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

Photoresponses of Müller’s larvae of the flatworm Maritigrella crozieri

Kevin B. Johnson,¹* and Richard B. Forward, Jr.^{2 1}Department of Marine and Environmental Systems, Florida Institute of Technology, 150 W. University Boulevard, Melbourne, Florida 32901, USA; ²Division of Coastal Systems Science and Policy, Nicholas School of Environment and Earth Sciences, Duke University Marine Laboratory, 135 Duke Marine Lab Road, Beaufort, North Carolina 28516, USA.

Larvae of the flatworm Maritigrella crozieri were examined for photoresponses, including spectral sensitivity, ontogeny of the phototactic pattern, and intensity threshold. Adult M. crozieri feed exclusively and generally live on the tunicate Ecteinascidia turbinata. They have a planktonic larval phase lasting longer than 3 weeks. We found that the primary spectral sensitivity maximum was at 500 nm, which may be an adaptation to the spectrum available underwater at twilight. The phototactic threshold changed with age; dark-adapted, young larvae (1 week old) had a threshold an order of magnitude higher than that of older larvae (3 weeks old). Flatworm larvae are relatively insensitive to light as compared to other invertebrate larvae. Young larvae were positively phototactic at high light intensities and negative at low. This is a pattern typical of a predator avoidance shadow response. In contrast, older larvae were only positively phototactic, which would be useful for transport to shallow-water adult habitats.

Habitat fragmentation in seagrass ecosystems: a preliminary investigation

Matthew W. Johnson* and Kenneth L. Heck, Jr. Dauphin Island Sea Lab, 101 Bienville Blvd., Dauphin Island, AL 36528, USA.

The role of habitat fragmentation is poorly understood in marine ecosystems. Previous work has concentrated primarily on growth of selected bivalve species in seagrass habitats, and on animal abundances in different sized patches of seagrass, algae, coral, oyster, and salt marsh habitats. Here, we present the baseline information gathered from a project using Artificial Seagrass Units (ASUs) to examine the processes that control seagrass community structure as patch size and shape change due to habitat fragmentation. ASUs, similar to those successfully used in previous seagrass studies, were constructed of 1.9 cm black Vexar mesh and the seagrasses Thalassia testudinium and Halodule wrightii were simulated using 5 mm and 2.5 mm green polypropylene ribbon. We placed ten replicate ASUs of four combinations of shape and size 5 m apart and 5 m from any living seagrass in two study sites (Big Lagoon, FL and Point Aux Pines, AL). ASU sizes were as follows: large stellate (area 0.2036 m², perimeter 1.6 m), large circular (area 0.2036 m², perimeter 3.265 m), small stellate (area 0.0487 m², perimeter 0.7825 m), and small stellate (area 0.0487 m², perimeter 1.6 m). After four weeks, the entire ASU was sampled by placing an appropriately shaped enclosure over the ASU and then removing the contents using a suction sampler. Preliminary results indicated that patch size and patch shape can influence macrofaunal community structure in both Big Lagoon and Point Aux Pines. However, our data indicate that perimeter:area ratios may be more important to ASU colonization than either patch size or shape. This baseline information, combined with the results of other proposed studies, should be helpful in making ecologically sound management decisions for the future conservation of seagrass habitats.


Factors controlling the distribution of the green algal species Codium fragile at the Isles of Shoals

Adam C. Jones*¹ and Larry G. Harris.^{2 1}Providence College, Providence, RI, USA; ²Department of Zoology, University of New Hampshire, Durham, NH, USA.

For a period of eight weeks during the summer of 2001, we investigated the association of the invasive green alga, Codium fragile ssp. tomentosoides, with the sacoglossan gastropod Placida dendritica (Gastropoda: Opisthobranchia) among the Isles of Shoals, off the coast of Portsmouth, NH USA. As the numerically dominant predator on the algae, we examined possible means by which the population of the sacoglossan might be regulated, and studied the correlation between C.fragile and P.dendritica densities in areas of variance in water motion. There was a positive impact of water motion on the C.fragile, and a significant decrease in Codium density in locations with high amounts of P.dendritica. However, we did not establish a relationship between water motion and the number of P.dendritica present. Laboratory experiments and field observations showed the green crab Carcinus maenus and the hermit crab Pagurus acadianus to be potential predators of P.dendritica, while similar trials with the wrasse Tautogolabrus adspersus yielded negative results.


The effects of maternal care on dispersal and genetic population structure of western North Atlantic haustoriid amphipods

Elizabeth Jones* and Scott C. France. University of Charleston, SC, USA.

Dispersal potential of larvae and juveniles plays an integral role in determining the population structure of many shallow-water benthic marine invertebrates. This study attempts to determine how maternal care of juveniles in amphipod crustaceans affects dispersal by examining the genetic population structure of several closely related species that differ in levels of maternal care. Two species of interest are Neohaustorius schmitzi and N. biarticulatus. These are free-burrowing haustoriid amphipods that inhabit the intertidal range of wave-protected sandy beaches along the western North Atlantic coast. Like all peracarid crustaceans, these species brood embryos within a ventral thoracic marsupium and possess direct development to a “crawl-away” juvenile stage. N. schmitzi is believed to exhibit maternal care, since juveniles have been observed to return to the marsupium after hatching and have been found within the marsupium of preserved specimens. The nature of maternal care in N. biarticulatus is currently being characterized. Patterns of variation in the mitochondrial Cytochrome Oxidase I gene will be used to determine the genetic population structure of both Neohaustorius species. We have sequenced approximately 600 base pairs of the COI gene from individuals in populations ranging from Cape Cod, MA to Charleston, SC. Sample sizes need to be increased before inferences concerning gene flow and population structure can be made; however, preliminary data suggests some genetic structure along the eastern coast of North America. Nine haplotypes have been found in seven populations of N. schmitzi, with sequence divergences ranging from 0 to 1%. Among three N. biarticulatus populations, two haplotypes have been seen, producing divergences ranging from 0 to 0.2%. Results from this study will help determine whether amphipods with maternal care suffer from higher degrees of inbreeding than those without, or conversely, if they benefit from greater dispersal due to higher juvenile survival rates.


Hydroid defenses against predators: importance of secondary metabolites vs. nematocysts

R. Channing Jones,¹* John J. Stachowicz,² and Niels Lindquist.^{1 1}Institute of Marine Sciences, University of North Carolina at Chapel Hill, Morehead City, NC 28557, USA; ²Section of Ecology and Evolution, University of California, Davis, Davis, CA, USA.

Marine hydroids are benthic invertebrates commonly found in all the world’s oceans. These particle-feeding invertebrates are commonly thought to be defended by organelles called nematocysts that penetrate predator tissues and inject proteinaceous venoms. But not all hydroids possess penetrating nematocysts. The increasing number of novel secondary metabolites isolated from marine hydroids suggests that some hydroids are chemically defended, which our recent studies have confirmed. Furthermore, chemically defended hydroids typically lack penetrating nematocyst, suggesting that unpalatable secondary metabolites and penetrating nematocysts represent alternative defensive strategies for hydroids. To test this hypothesis more rigorously and to determine the prevalence of chemical defense among hydroids, we have examined the palatability of hydroid polyps before and after deactivating their nematocysts and the crude extract palatability of forty-five hydroid species from North Carolina (temperate Atlantic), the Florida Keys (tropical Atlantic), California (temperate Pacific), and Papua New Guinea (tropical Indo-Pacific). Our results to date suggest that chemical defenses may be at least as common as nematocyst-based defenses among Florida and North Carolina hydroids and that the two represent largely alternative defensive strategies. In contrast, only a small proportion of hydroids from California and Papua New Guinea have been identified as chemically defended. The physical or biological causes of this apparent inter-ocean difference in the prevalence of chemically defended hydroids is unknown. Given their alternative defensive strategies and the apparent differences between Atlantic and Pacific faunas, hydroids offer an excellent system to investigate optimal defense theory and the evolution of defensive strategies among marine organisms.


Predation rates on juvenile oysters: laboratory interactions between exotic and native crabs on prey size selectivity

Michael L. Judge¹* and Andrew A. Forbes.^{2 1}Department of Biology, Manhattan College, Riverdale, NY 10471, USA; ²Department of Biology, Colgate University, Hamilton, NY 13346, USA.

In the restoration of degraded marine habitats, the role of predatory exotic species is poorly understood. When reliable evidence of interspecific interactions is lacking, restoration efforts may not be able to predict novel community impacts. We examined the potential impact of the invasive Asian shore crab Hemigrapsus sanguineus on attempts to re-establish oyster reefs. During the summer 2001, we conducted intertidal surveys to determine the abundance of H. sanguineus and a sympatric native mud crab (Dyspanopeus sayi) at seven (mud/rock) sites within the Hudson River estuary. During low tide, both crab species retreat under similar sized rocks (400-600cm²) with densities of 1 to 4 individuals per rock, either in single or mixed species groups. Based upon field distributions, we designed laboratory experiments to offer juvenile Crassostrea virginica (5-20mm length) to H. sanguineus (carapace width = 17.72.7mm) and D. sayi (c.w. = 18.43.2mm) in single or mixed species groups at either low (2 crabs/enclosure cage) or high density (4/cage). All predator trials were conducted in flow-through enclosure cages (25x20cm) within a 700L re-circulating seawater system and replicated 10 times. During 1h trials, we evaluated crab per capita consumption rates by oyster size, crab species and predator density. In trials with only two crabs per cage, we found no consistent differences among prey size, predator species, or crab interspecific interactions on oyster consumption rates (ANOVA, all p’s > 0.05). However, at a higher predator density, a significant prey size by crab species interaction developed (ANOVA, F₃,₁₄₃=4.284, p=0.006). Under these conditions, Hemigrapsus tended to select smaller oyster sizes, while Dyspanopeus ate larger oysters. This study suggests that size-specific predation risk to oysters results from a non-linear interaction between predator species and density and may not be directly inferred from single species trials conducted at low density.


The influence of temperature on activity and density relative to catch per unit effort in lobster traps

Steve Jury,* Walter Golet, Hunt Howell, and Win Watson. *Biology Department, SUNY New Paltz, New Paltz, NY 12561, USA; [e-mail]; Zoology Department and Center for Marine Biology, UNH, Durham, New Hampshire, USA 03824, USA; e-mail [e-mail], [e-mail].

It is widely accepted that catch per unit effort generally increases with increasing temperature primarily due to increases in activity (based on a seminal study by McLeese and Wilder in 1958). However, the role of temperature effects on catch has remained controversial. Increased activity could increase catchability by increasing 1) the probability of finding a trap and 2) the probability of entering that trap. However habitat selection for preferred temperatures may also increase the density of lobsters moving into a given area and thus increased density may ultimately lead to increased catch. Temperature may have effects on other factors as well including feeding behavior, satiation, probability of exit from a trap, and the probability of lobsters in a given fishing area molting into a ‘trappable’ size. All of these factors could be influencing ultimate catch per unit effort at a given temperature.

Based upon lab and field assessments of activity at seasonal temperatures, assessment of behaviors in and around traps using an in situ video monitoring system, (Lobster Trap Video-LTV), trapping studies, and SCUBA seasonal assessments of lobster densities we are gaining an understanding of the relationship between seasonal changes in temperature and the subsequent effects on catchability. Our data and a review of the literature suggest that while temperature affects both activity and density, catch is only temperature dependent at low temperatures while it is relatively temperature independent at higher temperatures.

Examining the effects of Dictyota epiphytism and secondary chemicals on neighboring reef biota using Halimeda tuna as a model organism

A. Kahn,¹* K. Beach,¹ H. Borgeas,¹ and L. Walters.^{2 1}University of Tampa, Tampa, Florida 33606, USA; ²University of Central Florida, Orlando, Florida 32816 USA, USA.

Since 1994, the phaeophyte Dictyota spp. has spread to cover as much as 70% of the benthic community at certain reef sites in the Florida Keys. Dictyota grows both saxicolously and epiphytically on numerous reef organisms. Beyond occupying space, it is unclear what impacts this macroalga is having on the reefs when in high abundance. The possible impacts such a high algal cover may have on epiphytized as well as neighboring benthic organisms were examined using the chlorophyte Halimeda tuna as a model. The growth rate and physiology of H. tuna were examined for both naturally epiphytized and unepiphytized individuals. The relationship between Dictyota and H. tuna was further elucidated by exploring the effects of the secondary chemicals leached from Dictyota into the surrounding seawater and onto epiphytized as well as around neighboring H. tuna. The presence of epiphytic Dictyota on H. tuna was found to decrease Pmax and growth rates as well increase levels of photosynthetic accessory pigments in epiphytized individuals. Such changes were consistent with the impact of shading by the epiphyte on H. tuna. Increased Rd was also observed in epiphytized H. tuna as well as unepiphytized H. tuna individuals exposed to Dictyota-conditioned water. Elevated respiration rates were inconsistent with the physiological impact of shading. In situ, no significant impacts were observed on the growth rate or physiology of unepiphytized H. tuna when neighboring Dictyota cover was experimentally increased on the reef. In conclusion, the spread of Dictyota over reefs in the Florida Keys impacts reef system by occupying space, shading, overgrowing organisms and negatively impacting metabolic processes of epiphytized hosts when the secondary metabolites from Dictyota reach high enough concentrations.


Monitoring changes in the fully protected zones of the Florida Keys National Marine Sanctuary

Brian D. Keller.* Florida Keys National Marine Sanctuary, P.O. Box 500368, Marathon, FL 33050, USA; e-mail [e-mail].

The Florida Keys National Marine Sanctuary is a 9,850 km² marine protected area managed by the U.S. National Oceanic and Atmospheric Administration and the State of Florida. A comprehensive management plan was implemented in 1997 to protect and conserve marine resources of the Florida Keys. One aspect of the management plan is the creation of a network of 24 fully protected zones (marine reserves). An ongoing monitoring program is designed to determine effects of “no-take” protection on heavily exploited fishes and invertebrates, benthic communities, and human activities. Data on the abundance and size of fish, spiny lobster, and queen conch; algal cover; coral cover, diversity, and recruitment; and zone usage are collected from fully protected zones and adjacent reference sites. Preliminary reports indicate increases within the fully protected zones in the number and size of heavily exploited species such as spiny lobster and certain reef fishes. Slower-growing benthic species such as corals and sponges have not shown significant changes within fully protected zones, possibly because the zoning plan was implemented less than five years ago.


The relationship between surface water nutrients, seagrasses and their associated epiphytes along Florida’s central gulf coast

Stephanie R. Keller,* Jaime M. Greenawalt, and Thomas K. Frazer. University of Florida, Department of Fisheries and Aquatic Sciences, 79222 NW 71st Street, Gainesville, Florida 32653, USA.

Seagrass coverage along Florida’s central Gulf coast is extensive. In fact, seagrass beds are often the dominant structural feature in the shallow coastal waters of the region. As such, seagrasses provide important refuge and forage habitats for a myriad of ecologically and economically important fauna. Approximately 85% of the exploited fishery species in Florida spend some portion of their life history in estuaries, and many of these are considered obligate seagrass inhabitants. Thus, seagrass beds are considered essential to the ecological integrity and health of Florida’s estuarine and nearshore coastal ecosystems. However, seagrass beds along the central Gulf coast of Florida are potentially threatened by increasing nutrient inputs. Such inputs can lead to increases in phytoplankton, macroalgae and epiphytic growth on seagrass blades, which reduce light availability and may decrease seagrass productivity. In extreme cases, extensive mortality of seagrass beds may occur with a concomitant shift in trophic structure and ecosystem function.

As part of an effort to understand the course of such changes, we described the relationship between surface water nutrient concentrations and epiphyte abundance on seagrasses over a broad and representative area of the central Gulf coast of Florida (from the Weeki Wachee River north to the Waccasassa River). A latitudinal gradient in nutrient (phosphorus) concentrations had previously been documented in this area. As predicted, epiphytes were most abundant on seagrasses in the northern portion of the study area where surface water phosphorus concentrations were also highest. Preliminary results from a nutrient enrichment experiment carried out in the southern portion of the study area suggest that further increases in phosphorus will stimulate epiphytic growth on seagrass blades.