Biodiversity,ecological structure,and change in the sponge community of different geomorphological zones of the barrier fore reef at Carrie Bow Cay,Belize

Changes in the relative abundance of benthic groups on the barrier fore reef at Carrie Bow Cay, Belize, point to a significant reduction of corals and an expansion of the sponge community in 1995–2009. Fifty‐one species are now present in the four geomorphological zones of this reef: the low‐relief spur‐and‐groove zone, the inner reef slope, the outer ridge, and the fore‐reef slope (to a depth of 30 m). Five species are new additions to the sponge fauna reported for Belize, and six species account for 42.6% of the total assemblage: Niphates erecta (9.60%), Aiolochroia crassa (8.8%), Niphates digitalis (6.9%), Callyspongia plicifera (6.63%), Aplysina archeri (5.37%) and Xestospongia muta (5.37%). Species richness, average density, diversity and evenness indexes are statistically similar in these four zones but some species appear to be more dominant in certain areas. In the same 30 years, coral cover has decreased by more than 90%, while the octocoral cover has greatly increased (by as much as 10‐fold in the low‐relief spur‐and‐groove zone). Thus the Carrie Bow fore reef appears to be undergoing a transition from coral dominance in the late 1970s to algae dominance today, with other benthic groups such as sponges and octocorals showing signs of gradual recovery.     

Keratose-dominated sponge grounds from temperate mesophotic ecosystems (NW Mediterranean Sea)

Differently from the North Atlantic Ocean, only few examples of sponge grounds are known from the Mediterranean Sea, mainly thriving in the deep sea. In this study, a novel temperate mesophotic ecosystem dominated by massive keratose sponges is reported from the Ligurian deep continental shelf. An extensive Remotely Operated Vehicle (ROV) survey allowed to study the structure and large-scale distribution of this biocoenosis. The sponge grounds here described are highly fragmented, being formed by a large number of dense, discrete aggregations of Sarcotragus foetidus (up to 7.7 specimens/m²) and other sponges, including Spongia lamella and Axinella polypoides. They mainly occur on flat, patchy and highly silted hardgrounds between 40 and 70 m depth. These sponge-dominated ecosystems have an exceptionally wide spatial distribution, estimated to cover up to nearly 200 hectares, with the largest sponge grounds occurring along the westernmost part of the Ligurian coast, probably in relation to more suitable oceanographic conditions. The dominant sponge species reach considerable heights (up to 65 cm), greatly increasing the habitat three-dimensionality and acting as poles of attraction for a diverse sessile and vagile fauna. In addition, the high abundance of the keratose sponge grounds at mesophotic depths might represent a larval source for shallow-water populations that in the last decades have been stricken by several mass mortality events.     

Acropora coral colonies as microhabitats for sponges in Tayrona National Natural Park,Colombian Caribbean

Sponges are sessile organisms capable of colonizing diverse substrata. In the Caribbean, coral reefs have suffered a drastic decline, and branching corals of the genus Acropora have been widely decimated. On dead coral skeletons and around surviving tissue the settling of sessile organisms can be observed, sponges being common. In order to investigate whether or not sponges have a preference for a particular species of coral, or for specific microhabitats of the colonies, we evaluated species composition, cover, richness and diversity of sponges colonizing the dead parts of still live colonies of the branching corals Acropora palmata and Acropora cervicornis in five locations of the Tayrona National Natural Park in the Colombian Caribbean. Ten colonies of Ac. palmata were quantified in each of the five locations, and eight Ac. cervicornis colonies in each of two locations. Quantification was carried out using video taken within 0.625‐m² photoquadrats. Seventeen sponge species were found, 13 of them associated with Ac. palmata and seven with Ac. cervicornis. Desmapsamma anchorata, Clathria venosa and Scopalina rutzleri were found to be common to all Ac. palmata locations, while De. anchorata occurred in the two Ac. cervicornis locations. On Ac. palmata, encrusting sponges dominated, while on Ac. cervicornis branched and lobed sponges predominated. Significant differences in sponge cover were not found among locations but were observed in the sponge species present. On Ac. palmata the species with highest cover were D. anchorata and Cla. venosa, while on Ac. cervicornis it was De. anchorata. The richness and diversity of sponges were low for both coral species, and their varying distribution can be attributed to the differences in available substrate for attachment, given coral colony morphology; for Ac. palmata, sponges predominated on the underside of the branches, semi‐cryptic areas and colony bases, whereas for Ac. cervicornis, they were located over the entire area of the cylindrical branches. Surviving colonies of Ac. palmata and Ac. cervicornis that are still erect offer additional microhabitats for reef sponges, some of which can be found directly interacting with live coral tissue, further threatening their recovery.     

Long‐term temporal and spatial patterns in bioeroding sponge distribution at the Abrolhos Bank,Brazil, Southwestern Atlantic

Bioeroding sponges belong to the most dominant bioeroders, significantly contributing to the erosion of coral reefs. Some species are tolerant or even benefit from environmental conditions such as ocean warming, acidification, and eutrophication. In consequence, increases in sponge bioerosion have been observed on some coral reefs over the last decades. The Abrolhos Bank is the largest coral reef system in the South Atlantic. It has been affected by sedimentation, eutrophication, overfishing, and climate change, mainly affecting coastal reefs, and at lesser intensity outer ones as well. This study aimed to describe spatial and temporal patterns in bioeroding sponge distribution in carbonate substrates in the Abrolhos Bank. Photo‐quadrats were used to compare bioeroding sponge abundance between two shallow reefs: a coastal, Pedra de Leste (PL), and an outer reef, Parcel dos Abrolhos (PAB). Each individual was delimitated over the substrate by determining the sponge surface through a line connecting the outermost papillae. The study was conducted over 6 years in 2008–2009 and 2013–2016. Four species of bioeroding sponges were identified: Cliona carteri Ridley, 1881, C. delitrix Pang, 1973, C. cf. schmidtii Ridley, 1881, and Siphonodictyon coralliphagum Rützler, 1971. The distribution and abundance of species varied between the inner and outer reefs and across the years, and displayed certain selectivity for the calcareous substrates recorded. Crustose coralline algae (CCA) were the main substrate excavated by the most abundant bioeroding species, C. carteri, and represented 70% of the substrate types occupied by this sponge (CCA, coral overgrown by CCA and plain coral). The highest abundance of bioeroding sponges observed in photo‐quadrats was 21.3 individuals/m² at the outer reefs (PAB) in 2014. The abundances or areal extents of bioeroding sponges were up to 10 times greater on the outer reefs than on the coastal ones, where sedimentation is higher and more strongly influenced by siliciclastic material. Moreover, a higher herbivorous fish biomass has been reported on outer reefs which could also influence the higher abundance of bioeroding sponges in outer reefs. During the study period of 6 years, an increase in bioeroding sponge abundance was observed at the outer reefs (PAB), with the sea surface temperature increase. As CCA have an important role in reefal cementation and carbonate production in the Abrolhos reefs, a bioerosion impact might be expected, in particular, on the outer reefs.     

Population dynamics and chemical ecology of New Zealand Demospongiae Latrunculia sp. nov. and Polymastia croceus (Poecilosclerida: Latrunculiidae: Polymastiidae)

For 3 years aspects of the population dynamics, growth, and bioactivity (measure of biologically active metabolite biosynthesis) of the Demospongiae Latrunculia sp. nov. and Polymastia croceus (Kelly‐Borges & Bergquist) were examined on a subtidal reef on the Wellington south coast, New Zealand. For both species, survival of adult sponges was high in all seasons, whereas juvenile sponges had poor survival. Recruitment of Latrunculia sp. nov. occurred in all seasons indicating that this species is reproductively active throughout the year. P. croceus recruited mostly in autumn, supporting previous work that found the sponge to be reproductively active in summer and early autumn only. For both sponge species, growth rates varied greatly between individuals and were unaffected by initial sponge size within the range examined. Sponges generally grew during winter and spring as the water temperature rose, and shrank during summer and autumn as the water temperature fell. This growth pattern may relate to seasonal variation in food abundance, and for P. croceus it may result also from seasonal differences in reproductive investment. After 2 years, Latrunculia sp. nov. and P. croceus had on average, halved and doubled in size, respectively. Latrunculia sp. nov. showed a seasonal pattern of bioactivity, being most active in spring possibly to prevent the surface overgrowth of fouling organisms. P. croceus had no seasonal pattern of bioactivity, but individuals were either very active or inactive. The bioactive metabolites in both species possibly aid in competitive interactions and prevent predation and biofouling.     

A Sponge-Eating Worm from Bermuda: Branchiosyllis oculata (Polychaeta,Syllidae)*,†

Abstract. Branchiosyllis oculata is a small, errant polychaete that lives only on the surface of sponges: among inshore Bermudian sponges, 9 out of 16 species surveyed were infested. All of these sponges were conspicuously colored, but the bodies and gut contents of associated polychaetes matched the sponge color only for Tedania ignis (red), Cinachyra alloclada (yellow) and Sphecio-spongia othella (brownish-black). For the remaining 6 sponge species, the polychaete bodies were uncolored and the polychaete gut contents were inconspicuously brown or grey. Uncolored polychaetes with grey gut contents were removed from a dark green Tethya actinia and placed on a red Tedania ignis: 2 days later, the polychaete gut contents were red, although the tissues were still uncolored. Acetone extractions of Tedania ignis and Cinachyra alloclada were prepared from sponge tissue and from the gut-free tissue of their respective polychaetes: absorption spectra matched for each sponge/polychaete pair. To test the influence of ingested sponge pigments on polychaete body color, red polychaetes from Tedania ignis were induced to autotomize their posterior ends, transplanted to other sponge species and allowed to regenerate new posterior segments for 20 days. At the end of the experiment the original segments were still red, but the regenerated ones were either yellow (for polychaetes transplanted onto Cinachyra alloclada, on which resident worms are yellow) or colorless (for polychaetes transplanted onto Chondrilla nucula or Tethya actinia, on which resident worms are uncolored). The foregoing observations suggest that (1) the polychaetes consume the soft parts of the sponges on which they live and (2) the pigments vary among sponge species: pigments from some sponges are stored in the polychaete body, while pigments from other sponges are not. Additional information on the morphology, distribution and natural history of Branchiosyllis oculata is presented and discussed.     

Studying interactions between excavating sponges and massive corals by the use of hybrid cores

Excavating sponges often compete with reef‐building corals. To study sponge–coral interactions, we devised a design of hybrid cores that allows sponges and corals to be arranged side by side with similar size and shape, mimicking the situation of neighbouring organisms. Compared to earlier methods that attached sponge cores onto coral surfaces, hybrid cores provide an opportunity to study organism interactions under conditions more equal to the interacting partners. The use of hybrid cores was demonstrated for the excavating sponge Cliona orientalis and the massive coral Porites, which commonly interact on the Great Barrier Reef. Cliona orientalis and massive Porites were cut into half‐moon shaped explants and combined as hybrid cores under replicate conditions. After 90 days in an aquarium setting, positive growth of Cl. orientalis along with net bioerosion were observed in sponge control cores that combined Cl. orientalis with blank substrate. However, when Cl. orientalis and massive Porites were in contact in interaction cores, the sponge displayed negative growth and undetectable bioerosion, and was slightly overgrown by the coral. Cliona orientalis may have developed tissue extension beneath the living coral tissue, but growth and net calcification rates of massive Porites were apparently not affected by Cl. orientalis when comparing the interaction cores to coral control cores that combined massive Porites with blank substrate. Overall, the present work demonstrated that hybrid cores can be used to generate conditions suitable for studying sponge–coral interactions in the laboratory, which can also be applied in the field.     

Dense aggregations of a hexactinellid sponge, Pheronema carpenteri, in the Porcupine Seabight (northeast Atlantic Ocean), and possible causes

Dense aggregations of the hexactinellid sponge, Pheronema carpenteri, were encountered in the Porcupine Seabight at depths between about 1000 and 1300m. In restricted areas within this bathymetric range the sponges attain numerical abundances of more than 1.5m⁻² and an estimated biomass of up to 372g m⁻² wet weight or about 10g m⁻² ash-free dry weight.These recently acquired samples, together with historical data, suggest that Pheronema occurs close to, but not within, regions of the upper continental slope where the bottom topography is expected to result in significant enhancement of the near-bottom tidal current velocities. It is suggested that the sponges may not be able to withstand the enhanced currents, but may nevertheless be dependent upon the resuspended or undeposited organic matter carried to them from these regions of increased tidal energy.     

Sedimentation limits the erosion rate of a bioeroding sponge

Coral reefs are increasingly threatened by anthropogenic disturbances and consequently coral cover and complexity are declining globally. However, bioeroding sponges, which are the principal agents of internal bioerosion on many coral reefs, are increasing in abundance on some degraded reefs, tipping them towards net carbonate erosion. The aim of this study was to identify the environmental factors that drive the erosion rates of the common Indonesian bioeroding sponge Spheciospongia cf. vagabunda . Sponge explants were attached to limestone blocks and deployed across seven sites characterized by different environmental conditions in the UNESCO Wakatobi Biosphere Reserve in Indonesia. Average bioerosion rates were 12.0 kg m^?2 sponge tissue year^?1 (±0.87 SE ), and were negatively correlated with depth of settled sediment (r  = ?.717, p  < .01) and showed weak positive correlation with water movement (r  = .485, p  = .012). Our results suggest that although bioeroding sponges may generally benefit from coral reef degradation, bioerosion rates may be reduced on reefs that are impacted by high sedimentation, which is a common regional stressor in the South‐East Asian Indo‐Pacific.     

Currents and turbulent diffusion in the bottom boundary layer of the Barents Sea

The numerical analysis of the stationary field of current velocity on the upper boundary of the bottom boundary layer in the Barents Sea is performed on the basis of a simplified model taking into account the fields of wind velocity and density of water for the principal periods of the seasonal cycle and the bottom topography. The analysis is based on the climatic BarKode database and the data on the wind velocity over the Barents Sea for the last 50 yr. The numerical results demonstrate that the field of bottom currents is fairly nonuniform and the current velocities vary from several fractions of 1 cm/sec to 5 cm/sec in the zones with noticeable slopes of the bottom. The estimates of the thickness of the bottom boundary layer are obtained for the constant coefficient of bottom friction C _f = 0.04. In the major part of the water area of the Barents Sea, the thickness of the bottom boundary layer is close to 1 m. In the regions with significant slopes of the bottom, it increases to 2–2.5 m and, in the two zones of intensification of the bottom currents, becomes as large as 5 m. The maximum estimate of the coefficient of turbulent viscosity is close to 5 cm²/sec. The mean value of the coefficient of vertical density diffusion K _S is equal to 2.34 cm²/sec and its standard deviation is equal to 1.52 cm²/sec. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 31–49, September–October, 2007.     

Environmental factors shaping boring sponge assemblages at Mexican Pacific coral reefs

Recent studies suggest a future increase in sponge bioerosion as an outcome of coral reef decline around the world. However, the factors that shape boring sponge assemblages in coral reefs are not currently well understood. This work presents the results of a 17‐month assessment of the presence and species richness of boring sponges in fragments collected from living corals, dead coral reef matrix and coral rubble from Punta de Mita and Isabel Island, two coral reefs from the central coast of the Mexican Pacific Ocean. Both localities have a high cover of dead corals generated by past El Niño Southern Oscillation events, but Punta de Mita was also highly exposed to anthropogenic impacts. Additionally, environmental factors (water transparency, water movement, temperature, sediment deposition, SST, and chlorophyll concentration) were assessed to test the hypothesis that environmental conditions which are potentially harmful for corals can enhance sponge bioerosion. Isabel Island and Punta de Mita showed a similar species richness (13 and 11 species, respectively) but boring sponge presence in both live and dead corals was higher at Isabel Island (57.6%) than at Punta de Mita (35.7%). The same result was obtained when each type of substrate was analysed separately: dead coral reef matrix (81.3% versus 55.5%), coral rubble (47.7% versus 20.0%) and living corals (43.7% versus 31.7%). A principal components analysis showed a higher environmental heterogeneity at Punta de Mita, as well as important environmental differences between Punta de Mita and Isabel Island, due to sediment deposition (2.0 versus 0.2 kg·m^?2·d^?1) and water movement (24.5% versus 20.5% plaster dissolution day^?1), that were also negatively correlated with boring sponge presence (r = ?0.7). By analysing the boring sponge assemblage, we found that environmental settings, together with habitat availability (i.e., dead coral substrate) differentiated assemblage structure at both localities. Major structural differences were largely due to species such as Cliona vermifera, Cliona tropicalis and Aka cryptica. In conclusion, factors such as habitat availability favored the presence of boring sponges but some environmental factors such as abrasion resulting from moving sediment acted restrictively, and exerted a major role in structuring boring sponge assemblages in the Mexican Pacific.     

海绵和海鞘中可培养放线菌的分离与多样性比较

在相同的分离培养条件下,为比较地域差别较大的福建海域海绵动物(山海绵Mycale sp.和网架海绵Stylissa sp.)和海南海域海鞘动物(皱瘤海鞘Styela plicata和乳突皮海鞘Molgula manhattensis)之间可培养放线菌多样性的差异,作者采用5种放线菌分离培养基和1种细菌通用培养基,对海绵和海鞘中的放线菌进行分离培养。采用16S rRNA 基因限制性片段长度多态性(Restriction Fragment Length Polymorphism, RFLP)分析和序列分析,揭示其多样性。共获得可培养放线菌198株,其中从海绵中分离到87株放线菌,从海鞘中分离到111株放线菌。RFLP分析表现为38种不同的图谱类型。16S rRNA基因序列分析表明,从海绵中分离到的放线菌包括6个放线菌属,其中有2株菌的16S rRNA基因序列与最相近的菌株相似性低于97%,可能是潜在的新菌株;从海鞘中分离到的放线菌包括7个放线菌属,有8株可能是潜在的新菌株。比较海绵和海鞘中可培养放线菌的多样性发现,从海绵中分离到的放线菌,除节细菌(Arthrobacter)以外,均包括在海鞘分离的放线菌属中。海鞘相关放线菌多样性水平不容忽视,是除海绵之外另一获得新型放线菌资源以及药用天然活性产物的重要来源。     

Substrate Effects on the Bioeroding Demosponge Cliona orientalis.2. Substrate Colonisation and Tissue Growth

Abstract Sponge bioerosion is a result of tissue expansion of endolithic sponges in calcium carbonate substrates. The efficiency of erosion by the sponges can be affected by substrate features, which are thus also likely to influence the way in which the sponge will grow. A field experiment was conducted, in which sponge tissue was grafted to biogenic blocks cut from the corals Goniopora tenuidens, massive Porites sp., Astreopora listeri, Favites halicora, Favia pallida, Goniastrea retiformis and Cyphastrea serailia, and the clam Tridacna squamosa, to investigate colonisation capabilities and growth patterns of Cliona orientalis Thiele, 1900 after 9 months of the experiment. C. orientalis is not substrate‐specific. It invaded > 90 % of the different substrate blocks and penetrated them to varying depths, but usually only down to slightly more than 1 cm. Lateral penetration clearly exceeded depth penetration. Enlargement of surface area versus restricted depth penetration benefits the symbiotic zooxanthellae located in the sponge's surface. Structural irregularities and barriers such as coral dissepiments temporarily deflected the direction of tissue growth and created characteristic tissue patch patterns in different substrates. Tissue growth may be more pronounced in substrates of higher density and lower pore volume, but evidence was only slight. Protection against predation is better in denser materials, which may stimulate the sponge's tissue growth especially in shallower substrate depth. In more porous substrates, favoured by grazers and corallivores, relatively more tissue was located in deeper layers.     

Epibiotic traits of the invasive red seaweed Acanthophora spicifera in La Paz Bay,South Baja California (Eastern Pacific)

The aim of this study was to analyze the interaction of a non‐native macroalga (Acanthophora spicifera) with native macroalgae (Sargassum spp.) and sponge assemblages in a subtropical embayment of the Mexican Pacific. The intensity of A. spicifera epiphytism on the native seaweed Sargassum varied significantly over time and was inversely related to the Sargassum density and size. The higher intensity (up to 28 individuals per host plant) occurred when Sargassum was smaller and was lower in density (senescence period). The lower intensity was recorded during the growth period of Sargassum and the subsequent increase in intensity was attributed to a high fragmentation period of A. spicifera, which was evidenced by a decrease in its average size and biomass and by the presence of larger free‐floating accumulations on the subtidal zone. The facultative interaction between A. spicifera and Sargassum appears to be neutral, as no negative or positive effects were found for epiphytic or basibiont seaweeds. However, this invasive seaweed characteristically monopolizes almost all types of hard substrate, and its effects on other algae and benthic organisms should be investigated. Moreover, A. spicifera was often epizoic on epilithic sponges. This invasive seaweed was found anchored on the sponge tissue by rhizome‐like structures. In addition, free‐floating fronds of A. spicifera were frequently found carrying small pieces of the basibiont sponge in its basis (60% of them with eggs and embryos), which suggests a novel facilitation mechanism for some sponge species, as the A. spicifera epizoism could favor fragmentation, dispersal and recruitment of these invertebrates. This study shows that A. spicifera is not only a species that adapts rapidly to the new conditions of the receiving environment but, due to its epibiotic traits, it can directly interact with and influence the life histories of some native species.     

海绵共附生微生物基因多态性的RAPD-PCR分析

采用传统分离手段对中国南海海域的细薄星芒海绵（Stelletta tenui（Lindgren,1897）1、皱皮软海绵（Halichondria rugosa（Ridley＆Dendy））、澳大利亚厚皮海绵（Craniella australiensis（Carter））、贪婪倔海绵（Dysidea avara（Schmidt））4种海绵体内的微生物进行了分离培养,随机挑选64株芽孢杆菌属细菌（每种海绵16株）进行了RAPD-PCR基因多态性分析。研究表明,一些海绵微生物是可以通过传统分离手段得到的,来自同一或者不同海绵的微生物均具有丰富的基因多态性。     

Coral colonization by the encrusting excavating Caribbean sponge Cliona delitrix

The Caribbean sponge Cliona delitrix is among the strongest reef space competitors; it is able to overpower entire coral heads by undermining coral polyps. It has become abundant in reefs exposed to organic pollution, such as San Andrés Island, Colombia, SW Caribbean. Forty‐four sponge‐colonized coral colonies were followed‐up for 13 months to establish the circumstances and the speed at which this sponge advances laterally into live coral tissue and the coral tissue retreats. Cliona delitrix presence and abundance was recorded at seven stations to interpret current reef space and coral species colonization trends. The spread of C. delitrix on a coral colony was preceded by a band of dead coral a few millimeters to several centimeters wide. However, the sponge was directly responsible for coral death only when live coral tissue was within about 2 cm distance; coral death became sponge advance‐independent at greater distances, being indirectly dependent on other conditions that tend to accelerate its retreat. Cliona delitrix advanced fastest into recently killed clean coral calices; however, sponge spread slowed down when these became colonized by algae. The lateral advance of C. delitrix was slower than other Cliona spp. encrusting excavating sponges, probably owing to the greater depth of its excavation into the substratum. Cliona delitrix prefers elevated portions of massive corals, apparently settling on recently dead areas. It currently inhabits 6–9% of colonies in reefs bordering San Andrés. It was found more frequently in Siderastrea siderea (the most abundant local massive coral), which is apparently more susceptible to tissue mortality than other corals. Current massive coral mortality caused by C. delitrix could initially change the relative proportions of coral species and in the long‐term favor foliose and branching corals.     

Differential effects of thermal and chemical stressors on tissue balls from scleractinian corals

Coral cell aggregates (tissue balls) from four species (Acropora muricata, Fungia repanda, Pavona cactus and Pocillopora damicornis) were used as an indicator to investigate the effects on the corals of thermal stress and of chemical extracts from three sponges (Adocia sp., Haliclona sp. and Lissodendoryx sp.) and one ascidian (Didemnum molle). The formation and disintegration of tissue balls were studied through exposure to a temperature range of 23–30 °C at time intervals of 0–90 min, and to sponge and ascidian crude extracts at concentrations of 50–200 µg ml^?1 at temperatures of 23 and 30 °C and at time intervals of 10, 60 and 120 min. The negative effect of temperature on overall tissue ball density (number per cm² of coral surface) was greatest at higher temperatures (28 and 30 °C) but varied among coral species. Tissue balls of P. damicornis were the most robust whereas those of A. muricata were the most sensitive. High concentrations of extracts of Adocia sp., Haliclona sp. and Lissodendoryx sp. generally inhibited the formation of tissue balls or caused their disintegration, or both, most markedly at 30 °C. Adocia sp. induced the least negative effects and Haliclona sp. the most. No tissue balls were formed in the presence of D. molle extracts (50 and 100 µg ml^?1), indicating a high level of interference with tissue ball formation. The differential susceptibility to thermal and chemical stressors exhibited by the corals under study have possible implications for the interactions of the corals with other sedentary reef organisms under climate change-driven ocean warming.     

Current trends of space occupation by encrusting excavating sponges on Colombian coral reefs

Some sponges of the genus Cliona (Porifera, Hadromerida, Clionidae) simultaneously excavate and encrust calcareous substratum, competing aggressively for illuminated space with corals and other organisms. To interpret current trends of reef space occupation, the patterns of distribution and size of three Caribbean species were examined at San Andrés Island and Islas del Rosario in Colombia. While Cliona aprica was ubiquitous, C. caribbaea (= C. langae) preferred deep and protected reef zones, and C. tenuis shallow and wave‐exposed settings. In contrast to the effect on other excavating sponges, chronic exposure to raw sewage did not significantly increase the abundance of the studied sponges. Substratum occupation/availability ratios showed a positive tendency of the sponges toward certain coral skeletons, and a negative or neutral tendency toward calcareous rock, indicating that establishment may be easier on clean, recently dead coral than on older, heavily incrusted substratum. High relief generally limits sponge size to that of the illuminated portions of the substratum. A generally lower proportion of small individuals than of larger ones indicates currently low recruitment rates and low subsequent mortality. Successful events of higher recruitment seem to have occurred for C. tenuis. These are related to the massive acroporid coral die‐off in the early 1980s and to asexual dispersion during storms, resulting in a current 10% substratum cover. Reefs with high coral mortality were and/or are thus more susceptible to colonization and subsequent space occupation by these sponges, although relief may prevent space monopolization.     

Comparative salinity tolerances of four siphonariid limpets in relation to habitat restriction of the rare and endangered Siphonaria compressa

The salinity tolerances of four South African species of limpet in the genus Siphonaria were experimentally tested, in the context that one of them, S. compressa, is South Africa's most endangered marine mollusc and is restricted to two lagoonal localities that normally experience little variation in salinity. Its habitat is additionally restricted in that it occurs only on the eelgrass Zostera capensis. The other three species, S. capensis, S. concinna and S. serrata, are abundant and widespread on temperate rocky shores. We hypothesised that S. compressa would have limited tolerance to low salinities, contributing to its absence from otherwise suitable estuaries that experience regular fluctuations of salinity. The percentage survival of the limpets was recorded in salinities ranging from 2 to 35 over that period. Both salinity and species significantly affected the survival of the limpets over the 96 hours. Survival was highest in salinities close to those of normal seawater, and greatly reduced in the hypo saline waters. S. compressa had the lowest salinity tolerance of the four species, its time-to-50% mortality in hyposaline waters being significantly less than that for the other three species, which differed in a manner that could be correlated with their zonation patterns. Restriction to eelgrass, coupled with low salinity tolerance, probably explains why S. compressa is found at only two localities, both of which normally experience salinities close to that of seawater. Even there, mass mortalities of S. compressa have been recorded in association with die-backs of eelgrass after abnormal freshwater flooding or sedimentation—further emphasising the vulnerability of S. compressa to extinction.