Release of dissolved organic carbon from the estuarine intertidal macroalga Enteromorpha prolifera

The estuarine macroalga Enteromorpha prolifera was collected from Coos Bay, Oregon, USA during 1981, and its release of photosynthate as dissolved organic carbon (DOC) was studied using ¹⁴C as a tracer. During photosynthesis in 30 S sea water, with a fixation rate averaging 7.37 mg C g^-1 dry wt h^-1, release ranged from 0.13 to 0.57 mg C g^-1 dry wt h^-1 and from 1.65 to 6.23% of total fixed carbon. Release of DOC appears to be linear with time over 3 h. As exposed algae become increasingly desiccated, their photosynthetic rates decline dramatically, but upon reimmersion the highly desiccated algae lose a larger fraction of their fixed carbon than the slightly desiccated algae. This loss comes in a pulse release of DOC over the initial 15 min, followed by declining release rates. The pulse loss due to rainfall is 5 times greater than that due to tidal resubmergence, and may briefly exceed the prior photosynthetic rate. Although lowering the salinity from 30 to 5 does not substantially alter photosynthetic rates, it does increase the DOC release range up to 1.02 mg C g^-1 dry wt h^-1 and 16.10% of fixed carbon. Heterotrophic microbes from the algal habitat readily use the available DOC at about 15% h^-1.     

Effect of microbial seeding of crude oil in seawater in a model system

The adding of a mixed culture of marine hydrocarbon-degrading bacteria to petroleum polluted seawater did not increase the hydrocarbon degradation capability of the water. All the strains of the mixed culture disappeared from the dominant microflora while the autochthonous bacteria showed a capacity for adaptation to petroleum degradation about four days after the oil spill. This confirms the advantage of natural bacterial communities. The oil spilled on the sea surface evolved very quickly under the influence of abiotic factors such as sunlight. Aromatic petroleum fractions were oxidized and polymerized. This chemical evolution causes a drastic decrease of the biodegradability of crude oil.     

Functional autotrophy of Heteroxenia fuscescens (Anthozoa: Alcyonaria): carbon assimilation and translocation of photosynthates from symbionts to host

The association of the alcyonarian Heteroxenia fuscescens (Ehrb.) with its cytosymbiotic algae shows structural and physiological adaptations optimizing the living together of the two partners as one functional unit. To enhance the energetic contribution of the autotrophic partner, the organization of the heterotrophic partner bears typical plant-like imprints. Up to 20% of the inorganic C photosynthetically fixed was translocated to the host (=2 mg C mg d.w.^-1 d^-1). This net C gain by the host is used for anabolic purposes including the deposition of storage material. Especially the wax-esters and triglycerides of the host-in contrast to those of the symbionts-were intensively labelled. The in-vivo ¹⁴C-fixation of zooxanthellae is more than double the in-vitro fixation. In both symbionts and host, the lipids show the highest relative ¹⁴C-incorporation. In particular the polyol component was strongly labelled. After 120 min of continuous incubation, approximately 40 labelled intracellular metabolites were detectable in the ethanol/water soluble fractions of zooxanthellae. Glycerol is the main low-molecular weight carbohydrate being transferred. This is corroborated by the deacylation of lipids of the host.     

Annual,semilunar, and diel reproductive rhythms in the Hawaiian labrid Thalassoma duperrey

In September 1978, 5 034 juvenile western rock (spiny) lobsters (Panulirus cygnus George) were tagged on a shallow coastal reef near Cliff Head in Western Australia. Of these, 26% were recaptured and removed from the population during the subsequent commercial fishery between 15 November 1978 and 30 June 1979. A resurvey of the tagging site in September 1979 found that size structure of the population was similar to the tagged population in September 1978 but that the 1979 population was composed of almost completely different individuals and only 2% of the rock lobsters tagged in September 1978 were recaught at this time. A wide range of movement was indicated by the recapture positions of 354 rock lobsters caught off the tagging site. Most travelled almost directly offshore but some also travelled offshore in a northwesterly direction. Both trends were shown in the data from the recaptures of 18 rock lobster released farther offshore from Cliff Head in September 1981, and of 19 released at a close inshore site in earlier years. Maximum offshore rates of movement of up to 622 m d^-1 were recorded for distances up to 37 nautical miles (ca. 68 km). Growth rates for the tagged individuals which moved off, and those that were caught on, the tagging site were similar and close to growth rate under optimal conditions for this species. Under the present high levels of exploitation few, if any, of the rock lobsters remain to become permanent residents in the coastal reefs. It is believed that the north-westerly movements of some of the pre-adult rock lobsters, on their way to the breeding grounds on the outer edge of the continental shelf, are due to the upstream movement of these rock lobsters in a current from the north. The north-westerly movements allow the rock lobster population increased utilization of the food supplies of the coastal area.     

Values of net compensation irradiation and their dependence on photosynthetic efficiency and respiration in marine unicellular algae

Daily compensation irradiation for net photosynthetic rates (ΣI _comp) of Skeletonema costatum (Greville) Cleve, Chaetoceros ceratosporum Ostenfeld, Nitzschia sp., Thalassiosira nordenskiöldii Cleve, and Chroomonas salina (Wislouch) Butcher were measured during 1979 to obtain values for use in ecological models describing compensation and critical depths of marine phytoplankton. Batch cultures of these unicellular algae were exposed to temperatures and photoperiods varying from 6° to 15°C and 8.4 to 16.0 h, conditions typical of surface water in Saanich Inlet, a fjord in Vancouver Island, British Columbia, Canada. Results obtained with S. costatum and T. nordenskiöldii provided estimates of ΣI _comp varying between 1.8 and 13 J cm^-2 d^-1, from which a mean value of 7.0 J cm^-2 d^-1 was calculated for use in ecological models with neritic phytoplankton. No seasonal variation in compensation irradiation was noted because photosynthetic efficiencies, which increased as division rates increased, were balanced by respiration rates, which increased as temperature increased. Results obtained with Chaetoceros ceratosporum, Nitzschia sp., and Chroomonas salina were difficult to interpret, because respiration rates were stimulated and depressed by light, respectively, for the first two species and the last one. This light effect was greatest when cells grew under conditions of low temperature and short photoperiod. Also, under winter and spring conditions, cells of Nitzschia sp. appeared to fix CO₂ in the dark and with low irradiances by mechanisms other than photosynthesis.     

Assimilation of symbiont-derived photosynthates in some solitary and colonial radiolaria

Evidence for host assimilation of ¹⁴C-labeled symbiont photosynthates is presented from laboratory studies of the solitary radiolarian Thalassicolla nucleata and the colonial species Collosphaera huxleyi. The amount of ¹⁴C-labeled product assimilated in the central capsule of T. nucleata is directly related to the amount of ¹⁴C incorporated by the symbionts. In C. huxleyi central capsules, the percentage of ¹⁴C-label occurring in the water-soluble fraction is 38% and in the lipid-soluble fraction is 20%, the remainder being in insoluble products. Within the lipid-soluble fraction, a substantial percentage of the ¹⁴C activity is associated with the triglyceride and wax ester fractions. The significance of these findings is discussed in relation to the possible physiological role of symbionts in sustaining the host and stabilizing the host-symbiont association.     

Indications from photosynthetic components that iron is a limiting nutrient in primary producers on coral reefs

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.     

A laboratory study of predation by Aurelia aurita on larval herring (Clupea harengus): Experimental observations compared with model predictions

Predation by the medusa Aurelia aurita L. on early first-feeding stage larvae of the herring clupea harengus L. was studied in the laboratory. The medusae were captured in Loch Etive, Scotland. Herring larvae were reared from the extificially fertilized eggs of spawning Clyde herring caught in March, 1982. Swimming speeds, volume searched”, capture efficiency and predation rates increased as medusa size increased. Predation rates on fish larvae increased with prey density, but appeared to approach a maximum at high prey densities; in 1 h experiments, a maximum rate of predation of 6.64 larvae h^-1 was estimated by fitting an Ivlev function. A model to predict predation rates was constructed from swimming speeds, sizes and densities of medusae and larvae, and capture efficiency. The rates of predation predicted from the model fell within the range of experimental data, but tended to underestimate rates and did not account for saturation of medusae. Swimming patterns of medusae changed after prey capture: (a) before capture, encounter rates were low and medusae were relatively less active; (b) after capture of 1 larva, encounter rates doubled, with the stimulated medusae exhibiting increased activity and an aftered “searching” path; and (c) after capture of many larvae, swimming speeds and encounter rates of medusae decreased.     

Colonization of meiobenthos in oil-contaminated subtidal sands in the lower Chesapeake Bay

In-situ manipulative experiments were conducted over a 3-month period (May–August 1980) to examine the rate at which meiobenthos colonizes oiled and untreated azoic fine sands at a shallow subtidal site in the lower York River, Virginia. Three concentrations of fresh Prudhoe Bay crude oil were added to sediments: 100, 2 500 and 10000 mg oil kg^-1 dry wt sediment. Untreated azoic and natural sediments served as controls. Within 16 d, meiofauna densities in all treatments were comparable to natural populations in surface oxidized sediments, but densities fluctuated greatly during the remainder of the sampling period. Nematodes slowly colonized the subsurface anoxic sediments below the redox potential discontinuity (RPD); some less common species did not significantly recover below the RPD in the two more heavily oiled treatments. Analysis of nematode community composition by reciprocal averaging ordination and numerical classification revealed generally lower abundances, but no distinct differences, in species composition in the oiled substrates as compared to untreated and natural community controls. Ordination of sequential samples suggested that the nematode species assemblages in the untreated controls fully recovered from these small-scale disturbances by 90 d. Life history characteritics and frequent tidal transport combine to make estuarine meiobenthos highly resilient following disturbance. Contrary to prior recolonization studies, a successional sequence was found for the colonizing nematodes which may be analogous to models of macrobenthic colonization (e.g. McCall, 1975). The comesomatid nematode Sabatieria pulchra, which is frequently dominant in polluted sediments, colonized relatively late in the experiment. Consequently, stress resistance and resilience may not be as coincident in meiofauna as in macrofauna because of differences in factors affecting their dispersal.