“Don’t go into the light!” – Using Light Traps to Sample Ichthyoplankton

By Amanda Croteau, UF PhD Student

The Original Light Trap

Meroplankton are animals that spend a portion of their lives (larval and early life stages) as plankton. These organisms eventually grow larger and become part of the nekton (animals that are able to swim and move independently of water currents) or benthic communities. Ichthyoplankton are the eggs and larvae of fish. Eggs are passive and dispersed by currents. Initially most larval fish have no or minimal swimming ability. As they develop, they become active swimmers.

It is important to study meroplankton and ichthyoplankton because they are indicators of the spawning population of adults, and the survival or mortality of meroplankton have a direct effect on adult population numbers. Species composition at a given location depends on the spatial distribution and reproductive habits (periodicity, fecundity, etc.) of adults, growth and larval stage duration, and abiotic factors that affect transport (currents, tides, salinity, etc.). Mortality depends on many factors such as predation, disease, food availability, and habitat. Habitat is important because individuals who fail to make it to their correct settlement or juvenile habitat are unlikely to survive. In estuarine environments, freshwater and tidal cycles play key roles in species distribution.

Mangroves and salt marshes provide vital juvenile habitat for many inshore, nearshore, and offshore marine species. Florida’s coastal habitats have been severely impacted by coastal development, and Tampa Bay has lost over 44% of its mangrove and salt marsh habitats (Lewis et al. 1985). Robinson Preserve is one of the largest (197 hectare) mangrove and salt marsh restoration efforts in Tampa Bay. Robinson Preserve was originally a coastal wetland that was ditched and drained in the 1920s for agricultural use. In 2006, tidal flow was restored through connections with Perico Bayou, Palma Sola Bay, and the Manatee River. Restoration also involved the planting of native upland and salt marsh vegetation. However, no efforts were made to supplement the aquatic flora and fauna, rather it was expected that they would colonize the preserve from neighboring populations. Ichthyoplankton and meroplankton abundances were selected as one metric to evaluate the quality of the restored ecosystem as nursery habitat.

Meroplankton and ichthyoplankton can be sampled in a variety of ways including light traps, benthic sleds, Miller high-speed samplers, push nets, tow nets, and light traps. As with any sampling gear, each method has its pros and cons and gear selection should be informed by target taxa, gear bias, and site constraints. Light traps utilize organisms’ natural attraction to light (photopositive) as bait. Photopositive taxa approach and enter the trap and are then funneled into a collection chamber. Light traps also allow you to sample continuously over an entire night at multiple locations.  Robinson Preserve is shallow (generally <2 m), with complex habitat types and obstructions. It is also a no motor zone. Due to these study site constraints, light traps were selected as the most efficient gear to sample ichthyoplankton and meroplankton within the preserve. The light trap designed by Jones (2006) was redesigned for deployment from shore and scaled down for use in shallow, estuarine systems (Figure 1 and 2).


Figure 1. Design of modified light trap. The trap is powered by a battery located on-shore. Fish are attracted by the light source in the entrance chamber. The size of the openings, restrict the size of the organisms that can enter the chamber. Organisms are then funneled into the collection chamber where a mesh screen allows water to exit, but prevents organisms from escaping. Floats keep the trap vertical in the water column, and it is anchored in place. In shallow tidal systems, the depth changes due to incoming and outgoing tides must be considered when placing the trap.


Figure 2. Light trap deployed along mangrove shoreline in Robinson Preserve.

Among the larger organisms (≥3 mm) collected, 18 major taxonomic groups have been identified to date. Overall community composition was dominated by isopods (19%), caridean shrimp (18.2%), fish (15.7%), and parasitic copepods (13.1%), though species assemblages varied by site and season (Figure 3). The greater taxonomic richness in sites 1 and 3 is likely related to their locations. Both of these sites were located in areas with slower currents than in sites 2 and 4, which may have allowed some less mobile species to enter the light traps than in the latter two sites. Larval and settlement stage fish were collected in nearly every sample (Figure 4), including fish from at least 8 families. This is similar to the degree of diversity noted in other light trap studies in similar habitats (Hernandez and Shaw 2003; Strydom 2003). Juvenile mullet (likely Striped Mullet Mugil cephalus) were always present in winter samples, while juvenile clupeids (likely menhaden Brevoortia spp.) were present in the winter and spring, which corresponds well with their respective peak spawning periods within this region.


Figure 3. Ichthyoplankton and meroplankton community composition for each site (1.DK in Mixing Zone, 2.B1 in Palma Sola Bay and Perico Bayou zone, 3.W in Upland Freshwater Drainage zone, and 4.PD in the Manatee River zone) by season.


Figure 4. Ichthyoplankton community composition for each site (1.DK in Mixing Zone, 2.B1 in Palma Sola Bay and Perico Bayou zone, 3.W in Upland Freshwater Drainage zone, and 4.PD in the Manatee River zone) by season.

The use of a modified light trap in Robinson Preserve proved to be an effective method for sampling ichthyoplankton and meroplankton, as well as some other groups. Several fish parasites were collected in large numbers during this study. Juveniles of the parasitic isopod family Cymothidae were by far the most dominant form of isopod present in the light trap samples. Parasitic copepods of the genera Argulus and Caligus were also collected in large numbers. The high abundance of external fish parasites collected with this method may provide a new and efficient means of surveying such taxa in estuarine systems.


Hernandez, F.J., and R. F. Shaw. 2003. Comparison of plankton net and light trap methodologies for sampling larval and juvenile fishes at offshore petroleum platforms and a coastal jetty off Louisiana. American Fisheries Society Symposium 36: 15-38.

Jones, D.L. 2006. Design, construction, and use of a new light trap for sampling larval coral reef fishes. NOAA Technical Memorandum NMFS-SEFSC-544.

Lewis, R. R., R. G. Gilmore, Jr., D. W. Crewz, and W. E. Odum. 1985. Mangrove habitat and fishery resources of Florida. Pages 281-336 in W. Seaman, Jr., editor. Florida aquatic habitat and fishery resources. Florida Chapter, American Fisheries Society, Kissimmee, Florida.

Strydom, N.A. 2003. An assessment of habitat use by larval fishes in a warm temperate estuarine creek using light traps. Estuaries 26(5): 1310-1318.


How to catch a Koi: A failed extraction adventure

By Allison Durland Donahue

UF PhD Student

What do you do when you receive a request from a concerned citizen asking for assistance rescuing her Koi from her neighbor’s pool? You excitedly accept the challenge and begin planning the best way to catch a Koi. You are the expert. You will know how to catch the darn fish when others have not been able to. Enter real life.

Last month, UF’s Aquatic Research Graduate Organization (ARGO) received a request to remove a Koi from a pool. This seemed like an excellent outreach adventure – catching a Koi and teaching citizens about fishing techniques, exotic species, and other fish things.

First question: How did the Koi get in the pool in the first place? Irma. During Irma, this area had major flooding (a creek became a lake). The Koi was moved over a mile with the flood waters. The owner assumed her prized Koi was lost, but her neighbor called with news that there was a Koi in his pool.

Next question: How many avid fisher people does it take to catch a Koi? More than three (plus a shellfish person). The four of us attempted to use our advanced degree trained minds and fishing expertise to design a plan to get the elusive Koi.

The challenge: An oddly shaped, 12-foot deep pool, a Koi that hangs out on the bottom, and three feet of water visibility.


Analyzing the challenge

Extraction method, take one: Deploy a seine with the hopes that the Koi will startle into the net. The seine was stretched across the width of the pool and drug through the water column, catching nothing but leaves.

Extraction method, take two: Use the seine on the surface and an ingeniously crafted seine on the bottom to cover the entire water column. The owners had built their own seine out of bamboo poles and chicken wire. Combined, the two seines could cover the entire water column. Or so we thought.

Extraction method, take three: Tie a weight to the seine to (hopefully) ensure that the net is reaching and staying on the bottom. The trick is to make sure the net is not ever dragging the weight. One person stood on the opposite end of the pool and pulled the weight on the bottom of the pool as the other two pulled the seine. Alas, no fish.

Conclusion: Either that Koi is the smartest Koi ever or it was removed from the pool via natural methods (i.e. an eagle ate it).


The only fish we caught

Even though the extraction failed, we were able to educate the owner about fish health requirements and various fishing methods. We left her with our last method idea: build a seine that is fourteen feet high with limited slack. And with that we hung our fishers’ heads in shame and swore at that elusive Koi.


Amanda Croteau

Amanda Croteau

Amanda is from northern Florida and received her BA in Marine Biology and Environmental Studies from New College of Florida. During an undergraduate internship Amanda became interested in restoration ecology and the human dimensions of conservation. She moved to Gainesville to begin a Master’s program in Natural Resource Recreation at the University of Florida, focusing on how visitors’ knowledge and beliefs affected their depreciative behaviors in a coastal preserve. Following her MS, Amanda began her Ph.D. in Fisheries and Aquatic Sciences at UF. Her dissertation focuses on ecology of a restored coastal preserve (salt marsh, mangrove, and seagrass), colonization and establishment of species assemblages, and assessment of water quality and habitat metrics. Amanda’s primary research interests include coastal ecology, conservation, and habitat restoration.


Vice President

Natalie Simon

Natalie Simon is from New Jersey and received her BS in Marine Sciences from Stockton University. While working at Rutgers’s Haskin Shellfish Research Laboratory as a hatchery technician, she found her love for oysters. Not long after, Natalie moved to Gainesville to attend the University of Florida (UF) for a Master’s degree in Fisheries and Aquatic Sciences and has since stayed to continue her academic career for a PhD. Her research interests include cryogenics, germplasm preservation, and molluscan aquaculture.


Allison Durland Donahou


Allison Durland Donahou is from Seattle, but ran away to warmer, sunnier weather ten years ago and has never looked back. She received her BA from the University of San Diego in Marine Biology and her MS from Nova Southeastern University in Marine Biology and Coastal Zone Management. While working with Alaskan fishing communities as a research assistant with NMFS, she discovered her interest in the human dimensions of fisheries. For her PhD, Allison is trying to tackle the challenge of managing invasive species, specifically examining the effects climate change will have on non-native fish distributions. When she finds “free” time, Allison loves partaking in water sports with her puppies and husband, as well as exploring what Gainesville restaurants have to offer.

University Liason

Lauren Kircher


Lauren is from western New York and received her BS in Marine Biology from University of New Haven. Lauren participated in several fellowships at University of New Haven and University of Southern California, nurturing her love of research. Following her BS, Lauren started a Ph.D. in Integrative Biology at Florida Atlantic University. Her dissertation focuses on natural and anthropogenic environmental influences on the movement of a tropical sportfish (common snook) in St. Lucie estuary. Lauren’s research interests include fisheries, movement ecology, behavioral ecology, and physiology.

Raising Funds to Support Dominican Fisherfolk

As a result of Hurricane Maria most Dominican fisherfolk lost their homes and gear. Please help us sponsor a fisher! $100 will purchase enough gear to get the Dominican fisherfolk back on the water, be able to restart their business and feed their fellow citizens! Each fisher sponsored will receive a kit of line, hooks, gloves etc. 100% of funds raised will go towards purchasing of these kits and I will use my own personal funds to travel to Dominica and manage distrubution.

Dominican fishers are the most helpful, resilient, giving people I have met. Right now they are acting as first responders post Maria and the least we can do is get them back to fishing!


Roger Rottmann Memorial Scholarship

At the 37th Annual Chapter Business meeting of The Florida Chapter of the American Fisheries Society two students recieved the Roger Rottmann Memorial Scholarship.

Award recipients:

  • PhD: Katie Lawson
  • MS: Natalie Simon

The Roger Rottmann Memorial Scholarship was established in memory of Roger Rottmann, one of the first fisheries biologists ever hired by the State of Florida University System. Roger conducted fisheries and aquaculture research for more than 20 years at the University of Florida, producing numerous scientific journal and educational publications and videos.

This scholarship was established to recognize outstanding students enrolled in Florida universities and colleges. Congratulations to our award recipients! #AFS147

Student Social at Lowry Park Zoo

We had a blast last night at the Lowry Park Zoo for the student social! We saw elephants, zebras, giraffes, and more. Students participated in Fisheries Scientist Bingo games to win #AFS147 swag like t-shirt, tumblers, and buffs!

Send us your pics of your zoo expierence to be featured on our blog by emailing Natalie Simon at nsimon921@ufl.edu