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Marine debris is a global issue with impacts on marine organisms, ecological processes, aesthetics and economies. Consequently, there is increasing interest in quantifying the scale of the problem. Accumulation rates of debris on beaches have been advocated as a useful proxy for at-sea debris loads. However, here we show that past studies may have vastly underestimated the quantity of available debris because sampling was too infrequent. Our study of debris on a small beach in eastern Australia indicates that estimated daily accumulation rates decrease rapidly with increasing intervals between surveys, and the quantity of available debris is underestimated by 50% after only 3 days and by an order of magnitude after 1 month. As few past studies report sampling frequencies of less than a month, estimates of the scale of the marine debris problem need to be critically re-examined and scaled-up accordingly. These results reinforce similar, recent work advocating daily sampling as a standard approach for accurate quantification of available debris in coastal habitats. We outline an alternative approach whereby site-specific accumulation models are generated to correct bias when daily sampling is impractical.

Soft corals from the Dendronephthya genus (family Nephtheidae) can change size over short periods by pumping water into their internal hydroskeletons. However, the drivers behind these size changes are not well understood. In a tidal-dominated estuary in eastern Australia, it was hypothesised that short-term changes in the size of Dendronephthya australis colonies occur in response to changes in tidal currents. This was tested by monitoring colonies over a period of several days using time-lapse photography. Colony extensions of up to 360 % were observed, and size changes exhibited a repeated pattern, with two maxima and two minima occurring in each tidal cycle, matching patterns in semi-diurnal tidal flows. A significant positive correlation between colony size and current velocity was identified, with size changes lagging currents. The results of the study provide valuable new information on the behaviour of D. australis and improve understanding of the environmental requirements for this species.

Intertidal rocky reefs are complex and rich ecosystems that are vulnerable to even the smallest fluctuations in sea level. We modelled habitat loss associated with sea level rise for intertidal rocky reefs using GIS, high-resolution digital imagery, and LIDAR technology at fine-scale resolution (0.1 m per pixel). We used projected sea levels of +0.3 m, +0.5 m and +1.0 m above current Mean Low Tide Level (0.4 m). Habitat loss and changes were analysed for each scenario for five headlands in the Solitary Islands Marine Park (SIMP), Australia. The results indicate that changes to habitat extent will be variable across different shores and will not necessarily result in net loss of area for some habitats. In addition, habitat modification will not follow a regular pattern over the projected sea levels. Two of the headlands included in the study currently have the maximum level of protection within the SIMP. However, these headlands are likely to lose much of the habitat known to support biodiverse assemblages and may not continue to be suitable sanctuaries into the future. The fine-scale approach taken in this study thus provides a protocol not only for modelling habitat modification but also for future proofing conservation measures under a scenario of changing sea levels.

Fish assemblages of unconsolidated sedimentary habitats on continental shelves are poorly described when compared to those of hard substrata. This lack of data restricts the objective management of these extensive benthic habitats. In the context of protecting representative areas of all community types, one important question is the nature of the transition from reefal to sedimentary fish assemblages. We addressed this question using Baited Remote Underwater Videos (BRUVs) to assess fish assemblages of sedimentary habitats at six distances from rocky reefs (0, 25, 50, 100, 200, and 400 m) at four sites in subtropical eastern Australia. Distance from reef was important in determining fish assemblage structure, and there was no overlap between reef sites and sedimentary sites 400 m from reef. While there was a gradient in assemblage structure at intermediate distances, this was not consistent across sites. All sites, however, supported a mixed 'halo' assemblage comprising both reef and sediment species at sampling stations close to reef. BRUVs used in conjunction with high-resolution bathymetric and backscatter spatial data can resolve differences in assemblage structure at small spatial scales (10s to 100s of metres), and has further application in unconsolidated habitats. Unless a 'reef halo' assemblage is being examined, a minimum of 200 m but preferably 400 m distance from any hard substrate is recommended when designing broader-scale assessments of fish assemblages of sedimentary habitats.

Extreme weather events such as floods are becoming more frequent, and pose a substantial threat to Australia’s nearshore marine communities. In March 2021, a 450 km stretch of the eastern NSW coastline experienced a La Niña-related rainfall event over several days, resulting in large volumes of freshwater ingress to marine systems. Port Stephens, an estuary 250 km north of Sydney, recorded its highest week of rainfall on record. This was followed by two more flood events in March 2022 and June 2022. Prior to 2021, the marine-dominant Eastern Port of Port Stephens was home to the world’s largest aggregations of Dendronephthya australis, an endangered species of soft coral endemic to the south-east coast of Australia. Using data from a 2019–2022 D. australis monitoring program in Port Stephens, spanning the unprecedented series of flood events in 2021–2022, we detail the impacts of flood events on the population. Prior to the floods, aggregations of colonies were persisting, and individuals were growing at two of the four monitored sites. However, flooding in March 2021 caused a 91% decline in the remaining areal extent of D. australis. Modelling of likely causative factors highlighted water depth as the most significant environmental variable correlated with coral loss. Corals in shallower waters experienced lower salinity and were the most impacted. Continued monitoring during 2021 and 2022 documented the loss of all remaining aggregations in the estuary after further La Niña-related rainfall events, to the point where D. australis is now on the brink of localised extinction.

The habitat-forming Endangered ‘cauliflower’ soft coral Dendronephthya australis, endemic to South-east Australia, is in rapid decline. To aid future conservation strategies, it is vital to understand the fundamental biological processes of this species, particularly reproduction. This study describes the first records of sexual reproduction and asexual clonal replication, with observations both in aquaria and in the wild. We used a combination of observations including histological analyses of fresh specimens, and images of colonies in situ taken over 19 years, to investigate the reproductive cycle of D. australis. Mature oocytes and spermaries were found to develop within colonies during February/March, 2022. We subsequently closed the life cycle of D. australis from colonies spawned in aquaria, documenting all stages of embryogenesis and larval development through to polyp metamorphosis, and successfully transplanted juvenile colonies back into the field and documented their growth over six months to a maximum 435 polyps in size. We also document autonomous fragmentation events to provide accounts of asexual clonal propagation. These records confirm that D. australis is gonochoric and likely a broadcast spawning species that is also capable of utilising asexual reproduction by clonal replication. Observations of mature gametes support the hypothesis that spawning activity coincides with the seasonal increase in water temperature, and is likely to be a continuous phenomenon over 5 months of the year (November–March). These observations not only contribute to the knowledge base for this species, but also provide invaluable information on reproductive strategies that will support conservation efforts to assist the recovery of D. australis populations.

Marine debris is recognised globally as a key threatening process to marine life, but efforts to address the issue are hampered by the lack of data for many marine habitats. By developing standardised protocols and providing training in their application, we worked with >300 volunteer divers from 11 underwater research groups to document the scale of the subtidal marine debris problem at 120 sites across >1000 km of the coast of NSW, Australia. Sampling consisted of replicated 25×5 m transects in which all debris was identified, counted, and, where appropriate, removed. Sites ranged from estuarine settings adjacent to major population centres, to offshore islands within marine parks. Estuaries and embayments were consistently found to be the most contaminated habitats. Fishing-related items (and especially monofilament and braided fishing line) were most prevalent at the majority of sites, although food and drink items were important contributors at sites adjacent to population centres. The results identified damaging interactions between marine debris and marine biota at some key locations, highlighting the need for management intervention to ensure habitat sustainability. This study reinforces the important contribution that volunteers can make to assessing conservation issues requiring broad-scale data collection. In this case, citizen scientists delivered data that will inform, and help to prioritise, management approaches at both statewide and local scales. These initial data also provide an important baseline for longer-term, volunteer-based monitoring programs.

AIM: High‐latitude coral reef communities composed of tropical, subtropical and temperate species are heralded as climate change refuges for vulnerable tropical coral reef species, giving them high, but as yet unrealized, conservation priority. We review the ecology of subtropical reefs in the context of climate change and evaluate management strategies ensuring both their own continuity and their potential to act as refuges for tropical species. LOCATION: Global high‐latitude coral reef environments. METHODS: We review the literature about refuges management, high‐latitude reefs, climate change effects on reef organisms and the conservation of reefs. RESULTS: High‐latitude coral reef systems are functionally different from their tropical counterparts, characterized by unique biogeographical overlap of taxa at their range margins, endemic species and strong seasonality in species composition. They are shaped by marginal environmental conditions, which are predicted to undergo greater changes than reefs at lower latitudes, resulting in community re‐assembly through range shifts, altered dispersal patterns, survivorship and habitat loss. The combined impact of these changes, however, is difficult to assess, as some effects may be antagonistic. Climate change conservation options include passive management strategies such as no‐take reserves that aim to minimize local disturbances, and active strategies such as relocating populations to refuge sites. Success of active intervention relies on the long‐term persistence of relocated populations, which is unlikely for high‐latitude populations once source tropical populations at lower latitudes are locally extinct. MAIN CONCLUSION: High‐latitude reefs are poised for rapid modification under climate change. Management should anticipate these changes by setting up no‐take reserves on suitable subtropical reefs now to foster ecosystem resilience through reduced anthropogenic impacts. Given the uncertainty over which species will arrive or depart and lack of knowledge about the history of most subtropical reef development, active management is presently not the best use of management resources.

The Sea Slug Census program in Australia engages with citizen scientists to record the diversity and distribution of sea slugs across multiple locations. The program has consistently recorded shifts in distribution patterns but a recent, nine-day census in subtropical eastern Australia recorded unprecedented range extensions of tropical species. Seven species (six chromodorids and one polycerid) were found further south of their previously known distribution with Hypselodoris bertschi being recorded for the first time in Australia. These observations suggested the recent transport of larvae via the East Australian Current with recruitment to coastal sites possibly promoted by a protracted period of strong onshore winds associated with the 2021/22 La Niña in the western Pacific. With the increasing frequency of poleward range extensions of marine taxa, citizen science programs such as the Sea Slug Census provide the opportunity to substantially increase monitoring efforts. Linking with iNaturalist strengthens the value of the observations through online peer review to confirm species identities as well as the incorporation of substantiated (Research Grade) records into international biodiversity databases such as GBIF.

Sea urchins of the genus Tripneustes are among the most abundant and ecologically important pan-tropical marine invertebrates. Recognized as potent ecosystem engineers due to their intense grazing of macroalgae and sea grass and highly valued for their gonads, wild populations of Tripneustes are commercially exploited for fisheries and aquaculture. Recently, a new species, Tripneustes kermadecensis (Bronstein et al. 2017), was described from the southern Pacific Ocean, off the Kermadec Islands, near the tropical/sub-tropical transition zone. Here, we explore the range of Tripneustes and, in particular, T. kermadecensis by morphological and genetic tools to determine whether it also occurs in Australia. We report, for the first time, the presence of a second Tripneustes species, T. kermadecensis, from Australia. We show that T. kermadecensis is in fact highly abundant throughout most of sub-tropical eastern Australia, where it occurs in association with coral and temperate reefs and has been recognized for decades as the ‘lamington sea urchin’. As commercial exploitation and stock-release programs of Tripneustes are rapidly expanding, and as global warming causes tropicalization of eastern Australia, driving the southern expansion of its congener T. gratilla, we call for re-evaluation of the conservation vulnerability of T. kermadecensis along the Australian continent and action by the aquaculture industry to genetically confirm the species identity of stocks in their facilities.