Effects of grazing and damselfish territoriality on internal bioerosion of dead corals : indirect effects

An experiment was performed on Britomart Reef, Great Barrier Reef (central region), to determine the relationship between fish grazing, damselfish territoriality, and internal bioerosion of dead coral substratum. The damselfish Hemiglyphidodon plagiometopon Bleeker (Pomacentridae) was used for the study because it actively excludes herbivorous fish, particularly scarids and acanthurids, from its territories, creating undergrazed patches in the environment. Its territories simulated conditions of naturally reduced grazing. Freshly killed pieces of the plating coral Pachyseris speciosa Dana were placed under four experimental conditions: (1) within cages, excluding grazing fish; (2) within damselfish territories; (3) beneath shade tops to control for light; and (4) outside damselfish territories, fully exposed to grazers. Internal bioeroders were identified by pattern of substratum excavation and characterization of borings, and were quantified by digitizing x-ray radiographs of the substratum. Three major categories of borers were identified: Cliothosa hancocki Topsent, “other sponges” (of the Cliona viridis Schmidt species complex), and “worms” (including polychaetes and sipunculids). Variations in grazing pressure were found to significantly alter the taxonomic composition of the bioeroder community. Bioerosion by C. hancocki, a boring sponge with large exposed papillae, was found to increase significantly when grazing was reduced within damselfish territories. By contrast, other boring sponges of the C. viridis complex decreased in abundance; they were not affected by higher sedimentation in cages. The response of bioerosion by “worms” was less clear but increased slightly within damselfish territories. This was due primarily to a shift in taxonomic composition and dominance from polychaetes to sipunculids (particularly Cleosiphon aspergillum Quatrefages). The effects of grazing on the internal bioeroder community were often altered or obscured in the caged treatments; this was most likely due to caging artifacts such as increased sedimentation and decreased light. In general, bioerosion rates of the substratum P. speciosa were low in comparison to rates established or estimated for corals with less dense skeletons. Total internal bioerosion rates did not vary significantly with changes in grazing pressure. This study implies that, overall, reduced grazing pressure will lead to production of fine sediments derived from internal bioeroders. Under high grazing pressures, the addition of external bioerosion effected directly by grazers would also produce coarse sediment, resulting in an increase in total bioerosion rates (internal and external) and an increased contribution of both coarse and fine sediments to the reef environment.     

Positive interactions between corals and damselfish increase coral resistance to temperature stress

By the century's end, many tropical seas will reach temperatures exceeding most coral species' thermal tolerance on an annual basis. The persistence of corals in these regions will, therefore, depend on their abilities to tolerate recurrent thermal stress. Although ecologists have long recognized that positive interspecific interactions can ameliorate environmental stress to expand the realized niche of plants and animals, coral bleaching studies have largely overlooked how interactions with community members outside of the coral holobiont shape the bleaching response. Here, we subjected a common coral, Pocillopora grandis, to 10 days of thermal stress in aquaria with and without the damselfish Dascyllus flavicaudus (yellowtail dascyllus), which commonly shelter within these corals, to examine how interactions with damselfish impacted coral thermal tolerance. Corals often benefit from nutrients excreted by animals they interact with and prior to thermal stress, corals grown with damselfish showed improved photophysiology (F_v/F_m) and developed larger endosymbiont populations. When exposed to thermal stress, corals with fish performed as well as control corals maintained at ambient temperatures without fish. In contrast, corals exposed to thermal stress without fish experienced photophysiological impairment, a more than 50% decline in endosymbiont density, and a 36% decrease in tissue protein content. At the end of the experiment, thermal stress caused average calcification rates to decrease by over 80% when damselfish were absent but increase nearly 25% when damselfish were present. Our study indicates that damselfish-derived nutrients can increase coral thermal tolerance and are consistent with the Stress Gradient Hypothesis, which predicts that positive interactions become increasingly important for structuring communities as environmental stress increases. Because warming of just a few degrees can exceed corals' temperature tolerance to trigger bleaching and mortality, positive interactions could play a critical role in maintaining some coral species in warming regions until climate change is aggressively addressed.     

The influence of territoriality and mating system on the evolution of male care: a phylogenetic study on fish

Evolution of male care is still poorly understood. Using phylogenetically matched-pairs comparisons we tested for effects of territoriality and mating system on male care evolution in fish. All origins of male care were found in pair-spawning species (with or without additional males such as sneakers) and none were found in group-spawning species. However, excluding group spawners, male care originated equally often in pair-spawning species with additional males as in strict pair-spawning species. Evolution of male care was also significantly related to territoriality. Yet, most pair-spawning taxa with male care are also territorial, making their relative influence difficult to separate. Furthermore, territoriality also occurs in group-spawning species. Hence, territoriality is not sufficient for male care to evolve. Rather, we argue that it is the combination of territoriality and pair spawning with sequential polygyny that favours the evolution of male care, and we discuss our results in relation to paternity assurance and sexual selection.     

Cleaner wrasse influence habitat selection of young damselfish

The presence of bluestreak cleaner wrasse, Labroides dimidiatus, on coral reefs increases total abundance and biodiversity of reef fishes. The mechanism(s) that cause such shifts in population structure are unclear, but it is possible that young fish preferentially settle into microhabitats where cleaner wrasse are present. As a first step to investigate this possibility, we conducted aquarium experiments to examine whether settlement-stage and young juveniles of ambon damselfish, Pomacentrus amboinensis, selected a microhabitat near a cleaner wrasse (adult or juvenile). Both settlement-stage (0 d post-settlement) and juvenile (~5 weeks post-settlement) fish spent a greater proportion of time in a microhabitat adjacent to L. dimidiatus than in one next to a control fish (a non-cleaner wrasse, Halichoeres melanurus) or one where no fish was present. This suggests that cleaner wrasse may serve as a positive cue during microhabitat selection. We also conducted focal observations of cleaner wrasse and counts of nearby damselfishes (1 m radius) to examine whether newly settled fish obtained direct benefits, in the form of cleaning services, from being near a cleaner wrasse. Although abundant, newly settled recruits (<20 mm total length) were rarely (2 %) observed being cleaned in 20 min observations compared with larger damselfishes (58 %). Individual damselfish that were cleaned were significantly larger than the median size of the surrounding nearby non-cleaned conspecifics; this was consistent across four species. The selection by settlement-stage fish of a microhabitat adjacent to cleaner wrasse in the laboratory, despite only being rarely cleaned in the natural environment, suggests that even rare cleaning events and/or indirect benefits may drive their settlement choices. This behaviour may also explain the decreased abundance of young fishes on reefs from which cleaner wrasse had been experimentally removed. This study reinforces the potentially important role of mutualism during the processes of settlement and recruitment of young reef fishes.     

The influence of medication on salivary flow of the elderly: preliminary study

doi:10.1111/j.1741‐2358.2009.00326.x
The influence of medication on salivary flow of the elderly: preliminary study Objective: This study was to evaluate the influence of medications on unstimulated and stimulated salivary flow in elderly men and women. Background: Several diseases and conditions are associated with decreasing salivary flow. Medications can be risk factors for hyposalivation due to the effect particular drug categories. Methods: Seventy‐five elderly of both gender (sixty years old or over) from the Geriatric Dental Clinic at the Federal Fluminense University Dental School, were interviewed about their health status and chronic use of medication. After the interview, unstimulated and stimulated saliva were collected from each subject. The collection time was five minutes, and the flow rate was calculated as ml/min. Results: The mean unstimulated salivary flow was 0.25 ml/min for women and 0.30 ml/min for men, while the mean for stimulated salivary flow was 1.23 ml/min for women and 1.31 ml/min for men, without both differences being non‐significant (p > 0.05). The difference between the mean production of unstimulated and stimulated salivary flow was statistically significant, regardless of gender (p < 0.01). A significant reduction of stimulated salivary flow was observed with the usage of cardiovascular agents (p < 0.05). Conclusion: Drugs used in cardiovascular disease influence the flow of stimulated saliva.     

Patterns of chemical defense among Caribbean gorgonian corals: a preliminary survey

Ship-board assays employing the common Caribbean wrasse Thalassoma bifasdatum (Bloch) were undertaken to determine the palatability of food pellets coated with freshly-extracted, lipid-soluble metabolites of 37 types of Caribbean gorgonian corals representing at least 19 species from 11 genera. Extracts of 19 types (51%) were highly unpalatable (zero or one of five pellets eaten), four types (11%) were moderately unpalatable (two or three of five pellets eaten) and 14 (38%) were palatable (four or five of five pellets eaten) to fish in feeding assays. Gorgonians of the genera Pterogorgia (three types) and Eunicea (nine types) were consistently highly unpalatable, those of the genus Plexaurella (four types) were palatable and those of the genus Plexaura were most frequently palatable (six of eight types). Further assays of serial dilutions of extracts from seven representative, unpalatable types revealed that extracts inhibited fish feeding at pellet concentrations near or below the concentrations that metabolites occur in the gorgonian soft tissue. Extracts of Erythropodium caribaeorum (Duchassaing and Michelotti) and Pseudopterogorgia rigida (Bielschowsky) deterred fish feeding at pellet concentrations less than an order of magnitude lower than those found in the soft tissues of the corresponding gorgonians. Thin layer chromatographic analyses of extracts revealed the presence of lipid-soluble, secondary metabolites in a majority of the highly unpalatable extracts, although secondary metabolites were also present in a smaller percentage of palatable extracts. These data support the hypothesis that the soft tissues of many gorgonian corals contain lipid-soluble feeding deterrents which act as a defense against predation.     

Escape response in the damselfish Chromis cyanea (Pisces: Pomacentridae): A quantitative study

Models of different sizes, shapes, and colours evoked, oriented escape responses in schools of Chromis cyanea in their natural coral-reef habitat. Divers filmed these responses; from the films, the distance of the school from the model at the instant of response (reaction distance) was calculated. For a given model, reaction distance was independent of the speed of the model's approach. Darker coloured models were more effective in causing escape (yielded greater reaction distance) than lighter coloured models, suggesting contrast as an important feature of the stimulus. Larger models were more effective than smaller ones. Habituation to repeated stimuli was absent for inter-trial intervals from 0·5 to 4 min. Natural behaviour of Chromis suggests that cues such as sound, vibration, and details of shape, colours, and motion also play a role in triggering escape.     

Recruiting juvenile damselfish: the process of recruiting into adult colonies in the damselfish Stegastes nigricans

Juveniles of Stegastes nigricans occur in adult colonies, solitarily, and occasionally in juvenile colonies. We concentrated on solitary juveniles and those in adult colonies. We examined the costs and benefits of different settlement strategies, quantified the territory requirements of adults, and investigated the process of how juveniles make the transition to adult territorial fish. An adequate adult territory lies next to those of other adults, is proportional in area to the size of the adult, and contains a refuge tunnel whose entrance is sufficiently large. Compared with solitary juveniles, those <4 cm total length inhabiting adult colonies experienced reduced heterospecific competition for algal food and consequently benefited from a greater density of algae. A cost of recruiting into an adult colony, however, was increased attacks by adults. Juveniles that settled in adult colonies avoided attacks by retreating into small holes inaccessible to adults. As juveniles in adult colonies grew, they were chased less often by adults, whereas they themselves chased adults and heterospecific fish more often. Because territory size correlated with fish size in adult colonies, its area had to expand as the young fish grew, and that expansion was done at the expense of neighbors. Obtaining the space needed by an adult may be possible only when the juvenile settles directly into an adult colony. Juveniles that first settle down solitarily, or in juvenile colonies, may later attempt to enter adult colonies. However, because they do so as larger juveniles, they would have difficulty insinuating themselves into small refuges, which is essential for retreat from the adults. Received in revised form: 4 January 2001 Electronic Publication     

Coral Bioerosion at Enewetak: Agents and Dynamics

Significant differences were found in the extent to which massive coral species at Enewetak are excavated by boring organisms: Goniastrea retiformis, 7.9%; Porites lutea, 2.5%; and Favia pallida, 1.2%. While polychaetes constituted the most abundant and diverse group of coral associates, clionid sponges accounted for approximately 70–80% of skeletal damage. Clionid boring rates are initially very high but burrowing ceases when a particular burrow size (˜0.6 cm) or distance from the surface (≦2 cm) is reached. Most coral skeletal excavation occurs within 2 cm of a dead surface. Therefore, bioerosional damage to corals depends primarily on the amount of skeletal surface not covered by live coral tissue. Damage to skeletons is inversely correlated with colony size but is not correlated with coral growth rates or water depth. Massive corals have a potential escape in size from catastrophic bioerosion. Models relating 1) coral growth forms to skeletal density and stability in currents, 2) resistance of coral skeletons to breakage by water movement and suspended rubble, and 3) dead surface area on coral heads to bioerosional damage and consequent probability of detachment from the substrate, are proposed.     

Observations on naturally and artificially diseased tropical corals: A scanning electron microscope study

Scanning electron microscopic (SEM) observations of naturally and artificially diseased corals reveal that the disease is characterized by a filamentous matrix of cyanobacterial andBeggiatoa filaments. Spiral bacteria are commonly embedded in the matrix. The artificial disease is not manifested as the characteristic black line disease and does not contain filaments of cyanobacteria. This suggests that cyanobacteria are necessary for the black line phenomenon. The colorless, sulfide-oxidizing bacteriumBeggiatoa, however, is always associated with the disease.     

Genotype and attachment technique influence the growth and survival of line nursery corals

The Caribbean staghorn coral, Acropora cervicornis, was once a dominant habitat creating coral, but its populations have declined dramatically in recent decades. Numerous restoration efforts now utilize coral gardening techniques to cultivate this species, growing colonies on fixed structures or from line/suspended nurseries. Line nurseries have become increasingly popular because of their small footprint and ease of use, replacing fixed structures in many nurseries. To evaluate the efficacy of the line technique, this study evaluated growth, condition, and survivorship of A. cervicornis nursery colonies of three distinct genotypes grown via two line nursery techniques (suspended and direct line attachment [vertical]). Direct line attachment of nursery colonies resulted in poor survival (43%) and growth (9.5 ± 1.33 cm/year), whereas suspended culture had 100% survival and increased growth (61.1 ± 4.19 cm/year). Suspended culture had significantly reduced disease prevalence and prevented colony predation. Suspended coral growth was also comparable to a neighboring fixed structure nursery (55.2 ± 7.86 cm/year), and found to be as effective in propagating corals as fixed structures.     

Sheep lymphocyte antigens: A preliminary study

Sera from 287 sheep were screened for cytotoxic antibodies against sheep lymphocytes. Forty four antisera were selected which provisionally define 13 lymphocyte antigens. The frequency of these antigens was studied in 305 sheep from 8 flocks of different breeds. Family studies confirm that inheritance of sheep lymphocyte antigens is controlled by the autosomal codominant genes of at least 2 linked loci.     

Bioerosion versus colonisation on Bivalvia: A case study from the Upper Miocene of Cacela (southeast Portugal)

A study of the bioerosion structures and the skeletobionts associated with the most common bivalves (infauna and epifauna) from the classic Upper Tortonian site of Cacela, Algarve region, SE Portugal, revealed 24 different ichnotaxa and five systematic groups of encrusters (Foraminifera, Annelida, Bryozoa, Balanomorpha and Bivalvia).Despite a relatively high ichnodiversity, the percentage of bioerosion in the specimens analysed is quite low (10-12%). This is explained by rapid sedimentation with only short periods of exposure on the sea-floor.The dominant bioerosion structures were linked to the boring activity of nonpredatory organisms. Algal microborings are the most common, followed by annelid borings (Caulostrepsis-Maeandropolydora), sponge borings (Entobia) and ctenostome bryozoans (Pinaceocladichnus).Spatial distribution of bioerosion structures and encrusters allow the reconstruction of three successive stages. The first was restricted to the biosubstrate lifetime, with structures showing a preferred orientation and situated exclusively on the outside of the shells. The second comprises the period immediately after death, with structures that extend outwards and start with the colonization of the interior of the valves, losing their initial orientation. The third stage relates to later postmortem colonisation, with structures on both sides of the valves and without a preferential orientation.     

The influence of habitat and adults on the spatial distribution of juvenile corals

Population distributions are affected by a variety of spatial processes, including dispersal, intraspecific dynamics and habitat selection. Within reef‐building coral communities, these processes are especially important during the earliest life stages when reproduction provides mobility among sessile organisms and populations experience the greatest mortality bottlenecks both before and immediately after settlement. Here, we used large‐area imaging to create photomosaics that allowed us to identify and map the location of 4681 juvenile (1–5 cm diameter) and 25 902 adult (>5 cm diameter) coral colonies from eight 100‐m² plots across the forereef of Palmyra Atoll. Using metrics of density, percent cover and the relative location of each colony within each plot, we examined abundance and spatial relationships between juvenile and adult coral taxa. Within coral taxa, juvenile density was generally positively related to the numerical density and percent cover of adults. Nearest neighbor analyses showed aggregation of juveniles near adults of the same taxon for two of the focal taxa (Pocillopora and Fungiids), while all other taxa showed random spatial patterning relative to adults. Three taxa had clustered distributions of juveniles overall. Additionally, we found that on a colony level, juveniles for five of nine focal taxa (accounting for >98% of all identified juveniles) associated with a specific habitat type, with four of those five taxa favoring unconsolidated (e.g. rubble) over consolidated substrata. The general lack of clustering in juvenile corals contrasts with consistent clustering patterns seen in adult corals, suggesting that adult spatial patterns are largely driven by processes occurring after maturity such as partial colony mortality, including fission and fragmentation. The association of many taxa with unconsolidated habitat also suggests that corals may play an important role in colonizing natural rubble patches that could contribute to reef stabilization over time.     

荧假单胞杆菌化感作用的初步研究

1　引　　言化感作用 (Allelopathy)是指一种植物或微生物通过产生化学物质而对其它生物产生的直接或间接的刺激或抑制作用[7] .虽然有关高等植物之间化感作用的研究已有大量报道 ,但微生物对高等植物的化感作用研究报道却较少 ,尤其是细菌在生态系统中的化感作用往往被忽视[1] .荧光假单胞杆菌 (P .fluorescens)是定殖于植物根际的优势细菌种群 ,此类细菌以其分布广、适应能力强、繁殖速度快、易于人工培养等特点 ,成为最具生防潜力和应用价值的生防菌[5] .对陕西农田土壤有益微生物的筛选研究中发现 ,一株荧光假单胞杆菌培养液对番茄灰霉…     

Distinguishing territoriality and privacy: Two studies

Two studies were designed to explore differences between human territoriality and privacy. Study I was designed to determine whether subjects would distinguish between settings offering (1) privacy, (2) territory, (3) both, or (4) neither, and whether they would be prepared to sacrifice privacy for territory (or vice versag in choosing settings for certain specified activities. Results showed that subjects did make these distinctions. Study II was a laboratory experiment designed to explore the separate psychological effects of territory and privacy. In it, subjects first territorialized individual experimental rooms then half completed dependent measures (focusing on attribution) in their new territories, while half worked in comparable rooms they had not seen before. Subjects were also divided so that half had privacy while completing the measures, while half had none. Results indicated that privacy led subjects to attribute their behavior less to the influence of others, and, independently, subjects working on their own territories attributed their behavior more to own personality. Private environments were also reported as being more stimulating and free, and subjects were more creative there.     

A comparative study of territoriality in intertidal and subtidal blennioids (Teleostei, Blennioidei)

This paper presents a comparative analysis of territoriality in three intertidal (Lipophrys pholis, Coryphoblennius galerita, Salaria pavo) and two subtidal (Tripterygion delaisi, Parablennius pilicornis) blennioid fishes. Focal-animal observations of males guarding eggs showed that: (i) intertidal species had smaller territories that were less frequently patrolled; (ii) in subtidal species feeding was limited to the territory, while in intertidal fishes a substantial proportion of the feeding acts occurred outside the defended area; (iii) intertidal species spent less time out of the nest and showed a lower level of locomotory activity; (iv) subtidal species were subjected to a higher number of territorial intrusions with more species intruding their territory, some of them potential egg predators; (v) subtidal species performed several water column displays that played a significant role in courtship, while in intertidal fishes these displays are almost absent. Signalling without the presence of a female was almost absent in intertidal species. It is argued that intertidal fishes minimize the time spent out of the nest and the loss of contact with the substrate, features that may be of high survival value in conditions of strong turbulence. Although intertidal species have a reduced time available for feeding, this may be compensated by lower levels of locomotory activity, territorial defense and risk of egg predation. This revised version was published online in August 2006 with corrections to the Cover Date.