Projects

Predicting the establishment potential of invasive tiger shrimp: The role of competition and predation

End Date: 1/31/17

Dauphin Island Sea Lab’s Jennifer Hill and Kenneth Heck will take a closer look at whether tiger shrimp, Penaeus monodon, are making their way into Alabama’s estuaries. Scientists fear this aggressive invasive species could compete with or even consume the native shrimp in the area.

Hill and Heck will first monitor and track tiger shrimp in the area in conjunction with educational trawling expeditions in Mobile Bay. They will also perform laboratory experiments to identify the preferred habitats of tiger shrimp, to understand whether area predators will provide a natural resistance to their invasion, and to determine whether interspecies contact between native and tiger shrimp will result in higher native shrimp mortality. The scientists will host educational forums about their findings throughout the process so that the public can be kept updated about this new threat to the Gulf ecosystem.

Abstract

Anthropogenic habitat modification and increased globalization have caused an increase in the number of invasive species that disrupt community structure, reduce biodiversity, and cause billions of dollars in damage to the US economy. Recently, tiger shrimp, Penaeus monodon, have been identified as a new threat to Gulf of Mexico estuarine ecosystems. The tiger shrimp’s broad diet, aggressive omnivory, large body size, and overlapping distribution with native shrimp and other invertebrates suggest that this species may compete with or consume native, commercially important shrimp species and be highly disruptive to community structure. However, there is no knowledge of how tiger shrimp interact with local species, or even species in their native range, which impedes predictions of their ecological or economic impacts. Here, we propose experiments to determine: a) the preferred habitats of tiger shrimp; b) whether invasive tiger shrimp will consume or compete with native shrimp species; c) if local predators provide biotic resistance to tiger shrimp invasion; and d) if interspecific interactions between tiger shrimp and native shrimp species result in greater mortality for native shrimp.

We hypothesize that tiger shrimp will competitively dominate native shrimp species and displace them from structured habitats and increase their mortality. In addition to laboratory experiments, we will also utilize the Dauphin Island Sea Lab’s educational trawling trips to establish a fisheries-independent monitoring program and track the local incidence of tiger shrimp. This program performs >140 trawls per year in lower Mobile Bay and has recorded tiger shrimp landings in previous years. This research and monitoring will be beneficial to multiple audiences, including resource and industry managers, academic researchers, and the general public. The independent monitoring program will also simultaneously educate students and teachers about invasive species and their impacts in coastal Alabama and Mississippi.

Objectives

We seek to document the occurrence and preferred habitats of invasive tiger shrimp and their impacts on native species as listed as a Sea Grant research priority for sustainable fisheries. The overall goals of our proposal are to: a) determine if biotic interactions between tiger shrimp and native brown and white shrimp species or their predators provide conditions likely to promote the establishment and proliferation of invasive tiger shrimp; and b) develop an independent assessment of tiger shrimp incidence and abundance in conjunction with ongoing educational programs. Specifically, our objectives are to:

  1. Establish the preferred habitat type of tiger shrimp (Part A. Year 1) 
  2. Examine if invasive tiger shrimp competitively displace or consume native shrimp species in common estuarine habitats (Part A. Year 1)
  3. Identify if tiger shrimp suffer different rates of predator mortality than native shrimp (Part A. Year 2)
  4. Determine if interspecific interactions between native and invasive shrimp species affect their susceptibility to predators (Part A. Year 2)
  5. Develop a fisheries-independent assessment of tiger shrimp incidence and abundance in coastal Alabama (Part B).

Methodology

We seek to document the occurrence and preferred habitats of invasive tiger shrimp and their impacts on native species as listed as a Sea Grant research priority for sustainable fisheries. The overall goals of our proposal are to: a) determine if biotic interactions between tiger shrimp and native brown and white shrimp species or their predators provide conditions likely to promote the establishment and proliferation of invasive tiger shrimp; and b) develop an independent assessment of tiger shrimp incidence and abundance in conjunction with ongoing educational programs. Specifically, our objectives are to:

  1. Establish the preferred habitat type of tiger shrimp (Part A. Year 1)
  2. Examine if invasive tiger shrimp competitively displace or consume native shrimp species in common estuarine habitats (Part A. Year 1) 2) Examine if invasive tiger shrimp competitively displace or consume native shrimp species in common estuarine habitats (Part A. Year 1)
  3. Identify if tiger shrimp suffer different rates of predator mortality than native shrimp (Part A. Year 2)
  4. Determine if interspecific interactions between native and invasive shrimp species affect their susceptibility to predators (Part A. Year 2) 4) Determine if interspecific interactions between native and invasive shrimp species affect their susceptibility to predators (Part A. Year 2)
  5. Develop a fisheries-independent assessment of tiger shrimp incidence and abundance in coastal Alabama (Part B).

Approach Part A: Laboratory experiments examining interspecific interactions of non-native tiger shrimp with native shrimp species and predators

Animal Collection and Maintenance Animal Collection and Maintenance 

Tiger shrimp will be obtained from shrimp aquaculture facilities. Currently, several aquaculture facilities in Hawaii and Florida have and/or can obtain tiger shrimp for scientific research. Since one possible source of the recent tiger shrimp invasion may be accidental release from Caribbean farming and aquaculture facilities (Fofenoff et al. 2003), using farmed shrimp species provides both a simple route to obtain tiger shrimp for research, as well as relevant specimens for interactions with native species.  However, if wild caught species are obtained from educational trawling surveys (Part B), these specimens may be used in experimental trials or compared with farmed tiger shrimp to understand differences in their behavior that may mediate interactions with native shrimp. The life history of tiger shrimp indicates adolescents, sub-adults, and adults often occupy estuarine habitats and littoral zones (Motoh, 1985) where they are likely to overlap with sub-adult and adult native brown and white shrimp (Figure 1; Minello and Zimmerman, 1991).  Thus, both adolescent and adult size classes are appropriate for research, but determination of the size class used will be dependent upon aquaculture availability. The corresponding size classes of both native brown and white shrimp will be collected locally via trawl and seine nets. All shrimp will be maintained in isolated self-contained indoor recirculating seawater systems to prevent any accidental release and overlap among species. Shrimp will be maintained on a diet of frozen brine shrimp and kept a minimum of one week before use in experiments.  All shrimp will be culled at the conclusion of experiments according to IACUC protocols.  both a simple route to obtain tiger shrimp for research, as well as relevant specimens for interactions with native species.  However, if wild caught species are obtained from educational trawling surveys (Part B), these specimens may be used in experimental trials or compared with farmed tiger shrimp to understand differences in their behavior that may mediate interactions with native shrimp. The life history of tiger shrimp indicates adolescents, sub-adults, and adults often occupy estuarine habitats and littoral zones (Motoh, 1985) where they are likely to overlap with sub-adult and adult native brown and white shrimp (Figure 1; Minello and Zimmerman, 1991).  Thus, both adolescent and adult size classes are appropriate for research, but determination of the size class used will be dependent upon aquaculture availability. The corresponding size classes of both native brown and white shrimp will be collected locally via trawl and seine nets. All shrimp will be maintained in isolated self-contained indoor recirculating seawater systems to prevent any accidental release and overlap among species. Shrimp will be maintained on a diet of frozen brine shrimp and kept a minimum of one week before use in experiments.  All shrimp will be culled at the conclusion of experiments according to IACUC protocols.

Year 1: Identifying preferred habitats of tiger shrimp and competitive/predatory interactions with native shrimp

To determine habitat preferences of tiger shrimp and their ability to competitively displace native shrimp from estuarine habitats, we will perform habitat choice experiments between tiger shrimp and native shrimp in a substitutive design (Coen et al. 1981) in three common estuarine habitats: oyster reef (Crassostrea virginica); salt marsh grass (Spartina alterniflora); and seagrass (Halodule wrightii).

Hypotheses: All shrimp species will prefer habitat structure to bare substrates. Tiger shrimp will prefer oyster reef and salt marsh and sea grasses over bare sand substrates and will competitively displace both native brown and white shrimp from structured habitats.

Null hypothesis: Shrimp will distribute themselves amongst habitats equally, regardless of habitat type or species combination.

Alternative hypotheses: Shrimp prefer bare substrates over habitat structure. Native shrimp competitively displace tiger shrimp from preferred habitats.

Oyster reef clusters, Spartina, and Halodule will be harvested from coastal environments by hand. Oysters will be submersed in fresh water prior to use in experiments in order to remove invertebrate crustaceans and epifauna.  Harvested grasses will be rinsed and planted in tanks at average natural densities.

Mesocosm tanks will be divided into two equal sections with habitat structure on one side and bare sand on the other with a divider between the two sections (Coen et al. 1981). We will then add one of three treatments to the tank: 10 tiger shrimp; 5 tiger shrimp and 5 native shrimp; and 10 native shrimp. Shrimp will initially be placed over the sand habitat and allowed to acclimate for approximately 1 hour, after which the divider will be removed and the experiment will begin. All experimental trials will be recorded via video camera to minimize artifacts from human observers. From videos, we will record the number of shrimp in each habitat over 10 minute time intervals for approximately 1-3 hours. We will also record behavioral interactions or predation events among shrimp. Potential behavioral interactions that may be documented include antennular flicking, extension of front pereiopods and chelae snapping or other agonistic interactions, burying in substrate, and escape responses (Coen et al. 1981; Kenyon et al. 1995). At least 10 replicates will be run of each treatment with both white and brown shrimp serving as native shrimp species. Ten controls trials consisting of tanks with only bare sand will also be run to examine any potential tanks artifacts that may affect shrimp distribution.  The number of shrimp in each habitat for each treatment will be analyzed by a split plot (or repeated measures) ANOVA. The number of agonistic behaviors or predatory interactions within each treatment will be examined by ANOVA. 

Year 2: Resistance of non-native tiger shrimp to native predators and indirect effects to native shrimp

To examine predation rates on native and non-natives shrimp and the role of interspecific interactions on shrimp predation, we will perform another laboratory mesocosm experiment where tiger shrimp and native shrimp in substitutive combinations will be subject to predation from two common estuarine predators, the blue crab (Callinectes sapidus) and the sub-adult red drum (Sciaenops ocellatus). Both of these predators co-occur in areas common to native brown and white shrimp and consume shrimp (Boothby and Avault, 1971; Overstreet and Heard, 1978; Zimmerman et al. 2002; Mascaro et al. 2003).

Hypotheses: Predators will consume tiger shrimp and native shrimp at equal rates when only one shrimp species is present. In combinations of tiger shrimp and native shrimp, tiger shrimp will displace native shrimp from habitat structure resulting in higher predation rates on native species.

Null hypothesis: Predators will consume all shrimp species equally, regardless of habitat Null hypothesis: Predators will consume all shrimp species equally, regardless of habitat type or species combination.

Alternative hypotheses: Predators will consume tiger shrimp or native shrimp at different rates when only one species is present. Native shrimp will displace tiger shrimp from preferred habitats resulting in higher predation rates on tiger shrimp.

All red drum and blue crab predators will be collected from coastal environments using trawls, traps, and seine nets and will be maintained on a diet of grass shrimp. Predators will be starved 48 hours prior to experiments. Predation experiments will be performed in mesocosm tanks setup similar to previous experiments in either preferred habitats and/or habitats where displacement of native shrimp often occurs. Mesocosm tanks will be divided into two equal sections with habitat structure on one side and bare sand on the other.  Shrimp will then be added to tanks in a substitutive design: 10 tiger shrimp; 5 tiger shrimp and 5 native shrimp; and 10 native shrimp. After 1 hour, either an adult blue crab (>10 cm carapace width) or red drum (15-25 cm total length) will be added to the tank. Predators will be allowed to forage on shrimp for a set time interval where on average approximately 40% of shrimp are consumed.  All trials will be recorded with a video camera to avoid observer artifacts, and  we will record the number of shrimp in each habitat over time, any behavioral interactions that affect predatory outcomes (i.e. antipredator behavior), and the number of each shrimp species consumed. These trials will be performed with both native brown and white shrimp and repeated at least 10 times per treatment. The number of shrimp found in each habitat for each treatment will be analyzed by a split plot (or repeated measures) ANOVA. The number of shrimp consumed by each predator and behavioral metrics among shrimps (i.e. activity, burying, escape responses, aggressive interactions) in each treatment will be examined by ANOVA. 

Approach Part B. Non-commercial assessment of tiger shrimp incidence and abundance

Currently, the incidence of tiger shrimp in coastal waters has been primarily reported by commercial shrimp trawlers in common commercial fishing grounds. As tiger shrimp become more common, commercial shrimp trawlers may be less likely to report invasive species sightings suggesting that independent monitoring will be needed to accurately record the abundance of tiger shrimp. To establish a non-commercial monitoring program, trawling surveys will be performed in conjunction with Dauphin Island Sea Lab’s Discovery Hall Program (DHP) and its University Programs (UP). Each year these programs perform approximately 140 trawling trips in lower Mobile Bay and surrounding areas in conjunction with educational classes for undergraduates and 6th -12th grade students. According to Figure 1, many of these same locations have previously reported sightings of tiger shrimp and several tiger shrimp have already been recovered by educational trawls this year (personal communication, Tina Miller-Way).

In order to use DHP and UP trawls to assess tiger shrimp incidence and abundance, we will coordinate with the educational staff to record the number of trawls performed by the programs, their GPS position, and the trawls in which tiger shrimp are recorded. Educational staff will be trained on the identification of tiger shrimp species and educational “Be on the lookout-BOLO” flyers will be posted on trawling vessels. When tiger shrimp are recovered in a trawl, specimens will be transported to the lab for further identification and data collection. We will document the GPS location, length, and weight of all specimens, and when possible, the general water characteristics (salinity, temperature, oxygen saturation etc.) of the sites where tiger shrimp are found. All tiger shrimp specimens will be frozen for possible later analysis of characteristics such as genetic identification and gut content analysis. If wild-caught tiger shrimp can be recovered and transported to the lab alive, the behavior of wild-caught shrimp can be compared to farmed tiger shrimp used in laboratory experiments to assure accuracy of experimental predictions.

Rationale

Anthropogenic habitat modification, species loss, and increased globalization have paved the way for the introduction of non-native species to new ecosystems around the world (Vitousek et al. 1996; Vitousek et al. 1997; Ricciardi, 2006). Whether these non-native species successfully establish new populations is a result of multiple factors, including the abiotic conditions of their new environment, their life history (reproduction cycle, life span etc.), the size of the introduced population, and the organism’s ability to withstand biotic pressures of competition and predation (Shea and Chesson 2002; Van Kleunen et al. 2010; Pysek and Richardson 2010).  Although only a small fraction of non-native species establish populations and become pests in their new environments, these invasive species are one of the leading causes of declining biodiversity (Vitousek et al. 1997, Sala et al., 2000) and cause approximately $120 billion dollars in economic damage in the US alone and globally inflict damages that amount to approximately 5% of the global gross domestic product (Pimentel et al., 2005).

In freshwater and marine ecosystems, many of these invasive species are crustaceans. Often classified as arthropod generalist predators, these invasive crustaceans consume prey from different trophic levels including other predators, herbivores, and detritivores and are spread by aquaculture, aquarium trades, and shipping traffic (Snyder and Evans, 2006; Weis, 2010). The introduction and establishment of these species can have large impacts on community structure through consumption of a variety of native species, displacement of native species from habitats, and cascading indirect interactions. Notable introductions of crustaceans in the United States include green crabs (Carcinus maenas), purple shore crabs (Hemigrapsus sanguineus), mitten crabs (Eriocheir sinensis), and a number of different freshwater crayfish species (Snyder and Evans, 2006).

Tiger shrimp, Penaeus monodon, have recently been identified as another potentially dangerous invasive crustacean species in the eastern coastal U.S. Although first noted in Alabama waters in 2006, reports of this species in commercial shrimp catches have increased and reached a high of 591 cases nationally (from North Carolina to Texas) in 2011 (Knott et al. 2013). Documented cases of tiger shrimp in Alabama by the Alabama Department of Coastal Natural Resources (ADCNR) reached 55 in 2011 (pers. communication, Craig Newton), whereas incidence in local Mississippi waters were less numerous at 22 (pers. communication, Mike Pursley). As no breeding population of tiger shrimp has been identified and their current source is unknown, this species is not yet considered established. However, the recent rise in incidence is concerning since propagule pressure (i.e., number of animals and frequency of introductions) is a primary predictor of the likelihood of invasive species establishment (Suarez et al. 2005; Colautti et al. 2006).