ALBERT

Notes: Abstract Oxygen evolution and uptake by whole thalli of the large marine alga Laminaria longicruris de la Pylaie were measured for 24 h, once every 2 weeks for a year, using large chambers to incubate the plants on the sea bed. Diel rates of photosynthesis and respiration were calculated from these measurements and continuous light measurements were used to extrapolate the data between observation dates. The resulting estimates were combined with measurements of growth and carbon content to give an annual carbon budget for a typical mature plant. Annual net assimilation was 6.8 mgC per cm2 of frond surface (71 cal cm-2). Approximately 45% of this appeared in the production of new frond tissue, and a further 12% was accounted for by storage of carbon in mature frond tissue. About 8% was needed for stipe growth, and the remaining 35% was assumed to be lost as dissolved organic carbon. Diel net photosynthetic rates reached a maximum in June and July and were negative only in November, indicating an ability to produce a photosynthetic surplus throughout winter. In early winter the plants drew on stored reserves to supplement photosynthesis in providing carbon for growth, but from January onwards photosynthesis provided more than enough carbon for growth.

Notes: Abstract The effects of swimming frequency and water temperature on shell growth, tissue mass, and stored energy reserves of juvenile sea scallops, Placopecten magellanicus Gmelin, were examined in a factorial laboratory experiment spanning six weeks in July and August 1992. Individually tagged scallops of similar initial size (22.5±0.1 mm shell height, n=240) were induced to swim to exhaustion at three different swimming frequencies (every day, twice a week, or not at all) in two different water temperature regimes (4 to 7 or 7 to 13°C). The scallops were fed an ad libitum mixture of cultured microalgae. At the end of the experiment, cumulative increase in shell height, dry weight of soft tissues, condition index of dry adductor muscle (adductor muscle dry weight/soft tissue dry weight x 100) and total carbohydrate content of dry adductor muscle were measured for each scallop. Scallops at the higher temperature had significantly greater shell heights, and were in better metabolic condition as evidenced by significantly higher condition indices and muscle carbohydrate contents. The dry soft tissue weights did not differ significantly from their low temperature counterparts. Swimming frequency had no significant effect on shell height, dry tissue weight, or carbohydrate content, but condition index of the adductor muscle increased significantly with swimming frequency. These results show that not only was there no cumulative cost of swimming in terms of shell growth, total soft tissue weight, or carbohydrate content in young scallops, but that condition of adductor muscle tissue was higher in scallops that swam.

Notes: Abstract An apparatus is described for incubating large marine algae in light and dark chambers on the sea floor, while providing vigorous circulation of water prefiltered to remove phytoplankton. Successful use of the equiment in over 500 h of incubations of Laminaria longicruris has shown that earlier methods in which strips of tissue are incubated in bottles greatly overestimates dark respiration rates and increases experimental error. The effect of these findings on long-term productivity estimates is discussed.

Notes: Abstract Because iron is not available generally in oxygenated sea water, it may be a limiting factor in marine primary production. This hypothesis was tested in the context of Davies Reef, Latitude 18°50′S (one of the coral reefs in the central region of the Great Barrier Reef system). Samples were collected for study in the period August, 1980 to March, 1981. Sea water around the reef contained ≦2x10-6 M Fe, surface sediments from the reef contained 66±26 (1 SD) ppm total Fe, and interstitial water near the surface contained ≧5x10-7 M Fe. Thus, Fe constituted a trace component of the reef environment, but limited Fe should be available to algae associated with the sediments. Specific biochemical analyses to test the Fe status of benthic photosynthetic organisms were carried out with a common blue-green alga, Phormidium sp., and a ubiquitous symbiotic dinoflagellate, Gymnodinium microadriaticum (zooxanthellae). The blue-green alga contained the electron transport protein, flavodoxin, which is found only in Fe-deficient organisms. Supporting evidence for Fe stress in this organism included chlorosis in the presence of plentiful biliprotein, and very low extractable photosynthetic cytochrome, c-553. The latter observations were shown to be the result of Fe deficiency in laboratory cultures of a blue-green alga, Synechococcus sp. These cultures showed that production of flavodoxin is not a universal response of algae to Fe stress, but that lowered cellular concentrations of Fe-containing proteins involved in photosynthesis probably is universal. The zooxanthellae from a soft coral, Sinularia sp., had three-fold lower total Fe and ferredoxin (an electron transport protein), than the same alga from a clam, Tridacna maxima. Thus, some algae in symbiotic associations may also suffer Fe-deficiency. It was concluded that the degree and extent of Fe-stress in primary producers on a coral reef may influence growth rates, biomass, and distribution of species.

Notes: Abstract The length, growth and survivorship of mature sporophytes of Ecklonia radiata (C.Ag.) J. Agardh were measured on two patch reefs within the lagoon of a high-latitude, coralreef atoll (Easter Group, Houtman Abrolhos; 28° to 29° S; 113°35 to 114°03′E) for 1 yr (1982–1983). The sites differed in their proximity to the perimeter reef, but had similar regimes of temperature, light, nutrient concentration and water movement. Kelp length, growth rate and survivorship differed significantly between sites, although plant density was similar (less than l m-2). At the site near the lagoon perimeter, the central lamina averaged 381 mm in length, grew at an annual mean rate of 1.28 mm d-1, and 56% of tagged individuals had died after one year. The corresponding values for the site near the centre of the lagoon were: 257 mm, 0.75 mm d-1 and 92%. Three other sites on the coastal limestone reefs near Perth (400 km to the south) were studied for various intervals over a 5 yr period (April 1979 to August 1984). The kelp from the low-latitude sites were smaller, grew more slowly, and suffered similar or greater mortality than their southern counterparts. Latitudinal comparisons were confounded by differences in kelp density between sites, but there is no evidence for density-dependent effects on the measured parameters across the range of natural densities observed. Growth rates at all sites were negatively correlated with ambient sea temperatures when these were above 20°C. There was no evidence of adaptation to the higher sea temperatures experienced at the Abrolhos, and temperature cannot be dismissed as a factor controlling the growth of the species near the northern limit of its distribution on the Western Australian coast. Other factors however must be involved in determining the latitudinal position of that limit.

Notes: Abstract Coral reefs cover some 600 thousand square kilometres of the earth's surface (0.17% of the ocean surface). First order estimates show coral reefs to contribute about 0.05% of the estimated net CO2 fixation rate of the global oceans. Gross CO2 fixation is relatively high (of the order 700×1012 g C year-1), but most of this material is recycled within the reefs. Excess (net) production of organic material (E) is much smaller, of the order 20×1012 g C year-1. We estimate that 3×1012 g C year-1 (15% ofE) is buried in reef structure, 2×1012 g C year-1 (10% ofE) is available for sustained human harvest, and the remaining 75% ofE is available for export from coral reefs to adjacent areas. Comparison of estimates for net production by reefs and their surrounding oceans indicates that the excess production by coral reefs is similar to new production in the photic zone of oligotrophic oceans. Consequently, estimates for global ocean production should as a first approximation include reefal areas with the surrounding ocean when assigning average net production rates. While there are significant uncertainties in these numbers, it can be concluded that organic production by reefs plays a relatively minor role in the global scale of fluxes and storage of elements. In comparison, the companion process of biologically-mediated inorganic carbon precipitation represents a major role for reefs. While reef production does respond on local scales to variation in ocean climate, neither the absolute rates nor the amount accumulated into organic pools appear to be either sensitive indicators or accurate recorders of climatic change in most reef systems. Similarly, the productivity of most reefs should be little affected by currently predicted environmental changes resulting from the Greenhouse effect.

Notes: Abstract.  The ecosystem concept has been applied to coral reefs since the time of Charles Darwin, perhaps because of the apparent integrity of the biotic-abiotic nexus. The modern model of the ecosystem as a hierarchy with emergent properties is exemplified in reefs as massive structures formed by small colonial organisms, the self-similarity of these structures across large spatial scales, and the uniformity of function by diverse biological communities. Emergent properties arise through the integration of processes up the levels of organization and larger spatial and temporal scales encompassed by a whole reef. The organic response of reef morphology to hydrodynamic forcing, the constancy and conservatism of organic production across a broad range of environments, and the global persistence of reefs in the face of massive evolutionary change in species diversity are interpreted as emergent properties. Coral reefs, of course, function by the same basic laws as other ecosystems, but there is cause to view them as an end member of a continuum because of their structural complexity and high internal cycling. Well-defined boundary conditions mean that highly integrative measures of ecosystem process based on physical and biogeochemical models (e.g. community metabolism) have provided the main applications of systems ecology to questions of coral reef function. Organism-population approaches are being reconciled with form-functional models to yield new insights to ecosystem processes and interactions among reefs and adjacent systems. The form and metabolism of reef production are strongly affected by phase shifts in benthic community structure, and most reef systems are more open to trans-boundary fluxes and external forcing than the early models suggest. The attractive paradigm of the reef as a self-sufficient ecosystem is dying slowly as research focus shifts from atolls to more open fringing and bank barrier reefs, and organic inputs to system production are measured. Coral reefs contribute little in a net sense to global ecosystem processes, but on an areal basis their exports of organic products are significant. Holistic models and measures of ecosystem processes incorporate the unusual whole-part relationship of reefs and are practically essential to answering the key questions facing coral reef science in the next millennium.