Expedition rocky reef: Using a remotely operated vehicle to explore the diversity of California’s marine protected areas

Colorful invertebrates cover a rocky habitat inside Sea Lion Gulch State Marine Reserve.
Caitlin Scully

After a month at sea, California Sea Grant and Ocean Protection Council funded researchers pulled into port in San Diego’s Mission Bay. Their expedition took a deep dive to explore one of California’s most diverse offshore ecosystems - rocky reefs. The team, led by former California Sea Grant extension director and Moss Landing Marine Laboratories scientist Rick Starr, is working to establish a better understanding of what organisms live within and beyond the boundaries of California's marine protected areas (MPAs). They return to the same areas on each expedition to look at how the region has changed since the MPAs were put into effect. Their goal is to establish a baseline understanding of how the MPAs are working and make evidence-based recommendations for their management. With the help of a remotely operated vehicle (ROV) the team explores and assesses rocky reefs along the entire length of California. On this expedition they also found a few surprises. 

Multifaceted rocky reef habitats

A rocky reef near Point Conception SMR teems with diverse residents. What lies beyond the well known kelp forests and sandy beaches of California’s coast? The mid-depth rocky reef ecosystem may not make the tourist brochures, but is one of the most important marine habitats in California’s waters. Found at depths of about 100 to 300 feet, these rocky reefs create multifaceted ecosystems that support fish and invertebrates at different life stages. Piles of rubble and and larger rock pinnacles create hiding places, homes, and hunting grounds for a multitude of ecologically and economically important species. 

Rocky reef habitats also experience a much greater likelihood of impact and alteration compared to shallow-water habitats due to the heavy use of trawls, traps, longlines, and gillnets in the deep water. However, little is known about these habitats due to the costs and challenges associated with sampling and monitoring at depth. 

To answer basic questions about what species are present, and determine if the MPAs are protecting habitats and species, California Sea Grant funded a three-year research project in 2019. Summer 2021’s ROV expedition was the final of the series of three.

Gaining an understanding of rocky reefs

The remotely operated vehicle (ROV) was an important tool for the research team. Departing from Crescent City, California’s northernmost town, the team motored slowly south stopping at MPAs along the way. The Marine Applied  Research & Exploration group’s ROV Beagle is one of the team's most important tools for the MPA research project. The Beagle is about the size of a ride-on lawnmower and it’s boxy bright green frame is equipped with vertical and lateral thrusters for maneuverability. It has the capability to dive 3,300 feet and features multiple high definition cameras to record the diversity of marine habitats.

Using the ROV, they explored inside and just outside of the MPAs with over 200 transects, totaling 1,000 km over 30 days. These ROV transect line “flyovers” allow the research team to take video and photos which can then be processed at a later time.

The ROV is just one part of a complexly choreographed dance. Above the surface, the team relies on the expertise of the experienced captains of Outer Limits Charters. Taking into account conditions above and below the waves, the captains must position the research vessel to the correct location and safely maneuver the ship so that the tethered ROV can reach the rocky reefs. Outer Limits Charters has worked with the research team on previous expeditions, and as a stakeholder recognizes the importance of understanding the MPAs from both the conservation and recreational fishing perspectives.

“Working with local fishermen and stakeholders, we have been able to expand our work through a mutual trust that comes from collaboration,” says Dirk Rosen, founder and Executive Director of Marine Applied Research and Exploration. “We all want our oceans to flourish and it means working together, trusting one another, to make it happen.”

The 2021 expedition was influenced by the recent catastrophic loss of kelp forests off of the Northern California coast. The extreme loss of 95% of the kelp forest habitat over the last few years has exposed new rocky seafloor habitats for the ROV team to explore. Many of the transects this year were in shallower waters that were once unnavigable for the ROV due to the dense kelp forests. The team was able to record an ecosystem in transition, capturing a new starting point for how things will change in the future.

“Capturing imagery of our deep-sea ecosystems allows us the opportunity to understand how these systems change and interact overtime” said Andrew Lauermann, Director of Science and Operations with Marine Applied Research and Exploration. “Technology has been a game changer for us - allowing us to regularly visit depths that are unsafe for conventional SCUBA diving. No longer do we wonder how it currently looks, we go and look at it and compare those images to assess changes over time."

Vermilion rockfish inside Farnsworth Offshore State Marine Conservation Area.The team is looking for more than just changes to the habitat, they are also looking for changes in biodiversity. Common to California’s mid-depth rocky reefs, rockfish are an important species for the state’s recreational fishery and are one of the main animals to be observed using the team's visual tools. Vermillion rockfish (Sebastes miniatus) are a long-lived species, and can live to be more than 20 years old and grow to be 22 inches long. MPAs provide safe havens for rockfish to grow larger, and the larger the fish, the more offspring produced—fully grown mature females can produce over 1,600,000 eggs. By protecting larger females with more eggs, it is believed that MPAs can ultimately increase fish populations in the surrounding waters over time.

Rockfish are not the only species of interest, the team was excited to see other, less commonly spotted creatures as well. Sixgill sharks (Hexanchus griseus) were spotted on a dive in the Reading Rock State Marine Reserve, a lesser-known deepwater shark species, Sixgills are one of the widest ranging of all shark species, with a global distribution from northern and temperate areas to the tropics. In the eastern North Pacific, they are found from Alaska’s Aleutian Islands to southern Baja California. The presence of large predators, like sixgill sharks, can be an indicator that a habitat is doing well.

The team was also pleased to find sunflower sea stars (Pycnopodia helianthoides), which had not been spotted at any ROV transect location since 2012. Sunflower sea stars, once regularly seen along California's coast, are one of the top invertebrate predators that keep a multitude of species that affect our deep-water ecosystems in check. The sunflower sea star fell victim to sea star wasting disease and were once common in northern Mexico and along the West Coast of the United States. Sunflower stars were listed as critically endangered by the International Union for Conservation of Nature in late 2020. They hope this may be a sign that the sunflower stars are beginning to slowly bounce back.

Sunflower Star near Sea Lion Gulch.

There were also a few unexpected surprises below the waves, from a previously unknown old shipwreck wrapped in ghostly-looking nets just one mile from shore off Santa Barbara, to airplane engines, and other large marine debris. The team also spotted a pod of orcas feeding on a fresh kill off of Point Arena, a rare and exciting species to spot in California’s waters, and an exhilarating experience for all.

Now that the 2021 expedition has concluded, the research team will begin the process of analyzing the 79 hours of video and 22,000 photos taken during the ROV transects. The research team will then compare the findings with those from previous expeditions and data to determine how things have changed over the last few decades.

Looking to the future

This project contributes to a larger effort to study the effects of marine protected areas in California. Through seven different three-year projects funded by California Sea Grant and the Ocean Protection Council, scientists across the state are comparing changes in marine populations inside and outside of MPAs.

A view of the research vessel from one of the remotely operated vehicle's many cameras.

Data from this research, combined with the knowledge gleaned from the other broader MPA monitoring efforts, will be used to inform marine policy decisions. These collaborative efforts strive to answer ecosystem questions from a multitude of different angles, and in turn, will lead to a better understanding of marine life and processes off of California and inform effective policymaking.