Monday, October 26, 2020

Estuary Resiliency Seen Post-Irma

COASTAL CONNECTIONS


Volunteer Sue Miller (left) and Reserve biologist Sarah Norris pull in the trawl net. Photos by Renee Wilson

Volunteer Sue Miller (left) and Reserve biologist Sarah Norris pull in the trawl net. Photos by Renee Wilson

Pat O’Donnell hardly ever pulls up an empty trawl net. As a fish biologist working in the Ten Thousand Islands for the past 20 years, Pat has seen a lot of changes. When he resumed his trawling program two weeks after Hurricane Irma swirled over Southwest Florida, he wasn’t sure what to expect.

Pat and his team of dedicated volunteers have been monitoring fish populations in the Rookery Bay Research Reserve to establish a reference dataset before the Everglades restoration work is fully completed in the Picayune Strand, just north of the Ten Thousand Islands. While many factors play a role for the fish community, the storm and recovery periods were remarkable.

Pat O’Donnell (right) looks through a clump of sponge for small crabs.

Pat O’Donnell (right) looks through a clump of sponge for small crabs.

On the first post-Irma survey trips, the net was empty 11 out of 12 pulls. The one time a fish was present, it was a non-native species of armored catfish (Plecostomos hypostomus). This species is commonly found in roadside canals and other freshwater bodies, but rarely shows up in an estuary where conditions are typically too salty.

Any fish or invertebrates caught in the net are kept in holding tanks until the data is recorded, then released.

Any fish or invertebrates caught in the net are kept in holding tanks until the data is recorded, then released.

In late September, several inches of rain fell across the entire peninsula – nearly a foot of rain fell in a 24-hour period, and as all that water made its way to the Gulf, it significantly diluted the salt water (salinity level) in local estuaries for several days. In addition to altering the salinity, the rainwater draining off the land brought with it an abundance of natural organic material, such as leaves, branches and dirt. This organic debris led to intense decomposition, which temporarily depleted the oxygen in the waters.

This red drum was one of many juvenile fish caught during post- Irma trawls.

This red drum was one of many juvenile fish caught during post- Irma trawls.

Pat believes the resident fish population moved out to open water in response to the lack of oxygen in the estuary. But not all marine creatures are able to seek out more desirable conditions. In addition to the absence of bony fish on September 30, the team did not catch any invertebrate animals. Crabs, shrimp and urchins have historically been very numerous in these trawls, especially in late September, but these species are generally unable to relocate to better conditions like fish can.

This Plecostomus was the only fish caught in the first 12 pulls of the trawl net.

This Plecostomus was the only fish caught in the first 12 pulls of the trawl net.

Salt levels remained lower than average for several weeks, but Pat’s catches soon began returning to a more normal composition. A few species dominated the typical catch, but throughout the recovery period catches became more diverse as oxygen levels rebounded. During the week of October 15, the trawls resulted in a lot more fish than the pre- vious effort. The most abundant was anchovy, but the team also counted mojarras, drums, spotted sea trout, redfish (usually found in freshwater marsh habitats at smaller sizes), toadfish, whiting, sea robin, spadefish, bumpers and even some pink shrimp and blue crabs. Most of the fish caught were juveniles, considered “young of the year,” which speaks to the importance of backwaters as nurseries for estuarine and marine fish.

 

 

Another indication of the post-hurricane recovery is the “bycatch.” While this study is targeting commercially and recreationally important fish and shellfish, the net is not selective, so whatever it encounters along the bottom is recorded as bycatch. Typical bycatch includes algae, sponges and tunicates, which are commonly associated with warmer, late-summer waters, and these were similarly scarce.

Hurricane Irma affected coastal systems in many ways, and it will be years before all the effects are realized. This is the value of having a long-term dataset that allows anomalies and aberrations to be detected before they become trends. This large-scale “change event” quickly impacted the estuary, but recovery was also relatively quick. Within a single month, the system had already begun to correct itself, demonstrating the amazing resiliency that abounds in natural coastal systems.

Rookery Bay Research Reserve protects 110,000 acres of coastal lands and waters between Naples and Everglades National Park. Now celebrating 40 years, the reserve is managed by the Florida Department of Environmental Protection and is one of 29 Research Reserves in NOAA’s national system. Learn more at rookerybay.org.

Renee Wilson is Communications Coordinator at Rookery Bay National Estuarine Research Reserve. She has been a Florida resident since 1986, and joined the staff at the Reserve in 2000.

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