Session 6: Fish
ASEC 205 Moderator: Danielle Aguilar
In 2011 the federal government received a petition to list the Saltmarsh Topminnow under the ESA. This species was believed to occur sporadically in marsh habitat along the Gulf of Mexico, from Galveston Bay, Texas to Escambia Bay, Florida. Past studies document this species occurring in very small isolated populations within the northern Gulf of Mexico. It was believed that the Galveston Bay population represented the western extent of this species. Current long-term coastal fisheries independent monitoring in Texas utilizes bag seines, trawls and gillnets which most likely under samples or cannot capture this species due to gear and habitat bias. Given this species potential limited range in Texas and projected development, subsidence and sea level rise, it is important to describe and document the occurrence and habitat associations of this species. Systematic surveys of coastal tidal creeks and wetlands were conducted during February 2014 to November 2014, and October 2016 to April 2018. Sampling was conducted using common sense seines and Breder Traps from Sabine Lake to Copano Bay. Data on fish community composition, water quality and adjacent land use was recorded. Based on analysis of the occurrence data it is apparent that Saltmarsh Topminnow are more common than previously believed and extend down to the middle coast of Texas. The range of environmental conditions and habitat types were this species are collected are presented along with recommendations for future conservation. Our study concurs with past research describing direct links between Saltmarsh Topminnow abundance and coastal tidal creek habitat associated with middle to lower salinity regimes. This project provided important information needed to conserve and protect Saltmarsh Topminnow within Texas and across the Gulf of Mexico, and will be useful in determining whether ESA listing is warranted.
Thursday, November 8
1:30
Characterization of Saltmarsh Topminnow - Fundulus jenkinsi populations along the Texas coast
George J. Guillen; Jenny Oakley; Cory Scanes; Mandi Gordon
Plastic pollution and the negative consequences of plastics entering marine food webs has gained public attention in recent years. Small pieces of plastic, microplastic (<500 µm), have been found globally in aquatic systems, such as oceans, bays, lakes and rivers. Corpus Christi Bay is a major bay in South Texas, surrounded by a large amount of petroleum-based industries and several cities. One of these cities is Corpus Christi, the 8th largest city in Texas and home to the 6th busiest port in the US. This produces various types of potential microplastic pollution sources. At the same time Corpus Christi Bay is an important juvenile nursery area for several fish species such as redfish (Sciaenops ocellatus), spotted seatrout (Cynoscion nebulosus), Atlantic croaker (Micropogonias undulatus) and anchovies (Anchoa spp). However, a baseline study of microplastic pollution in the water column, ingestion by early juvenile fish and effect on nutritional condition is lacking. Here, we examined the diet of selected species representing different foraging types. The hypothesis tested was, water column filter feeders (Anchoa spp.) will have higher amounts of plastic in their digestive tract than bottom feeders (M. undulatus). Preliminary results show that microplastic pollution is apparent in Corpus Christi Bay and that it is taken up by juvenile fish. Out of 75 fish, ~ 94% had some microplastic in their digestive tract. Blue and black colored fibers were the most abundant with a total of 134 for blue and 120 for black. Waste water treatment plants are the prime suspect to be the source as it is assumed that most of these fibers stem from shedding of clothes and enter the bay through. As a next step, the type of plastics found in the digestive tracts will be determined by a micro Fourier Transform Infra-red system.
Thursday, November 8
1:45
Microplastic in the diet of juvenile fish from Corpus Christi Bay
Polly A. Hajovsky*; Michelle J. Bromschwig; Simon J. Geist
The availability of food in terms of quantity and quality is an important factor regulating survival of early life stages of fishes, as it determines the rate of development of bodily function and somatic growth. Understanding food web interactions during the larval stage is thus an important component of predicting success of larval recruitment to adult fish populations. Coastal inlets pose a potential bottleneck for larval stages of Gulf of Mexico (GoM) fish species that utilize estuarine bays as juvenile nurseries. The trophic relationships among larval fish were investigated for larvae passing through a south Texas coastal inlet connecting the GoM to Corpus Christi Bay, Texas, during the fall spawning season 2017. The objectives of this study were to 1) describe the larval fish food web across the whole range of species collected, 2) determine how much the larval fish food web shifts throughout the fall spawning season, and 3) compare the diet of a representative larval fish species to the available prey field. Food web structure was assessed using δ13C and δ15N stable isotope analysis of selected larval fish species. Diet composition of an abundant species (Atlantic croaker, Micropogonias undulatus) was determined to the lowest taxonomic level possible via stomach content analysis. Stable isotope analysis showed that most larval fish species feed at the same trophic level, but that carbon sources varied among species. Gut content analysis of Atlantic croaker indicated that copepods were the most abundant diet item, and that croaker showed selectivity for certain species of copepods over others.
Thursday, November 8
2:00
Feeding ecology and food web structure of larval fish at a Gulf of Mexico coastal inlet
Michelle J. Bromschwig*; Polly A. Hajovsky; Simon J. Geist
Increased temperatures have allowed the black mangrove (Avicennia germinans) to expand its range and overtake salt marsh habitats typically dominated by smooth cordgrass (Spartina alterniflora) throughout much of the Louisiana coast. As this dramatic shift in dominant ecosystem type occurs over timescales as short as a few years, major questions that must quickly be answered involve the effect of this habitat shift on commercially and culturally important species that rely on these areas as essential to the completion of their life cycle. We assessed effects of this habitat shift on the diet and condition of white shrimp, Litopenaeus setiferus, and brown shrimp, Farfantepenaeus aztecus, in the salt marshes surrounding Port Fourchon, Louisiana, an area currently experiencing rapid mangrove encroachment. Shrimp primarily rely on algae-derived production, not on production derived from the macrophytes themselves, and as a result, resource use and energetic condition of shrimp was not influenced by the type and amount of dominant habitat type present within their home range. However, the structural change from salt marshes to mangroves may affect how shrimp acquire resources to meet their energetic demand. Thus, differences in the underlying variability in the ability of different bays to produce could temper the effect of this habitat shift on resident communities.
Thursday, November 8
2:15
Food web effects of mangrove encroachment on penaeid shrimp
Justin S. Lesser*; Jennifer Doerr; James A. Nelson
Estuaries are a transition zone between riverine and marine habitats, with waters ranging from freshwater to brackish to hyper-saline. This variability provides ideal conditions for the formation and maintenance of a wide range of aquatic habitats, including seagrass beds, saltmarshes, oyster reefs, and mud flats. Within these habitats, fluctuations in environmental conditions can lead to heterogeneity, both in habitat structure and community composition. This project sought to identify the effects of habitat heterogeneity on the biodiversity of estuarine fishes in Espiritu Santo Bay, Texas. Preliminary results indicate that biodiversity varied across sampling sites based on geographic location and varying environmental conditions, specifically temperature and dissolved oxygen. In addition, fish abundance and density were influenced by sampling month, with greater abundances in June and July. The presence and heterogeneity of submerged aquatic vegetation influenced the abundance of dominant fish species (pinfish, silversides, croaker, anchovies, and mojarra), with lesser impacts on overall fish biodiversity. Similar to other estuaries, connections between habitat characteristics and biodiversity suggest that habitat monitoring and protection are important management priorities in the western Gulf of Mexico.
Thursday, November 8
2:30
Influence of habitat heterogeneity on estuarine fish communities in Espiritu Santo Bay, Texas
Mallika R. Beach-Mehrotra*; Jeffrey R. Wozniak; Philip Matich
Predicting population- and ecosystem-level benefits of habitat restoration minimally requires an understanding of the link between the trophic ecology of a species and their use of a habitat. This study combined novel, non-lethal natural tracers of trophic ecology with acoustic tagging techniques to examine spatial and temporal patterns of habitat use of spotted seatrout (Cynoscion nebulosus) on Half Moon Reef (HMR), a recently restored oyster reef in Matagorda Bay, Texas. Forty-one spotted seatrout (408 ± 25 mm total length) were captured at HMR, surgically implanted with acoustic transmitters, and monitored by an array of underwater listening stations from December 2015 to August 2016. Patterns of presence-absence on HMR were strongly influenced by water temperature, and to a lesser extent, salinity and tidal height. Overall, spotted seatrout residency to HMR was low, with fish being present on the reef 24% of days. When present, individual fish exhibited strong site-attachment to small portions of the reef. Residency to HMR increased significantly with size, while scale stable isotope analysis revealed fish exhibiting high residency to HMR occupied significantly smaller isotopic niches. If indeed smaller fish with decreased residency rely upon a wider range of prey items across multiple habitats than larger, more resident individuals, restored oyster reef habitat may be expected to primarily benefit larger spotted seatrout.
Thursday, November 8
2:45