REVIEW: On the Front Line: frontal zones as priority at‐sea conservation areas for mobile marine vertebrates

Abstract

Summary1. Identifying priority areas for marine vertebrate conservation is complex because species of conservation concern are highly mobile, inhabit dynamic habitats and are difficult to monitor. 2. Many marine vertebrates are known to associate with oceanographic fronts -physical interfaces at the transition between water masses -for foraging and migration, making them important candidate sites for conservation. Here, we review associations between marine vertebrates and fronts and how they vary with scale, regional oceanography and foraging ecology. 3. Accessibility, spatiotemporal predictability and relative productivity of front-associated foraging habitats are key aspects of their ecological importance. Predictable mesoscale (10s-100s km) regions of persistent frontal activity ('frontal zones') are particularly significant. 4. Frontal zones are hotspots of overlap between critical habitat and spatially explicit anthropogenic threats, such as the concentration of fisheries activity. As such, they represent tractable conservation units, in which to target measures for threat mitigation. 5. Front mapping via Earth observation (EO) remote sensing facilitates identification and monitoring of these hotspots of vulnerability. Seasonal or climatological products can locate biophysical hotspots, while near-real-time front mapping augments the suite of tools supporting spatially dynamic ocean management. 6. Synthesis and applications. Frontal zones are ecologically important for mobile marine vertebrates. We surmise that relative accessibility, predictability and productivity are key biophysical characteristics of ecologically significant frontal zones in contrasting oceanographic regions. Persistent frontal zones are potential priority conservation areas for multiple marine vertebrate taxa and are easily identifiable through front mapping via EO remote sensing. These insights are useful for marine spatial planning and marine biodiversity conservation, both within Exclusive Economic Zones and in the open oceans.

Unique Sequence of Events Triggers Manta Ray Feeding Frenzy in the Southern Great Barrier Reef, Australia

“…Oceanic fronts concentrate and retain biological productivity resulting from nutrient-enrichment processes, attracting and shaping aggregation patterns of planktivores and other species [28,32]. Many marine vertebrates target oceanic fronts for foraging and migration, making frontal zones important sites for conservation [29,40]. Of particular ecological significance in the oceans are persistent mesoscale frontal zones [29,41,42].…”

“…The dynamic forces involved when two water masses come into proximity act to ensure there is convergence and mixing at their zone of intersection [28]. Tiny, weakly swimming organisms (such as zooplankton) will accumulate at the convergent frontal zone, where the distribution of food particles tends to be highly concentrated, attracting larger nektonic predators [28,29].…”

“…Remotely sensed thermal and ocean colour fronts mark the interface between cool, nutrient-rich upwelled water and surrounding warmer oligotrophic waters [29]. Eddy dynamics are thus essential to the enrichment, concentration and retention of nutrients and planktonic organisms in surface waters [9], with the peripheries of eddies forming fronts that attract and shape the aggregation patterns of planktivores that prey on the plankton [28,[30][31][32].…”

Assessing the Use of Area- and Time-Averaging Based on Known De-correlation Scales to Provide Satellite Derived Sea Surface Temperatures in Coastal Areas

“…However, users should be aware that SST measurements from polar-orbiting satellites (even with no area averaging) may be significantly different from in situ measurements and may not capture the full seasonal variability in short-term changes in temperature (such as the daily temperature ranges observed from the in situ data in this study). Such areas may be of high biological or ecological importance (Scales et al, 2014), thus the suitability of using SST as a proxy for in-water temperature will depend on localized conditions and specific temperature value of interest (e.g., weekly SST versus identifying "frontal" systems). For example, satellite derived measurements (regardless of whether they are areaand/or time-averaged) will not be able to capture the full variability in the ranges of temperatures experienced over short time scales (of hours rather than days) within the dynamic EAC separation zone, where, as previously discussed, warm-and coldcore eddies regularly detach from the EAC poleward flowing jet (Cetina Heredia et al, 2014).…”

The Structuring Role of Marine Life in Open Ocean Habitat: Importance to International Policy

“…Predictable, broad oceanographic features, such as frontal zones, which aggregate nutrients and food and attract predators, offer opportunities to delineate boundaries (Scales et al, 2014). But what exactly defines the habitat?…”