Effects of light intensity on photosynthesis and dark respiration in six species of marine phytoplankton

Using an oxygen polarographic electrode, the shapes of photosynthetic curves and the effects of light on dark respiration in 6 species of marine phytoplankton wer examined. The species used were Skeletonema costatum, Ditylum brightwellii, Cyclotella nana (Thalassiosira pseudonana) (all Bacillariophyceae), Dunaliella tertiolecta (Chlorophyceae), Isochrysis galbana (Haptophyceae), and Gonyaulax tamarensis (Dinophyceae). A hysteresis was observed in all species examined with respect to increasing and decreasing light. Compensation light intensities varied by over 4 orders of magnitude, suggesting that the 1% light depth is an ambiguous measure of the euphotic zone. The data suggest that dark respiration accounts for ca. 25% of gross photosynthesis, but is species-dependent. In addition, respiration versus cell size does not describe an inverse exponential function over the size scales examined.This research was performed under the auspices of the United States Energy Research and Development Administration under Contract No. EY-76-C-02-0016.     

Strain specificity in a tropical marine sponge

Grafting experiments have provided direct evidence for the occurrence of strain specificity in the marine demosponge Verongia longissima (Carter). All autografts accepted, all xenografts rejected, and there was both acceptance and rejection of allografts. Among allografts, groups of individuals could easily be identified which showed consistent acceptances and rejections of other individuals. The groups were designated as strains. Histological preparations of graft rejections showed the development of a cuticle between the surfaces of the two sponges in contact. The role of specificity in patterns of interactions between sponges in situ has been discussed from an ecological perspective.     

The effect of intensity and quality of illumination on the photosynthesis of some tropical marine phytoplankton

Using solar energy as a source of illumination, photosynthesis in 11 species of marine plankton algae was studied as a function of light intensity. From the photosynthesis-light curve for each organism, the saturation points (I _k ) in different organisms were determined. Among the diatoms and flagellates, the highest I _k (saturation point) values were found in Rhizosolenia styliformis and Dinophysis miles respectively. When the organisms were exposed to a portion of the visible spectrum starting from 700 m, the photosynthesis was found to be related to the radiant energy. The missing portions of the spectrum produced no significant change in the rate of photosynthesis. The photosynthetic response shown by the different organisms was strikingly similar, which signifies that, despite the qualitative dissimilarities which the organisms may possess in their pigment composition, they are capable of much chromatic adaptation.     

Respiration,photosynthesis and carbon metabolism in planktonic ciliates

Release of¹⁴C-labelled carbon dioxide from uniformly labelled cells was used to measure respiration by individual ciliates in 2-h incubations in 1989 and 1990. In a strictly heterotrophic ciliate,Strobilidium spiralis (Leegaard, 1915), release of labelled carbon dioxide was equivalent to ca. 2.8% of cell C h^–1 at 20°C, and there was no difference between rates in the dark and light. In the chloroplast-retaining ciliatesLaboea strobila Lohmann, 1908,Strombidium conicum (Lohmann, 1908) Wulff, 1919 andStrombidium capitatum (Leegaard, 1915) Kahl, 1932, release of labelled carbon dioxide was less in the light than in the dark in experiments done at 15°C. InL. strobila release of radiolabel as carbon dioxide was equivalent to ca. 2.4% of cell C h^–1 in the dark but ca. 1% at 50µE m^–2 s^–1, an irradiance limiting to photosynthesis. InS. conicum release of radiolabel as carbon dioxide was equivalent to ca. 4.4% of cell C h^–1 in the dark, but at an irradiance saturating to photosynthesis (250 to 300µE m^–2 s^–1) there was no detectable release of labelled carbon dioxide. InS. capitatum release of radiolabel as carbon dioxide was equivalent to ca. 4.3% of cell C h^–1 in the dark but at an irradiance saturating to photosynthesis was ca. 2.4% of cell C h^–1. These data, combined with data from photosynthetic uptake experiments, indicate that¹⁴C uptake underestimates the total benefit of photosynthesis by 50% or more in chloroplastretaining ciliates.Contribution no. 7510 from the Woods Hole Oceanographic Institution     

Symbiont photosynthesis increases both respiration and photosynthesis in the symbiotic sea anemone Anemonia viridis

Dark respiration of the symbiotic sea anemone Anemonia viridis (Forskäl) was observed to increase by 34% when anemones were exposed to hyperoxic sea water (150% oxygen saturation) overnight, and by 39% after exposure to 6 h in the light at a saturating irradiance of 300 E m^-2 s^-1 at normoxia (100% oxygen saturation). No increase due to light stimulation was observed in aposymbiotic control anemones. In darkness, the oxygen concentration of the coelenteric fluid was hypoxic. However, within 10 min of anemones being illuminated, coelenteric fluid was hyperoxic, and it remained elevated throughout a 12 h light period. When measured over a 24 h period (12 h light: 12 h dark), the dark respiration rate increased gradually over the first 6 h of the light period until it was 35% above the dark night-time resting rate. It remained elevated throughout the remaining light period and for 2 h into the following dark period, after which it fell back to the resting rate. Gross photosynthesis (P ^gross) increased significantly when anemones were exposed to either hyperoxia (150% oxygen saturation) or 300 E m^-2 s^-1 at normoxia. This increase was not observed when symbiotic anemones were illuminated at a low-light intensity of 100 E m^-2 s^-1. The results of this study suggest that respiration in the dark is limited by oxygen diffusion and that normal respiration is restored in the daytime by utilisation of the oxygen released by photosynthesis. Furthermore, it appears that the increased respiration following exposure to high-light intensities provides a CO₂-rich intracellular environment which further enhances the photosynthetic rate of the zooxanthellae.     

Growth,photosynthesis and carbon metabolism in the temperate marine diatom Skeletonema costatum adapted to low temperature and low photon-flux density

The temperate diatom Skeletonema costatum (Grev.) Cleve was grown in low temperature and/or low light conditions. The cultures were acclimatized for at least three months before experiments were begun. Our data indicate that the initial slope of the photosynthesis vs irradiance curve () is controlled predominantly by light history and the light-saturated photosynthesis (P _max) by temperature. The number of divisions per day decreased with decreasing light intensity, but was identical for cultures grown at 3° or 18°C. The metabolic pathways of inorganic carbon fixation were not fundamentally affected by low temperature or low light intensity, but both these factors increased labelling of C₃ compounds, synthesized by the Calvin-Benson cycle, and decreased that of phosphoenolpyruvate (PEP) and other metabolites. This indicates an enhancement of ribulose-1,5-bisphosphate (RuBP) carboxylase activity, which is the first step in the C₃ pathway (3-phosphoglycerate and sugar phosphate synthesis); this may optimize cell functions. At low temperatures, a seven-fold increase in RuBP carboxylase activity per cell was observed. S. costatum is able to adapt to low irradiance by increasing and decreasing I _k (the ratio of P _max:, light intensity at onset of light saturation), and to low temperature by increasing its cellular chlorophyll a and RuBP carboxylase content. However, in the latter case, adaptation is not optimal. This study revealed two main features: (1) there is evidence that RuBP carboxylase has a key function in adjustment to high rates of photosynthesis at suboptimal temperatures or irradiances; (2) adaptive mechanisms are dynamic processes and the role of the time scale in physiological adaptation should be considered.     

Effects of temperature on photosynthesis and respiration in hermatypic corals

Photosynthesis and respiration rates of the reef corals Pocillopora damicornis (Linn.), Montipora verrucosa (Lamarck), Porites compressa Dana and Fungia scutaria Lamarck were measured under controlled temperatures. Results indicate that coral metabolism is closely adapted to ambient temperature conditions. Tropical corals measured at Enewetak, Marshall Islands, showed greater primary production compared to maintenance requirements at elevated temperatures than did subtropical varieties of the same species in Hawaii. Photosynthesis: respiration (P:R) ratios were significantly and negatively related with temperature between 18° and 31°C for all Hawaiian corals, whereas at Enewetak this ratio generally showed a curvilinear relationship for this temperature range. Extrapolations of P:R regressions on temperatures to a value of 2.0 (estimated as a minimum required for long-term functional autotrophy) coincide for Hawaiian specimens with published upper lethal temperatures. Extrapolation of P:R regressions for Enewetak specimens at temperatures above 25°C suggests lethal temperatures for these corals to be 2 to 5 C° higher than for Hawaiian corals, in good agreement with recent experimental findings. Interspecific differences in P:R temperature regressions for Hawaiian corals correlating with upper lethal temperature tolerances are described.Contribution No. 505 of the Hawaii Institute of Marine Biology.     

Changes in pH as a measure of photosynthesis by marine macroalgae

An automatically operated method for high precision measurements of steady-state photosynthesis by macroalgae was developed. Changes in pH and oxygen content of seawater passing the algae in a flowthrough system, could be measured with extremely high accuracy over very long periods of time. The method is especially suitable for measurements on flowthrough systems with high rates of water exchanges (i.e. short retention time), and can be used to study exchange processes for marine plants, animals and small ecosystems. Since the same measuring unit is used for several flowthrough chambers, the method is very suitable for comparisons between different species, or between differently pretreated specimens of the same species (e.g. in toxicological studies). The method was used to study the ratio: [oxygen production] to [CO₂+H⁺ uptake] at different light intensities for several macroalgae belonging to different systematic groups and from different habitats. At lower photosynthetic rates this ratio was similar for all of the algae studied (1.17±0.02). For brown algae of the fucacean family, the ratio increased by 0.08 units at higher photosynthetic rates. This increase was thought to be related to the crassulacean acid metabolism (CAM)-like strategies connected to these algae. For all other algae studied, the ratio remained constant or decreased slightly (at most by 0.04 units) at higher photosynthetic rates. The relations between the abovementioned ratio and the photosynthetic quotient are discussed on a theoretical basis.     

Temperature acclimation of respiration and photosynthesis in the brown algaLaminaria saccharina

Sporophytes of the brown algaLaminaria saccharina (L.) Lamour grown at 15°C contained significantly more chlorophylla (chla) than did similar plants grown at 5°C. The increase in chla in 15°C plants was due to increased numbers of photosystem II reaction centes, and possibly to increased photosynthetic unit size, compared with 5°C plants. These changes were associated with increased values (photosynthetic efficiencies) in 15°C-grownL. saccharina relative to 5°C-grown plants. The changes in together with reduced respiration rates allowed 15°C-grownL. saccharina to achieve net photosynthesis and light-saturated photosynthesis at a lower photon fluence rate (PFR) than 5°C plants when both groups were assayed at the same temperature (15°C). The photon fluence rates necessary to reach the compensation point and achieve light-saturated photosynthesis (I _c andI _k , respectively) increased with increasing incubation temperature inL. saccharina grown at both 5 and 15°C. However, acclimation responses to growth temperature compensated for the short-term effect of temperature onI _c andI _k . Consequently, plants grown at 5 and 15°C were able to achieve similar rates of light-limited photosynthesis, and similarI _c andI _k values at their respective growth temperatures. These responses are undoubtedly important for perennial seaweeds such asL. saccharina, which frequently grow in light-limited habitats and experience pronounced seasonal changes in water temperature.Please address all correspondence and requests for reprints to I.R. Davison     

Complete carbon and nitrogen budgets for the hydromedusaCladonema californicum (Anthomedusa: Cladonemidae)

Complete carbon and nitrogen budgets were constructed for a single cohort of the hydromedusaCladonema californicum Hyman, 1947, collected in 1984 from Santa Catalina Island, California, USA. The budgets accounted for 62 to 84% (average = 74%) of ingested C and 60 to 108% (average = 84%) of ingested N. During most of the medusan life cycle, expenditures for growth exceeded those for metabolism and dissolved organic release (DOR). The gross growth efficiency was lower for C than for N; different conversion rates of C and N are discussed in terms of C:N ratios and budget balances for predator and prey. Growth rates, egg production, and C and N composition ofC. californicum were quite different from those of neritic ctenophores, indicating that gelatinous predators may be a physiologically diverse group.Please address all correspondence and requests for reprints to Dr Costello at his present address: Biology Department, Providence College, Providence, Rhode Island 02918-0001, USA     

Factors affecting respiration and photosynthesis by the benthic community of a subtical siliceous sediment

In a shallow, subtidal, siliceous sediment, benthic microalgal biomass (g chlorophyll a cm^-3) is influenced by light and physical sediment dynamics. The microalgal community is relatively dense, despite adverse conditions (7.0 g chlorophyll a cm^-3), and is able to respond rapidly to favorable conditions. Productivity of this community is significantly correlated (P0.05) with benthic light. In addition, productivity is influenced by temperature and bottom water NH₄ ⁺ and PO₄ ^-3 concentrations, especially as the concentrations fall to levels approaching the K _s (halfsaturation constant) of the microalgal community. Metabolic activity in this environment is dependent upon a continuous supply of organic carbon. Temperature is significantly correlated with respiration rate, but other factors (e.g. biomass and organic matter supply) are important also. Community respiration responds to overlying phytoplankton productivity in the same manner as deep-water benthic environments. Bacterial enumeration using CFU (colony-forming units) does not measure accurately the number of in situ metabolically active bacteria.This research was supported by Energy Research and Development Administration Contract AT (11-1) 3279, US AEC Contract AT (11-1) GEN 10, P.A. 20 and NOAA Sea Grant No. 04-3-158-22.     

Modeling estuarine-shelf exchanges in a deltaic estuary: Implications for coastal carbon budgets and hypoxia

The export of wetland-derived materials to the coastal ocean (i.e., the “Outwelling” hypothesis) has received considerable attention over the past several decades. While a number of studies have shown that estuaries export appreciable amounts of nutrients and carbon, few studies have attempted to estimate the importance of estuarine sources for the coastal carbon budgets in river-dominated coastal ecosystems. A novel tidal prism model was developed to examine estuarine-shelf exchanges in the Barataria estuary, a deltaic estuary located in the north-central Gulf of Mexico. This estuary has been the site of a massive wetland loss, and it has been hypothesized that carbon export from the eroding coastal wetlands supports the development of a large hypoxic zone in the coastal Gulf of Mexico. The model results show that the Barataria estuary receives nitrogen through the tidal passes and releases carbon to the coastal ocean. The mean calculated tidal water discharge of 6930 m³ s⁻¹ is equivalent to about 43% of the lower Mississippi River discharge. The annual total organic carbon (TOC) export is 109 million kg, or 57 gC m² yr⁻¹ when prorated to the total water area of the estuary. This carbon export is equivalent to a loss of 0.5 m of wetland soil horizon over an area of 8.4 km², and accounts for about 34% of the observed annual wetland loss in the estuary between 1978 and 2000. Compared to the lower Mississippi River, the Barataria estuary appears to be a very small source of TOC for the northern Gulf of Mexico (2.7% of riverine TOC), and is unlikely to have a significant influence on the development of the Gulf's hypoxia.     

Polychlorinated biphenyl (PCB) effects on marine phytoplankton photosynthesis and cell division

Inhibition of photosynthesis and cell division by polychlorinated biphenyls (PCBs) was studied using 7 marine phytoplankton species representing 4 algal classes. PCB concentrations as low as 1.0 g l^-1 reduced cell division of Thalassiosira pseudonana 3H and Isochrysis galbana. Both photosynthesis and cell division of T. pseudonana 3H, Chaetoceros socialis, Skeletonema costatum, T. pseudonana 13-1, Monochrysis, lutheri and I. galbana were inhibited at a PCB concentration of 10.0 g l^-1. The effects on photosynthesis were immediate and probably resulted in reduced rates of cell division. Interspecific differences in susceptibility were observed. These differences have significance with respect to primary production and the species composition of phytoplankton communities. The initial slopes of photosynthesis-irradiance (P-I) curves for the diatoms S. costatum and T. pseudonana 3H were reduced in the presence of PCBs. These results suggest that PCBs affect the photosynthetic light reactions.     

Microsensor studies of photosynthesis and respiration in the symbiotic foraminifer Orbulina universa

Oxygen and pH microelectrodes were used to investigate the microenvironment of the planktonic foraminifer Orbulina universa and its dinoflagellate endosymbionts. A diffusive boundary layer surrounds the foraminiferal shell and limits the O₂ and proton transport from the shell to the ambient seawater and vice versa. Due to symbiont photosynthesis, high O₂ concentrations of up to 206% air saturation and a pH of up to 8.8, i.e. 0.5 pH units above ambient seawater, were measured at the shell surface of the foraminifer at saturating irradiances. The respiration of the host–symbiont system in darkness decreased the O₂ concentration at the shell surface to <70% of the oxygen content in the surrounding air-saturated water. The pH at the shell surface dropped to 7.9 in darkness. We measured a mean gross photosynthetic rate of 8.5 ± 4.0 nmol O₂ h⁻¹ foraminifer⁻¹. The net photosynthesis averaged 5.3 ± 2.7 nmol O₂ h⁻¹. In the light, the calculated respiration rates reached 3.9 ± 1.9 nmol O₂h⁻¹, whereas the dark respiration rates were significantly lower (1.7 ± 0.7 nmol O₂ h⁻¹). Experimental light–dark cycles demonstrated a very dynamic response of the symbionts to changing light conditions. Gross photosynthesis versus scalar irradiance curves (P vs E _o curves) showed light saturation irradiances (E _k) of 75 and 137 μmol photons m⁻² s⁻¹ in two O. universa specimens, respectively. No inhibition of photosynthesis was observed at irradiance levels up to 700 μmol photons m⁻² s⁻¹. The light compensation point of the symbiotic association was 50 μmol photons m⁻² s⁻¹. Radial profile measurements of scalar irradiance (E _o) inside the foraminifera showed a slight increase at the shell surface up to 105% of the incident irradiance (E _d). Received: 26 January 1998 / Accepted: 11 April 1998     

Uptake of cadmium in tropical marine lamellibranchs,and effects on physiological behaviour

The effect of cadmium introduced as inorganic salts (chloride, nitrate, sulfate, carbonate, acetate and iodide) or organic chelates (with EDTA, NTA and humic acid) on the physiological behaviour of six species of tropical lamellibranchs — arcid blood clamsAnadara granosa andA. rhombea, venerid clamsMeretrix casta andKatelysia opima, and mytilid musselsPerna viridis andP. indica, collected from various intertidal areas in southern India from 1986 to 1989 — was evaluated. Inorganic salts of Cd are reported to completely ionize upon introduction to full-strength sea water and form predominantly (97%) chloride complexes. Some inorganic Cd salts, therefore, would hardly affect physiological parameters. However, bioaccumulation of Cd was greatest upon exposure to Cd introduced as sulfate, followed by iodide, acetate, chloride, nitrate and carbonate; 96-h LC₅₀'s also varied, but in a different order, being highest for chloride (3.5µg ml^–1), followed by nitrate, acetate, iodide and sulfate (1.8µg ml^–1). Furthermore, Cd levels increased linearly with time of exposure and levels in medium, and were species-specific, being highest in the arcid clams, followed by the venerid clams and mytilid mussels. The presence of other metals such as Zn reduced bioaccumulation of Cd significantly (P < 0.001), but the reverse was not true. Upon exposure to Cd in the presence of Cu, on the other hand, accumulation of both metals was reduced by 15 to 20%. In the presence of organic chelators — EDTA, NTA and reduced glutathione (GSH) — Cd accumulation was significantly inhibited, by 1/2 to 1/3. Humic acid, on the other hand, had no effect. Cd levels in soft tissues were inversely related to ambient salinity in the range of 12 to 32. However, both Zn and Cu significantly inhibited Cd accumulation irrespective of salinity. Cd increased the rate of filtration inAnadara granosa over the first 24 h by 28%, but on prolonged exposure (96 h) that rate decreased significantly, by 50%. Zn alone and in the presence of Cd, on the contrary, initially reduced filtration activity, which subsequently increased to control levels upon continued exposure. Cu alone and in combination with Cd and Zn also significantly (P < 0.001) inhibited filtration relative to controls. This combination also progressively reduced respiratory activity with time, the maximum decrease being 80% after 96 h of exposure. Furthermore, impact of all three metals on both filtration rate and oxygen consumption was initially synergistic, but changed to antagonistic upon prolonged exposure up to 96 h.Deceased. Please send all correspondence and requests for reprints to Dr. S. Patel at the same address     

温带湖泊周边湿地原生草地与人工林土壤碳释放差异性分析

采用红外气体分析法对东平湖湿地人工杨树林和自然草地土壤碳通量进行测定,分析了6:00到18:00两种生境下群落土壤碳通量日变化规律,及其对温度、水分等环境因子的响应。结果表明:(1)两种生境群落的土壤碳通量日动态都呈单峰曲线,但人为耕作过的土壤碳通量明显高于原生草地,土壤碳通量均在6:00达到最小值,杨树林土壤碳通量的最大值出现在12:00,而草地群落土壤碳通量最大值在14:00左右;(2)人工林土壤碳通量与近地面大气温度、土壤温度的相关性均低于草地,且两种生境群落土壤呼吸与近地面大气温度的相关性(P<0.01)均好于与土壤温度的相关性(P<0.05)。土壤碳通量对近地面大气温度的敏感性Q10值大于土壤温度的敏感性,人工林土壤呼吸温度敏感性Q10值小于草地。土壤碳通量与近地面大气相对湿度之间具有显著线性方程关系(P<0.01),人工杨树林和草地的相关系数分别为:0.399、0.29。杨树林土壤碳通量与土壤体积含水量相关性差(P<0.05),湿地草地土壤CO2释放量与土壤体积含水量的相关性不显著(P>0.05),这可能由于土壤体积含水量日变化较小,而不能很好的解释日变化尺度上的土壤呼吸变化;(3)对湿地地土壤碳通量的日变化与土壤养分和盐分相关分析得出,人工林土壤中的有机质和全盐与土壤碳通量具有显著关系(P<0.05),而草地土壤碳通量与土壤养分和盐分相关性均非常差,说明人工林生境土壤有机质和全盐是影响土壤碳通量的一个重要因素,而对草地的影响较小。该结果可以为华北平原东部地区以及温带湖泊湿地的土壤碳通量研究提供参考。     

Characterization of arsenic content in marine organisms from temperate, tropical, and polar environments

Arsenic is a widely distributed element which occurs in several chemical forms in the marine environment. Inorganic arsenic mediates the most toxic effects and predominates in sea water and sediments, while organisms generally accumulate non-toxic organic forms to concentrations probably reflecting species-specific characteristics in arsenic metabolism. This work represents an additional contribution to our knowledge on natural levels and chemical speciation of arsenic in marine organisms; basal concentrations were characterized in several species (bivalves, crustaceans, and fishes) from different environments (polar, temperate, and tropical latitudes), and results revealed an elevated variability with values ranging from less than 5 to about 200 μg g^-1. No significant effects were observed as a function of the geographical area, with the only exception of crustaceans always showing more elevated arsenic concentrations in Mediterranean species (about 45-110 μg g^-1) compared with tropical species (lower than 30 μg g^-1). Chemical speciation of arsenic was investigated in representative species from the three studied taxa; the predominance of organic forms confirmed the general tendency of marine organisms to bioaccumulate non-toxic arsenic compounds, probably resulting from a detoxification pathway.     

An apparatus for measuring photosynthesis and respiration of intact large marine algae and comparison of results with those from experiments with tissue segments

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.     

Variability in reproductive output across a water quality gradient for a tropical marine sponge

To establish a complete understanding of reproductive variability, larval supply and ultimately population demographics of a species it is important to determine reproduction across a broad spectrum of environmental conditions. This study quantified sexual reproduction of the brooding, gonochoristic sponge Rhopaloeides odorabile from populations across the shelf reefs of the central Great Barrier Reef (GBR). Histological sections of reproductive sponges collected at increasing distances from the coast were used to determine if numbers of reproductive sponges, reproductive output (using a reproductive output index), size at sexual maturity, and sex ratios varied according to their location (distance) from the coastline and therefore from influences of terrigenous/riverine discharge. Significantly higher proportions of reproductive sponges occurred with increasing distance from the coast. The proportion of all reproductive sponges (both male and female) on offshore reefs ranged from 77 to 90%, during November and December, the peak reproductive months of this sponge, compared to 47 to 50% for sponges occurring on coastal reefs. Levels of female reproduction increased with increasing distance from the coastline on two levels. First, oocytes from offshore sponges were significantly larger than oocytes from coastal sponges. Second, sponges from offshore reefs showed a reproductive index (proportions of oocytes, embryos and larvae mm⁻²) approximately 15 times higher than coastal reef sponges. Therefore, both numbers of oocytes, embryos and larvae in conjunction with larger oocytes contribute to a higher reproductive output index for offshore sponges. The production of spermatic cysts in males was consistent across the GBR. Sex ratios for coastal reef sponges showed a male bias while offshore sponges showed approximate equal sex ratios. The effect of terrigenous riverine input from coastal fluvial plains to the inner GBR is well established and is likely to contribute to the lower levels of reproduction associated with female sponges inhabiting coastal reefs of the central GBR.