Marginal tentacles of the corallimorpharian Rhodactis rhodostoma. 1. Role in competition for space

The corallimorpharian Rhodactis rhodostoma (Ehrenberg, 1934) forms aggregations that dominate patches on some coral reef flats in the Red Sea. The outcomes and mechanisms of competition for space between this corallimorpharian and other sessile organisms are poorly understood. Polyps of R. rhodostoma were observed to overgrow zoanthids, hydrozoan corals, sponges and encrusting macroalgae on a fringing reef at Eilat, northern Red Sea. R. rhodostoma polyps also damaged, and in some cases overgrew, reef-building corals in the families Poritidae, Acroporidae and Pocilloporidae, most of which form branching colonies with small polyps that are subordinate in coral competitive hierarchies. In contrast, most stony corals in the families Faviidae and Mussidae had standoff interactions with R. rhodostoma, in which they prevented the corallimorpharians from damaging them or approaching closer than 1 to 3 cm. The latter corals are ranked at the top of competitive hierarchies for Indo-Pacific corals, and they form massive colonies of large polyps which may develop aggressive organs termed sweeper tentacles. Some soft corals that exude allelopathic chemicals also avoided overgrowth by the corallimorpharians. Tentacles along the oral disk margin of R. rhodostoma polyps were swollen and bulbous during contacts with cnidarians. These bulbous marginal tentacles had significantly thicker ectoderm and a higher proportion of holotrichous nematocysts than did the normally filiform marginal tentacles of R. rhodostoma polyps. It is concluded that, on the reef flat at Eilat, this corallimorpharian damages and overgrows a variety of sessile competitors, including branching stony corals, via the application of specialised marginal tentacles filled with penetrating nematocysts. R. rhodostoma is an intermediate competitor in the aggressive hierarchy among Indo-Pacific Anthozoa, including the reef-building corals. Received: 1 July 1998 / Accepted: 24 March 1999     

Adaptation strategies of the corallimorpharian <Emphasis Type="Italic">Rhodactis rhodostoma</Emphasis> to irradiance and temperature

Corallimorpharians may dominate some habitats on coral reefs and compete with stony corals for access to light, yet little is known concerning their photosynthetic traits. At Eilat in the northern Red Sea, we observed that the abundance of individuals of the corallimorpharian Rhodactis rhodostoma decreased significantly with depth on the reef slope. Field and laboratory experiments revealed that they employ several mechanisms of photoadaptation to high irradiance on the shallow reef flat. Their endosymbiotic microalgae (zooxanthellae) varied significantly in both abundance and chlorophyll content with level of irradiance. Use of a diving pulse amplitude modulated fluorometer revealed that the zooxanthellae of R. rhodostoma effectively disperse excess light energy by expressing significantly higher values of non-photochemical quenching and maximum excitation pressure on photosystem II when experimentally exposed to high light (HL) versus low light (LL). Host corallimorpharian tissues mediated this response by shielding the algal symbionts from high irradiance. The endoderm of host tentacles thickened significantly and microalgal cells were located further from the mesoglea in HL than in LL. The clades of zooxanthellae hosted by the corallimorpharians also varied with depth. In shallow water, all sampled individuals hosted clade C zooxanthellae, while in deep water the majority hosted clade D. The photosynthetic output of individuals of R. rhodostoma was less affected by HL than was that of a stony coral examined. When exposed to both high temperature (HT) and HL, individuals of R. rhodostoma reduced their maximum quantum yield, but not when exposed to HL at low temperature (LT). In contrast, colonies of the scleractinian coral Favia favus reduced their photosynthetic output when exposed to HL in both temperature regimes. After 2 weeks of HT stress, R. rhodostoma polyps appeared to bleach completely but re-established their zooxanthella populations upon return to ambient temperature. We conclude that mechanisms of photoadaptation to high irradiance employed by both the endosymbiotic zooxanthellae and host corallimorpharians may explain in part the abundance of R. rhodostoma on some shallow reef flats. The ability to survive for weeks at HT while bleached also may allow corallimorpharians to repopulate shallow reef areas where scleractinians have been killed by thermal stress. B. Kuguru and G. Winters contributed equally to this work.     

A model-based approach to determine the long-term effects of multiple interacting stressors on coral reefs

The interaction between multiple stressors on Caribbean coral reefs, namely, fishing effort and hurricane impacts, is a key element in the future sustainability of reefs. We develop an analytic model of coral-algal interactions and explicitly consider grazing by herbivorous reef fish. Further, we consider changes in structural complexity, or rugosity, in addition to the direct impacts of hurricanes, which are implemented as stochastic jump processes. The model simulations consider various levels of fishing effort corresponding to' several hurricane frequencies and impact levels dependent on geographic location. We focus on relatively short time scales so we do not explicitly include changes in ocean temperature, chemistry, or sea level rise. The general features of our approach would, however, apply to these other stressors and to the management of other systems in the face of multiple stressors. It is determined that the appropriate management policy, either local reef restoration or fisheries management, greatly depends on hurricane frequency and impact level. For sufficiently low hurricane impact and macroalgal growth rate, our results indicate that regions with lower-frequency hurricanes require stricter fishing regulations, whereas management in regions with higher-frequency hurricanes might be less concerned with enhancing grazing and instead consider whether local-scale restorative activities to increase vertical structure are cost-effective.     

The effects of antifoulant-paint-contaminated sediments on coral recruits and branchlets

The 184-m cargo ship "Bunga Teratai Satu" ran aground on Sudbury Reef, within the Great Barrier Reef Marine Park, on 2 November 2000. Although no cargo or fuel was lost, the ship remained aground for 12 days and a large quantity of antifoulant paint containing tributyltin (TBT), zinc, and copper was scraped from the hull during the grounding and subsequent refloating operation. This resulted in extensive contamination of the reef sediments for up to 250 m surrounding the grounding site. Two laboratory-based experiments assessed the impact of contaminated sediments on the survival of both newly settled corals of Acropora microphthalma and branchlets of A. formosa. Newly settled corals exposed to sediments containing 8.0 mg kg^–1 TBT, 72 mg kg^–1 Cu, and 92 mg kg^–1 Zn or greater suffered significantly higher mortality after 72 h, compared to control or low-concentration treatments. Coral recruits exposed to 40 mg kg^–1 TBT (Sn), 306 mg kg^–1 Cu, and 403 mg kg^–1 Zn were all killed within 38 h. Branchlets from adult corals exposed to sediments with a high concentration of contaminants (TBT 160 mg kg^–1, Cu 1,180 mg kg^–1, and Zn 1,570 mg kg^–1) suffered significant mortality (38%), whereas branchlets placed in treatments with lower levels of contaminants suffered no mortality. Visual bleaching of the branchlets was observed at high contaminant levels, but an overall reduction in the symbiotic zooxanthellae populations was not observed in surviving corals. The photosynthetic yields of light-adapted zooxanthellae remained constant in live branchlets, indicating that the TBT-contaminated sediment may be more toxic to the host than the symbiont. Our results show that antifoulant contamination at ship-grounding sites has the potential to cause major mortality of resident coral communities and can have a negative impact on the recovery of adult populations.Communicated by P.W. Sammarco, Chauvin     

A long-term study of the effects of water-soluble fractions of No. 2 fuel oil on the survival,development rate,and growth of the mud crab Rhithropanopeus harrisii

Mud crabs, Rhithropanopeus harrisii (Gould), were exposed continuously for 6 months after hatching to water-soluble fractions (WSF) of No. 2 fuel oil. Survival, growth and development rate were monitored during this time. The zoeal stages were the most sensitive to fuel oil. A 20% WSF (0.36 ppm total naphthalenes, 1.26 ppm total hydrocarbons) was acutely toxic to these stages. Of the zoeal stages, the first stage appeared to be the most sensitive. The combined duration of the 4 zoeal stages was significantly increased by increasing WSF exposure concentrations. The megalopa and crab stages were not particularly sensitive to continued petroleum hydrocarbon exposure, particularly when compared to zoeal stages. However, mean duration of the megalopa and first crab stages was significantly affected by oil exposure. Individuals which survived the highest exposure concentrations as larvae appeared to grow larger during the crab stages, so that at the end of 6 months comparably staged crabs were equal to or larger than both control crabs and those exposed to low WSF concentrations. Stage distributions at the end of 6 months showed no differences due to WSF exposure. Sex ratios, which could be determined at the end of 6 months, were approximately 1, indicating no sex-related differential sensitivity to WSF exposure, at least as larvae or juveniles. The data indicate that these crabs possess considerable ability to recover from the effects of chronic sublethal exposure to petroleum hydrocarbons. The most deleterious effects of oil pollution on this species may be due to its impact on larval recruitment into the adult population.     

Synergistic effects of temperature,salinity and light on the hermatypic coral Montipora verrucosa

Temperature tolerance in the reef coral Montipora verrucosa (Lamarck) is affected by salinity and light. Low salinity reduces ability of the coral to survive shortterm exposure to elevated temperature. High natural light intensity aggravates damage sustained by corals at high temperature. In long-term growth experiments, high light intensity caused substantial loss of zooxanthellar pigment, higher mortality rates, reduced carbon fixation and lowered growth rate at both upper and lower sublethal temperatures Effects of light at optimal temperature were less dramatic. Interactions between physical environmental factors appear to be most important near the limits of tolerance for a given factor. Acclimation capability was indicated, and was influenced by both thermal history and pigmentation state of stressed corals.Contribution No. 543 of the Hawaii Institute of Marine Biology.     

Gonad development and the planulae of the temperate Australian soft coral Capnella gaboensis

Capnella gaboensis Verseveldt, 1977 was sampled at four sites in Sydney Harbour, during 1981–1984. This soft coral has an annual cycle of gonad development, with gonad number reaching a peak in May several weeks prior to spawning, and gonad size reaching a peak in May–June at spawning. The gonads develop during the warm months, and colonies spawn their gametes in late autumn and early winter. Gonad development is neither synchronous within colonies nor within populations, possibly reflecting the protracted nature of spawning. The histology of the developing oocytes and spermaries is described in detail C. gaboensis is a surface-brooder. The planulae are similar in structure to the larvae of other octocorals. The larvae are benthic, settling quickly upon suitable substratum, metamorphosing into polyps with mouths, tentacles and spicules, approximately one week after settling.     

The effects of an abnormal decrease in temperature on the Eastern Pacific reef-building coral Pocillopora verrucosa

Coral bleaching events are associated with abnormal increases in temperature, such as those produced during El Niño. Recently, a breakdown in the coral–dinoflagellate (genus Symbiodinium) endosymbiosis has been documented in corals exposed to anomalously cold-water temperatures associated with La Niña events. Given the ecological significance of such events, as well as the threat of global climate change, surprisingly little is known about the physiological response of corals to cold stress. This study evaluated some physiological effects of continuous temperature decline in colonies of the eastern Pacific reef-building coral Pocillopora verrucosa. Twenty days of incubation at 18.5–19.0 °C resulted in a substantial decrease in holobiont lipid and Chla content, as well as an increase in Symbiodinium density. These observations suggest a combination of symbiont acclimation due to the temperature decline and reallocation of carbon toward algal growth as opposed to translocation to the host coral. With a decreased availability of symbiont-derived carbon, the coral likely catabolized storage lipids in order to survive the stress event. Despite this stress and some tissue necrosis, no mortality was noted and corals recovered quickly when returned to the ambient temperature. As these results are in marked contrast to similar studies investigating elevated temperature on this coral from this same location, Pocillopora in the Mexican Central Pacific may be more prone to long-term damage and mortality during periods of ocean warming as opposed to ocean cooling.     

Experimental investigation into the effects of suspended sediment on fertilisation, larval survival and settlement in a scleractinian coral

Laboratory and field experiments were used to determine whether high (≃100 mg l⁻¹), low (≃50 mg l⁻¹) and control (≃0 mg l⁻¹) levels of suspended sediment affected fertilisation, larval survival, and larval settlement in the scleractinian coral Acropora digitifera (Dana, 1846). Both high- and low-sediment treatments significantly decreased fertilisation, but post-fertilisation embryonic development was not inhibited by suspended sediments. Larval survival and larval settlement were significantly reduced in high- and low-sediment treatments. No difference was found between high- and low-sediment treatments in any of the three post-spawning processes investigated, suggesting that they are susceptible to sediment concentrations which are not exceptionally high even under natural conditions (>50 mg l⁻¹). The introduction of an additional stress in the form of high levels of suspended sediments coupled with naturally high variability in recruitment may have a considerable effect on the successful supply and settlement of coral larvae to a reef. Given that many coral communities are open reproductive systems, the consequences of disturbance events are not likely to be restricted to the impact area. Recruitment to a population may be reduced significantly in the presence of high levels of suspended sediments because of effects on larval survival and settlement. Recruitment of larvae to adjacent populations may also be affected due to a decreased fertilisation success and potential increases in mortality of larvae passing through the affected site. Received: 13 August 1998 / Accepted: 22 July 1999     

土荆芥挥发油对豌豆根边缘细胞的诱导和胁迫作用

为探讨化感胁迫对根边缘细胞的诱导效应,实验采用悬空气培养法培养豌豆(Pisum sativum L.)露白种子,在保留根边缘细胞和去除根边缘细胞状态下,选取相对根长、根边缘细胞数量及死亡率、果胶甲基酯酶（PME）等指标研究了豌豆根边缘细胞对不同剂量土荆芥挥发油化感作用的响应。结果表明：1）与对照相比,随着挥发油处理剂量增加,根的伸长被显著抑制（P<0.05）。2）每个处理时间内,随着土荆芥挥发油剂量增加,根边缘细胞数量整体表现出先增加后减少的趋势,在低剂量2μL处理中达极大值。3）土荆芥挥发油诱导豌豆根边缘细胞死亡,随着处理时间的延长和处理剂量的增加,这种毒害效应程度加剧,除去边缘细胞实验组中10μL挥发油处理24 h时,根边缘细胞死亡率达到100%。在较低剂量挥发油作用下,保留根边缘细胞组的根边缘细胞死亡率高于去除根边缘细胞组,而在高剂量挥发油处理情况则相反。4）在同一处理时间,随挥发油剂量增加,各处理组PME活性持续升高,去处边缘细胞组处理24 h后不同剂量处理皆显著高于对照,而根边缘细胞数量总体表现先增加后减少。综合以上结果,保留根边缘细胞的根尖根边缘细胞的数量减少量较少,说明根边缘细胞能缓解土荆芥挥发油的化感胁迫;去除根边缘细胞组的PME活性升高较多,表明土荆芥化感胁迫诱导了根边缘细胞的产生。     

Short- and long-term effects of eutrophication on the secondary production of an intertidal macrobenthic community

Secondary production of a macrobenthic community at an intertidal mudflat was estimated for 33 successive months. Sampling was carried out along a eutrophication gradient, including non-eutrophied Zostera meadows, an intermediate muddy area, and a strongly eutrophied sand-muddy flat, where macroalgal blooms of Enteromorpha spp. usually occur. The Zostera meadows were always the most productive habitat (145–225 g ash-free dry weight m^–2 year^–1). In the short term, the macroalgal bloom benefited the total estuarine production by enhancing the annual production in the eutrophied area. Nevertheless, our results show that this increase was short lived and in no way sufficient to match the production in the Zostera meadows. In the long term, the present study provides evidence that the disappearance of macrophyte beds, as a result of ongoing eutrophication, constitutes a major threat to the sustainability of the estuarine ecosystem.Communicated by S.A. Poulet, Roscoff     

Cascading effects of long-term land-use changes on plant traits and ecosystem functioning

There is much concern that the functioning of ecosystems will be affected by human-induced changes in biodiversity, of which land-use change is the most important driver. However, changes in biodiversity may be only one of many pathways through which land use alters ecosystem functioning, and its importance relative to other pathways remains unclear. In particular, although biodiversity-ecosystem function research has focused primarily on grasslands, the increases in agricultural inputs (e.g., fertilization, irrigation) and grazing pressure that drive change in grasslands worldwide have been largely ignored. Here we show that long-term (27-year) manipulations of soil resource availability and sheep grazing intensity caused marked, consistent shifts in grassland plant functional composition and diversity, with cascading (i.e., causal chains of) direct, indirect, and interactive effects on multiple ecosystem functions. Resource availability exerted dominant control over above-ground net primary production (ANPP), both directly and indirectly via shifts in plant functional composition. Importantly, the effects of plant functional diversity and grazing intensity on ANPP shifted from negative to positive as agricultural inputs increased, providing strong evidence that soil resource availability modulates the impacts of plant diversity and herbivory on primary production. These changes in turn altered litter decomposition and, ultimately, soil carbon sequestration, highlighting the relevance of ANPP as a key integrator of ecosystem functioning. Our study reveals how human alterations of bottom-up (resources) and top-down (herbivory) forces together interact to control the functioning of grazing systems, the most extensive land use on Earth.     

Natural parthenogenesis,larval and juvenile development,and geographical distribution of the coral reef asteroid Ophidiaster granifer

Ophidiaster granifer Lütken is a small cryptic coral reef asteroid found in the Indo-West Pacific. Its mode of reproduction, shown by aquarium observations and gonad histology, is parthenogenetic. This is the first confirmation of natural parthenogenesis in the phylum Echinodermata, despite many studies showing artificial parthenogenesis in echinoderms. Populations of O. granifer from Micronesia, New Guinea and the Great Barrier Reef consisted only of females: no testes or spermatogenesis were found in any individual at any stage of gonad development of ca 400 individuals. Regular year-round population censuses at Guam, Micronesia, revealed a distinct 0-year class which grew to sexual maturity in two years. There was an annual reproductive cycle with apparently-synchronous spawning in early winter. The large eggs, ca 0.6 mm diameter, develop into lecithotrophic larvae. Some larvae are planktonic, while some remain attached under the rocks. The latter develop through metamorphosis in situ. Parthenogenetic reproduction leading to both stationary and dispersed larvae may be related to the low fecundity and low population densities of this small asteroid.     

Elevated CO2 affects the behavior of an ecologically and economically important coral reef fish

We tested the effect of near-future CO₂ levels (≈490, 570, 700, and 960 μatm CO₂) on the olfactory responses and activity levels of juvenile coral trout, Plectropomus leopardus, a piscivorous reef fish that is also one of the most important fisheries species on the Great Barrier Reef, Australia. Juvenile coral trout reared for 4 weeks at 570 μatm CO₂ exhibited similar sensory responses and behaviors to juveniles reared at 490 μatm CO₂ (control). In contrast, juveniles reared at 700 and 960 μatm CO₂ exhibited dramatically altered sensory function and behaviors. At these higher CO₂ concentrations, juveniles became attracted to the odor of potential predators, as has been observed in other reef fishes. They were more active, spent less time in shelter, ventured further from shelter, and were bolder than fish reared at 490 or 570 μatm CO₂. These results demonstrate that behavioral impairment of coral trout is unlikely if pCO₂ remains below 600 μatm; however, at higher levels, there are significant impacts on juvenile performance that are likely to affect survival and energy budgets, with consequences for predator–prey interactions and commercial fisheries.     

Effects of spatial variability and colony size on the reproductive output and gonadal development cycle of the Mediterranean red coral (Corallium rubrum L.)

Red coral (Corallium rubrum, L. 1758) is an over-exploited Mediterranean gorgonian. The gonadal development cycle of this gorgonian is examined at the Costa Brava (NW Mediterranean) taking into account for the first time colony size, depth and spatial horizontal variability. This study compares the gonad development and fertility in two colony size classes (colonies <6-cm height, and >10-cm height, both at 40–45-m depth), and two populations at different depths (16–18-m depth, and 40–45-m depth, both consisting of <6-cm high colonies) in a 15-month period. The fertility of seven size classes (<2 cm to >12 cm high colonies, in 2 cm intervals) was examined in the deep population, where large colonies were present. Furthermore, reproductive output was compared in 6 populations (distributed along more than 70-km coastline) one month before spawning (June). Red coral was found to be dioecious and gonochoric with a sex ratio of 1:1, which differs from other NW Mediterranean populations. On the other hand, fertility of different size classes indicates that small colonies of 2-cm height already produce gonads, which is in line with previous studies. Female and male polyp fertility and sperm sac size increase significantly with colony size [sperm sac diameter: 476±144 μm (mean±SD) and 305±150 μm in the >10-cm and <6-cm height colonies, respectively), whereas no significant effect on oocyte diameter was found (oocyte diameter: 373.7±18.7 μm). Depth staggered spawning, that is, an earlier release of gonads in the shallow populations, was observed in summer 2003, coinciding with the highest temperature gradient between shallow and deep water during the study period. Colonies of <6-cm height were significantly less fertile than colonies >12 cm, thus the recommendation of this study is that a minimum height should be incorporated into fishing regulations. The six studied populations at the Costa Brava showed a comparable reproductive potential, which demonstrates little variability within the homogenous population structure and range of size classes (due to overharvesting) found at the Costa Brava. The study of reproductive output is an important tool for ecosystem management, and this work recommends basing specific exploitation laws for distinctive populations on colony size, which is found to have a larger effect on reproductive potential than mesoscale variability. An erratum to this article can be found at     

Nitrate uptake by the reef coral Diploria strigosa: effects of concentration, water flow, and irradiance

The effects of several environmental variables on net nitrate uptake by the scleractinian coral Diploria strigosa were investigated under controlled flow conditions. D. strigosa exhibited nitrate uptake rates ranging from 1 to 5 nmol cm⁻² h⁻¹ at ambient concentrations of 0.1–0.3 μM that are typical of oligotrophic reefs such as Bermuda. Net uptake ceased at approximately 0.045 μM. The uptake was positively correlated with concentration up to a saturation concentration of approximately 3 μM. The uptake was also positively correlated with water velocity at 1 μM, but not at 6 μM, suggesting diffusional limitation at low concentrations and kinetic limitation at higher concentrations. Nitrate uptake by D. strigosa was not affected by light intensity or time of day, but was almost completely inhibited by 48 h exposure to ammonium levels found on many reefs.     

Sexual reproduction, larval development and benthic planulae of the solitary coral Monomyces rubrum (Scleractinia: Anthozoa)

The reproductive biology of the solitary ahermatypic coral Monomyces rubrum was studied in northeastern New Zealand between January 1996 and January 1998. The period of oogenesis lasted around 11 months, from late January to December, while spermatogenesis was more rapid, starting in late August and culminating in a spawning period in early December. Reproduction commenced at a polyp size of around 1,000 mm³ (5-6 years old) and the maximum estimated fecundity of the largest corals (7,000 mm³) was no more than 200 eggs. Oocytes were probably fertilized while within the mesentery and were shed into the coelenteron where they developed, via a solid blastula stage, for approximately 1 month. Planulae were relatively large, 3-4 mm in length and 1-2 mm diameter at the time of release, and crawled or swam immediately to the substratum. Peaks of planula shedding were semi-lunar in January 1997, but only one peak was observed in January 1998. The production of a few large rapidly settling larvae by this member of the family Flabellidae is consistent with the trend for solitary short-lived corals from other families to brood larvae rather than spawn gametes.