How do we protect ocean animals that drift with currents?

A blog post written by students in Bodega Marine Laboratory's Biological Oceanography Class: Sarah, Timothy & Helen (see more on their bios below!)

Sonoma Coast, CA. Photo: Wikipedia Commons

Sonoma Coast, CA. Photo: Wikipedia Commons

You might have heard how energy is transferred from the sun through living organisms to become the food that we eat. Sunlight is used as energy in plants via photosynthesis, cows eat plants, and we eat cows (or at least some of us do). We set aside huge spans of acreage for the cows to eat this grass. These are managed by farmers to ensure their cows get the ultimate choice in grass. But what if these well-picked grass fields drifted away?

In the ocean, organisms that make up the base of the food chain, phytoplankton, are always on the move, shifted around by currents and wind. The animals that rely on phytoplankton as a food source must, therefore, be able to move as well. Zooplankton rely on phytoplankton for food, and also drift around in the ocean hoping to encounter sufficient food to survive. They enter the open ocean when nearshore fish and invertebrates spawn eggs and larvae. As these offspring grow and develop they spend various lengths of time in the water column. Some zooplankton spend only a few hours drifting in the water before settling down into their adult habitats. This creates a challenge for marine ecologists: With the exception of those few species that spend little time in the zooplankton, it is difficult to predict where most marine larvae will end up after spending their youth drifting around in the currents.

Black Rockfish (Wikipedia Commons)

Black Rockfish (Wikipedia Commons)

Larvae of the black rockfish (Sebastes melanops) are residents of the zooplankton that travel in the California Current System. Black rockfish larvae spend a period of 83-174 days in the plankton before settling into their adult habitats. During this time, larvae have been found to disperse as far as 120km from their birthplaces! Unfortunately, like many other species, black rockfish have experienced population crashes due to overharvesting. Since the 1990s adult populations from AK to CA have been in a state of decline. For such species with dwindling adult populations, the supply of larvae and juveniles to appropriate habitats are critical to population persistence. Consequently, black rockfish, as well as many other species are of great concern in marine conservation efforts.

Marine Protected Areas (MPAs) have been employed to reduce pressure on harvested marine species and support the rebound of shrunken population sizes. MPAs are regulated by the government so that all or part of the natural and cultural resources within it can be protected. It is crucial that they are well enforced so that illegal harvesting can be minimized and the MPAs can stay effective.

For those drifting organisms, it is difficult to pick the right size and location to effectively protect them. The MPAs need to be large enough to protect the maximum distance that the larvae move away from their birthplaces as well as account for the route they take, which can be from 50 km to over 100km long. Rather than creating one large MPA, one strategy is to create networks of MPAs. The sites of connected MPAs have to be close enough to be effective, but not so close that they become independently self-sustaining. In many countries, "networks" of MPAs have successfully been created.  In California, MPA network design was adopted in the Master Plan for MPAs in 2008. These reserves directly or indirectly are connected to each other in an ecological sense and take into consideration larval and juvenile dispersal.

Designing MPA networks to protect species with dispersive larval stages is not easy. We need to understand more about the dynamic variations behind their dispersal to understand how the larvae connect the MPA’s to each other. This is why science-based policy design is crucial. It is the foundation of MPA guidelines that attempt to meet the goals of scientists, fisheries, conservationists, and the local community all in the context of our ever-changing global environment.

To learn more, please check out our linked videos above, and the following:

 

About the authors:

Sarah is a UC Davis undergraduate studying wildlife, fish, and conservation biology who wants to bring the ocean and the rest of the natural world into dining room conversations for its and our own preservation.

Timothy is an undergraduate student at UC Davis interested in behavioral adaptations of marine animals and how they related to other organisms

Helen is a second year PhD student at UC Davis, investigating the population ecology and biological oceanography of coastal marine ecosystems with a focus on the behavior and transport of planktonic organisms.

 

For more from students studying at Bodega Marine Laboratory, see below!