Seagrasses are key coastal ecosystems, providing many ecosystem services. Seagrasses increase biodiversity as they provide habitat for a large set of organisms. In addition, their structure provides hiding places to avoid predation. Seagrasses can grow in shallow marine coastal areas, but several factors regulate their growth and distribution. Seagrasses can uptake different kinds of organic and inorganic nutrients through their leaves and roots. Nitrogen and phosphorous are the most important nutrients for seagrass growth. Biological nitrogen fixation is the conversion of atmospheric nitrogen into ammonia by diazotrophic bacteria. This process provides a significant source of nitrogen for seagrass growth. The nitrogen fixation is controlled by the nif genes which are found in diazotrophs. The main goal of the project is to measure nitrogen fixation rates on seagrass sediments, in order to compare among various seagrass species from the Red Sea. Moreover, we will compare the fixing rates of the Vegetated areas with the bare sediments. This project will help to ascertain the role of nitrogen fixing bacteria in the development of seagrass meadows.

Seagrass beds of Zostera capricorni are an integral part of the estuarine landscape along the east coast of Australia forming important habitats for juvenile fish and macroinvertebrates. Seagrass beds can vary in their spatial structural such as their size, shape and patchiness of seagrass cover. They can also be located within the estuarine landscape context such as their proximity to other habitats or their location within the estuary. The influence or correlation of these landscape or seascape spatial features of seagrass beds on the assemblages of seagrass fauna (fish and macroinvertebrates) was tested in this thesis. It was found that the spatial structure of seagrass beds (size and shape), their patchiness of the seagrass cover and location within the estuary (close or far from estuary mouth) were correlated with the assemblages of fish within seagrass beds. In particular it was demonstrated that there were greater densities of small fish species in the small compared to the large beds of Z. capricorni. This occurred regardless of the placement of the seagrass bed within the estuary context, its proximity to other habitats or patchiness of cover. Further experimentation using artificial seagrass patches demonstrated that this effect of patch size was independent of the perimeter length or perimeter to area ratio of the seagrass beds. It was hypothesised that the greater density of small fish species in small seagrass beds could be attributed to the greater proportion of edge habitats in small beds i.e. edge-mediated effects. However, the number of fish species per net haul in edges and inner regions of small and large seagrass beds were measured and found not to be different. The outcomes of this research suggest that to conserve the small fish species within an estuary, it is essential to protect even the small and patchy seagrass beds. A network of seagrass beds from all regions of the estuary is also required and the adjacent mangrove forests must be included / Doctor of Philosophy (PhD)

Seagrasses provide an important habitat for gillfish, crustacea and migratory birds. Extensive losses of seagrass in the Northern Hemisphere have occurred since the 1930's in what has been described as a 'wasting disease'. More recently, point-source contamination by nutrient inflows, herbicides (anti-fouling agents used on commercial shipping), heavy metals and fresh water inflows have helped explain localised losses of seagrass amounting to 20% in the case of Adelaide's metropolitan coastline, South Australia. However, losses of seagrass acreage have also occurred in regions that are far removed from anthropogenic activity and these are less easily explained by pointsource contamination. Intertidal seagrasses, such as Zostera muelleri, are subjected to environmental pressures imposed on them by the marine and terrestrial environments. For the purpose of this thesis, the intertidal environment is regarded as a complex of several components or micro-environments, each imposing a selective pressure or stress upon seagrass. The many stress factors create a tolerance zone in which Z. muelleri can survive. Zostera muelleri has adapted its physiology and biochemistry to the selective pressures that operate within the intertidal region. Zostera muelleri's internal leaf morphology has many gas storage compartments (lacunae) that extend from the leaves to the roots of the plants and its photosynthetic biochemistry has also adapted to the intertidal region enabling the sequestering of carbon under conditions of high irradiance and temperatures. It is evident from the literature that the survival of intertidal seagrasses requires effective photosynthesis. It is also evident that events that interfere with the synthesis, translocation and release of photosynthesised oxygen from the roots of Z. muelleri will compromise seagrass survival. The present study has revealed that herbicides, used in broad- acre farming, can be transported to the intertidal environment and negatively impact upon Z. muelleri. Extensive studies by others have shown that transport mechanisms, such as 'spray drift' and 'run-off', can move herbicides from their point of usage. However, 'dust' (wind-eroded soil ) as a transport mechanism for herbicides to the intertidal environment is less well studied. This is surprising, inasmuch as there is a known rate of pedogenesis in Adelaide of five to ten tonnes per km2 per annum from the accretion of dust. Results of the present study suggest that farmed soils of the Yorke Peninsula have a range of potentials to form fine particulate matter ('dust') and this potential is likely determined by the soil type and farming practices. Soil surface applied herbicides, such as 2,4-D, are 'lost' from land at 5% of the applied rate while soil-incorporated herbicides, such as treflan (trifluralin), are lost at 1.5% of the applied rate. Indeed, such herbicides can be transported as dust for tens to thousands of kilometres. Instrumental analytical techniques used in the present study have detected 2,4-D, trifluralin and sulfonylurea herbicides on whole soil. Additionally, 2,4-D- like chemicals have also been detected in whole soil and in dust obtained from whole soil. Bioassay techniques using Z. muelleri have shown that its photosynthetic pathways are negatively impacted upon by micromolar concentrations of 2,4-D that are similar to the known losses of this herbicide from land. It is concluded that, at these concentrations, 2,4-D acts as an auxin, up-regulating growth in affected plants. Such up-regulation is unlikely to be problematic in terrestrial plants since gas flows to the external environment are largely controlled by stomata. However, seagrasses lack stomata and the auxin-like activity of 2,4-D appears to have a negative impact on Z. muelleri. This is probably caused by an up - regulation in oxygen production and a subsequent oxygen-inhibition of a key enzyme ( ribulose 1,5- bisphosphate carboxylase, RUBISCO ) used in the carbon-sequestering photosynthetic process. The proposed inhibition of RUBISCO is then likely to cause a carbon deficit and a subsequent energy deficit within affected plants. One interpretation of the results presented is that Z. muelleri simply outgrows its intertidal environment after a transient exposure to an auxin-like concentration of 2,4-D. With increasing use of auxin-like herbicides, and the associated increasing stress imposed on photosynthetic processes, it is likely that further negative impacts will occur on intertidal seagrass species. Continued depletion of seagrass acreage will further adversely affect fishing yields unless appropriate measures are not taken. Closer collaboration between regulators, farm managers and herbicide manufacturers is now necessary in order to minimise the negative impact of herbicides on intertidal species. / Thesis (M.App.Sc.)--School of Earth and Environmental Sciences, 2005.

Thesis (M.S.)--Mississippi State University. Department of Biological Sciences, 2006. / Title from Web page (viewed on Sept. 16, 2008). Includes bibliographical references (p. [30-35]).

Thesis (Ph.D.)--University of Melbourne, Dept. of Zoology, 2009. / Typescript. Includes bibliographical references (p. 108-119)

Thesis (M.S.)--University of North Carolina at Wilmington, 2005. / Includes bibliographical references (leaves: [37]-41)

System requirements, Adobe Acrobat reader, Microsoft Power Point. / Includes bibliographical references (Leaves: [289]-291)

Thesis (M.S.)--University of North Carolina at Wilmington, 2005. / Includes bibliographical references (leaves: [87]-88)

This study investigates early life stages of the southern sea garfish (Hyporhamphus melanochir) and their association with seagrass in Gulf St Vincent, South Australia. The overall aims were to identify and describe the early life stages of H. melanochir and to explore the possible relationship(s) between these life stages and seagrass habitat with the emphasis on seagrass as a requirement for spawning or as a food source. The reproductive biology of female H. melanochir from the commercial fishery was assessed by microscopic examination of ovaries, oocyte size distributions, gonadosomatic indices, and macroscopic ovarian stages. Five stages of oocyte development were identified and described: perinucleolar, yolk vesicle, yolk globule, migratory nucleus and hydrated. A coherence between histological and whole oocyte descriptions is demonstrated. Hyporhamphus melanochir are characterised as multiple spawners with group-synchronous oocyte development and indeterminate fecundity. A protracted spawning season from October to March was indicated by the occurrence of ripe ovaries and increases in gonadosomatic index. Females reach sexual maturity at 193 mm standard length, and batch fecundity ranged from 201-3044 oocytes depending on fish size. Spawning shoals are segregated by sex, as indicated by commercial samples, with a biased female-to-male ratio of 4.5:1 during the spawning season (1.2:1 during the non-spawning season). In addition, features of the oocyte surface were closely examined, which revealed that the filaments on the chorion of the hydrated oocyte are adhesive. These adhesive filaments presumably allow the fertilised egg to become attached to vegetative substrate by adhesion and/or entanglement. H. melanochir larvae were discriminated from another hemiramphid species, river garfish (H. regularis), which is also known to occur in the study area, based on species-specific amplification of part of the mitochondrial control region using a multiplex polymerase chain reaction (PCR) assay. The species were easily discerned by the number and distinct sizes of PCR products [H. melanochir, 443 bp; river garfish (H. regularis), 462 and 264 bp]. Although based on a single gene, this molecular method will correctly identify the species of individuals in at least 96% and 94% of tests for H. melanochir and H. regularis, respectively. Subsequent to verifying the identification of species by molecular discrimination, the larval development of H. melanochir and H. regularis were described. Larvae of H. melanochir and H. regularis had completed notochord flexion at hatching and are characterized by their elongate body with distinct rows of melanophores along the dorsal, lateral and ventral surfaces; small to moderate head; heavily pigmented, long straight gut; persistent preanal finfold; and extended lower jaw. Fin formation occurs in the sequence: caudal, dorsal and anal (almost simultaneously), pectoral, pelvic. Despite the similarities between both species and among hemiramphid larvae in general, H. melanochir larvae are distinguishable from H. regularis by: having 58-61 vertebrae (v. 51-54 for H. regularis); having 12-15 melanophore pairs in longitudinal rows along the dorsal margin between the head and origin of the dorsal fin (v. 19-22 for H. regularis); and the absence of a large ventral pigment blotch anteriorly on the gut and isthmus (present in H. regularis). A logistic regression analysis of body measurements also revealed interspecies differences in the combined measurements of eye diameter and pre-anal fin length. Both species can be distinguished from morphologically similar larvae found in southern Australia (other hemiramphids and a scomberosocid) by differences in meristic counts and pigmentation. Hyporhamphus melanochir larvae were successfully collected throughout Gulf St Vincent using a neuston net; however, attempts to sample eggs were unsuccessful. Abundances of larvae in the gulf averaged 4.8 and 12.3 larvae 1000⁻ ² of surface water in December 1998 and December 2000, respectively. Larvae exhibit fast growth, as indicated by otolith growth increments, with backcalculated spawning dates falling within the October-March spawning season. Spatial analysis of larval distributions revealed a positive spatial autocorrelation, i.e. non-randomness or clustering of similar abundance values. Most larvae were found in the upper region of the gulf, and the prevalence of seagrass habitat throughout this region supports the view that the demersal eggs of H. melanochir become attached to seagrass and/or algae following spawning. A gyre in waters of the upper gulf, influenced by prevailing southerly winds, the Coriolis effect, and land boundaries, may explain retention of larvae. The importance of seagrass beds to H. melanochir spawning is also supported by anecdotal evidence and available literature on eggs of other Beloniformes, which are also demersal and attach to marine plants. Dual stable isotope analysis (δ¹³ and δ¹⁵N) of larval, juvenile and adult H. melanochir and several potential food sources from the Bay of Shoals was carried out to estimate the importance of zosteracean seagrass towards the assimilated diet of H. melanochir. Although the diet of H. melanochir larvae is probably planktonivorous, their isotopic signatures partly reflect the parental diet due to the influence of pre–existing tissue in addition to growth. According to mixing model calculations, the signatures of juveniles can be explained by a diet consisting of 23–37% Zostera, 0–10% Halophila and the remainder zooplankton, whilst the diet of adults consists of 53–58% Zostera and the remainder zooplankton. These findings indicate an increasing dependence upon Zostera with growth of H. melanochir. The results of this study enhance the completeness of our understanding of the fisheries biology and ecology of H. melanochir. Significant contributions are provided in reproductive biology and larval biology, seagrass beds (in combination with mixed algae) are demonstrated to be an important habitat for spawning, and Zostera seagrass is shown to be a necessary food source in the diet of juveniles and adults. / Thesis (Ph.D.)-- University of Adelaide, School of Earth and Environmental Sciences, 2005.

This study investigates early life stages of the southern sea garfish (Hyporhamphus melanochir) and their association with seagrass in Gulf St Vincent, South Australia. The overall aims were to identify and describe the early life stages of H. melanochir and to explore the possible relationship(s) between these life stages and seagrass habitat with the emphasis on seagrass as a requirement for spawning or as a food source. The reproductive biology of female H. melanochir from the commercial fishery was assessed by microscopic examination of ovaries, oocyte size distributions, gonadosomatic indices, and macroscopic ovarian stages. Five stages of oocyte development were identified and described: perinucleolar, yolk vesicle, yolk globule, migratory nucleus and hydrated. A coherence between histological and whole oocyte descriptions is demonstrated. Hyporhamphus melanochir are characterised as multiple spawners with group-synchronous oocyte development and indeterminate fecundity. A protracted spawning season from October to March was indicated by the occurrence of ripe ovaries and increases in gonadosomatic index. Females reach sexual maturity at 193 mm standard length, and batch fecundity ranged from 201-3044 oocytes depending on fish size. Spawning shoals are segregated by sex, as indicated by commercial samples, with a biased female-to-male ratio of 4.5:1 during the spawning season (1.2:1 during the non-spawning season). In addition, features of the oocyte surface were closely examined, which revealed that the filaments on the chorion of the hydrated oocyte are adhesive. These adhesive filaments presumably allow the fertilised egg to become attached to vegetative substrate by adhesion and/or entanglement. H. melanochir larvae were discriminated from another hemiramphid species, river garfish (H. regularis), which is also known to occur in the study area, based on species-specific amplification of part of the mitochondrial control region using a multiplex polymerase chain reaction (PCR) assay. The species were easily discerned by the number and distinct sizes of PCR products [H. melanochir, 443 bp; river garfish (H. regularis), 462 and 264 bp]. Although based on a single gene, this molecular method will correctly identify the species of individuals in at least 96% and 94% of tests for H. melanochir and H. regularis, respectively. Subsequent to verifying the identification of species by molecular discrimination, the larval development of H. melanochir and H. regularis were described. Larvae of H. melanochir and H. regularis had completed notochord flexion at hatching and are characterized by their elongate body with distinct rows of melanophores along the dorsal, lateral and ventral surfaces; small to moderate head; heavily pigmented, long straight gut; persistent preanal finfold; and extended lower jaw. Fin formation occurs in the sequence: caudal, dorsal and anal (almost simultaneously), pectoral, pelvic. Despite the similarities between both species and among hemiramphid larvae in general, H. melanochir larvae are distinguishable from H. regularis by: having 58-61 vertebrae (v. 51-54 for H. regularis); having 12-15 melanophore pairs in longitudinal rows along the dorsal margin between the head and origin of the dorsal fin (v. 19-22 for H. regularis); and the absence of a large ventral pigment blotch anteriorly on the gut and isthmus (present in H. regularis). A logistic regression analysis of body measurements also revealed interspecies differences in the combined measurements of eye diameter and pre-anal fin length. Both species can be distinguished from morphologically similar larvae found in southern Australia (other hemiramphids and a scomberosocid) by differences in meristic counts and pigmentation. Hyporhamphus melanochir larvae were successfully collected throughout Gulf St Vincent using a neuston net; however, attempts to sample eggs were unsuccessful. Abundances of larvae in the gulf averaged 4.8 and 12.3 larvae 1000⁻ ² of surface water in December 1998 and December 2000, respectively. Larvae exhibit fast growth, as indicated by otolith growth increments, with backcalculated spawning dates falling within the October-March spawning season. Spatial analysis of larval distributions revealed a positive spatial autocorrelation, i.e. non-randomness or clustering of similar abundance values. Most larvae were found in the upper region of the gulf, and the prevalence of seagrass habitat throughout this region supports the view that the demersal eggs of H. melanochir become attached to seagrass and/or algae following spawning. A gyre in waters of the upper gulf, influenced by prevailing southerly winds, the Coriolis effect, and land boundaries, may explain retention of larvae. The importance of seagrass beds to H. melanochir spawning is also supported by anecdotal evidence and available literature on eggs of other Beloniformes, which are also demersal and attach to marine plants. Dual stable isotope analysis (δ¹³ and δ¹⁵N) of larval, juvenile and adult H. melanochir and several potential food sources from the Bay of Shoals was carried out to estimate the importance of zosteracean seagrass towards the assimilated diet of H. melanochir. Although the diet of H. melanochir larvae is probably planktonivorous, their isotopic signatures partly reflect the parental diet due to the influence of pre–existing tissue in addition to growth. According to mixing model calculations, the signatures of juveniles can be explained by a diet consisting of 23–37% Zostera, 0–10% Halophila and the remainder zooplankton, whilst the diet of adults consists of 53–58% Zostera and the remainder zooplankton. These findings indicate an increasing dependence upon Zostera with growth of H. melanochir. The results of this study enhance the completeness of our understanding of the fisheries biology and ecology of H. melanochir. Significant contributions are provided in reproductive biology and larval biology, seagrass beds (in combination with mixed algae) are demonstrated to be an important habitat for spawning, and Zostera seagrass is shown to be a necessary food source in the diet of juveniles and adults. / Thesis (Ph.D.)-- University of Adelaide, School of Earth and Environmental Sciences, 2005.