Understanding Fish Habitat in a Tidally Restricted Urban Lagoon

Dr. Christine Whitcraft, California State University, Long Beach
Dr. Christopher Lowe, California State University, Long Beach

Loss of coastal wetlands and their associated services during the past century has been extensive; in California, less than 10% of historical distributions remain intact. In urban Long Beach, the Colorado Lagoon (CO Lagoon) is a human-made feature located within the historical range of Los Cerritos Wetlands, which once boasted over 2,400 acres of coastal wetlands. Today, CO Lagoon is an 18-acre tidal water body connected to Alamitos Bay via a 268 meter long box culvert that runs under a neighboring park. Overall, this culvert restricts the tidal flows to the lagoon and impacts the lagoon’s water and habitat quality.

Culverts can significantly decrease the probability of fish movement among habitat patches if conditions exceed fishes' swimming abilities. Longer culverts, like the one at CO Lagoon, require fish to maintain speed for extended periods of time, leading to increased energy expenditure. In addition, physical or biological conditions at either end of a culvert may dissuade fish from entering or leaving even when passage itself is possible. Such conditions include increased or decreased temperatures, low dissolved oxygen, altered sediment quality, increased turbidity, or low food levels (phytoplankton or invertebrate or prey fish supply).

The CO Lagoon is currently undergoing a substantial restoration project. Phase 1 of the project was completed in July 2012 and involved storm drain redirection and extensive dredging to remove contaminated sediment from the lagoon. Phase 2 of the project (approved by City Council and seeking funding for design) targets improvements to the tidal connection by removing the culvert and replacing it with an open channel habitat. The stated goals of this removal include increasing tidal circulation in CO Lagoon via modification of the tidal connection in order to reduce algal blooms, to improve benthic habitats (such as eelgrass and invertebrates) and to increase habitat quality for fishes.

Dr. Whitcraft and Dr. Lowe will investigate the combination of fish movement and habitat conditions in the CO Lagoon by quantifying the degree of movement of estuarine fish predators between Alamitos Bay and CO Lagoon, and by describing the physical and food supply features to provide mechanistic explanations for these movement patterns. The overall project objective is to determine how, and to what degree, several economically important fish species utilize the newly-dredged CO Lagoon, only connected to Alamitos Bay via the culvert.

From a management perspective, more information is needed about the ecology and restoration status of CO Lagoon to both evaluate a completed dredging project and to advocate for a planned culvert removal that will provide potentially substantial functional boost to the Lagoon. As vice-president of Friends of Colorado Lagoon (http://www.coloradolagoon.org/history.html), Dr. Whitcraft has been directly involved with the planning and implementation of the dredging and restoration at CO Lagoon. Partnering this research with an active community and education organization that focuses on CO Lagoon will greatly facilitate the success of this project. The Lagoon itself and associated education buildings are owned by the State Lands Commission and managed by the City of Long Beach, which supports this proposal (see letter of support).

From the scientific perspective, this project will provide insight into how communities within natural estuarine environments recover from dredging projects and how the connectivity of mobile species between restored and natural habitats impacts transfer of energy within the food web.

For more information on this project, contact Ms. Phyllis Grifman, Associate Director.

2017 Research Update:

Study results show that habitat quality factors such as food availability and water temperature are not driving movements of the fish between the lagoon and the bay by way of the culvert. Rather, a fish’s ability to transit the culvert, which may include their size and swimming ability, is driving movements. Movement patterns showed that many fish were able to move quite freely between both sites and it was noted that the grates, and not the culvert itself, are likely limiting movements of larger fish. This study was shared with the City of Long Beach and helped guide decisions about ongoing restoration plans. Results have also been shared with the interagency review team charged with helping establish a mitigation bank at CO Lagoon. This will determine the monitoring requirements as well as acre credits for the proposed mitigation project that involves that culvert removal. More broadly, study results help us understand the functional recovery of estuaries and improvements for fish from culvert removal.