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

Fitness consequences of prey depletion for the common goby, Pomatoschistus microps

Angus C. Jackson,* Simon D. Rundle, and Martin J. Attrill. Department of Biological Sciences, University of Plymouth, Drake Circus, Plymouth. PL4 8AA, UK; telephone + 44 (0)1752 232953; fax + 44 (0)1752 232927; e-mail [e-mail].

Pomatoschistus microps (Pisces: Gobiidae), a predatory, benthic feeder, occurs in high densities in variable, shallow, muddy coastal waters where prey availability can be unpredictable. Here we investigate the effect and consequences of prey depletion on the body condition and nest building of adult male fish using manipulative mesocosm experiments in which the comparative value of meiofaunal and macrofaunal prey was investigated. Fish maintained in mesocosms from which macrofauna had been removed from the sediment had a significantly reduced hepatosomatic index (HSI) and were less likely to build nests than fish in mesocosms containing macrofauna and meiofauna. HSI was also a good predictor of nest quality (i.e. entrance diameter), suggesting an indirect link between prey availability and nest quality. This study suggests that reduced resource availability, in the form of scarcity of macrofauna, may have profound implications for the fitness of natural field populations. As fish in mesocosms from which macrofauna had been removed continued to feed, this reduced fitness may reflect a cost associated with plasticity in feeding behaviour.


Habitat characteristics affecting fish and decapod assemblages of seagrass (Zostera marina) beds around the coast of Jersey (English Channel)

E. L. Jackson,^1,2* M. J. Attrill,¹ S. J. Bossy,² M. B. Jones,¹ and A. A. Rowden.^{1,3 1}Department of Biological Sciences, University of Plymouth, United Kingdom; ²Department of Agriculture and Fisheries, States of Jersey, English Channel; ³Present address: Marine Biodiversity Group, NIWA, Wellington, New Zealand.

Although it is widely accepted that seagrass habitats are important nursery areas, refugia and feeding grounds for many species, including those of commercial value, little research establishing these roles has been conducted in Europe. In particular, studies of British seagrass beds are lacking, even though their (presumed) importance is highlighted in British fisheries management and conservation strategies (e.g. UK Biodiversity Habitat Action Plans). This study examines the spatial utilisation of sub-tidal seagrass beds by fish and decapods in the coastal waters of the island of Jersey in the English Channel. Previous results for total species richness and species density indicated that variability between sites explained more variation than bed location. Thus, habitat characteristics of ten seagrass beds were examined for potential influences on fish assemblage composition. Data for fish and decapods were coupled with corresponding seagrass habitat variables (including bed size, percentage cover, shoot density, water depth and sediment type), established from aerial photographic analysis, digital echo-sounder data and diver surveys. The contribution of these variables as predictors of fish and decapod assemblage measures were evaluated using multiple linear regression models. Comparisons are made with similar studies at different geographical locations. These data are valuable in distinguishing and understanding potentially important processes, and can be used by local fishery agencies to predict the relative importance of seagrass beds (to aid conservation designation) or the consequences of different perturbation scenarios.


Barnacles to worms: periodic hypoxia in the Chesapeake Bay shifts community composition, but does it facilitate invasion?

Elizabeth B. Jewett,^1,2* Anson H. Hines,¹ and Gregory M. Ruiz.^{1 1}Smithsonian Environmental Research Center, Edgewater, MD, USA; ²University of Maryland, College Park, MD, USA.

Hypoxia is increasing substantially in many marine and estuarine systems worldwide, primarily due to anthropogenic causes. Using fouling organisms in the Chesapeake Bay as an experimental system, we tested the hypothesis that periodic hypoxia (dissolved oxygen < 2 mg/l) may render the native fouling community more vulnerable to invasion by non-indigenous species. Some organisms may thrive due to reduced predation while others may capitalize on cleared space. PVC settling plates were deployed at shallow depths in spring 2001 at Gloucester Pt, Virginia and were manipulated biweekly from late June to early August. Manipulation involved placing individual panels in buckets and controlling DO (dissolved oxygen) levels (hypoxic, just above hypoxic and normoxic) and time exposures (6h, 12h and 24h) according to a 3x3 factorial experimental design (n=8). MDS (multi-dimensional scaling) results indicate a difference in the overall community composition according to DO manipulation. Only those plates subjected to the lowest oxygen level showed a difference according to time exposed with the communities exposed to hypoxia for 24 hours exhibiting a lower biomass and higher species diversity. Hypoxia did not affect species richness but it did affect the relative abundance of the organisms present. The percent cover of Hydroides dianthus, a native serpulid polychaete, increased with lower DO levels. The percent cover of Molgula manhattensis, a solitary tunicate of cryptogenic origin, and of Ficopomatus enigmaticus, an invasive serpulid, increased at the mid-DO level, which suggests an intermediate disturbance effect. According to SIMPER (similarity percent routine) analysis, community dominance shifted from barnacles to polychaete worms as hypoxia (and time exposed to hypoxia) increased. These findings may have implications for nutrient cycling and/or food chain dynamics in systems that experience periodic hypoxic conditions.


Population dynamics and movement patterns of blue crabs in estuarine salt marshes

Eric G. Johnson* and David B. Eggleston. Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695, USA.

A series of complimentary techniques were employed to quantify population demographics and describe patterns of movement of juvenile and adult blue crabs, Callinectes sapidus, in two tidal salt marsh habitats located in the Newport River estuary in Beaufort, NC during June - October of 2001. We tagged approximately 1,500 blue crabs (21 – 148mm carapace width) with individually coded microwire tags, and used a Jolly-Seber capture-recapture model to estimate population size, as well as probability of loss and recruitment. Microwire tags are an effective method for tagging marine crustaceans, because they provide a permanent internal tag that is rarely lost through molting, and the tag does not influence growth or mortality rates. Independent estimates of emigration were measured through the use of block nets, which sampled crabs moving out of and into the study site, and sampling for tagged individuals outside of the study areas. These independent estimates allowed us to partition crab loss from salt marshes into mortality and emigration. To examine patterns of movement within the salt marsh, crabs were tracked for 24-h using individually numbered floating tags that were affixed to the carapace of juvenile crabs (35- 68 mm CW). Juvenile crabs were mobile within the interstices of the marsh canopy during flood tide, and tended to remain buried in mud within the marsh during ebb tide. Juvenile crabs exhibited a high degree of site fidelity to a given marsh system during summer-fall, particularly smaller crabs, with the probability of mortality significantly higher than emigration. These results provide important information on the nursery role of salt marsh systems.


Nekton utilization of intertidal marsh interspersed with micro-rivulets in Chesapeake Bay

J. M. Johnson* and D. L. Meyer. Center for Coastal Fisheries Habitat Research, National Oceanic and Atmospheric Administration, 101 Pivers Island Rd, Beaufort, NC 28516, USA.

The use of intertidal marshes to provide refuge and a forage base for marsh resident nekton species such as Fundulus sp. and Cyprinodon variegatus is well documented. In areas of northern Chesapeake Bay these intertidal marshes are made up of hummocks of Spartina alterniflora and Phragmites australis interspersed by micro-rivulets. The amount of channelization present in these marshes varies widely. During the course of a previous study comparing nekton utilization of the two dominant intertidal marsh plant species, visual observations led to the hypothesis that the amount of marsh channelization, due to the presence of these micro-rivulets, influenced marsh resident nekton utilization. Subsequently the marshes were mapped to determine the amount of channelization present. All sites were located in the Kent Narrows area of Chesapeake Bay and sampled in the spring, summer and fall of 1997-1998. Regression analysis of the average combined densities of Fundulus sp. (F. heteroclitus, F. majalis, F. diaphanus, F. luciae) and C. variegatus versus the area ratio of hummocks/micro-rivulets present in the front meter of the marsh/creek interface indicated a quadratic relationship, accounting for 64% of the variation observed (p=0.045). The optimal area ratio for resident nekton species indicated by the regression model was 35% hummocks/65% micro-rivulets in the front meter of marsh. This suggests that the presence of these micro-rivulets, with the proper degree of channelization at the marsh/creek interface, allows greater access to the marsh interior earlier in the flood tide cycle for marsh resident nekton species while still offering protection from predation.