Joseph Bay Research Articles

VARIATIONS IN GROWTH AND REPRODUCTION OF BAY SCALLOPS (ARGOPECTEN IRRADIANS) (LAMARK, 1819) FROM SIX SUBPOPULATIONS IN THE NORTHEASTERN GULF OF MEXICO

Bay scallops, Argopecten irradians, sustained a valuable commercial and recreational fishery in Florida during the middle part of the last century. In 1994, after decades of declining stocks, state managers closed this fishery to commercial harvest and severely limited the recreational harvest. In Florida, most bay scallops reproduce only once, generally during the fall at an age of roughly 12. The current 10-week recreational harvest season, July 1 through September 10, occurs at a time when somatic and reproductive tissues are changing rapidly in preparation for the fall spawning season. This study describes changes in tissue weights (reproductive, somatic, visceral) during the 2002 harvest season in scallops collected from six subpopulations along Florida's Gulf of Mexico coast. We observed tissue-specific patterns of weight change during the 7-month study and also noted regional differences. In three Panhandle sites (St. Joseph Bay, Lanark Village, and St. Marks), a shift from somatic growth to reproductive growth occurred later in the year and was more intense than in peninsular sites (Steinhatchee, Homosassa and Anclote). We also monitored recruitment of juvenile scallops at three of the sites from July of 2001 through June of 2003. There were protracted fall and winter peaks within a background of constant, low-level recruitment. The harvest limits allow each person to collect two gallons (7.55 L) of whole scallops or one pint (0.47 L) of adductor muscle meat each day. In June, just prior to the harvest season, the number of whole scallops that would be collected varied significantly between sites (range 55–203), as did the equivalent yield of adductor muscles (range 143–342). Muscle size peaked in August or September, depending on location. The allowable number of scallops collected within the volume-based limits had decreased (41–112 whole scallops or 84–116 shucked scallops) and between-site variability in the numerical harvest was lower.

The effects of dietary protein concentration on feeding and growth of small Lytechinus variegatus (Echinodermata: Echinoidea)

Understanding the nutritional requirements of Lytechinus variegatus is essential to define its role in the marine environment and necessary for successful culture of this species. Protein is an essential component for growth, yet the requirements for protein in most marine organisms are not known. Small Lytechinus variegatus (ca. 14 mm diameter, n=160) were collected at St. Joseph Bay, Florida in March 2000. They were held in aquaria and fed ad libitum one of four diets varying in protein concentration (9, 15, 21, or 33% dry weight) for 14 weeks. Diets ≥21% dry weight protein were sufficient for maximal growth and survivorship. Individuals fed a diet low in protein compensated by consuming higher quantities of food per gram wet weight. However, the protein was insufficient to support maximal growth and survivorship. Total dry matter absorption, protein absorption, and carbohydrate absorption of the prepared feeds were higher than reported for natural diets. Total production and production efficiency was lowest in those fed the low-protein diet. Gonad production occurred in individuals with test diameters smaller than reported previously in field populations and was lowest in those fed the low-protein diet. The acini of both females and males were predominantly composed of nutritive phagocytes, suggesting that growing L. variegatus use the gonad primarily as a nutrient storage organ and not for reproduction. In females the growth rate of oocytes increased with dietary protein. In males, protein concentration ≥21% resulted in an increase in the volume of germinal epithelium and a decrease in the volume of nutritive phagocytes. The minimal requirement for protein in L. variegatus from approximately 1 g to 15 g total weight is >15% dry weight for the conditions of this experiment. The requirement for a diet >15% protein corroborates with field studies that indicate L. variegatus consumes epibionts and animal tissues preferentially to seagrass, and that the microbial, microfloral, and microfaunal community living on the seagrass may provide the extra protein required for growth and survival of small L. variegatus.

Effect of substrate availability and conspecific cues on communal oviposition in the apple murex snail Phyllonotus pomum

Communal oviposition, the sharing of a single substrate by conspecific individuals for depositing clutches of egg capsules, is common among gastropod molluscs. In soft-bottom habitats, communal oviposition may occur because of a limitation of suitable hard substrate. Conspecific cues may be responsible for aggregating females. This study examined the oviposition behavior of the apple murex snail Phyllonotus pomum in seagrass beds in St. Joseph's Bay, Florida. Movement pat- terns obtained from a mark-recapture study conducted during the 5 mo prior to egg-laying season suggest that females are capable of moving, and often move, farther than the distance at which sub- strate might become limiting. In field surveys, 1 to greater than 14 possible suitable substrates were available within a 4 m radius of communal oviposition events, yet females still oviposited commu- nally. In a caged field-substrate manipulation experiment, females contributed to a single communal egg-mass even when additional substrates were available within 0.25 m. When given a choice between substrate without and with fresh egg capsules (< 8 d old) in a caged field experiment, females deposited an equal number of clutches on each type of substrate. Communal oviposition in P. pomum was not mediated by substrate limitation, and previously laid conspecific egg capsules did not attract females or induce them to oviposit communally. Alternatively, there may be an adaptive advantage to communal oviposition in P. pomum. It is possible that the process of egg-laying from 1 individual attracts, aggregates and induces oviposition in neighboring females.

A Comparative Study of the Non-acidic Chemically Mediated Antifoulant Properties of Three Sympatric Species of Ascidians Associated with Seagrass Habitats

The present study investigated aspects of the antifoulant properties of three sympatric species of ascidians found in seagrass habitats of the Gulf of Mexico, Southern Atlantic Ocean, and Caribbean. Field observations in Saint Joseph Bay, Florida indicate that all three species are common and that the tunic of the solitary ascidian Molgula occidentalis is often heavily fouled, while the outer surfaces of both the colonial ascidians Amaroucium stellatum and Botryllus planus are free of fouling organisms. Antifoulant activities of a suite of increasing hydrophilic organic extracts prepared from the tunic of M. occidentalis and whole colonies of A. stellatum and B. planus were measured using both sympatric microbial (bacteria) and macroinvertebrate (cyprid larvae of Balanus amphitrite) fouling organisms in laboratory bioassays. In addition, field antifoulant assays were conducted by combining organic extracts with controlled-release resin and subsequently coating this material on to acrylic rods deployed in the field for a 72?h period. Extracts of the tunic of M. occidentalis generally did not inhibit bacterial growth. The exception was the methanol extract, which inhibited growth in one of the six marine bacteria tested. Moreover, only the highest concentrations of hexane and methanol tunic extracts tested prevented attachment of cyprid larvae. Field assays revealed no antifoulant activity on rods coated with resin containing extracts of M. occidentalis. Inhibition of both microbial growth and cyprid settlement were much more pronounced in whole-organism extracts of the two colonial ascidians. Most potent were the aqueous methanol extracts of colonies of B. planus and A. stellatum which inhibited growth in five of the six marine bacteria tested. In addition, hydrophilic and lipophilic extracts of the colonial ascidians significantly inhibited attachment of cyprid larvae, in many instances across a wide range of extract concentrations. Field antifoulant assays indicated that extracts of both colonial ascidians inhibited settlement of bryozoans and barnacles. The findings indicate that the colonial ascidians B. planus and A. stellatum possess chemical antifoulant properties. In contrast, the solitary ascidian M. occidentalis appears to either tolerate fouling or possess other non-chemical mechanisms to cope with the risks associated with epibiont overgrowth.

Thermal Tolerance Responses of Laboratory-Acclimated and Seasonally Acclimatized Atlantic Stingray, Dasyatis sabina

Abstract Atlantic stingrays, Dasyatis sabina, inhabit shallow bays subject to rapid temperature changes, yet little is known about their thermal tolerance strategies. We quantified critical thermal maxima (CTMaxima) and minima (CTMinima) of Atlantic stingrays from St. Joseph's Bay, Florida. Spiracle contraction cessation for more than one minute was the experimental endpoint. Laboratory-acclimated fish held at 10.8, 20.5, or 35.1 C exhibited CTMaxima of 35.7, 39.3, or 43.2 C, and CTMinima of 0.8, 4.8, or 10.8 C, respectively. Regression analysis revealed that CTMaxima increased by 0.31 C and CTMinima decreased by 0.41 C for every 1.0 C increase in acclimation temperature. Atlantic stingrays exposed to diel thermoperiods of 34.0–37.3 C and 7.0–11.0 C had CTMaxima of 43.1 and 33.4 C and CTMinima of 9.6 and 0.3 C, respectively, suggesting that fish acclimated to low cycle temperatures. A thermal tolerance polygon produced from laboratory data had an area of 978 C2, the third largest ever measured in a fish. ...

Assessment of Seagrass Plant Demography Within and Among Beds of Turtle Grass (Thalassia testudinum), Manatee Grass (Syringodium filiforme), and Shoal Grass (Halodule wrightii) From the Northern Gulf of Mexico

Variability in the demographic patterns of seagrasses may affect a variety of physical and biological processes in aquatic communities. We investigated seasonal seagrass demography, sediment size structure, and sediment organic carbon from two sites (north and south) in St. Joseph Bay, Florida, for Thalassia testudinum, Syringodium filiforme, and Halodule wrightii. Geologically, sands dominated both sites, but the south site had significantly greater proportions of fine and very fine sands, whereas the north site was dominated by coarse and medium sands. Within each site, demographic parameters were assessed for edge (<1 >m) and interior portions (>10 m) of grass beds. The objective was to quantify within-habitat demographic characteristics and assess whether differences in plant biomass and shoot density existed between edge and interior portions. Results for T. testudinum showed significantly greater shoot density (P < 0.05) and plant biomass (P < 0.001) from interior portions of the bed than from the edge for the north site, but there were no significant differences for the south site. Syringodium filiforme showed significantly greater shoot density from bed interiors than from edges for both the north and south sites (P < 0.0001, P < 0.001, respectively) as well as plant biomass (P < 0.0001, P < 0.01, respectively). Halodule wrightii showed a similar response, with greater shoot densities from the north interior (P < 0.008) and significantly greater plant biomass from interior portions of beds for both the north and south sites (P < 0.003, P < 0.01, respectively). Within-bay comparisons showed that plant biomass and shoot density were generally greater from the north site than from the south site for T. testudinum and H. wrightii, but the reverse was true for S. filiforme. Although sands dominated both sites, the south site showed greater percentages of finer sediments, and S. filiforme biomass has been shown to be inversely related to sediment size. Although we were unable to resolve within-habitat differences in sediment size structure, which may suggest sediment baffling and water velocity changes, we surmise that physical and sedimentary differences exist between edge and interior portions of seagrass beds. These differences may have dramatic effects on processes such as larval settlement, predator-prey interactions, and per unit area primary production. As such, further investigations into within-habitat variability and edge effects in plant demography and associated biological and physical processes are needed.

Arsenic and phosphorus in seagrass leaves from the Gulf of Mexico

Arsenic is a common contaminant in the marine environment, but little is known about arsenic in seagrasses. Arsenate is taken up by the phosphate uptake systems of plants, and there is often a relationship between P availability and As uptake. We sampled green leaves of the seagrass Thalassia testudinum from six estuaries in the Gulf of Mexico to document the As content of seagrasses and to determine the relationships between P availability and As. Arsenic content of seagrasses was generally lower than literature values of other marine primary producers. Arsenic content varied from 0.90 to 3.36 ppm and phosphorus content varied from 544 to 6294 ppm, and there were significant differences among the estuaries studied. Nutrient stoichiometry (N:P) indicated that there were differences in P availability among estuaries: Charlotte Harbor had high P availability, while St. Joseph Bay and Florida Bay were P-limited. The Homosassa River, the Anclotte Estuary and Tampa Bay had intermediate P availability. When data from all estuaries were pooled, there was a significant, negative relationship between P and As content, as predicted by the model of competitive uptake of As and P. However, more extensive sampling within one estuary (Florida Bay) showed a significant positive relationship between P and As, suggesting that factors other than strict competitive uptake kinetics influence the relative content of As and P. We suggest that the P and As availability ratio in estuaries, and therefore in the seagrasses that inhabit them, is largely controlled by the relative importance of freshwater and marine inputs of the two elements.

Comparison of predation pressure in temperate and subtropical seagrass habitats based on chronographic tethering

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 224:77-85 (2001) - doi:10.3354/meps224077 Comparison of predation pressure in temperate and subtropical seagrass habitats based on chronographic tethering Bradley J. Peterson1,*, Kip R. Thompson1, James H. Cowan Jr2, Kenneth L. Heck Jr2 1Department of Marine Sciences, University of South Alabama, Mobile, Alabama 36688, USA 2Dauphin Island Sea Laboratory, University of South Alabama, PO Box 369, Dauphin Island, Alabama 36528, USA *Present address: Department of Biological Sciences, Florida International University, University Park, Miami, Florida 33199, USA. E-mail: petersob@fiu.edu ABSTRACT: Chronographic tethering devices were used to investigate the effects of habitat type, prey type, tidal state and time of day on predation in the Damariscotta River, Maine (43°57¹N, 69° 35¹W) and in St. Joseph Bay, Florida (30°00¹N, 85°30¹W). Traditional tethering data (presence/absence) revealed that there were significant differences in the number of predation events between sites (p = 0.037) with more predation events occurring at the St. Joseph Bay site. In addition, there were significant differences in predation between prey types (p < 0.001). Regardless of site, significantly more Œsoft¹ bodied prey types (shrimp) were removed than Œhard¹ bodied prey types (brachyuran crabs). Separating the data by site revealed that there were significant differences between habitat types (seagrass interior, seagrass edge and unvegetated substrate) at the Damariscotta River site (p = 0.027), but not at the St. Joseph Bay site (p = 0.943). Using the time to predation recorded on the chronographic tethering devices, survival times were calculated. Based on prey survival time, comparisons were made between predation intensity in monotypic stands of the seagrasses Zostera marina L. (Damariscotta River) and Thalassia testudinum (St. Joseph Bay), and bare substrate and the grass edge at both study sites. There were no significant differences in survival time between habitats at the Damariscotta River site (p = 0874). However, the average prey survival time was significantly less for the seagrass bed edge at the St. Joseph Bay site than for the T. testudinum bed interior and unvegetated habitats (p = 0.019). In addition, the time to predation allowed the effect of tidal state and light versus dark on predation to be assessed. While neither tidal state nor light versus dark had any effect on predation at the Damariscotta River site (p = 0.096 and p = 0.481 respectively), at the St. Joseph Bay site, there were significantly more predation events during the day than at night (p < 0.001), regardless of tidal state (p = 0.664). The use of the chronographic tethering devices revealed that while there was no significant difference in the number of predation events or rate of predation at the St. Joseph Bay site, the interface (i.e. Œedge¹) between bare or unvegetated substrates and seagrass assemblages was associated with the highest predation risks. KEY WORDS: Chronographic tethering · Edge effects · Predation · Thalassia testudinum · Zostera marina Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 224. Online publication date: December 18, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Effects of experimental manipulation of pH and salinity on Cd(2+) uptake by the sponge Microciona prolifera and on sponge cell aggregation induced by Ca(2+) and Cd(2+).

Marine sponges (Microciona prolifera) collected in St. Joseph Bay, Florida panhandle, were exposed for 2 h to pH/salinity unit combinations of 7.4/30, 6.3/30, 7.4/11, and 6.3/11. Cell suspensions from these were aggregated with 24 microM of either CaCl(2) or CdCl(2). Cells exposed to the low/low (11/6.3) combination aggregated spontaneously (no added stimulus) in 8/11 experiments, suggesting a significant disturbance of normal function, possibly involving disrupted ion uptake. In all other combinations aggregation proceeded normally and there were no statistically significant differences among the groups. CdCl(2) was as effective an aggregation stimulus as CaCl(2). The calcium channel blocker verapamil (100 microM) reduced calcium-induced aggregation by 15% but had no effect on cadmium (Cd)-induced aggregation, indicating that L-type calcium channels do not play a major role in aggregation induced by these divalent cations. Sponge tissue was exposed for 48 h to the same pH/salinity combinations but containing Cd (15 or 150 microg/ml) and then dried and analyzed for Cd. All sponges concentrated Cd but those exposed to low salinity concentrated it most (in one case x13). Low pH alone had no appreciable effect but appeared to increase the effect of low salinity. One sponge with a native Cd content of 47.2 microg/g dry weight had the highest acquired Cd content. The results of this study indicate that low levels of salinity and pH, similar to those we recorded in the study area, facilitate the accumulation of Cd, but not via L-type calcium channels, and disrupt normal aggregation responses of the cell. These results may help explain a previous observation that cells from M. prolifera from this area, with high native levels of Cd, failed to aggregate in response to CaCl(2)[Philp RB (1999) Comp Biochem Physiol 124C:41-49] and also the frequent die-offs of Microciona that have virtually eliminated this sponge from its local habitat.

An experimental test of the mechanism by which suspension feeding bivalves elevate seagrass productivity

A field experiment utilizing mussel mimics and sediment nutrient enrichment was con- ducted to examine the effect of the mussel Modilous americanus on meadows of the seagrass Tha- lassia testudinum. The experimental design tested the separate factors of increased habitat structure and increased nutrient enrichment resulting from the presence of the mussels. Nutrient enrichment had a significantly positive effect on sediment porewater nutrient concentrations and a significantly negative effect on leaf tissue C:N, C:P and N:P ratios. Increased habitat structure had a significantly positive effect on epiphytic grazer densities and a significantly negative effect on epiphytic biomass. In addition, calculated % light reduction by epiphytes was significantly reduced by structure and significantly increased by nutrient enrichment. This study showed that the direct effect of nutrient enrichment by mussel biodeposition produced the greatest positive response in productivity of T. testudinum in the seagrass meadows of St. Joseph Bay, Florida. In other systems experiencing eutrophication, however, it is possible that increased habitat complexity may have the greater effect on seagrass productivity.

Effects of nutrient enrichment and small predator density on seagrass ecosystems: An experimental assessment

We used a field experiment to assess the individual and combined effects of removing top predators and enriching water column nutrients (nitrogen‐N and phosphorus‐P) on seagrass ecosystem structure and function. Experiments were conducted in turtlegrass (Thalassia testudinum) habitats in St. Joseph Bay, FL, an aquatic preserve in the northern Gulf of Mexico that exhibits low ambient nutrient concentrations and contains abundant populations of small crustacean and gastropod mesograzers. We stocked 7.0 m 2 enclosures with elevated (≈4ࢤ8× ambient) densities of juvenile pinfish (Lagodon rhomboides), the dominant fish species in local seagrass habitats, to simulate the first‐order effects of large predator reductions, and we used an in situ delivery system to supplement N and P to ≈3× ambient levels in nutrient addition treatments. Monthly determinations of water column nutrients and Chl a, along with measurements of the biomass and abundance of leaf epiphytes and seagrass production, biomass, and shoot and leaf densities were used to evaluate the relative effects of manipulating nutrient supply and altering food web structure.In contrast to our expectations, results showed few significant nutrient effects, or fish × nutrient enrichment effects on any of the parameters measured. However, there were many significant fish effects, most of which were unexpected. As predicted, increased pinfish density reduced mesograzer numbers significantly. Not anticipated, however, was the reduced epiphyte biomass in fish enclosure treatments, apparently brought about by the pinfish consuming significant amounts of epiphytes as well as mesograzers. This reduction in epiphyte biomass produced positive indirect effects on seagrass biomass, shoot number, and rates of primary productivity in pinfish enclosure treatments.Our results also showed important top‐down effects in determining the composition and abundance of seagrass‐associated plants and animals in this pristine environment. Although we did not observe simple trophic cascades, most likely because pinfish fed at more than one trophic level, and because the dense seagrass prevented small grazers from being reduced to low numbers, pinfish produced important changes in the epibiota as well as the seagrasses themselves. These data, while contrasting with studies reporting significant negative nutrient enrichment effects on seagrasses, support the results of recent experimental studies in showing that: (1) small grazers can often control the abundance of epiphytes; and (2) it is unlikely that a full understanding of the consequences of nutrient enrichment for seagrass ecosystems can be gained without knowing how grazer population are regulated.

Demographic Characteristics of Lytechinus variegatus (Echinoidea: Echinodermata) from Three Habitats in a North Florida Bay, Gulf of Mexico

Abstract. The population densities, spatial distributions, size frequencies, growth rates, longevity and reproductive activities of sub‐populations of the sea urchin Lytechinus variegatus were investigated over a two‐year period. Sea urchins were examined in three habitats in Saint Joseph Bay, Florida, which is within the northern limits of their distribution. Densities of sea urchins, which ranged as high as 35 individuals ·−2, fluctuated seasonally at all sites and were higher in seagrass beds comprised of Thalassia testudinum than Syringodium filiforme or on a sand flat. A cold front caused large‐scale, catastrophic mortality among adult, and especially juvenile, sea urchins in nearshore habitats of the Bay in the spring of 1993, leading to a dramatic decline in sea urchin densities at the Thalassia seagrass site. The population recovered over 6 months at this site and was attributable to immigration of new adults. Juvenile recruitment displayed both interannual and site‐specific variability, with recruitment being highest in seagrass habitats in fall and spring. The most pronounced recruitment event occurred in fall 1993 at the Thalassia site. Spatial distributions of adult individuals ascertained monthly never varied from random in the seagrass beds (T. testudinum and S. filiforme) or during spring, summer or fall months on the sand flat. Nonetheless, aggregations of adult sea urchins were observed on the sand flat in the winter months and were associated with patchy distributions of plant food resources. Juvenile sea urchins (&lt; 25 mm test diameter) exhibited aggregations at all sites and 67 % of all juveniles under 10 mm test diameter (91 of 165 individuals observed) were found under the spine canopies of adults. Measurements of the inducibility of spawning indicated peak gametic maturity in all three sub‐populations in spring and summer. Gonad indices varied between habitats and years, but distinct maxima were detected, particularly in spring 1993 and late summer 1994. The mean gonad index of individuals at the Syringodium seagrass site was 2‐ to 4‐fold higher than the other sites in spring 1993 and gonad indices were much higher at all sites in spring of 1993 than 1994. Estimates of growth based on changes in size frequency cohorts coupled with measurements of growth bands on lantern demipyramids indicated that L. variegatus in three habitats of Saint Joseph Bay have similar growth rates and attain a mean test diameter of approximately 35 mm in one year. In contrast to populations within the central biogeographical range of the species, which may attain test diameters up to 90 mm, the largest individuals recorded in Saint Joseph Bay were 60 mm in test diameter, and almost all individuals were no more than 45 mm in test diameter or two years of age. The demographics of L. variegatus in the northern limits of their distribution appear to be strongly influenced by latitudinally driven, low‐temperature events and secondarily by local abiotic factors, especially springtime low salinities, which may negatively impact larval development and recruitment.

Role of sea urchin Lytechinus variegatus grazing in regulating subtropical turtlegrass Thalassia testudinum meadows in the Florida Keys (USA)

In previous work, in St. Joseph Bay, Florida (30° N, 85.5° W), in the northeastern Gulf of Mexico, we found that sea urchin Lytechinus variegatus grazing usually controlled seasonal changes in turtlegrass Thalassia testudinum abundance. In this study, we tested the generality of those conclusions by conducting new grazing studies in 2 turtlegrass habitats in the subtropical Florida Keys (USA). In the first experiment, we varied the duration of sea urchin grazing bouts in order to understand the impacts of temporally varying herbivory on seasonal changes in turtlegrass biomass in shallow water (<2 m) near Big Pine Key (∼25° N, 85°W). In the second experiment, we examined the effects of chronic low levels of grazing on seagrass growth and biomass in a deeper-water seagrass habitat (6 to 7 m) in Hawk Channel (∼25° N, 80° W). These new studies suggest that the impacts of sea urchin grazing are highly variable in the Florida Keys. Depending on the season, urchin grazing (at densities of 20 ind. m -2 ) had both negative and positive effects on seagrass biomass in Big Pine Key. If grazing occurred during spring, turtlegrass biomass was significantly reduced by short bouts of sea urchin herbivory. The impacts of this spring grazing extended into early summer. If grazing occurred in summer, sea urchins reduced turtlegrass biomass for only short periods of time, after which urchin grazing stimulated turtlegrass production. These findings are similar to those of previous grazing experiments conducted in St. Joseph Bay. In contrast, we found little evidence that ambient (0 to 8 ind. m 2 ) densities of sea urchins could control either seagrass production or biomass in the deeper waters of Hawk Channel. The differences we found in grazer impacts on turtlegrass growth and abundance, in a well-lit shallow water habitat and deeper-water habitat with less light, suggest that there is a critical need not only to repeat experiments in environments with differing physical conditions but also to develop a more complete understanding of the mechanisms by which seagrasses can compensate for losses of tissues to marine herbivores under varying environmental conditions.

Relationship Between Pea Crab (Pinnotheres maculatus) Parasitism and Gonad Mass of the Bay Scallop (Argopecten irradians)

We investigated the prevalence of pea crabs (Pinnotheres maculatus) in bay scallops (Argopecten irradians) from 1994 through 1996 in a scallop population from St. Joseph Bay, Florida. We also assessed their impacts on scallop reproductive potential. Our results showed that prevalence in bay scallops varied between 0 and 20% and were extremely low during 1996 (<2%). Comparing Gonadal-Somatic Indices (GSI) between infested and non-infested bay scallops in samples assessed the impact of pinnotherid parasitism. Results showed that GSI was significantly reduced in infested individuals compared to non-infested individuals of the same size range (t12 = 2.3, P <0.04). These results suggest that P. maculatus infestation may lower the reproductive potential of individual scallops, but the low rates of parasitism may only minimally impact the host population.

Cadmium content of the marine sponge Microciona prolifera, other sponges, water and sediment from the eastern Florida panhandle: possible effects on Microciona cell aggregation and potential roles of low pH and low salinity

Marine sponges from shallow bays and estuaries along the Florida panhandle contained cadmium (Cd), 1.78–27.9 μg g −1 (dry weight). Levels>7 μg g −1 were never found in a variety of other benthic invertebrates. Water levels of Cd were of the order 0.22–0.43 μg ml −1 and did not differ significantly between the two study areas (Panacea and St. Joseph Bay). Cd in organic sediment however, was significantly ( P=0.033) higher around Panacea (0.343±0.063 S.E.M.) than in St. Joseph Bay (0.18±0.223 S.E.M.). Salinity of 10 and pH 6.5 were recorded following heavy rains, and can constitute a hostile environment for these organisms. Temporal variations of Cd and Cu but not Zn were observed in Microciona prolifera over a period of 2 years in St. Joseph Bay, and a negative correlation was observed between Cd content and the Ca 2+-induced aggregation of Microciona cells suspended in Ca 2+/Mg 2+-free artificial seawater. Cells unresponsive to Ca 2+ aggregated in response to releasers of Ca 2+ from internal stores (thapsigargin, A23187 and tetredecylamine), suggesting that they were viable but dormant. In vitro studies showed that Cd 2+ is about equipotent with Ca 2+ in inducing aggregation of Microciona cells, whereas lower concentrations (1–2×10 −3 M), added 10 min before inducing aggregation with CaCl 2, inhibited aggregation, possibly by blocking Ca 2+ uptake. Microciona contained a metallothionein (MT)-like protein. Taken together these results suggest that naturally-acquired Cd may interfere with cell regulatory processes in Microciona. Possible effects of low pH and salinity on Cd uptake and detrimental effects on cell function are discussed.

Differential predation and growth rates of bay scallops within a seagrass habitat

The bay scallop, Argopecten irradians, is a common and commercially important bivalve species residing in shallow marine ecosystems dominated by seagrasses. However, unlike most bivalves, scallops have the ability to move considerable distances within and among habitats. Consequently, their adult distribution may not be set by larval settlement patterns. In St. Joseph Bay, FL, USA, scallops were significantly more abundant at edges of turtle grass (Thalassia testudinum) beds (x=0.75 m−2) than in their interior (x=0.375 m−2) or in nearby unvegetated sediments (x=0.00). This difference in habitat use was shown by field experiments to have two important consequences. First, scallops living along edges of T. testudinum beds experience significantly higher predation potential (>20% loss to predation day−1) than scallops living in the interior of grass beds or on open sediment (<5% predation loss day−1). Second, scallops living along the edge of grass beds showed significantly higher growth rates (0.031 mg dry wt. day−1) than individuals living on open sediment (0.012) or in the interior of beds (0.019). Therefore, individual scallops appear to trade off higher predation risk for increased growth rates.

The Population Dynamics of the Brittlestar Ophioderma brevispinum in Near- and Farshore Seagrass Habitats of Port Saint Joseph Bay, Florida

The population dynamics of the brittlestar Ophioderma brevispinum were followed monthly from Jan. 1995 to March 1996 in a near- and farshore seagrass bed in Saint Joseph Bay, FL. Abiotic (sea water temperature and salinity) and biotic (seagrass cover and sublethal predation) factors that could influence populations were also measured. Densities of individuals at both sites peaked in winter and spring, then declined dramatically in early summer months, and increased once again in the early fall at the offshore site and in the late fall at the nearshore site. Mean monthly disc diameters of individuals did not reveal any evidence of juvenile recruitment, suggesting seasonal migrations of adults into and out of near- and farshore seagrass beds. Seagrass cover at both sites varied substantially with season, with the highest cover in the summer months when brittlestar densities were lowest. Sublethal predation, as measured indirectly by counting the numbers of arm tips regenerating in individuals, did not differ significantly between sites except for the month of Feb. 1995, when levels of arm tip regeneration were higher among individuals at the nearshore site. The high overall incidence of individuals with regenerating arms at both sites suggests that predators exert persistent sublethal predatory pressure and may contribute to mortality. Individuals may migrate into deeper water during summer months to avoid thermal stress, hypoxia, or high levels of ultraviolet radiation and to avoid predation when predator densities are likely to be highest.

Food Resource Utilization in the Sea Urchin Lytechinus variegatus in Contrasting Shallow-Water Microhabits of Saint Joseph Bay, Florida

The feeding activity and relative percentages of different foods consumed by the regular sea urchin Lytechinus variegatus in three contrasting microhabitats were examined over a 2-yr period in Saint Joseph Bay, FL, at its northern limits of distribution. In 1993, feeding activity levels of individuals at a site dominated by the seagrass Thalassia testudinum were higher on average than at a site characterized mostly by sand substrates alone or a site dominated by the seagrass Syringodium filiforme. No other significant difference in feeding activity levels was detected between sites or years. Feeding activity was markedly reduced at all sites in winter months of both years. Lytechinus variegatus in Saint Joseph Bay displayed generalist feeding behaviors with diets that appeared to be governed by the availability and palatability of food items. Foods consumed by sea urchins varied seasonally at each site, apparently in response to changes in food availability. Some seasonally abundant algae (e.g., the fleshy red alga Laurencia porteaur) were not consumed, presumably due to chemical defenses. Seasonal depressions in resource utilization and changes in food types likely impact aspects of growth and reproduction of individuals comprising subpopulations of L. variegatus that fringe on the northern limits of their biogeographic distribution.

Recruitment of bay scallops Argopecten irradians in Floridan Gulf of Mexico waters:scales of coherence

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 170:143-157 (1998) - doi:10.3354/meps170143 Recruitment of bay scallops Argopecten irradians in Floridan Gulf of Mexico waters: scales of coherence William S. Arnold*, Dan C. Marelli, Catherine P. Bray**, Melissa M. Harrison Florida Department of Environmental Protection, Florida Marine Research Institute, 100 Eighth Avenue Southeast, St. Petersburg, Florida 33701-5095, USA *E-mail: arnold_b@epic7.dep.state.fl.us **Present address: Florida Department of Environmental Protection, Apalachicola Shellfish Laboratory, 260 Seventh Street, Apalachicola, Florida 32320, USA ABSTRACT: Conventional wisdom suggests that pelagically borne marine invertebrate larvae are dispersed considerable distances from their source population, but recent research provides evidence that at least in some instances larvae may be retained within the local environment. From June 1995 through June 1996, we monitored adult abundance and juvenile recruitment in 4 geographically separated bay scallop Argopecten irradians populations occurring along the Gulf of Mexico coast of Florida, USA. Populations at our Anclote and Homosassa study sites had low adult abundances (generally <5 scallops per 600 m2 survey transect) during 1995 and 1996, whereas populations at our Steinhatchee and St. Joseph Bay study sites had considerably higher adult abundances (generally >25 scallops per 600 m2 survey transect) during those years. Similarly, recruitment to artificial spat collectors was a rare event at Anclote and Homosassa, where we typically collected fewer than 0.1 scallops per collector per day. In contrast, recruits were common at Steinhatchee and St. Joseph Bay, where daily recruitment rates exceeded those observed at Anclote and Homosassa by 1.5 to 2 orders of magnitude. Whereas differences in adult abundance and juvenile recruitment were pronounced among sites, differences among stations within each site were minor and generally not significant. Based upon these observations and knowledge of the distribution and abundance of bay scallops in Floridan Gulf of Mexico waters, our results suggest that during 1995-96, dispersal of bay scallop larvae was widespread within each study site but that transport of larvae away from the adult habitat was uncommon and ultimately unsuccessful. We discuss oceanographic features that may support local retention of bay scallop larvae along the west coast of Florida, and we suggest that periodic interruptions of those oceanographic processes may explain the previously reported genetic homogeneity among bay scallop populations in Florida. KEY WORDS: Dispersal · Recruitment · Argopecten irradians · Self-seeding Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 170. Publication date: September 03, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Regulation of fish reproduction by a predatory gastropod: an experimental investigation of indirect effects in a seagrass community

The indirect effects of the horse conch, a predatory gastropod, on reproduction in a suite of fishes that use the shells of the gastropod's main prey (the pen shell Atrina rigida (Sol.)) as nest sites in St. Joseph Bay, Florida, was investigated by examining the two links (direct interactions) that create the indirect effect. The horse conch– A. rigida predator–prey interaction was quantified by measuring predator feeding rate and distribution across a range of prey density. To determine the effect of A. rigida mortality on fish reproduction, the rate of shell availability was experimentally manipulated and egg production measured in four fish species. Horse conch feeding rate and distribution were not functions of prey density, but A. rigida mortality was correlated with conch abundance, supporting previous evidence that horse conchs regulate new shell availability. Increased rates of shell availability caused increases in the number of clutches laid and average clutch size in one fish species, Chasmodes saburrae Jordan & Gilbert, probably because new shells provide a greater surface area for eggs compared to older shells. These results suggest that horse conchs indirectly affect C. saburrae reproduction both at the level of the individual (clutch size) and the population (egg production) by regulating the availability of new shells. Because prey density had little effect on the predator, variation in the indirect effect of conchs on fish reproduction will be primarily influenced by the distribution of the predator, not A. rigida.