Shoal Bay Research Articles

Commissioning of the multiparametric geophysical observatory at Shoal Bay, South Andaman and the preliminary results

The Indian Institute of Geomagnetism (IIG) is operating Multiparametric Geophysical Observatory (MPGO) at Port Blair in South Andaman. We report here on the commissioning of MPGO and the quality of data collected by this observatory. The base line values are regularly computed with the aid of the declination inclination magnetometer, in house developed proton precession magnetometer and the flux gate magnetometer. The total field computed by the vector magnetometer is all time compared with direct measurements from the scalar magnetometer. An attempt to co-relate the precursor seismo-electromagnetic emissions of the earthquake event by the induction coil magnetometer is made. The seismic station of the observatory is capable of recording seismic events within the vicinity of ≈200 km. Further MPGO is upgrading and some more experiments are planned for the future.

Analysis of ring operation from south Andaman Fish Landing Centres (FLC)

A study was carried out during 2014-2018 to find out the major fish catches through the Gear Ring net at the coast of Andaman Islands. The data were collected from four major Fish Landing Centres (FLC) viz Junglighat, Dugnabad, Guptapara and Wandoor which are located at South Andaman. Altogether 1097 FLC visits have been carried out during the study period at all four FLC with an average of 219 visits / year. Altogether 1379 operations of Ring net were observed from two FLC i.e. Junglighat (1322) and Dugnabad (57) amongst four FLC. The total fishes captured were 1609 tons from the two FLCs, i.e. 1594 tons from Junglighat FLC and 15 tons from Dugnabad FLC respectively. The contribution of gear the Ring net was 41.5 % amongst the other gears operated from all four FLCs. The major fish catch by ring net were Scombrids (52.3%), followed by Sardines (22.4%), Carangids (21.3%), Anchovies (2.7%) and others (1.2%). 39 ring net fishing ground identified during the period around the coast of Andaman Islands. The maximum fish catch occurred at around the coast of Havelock Island (15.5%) followed by Rutland (10.5%), Chidiatappu (8 %), Shoal Bay (7.6%), Baratang (7 %), Carbyns cove (6 %), Burmanallah (5.2%), Madhuban (5.2%), Out-drum Island (4.7%), Mayabunder (4 %), Colinpur (3.3%), Long Island (3.3%), Wandoor (2.1%) etc and minimum fish catch was observed at the coast of Pachim Sagar (0.02%) . PFZ forecast disseminated to the Ring netters and validated during the study period. Forty nine operations of gear the ring net were observed at PFZ with an average of 9.8 operations /year. The fishes captured from the PFZ were 91.1 tons with an average of 18.2± 5.6 tons / year. Similarly 49 operations of ring net were also observed at Non-PFZ with an average of 9.8 operations /year. The fishes captured from the Non PFZ were 23.77 tons with an average of 4.5±1.5 tons / year. The Length-weight measurements of the pelagic fishes viz Atule mate, Decapterus russelli, Sardinella albella, Sardinella sirm, Herklotsichthys quadrimaculatus and Rastrelliger kanagurta caught from both the zones have been done. 12 Class Intervals with respect to length were observed from the catch of all the fishes i.e. 81-100 mm, 101-120, 141-160 mm,........301- 320 mm. In the Class Intervals, the length category 121-140 mm was the most representating class for Atule mate with 128 specimens (19.1%) at PFZ and 159 specimens (23.7%) at Non-PFZ respectively. It has been observed for other fishes i.e. for Decapterus russelli, Sardinella albella, Sardinella sirm, Herklotsichthys quadrimaculatus and Rastrelliger kanagurta which collected from the PFZ were class 161-180 mm with 172 specimens (48.6%), 141-160 mm with 195 specimens (53.1%), 221- 240 mm with 177 specimens (48.2%), 121-140 mm with 189 specimens (47.7%) and 261-280 with 199 specimens (30.9%) respectively. The same species were collected at the Non-PFZ were 141-160 with 173 specimen (49.0%), 121-140 with 194 specimens (53.3%), 221-240 with 159 (45.4%), 101-120 with 173 (49.4%) and 201-220 with 144 specimens (23%) respectively. The water samples have been collected during day time from various sites of PFZ and Non-PFZ during the study period and analysed. The average visibility at PFZ and Non-PFZ were 15.49±0.28 m and 16.74 ± 0.25 respectively. The average dissolved oxygen (DO) at PFZ and Non-PFZ were 6.30±0.05 mg/lit and 5.94 ±0.06 mg/lit respectively. Due to density of phytoplankton and Eddies the dissolved oxygen increased at PFZ than Non-PFZ. Alkalinity was at PFZ 111.16±1.09 ml/lit and Non PFZ 113.68 ± 1.28 ml/lit respectively.

Multi-scale morphodynamics of an estuarine beach adjacent to a flood-tide delta: Assessing decadal scale erosion

Estuarine beaches are ubiquitous, yet understudied, coastal systems. The mixed hydrodynamic processes – such as combined tidal and wave forcing – and the influence of adjacent sedimentary features – such as flood-tide deltas (FTDs) – leads to complex morphodynamic processes. As such, the dynamics and evolution of these important coastal systems are poorly understood. This study synthesises a set of analyses conducted on an estuarine beach, in southeast Australia, over multiple temporal scales. Nearshore waves and currents were measured and used to determine the processes driving seasonal to yearly beach change between 2007 and 2010. These results were compared to decadal scale beach change determined from aerial photos between 1963 and 2006. We found the westward transport of sediment towards the inner estuary was the dominant nearshore process leading to erosion in the eastern regions of the beach (near the estuary entrance) and accretion in the west over yearly time scales. Cross-shore sediment transport occurred during winter storm swell conditions leading to erosion in more exposed sites and some limited accretion in sheltered zones, most likely due to sediment input from the flood-tide delta. However, severe storm swell events that propagated into the estuary led to a loss of sediment and erosion across the entire beach which was not recovered during the study period. It is likely that the erosion processes observed in the short- to medium-term (days to years) analyses are the conditions that led to the long-term shoreline retreat observed in the aerial photograph record. The long-term shoreline retreat since 1963 is likely a result of a negative sediment balance due to movement of the FTD and a lack of sediment input in the eastern regions of Shoal Bay. Shoreline retreat will likely continue unless increased sediment input occurs from marine sources or shoreline interventions are maintained.

Impact of hydrotalcite deposition on biogeochemical processes in a shallow tropical bay

The biogeochemistry of a tropical shoal bay (Melville Bay, Australia) impacted by the effluent release, precipitation, and deposition of hydrotalcite from an alumina refinery was studied in both wet and dry seasons. Within the deposition zone, sulfate reduction dominated benthic carbon cycling accounting for ≈100% of total microbial activity, with rates greater than those measured in most other marine sediments. These rapid rates of anoxic metabolism resulted in high rates of sulfide and ammonium production and low C:S ratios, implying significant preservation of S in stable sulfide minerals. Rates of total microbial activity were significantly less in control sediments of equivalent grain size, where sulfate reduction accounted for ≈50% of total benthic metabolism. Rates of planktonic carbon cycling overlying the deposition zone were also greater than those measured in the control areas of southern Melville Bay. At the sediment surface, productive algal and cyanobacterial mats helped stabilize the sediment surface and oxidize sulfide to sulfate to maintain a fully oxygenated water-column overlying the impacted zone. The mats utilized a significant fraction of dissolved inorganic N and P released from the seabed; some nutrients escaped to the water-column such that benthic regeneration of NH 4 + and PO 4 3− accounted for 100% and 42% of phytoplankton requirements for N and P, respectively. These percentages are high compared to other tropical coastal environments and indicate that benthic nutrient recycling may be a significant factor driving water-column production overlying the deposition zone. With regard to remediation, it is recommended that the seabed not be disturbed as attempts at removal may result in further environmental problems and would require specific assessment of the proposed removal process.

PREDATOR–PREY INTERACTIONS BETWEEN LEPSIELLA (BEDEVA) PAIVAE (GASTROPODA: MURICIDAE) AND KATELYSIA SCALARINA (BIVALVIA: VENERIDAE) IN PRINCESS ROYAL HARBOUR, WESTERN AUSTRALIA

On a sandy beach at Shoal Bay in Princess Royal Harbour, Albany, southwestern Western Australia, lives a small muricid gastropod that feeds virtually monotonically on the overwhelmingly dominant resident bivalve Katelysia scalarina. Lepsiella paivae lives buried in the sand and attacks its prey within it. Because of its small size (,13 mm shell height), bivalve prey is also small and this study demonstrates a preference for K. scalarina of 5 mm shell length, i.e. juveniles. Laboratory experiments also suggested a possible preference for attack of the right valve. Lepsiella paivae can and does, however, attack larger prey (up to 15 mm shell length), but cannot consume them completely. A second visit to Princess Royal Harbour in the Austral winter, when there was no juvenile K. scalarina present, showed L. paivae to be attacking at the sand surface, also by drilling, the small (,4 mm) gastropod Hydrococcus brazieri (Hydrococcidae). SEM studies of experimentally determined drill holes of L. paivae show them to be of variable form, some straight sided, others bevelled (like a naticid) and ,500 mm in diameter. On this sheltered Southern Ocean beach, therefore, L. paivae has specialized to attack juvenile bivalves by burrowing after them. It can, however, attack other species opportunistically on the sand surface when seasonally favoured juvenile bivalve prey are not present.

PREDATOR--PREY INTERACTIONS BETWEEN LEPSIELLA VINOSA (GASTROPODA: MURICIDAE) AND XENOSTROBUS INCONSTANS (BIVALVIA: MYTILIDAE) IN A SOUTHWEST AUSTRALIAN MARSH

At Shoal Bay, Princess Royal Harbour, Albany, in southwestern Australia, at the western extremity of its range, the muricid Lepsiella vinosa feeds monotonically, mostly by drilling, on the mussel Xenostrobus inconstans. Because it lives anterior down in a mat of byssal threads, the mussel is attacked posteriorly by L. vinosa. In laboratory experiments, however, attacks were predominantly anterior, above the visceral mass. Xenostrobus inconstans has an intertidal vertical range that extends from within a supralittoral marsh of rushes and sedges down into the seaward eulittoral zone, but was most abundant above and below the marsh margin. Sympatric with X. inconstans but most numerous at the marsh margin, is another mussel, the larger, strongly ribbed Brachidontes erosus which L. vinosa rarely attacks. The intertidal range of L. vinosa matches that of the two mussels and the field preference for X. inconstans was confirmed by laboratory experiments in which it was consumed first, followed over a much longer time interval by attacks on B. erosus. Laboratory experiments further revealed that L. vinosa has a size preference for X. inconstans of between 10 and 20 mm, the largest individuals (25 mm) being less frequently attacked and small ones (5 mm) more rarely, except when all others have been consumed. In southeastern Australia, L. vinosa feeds on littorines and barnacles in mangroves, and on barnacles, tube‐building polychaetes and mussels on rocky shores. Throughout its wide longitudinal range Lepsiella vinosa feeds, typically high on the shore, by drilling littorines, barnacles or mussels. It can attack its prey when immersed or, less frequently, emersed and both by drilling and marginal access with its proboscis. Longitudinal differences in prey choice are related to community differences in prey availability.

Three Aboriginal shell mounds at Hope Inlet: Evidence for coastal, not maritime Late Holocene economies on the Beagle Gulf mainland, northern Australia

Many hundreds of Aboriginal shell mounds exist on the northern coasts of Australia. Though these archaeological features increasingly figure in broad constructions of past coastal hunter-gatherer economies, few have been analysed in any detail. This paper describes the excavation and analysis of three Anadara-dominated shell mounds situated in adjacent microenvironments at Hope Inlet, Shoal Bay near Darwin on the Northern Territory coast. These stratified deposits, formed over some 15 centuries between about 2000 and 500 years B.P., provide a relatively finegrained record of subsistence and settlement strategies of hunter-gatherer peoples during this Late Holocene period. This study finds that these North Australian coastal groups practiced not a specialised marine or maritime subsistence economy focused on offshore resources, but a generalised and flexible coastal subsistence economy tied to the land.

THE DIETARY PREFERENCES OF A SUITE OF CARRION-SCAVENGING GASTROPODS (NASSARIIDAE, BUCCINIDAE) IN PRINCESS ROYAL HARBOUR, ALBANY, WESTERN AUSTRALIA

On the seafloor of Shoal Bay, Princess Royal Harbour, Albany, Western Australia, lives a suite of four scavenging gastropod species: Nassarius pyrrhus, N. pauperatus (Nassariidae), Cominella eburnea and C. tasmanica (Buccinidae). Field and laboratory experiments were designed to test whether any of these scavengers showed a preference for (i) either fresh fish or bivalve tissues, (ii) fresh fish or 24-, 48- or 72-h-old fish. In baited-trap field experiments, no preferences were detected, and N. pyrrhus always arrived first, usually followed by either N. pauperatus or C. eburnea, and last by C. tasmanica. Numbers of scavengers on all baits peaked at about 70 min postdeployment and arrived from an estimated surrounding area of 0.5-2.5 m 2 . In laboratory experiments, bait preference results were similar, although fewer N. pyrrhus and N. pauperatus arrived at the 72-h-old fish, and C. eburnea was not attracted to such decaying bait.

Storm impact and evolution of a mangrove-fringed chenier plain, Shoal Bay, Darwin, Australia

Storms are considered to have significant impacts on the development of chenier plains, particularly through the devastation of mangrove vegetation, but also in terms of winnowing sand and shell from mudflats and forming chenier ridges. Shoal Bay, in the Beagle Gulf, northern Australia, contains a small chenier plain, which was struck by a severe tropical cyclone, Cyclone Tracy, on Christmas Day 1974 as it devastated the city of Darwin. The morphology, vegetation and stratigraphy of the plain are described. The plain is underlain by lower intertidal sand with shell hash. A radiocarbon age of 6130 years BP, indicates mangrove colonisation of this flat at the time that sea level stabilised around its present level after the postglacial transgression. Subsequently, progradation of mudflats has occurred, especially around 2300 years ago, and shells of this age are found both in growth position from within the mudflats, and incorporated into the shelly chenier ridges. A further phase of build-out, and subsequent erosion is reflected by stumps and in situ bivalves being excavated presently on the foreshore, radiocarbon dating about 900–1100 years BP. Within this context of evolution, Cyclone Tracy can be seen to have had severe consequences upon the patterning of mangroves, with extensive windthrow of Ceriops, and defoliation of Rhizophora at the western end of the plain. Recovery of the mangrove vegetation has been gradual, and is still incomplete. However, the storm had little influence on the pattern of landform development. Indeed, the aerial photographic sequence indicates a trend by which sand shoals are gradually reworked landwards, in places moving through mangrove vegetation. The study suggests that rather than pronounced regional episodes of alternative mudflat buildout and erosion, both processes occur simultaneously at different points along this foreshore.

Epizonal I- and A-type granites and associated ash-flow tuffs, Fogo Island, northeast Newfoundland

Magmatic activity of Silurian–Devonian age is widespread in the Appalachian–Caledonian Orogen. A marked characteristic of this magmatism is the composite nature of the igneous suites, which range from peridotite to granodiorite in single plutonic bodies. The origin of these suites is still enigmatic, and the assumption that all are the same not proven. Such a suite of intrusive rocks, ranging in composition from minor peridotite to granodiorite, intrudes an openly folded sequence of Silurian volcanogenic sandstones and ash-flow tuffs on Fogo Island, northeast Newfoundland. Two units, the Rogers Cove and Hare Bay microgranites, consist of fine-grained hastingsite granites with spherulitic and flow-banded textures, and exhibit drusy cavities and microfractures that contain the mineral assemblage hastingsitic hornblende + plagioclase + magnetite + zircon. These rocks are characterized by elevated high field strength element contents (e.g., Zr = 74–672 and Y = 21–103 ppm), very high FeO*/MgO ratios (FeO*/MgO = 2.4–93.5), and 10 000 Ga/Al ratios of 1.67–10.52, indicating an A-type granitoid affinity. A third and the most voluminous granitic unit, the Shoal Bay granite, is an alkali-feldspar-phyric, medium-grained, equigranular biotite–hastingsite granite with hastingsite and annitic biotite interstitial to euhedral plagioclase, anhedral quartz, and perthite crystals. The Shoal Bay granite exhibits mineral parageneses similar to the microgranites, but chemical characteristics more typical of calc-alkaline, I-type granitoids. Volcanic–sedimentary sequences spatially associated with the granitic rocks include dense, welded, high-silica, hastingsite-bearing ash-flow tuffs with compositions that suggest they represent erupted equivalents of fractionated end members of the Shoal Bay granite. The rocks making up the Fogo Island batholith have been directly equated with the bimodal, calc-alkaline Mount Peyton batholith of northeast Newfoundland, but the specialized A-type nature of the Fogo granites suggests differing source conditions for the two suites.

Late Albian ammonites from the Northern Territory, Australia

Thirty ammonite taxa are recognised in the Wangarlu Mudstone of the Bathurst Island Group from the Cox Peninsula and Shoal Bay, Northern Territory, Australia. Included are a new heteromorph genus Notostreptites, type species N. exilis, and four additional new species and subspecies: Pseudhelicoceras gracilis, Labeceras (L.) tumidum, Labeceras (Appurdiceras) decorum, and Idiohamites dorsetensis laticostatus. The assemblage is best collectively correlated with the Mortoniceras (M.) inflatum Zone of the standard European Albian zonation but some of its members may represent the lower part of the Stoliczkaia dispar Zone. It is broadly correlative with faunas from the Eromanga Basin, which relate to an extensive eastern Australian Late Albian epicontinental sea, but is strikingly different in aspect. The Wangarlu Mudstone assemblage has relatively high diversity and an abundance of cosmopolitan heteromorph taxa well known from Europe and elsewhere, whereas Eromanga Basin assemblages are of relatively low diver...

Pleistocene and recent studies of Waitemata Harbour

Summary The peninsula of North Shore is a spur of Tertiary sedimentary rocks (Waite-mata Formation) that has been subject to considerable marine erosion along1 its northern side. Deep excavation by an ancient Shoal Bay Stream, and its tributaries during glacial times divided the spur into blocks which became isolated by subsequent rise of sea-level. Two groups of volcanoes were active in Recent times and further modified the peninsula.