Persistence of coral assemblages at East and West Flower Garden Banks,Gulf of Mexico

Since 1989 a federally supported long-term coral reef monitoring program has focused on two study sites atop East and West Flower Garden Banks in the northwestern Gulf of Mexico. We examined 25 yr of benthic cover data to provide a multi-decadal baseline and trend analysis of the community structure for this coral reef system. Despite global coral reef decline in recent decades, mean coral cover at East and West Flower Garden Banks was above 50% for the combined 25 yr of continuous monitoring, and represented a stable coral community. However, mean macroalgal cover increased significantly between 1998 and 1999, rising from approximately 3 to 20%, and reaching a maximum above 30% in 2012. In contrast to many other shallow water reefs in the Caribbean region, increases in mean macroalgal cover have not been concomitant with coral cover decline at the Flower Garden Banks.     

Diversity of Meiofauna from the 9°50′N East Pacific Rise across a Gradient of Hydrothermal Fluid Emissions

Background

We studied the meiofauna community at deep-sea hydrothermal vents along a gradient of vent fluid emissions in the axial summit trought (AST) of the East Pacific Rise 9°50′N region. The gradient ranged from extreme high temperatures, high sulfide concentrations, and low pH at sulfide chimneys to ambient deep-sea water conditions on bare basalt. We explore meiofauna diversity and abundance, and discuss its possible underlying ecological and evolutionary processes.

Methodology/Principal Findings

After sampling in five physico-chemically different habitats, the meiofauna was sorted, counted and classified. Abundances were low at all sites. A total of 52 species were identified at vent habitats. The vent community was dominated by hard substrate generalists that also lived on bare basalt at ambient deep-sea temperature in the axial summit trough (AST generalists). Some vent species were restricted to a specific vent habitat (vent specialists), but others occurred over a wide range of physico-chemical conditions (vent generalists). Additionally, 35 species were only found on cold bare basalt (basalt specialists). At vent sites, species richness and diversity clearly increased with decreasing influence of vent fluid emissions from extreme flow sulfide chimney (no fauna), high flow pompei worm (S: 4–7, H''_loge: 0.11–0.45), vigorous flow tubeworm (S: 8–23; H''_loge: 0.44–2.00) to low flow mussel habitats (S: 28–31; H''_loge: 2.34–2.60).

Conclusions/Significance

Our data suggest that with increasing temperature and toxic hydrogen sulfide concentrations and increasing amplitude of variation of these factors, fewer species are able to cope with these extreme conditions. This results in less diverse communities in more extreme habitats. The finding of many species being present at sites with and without vent fluid emissions points to a non endemic deep-sea hydrothermal vent meiofaunal community. This is in contrast to a mostly endemic macrofauna but similar to what is known for meiofauna from shallow-water vents.     

Population fluctuation and vertical distribution of meiofauna in the Red Sea interstitial environment

The composition and distribution of the benthic meiofauna assemblages of the Egyptian coasts along the Red Sea are described in relation to abiotic variables. Sediment samples were collected seasonally from three stations chosen along the Red Sea to observe the meiofaunal community structure, its temporal distribution and vertical fluctuation in relation to environmental conditions of the Red Sea marine ecosystem. The temperature, salinity, pH, dissolved oxygen, and redox potential were measured at the time of collection. The water content of the sediments, total organic matters and chlorophyll a values were determined, and sediment samples were subjected to granulometric analysis. A total of 10 meiofauna taxa were identified, with the meiofauna being primarily represented by nematodes (on annual average from 42% to 84%), harpacticoids, polycheates and ostracodes; and the meiofauna abundances ranging from 41 to 167 ind./10 cm². The meiofaunal population density fluctuated seasonally with a peak of 192.52 ind./10 cm² during summer at station II. The vertical zonation in the distribution of meiofaunal community was significantly correlated with interstitial water, chlorophyll a and total organic matter values. The present study indicates the existence of the well diversified meiofaunal group which can serve as food for higher trophic levels in the Red Sea interstitial environment.     

Weak meiofaunal trophic linkages in Crangon crangon and Carcinus maenus

To document the relative importance of meiofauna as prey for juvenile Crangon crangon and Carcinus maenus, short interval (1.5-2 h) collections were made in the muddy Lynher Estuary (Plymouth, Great Britain) and in the sandy-bottom Ythan Estuary (Aberdeenshire, Scotland) in 1990. Gut passage times of Crangon fed flaked fish food and fluorescent tracer in the laboratory at 13 °C ranged from 4 to 20 h. Wild shrimp exhibited feeding periodicity, with guts fullest during high tide in both locations. Visual and immunological gut contents analyses revealed that meiofaunal nematodes and harpacticoid copepods were present only in recently settled shrimp from 8 to 12 mm total length on muddy bottoms. Larger shrimp collectively consumed up to 33 different macrobenthic prey types. Shrimp were fullest at night (mean gut contents weight = 8% wet body weight, Lynher) or at dawn (6%, Ythan). The Lynher Carcinus gut contents—from animals 8 to 30 mm carapace width, examined visually only—contained mostly fluids, green benthic algae, sediment particles, and masses of unidentifiable prey remains plus digestion-resistant hard parts visually identifiable as macrobenthic in origin. None of the 203 crabs examined from the 24-h collection contained meiofaunal prey. Crangon shrimp probably eat meiofaunal prey for only a brief period of time after their initial settlement to the bottom. Evidence for significant top-down impacts on meiofauna from these two abundant shallow-water predators was weak. More trophic studies are needed on newly settled epibenthic predators to test the hypothesis that biological control of shallow-water meiofauna is important.     

A Thiobios Does Exist - Gnathostomulid Domination of the Canyon Community at the East Flower Garden Brine Seep

A community of organisms dominated by gnathostomulids has been discovered at the East Flower Garden Brine Seep. This discovery clearly demonstrates that specialized communities of micro-metazoans exist in and below sulfide-dependent chemoclines. The term thiobios should be retained to describe these communities.     

Duration and frequency of non-flow periods affect the abundance and diversity of stream meiofauna

1. Intermittent streams (IS) comprise a large proportion of the drainage network in many parts of the world. The non-flow period of IS are known to impact stream biota because aquatic habitats dry out. However, less well understood are the relative effects of the temporal component of these drying events including their duration and frequency.
2. Here, we characterised effects of temporal component of drying events on abundant and species-rich meiofauna. The effects were assessed in 22 streams in the north-eastern Iberian Peninsula. The duration and frequency of non-flow events was characterized over a period of 250 days prior to sampling the sediment-dwelling meiofauna in riffle zones that completely dried out.
3. Overall, meiofauna abundances were amongst the highest ever reported for streambeds. Most meiofaunal taxa correlated positively with the frequency of drying events and correlated positively with the length of dry periods recorded shortly before sampling, suggesting that the community was able to recover quickly. Tardigrades were the only group to correlate positively with the longest dry periods, suggesting that they had the best resilience capabilities in streams that had experienced the longest droughts.
4. On average, nematodes made up half of the meiofauna. We identified a total of 113 different nematode species. The nematode community was more taxonomically diverse in IS, with a smaller proportion of bacterivores and a higher proportion of fungivore species such as Filenchus vulgaris. Thereby resembling the trophic structure commonly observed in soil ecosystems.
5. Our results show that most meiofauna were positively influenced by drying disturbance, that is being able to quickly recover after them. This suggests outstanding resilience capabilities, and points out meiofaunal organisms as key players for kick-starting stream food webs and functions once flow returns.

     

The nematode fauna in the sulphide–rich brine seep and adjacent bottoms of the East Flower Garden, NW Gulf of Mexico. II. Monhysterida

Eight nematode species of the order Monhysterida are described from the East Flower Garden at 72 m depth in the north–western Gulf of Mexico. The material is from sandy and rocky bottom samples influenced or beyond the influence o f a sulphide–rich brine seep. Seven species are new to science: Monhystera anoxybiotica sp.n., Gonionchus intermedius sp.n., Theristus (Theristus) coplatus sp.n., Theristus (Theristus) rezaki sp.n., Xyala oxybiotica spa., Desmolaimoides thiobioticus gen. et sp.n. and Linhomoeus gittingsi sp.n. Specimens of a Linhomoeus species are also described. The species is probably new to science, but the available material only includes females and juveniles.     

Adaptations to life in the sulfide system: a comparison of oxygen detoxifying enzymes in thiobiotic and oxybiotic meiofauna (and freshwater planarians)

Summary Although thiobiotic meiofauna live under anoxia, they have higher levels of the oxygen-detoxifying enzymes catalase and superoxide dismutase (SOD) than oxybiotic species. Microoxyphilic oxybios have lower enzyme activities than other oxybiotic species. All meiofauna have lower activities than oxybiotic macrofauna. Catalase and SOD activities increased in direct proportion to sulfide tolerance in thiobios and to ambient oxygen concentration in oxybios. All meiofaunal species studied, including oxybios, are usually exposed to lower O₂ concentrations than burrow-dwelling macrofauna and so have lower catalase and SOD activities. Enzyme activities in thiobios must be related to sulfide concentration and sulfide metabolism because simple oxygen exposure is an unlikely explanation. Thiobiotic catalase is insensitive to both azide and 3-amino-1,2,4-triazole, similar to a sulfide-insensitive bacterial enzyme called pseudocatalase. Catalase and SOD activities are inversely proportional to light sensitivity in three planarian species, suggesting a photo-protective role for these enzymes in these species.     

Experimental evidence of predation by juvenile flounder, Platichthys flesus, on a shallow water meiobenthic community

In the northern Baltic Sea juvenile flounder, Platichthys flesus, occur in high abundances on shallow sandy bottoms in late summer and autumn. They feed mainly on meiofauna and the ontogenetic switch to macrofaunal sized food occurs at a larger size here than in other areas, exemplifying the high relative importance of meiofauna. Consequently, juvenile P. flesus in the Baltic feed for a longer period on meiofauna, and could thus be expected to have a stronger predation effect on the meiofaunal assemblages. In this study the predation effects of juvenile P. flesus on meiofaunal abundances and community structure were studied using microcosms that were sampled repeatedly over a 3-week period. Significant differences between treatment and control were found for the total number of taxa, for abundances of harpacticoids, copepod nauplii and ostracods. The nematode community was not affected, but one genus, Axonolaimus, was negatively affected by predation. The predation affected meiofaunal community structure as the major taxon diversity was significantly reduced. The results suggest that the meiofauna on shallow sandy bottoms may be structured by juvenile P. flesus, and the combined predation pressure of juvenile flounder and other epibenthic predators in the area might be considerable. Microcosms are effective in testing natural predation, especially on meiofaunal communities, but field experiments should be conducted to account for the physical characteristics of the area studied.     

Meiofaunal distribution in Hornsund fjord,Spitsbergen

The meiofaunal community structure at 32 stations in Hornsund fjord (77°N) was investigated, and results were compared with data from another Spitsbergen fjord, Kongsfjorden (79°N). Steep environmental gradients of sedimentation, organic matter content, and salinity from the inner to the outer basin of the fjord are present due to intensive glacial discharges of meltwater and ice. As the natural environmental disturbances were described for macrofauna benthic communities before, we aimed to check whether the same pattern occurs among meiofauna. A total of 12 higher meiofaunal taxa were recorded, with nematodes predominating at all stations. Non-parametric multivariate analyses demonstrated clear differences in meiofaunal abundance and composition between stations in the glacial bay and in the outer part of the fjord. Meiofaunal abundance increased with increasing distance from the source of disturbance, which in our study is tidal glaciers. Therefore, the current study demonstrates that the spatial structure of meiofauna is affected by the natural environmental disturbance, and analysis of meiofaunal assemblages can be used to assess the effect of such disturbances.     

Aspects of the Ecology of the Deep-water Fauna of the Gulf of Mexico

Recent transects across the continental slope off western Louisiana,the Mississippi River delta, and the Florida peninsula in thegeneral depth range of 300–3,000 m have provided informationon habitat variables and on faunal composition, density, anddepth zonation. In the meiofauna (retained by 63µm screens)nematodes, harpacticoid copepods, nauplii, polychaetes, ostracods,and kinorynchs were numerically dominant, in that order, andtogether these groups made up 98% of the fauna. The macrofauna(retained by 0.3 mm screens) was dominated by polychaetes, ostracods,bivalves, tanaids, bryozoans, and isopods in that order, andtogether these made up 86% of the fauna. Densities of both groupswere highest on the Central Transect, and densities of bothtended to decrease with depth. Between the depths of 300 m and3,000 m there was a threefold decrease in meiofaunal and a twofolddecrease in macrofaunal density. Among the megafauna (collectedby otter trawl) invertebrate densities, dominated by crustaceans,were four to five times as great as fish densities at all depthsand on all transects. Densities were greatest on the Easternand least on the Central Transect, and on all transects theydecreased with depth. On the slope off Louisiana and East Texas,in the depth range of 400–900 m, dense biological communitieshave been encountered at about 40 locations aggregated aroundoil and gas seeps. These organisms include clusters of largetube worms (vestimentiferans), vesicomyid clams, mussels, galatheidcrabs, bresiliid shrimps, neogastropods, limpets, and fishes.This community is trophically dependent upon chemoautotrophicbacteria (which utilize hydrogen sulfide), although some musselsdirectly utilize methane as a carbon source. This communityis closely related to that of the hydrothermal vent systemsof the East Pacific Rise and to the seep communities at thebase of the Florida escarpment. The megafauna of the northernand eastern Gulf of Mexico falls naturally into the followingdepth distribution pattern: Shelf/Slope Transition Zone (118–475m), Archibenthal Zone—Horizon A (500–775 m), ArchibenthalZone—Horizon B (800–975 m), Upper Abyssal Zone (1,000–2,275m), Mesoabyssal Zone (2,300–3,225 m), and Lower AbyssalZone (3,250–3,850 m). Biological characteristics of eachzone are discussed.     

Recolonisation of meiofauna after catastrophic iceberg scouring in shallow Antarctic sediments

A series of 10 samples from sediment in and adjacent to a shallow coastal iceberg scour at Signy Island, Antarctica, were taken by hand coring from 17 December 1993 until 23 August 1994. Scouring by the iceberg led to more than a 95% decrease in meiofaunal abundance and to a certain degree of reduction in diversity. Nematodes were always the most dominant group of meiofauna. The return of major meiofauna groups to control levels was accomplished in 30 days, although a decrease in abundance on the 50th day made interpretation difficult. The pioneering meiofaunal colonisers were copepods and ostracods, followed by nematodes. Microlaimus sp.1 was dominant among the nematodes throughout the whole period. Epistratum feeders and non-selective deposit feeders were highly dominant over selective deposit feeders and predators/omnivores. The Maturity Index, a measure for stress within nematode communities, was relatively low at all times and in controls, which indicates that r-strategists prevail in this community. In spite of the catastrophic destruction, nematode community structure was not affected by the iceberg impact, and there was no evidence of succession during recovery. This suggests that the nematode community in the shallow subtidal coast at Signy Island is well adapted to ice disturbance.     

Putting the meio- into stream ecology: current findings and future directions for lotic meiofaunal research

• 1 There is a paucity of research on epigean freshwater lotic meiofauna. This may result from a previous emphasis on interstitial (groundwater and hyporheic) meiofauna and/or a reliance on sampling methodologies in lotic systems which are inappropriate for meiofauna.
• 2 Meiofauna contribute much to the diversity of lotic ecosystems. Species lists for seven streams reveal that meiofauna contribute 58–82% of total species numbers, with rotifers and chironomids dominating most systems. The absence of taxonomic keys for most meiofaunal taxa in large areas of the world precludes a wider analysis of their contribution to lotic diversity and an assessment of biogeographical patterns and processes.
• 3 The trophic and functional role of meiofauna in lotic ecosystems is unclear. There are few estimates of meiofaunal production in freshwaters and biomass spectra have produced conflicting results for lotic meiofauna. Present static estimates suggest that the contribution of meiofauna to lotic productivity and biomass is small to moderate, but further studies incorporating a temporal component may provide a more realistic picture of the total contribution of meiofauna to biomass size spectra.
• 4 Meiofauna differ from macroinvertebrates in several respects apart from size and conceptual models for lotic ecosystems should include all metazoans if they are to be truly representative.
• 5 Information on the basic ecology of certain lotic meiofauna (i.e. nematodes, tardigrades, microturbellarians) is urgently required. For those groups whose distributional patterns are better understood (e.g. microcrustaceans), the mechanisms underpinning these patterns should be explored. It is essential that the importance of meiofauna is recognised by lotic ecologists; the only realistic way forward is for greater collaboration among meiofaunal ecologists and taxonomists and other lotic scientists.

     

All creatures great and small: patterns in the stream benthos across a wide range of metazoan body size

SUMMARY 1. The whole metazoan community (i.e. including the meiofauna) of an acidic, fishless stream in south-east England was surveyed over 14 months between March 1999 and April 2000. Invertebrate density, biomass and taxonomic richness were assessed on each sampling occasion in relation to physico-chemical variables.
2. The meiofauna were more numerous and diverse than the macrofauna, while their total biomass occasionally equalled that of the macrofauna.
3. The meiofaunal and macrofaunal assemblages appeared to respond to different environmental factors. The meiofauna showed genuine species turnover through the year, while the macrofauna varied less in taxonomic composition though there were substantial variations in density.
4. These data suggest that the meiofauna and macrofauna exist at different temporal and spatial scales and perceive their environment with a different 'grain'.     

Role of meiofauna in estuarine soft-bottom habitats*

Meiofauna are ubiquitous in estuaries worldwide averaging 10⁶ m^?2. Abundance and species composition are controlled primarily by three physical factors: sediment particle size, temperature and salinity. While meiofauna are integral parts of estuarine food webs, the evidence that they are biologically controlled is equivocal. Top down (predation) control clearly does not regulate meiofaunal assemblages. Meiofauna reproduce so rapidly and are so abundant that predators cannot significantly reduce population size. Food quantity (bottom up control) also does not appear to limit meiofaunal abundance; there is little data on the effect of food quality. In estuarine sediments meiofauna: (i) facilitate biomineralization of organic matter and enhance nutrient regeneration; (ii) serve as food for a variety of higher trophic levels; and (iii) exhibit high sensitivity to anthropogenic inputs, making them excellent sentinels of estuarine pollution. Generally mineralization of organic matter is enhanced and bacterial production stimulated in the presence of meiofauna. Tannins from mangrove detritus in northern Queensland appear to inhibit meiofaunal abundance and therefore the role of meiofauna in breakdown of the leaves. Meiofauna, particularly copepods, are known foods for a variety of predators especially juvenile fish and the meiofaunal copepods are high in the essential fatty acids required by fish. The copepod’s fatty acid composition is like that of the microphytobenthos they eat; bacterial eaters (nematodes?) do not have the essential fatty acids necessary for fish. Most contaminants in estuaries reside in sediments, and meiofauna are intimately associated with sediments over their entire life-cycle, thus they are increasingly being used as pollution sentinels. Australian estuarine meiofauna research has been concentrated in Queensland, the Hunter River estuarine system in New South Wales, and Victoria’s coastal lagoons. Studies in northern Queensland have primarily concentrated on the role of nematodes in mineralization of organic matter, whereas those from southern Queensland have concentrated on the role of meiofauna as food for fish and as bacterial grazers. The New South Wales studies have concentrated on the Hunter River estuary and on the structure and function of marine nematode communities. In Victoria, several fish have been shown to eat meiofauna. The Australian world of meiofaunal research has hardly been touched; there are innumerable opportunities for meiofaunal studies. In contaminated estuarine sediments reduced trophic coupling between meiofauna and juvenile fish is a basic ecological question of habitat suitability, but also a question with relevance to management of estuarine resources. Because meiofauna have short lifecycles, the effects of a contaminant on the entire life-history can be assessed within a relatively short time. The use of modern molecular biology techniques to assess genetic diversity of meiofauna in contaminated vs uncontaminated sediments is a promising avenue for future research. Much of the important meiofaunal functions take place in very muddy substrata; thus, it is imperative to retain mudflats in estuaries.     

Interrelationships of bacteria,meiofauna and macrofauna in a Mediterranean sedimentary beach (Maremma Park,NW Italy)

Collelungo beach (Maremma Park, NW Italy), was sampled quantitatively for macrofauna, meiofauna and bacteria in May 2003; several physicochemical variables and variables associated with food availability and sediment structure were also measured. Replicated samples were collected from three sites representing natural conditions, an erosion regime, and the influence of the Ombrone River, respectively, as well as from four stations each located in the surf and sublittoral zones. Both uni- and multivariate techniques were used to assess the benthic community structure and the associated environmental variables. Different diversity indices revealed no pattern; in contrast, multivariate techniques applied on the macrobenthic fauna and the polychaete taxocommunity distinguished between the sites located in natural and eroding conditions from the one located nearby the discharges of the Ombrone river. Τhe community patterns deriving from meio- and macrofauna are clearly divergent. The overall benthic faunal community appears to be influenced by both groups of organisms. The patterns of the meio- and macrofaunal communities seem to be affected synergistically by a number of environmental variables, in accordance with the multicausal environmental severity hypothesis. Meiofaunal patterns are more often correlated with bacteria and the protein concentration than are macrofaunal patterns, indicating a potential utilization of bacteria as a food source by the meiofaunal organisms. Total bacterial numbers are associated with the macrofaunal pattern under the erosion regime, probably as a consequence of competition for food between macrofauna and meiofauna.     

A Brine Seep at the East Flower Garden Bank,Northwestern Gulf of Mexico

Dissolution of Triassic-Jurassic, intrusive salt deposits within 150 m of the sea floor produces a hypersaline brine seep (∼200 0/00) at 71 m water depth on the East Flower Garden Bank. The anoxic, sulfide-rich brine supports large populations of sulfur oxidizing bacteria. Toxic effects of the brine on surrounding epifauna, infauna and fishes are limited to the brine and a very narrow surrounding zone. Leafy algae, coralline algae, foraminifers, sponges, bryozoans, anemones, polychaetes, sipunculids, amphipods and pelecypods live on the hard substratum within 2 cm of the brine-seawater interface. Sixty meters from the brine outflow, at dilutions of 50 to 1, the carbonate sand harbors polychaetes, ostracods, nematodes, amphipods, tanaidaceans, isopods, copepods, pelecypods and gastropods. Certain species of fish momentarily enter the brine and brine-seawater mixtures.     

Effects of organic enrichment on meiofaunal abundance and community structure in sublittoral soft sediments

In experimental mesocosms established at Solbergstrand, Oslofjord, Norway, organic enrichment was effected by the addition of powdered Ascophyllum nodosum (L.) Le Jol., in quantities equivalent to 50gC·m^?2 and 200gC·m^?2, to boxes of sublittoral soft sediment. After 56 days, the structure of the meiofaunal communities in these treatments was compared with that of the control boxes. At this time the meiofaunal communites at each level of organic enrichment were markedly different from each other and from that in the control sediment. The responses of the two major components of the meiofauna, however, were different. Although the abundance of nematodes was slightly reduced in the high dose treatment this was not accompanied by detectable changes in community structure. Harpacticoid copepods, on the other hand, increased significantly in abundance in the treatment boxes and showed a general trend towards increased dominance and decreased diversity with increasing levels of organic enrichment, although in the low dose treatment there was also an increase in the number of species present. It is also shown that the nematode/copepod ratio is unreliable as a biomonitoring tool and it is suggested that the differential responses in community structure between the nematode and copepod components of the meiofauna might be a better indication of stress at the community level.