A casual glance at the ocean and you may just see a mass of blue. But take a closer look. There are waves, different colours, and different levels of water clarity. If you could peel back the layer of water, you would see environments that are not entirely alien - like mountains, canyons, forests, grass meadows, sand, mud, and volcanoes. The ocean is a mosaic of the most wondrous and splendid habitats, hosting a magnificent array of life. Whilst the terrain itself may remain fairly stable, the ocean itself moves. It's not just the waves you can see breaking on the beach, nor the movement of the tides, or even those rip currents you really don't want to find yourself stuck in. Beneath the surface, you will also find movement like currents flowing at different depths, upwellings that bring cold, nutrient rich waters to the surface, and internal waves as tall as 244 meters. Sometimes you get two water masses moving either towards or way from each other, creating oceanic fronts.
Broadly speaking there are two types of oceanic fronts. Convergent fronts occur when the masses move towards each other. Here the water tends to be warmer than the surrounding area, and accumulate all sorts of marine critters, algae, and even litter. In divergent fronts, where the water masses are moving away from each other, upwellings are created bringing up nutrients from the deep. These nutrients support phytoplankton growth, which in turn supports zooplankton, which in turn supports other marine life – including species under threat, and species we like to eat. The thing about fronts (as with many oceanographic features) is that they are not necessarily permanent features that remain in the same place. The ocean is dynamic and as a result the habitat for many critters that live in the water column is also dynamic.
Even though it may sound difficult, ocean dynamism isn’t necessarily a barrier to managing our activities in these hotspots of biodiversity. Dynamic ocean management is, as Sara Maxwell from Stanford University succinctly explains*, " management that changes in space and time in response to the shifting nature of the ocean and its users based on the integration of new biological, oceanographic, social and / or economic data " . Recently, Kylie Scales from Plymouth University and colleagues from around the UK have joined a growing number of people (including myself) suggesting that dynamic ocean management is not just an idea worth exploring, but potentially an essential part of ocean management. As for fronts well these, argues Kylie, are ideal candidates for dynamic ocean management.
Although there are two primary types of frontal systems (convergent and divergent), there are many different types. In her paper, Kylie describes a host of these, like the Southern Ocean frontal zones which are more permanent large scale features that support a host of species like penguins, seals, and whales, or more fine scale tidal topographic fronts that form over banks resulting in a layer of phytoplankton (the subsurface chlorophyll maxima). These biodiversity hotspots – especially persistent fronts - are also the focus of activities like fishing. Makes sense right - if you want to fish you go were the fish are. Unfortunately fishing in frontal systems also results in a fair bit of bycatch – the accidental capture of species (or subset of a species, like juveniles) during fishing operations. In fact, bycatch from fishing in these sorts of dynamic hotspots has been heavily implicated in the decline of many of the oceans top predators. It’s not just fishing that’s an issue, Kylie notes. These convergent fronts accumulate debris, and development like oil and gas platforms, and renewable energy installations can occur in frontal systems.
But wait a minute - I said that these fronts don’t necessarily hang about. So if they are dynamic, how do we know where they are to manage our activities in them? Kylie looks at this too, noting that technology like remote sensing, autonomous marine vehicles, and biologging (tagging marine animals with devices that collect movement and environmental data) allow us to uncover the times and places these fronts are, and in particular what species are in them. The idea isn’t far-fetched at all. In Australia, CSIRO scientist Alistair Hobday and colleagues already use remote sensing to reduce bycatch of the critically endangered southern Bluefin tuna (Thunnus maccoyii) as it moves up the east coast of Australia into the grounds of the Eastern Tuna and Billfish Fishery. As for more static front systems, well some of these have been included in static marine protected area design in the UK and the Mediterranean.
We have the technology to implement dynamic ocean management on frontal systems, and we know that there is a need to do so. Of course implementing such measures isn’t straight forward, not least because we still have a lot to learn about the ocean and the species that live in it. Kylie notes that increasing integration between fisheries management, oceanography, remote sensing, and spatial ecology will improve ocean conservation efforts, for the long term persistence of marine species and fisheries.
An open access early view of the paper is published on the online version of the Journal of Applied Ecology. Take a peek of it here http://www.dx.doi.org/10.1111/1365-2664.12330
*Sara’s paper, where this description came from, is currently in review.
An extended version of this article also appeared in Biosphere Magazine.