Physical and biological conditions on a steep intertidal gradient at Rottnest Island,Western Australia

Seven species of grazing molluscs, two littorinids, one nerite, three limpets and one chiton, lived on the vertical intertidal rock wall at the landward edge of the coastal limestone platforms at Rottnest Island, Western Australia. On the average, the vertical ranges of these species overlapped broadly, although a consistent zonation pattern was conspicuous from the platform surface upwards for 2 m. On these vertical intertidal shores, physical and biological conditions were predicted quantitatively from easily made measurements of vertical height on the shore; the percentage of time any shore level was immersed in seawater, the percent weight loss of plaster clods, the standing crop of algae, and the growth rate of the limpet, Notoacmea onychitis, all decreased linearly or semi-logarithmically with increasing height on the shore. The standing crop of animals was greatest, largely due to the presence of the chiton, between 40 and 70 cm from the platform surface and decreased rapidly down the shore and more gradually towards higher shore levels. We interpret this information and the positive correlation between algal production rate, and egestion rate of the animal community at various levels of the shore as evidence supporting the idea that food may be in short supply on these shores.     

The nemerteans (Nemertea) of Rottnest Island, Western Australia

Seventeen species of marine nemerteans are reported from Rottnest Island, Western Australia. Eight new species and four new genera are described and illustrated; these are the heteronemerteans Kohnia rottnestensis gen. et sp. n., Lineus bioculatus sp. n., Lineus gilviceps sp. n., Micrura callima sp. n. and Uricholemma nigricans gen. et sp. n., and the monostiliferous hoplonemerteans Aenigmanemertes norenburgi gen. et spn. n., Crybelonemertes arenicolus gen. et sp. n. and Tetrastemma tristibruna sp. n. A key for the field identification of the nemerteans of Rottnest Island is provided.     

Refugia under threat: Mass bleaching of coral assemblages in high‐latitude eastern Australia

Environmental anomalies that trigger adverse physiological responses and mortality are occurring with increasing frequency due to climate change. At species' range peripheries, environmental anomalies are particularly concerning because species often exist at their environmental tolerance limits and may not be able to migrate to escape unfavourable conditions. Here, we investigated the bleaching response and mortality of 14 coral genera across high‐latitude eastern Australia during a global heat stress event in 2016. We evaluated whether the severity of assemblage‐scale and genus‐level bleaching responses was associated with cumulative heat stress and/or local environmental history, including long‐term mean temperatures during the hottest month of each year (SST_LTMAX), and annual fluctuations in water temperature (SST_VAR) and solar irradiance (PARZ_VAR). The most severely‐bleached genera included species that were either endemic to the region (Pocillopora aliciae) or rare in the tropics (e.g. Porites heronensis). Pocillopora spp., in particular, showed high rates of immediate mortality. Bleaching severity of Pocillopora was high where SST_LTMAX was low or PARZ_VAR was high, whereas bleaching severity of Porites was directly associated with cumulative heat stress. While many tropical Acropora species are extremely vulnerable to bleaching, the Acropora species common at high latitudes, such as A. glauca and A. solitaryensis, showed little incidence of bleaching and immediate mortality. Two other regionally‐abundant genera, Goniastrea and Turbinaria, were also largely unaffected by the thermal anomaly. The severity of assemblage‐scale bleaching responses was poorly explained by the environmental parameters we examined. Instead, the severity of assemblage‐scale bleaching was associated with local differences in species abundance and taxon‐specific bleaching responses. The marked taxonomic disparity in bleaching severity, coupled with high mortality of high‐latitude endemics, point to climate‐driven simplification of assemblage structures and progressive homogenisation of reef functions at these high‐latitude locations.     

Weather and hydrographic conditions associated with coral bleaching: Lee Stocking Island, Bahamas

Thermograph, current-meter, and coastal-weather data from Lee Stocking Island, Exuma Cays, Bahamas, are used to investigate hydrographic and meteorological conditions preceding and during a bleaching event in August 1990. Shelf water temperatures recorded at three locations rise to just over 30 °C. Weather data provide estimates of local heating and cooling by insolation, net outgoing long-wave radiation, and sensible and latent heat fluxes. Weather data do not indicate a period of unusually clear skies during the days and weeks preceding the bleaching event. Rather, calculations suggest that low wind speeds during late July and early August reduced evaporative cooling. A tidal channel near the bleaching site provided a source of hyperpycnal 31 °C water that had been heated in the shallow waters of Great Bahama Bank. Current-meter data suggest an along-shelf transport of water from the mouth of the tidal channel to the bleaching site. A comparison of wind-stress and water-temperature data suggests that a downwelling pattern contributed to heating at the reef by flooding the shelf with warm surface water. Results suggest that heating at the reef was a combination of local warming, enhanced by reduced evaporation, and advective warming resulting from both an along-shelf transport of bank water and a landward across-shelf transport of warm surface water.     

Patterns of scleractinian coral recruitment at Lord Howe Island,an isolated subtropical reef off eastern Australia

Changing oceanic conditions, particularly ocean warming and altered currents, can affect the reproductive success of corals. Improving the knowledge of coral reproductive processes at the marginal range limits of coral reefs is important for understanding the ecology of subtropical coral communities and the potential for coral species to expand their ranges in higher latitudes in the future. The extent of live coral cover around subtropical Lord Howe Island (LHI; 31°33′S, 159°05′E) approximately 600 km off the east coast of Australia, has been relatively stable over the last several decades; however, shifts in dominant species in the adult coral community have been reported. To examine the potential influences of recent altered currents and shifts in dominant scleractinian taxa within this community, this study examined spatial and seasonal variation of coral larval settlement at different habitats within the LHI reef lagoon. The study also assessed whether the assemblage of scleractinian corals settling at LHI has changed between 1990–1991 and 2011–2012. Mean densities of coral settlement in 2011–2012 (230 spat m^?2 yr^?1) were consistent with those reported in 1990–1991 and in other regions. However, changes in taxonomic composition were apparent with increases in the proportion of Acroporidae spat at some sites. Settlement of all taxa was highest over summer months, whereas during winter only one coral spat (Pocilloporidae) was detected. Coral settlement was highest and most taxonomically diverse at sites closest to the reef crest, where mortality of settled spat was also greatest. Rates of settlement were high compared with juvenile densities; hence, post-settlement mortality is also likely to be high. Post-settlement processes, influenced by local environmental conditions, are likely to be very important in structuring the adult coral communities within the LHI reef lagoon.     

Elevated temperatures and bleaching on a high latitude coral reef: the 1988 Bermuda event

Sea temperatures were normal in Bermuda during 1987, when Bermuda escaped the episodes of coral bleaching which were prevalent throughout the Caribbean region. Survey transecs in 1988 on 4–6 m reefs located on the rim margin and on a lagoonal patch reef revealed bleaching only of zoanthids between May and July. Transect and tow surveys in August and September revealed bleaching of several coral species;Millepora alcicornis on rim reefs was the most extensively affected. The frequency of bleaching in this species,Montastrea annularis and perhapsDiploria labyrinthiformis was significantly higher on outer reefs than on inshore reefs. This bleaching period coincided with the longest period of elevated sea temperatures in Bermuda in 38 years (28.9–30.9°C inshore, >28° offshore). By December, when temperatures had returned to normal, bleaching of seleractinians continued, but bleaching ofM. alcicornis on the outer reefs was greatly reduced. Our observations suggest that corals which normally experience wide temperature ranges are less sensitive to thermal stress, and that high-latitude reef corals are sensitive to elevated temperatures which are within the normal thermal range of corals at lower latitudes.     

Diving deeper into the underlying white shark behaviors at Guadalupe Island,Mexico

1. Fine‐scale movement patterns are driven by both biotic (hunting, physiological needs) and abiotic (environmental conditions) factors. The energy balance governs all movement‐related strategic decisions.
2. Marine environments can be better understood by considering the vertical component. From 24 acoustic trackings of 10 white sharks in Guadalupe Island, this study linked, for the first time, horizontal and vertical movement data and inferred six different behavioral states along with movement states, through the use of hidden Markov models, which allowed to draw a comprehensive picture of white shark behavior.
3. Traveling was the most frequent state of behavior for white sharks, carried out mainly at night and twilight. In contrast, area‐restricted searching was the least used, occurring primarily in daylight hours.
4. Time of day, distance to shore, total shark length, and, to a lesser extent, tide phase affected behavioral states. Chumming activity reversed, in the short term and in a nonpermanent way, the behavioral pattern to a general diel vertical pattern.

     

Spatiotemporal patterns of coral disease prevalence on Heron Island,Great Barrier Reef,Australia

Despite increasing research effort on coral diseases, little is known about factors driving disease dynamics on the Great Barrier Reef (GBR). This is the first study to investigate the temporal patterns of coral disease prevalence and potential drivers of disease around Heron Island, in the southern Capricorn Bunker sector of the GBR. Surveys were conducted in two austral summers and three winters between November 2007 and August 2009 on six sites around the island. Six diseases were detected: brown band syndrome (BrB), growth anomalies (GA), ulcerative white spots (UWS), white syndrome (WS), skeletal eroding band disease (SEB) and black band disease (BBD). The lowest overall mean disease prevalence was 1.87 ± 0.75% (mean ± SE) in November 2007 and the highest 4.22 ± 1.72% in August 2008. There was evidence of seasonality for two diseases: BrB and UWS. This is the first study to report a higher prevalence of BrB in the winter. BrB had a prevalence of 3.29 ± 0.58% in August 2008 and 1.53 ± 0.28% in August 2009, while UWS was the most common syndrome in the summer with a prevalence of 1.12 ± 0.31% in November 2007 and 2.67 ± 0.52% prevalence in January 2008. The prevalence of GAs and SEB did not depend on the season, although the prevalence of GAs increased throughout the study period. WS had a slightly higher prevalence in the summer, but its overall prevalence was low (<0.5%). Sites with high abundance of staghorn Acropora and Montipora were characterised by the highest disease prevalence (12% of Acropora and 3.3% of Montipora species were diseased respectively). These results highlight the correlations between coral disease prevalence, seasonally varying environmental parameters and coral community composition. Given that diseases are likely to reduce the resilience of corals, seasonal patterns in disease prevalence deserve further research.     

Mass-transfer-limited nitrate uptake on a coral reef flat,Warraber Island,Torres Strait,Australia

Previous research has identified a relationship between the rate of dissipation of turbulent kinetic energy, , and the mass-transfer-limited rate of uptake by a surface, herein called the ^1/4 law, and suggests this law may be applicable to nutrient uptake on coral reefs. To test this suggestion, nitrate uptake rate and gravitational potential energy loss have been measured for a section of Warraber Island reef flat, Torres Strait, northern Australia. The reef flat section is 3 km long, with a 3 m tidal range, and on the days measured, subject to 6 m s^–1 tradewinds. The measured nitrate uptake coefficient, S , on two consecutive days during the rising tide was 1.23±0.28 and 1.42±0.52×10^–4 m s^–1. The measured loss of gravitational potential energy across the reef flat, GPE , on the same rising tides over a 178 m section was 208±24 and 161±20 kg m^–1 s^–2. Assuming the GPE is dissipated as turbulent kinetic energy in the water column, and using the ^1/4 law, the mass-transfer-limited nitrate uptake coefficient, S_MTL , on the two days was 1.57±0.03 and 1.45±0.04×10^–4 m s^–1. Nitrate uptake on Warraber Island reef flat is close to the mass-transfer limit, and is determined by oceanographic nitrate concentrations and energy climate.Communicated by B.C. Hatcher     

Habitat associations of juvenile fish at Ningaloo Reef, Western Australia: the importance of coral and algae

Habitat specificity plays a pivotal role in forming community patterns in coral reef fishes, yet considerable uncertainty remains as to the extent of this selectivity, particularly among newly settled recruits. Here we quantified habitat specificity of juvenile coral reef fish at three ecological levels; algal meadows vs. coral reefs, live vs. dead coral and among different coral morphologies. In total, 6979 individuals from 11 families and 56 species were censused along Ningaloo Reef, Western Australia. Juvenile fishes exhibited divergence in habitat use and specialization among species and at all study scales. Despite the close proximity of coral reef and algal meadows (10's of metres) 25 species were unique to coral reef habitats, and seven to algal meadows. Of the seven unique to algal meadows, several species are known to occupy coral reef habitat as adults, suggesting possible ontogenetic shifts in habitat use. Selectivity between live and dead coral was found to be species-specific. In particular, juvenile scarids were found predominantly on the skeletons of dead coral whereas many damsel and butterfly fishes were closely associated with live coral habitat. Among the coral dependent species, coral morphology played a key role in juvenile distribution. Corymbose corals supported a disproportionate number of coral species and individuals relative to their availability, whereas less complex shapes (i.e. massive & encrusting) were rarely used by juvenile fish. Habitat specialisation by juvenile species of ecological and fisheries importance, for a variety of habitat types, argues strongly for the careful conservation and management of multiple habitat types within marine parks, and indicates that the current emphasis on planning conservation using representative habitat areas is warranted. Furthermore, the close association of many juvenile fish with corals susceptible to climate change related disturbances suggests that identifying and protecting reefs resilient to this should be a conservation priority.     

Estimating the role of three mesopredatory fishes in coral reef food webs at Ningaloo Reef,Western Australia

Within the complex food webs that occur on coral reefs, mesopredatory fish consume small-bodied prey and transfer accumulated biomass to other trophic levels. We estimated biomass, growth and mortality rates of three common mesopredators from Ningaloo Reef in Western Australia to calculate their annual turnover rates and potential contribution to local trophic dynamics. Biomass estimates of the serranid Epinephelus rivulatus (4.46 ± 0.76 g m⁻²) were an order of magnitude greater than two smaller-bodied mesopredatory fishes, Pseudochromis fuscus (0.10 ± 0.03 g m⁻²) and Parapercis clathrata (0.23 ± 0.31 g m⁻²). Growth parameters generated from a von Bertalanffy growth function fitted to size-at-age data, however, indicated that mortality rates for the three mesopredators were similar and that 32–55 % of fish survived each year. Consequently, interspecific differences in annual turnover rates among E. rivulatus (1.9 g m⁻² yr⁻¹), Pa. clathrata (0.10 g m⁻² yr⁻¹) and Ps. fuscus (0.07 g m⁻² yr⁻¹) were an artefact of differences in local biomass estimates. The rapid turnover estimates for E. rivulatus suggest this species is an important conduit of energy within the isolated patch reef habitat where it is typically found, while Ps. fuscus and Pa. clathrata channel smaller amounts of energy from specific habitats in the Ningaloo lagoon. Apparent differences in habitat, diet and turnover rates of the three species examined provide an insight into the different roles these species play in coral reef food webs and suggest that life-history traits allow for variability in the local and spatial contribution of these species at Ningaloo Reef. Moreover, calculating turnover rates of a broader suite of fish species from a range of trophic groups will help better define the role of fishes in coral reef trophic dynamics.

     

Short- and long-term movements of painted lobster (Panulirus versicolor) on a coral reef at Northwest Island, Australia

Understanding movements of palinurid (spiny) lobsters is important to fisheries management. However, movement data obtained with mark-capture techniques are often influenced by artefacts (e.g., displacement, tag-loss, tag-induced injury). To avoid these problems, a novel approach was employed to investigate the movements of an important coral reef palinurid, the painted lobster (Panulirus versicolor). Eighty adult individuals were captured by hand near Northwest Island, Australia. Each lobster was tagged internally (with elastomer) and externally (with plastic zip-ties) to enable both short- (1–10 days) and long-term (6–24 months) observations. Shortly thereafter, all lobsters were manually returned to their shelters (dens). After 6–24 months, 44 lobsters were recaptured, giving an overall recapture rate of 55%. All of these individuals were recaptured within 500 m of their original den, thus indicating a high level of site-fidelity for this species. Short-term observations revealed that individuals moved frequently to and from nearby dens, and that male lobsters typically moved further than female lobsters. It is hypothesized that male lobsters move about their home range more actively, perhaps to seek mating opportunities or to defend resources. The significance of these observations is discussed with respect to the management of this important fishery resource.     

High spatial variability in coral bleaching around Moorea (French Polynesia): patterns across locations and water depths

Mass coral bleaching events are one of the main threats to coral reefs. A severe bleaching event impacted Moorea, French Polynesia, between March and July 2002, causing 55+/-14% of colonies to suffer bleaching around the island. However, bleaching varied significantly across coral genera, locations, and as a function of water depth, with a bleaching level as high as 72% at some stations. Corals in deeper water bleached at a higher rate than those in shallow water, and the north coast was more impacted than the west coast. The relatively small scale of variability in bleaching responses probably resulted from the interaction between extrinsic factors, including hydrodynamic condition, and intrinsic factors, such as differential adaptation of the coral/algal association.