Marine and Freshwater Research
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Hydrological stucture and phytoplankton distribution in the region of a warm-core eddy in the Tasman Sea The distribution of temperature, salinity, density, dissolved oxygen, phosphate, silicate, and nitrate to 2000 m depth, and phytoplankton to 150 m depth is described in the region of an anticyclonic mesoscale eddy located in the Tasman Sea. Vertical discontinuities in the hydrological properties showed that the eddy had entrained several surrounding water types at the surface and at depths of up to 500 m. In particular, Bass Strait water normally found among the slope waters along the New South Wales coast was entrained by the eddy and transported to positions 200 km from the coast. The temperature and salinity of the eddy appeared to have been increased below the core of the eddy at depths of 300-600 m. due to the entrainment of and mixing with Bass Strait water. The distribution of density, oxygen, nutrients and phytoplankton in the central portion of the eddy between 60 and 240 m depth showed differences between adjoining positions which were attributed to vertical water movements within the eddy core. These movements appeared to be responsible for increases of phytoplankton biomass within the eddy, of up to 10 times that of the surrounding ocean.
Marine and Freshwater Research - Tập 32 Số 4 - Trang 479 - 1981
Edge enrichment in an ocean eddy In October 1981, relatively high concentrations of surface phytoplankton (chlorophyll a~1.5 �g1-1 relative to a background of ~0.4 �g 1-1) were observed in a cyclonic crescent of cool water along the south-eastern margin of a warm-core eddy in the south-westem Tasman Sea. Associated with this phytoplankton peak were relatively high concentrations of surface nitrate (~50�g I-1), low concentrations of oxygen (<90% satn), and a population of a copepod (Calanoides carinatus) often associated with upwellings. The salinity, oxygen and nitrate distributions suggest that an upwelling-downwelling circulation cell existed at the interface between (anticyclonic) eddy and (cyclonic) crescent. Biological enrichment was greater at the site of the crescent than where the margin of the eddy was comparatively straight. The hypothesis is advanced that such enrichment may be the basis for the association that exists between schools of southern bluefin tuna and sharp surface temperature fronts.
Marine and Freshwater Research - Tập 34 Số 4 - Trang 665 - 1983
Age and growth of Murray Cod, Maccullochella peelii (Perciformes: Percichthyidae), in the Lower Murray-Darling Basin, Australia, from thin-sectioned Otoliths Transverse thin sections (0.5 mm thick) of sagittal otoliths from 290 Murray cod up to 1400 mm
in total length and 47.3 kg in weight were used to establish the age and growth of cod in the lower
Murray-Darling Basin, including comparisons of recent (1986-91) and past (1949-51) growth rates and
growth in different waters. The maximum estimated age was 48 years. Quantitative and qualitative
analysis of the seasonal changes in otolith marginal increments showed that annuli in fish of all ages
were laid down each spring, and 1 October was assigned as the birthday. The thin-sectioning method
was validated by comparing age estimates for 55 Murray cod from Lake Charlegrark (age 0-21 years),
which had been validated by using burnt and polished half-otoliths. The new method had an accuracy
of 96.4% and it offers major advantages in ease of preparation, reading, and batch-handling of large
numbers of otoliths. The precision of the method, estimated as an average error for four readers,
was 5.4% (3.0% after ignoring discrepancies in relation to annuli on otolith edges). There was a linear
relationship between otolith weight and fish age and an exponential relationship between otolith weight
and fish length. Both otolith length and otolith width reached an asymptote at about 15 years, when
fish length also approached its maximum. However, otolith thickness continued to increase throughout
the life of the fish and, after about 15 years, contributed most to the increase in otolith weight.
This confirmed that otoliths continued to grow in thickness and that annuli were laid down throughout
life, and that cod could be aged reliably to the maximum age. The annulus pattern is very clear and
distinct, and the reading techniques are fully described, including recognition of 'larval' and 'false' rings.
Various differences were found in the growth rates, and the length-weight relationships for males and
females, for cod caught in 1986-91 and those caught in 1949-51, and various subpopulations are
discussed. The von Bertalanffy growth parameters (all individuals combined) were estimated at
L∞ = 1202 mm, k=0.108 and t0= -0.832. The availability of a reliable ageing method provides the
first opportunity to determine year of birth and thus to examine the age structure of populations and
to effectively manage cod populations that have declined in abundance.
Marine and Freshwater Research - Tập 43 Số 5 - Trang 983 - 1992
In situ effects of human disturbances on coral reef-fish assemblage structure: temporary and persisting changes are reflected as a result of intensive tourism
Non-lethal human disturbances are often drivers of change in animal population and community structure. To gauge their severity, short-term behaviour (e.g. avoidance and habituation) has been argued to be a sensitive measure. However, many of these behavioural changes may occur only if disturbance-free habitat is readily accessible. In coral-reef fish, we tested whether human disturbances from intensive (i.e. loud music, swimming, snorkelling, splashing and fish feeding by numerous visitors) tourist visitations resulted in assemblage structure shifts led by short-term behaviour. We monitored fish assemblage before, during and after tourist visitations to monitor changes associated with behaviour. Additionally, we monitored two adjacent reefs not visited by tourists because of difficult approach by boat. We posited that if short-term benefits of relocating to disturbance-free habitat outweigh the costs of tolerating disturbances, fish assemblage structure should shift along with tourist visitation levels. By contrast, if sensitive species are unable or unwilling to relocate, we predicted greater levels of assemblage heterogeneity between the visited and control reefs. Our results showed that in situ human visitations led to significant shifts in assemblage structure, resulting from short-term behavioural changes. Additionally, we showed significant between-reefs differences, whereby control reefs were characterised by higher species richness, larger fish sizes and variations in relative trophic guild prevalence. Our results suggest that short-term relocations to adjacent disturbance-free reefs may not mitigate the effects of human disturbances.
Marine and Freshwater Research - Tập 66 Số 1 - Trang 23 - 2015
Relating species traits to environmental variables in Indonesian coral reef sponge assemblages A key goal in ecology is to understand how species with given traits vary with changing environmental conditions. In the Spermonde Archipelago, Indonesia, we identified environmental gradients associated with significant variation in sponge species traits. These were (1) an on-to-offshore gradient, (2) a gradient from locally perturbed reef sites characterised by fluctuating sediment load concentrations and poor water transparency to locally pristine sites characterised by good water transparency and (3) a depth gradient. Species with a massive growth form were associated with inshore reef environments, whereas species with a cup growth form were linked to offshore reefs with a high coral cover. Weakly bioactive species and species with a globular, fan or fistulose growth form were associated with locally perturbed reef environments as indicated by fluctuating sediment levels and reduced water transparency, whereas strongly bioactive species and species with a massive-encrusting and tube growth form were associated with more pristine reef environments with good water transparency. With respect to depth, oviparous species and species with a cup and massive growth form were most strongly associated with deeper transects, whereas species with a ramose, massive creeping and massive-encrusting growth form were most strongly associated with shallower transects. Results of the present study indicate that environmental conditions and species traits interact to determine the composition of sponges across coral reefs.
Marine and Freshwater Research - Tập 58 Số 3 - Trang 240 - 2007
Environmentally influenced variability in the morphology of Cinachyrella australiensis (Carter 1886) (Porifera : Spirophorida : Tetillidae)
The influence of environmental variability on body form and tissue structure
of Cinachyrella australiensis is reported for
populations from three sites within Darwin Harbour, Northern Territory,
Australia, that varied considerably in hydrological conditions. External
morphology of these sponges differed among sites ranging from typical
spherical shapes to flattened forms. A large proportion of dry weight
consisted of inorganic matter, i.e. silica spicules, varying between
62.9% and 78.2%. Sites with highest water velocity and sediment
size were significantly correlated with sponge populations having the greatest
inorganic content and lowest organic cellular content and the thickest oxea.
Thicker oxea may in part account for the higher structural content of sponges
at these sites. There was no significant difference in oxea length among
sites. It is concluded that sponges subjected to highly perturbed environs
with large water flow and sedimentation regimes may devote more energy to
spicule reinforcement relative to organic content. These robust sponges have
the potential to make an important structural contribution to their habitats.
Marine and Freshwater Research - Tập 53 Số 1 - Trang 79 - 2002
Benthic communities of the Gippsland Lakes, Victoria Samples of benthos from muddy or sandy bottoms along the axis of the Gippsland Lakes, Victoria, and on shallow seagrass beds were taken between November 1978 and October 1979. The benthic communities are described and the likely effects resulting from changes in water usage in the catchment discussed. Gradients in environmental parameters (salinity, temperature, dissolved oxygen and suspended solids) were not regular but were steepest near a constriction in the system, McLennans Strait. Ninety species of benthic fauna were recorded, with greatest diversity and density at the seagrass sites. The fauna was similar to that recorded in other south-eastern Australian estuaries except for its rich amphipod fauna and depauperate bivalve fauna. Densities, especially on seagrass, were higher than recorded in other estuaries although the number of species was lower. Temporal changes in the fauna could not be related clearly to seasonal changes in temperature or other environmental factors. Classification of the data revealed a seagrass community and smaller groups of species and stations, only loosely indicating a faunal gradient along the lakes. A distinct marine fauna was recognized on well-sorted sand at the lower end of the lakes, Reeve Channel, and a freshwater component at the opposite end. Physical structures such as McLennans Strait are responsible for the major differences between the faunas of adjacent areas in the greater part of the system. It is suggested that increased salinity in the future may allow establishment of euryhaline species in more placid parts of the lakes but that deoxygenation of bottom water and high benthic mortalities may occur if a salt wedge is maintained.
Marine and Freshwater Research - Tập 33 Số 5 - Trang 901 - 1982
Benthic communities in an estuary with periodic deoxygenation The relationship between spatial patterns in the physical environment and patterns in community and trophic structure in the benthic fauna was investigated in an estuary with periodic deoxygenation of the near- bottom water. Six sites were sampled between intertidal mangroves and an 8 m deep basin of Port Hacking, N.S.W. A total of 163 species was collected, ranging from 11 to 94 at each site. Both frequency and biomass were least in the central basin and highest in a bed of the seagrass Zostera capricorni Aschers. The abundances at these sites encompass the range of values previously recorded for estuaries on the east coast of Australia. The dominant species differed from those reported from other New South Wales estuaries, although the same species were usually present. The distribution of common species was limited by fluctuations in dissolved oxygen levels, but not obviously so by sediment differences or short-term fluctuations in water temperature or salinity. Frequency-based diversity and evenness values were similar to those from other estuarine areas. Biomass-based values were lower at most sites than frequency-based values. Patterns of diversity and evenness could not be simply interpreted as indicators of environmental harshness in the community.
Marine and Freshwater Research - Tập 32 Số 2 - Trang 227 - 1981
Threatening processes and conservation management of endemic freshwater fish in the Mediterranean basin: a review Mediterranean endemic freshwater fish are among the most threatened biota in the world. The Mediterranean basin has experienced substantial reductions in precipitation and water availability, which will worsen with climate change. Current water policy is directed to increase water-supply demands, especially for agriculture, and not to improve water-use efficiency and implement integrated and sustainable water management. Illegal extractions are common, exacerbating problems for important protected areas. Management is needed to mitigate the conflicts between environmental water and human demand, and ensure availability of water to maintain ecological processes and Mediterranean freshwater biodiversity. Water availability is not the only threat, although it is exacerbated by pollution and invasive species. The uneven spatial distribution of threats across the Mediterranean basin requires different strategies to conserve freshwater biodiversity. Implementation of multi-national laws (e.g. Water Framework Directive in the European Union) will help future management of freshwater ecosystems. Management actions must be planned at whole-catchment scales, with collaboration among different countries and water-management authorities. The current reserve area is small compared with other areas in the world and driven by terrestrial interests, and should be evaluated for its effectiveness to protect the Mediterranean freshwater biodiversity.
Marine and Freshwater Research - Tập 62 Số 3 - Trang 244 - 2011
Toxic blooms of cyanobacteria in Lake Alexandrina, South Australia — Learning from history Early accounts by European explorers and settlers of South Australia contain numerous references to
scums or discoloured water that are consistent with cyanobacterial blooms. Documented reports refer
back to at least 1853. The first detailed scientific account of toxic cyanobacteria appeared in 1878. In
a perceptive and prescient paper in Nature, the Adelaide assayer and chemist George Francis reported
on stock deaths at Milang on the shores of Lake Alexandrina in South Australia. Francis attributed
the deaths to the ingestion and toxicity of scums of the cyanobacterium Nodularia spumigena. Reports
of cyanobacterial blooms, scums and associated problems in Lake Alexandrina and in the River Murray
between about 1851 and 1888 are discussed and comparisons are made with the reactions to blooms a
century later.
Marine and Freshwater Research - Tập 45 Số 5 - Trang 731 - 1994
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