Mike Van Keulen

Invertebrate coral predators can have a great impact on coral reef communities. Understanding the taxonomy of these corallivorous species, their distributions, behaviour, and ecology, is crucial for effective management of coral reefs. The six currently recognised species of Drupella (Gastropoda: Muricidae) occur in the Indo-Pacific, where they are predominantly obligate corallivores, and three of these species, including D. cornus, are sometimes associated with high levels of coral reef destruction when in elevated densities. Here, we used an integrative approach to delimit species of Drupella. We found evidence to support the presence of two species within the described species D. cornus, one which is widespread across the Indian Ocean and another that is widespread across the Pacific Ocean. We also found support for a previous suggestion that separated D. margariticola into ‘oceanic’ and ‘continental’ species. Our results also show wider geographic distribution for D. fragum and document new distribution records for D. eburnea on the Great Barrier Reef. These findings demonstrate the need for further research to understand the ecological differences between these species. Furthermore, it is important to assess the causes of proposed distributional changes in high-impact Drupella species, including the potential influence of increasing water temperatures.

Seagrass loss is impacting coastal communities globally, and significant efforts are being spent to address this loss through restoration. Yet, the success of restoration projects and methodologies has rarely been assessed over decades. In this case study, we reviewed past and continuing seagrass restoration projects (66 restoration sites from 1990s to 2020s) in Cockburn Sound and Owen Anchorage, temperate Western Australia, to (1) address whether they were successful in rehabilitating seagrasses, (2) whether seagrasses could be restored at appropriate scales, and (3) what the requirements for successful seagrass restoration were. In 2022, 28 individual restoration sites were revisited to establish long-term restoration success. Methods of seagrass restoration included shoots (as sprigs, plugs, cores, and sods), seedlings, and seeds. Approximately 70% of sites revisited in 2022 showed demonstrable success in restoring seagrasses. Project extent ranged from meters to hectare scales, including a study that restored 3 ha using sprigs. In the 2010s, seed-based restoration research became a major success at hectare scales. Pre-existing environmental conditions and processes were extremely important in determining restoration success, which was both site-and time-specific and influenced the choice of restoration methods. Restoration required the environment to be suitable for natural seagrass revegetation, or it needed modification. Researchers' focus on small-scale experiments testing methods across a range of environments has prepared us for scaling up to hectares. In long-lived seagrasses, decades of hysteresis were overcome with restoration, as it assisted natural recovery.

Understanding connectivity in high impact corallivores is crucial for coral reef management. The obligate corallivorous Drupella cornus (Röding, 1798) has caused extensive damage to some Indian Ocean coral reef areas in the last four decades. This study used novel and previously published Cytochrome Oxidase I (COI) sequences to reveal patterns of genetic diversity, phylogeography and connectivity within D. cornus across the Indian Ocean. The genetic compositions of the Western Australian D. cornus groups from Ningaloo Reef, Houtman Abrolhos Islands, and a recently discovered group at Rottnest Island, were analysed and compared to D. cornus groups from the western Indian Ocean (Tanzania and the Gulf of Eilat). The findings indicated that these groups all belong to the same species, except for a few individuals from Rottnest Island, which were excluded from subsequent analyses. No genetically distinct D. cornus groups along the Western Australian coastline were found, whereas molecular population differences were seen between the western Indian Ocean D. cornus groups and the Western Australian D. cornus groups. The molecular differences between the Western Australian and Tanzanian groups were statistically significant; however, there was evidence of historic connections and possibly also occasional long-distance gene flow between these groups. We hypothesise that high-density D. cornus outbreaks have played an important role in the dispersal of this species across Western Australia and, more broadly, the Indian Ocean. This is important as Drupella spp. outbreaks are being reported more frequently in the Indo-Pacific, affecting coral reef health and ecosystem function.

Benthic ecosystem has been widely considered as an important feature of seagrass associated fauna, and its function as a grazer and linkage between primary producers and higher trophic level is well known. Though the importance of benthic fauna in seagrass ecosystems has been indicated in many studies, its biodiversity in spatial scale has often been poorly studied. This study aimed at examining the assemblages and diversity of benthic associated fauna in conservation areas (CA) and non-conservation areas (NCA) across the seagrass meadows in Bali and Lombok. This study found that the assemblages and diversity of benthic fauna greatly varied between the meadows. A total of 430 individuals associated to benthic fauna from 24 species were identified in Bali and Lombok. Of these, Gastropods were the highest class of taxa recorded in this study, followed by Bivalvia, Echinodermata, Decapoda, and Amphipoda. Permutation multivariate analysis of variance (PERMANOVA) revealed a significantly different benthic fauna diversity between sites. Non-metric Multidimensional Scaling (nMDS) and Bray–Curtis analysis showed a clear distinction of benthic fauna assemblages between CA and NCA, both in Bali and Lombok. These results indicated that from spatial perspective, different characteristics of seagrass meadows may represent different biodiversity of associated fauna. These differences might be driven by different anthropogenic pressure and variation of substrates among the meadows which may affect the composition of the benthic fauna ecosystems. The implication of this study was to providing baseline data on guiding the appropriate approach and strategies for management and conservations of seagrass ecosystems.

With increasing sea water temperatures, higher latitude temperate and sub-tropical coral reefs are becoming increasingly tropicalised. Although these cooler areas might offer refuge to tropical species escaping the heat, the reshaping of ecosystems can have devastating effects on the biodiversity in these areas, especially when habitat structure is affected. Recently, feeding aggregations of corallivorous gastropod Drupella cornus, a tropical species capable of large-scale reef degradation, were found at Rottnest Island in Western Australia (32°S). We provide evidence that D. cornus spawned at Rottnest Island for 2 consecutive years in 2021 and 2022, and Drupella veligers from an egg case collected at the island hatched and grew at temperatures in the laboratory that were predominantly lower than those at Rottnest Island at the same time. The spawning was possibly triggered by higher than usual La Niña-associated SSTs during the survey period, or the long period of high sea water temperature anomalies recorded around Rottnest Island. A spawning population of D. cornus can greatly affect these higher latitude reef areas, especially when accompanied by increased heat stress. Monitoring and management should be implemented to further understand what effects a breeding population of D. cornus has on Rottnest Island.

Ruminant farming represents the largest anthropogenic source of methane, a greenhouse gas with ~30 times the global warming potential of carbon dioxide. To reduce enteric methane production in ruminants, macroalgae, such as Asparagopsis (Rhodophyta), have been trialed as feed additives. In vivo trials have reported up to a 98 % reduction in methane from cattle, when Asparagopsis taxiformis is included in their feed at 0.2 % organic matter. These observations have been widely attributed to the high bromoform content of Asparagopsis. However, inclusion of Asparagopsis has also been shown to adversely impact production of volatile fatty acids and feed intake. There are inconsistent results reported in the literature surrounding the effects of bromoform-containing seaweeds on ruminants, with the cause of rumen modification from in vivo trials not fully elucidated. On top of this, there are current difficulties surrounding the cultivation and distribution of Asparagopsis, both presenting barriers to its implementation on large scales. Further, detailed studies are required to implement this technology in a manner that is safe and effective for both animals and humans. This review aims to provide an overview of the current scientific standings of this technology and summarises the areas which require further investigation.

Sea urchins are keystone herbivores in many marine benthic habitats and can significantly influence coral-algae phase shifts and reef carbonate budgets. Hall Bank Reef in Western Australia is a unique high latitude reef with high hermatypic coral cover but lacking macroalgae and soft corals. Since the reef status is thought to result from grazing of the urchin Centrostephanus tenuispinus, this study was focused on evaluating bio-erosion by C. tenuispinus with respect to size structure and seasonality. Monthly samples of urchins were collected during 2014–2016 and gut composition was analysed. Gut evacuation rates were calculated using urchins dissected at time intervals up to 96 h. Reworked CaCO3 was calculated using caged urchins in a nearby seagrass bed. Mean percentages of organic, CaCO3, and siliceous components in C. tenuispinus gut contents were 86.3 ± 3.2, 10.3 ± 2.8, and 3.4 ± 1.5%, respectively. Gut evacuation rates for autumn, winter, spring, and summer were 0.70, 0.24, 0.48, and 0.72 day −1. Bio-erosion rates were significantly higher in summer (3.5 g CaCO3 m−2 day−1) than in winter (1.3 g CaCO3 m−2 day−1) and higher rates recorded for large urchins. Urchin bio-erosion was 1 kg CaCO3 m−2 annum−1. Variation in food ingestion rates in response to seawater temperature changes was found to be the main driver for differences in seasonal bio-erosion rates, which likely contribute to the absence of macroalgae and the maintenance of high coral cover on Hall Bank Reef. This study provides baseline data on bio-erosion by a sea urchin at Hall Bank Reef, which will be essential in monitoring and managing reefs in this region, especially under current trends in climate change.

Seagrass habitats at the Cocos (Keeling) Islands (CKI), a remote atoll in the Indian Ocean, have suffered a catastrophic decline over the last decade. Seagrass monitoring (1996–2020) in relation to dredging and coastal development works (2009 to 2011) provide a historical baseline, and document the decline of mixed tropical seagrass Thalassia hemprichii and macroalgal (predominantly Caulerpa spp.) beds over a decadal scale time series. Attribution of loss to coastal development is confounded by lagoon-wide die-off events in 2007, 2009 and 2012 and high air and water temperatures from 2009 to 2016, with evidence of broad scale changes, visible in satellite imagery between 2006 and 2018. We conclude that up to 80% of seagrass habitats in the CKI lagoon (~1200 ha) have been lost due to multiple stressors including episodic die-off events related to high temperatures and calm conditions, and loss due to sediment disturbance and increased turbidity. Grazing pressure from the resident green sea turtles (Chelonia mydas) may have also exacerbated the loss of seagrass, which in turn poses a dire threat to their ongoing health and survival. This study highlights the fragility of tropical seagrass habitats and the cascading effect of system imbalance as a result of anthropogenic pressures and climate drivers. Although small in comparison to global estimates, the loss of seagrass habitats at CKI could change the entire ecosystem of a remote atoll. Due to the significance of the Thalassia beds for coastal stability, as food for an isolated population of green sea turtles and as a fish nursery, rehabilitation efforts are warranted.

The use of LEDs for the commercial cultivation of macroalgae is becoming commonplace, as is adding value to glass structures such as green houses and aquaculture ponds via the use of transparent photovoltaic cells. The effect on photosynthesis and primary production by down regulating light to the red (600–700 nm) and blue (400–525 nm) parts of the spectrum was assessed on a consortium of two filamentous chlorophyte macroalgae species (Rhizoclonium sp. and Ulothrix sp.). The aim of the study was to determine the optimal wavelength for growth and to assess potential nutrient removal rates in anaerobic digestion piggery effluent. Under red and blue light oxygen evolution was reduced compared to the white light controls (WL = 3.490 > RL = 2.700 > BL = 0.800 mg O2 g biomass−1 h−1). Spectrum-adapted chlorophyll fluorescence results indicated that the highest rETRmax (9.080 ± 0.380 μmol electrons m−2 s−1) occurred when blue light was used. This was 10% greater than rETRmax when red light was used. Both blue and red light grown macroalgae showed significantly higher rETRmax compared to white light. Long-term adaptation to blue light yielded the highest rETRmax (5.550 ± 0.230 μmol electrons m−2 s−1), with an effective quantum yield (Fq/Fm′) of 0.75 ± 0.003. Productivity of the macroalgal consortium was greatest under white light (WL = 0.210 > RL = 0.129, BL = 0.110 g L−1 d−1); however red light yielded a three-fold increase in productivity when standardized against the irradiance received at the Light Harvesting Complex (RL = 6.45 × 10−3 > BL = 4.036 × 10−3 > RL = 2.377 × 10−3 g L−1 d−1 μmol photons m−2 s−1 (±SE)). These results indicate that red light provides the optimal light wavelength for maximum growth of the macroalgal consortium used.