Joseph J. Luczkovich

Organizing and understanding a winter’s seagrass foodweb network through effective trophic levels

Trophic structure of ecosystems is a unifying concept in ecology; however, the quantification of trophic level of individual components has not received the attention one might expect. Ecosystem network analysis provides a format to make several assessments of trophic structure of communities, including the effective trophic level (i.e. non-integer) of these components. We applied network analysis to a Halodule wrightii community in Goose Creek Bay, St. Marks National Wildlife Refuge, Florida, USA, during January and February 1994 where we sampled a wide variety of taxa. Unlike most applications of network analysis, the field sampling design was specific for network construction. From these data and literature values, we constructed and analyzed one of the most complex, highly articulated and site specific foodweb networks to be done. Care was taken to structure the network to reflect best the field data and ecology of populations within the requirements of analysis software. This involved establishing internally consistent rules of data manipulation and compartment aggregation. Special attention was paid to the microbial components of the food web. Consumer compartments comprised effective trophic levels from 2.0 (herbivore/detritivore) to 4.32 (where a level 4.0 represents ‘secondary carnivory’), and these values were used to organize data interpretation. The effective trophic levels of consumers tended to aggregate near integer values, but the spread from integer values increased with increasing level. Detritus and benthic microalgae acted as important sources of food in the extended diets of many consumers. ‘Bottom-up’ control appeared important through mixed trophic impact analysis, and the extent of positive impacts decreased with increasing trophic level. ‘Top-down’ control was limited to a few consumers with relatively large production or biomass relative to their trophic position. Overall, ordering results from various network analysis algorithms by effective trophic level proved useful in highlighting the potential influence of different taxa to trophodynamics. Although the calculation of effective trophic level has been available for some time, its application to the evaluation of other analyses has previously not received due consideration.

DELIMITING SPAWNING AREAS OF WEAKFISH CYNOSCION REGALIS (FAMILY SCIAENIDAE) IN PAMLICO SOUND, NORTH CAROLINA USING PASSIVE HYDROACOUSTIC SURVEYS

ABSTRACT Exact locations of spawning areas used by marine fishes are needed to design marine reserves and estimate spawning stocks. The location of spawning areas of soniferous fishes such as weakfish Cynoscion regalis can be determined by means of passive hydroacoustic surveys. We conducted nocturnal hydrophone surveys at 12 locations in Pamlico Sound in May of 1996 and 1997. Digital audio tapes were made of weakfish “purring” sounds, the tapes were analyzed spectrographically and compared with ichthyoplankton surveys taken at the same stations and times. All weakfish “purring” sounds were recorded at stations near inlets. Maximum sound pressure levels recorded after sunset were 127 dB (re 1 (μPa) for individual weakfish, but reached a maximum of 147 dB when weakfish and other fish were producing sounds simultaneously. The maximum distance that an individual weakfish “purr” can be detected above the background sound, assuming a cylindrical spreading model, is approximately 50 m. There was a strong associ...

Listening to Fish

Abstract Passive acoustics is a rapidly emerging field of marine biology that until recently has received little attention from fisheries scientists and managers. In its simplest form, it is the act of listening to the sounds made by fishes and using that information as an aid in locating fish so that their habitat requirements and behaviors can be studied. We believe that with the advent of new acoustic technologies, passive acoustics will become one of the most important and exciting areas of fisheries research in the next decade. However, a widespread lack of familiarity with the technology, methodologies, and potential of passive acoustics has hampered the growth of the field and limited funding opportunities. Herein, we provide an overview of important new developments in passive acoustics together with a summary of research, hardware, and software needs to advance the field.

The role of ecomorphological studies in the comparative biology of fishes

The goal of an ecomorphological study is to understand the interactions between the morphology of organisms and their ecology. Both the morphology and the ecology presented by an organism are directly or indirectly under the influence of the environmental conditions that the organism experiences and its heritable composition. The development and interpretation of the central element of ecomorphological studies, the comparison between patterns of variation of morphological and ecological characters, depends heavily on the mechanistic framework provided by functional morphological and biomechanical studies. The cause-and-effect hypotheses derived from this comparison can be tested with performance trials. Ecomorphology forms an integral part of comparative biology, along with ecophysiology, behavioral ecology, and evolutionary ecology. Current issues in ecomorphological research that are addressed in this volume include application of a more functional approach to the choice of characters, integration of morphological, behavioral, and physiological information to address adaptation, and the expansion of spatial and temporal (ontogenetic and evolutionary) scales of ecomorphological questions. Future directions for Ecomorphology include broadening the knowledge base, further integration of information from other disciplines, examination of the role of environmental and genetic factors in producing and maintaining ecological and morphological diversity, and application of ecomorphological insights to questions of community structure.

Perspectives on the ecomorphology of bony fishes

The field of ecomorphology has a long history with early roots in Europe. In this half of the century the application of ecomorphology to the biology of fishes has developed in the former Soviet Union, Poland and Czechoslovakia, The Netherlands, and in North America. While the specific approaches vary among countries, many North American studies begin by comparing morphological variation with variation in ecological characteristics at the intra or interspecific levels. These initial correlative studies form the ground work for hypotheses that explore the mechanistic underpinnings of the observed ecomorphological associations. Supporting these mechanistic hypotheses are insights from functional studies which demonstrate the limits to potential resource use resulting from a particular morphology; however, the actual resource use is likely to be more limited due to additional constraints provided by internal (e.g., behavior, physiology) and external (e.g., resource abundance, predator distribution) factors. The results from performance studies in the laboratory or field can be used to test specific ecomorphological hypotheses developed from the initial correlational and functional studies. Such studies may, but rarely do, incorporate an ontogenetic analysis of the ecomorphological association to determine their effect on performance. Finally, input from phylogenetic analyses allow an investigator to examine the evolution of specific features and to assess the rates and directionality of character evolution. The structural and ecological diversity of fishes provides a fertile ground to investigate these interactions. The contributions in this volume highlight some of the specific directions for ecomorphological research covering a variety of biological processes in fishes. These include foraging, locomotion, reproduction, respiration, and sensory systems. Running through these papers are new insights into universal ecomorphological issues, i.e., the relationships between form and ecological role and the factors that modify these relationships.

The influence of oral anatomy on prey selection during the ontogeny of two percoid fishes, Lagodon rhomboides and Centropomus undecimalis

Ontogenetic increases in mouth size and changes in dentition of percoid fishes may affect the size and species of prey selected, thus influencing the fundamental trophic niche. To examine the influence of oral anatomy on prey selectivity by pinfish, Lagodon rhomboides, and snook, Centropomus undecimalis, two co-occurring percoid fishes with contrasting mouth morphologies, the mouth size, dentition, stomach contents, and available prey during ontogeny were quantified. Based on the presence of prey fragments in stomach contents and direct behavioral observation, prey were categorized by the feeding mode used during capture (suction/ramfeeding or biting). Centropomus has a larger size-specific gape than Lagodon during all ontogenetic stages. Although both feeding modes were used by Lagodon during ontogeny, the amount of prey captured using suction/ram-feeding declined and the amount of prey captured by biting increased with standard length. This change in feeding mode was associated with a change in incisor shape and width: Lagodon 40 mm SL possessed wide, flat-topped incisors and significantly increased their selectivity for polychaetes, which are captured by biting. Centropomus used ram-feeding to capture prey at all ontogenetic stages. Size-selective feeding by Centropomus was apparent but could not be due to gape-limitation alone, because average prey body depth was only 45% of gape and was not proportional to absolute mouth size increase during ontogeny. Dietary diversity was greatest during the transition from suction/ram-feeding to biting in Lagodon. Lagodon had a higher dietary diversity at all ontogenetic stages than Centropomus, due in part to Lagodons use of multiple feeding modes.

Passive Acoustics as a Tool in Fisheries Science

Abstract Many fishery biologists that are interested in documenting fish habitat and following the movements and behavior of fishes use acoustic tags. Because over 700 fish species naturally produce low-frequency, species-specific sounds, these can be used as natural acoustic tags. Passive acoustic approaches (monitoring sound-producing fishes with hydrophones) show great promise for gathering data in a noninvasive and continuous manner. In this special section, authors review past studies and contribute new findings based on the concept of passive acoustics, in which the sounds produced by fish are used to identify the species present and quantify their relative abundance. Fish have long been known to produce low-frequency sounds, especially members of the families Sciaenidae, Gadidae, Ictaluridae, Cyprinidae, Batrachoididae, Haemulidae, Lutjanidae, and Serranidae. Passive acoustic methods include the use of low-frequency hydrophones, digital recorders, autonomous recording sonobuoys and data loggers, an...

SOUNDS OF SEX AND DEATH IN THE SEA: BOTTLENOSE DOLPHIN WHISTLES SUPPRESS MATING CHORUSES OF SILVER PERCH

ABSTRACT Prey often exhibit avoidance behaviors when predators are present. We observed diminished loudness of mating choruses of male silver perch Bairdiella chrysoura in spawning areas when vocalizing bottlenose dolphins Tursiops truncatus, which hunt fish acoustically, were present. Experimental playback of bottlenose dolphin sounds revealed that male silver perch mating calls were reduced by an average of 9 dB. This “acoustical avoidance” behavior, demonstrated previously for interactions involving bats hunting insects and frogs, may also be a common phenomenon in acoustically mediated predator-prey interactions in the sea.

Determining the trophic guilds of fishes and macroinvertebrates in a seagrass food web

We established trophic guilds of macroinvertebrate and fish taxa using correspondence analysis and a hierarchical clustering strategy for a seagrass food web in winter in the northeastern Gulf of Mexico. To create the diet matrix, we characterized the trophic linkages of macroinvertebrate and fish taxa present inHalodule wrightii seagrass habitat areas within the St. Marks National Wildlife Refuge (Florida) using binary data, combining dietary links obtained from relevant literature for macroinvertebrates with stomach analysis of common fishes collected during January and February of 1994. Heirarchical average-linkage cluster analysis of the 73 taxa of fishes and macroinvertebrates in the diet matrix yielded 14 clusters with diet similarity ≥ 0.60. We then used correspondence analysis with three factors to jointly plot the coordinates of the consumers (identified by cluster membership) and of the 33 food sources. Correspondence analysis served as a visualization tool for assigning each taxon to one of eight trophic guilds: herbivores, detritivores, suspension feeders, omnivores, molluscivores, meiobenthos consumers, macrobenthos consumers and piscivores. These trophic groups, corss-classified with major taxonomic groups, were further used to develop consumer compartments in a network analysis model of carbon flow in this seagrass ecosystem. The method presented here should greatly improve the development of future network models of food webs by providing an objective procedure for aggregating trophic groups.

Identifying Sciaenid Critical Spawning Habitats by the Use of Passive Acoustics

Abstract Sounds produced by spawning fishes in Pamlico Sound, North Carolina, have been recorded both under captive conditions and in hydrophone and sonobuoy field surveys. These sounds, produced by males, are species specific, are associated with spawning, and are most likely used for advertisement to attract females. Sounds can be discriminated by use of spectral analysis (oscillograms and spectrograms) of recordings, and the peak frequencies produced by each species can be correlated with species and fish size. Sonobuoys were used for passive acoustic surveys, which were “sound truthed” from recordings of captive fishes to determine the timing and location of spawning sites for four species in the family Sciaenidae: Red drum Sciaenops ocellatus, spotted seatrout Cynoscion nebulosus, weakfish C. regalis, and silver perch Bairdiella chrysoura. During May-September 1998, sounds were first detected in the early evening, increased in loudness after sunset, and ended by sunrise. Weakfish and silver perch wer...