Recruitment of Antarctic marine eukaryotes onto artificial surfaces

Activities related to Antarctic research stations have caused significant local impacts on the marine environment, potentially affecting the recruitment of benthic invertebrates. Herein, we report the community structure of recruiting marine eukaryotes onto artificial substrata using molecular techniques. Slides were deployed at three sites adjacent to McMurdo Station, Scott Base, and Cape Armitage in McMurdo Sound. Denaturing gradient gel electrophoresis (DGGE) analysis revealed complex and diverse eukaryotic communities had established on artificial surfaces deployed at a range of site and depth regimes after 12 months. Analysis of similarity results detected significantly greater variability in community profiles among sites than within sites. The nonmetric multidimensional scaling plot constructed from DGGE banding patterns revealed different benthic communities had established at 12 and 18 m depths. Despite this, the variation in community composition was greater among sites than between depths, especially at Cape Armitage and Scott Base. Sequence analysis of excised DGGE bands revealed a predominance of arthropod and dinoflagellate sequences at Cape Armitage. In contrast, a wide diversity of phyla including cnidaria, bryozoa, protozoa, dinoflagellates, arthropods, platyhelminths, and annelids were present adjacent to the two research stations. The abundance of diatoms detected in Cape Armitage benthic assemblages exceeded the abundance of diatoms from McMurdo Station and Scott Base by almost two orders of magnitude. The discovery that distinct eukaryotic communities recruit at different sites and depths is probably due to complex interactions between multiple factors including water quality, larval supply, and light. The detection of sessile phyla on slides at each of the sites indicates that the pollution profiles present at each site is not an impediment to successful recruitment of these species.     

Nearshore subtidal community structure compared between inner coast and outer coast sites in Southeast Alaska

Processes that structure subarctic marine communities, particularly in glaciated regions, are not well understood. This understanding is needed as a baseline and to manage these communities in the face of future climate-driven changes. This study investigates two coastal regions of Southeast Alaska with the goals to (a) identify and compare patterns of subtidal community structure for macroalgal, fish, macroinvertebrate (>5?cm), and small epibenthic invertebrate (<5?cm) communities between inner coast and outer coast sites and (b) link patterns of community structure to habitat and environmental parameters. Species assemblage and benthic habitat data were used to compare species diversity and community composition at 6?m and 12?m depths at nine inner coast and nine outer coast sites. Multivariate analysis was applied to reduce environmental variables to major gradients, to resolve community structure, and to relate community structure to habitat and environmental variables. Increased salinity and decreased temperature at outer coast sites compared with inner coast sites were associated with community structure, with greater species diversity at outer coast sites at 6?m depth. Invertebrate community composition was associated with benthic habitat, including crust and coralline algae for macroinvertebrates, and algal cover and substrate for small epibenthic invertebrates. This research suggests that marine communities in glaciated regions are strongly influenced by freshwater input and that future climate-driven changes in freshwater input will likely result in marine community composition changes.     

The control of the development of a marine benthic community by predation on recruits

Recruitment is an important process in regulating many marine benthic communities and many studies have examined factors controlling the dispersal and distribution of larval immigrants. However, benthic species also have early post-settlement life-stages that are dramatically different from adult and larval stages. Predation on these stages potentially impacts measured recruitment and the benthic populations and communities that ultimately develop.We examined the consequences of post-settlement predation on 1-day-old to 1-month-old recruits of sessile invertebrates at two field sites in southern New England. One site (Breakwater) was in a protected area with few predators and the other (Pine Island) was <1 km away in an open coast area with three different predator guilds: small and large invertebrates and fish. The Breakwater site had been dominated for >10 years by colonial and solitary ascidians. These species were absent from the Pine Island site which was dominated by bryozoans. Our goal was to examine whether post-settlement predation influenced the development and subsequent structure of the epifaunal community.Here we examine long-term changes in community development resulting from post-settlement predation, and contrast these results to those of earlier experiments examining the reductions in observed recruitment by post-settlement predation. Our first long-term experiment examined natural community development at the two sites and whether transplanted communities changed when exposed to the different levels of predation at these sites. The communities that developed at both sites were consistently different from each other and similar to resident communities at their respective sites. On panels transplanted from the Breakwater to Pine Island, solitary ascidians and the colonial ascidian, Botryllus schlosseri, suffered high mortalities on both caged and uncaged treatments, indicative of predation by small predators that could enter cages. Some solitary ascidians did survive inside cages and the colonial ascidian, Botrylloides violaceus, became dominant on all transplanted treatments. On panels transplanted from Pine Island to the Breakwater, ascidians invaded and dominated all treatments except those that were originally caged at Pine Island.In the second long-term experiment, natural communities were allowed to develop on panels exposed at the Breakwater for 1, 2, 3, and 4 weeks. Each set was transplanted to three treatments at Pine Island: open uncaged pilings, caged pilings to exclude fish and large invertebrates, and racks suspended above the bottom to exclude all predators. When 1-week-old communities were transplanted, after 2-3 weeks only bryozoans were found on the open and caged pilings, while colonial ascidians dominated the suspended rack treatment. When older 2-week-old communities were transplanted, colonial ascidians also became dominant in the caged piling treatment and when 3- and 4-week-old communities were transplanted colonial ascidians dominated all three treatments. Solitary ascidians were never abundant on open pilings exposed to fish and large benthic invertebrate predators.Post-settlement predator-prey interactions involved newly settled and juvenile life-stages of a variety of prey species and many invertebrate and vertebrate predator species. The effects of these interactions on recruitment did result in differences in the development and eventual species composition of the communities, even though predators had little if any effect on the adults of the prey species.     

Facteurs influençant la structure des groupements de macro-invertébrés benthiques et phytophiles dans la zone littorale du Saint-Laurent (Québec)

In the littoral zone of the St-Lawrence River (Quebec, Canada), benthic and phytophilous macroinvertebrates were studied in order to find and to explain relationships between structure of these animal communities and abiotic (substrate, water depth, current velocity) or biotic (marophytes species) factors. Benthos was sampled at 16 sites in spring, when there was no macrophytic vegetation, and in summer. Phytomacrofauna was sampled at 30 sites in summer. The data were analyzed using simple and partial correlations, stepwise regression, reciprocal averaging and canonical correlation analysis.

     

Depth-related patterns of meiofauna on the Indian continental shelf are conserved at reduced taxonomic resolution

Taxonomic sufficiency (TS) has been used in impact assessment studies of various pollution effects on marine benthic communities and found appropriate to identify the effects of pollution on marine communities. Cost, in terms of the expertise and time needed to identify organisms, increases with the level of taxonomic accuracy. Recently, TS has been adopted to study spatial patterns of macrobenthic community structure. In order to accept TS as a routine approach in wider benthic studies, it needs to be proved valid for various taxa and in geographically different areas. The present study investigates the value of TS in meiofaunal nematodes by analyzing an extensive data set based on samples collected from a wide geographical area covering a large depth gradient. For this study, samples were collected from every degree square of the western Indian continental shelf (7°–22°N latitudes). Our high resolution data showed that with increase in depth, nematode species richness and diversity decreased and communities showed significant variation between shallow and deeper waters. The present study tests whether lower taxonomic resolution nematode data can explain community shifts along a depth gradient in a similar way to species level data from the same data set. Meiofauna have often been neglected from benthic studies, and most attention has been given to macrofauna. This is mainly due to the difficulty in the taxonomic identification of meiofauna. The results of this study based on univariate and multivariate analyses support the use of family level data of nematodes to explain some aspects of depth variation in a similar way to species level data.     

Rhodolith beds at the easternmost extreme of South America: Community structure of an endangered environment

Rhodolith beds are built by the aggregation of free living marine benthic coralline algae. Herein, we described phytobenthic communities associated with subtidal rhodolith beds in northeastern Brazil and tested the hypothesis that depth affects their structure. We compared macroalgal assemblages from depths of 10, 15 and 20 m. The genus Lithothamnion was dominant in these beds. Rhodolith density was similar at different depths, but volume decreases as depth increases. Sixty-seven species of fleshy algae were collected. The red algal order Ceramiales was dominant. A distinct community corresponds to each sampled depth. The shallower depth presented higher values for biomass, number of species, Shannon-Wiener diversity, and Pielou's evenness. When depth and water transparency increased, the number of species and the abundance of macroalgae decreased.     

Does a warmer lake mean smaller benthic algae? Evidence against the importance of temperature–size relationships in natural systems

Ectotherms decrease in size with increasing ambient temperature. Temperature–size relationships (TSR) have been observed experimentally in a wide range of animals, algae, protozoans and bacteria. However, it is still unclear whether temperature is an important factor controlling the size of organisms in natural populations. In this study, we used natural variability in water temperature in the nearshore areas of a single lake to test TSR in populations of benthic diatoms. We deployed standard tile substrates at 5 m depth (similar light availability) at cold and warm sites that were exposed to different hydrodynamic forces. We compared cell sizes of three species of diatoms (Achnanthidium minutissimum, Gomphonema acuminatum and Gyrosigma acuminatum) at these sites. Counter to the TSR, diatom cells at warm sites were either larger (Achnanthidium, Gomphonema) or similar in size (Gyrosigma) compared to those at colder sites. Diatom size was also related to site exposure (hydrodynamic forces), but differently for species with different architectures. TSR were not detectable in the field for these three species of benthic diatom, even when tested within a single ecosystem at a given time of the year. The size of benthic diatoms, however, varied in a predictable way between sites, and such differences could affect the functioning of these primary producers in different parts of the littoral zone.     

Biotic disturbance and benthic community dynamics in salmon-bearing streams

1. Organisms can impact ecosystems via multiple pathways, often with positive and negative impacts on inhabitants. Understanding the context dependency of these types of impacts remains challenging. For example, organisms may perform different functions at different densities. 2. Anadromous salmon accumulate > 99% of their lifetime growth in marine ecosystems, and then return to spawn, often at high densities, in relatively confined freshwaters. While previous research has focused on how salmon nutrients can fertilize benthic communities, we examined how an ecosystem engineer, sockeye salmon Oncorhynchus nerka, influences seasonal dynamics of stream benthic communities through their nest-digging activities in south-western Alaska, USA. Benthic invertebrate and algal abundance were quantified every 7-14 days during the open water seasons of 10 streams in riffle and run habitats across multiple years, leading to 25 different stream-year combinations that spanned a large gradient of salmon density. 3. In streams with few or no salmon, benthic algal and insect biomass were fairly constant throughout the season. However, in streams with more than 0.1 salmon m(-2), algal and insect biomass decreased by an average of 75-85% during salmon spawning. Algal biomass recovered quickly following salmon disturbance, occasionally reaching pre-salmon biomass. In contrast, in streams with more than 0.1 salmon m(-2), aquatic insect populations did not recover to pre-salmon levels within the same season. We observed no positive impacts of salmon on algae or insects via fertilization from carcass nutrients. 4. Salmon, when their populations exceed thresholds in spawning density, are an important component of stream disturbance regimes and influence seasonal dynamics of benthic communities. Human activities that drive salmon densities below threshold densities, as has likely happened in many streams, will lead to altered seasonal dynamics of stream communities. Human activities that alter animal populations that are sources of biogenic disturbance can result in shifts in community dynamics.     

Structure and diversity of shallow soft-bottom benthic macrofauna in the Gulf of Lions (NW Mediterranean)

Samples of soft-sediment macrobenthos from 92 sites between 10 and 50 m depth were used to assess (1) the main soft-bottom macrofauna communities in the Gulf of Lions, (2) the different components of the diversity of benthic macrofauna in this area, and (3) the relevance of the use of major taxonomic groups as surrogates for the analysis of the structure and diversity of total macrofauna. Three main communities were identified by cluster analysis and associated procedures. These communities corresponded well to the assemblages recently identified on the basis of polychaete composition. The α-diversity indices were in accordance with those reported for similar communities in the Mediterranean. Conversely, the β-diversity value was higher than the few other data available in the literature for marine soft-bottom macrofauna. The total number of species in the studied area estimated by the “total species accumulation curve” (TS) method was 2,319, which was only 10% higher than the number obtained by extrapolation of the species–area curve. The similarity matrix based on polychaetes correlated best with the one based on total macrofauna. Polychaetes and crustaceans were also the best surrogates of total macrofauna when assessing α-diversity (except in the case of Δ*). Conversely, molluscs were the best surrogates of total macrofauna β-diversity. Our results show that the choice of an optimal surrogate for total benthic macrofauna depends on the characteristic of the benthic macrofauna to be studied. Moreover, this choice is also dependent on the environment to be studied.     

Variation of scavenger richness and abundance between sites of high and low iceberg scour frequency in Ryder Bay,west Antarctic Peninsula

Physical disturbance, particularly from iceberg scour, is a major structuring force in polar benthic communities at shelf depths. Scouring kills and damages benthic organisms providing food for the abundant scavenging fauna of coastal Antarctic waters. This trophic group is likely to be strongly affected by changes in iceberg scouring. A baited underwater camera system was used to examine the distribution of scavenging fauna in relation to the spatial variation in exposure to iceberg impacts experienced at different iceberg scouring conditions and depths within Ryder Bay. The results indicate that the relationships between depth and scavenger abundance and assemblage composition differed between high and low scour sites. Scavenger abundance increased with depth at high scour sites and fell with depth a low scour sites. There was also significant difference in community composition between sites within each scouring condition. Scavenger species richness also exhibited an increase with depth at most sites consistent with the established pattern of declining iceberg scouring frequency with depth. Shannon–Wiener diversity increased with depth but significantly more steeply in highly scoured sites. Our results suggest that depth and exposure to icebergs interact to shape the scavenger community. The significant differences within the high and low scour groups suggest that other factors remain to be investigated and that there is probably a nonlinear relationship between scouring intensity and the favourability of a site for scavengers.     

Imperfect detection distorts depth‐related trends in marine macrofaunal species richness

Ecology and biodiversity research are underpinned by species richness patterns and their environmental drivers. However, a key topic in this discussion is the accuracy of these patterns which are greatly dependent on species detection probabilities. Due to variations in detection of species, true ecological patterns may be distorted. This is particularly true for subtidal macro‐infaunal communities. We tested three hypothesized relationships between marine benthic macrofaunal diversity and depth using species richness per site estimated with a capture–recapture heterogeneity model that accounts for variable detection probabilities. These metrics were based on data from 42 replicated sites across the continental shelf of the Southern Benguela. Average detection probability decreased with greater depth but species richness increased along the same depth gradient. The conflation of these trends in observed diversity data resulted in a positively near‐linear depth–diversity relationship, while accounting for variable species detection revealed a much stronger relationship. Ignoring species detection in ecosystems with imperfect detection could therefore distort species richness patterns, which has implications for ecological theory, management and conservation.     

Depth distribution of photosynthetic pigments and diatoms in the sediments of a microtidal fjord

The depth distribution of photosynthetic pigments and benthic marine diatoms was investigated in late spring at three different sites on the Swedish west coast. At each site, sediment cores were taken at six depths (7–35 m) by scuba divers. It was hypothesized that (1) living benthic diatoms constitute a substantial part of the benthic microflora even at depths where the light levels are <1% of the surface irradiance, and (2) the changing light environment along the depth gradient will be reflected in (a) the composition of diatom assemblages, and (b) different pigment ratios. Sediment microalgal communities were analysed using epifluorescence microscopy (to study live cells), light microscopy and scanning electron microscopy (diatom preparations), and HPLC (photosynthetic pigments). Pigments were calculated as concentrations (mg m^–2) and as ratios relative to chlorophyll a. Hypothesis (1) was accepted. At 20 m, the irradiance was 0.2% of surface irradiance and at 7 m, 1%. Living (epifluorescent) benthic diatoms were found down to 20 m at all sites. The cell counts corroborated the diatom pigment concentrations, decreasing with depth from 7 to 25 m, levelling out between 25 and 35 m. There were significant positive correlations between chlorophyll a and living (epifluorescent) benthic diatoms and between the diatom pigment fucoxanthin and chlorophyll a. Hypothesis (2) was only partly accepted because it could not be shown that light was the main environmental factor. A principal component analysis on diatom species showed that pelagic forms characterized the deeper locations (25–35 m), and epipelic–epipsammic taxa the shallower sites (7–20 m). Redundancy analyses showed a significant relationship between diatom taxa and environmental factors – temperature, salinity, and light intensities explained 57% of diatom taxa variations.     

Complex metacommunity structure for benthic invertebrates in a low‐diversity coastal system

The majority of studies in metacommunity ecology have focused on systems other than marine benthic ecosystems, thereby providing an impetus to broaden the focus of metacommunity research to comprise marine systems. These systems are more open than many other systems and may thus exhibit relatively less discrete patterns in community structure across space. Metacommunity structure of soft‐sediment benthic invertebrates was examined using a fine‐grained (285 sites) data set collected during one summer across a large spatial extent (1700 km²). We applied the elements of metacommunity structure (EMS) approach, allowing multiple hypothesis of variation in community structure to be tested. We demonstrated several patterns associated with environmental variation and associated processes that could simultaneously assemble species to occur at the sites. A quasi‐Clementsian pattern was observed frequently, suggesting interdependent ecological relationships among species or similar response to an underlying environmental gradient across sites. A quasi‐nested clumped species loss pattern was also observed, which suggests nested habitat specialization. Species richness declined with depth (from 0.5 to 44.8 m). We argue that sensitive species may survive in shallower water, which are more stable with regard to oxygen conditions and present greater habitat complexity, in contrast to deeper waters, which may experience periodic disturbance due to hypoxia. Future studies should better integrate disturbance in terms of temporal dynamics and dispersal rates in the EMS approach. We highlight that shallow water sites may act as sources of recruitment to deeper water sites that are relatively more prone to periodic disturbances due to hypoxia. However, these shallow sites are not currently monitored and should be better prioritized in future conservation strategies in marine systems.     

Coral Reefs at the Northernmost Tip of Borneo: An Assessment of Scleractinian Species Richness Patterns and Benthic Reef Assemblages

The coral reefs at the northernmost tip of Sabah, Borneo will be established under a marine protected area: the Tun Mustapha Park (TMP) by the end of 2015. This area is a passage where the Sulu Sea meets the South China Sea and it is situated at the border of the area of maximum marine biodiversity, the Coral Triangle. The TMP includes fringing and patch reefs established on a relatively shallow sea floor. Surveys were carried out to examine features of the coral reefs in terms of scleractinian species richness, and benthic reef assemblages following the Reef Check substrate categories, with emphasis on hard coral cover. Variation in scleractinian diversity was based on the species composition of coral families Fungiidae (n = 39), Agariciidae (n = 30) and Euphylliidae (n = 15). The number of coral species was highest at reefs with a larger depth gradient i.e. at the periphery of the study area and in the deep South Banggi Channel. Average live hard coral cover across the sites was 49%. Only 7% of the examined reefs had > 75% hard coral cover, while the majority of the reef sites were rated fair (51%) and good (38%). Sites with low coral cover and high rubble fragments are evidence of blast fishing, although the observed damage appeared old. Depth was a dominant factor in influencing the coral species composition and benthic reef communities in the TMP. Besides filling in the information gaps regarding species richness and benthic cover for reef areas that were previously without any data, the results of this study together with information that is already available on the coral reefs of TMP will be used to make informed decisions on zoning plans for conservation priorities in the proposed park.     

The inshore marine ecosystem off the Vestfold Hills,Antarctica

The planktonic, ice/water interface, and benthic communities at three sites off the coast of the Vestfold Hills, Antarctica, were examined over a complete year.The planktonic flora and fauna were composed predominantly of oceanic species with diatoms and copepods the numerically dominant groups. Primary production was largely restricted to the summer months except for epontic algae which developed in spring. The zooplankton exhibited a similar seasonal cycle but lagged some months behind that of the phytoplankton.The ice/water interface (epontic) fauna consisted of species from the plankton and benthos. Copepods were major contributors; however, two amphipod species dominated. Seasonality of the fauna in this habitat was determined by ice formation and breakout, and development of ice algae.Each of the benthic substrates supported a characteristic macrofaunal assemblage, although infaunal amphipods and tanaids were similar at each site. Infauna exhibited a distinct seasonal cycle related to that of the primary producers whereas macrofauna showed no seasonal changes in abundance.Species composition of each community in this coastal antarctic region was comparable with that of similar habitats in other antarctic coastal areas, supporting the circumpolarity of antarctic marine communities.     

Mussels as ecosystem engineers: Their contribution to species richness in a rocky littoral community

Mussels are important ecosystem engineers in marine benthic systems because they aggregate into beds, thus modifying the nature and complexity of the substrate. In this study, we evaluated the contribution of mussels (Brachidontes rodriguezii, Mytilus edulis platensis, and Perna perna) to the benthic species richness of intertidal and shallow subtidal communities at Cerro Verde (Uruguay). We compared the richness of macro-benthic species between mussel-engineered patches and patches without mussels but dominated by algae or barnacles at a landscape scale (all samples), between tidal levels, and between sites distributed along a wave exposition gradient. Overall, we found a net increase in species richness in samples with mussels (35 species), in contrast to samples where mussels were naturally absent or scarce (27 species). The positive trend of the effect did not depend upon tidal level or wave exposition, but its magnitude varied between sites. Within sites, a significant positive effect was detected only at the protected site. Within the mussel-engineered patches, the richness of all macro-faunal groups (total, sessile and mobile) was positively correlated with mussel abundance. This evidence indicates that the mussel beds studied here were important in maintaining species richness at the landscape-level, and highlights that beds of shelled bivalves should not be neglected as conservation targets in marine benthic environments.     

Detecting benthic community differences: Influence of statistical index and season

An accurate assessment of estuarine condition is critical to determining whether there has been a change from baseline or ‘natural’ conditions; benthic communities are routinely used as an ecological endpoint to make this assessment. We addressed two issues, which arise when attempting to detect differences between benthic communities. The first is the varying sensitivity of metrics, e.g. one metric may not be able to detect differences between two communities where another metric can. The second is the influence of season on the detection of differences between benthic communities from different estuarine systems. In this study, benthic communities taken from depositional sites were sampled in three seasons, at three sites within two relatively pristine estuaries located in southern Massachusetts, USA. Statistical comparisons of benthic community data from the two estuaries were made using three common metrics: species richness, Shannon diversity and Bray–Curtis similarity indices. Significant community differences were found depending upon the index. The Bray–Curtis index, using permutation testing, was the only metric that detected differences between estuaries despite disparate seasonal sampling. This suggests that researchers do not need to be overly constrained to sampling in the same season when testing for differences in benthic communities between estuaries. Additionally, we propose an analytical method to identify anthropogenically impacted estuarine systems.     

The soft-bottom macrobenthos of Gray's Reef National Marine Sanctuary and nearby shelf waters off the coast of Georgia, USA

As part of an ongoing ecological assessment of the Gray's Reef National Marine Sanctuary (GRNMS), a 58-km² marine protected area 32 km off the coast of Georgia, USA, surveys of benthic macroinfaunal communities, contaminant levels in sediments and biota, and general habitat conditions were conducted during 2000-2002 at 20 stations within the sanctuary and along three cross-shelf transects in nearby shelf waters. Macroinfaunal community structure and composition exhibited distinct cross-shelf patterns associated with sediment granulometry, depth and possibly other factors related to shoreline proximity (e.g., erosional effects, recruitment of estuarine species). Finer-scale spatial patterns of benthic fauna among stations within the sanctuary appear to be related to proximity to live-bottom habitat and other features of seafloor structure (e.g., rippled vs. flat sand). Population densities of dominant fauna within the sanctuary also varied considerably among years, resulting in shifts in the ranking of dominants at most stations. Chemical contaminants generally were at low background concentrations below probable bioeffect levels and thus are not a likely cause of the observed spatial patterns of benthic fauna. However, trace concentrations of pesticides, PCBs, and PAHs were detectable in sediments and biota throughout the study area, demonstrating that chemicals originating from human activities are capable of reaching the offshore sanctuary environment, possibly from atmospheric deposition or cross-shelf transport of materials outwelled through coastal sounds. Highly diverse infaunal assemblages also were observed within the sanctuary and nearby sites of similar depth, suggesting that the sanctuary is an important reservoir of marine biodiversity. Results of this study should be useful in addressing long-term science and management needs of the GRNMS and in furthering our understanding of broader ecological patterns and dynamics of the surrounding South Atlantic Bight (SAB) ecosystem.     

Quantification of biogenic 3-D structures in marine sediments

Burrow and tube structures of marine infauna were quantified in sediments from cores obtained at 3 depths (75, 95 and 118 m) at 3 occasions over a 1-year period. The benthic communities at the two deeper stations were re-establishing subsequent to re-oxygenation after hypoxic conditions; the shallow station was a reference station unaffected by hypoxia. The benthic macrofauna was simultaneously quantified from sieved grab samples. The sediment cores were frozen and later sliced with a plane in horizontal layers. Biogenic structures in these sections were digitally analysed for numbers, area and volume. Number of tubes and burrows showed a general decline with depth in the sediment. The biogenic structures in the sediment at the reference station increased the sediment-water interface about 1.5 times compared to the surface area. The surface areas of burrows and tubes were 2 to 3 times larger at the reference station than at the deeper stations. The benthic fauna at the 95-m and 118-m stations showed a temporal increase in density and number of species. In contrast, development of biogenic surface areas in the sediment at these stations showed no significant temporal trend during the benthic faunal succession. Relic tubes of Melinna cristata were found throughout the sampling period at the 118-m station. The ecological importance of bioirrigation for biogeochemical processes is discussed.     

Towards an understanding of resilience in isolated coral reefs

In 1998, seawater temperature anomalies led to unprecedented levels of coral bleaching on reefs worldwide. We studied the direct effects of this thermal event on benthic communities and its indirect effects on their associated coral reef fish communities at a group of remote reefs off NW Australia. Long‐term monitoring of benthic and fish assemblages on these reefs allowed us to compare the responses of these communities to coral bleaching using a data series that included 4 years before, and 6 years following, this bleaching event. While bleaching mortality was evident to >30 m depth, it was patchy among the shallower survey sites with decreases in live coral cover ranging from 30% to 90% across seven surveyed locations Within 2 years of the bleaching, hard coral recovery had begun at all sites and by 2003 reef‐wide coral cover had increased to ～39% of its preimpact levels. We exploited this pattern of differential survival of corals among sites, the associated changes in these benthic communities, and their patterns of recovery, to better understand links between benthic community dynamics and their associated fish communities. Temporal changes in the resident fish communities strongly reflected the differential shifts in the benthic communities, but were lagged by 12–18 months. Five years after the bleaching event, the fish communities on five of the seven surveyed locations showed evidence of recovery, however, none had regained their preimpact structures. Analyses of these communities by taxonomic family revealed a range of responses to the disturbance reflective of their life‐histories and trophic and habitat affiliations. The slow but recognizable recovery of this isolated reef system has parallels with other relatively isolated systems that displayed resilience to the 1998 bleaching event, e.g. the Chagos archipelago, but it also contrasts sharply with low levels of resilience documented in other isolated reef systems subject to the same disturbance, e.g. the Seychelles. In this context, our results highlight the significant knowledge gaps remaining in understanding the resilience of these ecosystems to disturbance.