Mud Habitats Research Articles

Subtidal benthic community respiration and production near the heavily oiled Gulf coast of Saudi Arabia

As part of the NOAA/ROPME/MSRC sponsored assessment of the coast of Saudi Arabia, heavily impacted by the large oil spills of the 1991 Gulf War, we measured benthic community respiration (R) and primary production (P) rates in shallow subtidal basins near heavily oiled coastlines. Study sites were located in zones predicted to be basins of maximum deposition of any oiled sediments likely to wash off the adjacent coast and in reference bays predicted to be clean and unaffected. We measured oxygen exchange using in situ benthic respirometers and analysed petroleum hydrocarbon (PHC) levels in the near surface sediments at five stations. We concentrated our efforts in mud habitats to complement related studies in seagrass habitats. Measured community R rates ranged from a low of 700 μM m 2 h −1 in coarse sand sediments with total organic carbon content (TOC) of only 0.16% of dry wt to the highest rate of 2184 μm m −2 h −1 in finer mud-sand habitats with 0.39% TOC. All measured rates were in the range of literature values for shallow marine sediments at temperatures of 17 to 19°C. Sediment oil content was 13–540 μg g −1 dry wt by ultraviolet fluorescence (UVF) analysis and 0.5–103 μg g −1 by gas chromatography (GC). Benthic P rates, calculated as light minus dark changes in dissolved oxygen, ranged from a low of 1162 μm m −2 h −1 at the most heavily oiled site to a high of 5216 μm m −2 h −1 at less oiled sites. While a weak inverse relationship between benthic P and sediment oil content was not significant statistically due to the small number of samples, a significant inverse relationship was found between the ratio of production to respiration (P/R) and the total petroleum content of the sediments by UVF. The effect appears to be driven more by differences in production than an effect on respiration which showed little relationship with either oil content or productivity. We conclude that within 1 year after the oil grounded on the intertidal sands of Saudi Arabia, the levels of oil in subtidal benthic sediments had decreased in most habitats to levels that did not show community stress by our oxygen measurements. Rather, long term damage to benthic subtidal habitats was limited only to enclosed bays adjacent to the most heavily oiled coastlines. Preliminary estimates of yearly P converted to carbon units indicates that the shallow mud sediments of the Gulf are at least as productive as most oligotrophic water columns. Since benthic habitats covered by seagrass, algae beds or coral reefs are likely to have even higher production rates, we conclude that benthic processes contribute significantly to the overall carbon flux in the Gulf ecosystem.

Survival and vertical distribution of larvae of Culicoides variipennis (Diptera: Ceratopogonidae) in drying mud habitats.

The ability of third and fourth instars of Culicoides variipennis (Coquillett) to survive in drying sandy loam soil was tested under simulated field conditions. Two hundred larvae were added to each of a number of soil-filled, plastic tubes, which were buried in the field and retrieved after 2, 5, and 7 d. Of 306 pupae or pupal exuviae recovered, 98.1% were in the top 2 cm of mud. Estimated larval mortality on day two ranged from 25.6 to 87.1% among three trials, and 92.3% of live larvae were in the top 2 cm. Estimated larval mortality on day 5 ranged from 81.4 to 97.2%, and 75.5% of live larvae were in the top 2 cm. On day 7 mortality was 95.2-100%, and 63% of surviving larvae were in the top 2 cm. Some larvae dispersed as deep as 7-10 cm (the maximum depth in the tests). Larval tolerance of unfavorable drying conditions may allow relic populations to persist in some situations, but probably this is of little concern in control of this species through water management in most settings.

Are Infaunal Predators Important in Structuring Marine Soft-Bottom Communities?

The role of infaunal predators in structuring marine soft-bottom communities was evaluated according to these predators': 1) effects on prey density based on manipulative field experiments, 2) feeding rates, 3) effects on prey distribution, 4) effects on species diversity, and 5) interactions with their prey. Estimates of feeding rates indicate that many predatory taxa have the potential to reduce the size of prey populations and suggest that nemerteans are likely to have a larger impact on infaunal abundances than polychaetes. Infaunal predators have been demonstrated to have a significant effect on infaunal densities and to affect the spatial and temporal distribution of their prey. The effects of these predators on species diversity apparently depend on the predator and the diversity of the system. These conclusions may not be applicable to all soft-bottom habitats or all groups of infaunal predators because they are based on studies of very few taxa conducted almost exclusively in intertidal, unvegetated, mud habitats. Additional studies are needed on the effects of predation by infauna on infaunal population dynamics and on the mechanisms of interactions between predator and prey. Further investigation will probably reveal that different groups of infaunal predators play different roles in structuring soft-bottom communities.

POPULATION ECOLOGY OF THE HERMIT CRAB CLIBANARIUS VITTATUS (DECAPODA: DIOGENIDAE) AT SEBASTIAN INLET, FLORIDA

ABSTRACT Analysis of monthly quadrat samples taken between November 1985 and December 1986 at Sebastian Inlet, Florida, revealed a variable seasonal abundance of Clibanarius vittatus (Bosc, 1802) and spatial distribution of hermit crabs. Mean annual abundance of C. vittatus was 7.7 hermit crabs per m2 with maxima in November (13.9 crabs per m2) and in March (13.8 crabs per m2) and a minimum in January (1.5 crabs per m2). Fine mud and sea-grass habitats appear to be preferred over sandy bottoms. The average sex ratio of females to males was 3.1:1, but January and April samples approached 1:1. Large males (shield length > 10 mm) emigrated during late fall and returned in April, while females and small males remained in the study area. Egg production occurred during April through September, while recruitment of small crabs (SL < 2 mm) into shells began in September and peaked in the winter months. Females tended to have a unimodal size distribution, while males showed a polymodal size distribution with a broader range of size classes. Laboratory experiments showed that C. vittatus significantly reduced the number of amphipods, tanaidaceans, and nemerteans in areas of sea grass, and significantly reduced the number of polychaetes and isopods in areas of bare sand. It is suggested that disturbance of the substratum may explain this reduction.

Atherospio Distichagen. et sp. nov. (Polychaeta: Spionidae) from Loch Tuirnaig, West Coast of Scotland

Abstract Atherospio disticha gen. et sp. nov. is described from a shallow (27 m) mud habitat in a Scottish sea loch. The main characteristic of the genus is the possession of aristate spines in the neuropodia of setigers 4 and 5. The generic affinities of the genus are discussed. Atherospio is most closely related to Pygospiopsis Blake, 1983.

Benthic studies of waterfowl breeding habitat in south-western New South Wales. II. Chironomid populations

The dynamics of chironomid populations in waterfowl breeding habitat were investigated. Of 12 species recorded, Chironomus 'alternans a', C. tepperi, Kieflerulus intertinctus, Polypedilum nubifer and Procladius villosimanus were common in the mud habitats. C. 'alternans a' was the most commonly recorded species over the whole study, and C. tepperi dominated the faunas afier flooding. Dicrotendipes conjunctus and Dicrotendipes sp. 2 were the major species occurring on stick substrata, and Dicrotendipes sp. 2 and Polypedilum nubifer were dominant on plant substrata. Production of chironomids was high in the first 2 years following an extensive flood but thereafter fell rapidly. Correlative evidence is presented that suggests a relationship between abundance of C. tepperi larvae and breeding by waterfowl.

The Importance of Predation and Intra‐ and Interspecific Competition in the Population Biology of Two Infaunal Suspension‐Feeding Bivalves, Protothaca staminea and Chione undatella

The Importance of Predation and Intra‐ and Interspecific Competition in the Population Biology of Two Infaunal Suspension‐Feeding Bivalves, Protothaca staminea and Chione undatella

Seasonal Abundance and Pattern of Chydorid, Caldocera in Mud and Vegetative Habitats

Pattern sampling (Whiteside and Williams 1975) was employed to study the population changes, habitats and spatial arrangements (pattern) of littoral cladocera in Lake Itasca, Minnesota during 1974. Population dynamics of the 19 most abundant species of chydorids had changes similar to other populations studied in north—temperate lakes. All species had either spring or fall maxima, or both, a mid—summer low in numbers. Population trends were the same for vegetative and mud habitats. In a comparison of Chara vs. mud habitat we found Chydorus piger, Leydigia leydigi, Alona quadrangularis, Pleuroxus aduncus, and Alona circumfibriata to live mainly in littoral mud. Kruzia latissima, Camptocerus rectirostris and Chydorus faviformis were most restricted to the vegetative habitat, while other species were more ubiquitous. Pielou's (1974) terms describing pattern, phase, mosaic, grain, and intensity are discussed. We redefined intensity as describing the visual effect of density. The changes of intensity accompanying changes in density typified 1974 patterns, while no changes in the other parameters were evident. Preliminary experiments exploring the behavior of chydorids suggest that visual stimuli are very important in directing movements, followed by tactile and chemical clues.

Temporal Variation in Upper Bay Mesohaline Benthic Communities: I. The 9-m Mud Habitat

Yearly and seasonal changes in the structure of the macrobenthic (>1.0 mm) community occurring in the 9-m mud habitat of the Calvert Cliffs region of the Chesapeake Bay were examined for three years. Seasonal changes in the numerically dominant species resulted in varying community structure and was characterized by a near total faunal depletion during summer, initial recolonization during early fall, secondary recolonization during late fall, and growth and structural development during winter and spring. The faunal depletion that occurred each summer caused the cycle to repeat on an annual basis. The structure of the community was similar each year during initial recolonization (fall), but varied during secondary recolonization (winter and spring), reflecting the recruitment success of species that reproduce in the fall (i.e.,Macoma balthica, Mulinia lateralis, Nereis succinea, andParaprionospio pinnata). These findings have profound implications for the design and interpretation of power plant preoperational-postoperational impact studies.

The role of pharyngeal haemoglobin in the feeding of the marine nematode, Enoplus brevis

The rate of feeding of E. brevis, which contains haemoglobin in the pharynx, was measured over a wide range of oxygen concentrations, and compared with similar results for a second species, E. communis, which lacks haemoglobin in its pharynx. The nematodes were added to a mixture of mud and amaranth, in varying oxygen regimes, and the dye content of the disrupted individuals was measured two days later by a spectrophotometric technique. The feeding rate of E. brevis was less affected than that of E. communis by partial pressures of oxygen between 8 and 40 mmHg, but both species ingested some mud in almost anaerobic conditions. Comparison of the vertical distribution of E. brevis with the redox potential of its mud habitat showed that the animal is only occasionally found in anoxic mud. It is suggested from these results, and from previous work, that the facilitation of oxygen diffusion by the haemoglobin in the pharynx of E. brevis helps this nematode to feed in the low and fluctuating oxygen regime of its habitat.

Foraging by Cave Beetles: Spatial and Temporal Heterogeneity of Prey

This study assesses the effect of temporal and spatial heterogeneity of preferred prey on the foraging strategies of two carabid cave beetles, Neaphaenops tellkampfii and Pseudanophthalmus menetriesii. Neaphaenops tellkampfii prefers the eggs and nymphs of the common cave cricket (Hadenoecus subterraneus) which are patchy in time but not in space. Cave cricket eggs are laid in sandy habitats which support few alternate prey. As a result N. tellkampfii is forced to switch diet, habitat, and foraging mode in the fall when cricket eggs and nymphs become rare. Pseudanophthalmus menetriesii preys on collembola that are confined to habitats with organic matter. These items are patchily distributed but continuously available. In sand or mud habitats collembola are rare and P. menetriesii appears to incur higher foraging costs in these habitats than in litter areas. As a result P. menetriesii shows restricted habitat preference and tracks its prey between various organic patches.

Development of the mud habitat during the filling of two new lakes

SummaryAn attempt is made to illustrate some of the principles of early development of muds in two contrasting lake basins which were devoid of vegetation cover before filling. Essentially the changes involve the dispersion and redistribution of particles in the newly flooded lake bottom. Field and laboratory observations are presented to demonstrate the interaction that exists between water chemistry, wave erosion and the burrowing activity of mud‐dwelling insect larvae, and the effect of these factors on particle size sorting in the substrate. These characteristic changes in the mud during filling are compared with post‐filling stage developments in which the role of extraneous material, including organic matter, may predominate.

DEVELOPMENT OF SOME LAKE ECOSYSTEMS IN TROPICAL AFRICA, WITH SPECIAL REFERENCE TO THE INVERTEBRATES

Summary1. The flooding of a lake basin initiates a series of changes leading eventually to a more stable climax situation after some years. Sequential physical and chemical changes in the mud and water and related changes in the animal and plant populations of three types of tropical African lakes are considered. The giant man‐made lakes, Kariba and Volta, both several thousand square kilometres in area, provide the bulk of the material for this review. Two other kinds of tropical lake, the annual storage‐reservoirs like Jebel Aulia and Sennar in the Sudan, and natural lakes subject to periodic droughts, like Lake Chilwa in Central Africa, are also considered. Evidence is often patchy but suggests a number of generalizations regarding the course and causes of the developmental changes in these tropical ecosystems.2. On the evidence available, the course of development appears to fall conveniently into two periods based on water level changes, the filling phase and the post‐filling phase. The former is characterized by sudden appearances of organisms and explosive growths of animal and plant populations. This unstable behaviour, especially characteristic of tropical lakes, is associated with the destruction of old habitats and the creation of new ones, the increasing area and volume of the new lake environment and the introduction of materials to the system at the advancing shore‐line. By the time that filling is complete, the situation has stabilized to a large extent and the ecosystem enters a new phase.3. This post‐filling phase is characterized by the development and exploitation of existing habitats. Examples considered here are: the development of the mud habitat under the influence of processes like sedimentation and beach formation; the development of submerged woodland as a habitat for bottom dwelling animals; the spread of rooted aquatic plants and their effect on the mud; and the role of fluctuation in water‐level on the post‐filling phase. All four phenomena result in a modification of the substrata originally flooded, in a way that directly effects the associated fauna and flora. Apart from influencing the first three processes, water‐level fluctuations also result in an interaction between the aquatic and terrestrial ecosystems which brings about important changes in itself.4. The relative importance of these two phases varies with the type of lake, filling‐phase phenomena obviously dominating in the annual storage reservoirs while post‐filling phase characteristics are fully expressed in the large lakes made by man.5. In contrast to the development of temperate lake ecosystems, succession of species in these tropical examples is not so much interrupted by major annual temperature changes. In addition, both the course of succession and the climax communities achieved are different. This may be largely due to the more rapid decomposition of organic matter in the muds which has two main consequences. In the first place, extraneous organic material brought in to the system during flooding, is rapidly broken down. Early filling stages, therefore, are associated with anoxic conditions and development of conspicuous communities of algae and large aquatic plants. The result is an overlapping of what in temperate systems are two distinct episodes: the early extraneous and later self‐contained systems. Secondly, the replacement of chironomids by an oligochaete climax in the mud as seen in temperate lakes does not normally occur, apparently because of the lack of accumulated organic material. The presence in Africa of the may‐fly Povilla adusta, on the other hand, provides an extra stage in the colonization of submerged woodland, replacing the earlier chironomid communities.

Direct Peristaltic Progression and the Functional Significance of the Dermal Connective Tissues During Burrowing in the Polychaete Polyphysia Crassa (Oersted)

ABSTRACT Polyphysia excavates its burrow in soft, sublittoral mud by sinusoidal waves of the septate anterior region of the body and the lateral scraping action of the prostomial horns. Associated with discrete, direct peristaltic constrictions, in which the longitudinal muscles shorten to 40%, and the circulars to 80%, of their distended lengths, hydraulic deployment of coelomic fluid converts the periodic advance of the trunk segments into continuous head progression. Direct peristaltic progression advances the body by one-fifth or less of a wavelength per cycle, which is comparable to the figure for earthworm locomotion. A three-dimensional dermal collagen fibre lattice accommodates extensive folding of the cuticle and epidermis while permitting a three-to fourfold increase in the radial dimension of the body wall during peristaltic constriction. Elastic fibre columns oppose the radial distension and control the cuticular folding. These features are seen as adaptations to burrowing in the soft mud habitat. The high degree of body-wall flexibility permits the transition from contracted to distended configuration within the length of one segment. Some three-quarters of the body surface may be in contact with the burrow wall at any one time. Unlike other soft-bodied burrowing animals the force exerted on the burrow wall is unidirectional and the applied pressure is probably small, relatively constant and spread over a wide area.