Meelis,et al.  Seagrass distribution and seasonal biomass changes in relation to dugong grazing in the Moluccas, East Indonesia , 1995 .

[42]  Donna Kwan.  Towards a sustainable indigenous fishery for dugongs in Torres Strait : a contribution of empirical data analysis and process , 2002 .

[43]  R. Coles,et al.  Distribution of seagrasses and associated juvenile commercial penaeid prawns in north-eastern Queensland waters , 1987 .

[44]  W. Maxwell,et al.  Atlas of the Great Barrier Reef , 1968 .

[45]  James K. Sheppard,et al.  Movement heterogeneity of dugongs, Dugong dugon (Müller), over large spatial scales , 2006 .

[46]  I. Lawler,et al.  Comparison of the diets of sympatric dugongs and green turtles on the Orman Reefs, Torres Strait, Australia , 2005 .

[47]  David J. Augustine,et al.  EFFECTS OF MIGRATORY GRAZERS ON SPATIAL HETEROGENEITY OF SOIL NITROGEN PROPERTIES IN A GRASSLAND ECOSYSTEM , 2001 .

[48]  G. Hays,et al.  The diving behaviour of green turtles undertaking oceanic migration to and from Ascension Island: dive durations, dive profiles and depth distribution. , 2001, The Journal of experimental biology.

[49]  I. Lawler,et al.  Diving behaviour of dugongs, Dugong dugon , 2004 .

[50]  P. Young,et al.  Patterns of some seagrass distribution in the Torres Strait, Queensland , 1982 .

[51]  J. Shenk,et al.  New Standardization and Calibration Procedures for Nirs Analytical Systems , 1991 .

[52]  C. Duarte.  Seagrass nutrient content , 1990 .

[53]  Lemnuel V. Aragones,et al.  Impact of Dugong grazing and turtle cropping on tropical seagrass communities , 1999 .

[54]  F. Short,et al.  Global seagrass research methods , 2001 .

[55]  J. Prescott,et al.  Distribution of Seagrasses, Substratum Types and Epibenthic Macrobiota in Torres Strait, with Notes on Pearl Oyster Abundance , 1992 .

[56]  J. Morrissey,et al.  Analysis of Stomach Contents of Dugongs From Queensland. , 1982 .

[57]  W. Foley,et al.  Near-Infrared Reflectance Spectroscopy is a Rapid, Cost-Effective Predictor of Seagrass Nutrients , 2006, Journal of Chemical Ecology.

[58]  W. Baethgen,et al.  A manual colorimetric procedure for measuring ammonium nitrogen in soil and plant Kjeldahl digests , 1989 .

[59]  Len J. McKenzie,et al.  Chapter 5 – Methods for mapping seagrass distribution , 2001 .

[60]  A. Newton.  Dynamics of Tropical Communities , 1999 .

[61]  H. Olff,et al.  Species-richness of African grazer assemblages: towards a functional explanation. , 1998 .

[62]  Kenneth H. Pollock,et al.  Aerial surveys and the potential biological removal technique indicate that the Torres Strait dugong fishery is unsustainable , 2004 .

[63]  R. Watson,et al.  Simulation Estimates of Annual Yield and Landed Value for Commercial Penaeid Prawns from a Tropical Seagrass Habitat, Northern Queensland, Australia , 1993 .