Soft Coral Colonies Research Articles

Genetic differentiation in the threatened soft coral Dendronephthya australis in temperate eastern Australia

AbstractThe endangered soft coral Dendronephthya australis faces substantial population decreases in central eastern Australian waters. Despite uncertainty about the cause of these declines, the population genetics of the species has not been investigated. Genetic analysis suggests that D. australis is a single species within the family Nephtheidae, confirming identifications based on morphological characteristics only. Soft coral colonies were distributed from Seahorse Gardens in Port Stephens to Jervis Bay in temperate Australian waters, a distance of some 400 km. Genetic differentiation was observed along this distribution using SNP genotyping. Relatively high levels of genetic differentiation were observed between Jervis Bay and the other sites, indicating limited gene flow between this location and others. Moreover, the genetic distinctiveness, low diversity and heterozygote excess at this southern location suggested that it was subjected to a recent population decline and genetic bottleneck. Colonies at Seahorse Gardens and Ettalong, approximately 150 km south of Seahorse Gardens, displayed greater genetic diversity, making these sites more likely to host ancestral populations and to have acted as refugia. Recent substantial decreases in population sizes at these locations are particularly concerning, and these locations require immediate conservation attention.

Cold-Water Soft Corals (Cnidaria: Nephtheidae) as Habitat for Juvenile Basket Stars (Echinodermata: Gorgonocephalidae)

Nephtheidae soft corals are a common component of benthic ecosystems in the Northwest (NW) Atlantic and in the Arctic, but little is known about their functional roles. Here we investigated their role as habitat for basket stars (Ophiuroidea). By examining over 4500 soft coral colonies of Drifa glomerata, Duva florida, Gersemia spp., and Pseudodrifa racemosa collected during trawl surveys in the regions of Newfoundland, Labrador and West Baffin Bay, we show that Nephtheidae soft corals are habitat for juvenile Gorgonocephalus sp. basket stars. Juvenile Gorgonocephalus sp. were found on all soft corals species, but Drifa glomerata was the soft coral species with the highest occurrence of associated juvenile basket stars (32%), with a maximum of 111 basket stars found on a single 4.8 cm tall (contracted state) colony. Individual basket star disc diameter did not change with colony height, but it varied with season for individuals found on D. glomerata. On the other hand, colony height was positively related with maximum disc diameter (D. glomerata), and presence and number of basket stars on a colony (D. glomerata and D. florida). One very young ophiuroid was found within one polyp of a D. florida colony collected in July. We also examined bottom trawl survey data from 2011-2017 from Newfoundland to Baffin Bay, and other locations in the Eastern Canadian Arctic and found that for our largest database, 45% of trawl sets that contained basket stars also contained corals, of which 67% were Nephtheidae soft corals. In this study we show that all four Nephtheidae soft coral taxa studied act as habitat for juvenile basket stars, which are conspicuous components of benthic communities in cold-water environments. Soft corals are commonly exposed and vulnerable to bottom fishing gear in the North Atlantic. We urge future studies evaluating the nature of this relationship, the potential role of soft corals as nurseries, and the potential degree of dependency/preference between basket stars and soft corals in relation to other organisms.

The effects of predation on the condition of soft corals

Soft corals are well known for producing toxic and unpalatable compounds to deter predation. In spite of these antipredation defences, a suite of specialised predators has coevolved to feed on soft corals. Direct quantification of this predation, however, has been minimal and the influence of predation on soft corals is yet to be investigated. In this study, the intensity and importance of predation by fishes on soft corals were evaluated across two locations using descriptive and experimental approaches. Thirty-six percent of soft coral colonies surveyed in the Palm Islands were found to have bite marks, with up to 40 bite marks observed on a single colony. Soft coral was also the major dietary component of the two fish species studied, representing up to 90% of bites taken by Chaetodon melannotus and 87% of bites by Neoglyphidodon melas, despite constituting less than 30% of the substratum. Simulated predation in manipulative experiments was found to have no clear effects on colony condition for two soft coral genera of contrasting morphology (Litophyton: branching and upright colonies, and Lobophytum: massive and lobate colonies). Both species showed a high capacity for recovery, with bites healing over the duration of the experiments and in most instances within 31 days. In contrast to the widespread assumption that predatory interactions between fishes and soft corals are minimal, the results of this study indicate that predation can be intense but is not immediately important to soft coral colonies under current climatic conditions.

Transcript response of soft coral (Scleronephthya gracillimum) on exposure to polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are the most persistent organic pollutants in worldwide aquatic environments. The extensive isolation of genes responsive to PAH pollution in soft coral (Scleronephthya gracillimum) is described herein. Soft coral colonies were exposed to 100μg/L of a standard mixture of PAHs. Gene candidates with transcript levels that changed in response to PAH exposure were identified by differential display polymerase chain reaction (DD-PCR). There were 37 types of candidate genes identified, of which 20 were upregulated in expression and 17 were downregulated. The functions of the genes identified included oxidative stress response, ribosomal structure maintenance, molecular chaperone activity, protein kinase activation and tumorigenesis, defense mechanisms, transcription, and other biological responses. mRNA quantification was carried out using real-time quantitative PCR in eight selected genes: cytosolic malate dehydrogenase, protein disulfide isomerase, ribosomal protein L6, ral guanine nucleotide dissociation stimulator-like 1, poly(ADP-ribose) polymerase 4, peptidylglycine α-hydroxylating monooxygenase, a disintegrin and metalloproteinase (ADAM) metallopeptidase protein, and eukaryotic initiation factor 4 gamma 3. Changes in transcript levels were consistent with DD-PCR results. The gene candidates isolated in this study were differentially expressed and therefore have potential as molecular biomarkers for understanding coral responses to environmental stressors.

Acanthaster planci preying on soft corals in southern Japan

The crown-of-thorns starfish Acanthaster planci is well known as a destructive predator on shallow water Scleractinia, and in particular Acropora spp. (Pratchett 2007). Outbreaks of Acanthaster planci have caused serious damage to coral reefs. However, it is less well-known that the crown-of-thorns does occasionally prey upon other benthic cnidarians (e.g. zoanthids in Obuchi and Reimer 2011). In October 2011, we observed A. planci preying on soft corals, primarily from the genera Lobophytum and Sarcophyton, at the coast of Ei-cho Town, Kagoshima. The southern Satsuma Peninsula coast has experienced a severe outbreak of A. planci since 2007 (Ministry of the Environment 2008), and it was noted that at the dive site at Ei-cho that there was no live coral cover but many dead scleractinians covered with algae. Many individuals were observed exclusively on soft coral colonies (Fig. 1). The individuals were fully grown, approximately 30-40 cm in diameter. It has previously been observed that in the absence of favored scleractinian prey that A. planci will prey upon soft corals, with reports from Guam (Chesher 1969) and Australia (Laxton 1974), although reports are scarce. De’ath and Moran (1998) theorized that such a situation is most likely to occur at the end of A. planci outbreaks, and given the timing of the A. planci outbreak, the lack of live Scleractinia observed and the presence of recently (e.g. within past 1-2 years) dead corals, this is a likely explanation for the unusual feeding behavior of A. planci in Ei-cho. With the scleractinian community of southern Satsuma already devastated, it appears the remaining benthic soft corals are becoming the next victims of the A. planci outbreak, and continued monitoring should assess if the starfish then move on to decimate the only remaining benthic cnidarians, the sea anemones (Actiniaria). Continued observations could demonstrate if A. planci Acanthaster planci preying on soft corals in southern Japan

Isolation of hyperthermal stress responsive genes in soft coral (Scleronephthya gracillimum)

The extensive isolation of genes responsive to hyperthermal stress conditions in soft coral (Scleronephthya gracillimum) is described. Soft coral colonies were exposed to high seawater temperature conditions. Gene candidates whose transcript levels changed in response to hyperthermal conditions were identified by differential display polymerase chain reaction (DD-PCR). Twenty-four types of candidate genes were identified, 18 of which were upregulated in expression and 6 of which were downregulated. The genes were found to function in post-translational modification, protein turnover and chaperones (O); translation, ribosomal structure and biogenesis (J); signal transduction mechanisms (T); defense mechanisms (V); inorganic ion transport and metabolism (P); energy production and conversion (C); cytoskeleton (Z); cell cycle control, cell division and chromosome partitioning (D); lipid transport and metabolism (I); chromatin structure and dynamics (B); transcription (K); replication, recombination and repair (L); secondary metabolites biosynthesis, transport and catabolism (Q); extracellular structures (W); general function prediction (R); and finally, unknown function (S) based on KOG classification. Among these candidates, their expressional changes were confirmed by real-time quantitative PCR (qRT-PCR). These 24 isolated gene candidates were differentially expressed and therefore have great potential as molecular biomarkers for the identification of environmental stressors.

Reef walking on Red Sea reef flats – Quantifying impacts and identifying motives

Reef walking on the shallow reef flats of fringing reefs is an activity commonly observed on Red Sea coral reefs. Of the 137 in-water observations of reef walkers made at Ras Um Sidd, Sharm El Sheikh, South Sinai, 12.4% caused coral damage. Eighteen incidents of coral damage were recorded, 44.4% being breakages of branching corals, 39.8% abrasions of various growth forms and 16.7% detachments of soft coral colonies. Sediment was stirred-up on 31.4% of observations. Tramplers broke 0.1 branches per minute and raised 1.5 sediment clouds, thereby causing more damage than reported from divers. Damage caused depended on coral community structure and past trampling history, with communities dominated by fragile branching corals being most susceptible to mechanical damage and communities heavily trampled in the past being less susceptible. Given that main motives for reef walking included crossing the reef flat, adjusting gear or communicating, management interventions, such as the construction of a walkway combined with a public awareness campaign, could reduce the numbers of reef walkers by up to 39%.

제주도 문섬 조하대에 서식하는 연산호군락의 태풍에 의한 영향 분석

Impacts of Typhoon Maemi on a soft-coral community located on subtidal cliff at Munseom, Jeju were investigated in this study using underwater photography. Typhoon Maemi hit Jeju Island in late September 2003 and its impact was strong enough to destruct most shallow water sessile benthos including soft corals. To estimate numbers and size of soft-coral colonies, a line transect was installed on the cliff at depth from 3 to 9 m and photographs were taken serially by every 1m. From each underwater photograph, species and size of soft-coral colony was determined. Number of soft-coral colony and its Percent coverage (PC) in each quadrat was calculated. Soft corals Scleronephthya gracillium, Dendronephthya gigantea, D. spinulosa and D. castanea were identified from the photographs. Dendronephthya sp. was mainly distributed at 3-6m while S. gracillimum was mostly occurred at . A survey conducted before the typhoon showed that number of the soft-coral colonies at was 17, 24, 20, 23, 18 and 30 or 21, 48, 36, 28, 24 and 43%, respectively. After the typhoon, number of soft-coral colonies in the transect increased, 31, 35, 21, 10, 21 and 50 while PC was remarkably decreased as 21, 23, 21, 5, 9 and 13%, respectively. Our data suggested that the impact was limited in larger colonies; larger soft coral colonies were selectively destroyed and removed while the small colonies underneath the larger colonies remained undestroyed

Cell growth and calcification result from uncoupled physiological processes in the soft coral Litophyton arboreum

Cellular growth and calcification were measured in branch tips of the soft coral Litophyton arboreum (Cnidaria, Octocorallia, Alcyonacea). We measured cell growth rates as 3 H-thymidine incorporated into tissues, and calcification as 45 Ca incorporated into sclerites, during 2 h incubations in labelled seawater. Both parameters were normalised against soft coral protein content and analysed separately as stem and polyp responses. The experiments were run at various points during coral recovery from dissection. Stems and polyps showed their lowest cell growth rate immediately after injury due to cutting (Days 1 to 3), and their highest cell growth rate during recovery time (Days 7 to 49). In all experiments, the cell growth rate of stems was significantly higher than that of polyps. By contrast, no significant difference was detected between calcification rates of stems and polyps of the fully recovered microcolonies (Days 7 to 81). This study documents for first time the independent progress of cell growth and calcification mechanisms in tropical corals. It also demonstrates the contrasting physiological potential between the body regions of soft coral colonies.

Long-term persistence of low coral cover and abundance on a disturbed coral reef flat in the northern Red Sea

Levels of coral cover and abundance on a coral reef flat in Eilat (Israeli Red Sea) were estimated in 2001 by surveying nineteen 10-m transects, and compared to the levels reported in the same area between 1966 and 1973. Lower values compared to 1966 levels are evident, and there has been only a modest recovery following a catastrophic low tide that killed a large proportion of the corals in 1970. Percent cover of soft and stony corals (16.1%) was less than half of that reported for 1969 (35%), when a sharp decrease in coral abundance had already been observed. The total number of soft and stony coral colonies observed was 300, compared to 541 in 1966. In contrast to 1966, when half of the transects surveyed contained more than 30 coral colonies, no transects with this number of corals were observed. The cover of seven of the most common stony coral species was 841 cm, which is twice the coral cover of that in 1973, but only 22% of the 1969 level. Millepora dichotoma, an abundant species before 1970, has almost disappeared, and the soft coral Litophyton, abundant in 1972, was not observed. Anthropogenic nutrient enrichment is apparently among the causes for the lack of coral recovery in the studied reef flat. Reefs located further away from sources of pollution have recovered quickly after natural and anthropogenic disturbances and have retained their coral abundance and diversity.

Discrimination between several diterpenoid compounds in feeding by Gambusia affinis

The alcyonacean soft coral Sinularia flexibilis Quoy and Gaimard produces a number of bioactive complementary (secondary) metabolites. The ability of three of these diterpenes — flexibilide, sinulariolide and dihydroflexibilide — to elicit differential discriminatory feeding behavior in Gambusia affinis was assessed in a feeding deterrence study. Terpene-impregnated fish flakes were offered to fish trained to feed on such food, and their responses (acceptance, rejection, avoidance, or no response) were assessed as indicative of feeding deterrence. Food treated with sinulariolide (a compound previously determined to be non-bioactive) was generally accepted at a 1% concentration. It was avoided and rejected, however, at a concentration of 10%, a concentration level generally restricted to polyp-rich branchlets. This indicated negative olfactory and palatability cues, respectively. Flexibilide-treated flakes were accepted to some extent by the fish at the 1% concentration, but strongly avoided at the 10% concentration, indicating effective feeding deterrence via olfaction. Dihydroflexibilide-impregnated flakes were strongly rejected even at low concentrations (1%) after tasting, indicating a negative palatibility cue. They were strongly avoided or rejected at higher concentrations (10%), indicating a negative olfactory cue as well. This response at higher concentrations indicates that sinulariolide and flexibilide become effective at concentrations between 1% and 10%. Such concentrations may be found in the polypary (polyp-bearing portion) of the soft coral colonies. Dihydroflexibilide elicited the strongest negative palatability response from these test fish. The feeding deterrence characteristics of the compounds determined here represent the potentials of individual compounds to elicit differential feeding responses in organisms like Gambusia which are capable of discriminating between different but closely related complementary (secondary) metabolites.

An association between a dendronotid nudibranch (Mollusca, Opisthobranchia) and a soft coral (Octocorallia, Alcyonaria) from the Red Sea

The association between a dendronotid nudibranch and the soft coral Parerythropodium fulvum fulvum (Forskål, 1775) is described from the Red Sea. The nudibranch is a new species of the genus Marioniopsis Odhner, 1934 (Nudibranchia: Dendronotacea). This species feeds on the alcyonacean octocoral P. f. fulvum, and the slugs do not take zooxanthellae from their prey. The nudibranchs are randomly distributed on the soft coral host, usually one slug per colony, and 24.5% of the soft coral colonies found are occupied by slugs. The nudibranch matches the colour of its prey and the gill clusters have a shape similar to that of the soft coral polyps, and because of these they are very cryptic on its surface. Marioniopsis fulvicola sp. n. is characterized by a thin, elongated body with a smooth dorsal surface, a narrow foot, seven to nine clusters of gills, three to four velar processes per side, 22–32 stomach hard plates, and jaws with more than 100 denticles arranged in four to five rows. The radula presents a median tricuspid tooth, a simple first lateral, and the rest of laterals hamate, without denticles. Marioniopsis fulvicola sp. n. is usually brown-yellow in colour, with brown transverse stripes forming darker patches between the gill clusters. Rhinophores and gills have a bluish coloration.

Effects of the soft coral Xenia puertogalerae on the recruitment of scleractinian corals

The effects of Xenia puertogalerae on the recruitment of juvenile corals was studied at two levels, involving early and more advanced settlement stages. Inhibition by X. puertogalerae was evident. Terracotta tiles established near soft coral colonies had fewer recruits than those located away from the soft corals. This inhibitory effect may be selective as acroporids were able to settle and survive in the presence of Xenia. This selectivity in allowing recruitment implies an important role for X. puertogalerae in determining succession and community structure. It may affect community structure by favouring the establishment of tolerant species, but effectively deters settlement of other corals in the area.

Chemical consequences of relocation of the soft coral Lobophytum compactum and its placement in contact with the red alga Plocamium hamatum

Seven colonies of Lobophytum compactum Tixier-Durivault, 1956, which produce isolobophytolide as the major secondary metabolite, were selected from a fringing reef in the Pelorus Channel, Palm Island Group (18°34′S; 146°29′E), North Queensland, Australia. In September 1991, they were sectioned to afford two portions which were relocated to a grid, and a significant part of the parent colony which was left in place. The aim of the experiment was to determine the effect of relocation and contact with a toxic alga on the secondary metabolite content of a soft coral. A significant increase in the concentration of isolobophytolide was observed for all relocated colonies (n=14, p=0.001) compared to the non-relocated control colonies. This decreased after 2 mo, and was not significantly different from that of the non-relocated control colonies (n=14, p=0.881). After 1 mo, Plocamium hamatum J. Agardh plants were placed in direct contact with 50% of the relocated colonies. All soft-coral colonies in contact with the alga (n=7), showed tissue necrosis on the parts in direct contact with the alga after a further 2 wk. Tissues of the relocated control colonies (n=7), and those portions of treated colonies which were not in direct contact with the alga, were not affected. The parts of the colonies in contact with the alga showed a significant decrease in lipid content over time (n=7, p=0.001) and also a decrease in the concentration of the diterpene isolobophytolide (n=7, p=0.001). The effects of P. hamatum on the soft coral were essentially restricted to contract necrosis; chemical variations in the affected tissue were the outcomes of this necrosis. These results indicate that stress due to relocation is a more important factor in the variation of isolobophytolide levels in the soft coral L. compactum than is contact with the alga P. hamatum.

Animal-plant defense association: the soft coral Sinularia sp. (Cnidaria, Alcyonacea) protects Halimeda spp. from herbivory

An associationsl refuge occurs when an organism escapes predation by being closely associated with another organism. We describe a refuge provided by the soft coral Sinularia sp. for algae of the genus Halimeda growing at its bases. Total algal biomass was significantly greater in the 0–10 cm zone than in zones 10–20 and 20–30 cm around individual soft coral colonies. Total algal biomass was also significantly greater within clusters of colonies than in zones 0–10, 10–20, and 20–30 cm around the perimeter of the clusters. Halimeda incrassata (Ellis) and Halimeda opuntia (Linnaeus) Lamouroux comprised the bulk of the total algal biomass and were the only species that showed a pattern of growth similar to the total biomass. Fishes consistently grazed less algae ( Halimeda incrassata and Acanthophora spicifera (Vahl) Boergesen and seagrass ( Halodule uninervis Ascherson) strands placed next to soft corals than farther away. Fishes grazed indiscriminately around objects (rocks or outcrops of dead hard coral), whereas differential grazing occurred around soft corals. This suggested that the presence of an object alone is not responsible for reduced grazing next to the soft coral. When soft corals were removed, the pattern of grazing was disrupted, whereas around intact colonies the pattern persisted. Subsequently, funnel-shaped carrageenan models, that resembled the arborescent shape of Sinularia sp., produced a similar grazing pattern. Removing soft corals did not appear to encourage grazing of exposed Halimeda spp. by fishes. This may be explained by the chemically deterrent or heavily calcified nature of Halimeda spp. (the dominant algae around soft corals) which would prohibit vigorous consumption by herbivorous fishes. Algal species richness did not appear to be enhanced by the presence of Sinularia sp. We found no evidence for chemical defense in experiments with soft coral extracts, carrageenan models, and rehydrated Sinularia sp. colonies. Just as much seagrass was grazed around models and colonies with added extracts as around controls, suggesting that terpenes and other metabolites present in the extracts were not responsible for the protective refuge provided by the soft coral. However, a significant effect of distance was consistently obtained in experiments with funnel-shaped models and rehydrated soft corals, whereas, no effect of distance occurred with beaker-shaped models. These results suggest that the arborescent shape of Sinularia sp. provides a refuge for young recruits of Halimeda spp., and allows the algae to mature until they are not preferred by herbivorous fishes. This study is the first to directly test whether morphological features or chemical properties of a benthic marine organism are responsible for protecting closely associated algae.

Predation on soft corals (Octocorallia: Alcyonacea) on the Great Barrier Reef, Australia

Quantitative evidence on predation rates on soft corals is presented for the first time. These measured predation rates were low. Less than 1% of the soft coral colonies present in mapped areas at Heron Island and Beaver Reefs had bite marks. Evidence suggests that over 51% of these bite marks were more than two months old. Predators included the mollusc Ovula ovum and two species of chaetodontid fishes that have not been recorded before as feeding on soft corals.

Colony fission increases particle capture rates of a soft coral: Advantages of being a small colony

The rate at which a passive suspension feeder captures food particles depends on the rate at which ambient currents bring particles into contact with its feeding apparatus. This flux of particles is controlled in part by the turbulence and velocity of water as it moves over a surface of a given topography, and is thus strongly influenced by the size and shape of an organism, and by the size and spatial distribution of neighboring individuals. The effects of (1) colony size and (2) the presence of conspecific neighbors on particle capture rates were quantified in laboratory experiments conducted with colonies of an undescribed species of alcyonacean soft coral. Soft coral colonies were observed feeding in a recirculating flow tank at freestream flow speeds ranging from 0.04-0.51 m/s. At all experimental flow speeds, per polyp particle capture rates decreased as colony size increased. At low flow speeds, colonies had lower particle capture rates when surrounded by neighboring colonies than when neighbors were absent; however, at high flow speeds, particle capture rates were enhanced slightly in the presence of neighboring colonies. These alcyonacean colonies, as well as other colonial organisms in diverse taxa, undergo continual asexual fission as they grow, thereby forming aggregations of small, physiologically discrete daughter colonies. The results obtained here suggest that this growth strategy may be an effective means of maximizing nutrient intake (hence growth rate and sexual reproductive potential) per unit biomass of the genotype. The experimental results can be used to predict the size at which a colony should undergo fission in a given flow environment in the absence of other selective forces acting on colony size.

Depth distribution and abundance of benthic organisms and fishes at the subtropical Kermadec Islands

Abstract Subtidal areas of the Kermadec Islands have not previously been described; samples from a bay at Raoul Island are discussed here. Abundances and percentage cover of benthic organisms were assessed from the high intertidal to 20 m depth using quadrat sampling. Fish abundances were assessed subtidally by random transects in shallow (3–6 m deep) and deep (14–20 m) areas of the reef. Hard corals occurred at 2–18 m depths at densities of 5 colonies per m2, but colonies were generally small. Soft coral colonies occurred at similar densities, but were confined to depths of 5–13 m. The mean percentage cover of corals did not exceed 20% at any one depth, and coral reefs did not occur. Fucalean and laminarian algae were not seen. The most abundant algae were foliose and filamentous species, and encrusting red algae. These covered over 80% of the reef at some depths. Grazing invertebrates were not abundant. Echinoids were found primarily in shallow water, reaching a density of 5 per m2 at 5 m depth. The mos...