Changes in the abundance and distribution of sav along Florida’s springs coast: a comparison based on aerial photography acquired in 1992 and 1999

Changes in the abundance and distribution of SAV along Florida’s springs coast: a comparison based on aerial photography acquired in 1992 and 1999

Jason A. Hale* and Thomas K. Frazer. University of Florida, Department of Fisheries and Aquatic Sciences, 7922 NW 71st Street, Gainesville, Florida, 32653, USA; e-mail [e-mail]; [e-mail].

Two sets of approximately 100 aerial photographs each were interpreted for SAV coverage along Florida’s Springs Coast (from Anclote Key to the mouth of the Withlacoochee River) to describe differences in abundance and distribution between 1992 and 1999. Both data sets were interpreted using a modified Braun-Blanquet scale of vegetation abundance. The original ground-truth data were collected as estimates of SAV cover per square meter: up to 25% coverage = Braun-Blanquet class 2; 25% - 50% coverage = BB class 3; 50% - 75% coverage = Braun-Blanquet class 4; and greater than 75% coverage per square meter = Braun-Blanquet class 5. This classification scheme is quantitative, can be adapted to changes in project purpose or in response to preliminary accuracy assessments, and is commonly used by other investigators.

We interpreted approximately 1000 km² of benthic habitat from the 1999 set of photographs. About half of this area was determined to have at least 25% SAV coverage, and about one third of the total area was greater than 75% coverage. Over half of SAV coverage in 1999 occurred in water less than about 1 m deep, while approximately 20% occurred in water greater than 2 m in depth. About 750 km² of nearshore bottom was common to the two sets of photographs and available for change analysis. . Approximately twice as much area of SAV thickened as thinned from 1992 to 1999. Notable areas of SAV thinning occurred near Tarpon Springs, as well as areas adjacent to the Weeki Wachee and Crystal rivers. Conversely, SAV adjacent to the Homosassa River and St. Martins Keys thickened between 1992 to 1999. When analyzed with respect to depth intervals, areas thickened exceeded areas thinned by about 2 to 1.

Fragments of the seagrasses Halodule wrightii and Halophila johnsonii as potential recruits in Indian River Lagoon, Florida

Lauren M. Hall,¹* M. Dennis Hanisak,² and Robert W. Virnstein.^{3 1}St. Johns River Water Management District, 525 Community College Pkwy, Palm Bay, FL 32909, USA; ²Harbor Branch Oceanographic Institution, 5600 US1 North, Fort Pierce, FL 34946, USA; ³St. Johns River Water Management District, PO Box 1429, Palatka, FL 32178, USA.

The concept of vegetative seagrass fragments as a dispersal and recruitment mechanism in Indian River Lagoon, Florida has not been explored. Research on the potential of vegetative fragments can help us better understand the ability of seagrass beds to recover from disturbance events. The objectives of this study are to: (1) determine the viability of drifting Halodule wrightii and Halophila johnsonii vegetative fragments as a function of time, (2) examine the seasonal aspect of recruitment potential, (3) determine if the source of the H. johnsonii fragments influences viability (4) determine how fragment position in the water column is influenced by time, and (5) determine the frequency of fragment rooting versus time.

Mesocosm experiments demonstrate that H. wrightii fragments remain viable for up to 4 weeks with a marked decline in success after 2 weeks of drifting during spring. Fall plants had a shorter period of viability with only 5% of fragments remaining viable by week 2. Although the source of the fragment did not influence viability for H. johnsonii, day and season was highly significant, with spring plants remaining viable for up to 4 days and fall remaining viable for twice as long. The short viability of H. johnsonii illustrates the importance of rapid settlement when uprooted from a source bed, limiting dispersal to shorter distances. H. wrightii appears to maintain its viability for a longer period of time, indicating that this species may be able to utilize fragments as a dispersal mechanism over longer distances. The fragments’ positions in the water column followed a trend with a decrease in floating fragments while sediment level and rooting fragments increased over time. Both H. wrightii and H. johnsonii had the ability to settle and root on their own, indicating that this may be a recruitment mechanism occurring for these species.

The effects of zinc on arm regeneration rates and tissue development patterns in the brittlestars Ophiothrix angulata and Amphipholis gracillima

Rosemary E. Hall* and Steve E. Stancyk. Marine Science Program, University of South Carolina, Columbia, SC 29208, USA.

Brittlestars are cosmopolitan echinoderms that are key in ecosystem dynamics. They can influence habitat structure and are important food sources for some fish, crabs, and shrimp. Burrowing species in particular affect infaunal communities by aerating their burrows. Because of their ability to rapidly regenerate injured or autotomized arms, they can also show the effects of toxicants even after a pollutant’s concentration has decreased in the environment. Zinc is of particular interest because it is a common pollutant, yet has a natural role in nervous system and enzyme function. Toxic levels of zinc can be expected to inhibit nervous function and therefore interfere with regeneration. In this investigation, we hope to examine the potential for using regenerating species to observe effects of toxicants in an environment, and to further investigate patterns of regeneration as they may relate to the ophiuroid nervous system. In initial rangefinder experiments, we found that environmentally relevant concentrations of zinc caused rapid mortality. Furthermore, increasing, nonlethal concentrations of zinc were associated with decreasing rates of regeneration in both species.


Using automated sampling equipment and estuary scale modeling to investigate the physical-biological coupling of larval transport

John F. Hamilton,¹* Robert B. Whitlatch,¹ and Richard W. Osman.^{2 1}University of Connecticut, Groton, CT 06340, USA; ²Academy of Natural Sciences, St. Leonard, MD 20685 USA, USA.

For many benthic invertebrates a free-swimming larval stage links a reproductively active adult to the successful establishment of a new sessile individual or colony. Larvae range from those that are long lived and dispersed regionally to those that are short lived and dispersed more locally. For those species with a short lived larval stage, the success at colonizing a suitable habitat may be strongly influenced by the pattern of tidally induced water movement and the availability of reproductively active adults upstream of the selected site.

We have been utilizing colonial ascidians that feature a short lived larval stage to discern the extent to which recruitment success is coupled to tidal flow patterns for this type of life history. We utilize a system of automated sampling equipment to help investigate the relationship between the biological and physical processes of larval release, larval transport, and settlement. The equipment exposes substrates to the water column to collect individuals settling out of the plankton, separating the settlement activity into distinct portions of the tidal cycle. A survey of the estuary provides an estimate of the likely source regions; this information is coupled with known life history traits and a hydrodynamic model to predict the extent of settlement at the locations of the automated instruments. Comparison of the model predictions to the results from the sampling equipment indicates that the modeled processes are responsible for only a portion of the population dispersal in this system.

Genetic evidence for an apicomplexan-Dichocoenia sp. association

Andrew R. Hannes,* Tamar L. Goulet, and Mary Alice Coffroth. Department of Biological Sciences, State University of New York at Buffalo, Hochstetter Hall, Buffalo, New York 14260-7022, USA.

Several lines of evidence suggest that organisms from the phylum Apicomplexa are found in association with marine host-algal symbioses. We provide genetic evidence suggesting the presence of an apicomplexan in a scleractinian host and suggest that these associations may be a common occurrence in reef cnidarians. Analysis of the small subunit ribosomal DNA (18S-rDNA), amplified from the scleractinian, Dichocoenia sp. using a zooxanthellae specific primer set, yielded a previously uncharacterized restriction fragment length polymorphism (RFLP) genotype. RFLP of 18S-rDNA is the generally accepted technique utilized for cladal classification of zooxanthella. For this reason, it is important to determine what organism is responsible for this aberrant genotype. A phylogenetic analysis of 18S-rDNA nucleotide sequences from a variety of apicomplexans and dinoflagellates, as well as, the suspect sequence showed that the organism responsible for the uncharacterized genotype is most closely related to protozoans of the phylum Apicomplexa, order Coccidia.


Sliding baselines, stealth predators, and cascading impacts to functional responses in Gulf of Maine benthic communities

Larry G. Harris.* Zoology Department, University of New Hampshire, Durham, NH, USA.

Over the last 30 years, benthic communities in the Gulf of Maine have undergone major shifts in composition. Kelp bed communities gave way to urchin barrens about 1980 and overfishing of sea urchins has been followed by the reestablishment of algal dominated communities. The new algal communities have included a series of opportunistic and invasive species not present in previous kelp bed systems. The most drastic changes in community composition has occurred in the southeastern portion of the Gulf of Maine, where kelp beds are being replaced by Codium beds with an understory dominated by invasive red algae, blue mussels, and two invasive colonial tunicate species. The introduced bryozoan Membranipora is a dominant epizooite on a wide variety of algal species. The structure, composition, and interactions within this new community state are changing quickly as associated fauna and flora respond to newly abundant substrates and food sources. Extensive subtidal Mytilus beds have facilitated increased sea star, crab, and wrasse populations as well as two flat worm species, the invasive acoel Convoluta and the poorly studied polyclad Notoplana. The Common Eider is also a major neglected predator on mussels and other benthic fauna. The combined predator load has shifted the role of mussel beds from dominant space occupiers into ephemeral disturbance events. Predator increases are also impacting herbivore populations that may favor ephemeral algae over the previous climax species in these communities.


Growth rates of juvenile pinfish (Lagodon rhomboides): effects of habitat and predation risk

Stacey L. Harter* and Ken Heck, Jr. Dauphin Island Sea Lab, University of South Alabama, USA.

Predation is often one of the largest sources of mortality for juvenile fishes and, because of this, many young fish exhibit rapid growth that allows them to outgrow predators. However, predation risk often forces young fish into suboptimal foraging habitats, thereby compromising rapid growth. Field caging experiments were performed in Big Lagoon, Florida to examine the effects of flounder predation risk on the growth rates of juvenile pinfish in three different habitats: sand, low density, and high density of shoal grass (Halodule wrightii). Preliminary results suggest that the interactions between growth rates, habitat, and predation risk vary with season. During late spring-early summer, pinfish grew the most in seagrass habitats and predation risk significantly reduced growth. However, during the fall, pinfish grew most in sand and predation risk did not significantly affect growth. We conclude that when pinfish are smallest and most vulnerable, predation risk reduces growth rates, but as pinfish reach a larger size (> 80 mm TL) it appears they approach a size refuge from predation.


A comparison of growth rates of juvenile Callinectes sapidus along a salinity gradient in the Cape Fear River estuary