Spatial and temporal settlement patterns of blue crab (Callinectes sapidus and Callinectes similis) megalopae in a drought-prone Texas estuary
Graphical abstract
Introduction
Blue crabs (Callinectes sapidus and C. similis) are an important food source for the migratory endangered whooping crane (Gus americana, Linnaeus, 1758) population which overwinters in or near the Aransas National Wildlife Refuge in Texas (Westwood and Chavez-Ramirez, 2005). It is also a major food source for sport finfishes such as black drum (Pogonias cromis, Linnaeus, 1766), red drum (Sciaenops ocellatus, Linnaeus, 1766), and spotted seatrout (Cynoscion nebulosus, Cuvier in Cuvier & Valenciennes, 1830) in Texas bays and estuaries (Scharf and Schlicht, 2000, Vanderkooy 2013). The Atlantic blue crab (C. sapidus) is also regarded as an important commercial fishery throughout its range including Texas (Sutton and Wagner, 2007). Picariello and Rosenberg (2015) reported that 1.9 million pounds of blue crab, valued at 2.3 million dollars, were landed in Texas in 2013. However, the Texas Parks and Wildlife Department (TPWD, 2007) has reported declining commercial landings of Atlantic blue crab in Texas waters since 1987. Many factors could be contributing to the downward population trends such as limited freshwater inflow into the estuarine system (Guillory et al., 2001: Picariello and Rosenberg, 2015), habitat alteration and/or loss (Guillory et al., 2001), reduced larval recruitment (Longley, 1994), and increased predation by regulated sportfishes (Guillory and Prejean, 2001; Picariello and Rosenberg, 2015).
Interest in blue crab population dynamics in South Texas has increased due to their importance in the diet of the endangered whooping crane (Nelson et al., 1996). The whooping crane is the tallest bird in North America and nearly went extinct in the middle of the 20th Century (Urbanek and Lewis, 2015). In 2008, after years of steady population increases, 28 birds died in the winter of 2008–2009 and it was suggested that these deaths were due in part to reduced blue crab populations that resulted from drought conditions and diversions of freshwater from the Guadalupe and San Antonio Rivers (Gulley, 2014).
Atlantic blue crabs undergo a complex life cycle as they transition from larval to adult stages and utilize a variety of habitats including the lower, middle, and upper estuary as well as adjacent nearshore coastal waters of the Gulf of Mexico (Perry and McIlwain, 1986). Zoeae (first larval stage) hatch in the higher salinity waters of the Gulf of Mexico and drift among other plankton for several months undergoing 5–7 zoeal stages until metamorphosing into the megalopae postlarval stage (Epifanio, 2007). Megalopae are then transported into the estuary by nearshore currents, flood tides, and wind driven processes (Tilburg et al., 2009; Epifanio and Garvine, 2001) where they settle into a primarily benthic existence and metamorphose a final time into the juvenile crab stage (Lipcius et al., 1990). As juvenile blue crabs grow and molt to maturity, they tend to utilize less saline shallow waters of the estuary, occupying areas of structured habitats such as seagrass beds, salt marshes, and oyster reefs as well as soft muddy and sandy non-structured substrates (Lipcius et al., 2005). As adults, males prefer less saline waters of the upper estuary whereas female crabs usually occupy the middle to lower estuary with higher salinities. Mating usually occurs in the lower saline waters of the upper estuary, then female blue crabs migrate to the higher saline waters of the lower estuary and adjacent coastal waters of the Gulf of Mexico when ready to release their larvae (Perry and McIlwain, 1986).
Although reduced recruitment of blue crab at the megalopae stage may be a factor contributing to their declining populations in the Mission-Aransas Estuary, very little is known about their recruitment patterns in the area. Larval recruitment may be an especially important component of blue crab population dynamics on the South Texas coast, since connections between local estuaries and the Gulf of Mexico are limited by nearly continuous barrier islands with widely separated narrow passes. The behavioral adaptation that allows weakly swimming planktonic blue crab larvae to be transported from the coastal ocean to estuaries is known as selective tidal-stream transport (Forward et al., 2003). By responding to environmental variables including light, changes in salinity, and turbulence, blue crab larvae move into the estuary by swimming up into the water column during nocturnal flood tides of increasing salinity and remain on the bottom during ebb tides with decreasing salinity. Freshwater inflows into South Texas estuaries are often reduced due to extended periods of drought, increased demand for freshwater by agriculture and municipal purposes, and capture of water in reservoirs (Montagna and Kalke, 1992). These factors lead to increased salinity in South Texas estuaries, and experimental and modeling studies indicate that increased salinity can lead to reduced transport of blue crab larvae by selective tidal-stream transport (Bittler et al., 2014).
A simple but labor-intensive method for estimating the recruitment of blue crab larvae involves the deployment of standardized settlement collectors constructed of an artificial substrate (air-conditioning filter) in a cylindrical design over a 24 h period (Metcalf et al., 1995). A citizen science larval blue crab monitoring project was started in 2012 to better understand the potential role of larval recruitment in the population dynamics of blue crabs in the winter feeding grounds of the whooping crane, and to investigate whether reduced freshwater inflows and resulting hypersalinity in estuaries of south Texas affected larval recruitment. Using settlement collectors this study gained insight into the proportion of blue crab larvae that recruit into the estuary from the Gulf of Mexico, how far these larvae travel into the estuary before metamorphosing into juveniles, and the seasonal pattern of larval recruitment in subtropical south Texas.
Section snippets
Study area
The Mission-Aransas National Estuarine Research Reserve (NERR), located along the south-central coast of Texas, encompasses 751.5 sq. km of terrestrial, wetland and marine habitats characteristic of western Gulf of Mexico estuaries (Diener, 1975; Mission-Aransas NERR, 2015) and includes the Aransas National Wildlife Refuge, winter home to the last wild whooping crane flock. The extensive shallow bays within the reserve boundaries are diverse with an array of complex habitats such as seagrass
Data summary
The complete daily time-series of megalopae settlement for each of the 5 sites analyzed in this study differed greatly in length and temporal coverage (Fig. 3; see also Methods). There were also distinct differences in megalopae settlement between sites (Fig. 3, Table 2). Overall, the average number of megalopae settling on collectors in the open Gulf of Mexico at HC was anywhere from 3 to 5 orders of magnitude higher than the average settlement at the estuary sites. Also, the relative
Discussion
One goal of this study was to gain insight into the recruitment dynamics of blue crab larvae in arid South Texas, examining a hypothesized relationship between periods of drought, high salinity in estuaries and the decline in adult and juvenile blue crab populations, which in turn might reduce food supply to winter flocks of whooping cranes (Gulley, 2014). Due to an extended period of drought during this study and the high variability in crab larvae collected a clear relationship between
Author contribution statement
T.F.W. carried out identification and analysis of crab larvae, assisted with data collection, and contributed to writing and editing the manuscript. L.P.S. performed data analysis and contributed to study design, writing and editing the manuscript. E.J.B. conceived and designed this study, supervised data collection, assisted with data analysis, and contributed to writing and editing the manuscript.
Role of the funding source
The funding sources had no role in study design, collection, analysis and interpretation of data; in the writing of the manuscript or the decision to submit the manuscript for publication.
Declarations of interest
None.
Acknowledgments
This research was funded by the National Oceanic and Atmospheric Administration (NOAA), USA through operations grants to the Mission-Aransas National Estuarine Research Reserve, USA (NA12NOS4200110, NA13NOS4200119, NA14NOS4200129, NA15NOS4200133) and by additional funding provided by the Texas State Aquarium, USA (UTA14-001260). Dr. Zack Darnell and Cammie Hyatt provided technical assistance; Colleen McCue Simpson and Nicole Poulson organized the volunteers. We would especially like to
References (58)
- et al.
Making marine and coastal citizen science matter
Ocean Coast Manag.
(2015) - et al.
Larval transport on the Atlantic continental shelf of North America: a review
Estuar. Coast Shelf Sci.
(2001) - et al.
Photoresponses of crab megalopae in offshore and estuarine waters: implications for transport
J. Exp. Mar. Biol. Ecol.
(1994) - et al.
Blue crab megalopal influx to Chesapeake Bay: evidence for a wind-driven mechanism
Estuar. Coast Shelf Sci.
(1989) - et al.
Density, abundance and survival of the blue crab in seagrass and unstructured salt marsh nurseries of Chesapeake Bay
J. Exp. Mar. Biol. Ecol.
(2005) - et al.
Global change and local solutions: tapping the unrealized potential of citizen science for biodiversity research
Biol. Conserv.
(2015) A study of the blue crab fishery in Louisiana. Louisiana Wildlife and Fisheries Commission
Technical Bulletin
(1972)The Ecology of Blue Crab (Callinectes sapidus) Megalopae in the Mission-Aransas Estuary: Salinity, Settlement and Transport
(2013)- et al.
Freshwater inflows and blue crabs: the influence of salinity on selective tidal stream transport
Mar. Ecol. Prog. Ser.
(2014) National Estuarine Research Reserve System Centralized Data Management Office
(2018)
Citizen science as an ecological research tool: challenges and benefits
Annu. Rev. Ecol. Evol. Syst.
Cooperative Gulf of Mexico Estuarine Inventory and Study, Texas: Area Description NOAA Technical Report NMFS CIRC 393
Larval biology
Settlement of blue crab Callinectes sapidus megalopae in a North Carolina estuary
Mar. Ecol. Prog. Ser.
Effects of environmental cues on metamorphosis of the blue crab Callinectes sapidus
Mar. Ecol. Prog. Ser.
Molting of megalopae from the blue crab Callinectes sapidus: effects of offshore and estuarine cues
Mar. Ecol. Prog. Ser.
Endogenous swimming rhythms of blue crab, Callinectes sapidus, megalopae: effects of offshore and estuarine cues
Mar. Biol.
Selective tidal-stream transport of the blue crab Callinectes sapidus: an overview
Bull. Mar. Sci.
Evaluation of blue crab, Callinectes sapidus, megalopal settlement and condition during the Deepwater Horizon Oil Spill
PLoS One
Red drum predation on blue crabs (Callinectes sapidus)
The Blue Crab Fishery of the Gulf of Mexico, United States: a Regional Management Plan
Fifth circuit decision in the Aransas project v. Shaw: the whooping crane case
Texas Water Journal
Settlement patterns of brachyuran megalopae in a Louisiana estuary
Estuaries
A Study of Migratory Patterns of Fish and Shellfish through a Natural Pass
Planktonic availability, molt stage and settlement of blue crab postlarvae
Mar. Ecol. Prog. Ser.
Settlement of brachyuran postlarvae along the North Carolina coast
Bull. Mar. Sci.
Settlement indices for blue crab megalopae in the York River, Virginia: temporal relationships and statistical efficiency
Bull. Mar. Sci.
Mission-aransas National Estuarine Research Reserve Management Plan 2015-2020
Cited by (6)
Challenges and perspectives for the Brazilian semi-arid coast under global environmental changes
2021, Perspectives in Ecology and ConservationCitation Excerpt :Coastal ecosystems located in warm (>27 °C) semi-arid climates (Fig. 1) are under high-temperature and low-precipitation regimes with high solar radiation and evaporation rates (Huxman et al., 2004; Schwinning et al., 2004; Poulter et al., 2014). Thus, it is common for such environments to present stressful conditions, such as low humidity and hypersalinity (Largier, 2010; Douglas et al., 2021), for many species, which leads to physiological stress related to freshwater scarcity (e.g., high physiological costs of osmoregulation), changes in recruitment rates, and reduced productivity compared to ecosystems not limited by water availability (Weatherall et al., 2018; Breaux et al., 2019; Adame et al., 2020). Moreover, the increased salinity in dry regions may trigger large-scale mortality events of key tropical ecoengineering species (e.g., seagrasses) and/or stress-sensitive species across distinct taxa (e.g., fishes and mangroves) (Johnson et al., 2020).
A Biogeochemical Alkalinity Sink in a Shallow, Semiarid Estuary of the Northwestern Gulf of Mexico
2023, Aquatic GeochemistryResearch of an experimental crane frame
2020, AIP Conference ProceedingsSelection and use of artificial floating wetland habitats for larval Chinese mitten crab in the Yangtze Estuary
2020, Journal of Fishery Sciences of ChinaSelection and use of artificial floating wetland habitats for larval Chinese mitten crab in the Yangtze Estuary
2020, Journal of Fishery Sciences of China