Seasonal fluctuations of benthic macrofauna in the apalachicola estuary,Florida, USA: The role of predation

Long-term monitoring studies revealed a negative correlation between the abundance of bottom-feeding fishes (Leiostomus xanthurus and Micropogonias undulatus) and benthic macrofaunal density, suggesting a causal relationship. To test this hypothesis, large (3x3 m) topless predator-exclusion cages (mesh opening=6 mm) of a design that produced minimal physical artifacts were constructed at two shallow mud-bottom oligohaline stations. Two-sided control cages and uncaged control areas were also sampled Experiments coincided with maximum abundances of bottom-feeding fishes in the spring and motile macroinvertebrates (penaeid shrimp) in the fall. During short-term (two-month) exclusion experiments in the spring and fall of 1980, large predators (those excluded by 6-mm mesh) were not a major factor in regulating the densities of most macrofaunal species. Predation may be important during other seasons, although this possibility was not tested. Densities of Leiostomus xanthurus and Penaeus setiferus during 1980 were lower than in previous years. Despite the reduced abundance of bottom-feeding fishes, macrofaunal densities still declined during late winter/early spring. It is postulated that increased river flow and lowered salinities during the late winter/early spring may contribute to the decline of macrofaunal densities by reducing larval recruitment.     

Distribution and abundance of marine fish larvae in relation to effluent plumes from sewage outfalls and depth of water

Fish larvae were sampled in and below three separate sewage plumes associated with the cliff-face (shoreline) outfalls at North Head, Bondi and Malabar, and at three control (non-plume) sites located>8 km away from the sewage outfalls, at Long Reef, Port Hacking and Marley Beach, in nearshore waters off Sydney, south-eastern Australia. Samples were collected at the surface and at 20 m depth during three periods: December 1989, April/May 1990 and August/September 1990. In December 1989, a greater number of taxa were caught at both depths at the plume sites compared to the control sites, but this did not occur during the other two sampling periods. Similarly, in April/May 1990, greater numbers of the clupeid Hyperlophus vittatus but fewer anthiines were caught at both depths near the outfalls (plume sites). Myctophids were more numerous in surface samples, but not at 20 m, at the plume sites in both April/May and August/September 1990, whereas in April/May 1990, labrids and anguilliformes were less abundant at 20 m at the plume sites compared to the control sites. These differences in the numbers of fish larvae caught may have been an effect of the effluent plumes, but these results were only correlative. The results most probably reflect spatial heterogeneity in the distribution and relative abundance of fish larvae nearshore to Sydney. There were striking differences, however, in the number of fish larvae caught at the surface and at 20 m, and among sampling periods, but these differences were similar across all sites. Of the 46 taxa considered common, 33 occurred in greater numbers at 20 m than at the surface, whereas only 8 taxa were caught in greater numbers at the surface. The composition of the fish larvae also differed markedly among sampling periods; few taxa were common to all three sampling periods. Greater numbers of fish larvae were caught in April/May and August/September 1990 than in December 1989, particularly at 20 m depth. The data highlight the large spatial and temporal heterogeneity in the distribution and relative abundance of fish larvae nearshore to Sydney and the difficulty of identifying effects that are solely due to sewage plumes.     

Defining Forest Fragmentation by Corridor Width: The Influence of Narrow Forest-Dividing Corridors on Forest-Nesting Birds in Southern New Jersey

In studies of forest fragmentation, a fundamental inconsistency exists in the distance criterion used to define the discreteness of forest fragments. We examined three types of ubiquitous, narrow, forest-dividing corridors for effects that influence the relative abundance and community composition of forest-nesting birds. Fixed-radius (100-meter) point counts were conducted on 54 transects established along three width classes of corridors: unpaved roads (8 meters wide), paved roads (16 meters wide), and powerlines (23 meters wide). Transect locations were distributed equally among corridor edge, forest margin 100 meters from corridor edge, and forest interior 300 meters from corridor edge. Forest-interior species of Neotropical migrants had significantly reduced relative abundances on edge transects along 16- and 23-meter corridors, compared with 8-meter corridors and with forest interior points along all three corridor-width classes. At a landscape scale, the consequences of apparently small reductions in forest area by the presence of narrow forest-dividing corridors may be cumulatively significant for abundances of forest-interior species. Brown-headed Cowbirds were more abundant than 20 of 21 forest-interior Neotropical migrants. We found surprisingly high abundances of cowbirds associated with narrow forest-dividing corridors, especially those with mowed grass. Corridor widths as narrow as 8 meters produce forest fragmentation effects in part by attracting cowbirds and nest predators to corridors and adjacent forest interiors. The most serious implication of this study is that narrow forest-dividing corridors may function as ecological traps for forest-interior Neotropical migrants. We suggest that these widespread corridors may be inconspicuous but important contributors to declines of forest-interior nesting species in eastern North America.     

Recovery of benthic communities at Macquarie Island (sub-Antarctic) following a small oil spill

Intertidal communities at Macquarie Island (sub-Antarctic) were re-evaluated seven years after a small oil spill resulting from the grounding of the “Nella Dan”, and six years after the first assessment of biological impact. Sampling was conducted to evaluate community structure in three zones of the exposed rocky shore (upper red, kelp, and lower red) and in samples of Durvillaea antarctica holdfasts. There were no significant differences between the community structure in oiled and control locations in any of the three shore zones, but holdfast macrofaunal communities at oiled sites still showed evidence of impact. Holdfast community-structure in samples from heavily oiled sites showed moderate levels of recovery, with increased abundances of species which were considered sensitive to the oiling in the first post-impact studies and decreased abundances of opportunistic polychaete and oligochaete worms. In contrast, samples collected from the moderately oiled location at Secluded Bay showed little evidence of recovery. Holdfasts at this site were filled with sediment containing traces of diesel oil, and the macrofaunal community was dominated by opportunistic worms. This study clearly indicates that even small incidents of anthropogenic perturbation can have long-lasting consequences for marine communities at Macquarie Island. Received: 23 July 1997 / Accepted: 5 February 1998     

Experimental Rock Outcrops Reveal Continuing Habitat Disturbance for an Endangered Australian Snake

Abstract: Protected areas are commonly viewed as safe havens for endangered species. To test this notion, we experimentally constructed small rock outcrops for the endangered broad-headed snake (   Hoplocephalus bungaroides ) within a national park near Sydney, Australia. Rock outcrops provide vital shelter sites during the cooler months of the year. Constructed rock outcrops (3 × 5 m) were placed at 11 paired sites located near (≤250 m) and far from (>400 m) walking tracks and roads. Eight of our 22 rock outcrops were disturbed by people over a 15-month period. Disturbance consisted of displacement of some rocks or complete destruction of the outcrop. Disturbed outcrops occurred up to 450 m from a walking track or road. Disturbance to natural outcrops has also been observed in this park. This demonstrates a continuing decline in the quality of this snake's habitat. Twenty of our rock outcrops were colonized by velvet geckos ( Oedura lesueurii ), the primary prey of this snake. One broad-headed snake was found in one outcrop. According to these findings, attempts to restore the habitat of this endangered snake should be centered on sites located ≥500 m from a walking track or road. Our study highlights the value of targeted experiments that precede larger-scale habitat restoration.     

Predation on walleye pollock (Theragra chalcogramma) eggs in the western Gulf of Alaska: the roles of vertebrate and invertebrate predators

Estimates were made of the predation rate upon eggs of walleye pollock (Theragra chalcogramma) in Shelikof Strait in the western Gulf of Alaska by midwater and near-bottom fish and invertebrate predators during April 1990. Adult and juvenile walleye pollock were the dominant (99% of total abundance) planktivores collected in midwater samples. Based on visual inspection of stomach contents, a high percentage of the sampled fish were found to have consumed pollock eggs. Daily egg consumption by older age groups of walleye pollock was estimated to be <1% of the eggs available at all sampling locations. The only other fishes found to consume pollock eggs were flatfishes collected in bottom trawls but their abundances and egg consumption were very low. Gammarid and hyperiid amphipods were important invertebrate predators on eggs in the water column, as determined by immunoassays using antibodies developed specifically to ascertain the presence of pollock egg-yolk protein. Decapod shrimp showed a high proportion of positive assays in near-bottom collections. Invertebrate predators may have consumed up to 4% of the total number of eggs available in the water column, but <1% of the total near the bottom on a daily basis. Although we were not able to account for the entire daily egg mortality estimated for this stock, our method of using a combination of techniques is promising in terms of future attempts at estimating total predation mortality.     

Fish assemblages in seagrass beds are influenced by the proximity of mangrove forests

Mangrove forests and seagrass beds frequently occur as adjacent habitats in the temperate waters of southeastern Australia. At low tide when fish cannot occupy mangroves they might utilise adjacent habitats, including seagrass. We first sampled small fish from seagrass beds close to and far from mangroves in the Pittwater estuary, NSW, Australia. Seagrass beds close to mangroves had a greater density of fish species than beds far from mangroves (close: mean 16.0 species net⁻¹, SE 1.0; far: 13.2, 1.3; P < 0.05). In particular, juvenile fish were in greater densities near to than far from mangroves (close: 5.3, 0.4; far: 3.1, 0.4; P < 0.05). We then sampled the mangrove forests during the high tide and seagrass beds during the low tide, in beds along a continuum of distances from mangroves. Multivariate analysis showed that fish assemblages differed with distance from mangroves, and the differences were attributed to the composition of the fish assemblage (i.e. presence/absence of fish species), not the abundances of individual species. In particular, fish that utilise mangrove forests at high tide were found in greater species densities and species richness in seagrass nearer to mangroves. A negative relationship was found between the density of mangrove-utilising fish species and the distance of the bed from mangroves (R ² = 0.37, P < 0.05). This confirms the important connectivity between mangroves and seagrass for fish in temperate Australian waters.     

Movements of <Emphasis Type="Italic">Ilyanassa obsoleta</Emphasis> (Gastropoda) on an intertidal sandflat

The gastropod Ilyanassa obsoleta (Say) is native to the east coast of North America where it is locally abundant on sandflats, mudflats, and in saltmarsh creeks. The local disturbances created by snails and their movements affect soft-sediment community composition. Movements of individually marked snails were followed on an intertidal sandflat on Cape Henlopen, Delaware, U.S.A. In June 1991, 1,200 snails that had tested as trematode-uninfected were released and over 5 months 554 were sighted 971 times. Mean daily net distance moved was 1.7 m, but snails often moved 10–20 m day⁻¹ and one snail was 180 m distant after 130 days. Net dispersal of the released population was attained in ≈10 days, by which time, a typical distance from release was 15–20 m. Snails were not found crossing sandbars and most moved away from shore into a tidal gully. In June 1993, 500 snails, both uninfected and trematode-infected, were released at the same position and over 6 months, 350 snails were sighted 949 times. Sandbars were again barriers to movement, but their changed positions allowed wider dispersal. Net dispersal was complete in ≈20 days by which time a typical distance from release was 30–40 m. Mean daily net distance moved was 2.2 m, but within 10 days snails had moved 50–100 m. In both years, following initial dispersal, snails (infected or not) took up random directions from move to move. Infected and uninfected snails dispersed equal distances, but had different mean final dispersal directions. Dispersal of I. obsoleta individuals was extensive and affected by shifting sandbar positions and parasitism. Recognizing this will be important in appreciating the ecological dynamics of this gastropod and in determining its effects on soft-bottom communities.Electronic Supplementary Material Supplementary material is available for this article at     

Spatial and temporal variation in a soft-bottom fish assemblage in St Vincent Bay,New Caledonia

Monthly trawl surveys were performed in 1989 in North Bay and South Bay of St Vincent (New Caledonia) with both a shrimp trawl and fish trawl to produce a reference standard of the natural variability of an unexploited tropical soft-bottom fish assemblage. A total of 230 species belonging to 62 families were recorded. The mean density and biomass were 0.18 fishes m^-2 and 4.31 g m^-2, respectively. The major variations were explained by spatial factors. Species richness, density and biomass were greater in South Bay (204 species, 0.26 fishes m^-2 and 5.90 g m^-2) than in North Bay (105 species, 0.10 fishes m^-2 and 2.71 g m^-2), 34% of the species being present in both areas. The North Bay assemblage was characterized by four abundant benthic species (Saurida undosquamis, Gerres ovatus, Secutor ruconius and Upeneus moluccensis) and by numerous pelagic species (Carangidae, Sphyraenidae and Scombridae). The South Bay assemblage was characterized by several Mullidae, Bothidae and Balistidae, and by some rare species usually found on coral reefs (Pomacentridae and Chaetodontidae). These differences were induced by the physical and benthic characteristics of the two bays. North Bay was an homogeneous, confined, deposit area with few benthic organisms, whereas the substrate was more heterogeneous and the benthic organisms more diversified and abundant in South Bay, which was connected to the adjacent reef lagoon. Species richness remained stable in time, except in January when a hurricane disturbed the environment. Seasonal tendencies in species composition were evidenced in North Bay, with an autumn-winter structure opposed to a spring-summer structure, and characterized by the relative importance of the major species. No seasonal tendencies were observed in the organization of the South Bay assemblage. Nevertheless, mean density and biomass were at a minimum in summer in both bays; maxima occurred in winter. Biomass was negatively correlated to both temperature and rainfall, and reflected the population variations of the main species, particularly their reproductive migrations. Thus, the soft-bottom fish assemblages were strongly organized spatially in New Caledonia, but remained relatively stable over time.     

Influence of an artificial reef on the surrounding infaunal community

Artificial reefs have been constructed throughout the world, but their effects on adjacent soft-bottom communities are largely unknown. In December 1986, we investigated the influence of Pendleton Artificial Reef (PAR) in Southern California on the abundance of infauna in the surrounding sand bottom. PAR was constructed in 1980 of quarry rock placed in eight piles, or modules. The artificial reef altered the grain-size distribution of sediments around the reef; sediments close to the modules were coarser than those 10 or 20 m away from the modules. Densities of one of the two most common species, the polychaetePrionospio pygmaeus, were lower near the reef, perhaps due to foraging by reef-associated predators or because the habitat near the reef was less suitable. We found no evidence that foraging by reef-associated fishes caused a widespread reduction in infaunal densities near the reef, and in fact the other most common taxon,Spiophanes spp., had higher densities near the reef. The most conspicuous effect of the artificial reef concerned the tube-dwelling wormDiopatra ornata, which only occurred in close association with the modules. In addition, total infaunal density and the densities of decapods, echinoderms and sipunculids were higher withinD. ornata beds than outside the beds. These results indicate that the densities of some species were enhanced, and others depressed, around the reef, but that the overall effect of the artificial reef on the surrounding infauna was limited to a small area near the modules.     

Interlinked temporal changes in environmental conditions, chemical characteristics of sediments and macrofaunal assemblages in an estuarine intertidal sandflat (Seto Inland Sea, Japan)

Five field surveys were conducted in an estuarine intertidal sandflat of the Seto Inland Sea (Japan) between April 1994 and April 1995. Chlorophyll a, pheopigments, total organic carbon and acid-volatile sulphides (AVS) of surface and subsurface sediments, and macrofaunal assemblages were investigated in parallel at 15 stations. Monthly hydrological data of low-tide creek water adjacent to the flat were used as a complementary environmental characterisation of the study area. Strong temporal changes were found among sampling dates, most remarkably in autumn with a major increase of algal detritus and AVS, a sharp reduction in macrofaunal abundances and species richness, and a massive mortality of the clam Ruditapes philippinarum. This dystrophic event was preceded by a photoautotrophic and hypertrophic spring–summer characterized by abundant fresh (i.e., living) algal material, including microphytobenthos and macroalgae (Ulva sp.). In summer, abundant macrofaunal assemblages reached the highest biomass values (455 g wet weight m⁻² or 60.6 g ash free dry weight m⁻²), with a major contribution of filter-feeding bivalves Musculista senhousia and R. philippinarum. These are among the highest values reported in the literature for sedimentary shores. From autumn, there was a progressive recolonisation of macrofauna, initiated by few opportunistic polychaetes (e.g., Cirriformia tentaculata and Polydora sp.), apparently promoting a fast sediment recovery in winter, and followed by new bivalve recruits in the next spring. This study provides the first evidence of significant and interlinked within-year changes in chemical characteristics of sediments and macrofaunal assemblages in an estuarine intertidal flat at a small spatial scale (i.e., tens of meters). This demonstrates the high temporal variability of species–environment relations in these systems and a close relationship in seasonally driven trophodynamic processes among primary producers and benthic consumers. We conclude that a thorough parallel evaluation of the temporal changes in chemical characteristics of sediments should be taken into account in assessing the year-round distribution and changes of intertidal macrofauna, particularly in eutrophic, estuarine intertidal flats.An erratum to this article can be found at     

The Effect of Edge on Avian Nest Success: How Strong Is the Evidence?

Wildlife biologists historically considered the edge between adjacent habitat types highly productive and beneficial to wildlife. A current dogma is that edges adversely affect a wide range of avian species by increasing depredation and parasitism rates of nests. I critically evaluated existing empirical evidence to test whether there was a gradation in nest success as a function of distance from an edge. Researchers investigating this question have been inconsistent in their experimental designs, making generalizations about edge-effect patterns difficult. The majority of studies I examined found nest success varied near edges, with both depredation rates (10 of 14 artificial nest studies, and 4 of 7 natural nest studies) and parasitism rates (3 of 5 studies) increasing near edges. In addition, there was apositive relationship between nest success and patch size (8 of 8 studies). The most conclusive studies suggest that edge effects usually occur within 50 m of an edge, whereas studies proposing that increased depredation rates extend farther than 50 m from an edge are less convincing. Prior research has probably focused on distances too far from an edge to detect threshold values, and future research should emphasize smaller scales. 100–200 m from an edge at 20–25 m increments. Researchers often use relatively arbitrary habitat characteristics to define an edge. Therefore, I propose that only openings in the forest canopy with a diameter three times or more the height of the adjacent trees should be included in edge analyses. This review suggests that fragmentation of eastern North American temperate forests could lead to increased nest predation and parasitism, and there is need to determine if similar processes occur in other forested regions of North America.     

FADs influence on settlement and dispersal of the young-of-the-year greater amberjack (<Emphasis Type="Italic">Seriola dumerili</Emphasis>)

FADs are fish aggregating devices applied worldwide over the centuries to increase fish catch. However, the utilisation of such floating devices can influence dispersion patterns of some fish species. At present it is still not clear if FADs play a role in the shoreward migrations of juvenile fish of reef associated species, such as the greater amberjack Seriola dumerili. In this study, we hypothesised that FADs located along a distance gradient from the shore might lead the greater amberjack inshore. In such case, mean abundance of S. dumerili should decrease over time in offshore FADs and increase in inshore FADs. To test the hypothesis three FAD systems were positioned in the Gulf of Castellammare (Sicily, Italy), between July and September 2001, at increasing distances from the coast. During the study period, five visual censuses were carried out within FADs fields. During the first sampling period, no significant difference in abundance and size of juvenile S. dumerili was found between the three FAD systems. All the other sampling periods reported higher abundances and sizes in the offshore FADs than in the two inshore FADs. The findings suggest that FAD systems might be exerting two different effects on young of the year (YOY) S. dumerili distribution: (a) offshore FADs tend to retain associated fish for longer periods of time, (b) coastal FADs favour the transition of YOY S. dumerili from the pelagic to the benthic domain.     

Predators of juvenile sea urchins and the effect of habitat refuges

We evaluated the effects of potential predators from intertidal habitats on Strongylocentrotus purpuratus survival using laboratory experiments and assessed abundances of main predatory species along the Pacific coast of North America. The interactive effects of urchins’ and predators’ sizes in mediating predation were quantified. Habitat complexity (substrate pits, adult spine canopy) was manipulated to examine its effects on predation of most susceptible individuals (<14 mm). Pachygrapsus crassipes was identified as a major predator of urchins up to ≈30 mm. A positive effect of predator size on consumption of progressively larger urchins was detected, probably due to a mechanical limitation on crabs’ ability to consume large prey. Larger claws of males with respect to females of comparable sizes facilitated the handling of larger prey. Substrate refuges significantly reduced mortality on juvenile urchins. These results show that crab predation may be important in organizing intertidal communities, despite multiple ecological mechanisms promoting sea urchin survival.     

Species-specific predation on amphipod crustacea by the pinfish Lagodon rhomboides: Mediation by macrophyte standing crop

The amphipod species consumed by Lagodon rhomboides represented only a small subset of the amphipod assemblage available at three seagrass habitats in Apalachee Bay, Florida (USA). Predatory preferences were related most closely to the microhabitat of prey species and were unrelated to amphipod abundances. Important prey species were all epifaunal types. Consumption of preferred amphipod species was non-selective at a site with sparse macrophyte cover, but selectivity increased with macrophyte biomass. The amphipod species that were preferentially selected as prey by pinfish correspond with those that have been suggested as being limited by fish predators. It was suggested that mediation of predator behavior by physical structure in seagrass meadows may play an important role in the regulation of species richness and abundances. Species-specific identification of prey is recommended for food-habit studies.     

Sea-bird aggregation at a deep North Pacific seamount

During June 1991, we studied sea birds at a mid-ocean seamount (Fieberling Guyot) in the eastern North Pacific Ocean. Avifaunal composition changed from small Procellariiformes [a storm-petrel; Oceanodroma leucorhoa (Vieillot)] away from the seamount to an assemblage dominated by larger tubenoses [mostly black-footed albatross Diomedea nigripes Audubon and Cook's petrel Pterodroma cookii (Gray)]. Compared to adjacent waters, sea-bird density and biomass within a 30-km radius centered on the seamount summit were 2.4 and 8 times higher, respectively. Individual sea-bird taxa were 2 to 40 times more abundant at the seamount relative to values reported previously from large-scale surveys of deep-ocean regions in the central North Pacific. In September 1991 we studied potential prey of sea birds in the upper water column using a neuston net and multiple opening-closing net system (MOCNESS) tows. Most potential prey types in the neuston exhibited no significant enhancement over the seamount. MOCNESS samples at 10 m depth, however, showed several prey types to be more abundant over the seamount, and the dominant size class of fish was slightly larger. We attribute the sea-bird aggregation observed at this seamount to changes in the abundance and/or behavior of pelagic organisms in the deep scattering layer (not adequately sampled in this study), perhaps augmented by migrations of seamount residents into the surface layers. Processes on and in the vicinity of seamounts may provide spatially-predictable prey to wide-ranging aerial sea birds foraging in this relatively austere environment.     

Statistical modeling of seasonal and environmental influences on the population dynamics of an estuarine fish community

A statistical modeling study was performed on the population fluctuations of the 15 commonest fish species frequenting the tidal Scheldt estuary in Belgium. These included marine juvenile and seasonal visitors, estuarine residents and diadromous fish species that were recorded on the filter screens of a power plant cooling-water intake between September 1991 and April 2001. The species population abundance was regressed against a candidate set of 6 environmental variables and 13 instrumental variables, accounting for seasonality and long-term trends present in the data. Population abundances of the different species were, in general, best described by seasonal variables. Seasonal components contributed, on average, up to 63.8% of the variance explained by the models. Ten species were found to show a slightly negative, though significant, trend over the period of the survey. Most models also included at least one environmental variable, and 25.4% of the explained variance could be attributed to environmental fluctuations. Of all physico-chemical variables, dissolved oxygen was the most important predictor of fish abundance, suggesting that the estuary suffered from poor water quality during the survey. Temperature, salinity, freshwater flow, suspended solids and chlorophyll a concentrations were minor determinants of fish abundance.Communicated by O. Kinne, Oldendorf/Luhe     

Molecular phylogeny of mud crabs (Brachyura: Panopeidae) from the northwestern Atlantic and the role of morphological stasis and convergence

 Mud crabs of the family Panopeidae are common organisms in coastal soft-bottom, vegetated, rubble, and oyster-bed communities along the temperate and tropical coastlines of the American continent. Similar morphology among many species renders their distinction and classification difficult. Here, we present phylogenies of western Atlantic Panopeidae based on DNA sequences of the mitochondrial large subunit rRNA (16S; 529 basepairs) and cytochrome oxidase I (COI; 640 basepairs) genes. Results suggest that the speciose genera Panopeus and Eurypanopeus are not monophyletic and that their taxonomy does not accurately reflect evolutionary partitions. In two cases (P. herbstii complex and E. depressus and allies), the molecular findings strongly support sister-species relationships that differ from previous morphology-based assumptions. We suggest that convergence or morphological stasis are responsible for the phenotypic similarities between divergent evolutionary lineages. Received: 23 July 1999 / Accepted: 5 April 2000     

How well do sunken vessels approximate fish assemblages on coral reefs? Conservation implications of vessel-reef deployments

The amount of artificial habitat (termed ??artificial reef??, AR) in marine systems is rapidly increasing, yet the effect of most types of AR on reef communities remains unknown. We examined the role of well-established vessel-reefs in structuring coral reef fish assemblages by comparing assemblages on 7 World War II wrecks (>65?years old) to those on interspersed coral patch reefs of comparable size in a tropical lagoon. Fish abundance, species richness, diversity and feeding guild structure on wrecks were similar to natural reefs; however, species composition differed between the two reef types (R?=?0.189?C0.341, average dissimilarity: 67.3?C68.8?%). Despite being more species-rich and diverse, fish assemblages on larger wrecks were less similar to assemblages on their adjacent natural reefs than smaller wrecks. Wrecks may also have affected fish abundance on adjacent natural reefs, with reefs adjacent to larger wrecks supporting higher abundances than reefs adjacent to smaller wrecks. Our results indicate that increases in vessel-reef habitat may not greatly affect reef fish assemblage parameters, but may affect the relative abundances of particular species.     

Exploited species impacts on trophic linkages along reef-seagrass interfaces in the Florida Keys

The removal of fish biomass by extensive commercial and recreational fishing has been hypothesized to drastically alter the strength of trophic linkages among adjacent habitats. We evaluated the effects of removing predatory fishes on trophic transfers between coral reefs and adjacent seagrass meadows by comparing fish community structure, grazing intensity, and invertebrate predation potential in predator-rich no-take sites and nearby predator-poor fished sites in the Florida Keys (USA). Exploited fishes were more abundant at the no-take sites than at the fished sites. Most of the exploited fishes were either omnivores or invertivores. More piscivores were recorded at no-take sites, but most (approximately 95%) were moderately fished and unexploited species (barracuda and bar jacks, respectively). Impacts of these consumers on lower trophic levels were modest. Herbivorous and smaller prey fish (< 10 cm total length) densities and seagrass grazing diminished with distance from reefs and were not negatively impacted by the elevated densities of exploited fishes at no-take sites. Predation by reef fishes on most tethered invertebrates was high, but exploited species impacts varied with prey type. The results of the study show that, even though abundances of reef-associated fishes have been reduced at fished sites, there is little evidence that this has produced cascading trophic effects or interrupted cross-habitat energy exchanges between coral reefs and seagrasses.