Abstract
Temperate subtidal reefs are increasingly exposed to gradual warming and short periods of high temperatures (marine heatwaves; MHWs). These pressures can directly and indirectly affect the mobile invertebrate communities on these reefs. We investigate changes in mobile invertebrate communities from benthic surveys 15 yr apart (1999-2001 vs 2016-2019), spanning a 4° latitudinal gradient in Western Australia (30-34°S), expecting the biggest changes to the communities in the lower latitudes, where the cumulative effect of MHWs and warming is largest. The urchinsCentrostephanus tenuispinus(warm temperate affinity) andPhyllacanthus irregularis(cool temperate affinity) showed trends toward opposite responses over time; whileP. irregularisdensities declined (non-significantly at all sites),C. tenuispinusdensities increased (significantly at one of 3 sites). The magnitude of the responses appeared to decrease with increasing latitude, withC. tenuispinusrecorded in significantly higher densities only at the lowest latitude location. Neither the densities, nor change in density over time of cool temperate gastropodLunella torquatusand urchinHeliocidaris erythrogrammareflected a latitudinal gradient, suggesting other localized factors play a larger role in determining abundances of these species. However, size distributions ofL. torquatuspopulations at the lower latitude locations were clearly impacted by the 2011 MHW, while those at higher latitudes remained relatively consistent. Overall, the biggest changes over time were seen at the warm edge of the temperate ecosystem. As temperatures continue to rise, the magnitude of these changes is not only expected to increase, but also to occur at higher latitudes.
Highlights
Ocean temperatures have been gradually increasing globally for decades, and are projected to continue to rise in the foreseeable future (IPCC 2018)
While the sea surface temperature (SST) anomaly during the marine heatwaves (MHWs) at each location was of comparable magnitude (2− 3°C; Fig. 2B), the higher SSTs at lower latitudes resulted in higher peak temperatures during the MHW (27.97, 26.37, and 24.32°C from low to high latitude; Table 1)
There was a latitudinal gradient seen in the BrayCurtis dissimilarities over time at each location, with dissimilarities decreasing with increasing latitude
Summary
Ocean temperatures have been gradually increasing globally for decades, and are projected to continue to rise in the foreseeable future (IPCC 2018). Mar Ecol Prog Ser 656: 227–238, 2020 most extreme MHWs recorded globally occurred in WA (Pearce & Feng 2013, Wernberg et al 2013a, Wernberg 2020), and was followed by 2 summers of anomalously high temperatures (Caputi et al 2015). When considering both gradual warming and MHWs, Western Australian reefs are among the fastest warming locations in the world (Hobday & Pecl 2014). In temperate WA, Ecklonia radiata is the dominant macroalga, and supports a productive (De Bettignies et al 2013), diverse (Kerswell 2006), and economically valuable ecosystem (Bennett et al 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
