Mapping the impacts of multiple stressors on the decline in kelps along the coast of Victoria, Australia

Abstract

Aim: Kelp forests throughout temperate regions of the world serve as foundation species that play a critical role in sustaining the health and function of marine ecosystems but are experiencing declines in abundance due to a loss in resilience as the ocean climate changes. Ocean warming along southeast Australia has already been linked to dramatic losses of kelp species and is contributing to the range expansion and population increases of two species of sea urchin. This research attempts to understand the impact of multiple stressors on the decline in kelps in this region.Location: Coastal Waters of Victoria, Southeast Australia. Methods:In this study, we use long-term (>20 years) datasets on biological observations across Victorian waters to determine trends in coverage and the impact of multiple environmental variables (oceanography, habitat, and urchin abundances) on two important kelps that serve as foundation species (Phyllospora comosa and Ecklonia radiata) using boosted regression trees. These models were then used to develop predictive distribution models for each species and also to project abundance distributions into the future. Results:We found that both kelp species are decreasing in percent coverage over time with multiple environmental variables contributing to these declines, including increasing temperatures, intensifying wave energy, changes in currents and recruitment patterns, and increases in urchin populations. Additionally, future projections of temperature, wave energy, and urchin populations show that both species will continue to decrease across 62%-94% of their range by 2090. Main conclusions:Long-term biological datasets allowed us to develop maps of the past, current, and future distributions of these important foundation species, providing valuable information to managers for prioritization of areas for targeted urchin management and restoration of kelps. Understanding the environmental factors affecting their distribution helps guide manager restoration investments in regions where kelp populations are most likely to persist in the future.

Population distribution and drivers of habitat use for the Burrunan dolphins, Port Phillip Bay, Australia

“…Therefore, dolphins may prefer to forage in less dense seagrass patches (Mann et al., 2021) or on the edge of seagrass beds, in transitional zones (Allen et al., 2001; Nowacek, 2005), where acoustic detection of prey is more efficient. Infralittoral reefs are key habitats for many fish species because they can provide a source of food and shelter (Davis et al., 2020; Young et al., 2022). Anderson (2003) also found that sand‐associated fish species such as sand flatheads were more common in close proximity to structured rather than completely unvegetated habitats, which further supports findings from Ferrell and Bell (1991) that non‐seagrass fish species are more abundant in sand within 10 m of seagrass (Smith et al., 2008).…”

“…where acoustic detection of prey is more efficient. Infralittoral reefs are key habitats for many fish species because they can provide a source of food and shelter (Davis et al, 2020;Young et al, 2022).…”

Morphological variation of the kelp Ecklonia radiata in northeastern New Zealand and across its Australasian range

“…Although no relationship between temperature and morphology was found, increases in temperature may still impact the effectiveness of morphological adaptations to other stressors. Thermal stress is known to increase tissue fragmentation in kelps (Simonson et al, 2015), therefore increased temperatures may restrict the effectiveness of morphological responses to drag stress , Young et al, 2023. It is also likely that the extent to which such multi-stressor effects will impact Australasian E. radiata will vary across existing environmental gradients.…”

“…The success of E. radiata across its geographical range, and its function as a habitat modifier, is likely related to the species ability to morphologically acclimate to a wide variety of environmental conditions. Despite this, the effects of climate change are already pushing some populations past thresholds where morphological acclimation is effective (Young et al, 2023). Greater synthesis and understanding of the existing variability in E. radiata morphology is therefore of pertinence.…”

Cool-edge populations of the kelp Ecklonia radiata under global ocean change scenarios: strong sensitivity to ocean warming but little effect of ocean acidification

“…Moreover, the gametophyte life stage displays evidence of acclimatization or adaptation to local thermal regimes, with higher thermal optima positively correlated with higher in situ temperatures [41]. Recent modelling work by Young et al [42] demonstrated the potential for declines in E. radiata cover in cool-edge populations of the southeastern Australian state of Victoria, with one of the main drivers being increased sea surface temperatures. However, there is little understanding of the thermal tolerance of E. radiata sporophytes at the physiological level from populations at the cool edge of its distribution, and no studies have assessed whether thermal performance is likely to change with the elevated levels of CO 2 projected under global ocean change.…”