Benthic Copepods Research Articles

Sensitivity of the marine benthic copepod Tisbe biminiensis (copepoda, harpacticoida) to potassium dichromate and sediment particle size

For the future use of the marine benthic copepod Tisbe biminiensis in solid-phase sediment toxicological bioassays, the present study investigated the effect of muddy sediment from the Maracaípe estuary (northeastern Brazil), sediment particle size and the reference toxicant potassium dichromate on the species. Muddy sediment from Maracaípe can be used as control sediment, since it does not interfere in the copepod life-cycle and has metal contamination levels that are unlikely to produce any detrimental biological effects on benthic invertebrates. Neither survival nor fecundity was affected by grain size, suggesting that this species can be used with any kind of sediment from muddy to sandy. The sensitivity of T. biminiensis to K2Cr2O7 in acute tests was similar to that of other organisms. The LC50 (lethal concentration to 50% of the test organisms) medium values for T. biminiensis were 7.51, 4.68 and 3.19 mg L-1 for Cr in 48, 72 and 96 h, respectively. These results suggest that T. biminiensis is a promising organism for use in solid-phase sediment toxicity assessments.

Increased production of faecal pellets by the benthic harpacticoid Paramphiascella fulvofasciata: importance of the food source

The re-use of faecal pellets in the water column before sinking to the seaXoor is known as an important pathway in marine food webs. Especially planktonic cope- pods seems to be actively use their faecal pellets. Since benthic copepods (order Harpacticoida) live in the vicinity of their pellets, it remains unclear how important these pel- lets are for their feeding ecology. In the present study a lab- oratory experiment was conducted to analyse the importance of faecal pellets for the feeding ecology of the harpacticoid Paramphiascella fulvofasciata and its grazing pressure on two diatom species (Seminavis robusta, Navic- ula phyllepta). By quantifying the amount and volume of the produced faecel pellets in diVerent treatments, it was tested to what extent the food source and the lack of faecal pellets would inXuence the production of faecal pellets. We found that the grazing pressure of P. fulvofasciata depended on the diatom density since only a top-down eVect could be found on the smaller Navicula cells during its initial exponential growth phase. The grazer had a nega- tive eVect on the diatom growth and controlled the cell den- sity to about 4,000 cells/cm 2 . In spite of the fact that the addition of faecal pellets did not show a signiWcant positive eVect on the assimilation of diatoms, the removal of faecal pellets strongly promoted the pellet production. Especially when grazing on Navicula the harpacticoid P. fulvofasciata produced signiWcantly more and smaller faecal pellets when the pellets were removed. This outcome illustrates the need for faecal pellets of this harpacticoid copepod when grazing on the diatom Navicula. Apart from its selection for smaller diatom cells, it was suggested that the colonisation of heterotrophic bacteria enriched these pellets. This study is the Wrst to indicate that trophic upgrading occurs on fae- cal pellets and not only on the initial autotrophic food sources per se.

Abundance of benthic copepods in a saline lake in East Antarctica

Abundance of benthic copepods in a saline lake in East Antarctica

Comparison of methods for evaluating acute and chronic toxicity in marine sediments

Sublethal test methods are being used with increasing frequency to measure sediment toxicity, but little is known about the relative sensitivity of these tests compared to the more commonly used acute tests. The present study was conducted to compare the sensitivity of several acute and sublethal methods and to investigate their correlations with sediment chemistry and benthic community condition. Six sublethal methods (amphipod: Leptocheirus plumulosus survival, growth, and reproduction; polychaete: Neanthes arenaceodentata survival and growth; benthic copepod: Amphiascus tenuiremis life cycle; seed clam: Mercenaria mercenaria growth; oyster: Crassostrea virginica lysosome destabilization; and sediment-water interface testing with mussel embryos, Mytilus galloprovincialis) and two acute methods (amphipod survival with Eohaustorius estuarius and L. plumulosus) were used to test split sediment samples from stations in California. The test with Amphiascus proved to be the most sensitive sublethal test and the most sensitive overall, identifying 90% of the stations as toxic. The Leptocheirus 10-d test was the most sensitive of the acute tests, identifying 60% of the stations as toxic. In general, the sublethal tests were not more sensitive to sediments than the acute tests, with the sublethal tests finding an average of 35% of the stations to be toxic while the acute found 44%. Of the sublethal tests, only the Amphiascus endpoints and Neanthes growth significantly (p <or= 0.05) correlated with sediment chemical concentrations. Poor correspondence occurred between the toxicity endpoints and the indicators of benthic community condition. Differences in test characteristics such as mode of exposure, species-specific contaminant sensitivity, changes in contaminant bioavailability, and influence of noncontaminant stressors on the benthos may have been responsible for variation in response among the tests and low correspondence with benthic community condition. The influence of these factors cannot be easily predicted, underscoring the need to use multiple toxicity methods, in combination with other lines of evidence, to provide an accurate and confident assessment of sediment toxicity.

Climate change and increased environmental variability: Demographic responses in an estuarine harpacticoid copepod

Climate change models predict that in the future, extreme events will be more common and of greater magnitude. In the southeastern United States, this is expected to include increased precipitation and more frequent extreme precipitation events, resulting in more freshwater runoff into coastal habitats. Marine and estuarine communities in this region can expect more frequent and larger salinity reductions if climate change model predictions are realized. We studied a benthic harpacticoid copepod to test the effects of environmental variability, in the form of estuarine salinity reductions, on vital rates. Specifically, we tested the effects of 3-day salinity reductions on the harpacticoid copepod Amphiascus tenuiremis. We varied the magnitude of salinity reduction (pre-storm: 30‰, reduced to 10 or 15‰) and the timing of salinity reduction relative to life stage (naupliar, copepodite, adult). Survival and fecundity decreased with salinity reductions of greater magnitude and with exposure during earlier life stages. An age-classified Leslie matrix model constructed using these data predicted lower population growth rates with exposure to salinity reduction of greater magnitude or during an earlier life stage, although this trend was not significant. We modeled the effects of environmental variability on copepods using a 98-year salinity record for coastal South Carolina. Population growth rate was highly variable in short-term simulations (3-week, 10-week), depending upon the salinity levels dictated in simulations by the natural salinity record. Cohorts “born” into a sequence with little or no salinity reduction had higher population growth rates than cohorts that experienced salinity reduction during a simulation. The greater the frequency of salinity reduction, the lower the population growth rate of that cohort. If climate change models are correct in predicting greater frequency and magnitude of extreme events such as precipitation and estuarine salinity reductions, then benthic copepod populations are likely to have even lower population growth rates than those described here, which could include population declines. As an important food source for higher trophic levels, harpacticoid population reductions could impact many other estuarine species, as well as species from other habitats whose young develop in the estuary.

Mixtures of metals and polynuclear aromatic hydrocarbons elicit complex, nonadditive toxicological interactions in meiobenthic copepods

The acute toxicity of metal-polynuclear aromatic hydrocarbon (PAH) mixtures (i.e., Cd, Hg, Pb, fluoranthene, and phenanthrene) associated with sediments was assessed in two benthic copepods. Schizopera knabeni was exposed to sediment amended with single contaminants and mixtures. Adult S. knabeni were highly tolerant of single-contaminant exposures to phenanthrene, Cd, Hg, and Pb as well as a mixture of Cd, Hg, and Pb. Binary experiments revealed that although phenanthrene was synergistic with Cd and Hg, the phenanthrene-Cd synergism was much stronger (2.8 times more lethal than predicted). When a mixture of Cd, Hg, and Pb was combined with phenanthrene, a synergistic response was observed, eliciting 1.5 times greater lethality than predicted. A Cd-phenanthrene synergism in S. knabeni was also observed in aqueous exposures, suggesting that the interaction was related to a pharmacological insult rather than a sediment-related exposure effect. An antagonism between Cd, Hg, and Pb was indicated, and this antagonism may have moderated the Cd-phenanthrene synergism in mixtures containing Cd, Hg, Pb, and phenanthrene. Experiments with Amphiascoides atopus revealed that phenanthrene and fluoranthene were each synergistic with Cd in aqueous exposures. Our studies suggest that interactive toxicity among metal-PAH mixtures may be common among benthic copepods and that strong synergistic effects observed in binary mixtures may be moderated in more diverse contaminant mixtures. However, the strength of the observed synergisms raises concerns that established sediment quality criteria may not be protective for organisms jointly exposed to PAH and metals, especially Cd-PAH mixtures.

Silica gel as a particulate carrier of poorly water-soluble substances in aquatic toxicity testing

Aquatic toxicity tests were originally developed for water-soluble substances. However, many substances are hydrophobic and thus poorly water-soluble, resulting in at least two major implications. Firstly, toxicity may not be reached within the range of water solubility of the tested compound(s), which may result in the formation of solids or droplets of the tested substance and consequently an uneven exposure. Secondly, because of multi-phase distribution of the tested substance it may be complicated to keep exposure concentrations constant. To overcome such problems, we have introduced silica gel as a particulate carrier in a toxicity test with the benthic copepod Nitocra spinipes. The main objective of the current study was to evaluate whether a controlled exposure could be achieved with the help of silica gel for testing single poorly water-soluble substances. A secondary objective was to evaluate whether an equilibrium mass balance model could predict internal concentrations that were consistent with the toxicity data and measured internal concentrations of two model hydrophobic substances, i.e., the polybrominated diphenyl ethers BDE-47 and BDE-99. Larval N. spinipes were exposed for 6 days to BDE-47 and BDE-99, respectively, in the silica gel test system and, for comparative reasons, in a similar and more traditional semi-static water test system. Via single initial amounts of the model substances administered on the silica gel, effects on both larval development and mortality resulted in higher and more concentration-related toxicity than in the water test system. We conclude that the silica gel test system enables a more controlled exposure of poorly water-soluble substances than the traditional water test system since the concentration–response relationship becomes distinct and there is no carrier solvent present during testing. Also, the single amount of added substance given in the silica gel test system limits the artefacts (e.g., increased chemical load in test system) that a semi-static renewal may introduce when testing substances that partition to non-water phases. However, measured and modelled internal concentrations did not match toxicity, which may indicate that chemical equilibrium was not reached during the test. Further experiments are thus needed to explain the processes behind the observed positive effects of silica gel and a kinetic model would likely also be more appropriate to describe the concentrations and distributions in the two test systems.

Simulated sequestration of anthropogenic carbon dioxide at a deep-sea site: Effects on nematode abundance and biovolume

One proposal for ameliorating global warming is to sequester large amounts of carbon dioxide in the deep ocean, but the environmental consequences of sequestration for sediment-dwelling animals are poorly known. In a previous publication, we reported that ∼80% of benthic copepods were killed in an experimental release of CO 2 off northern California at 3262 m. The effects of this release on nematodes are reported here. We examined samples of nematodes taken inside two ‘corrals’ into which CO 2 was directly injected (providing an extreme endpoint for CO 2 exposure) and taken near to and far from this CO 2 source. After 30 days, pore-water pH was unchanged (∼7.8) at the sediment–water interface far (∼40 m) from corrals, but pH profiles were reduced by ∼0.75 near (∼2 m) corrals. Corral pH was highly acidic (5.4 in a measurement from a subsequent experiment). Fifty randomly selected nematodes from each of four vertical layers from the 14 cores were photographed. They were assigned to a tail group (based on morphology), and individual biovolume was estimated from measurements of body length and width. Although nematode abundance (expressed as total nematodes and by tail group) was not affected, length, width, and individual biovolume significantly differed between near and far samples. Median nematode biovolume examined across tail group and core layer increased by ∼48% inside and near corrals. Differences between near and corral samples were always less than differences between near and far samples. However, nematode length:width ratio did not differ between near and far, and the shapes of length, width, and biovolume frequency distributions were similar in all samples. We postulate that the nematode community throughout the upper 3 cm suffered a high rate of mortality after exposure to CO 2, and that nematodes were larger because postmortem expansions in body length and width occurred. Decomposition rates were probably low and corpses did not disintegrate in 30 days. The observable effects of a reduction in pH to about 7.0 after 30 days were as great as an extreme pH reduction (5.4), suggesting that ‘moderate’ CO 2 exposure, compared to the range of exposures possible following CO 2 release, causes high mortality rates in the two most abundant sediment-dwelling metazoans (nematodes and copepods).

Incipient speciation through niche expansion: an example from the Arctic charr in a subarctic lake

Two reproductive isolated morphs of Arctic charr (Salvelinus alpinus), termed profundal and littoral charr according to their different spawning habitats, co-occur in the postglacial lake Fjellfrøsvatn in North Norway. All profundal charr live in deep water their entire life and have a maximum size of 14cm, while the littoral charr grow to 40cm. Some small and young littoral charr move to the profundal zone in an ontogenetic habitat shift in the ice-free season and the rest of the population remains in epilimnic waters. The two morphs had different diet niches in the profundal zone: the profundal charr ate typical soft-bottom prey (chironomid larvae, pea mussels and benthic copepods), while the young littoral charr mainly consumed crustacean zooplankton. In four other lakes without a profundal morph (i.e. monomorphic populations), young charr also performed ontogenetic habitat shifts to the profundal zone and fed on zooplankton. The profundal morph of Fjellfrøsvatn therefore utilize a food resource niche that neither the littoral morph nor comparable monomorphic populations exploit. This suggests that intraspecific resource competition has driven incipient ecological speciation of the profundal charr of Fjellfrøsvatn. The exploitation of the soft-bottom resources by the profundal charr supports earlier experimental findings that the profundal morph is genetically different in trophic behaviour and morphology. The sympatric ecological divergence within the profundal habitat is possible because unexploited food resources (soft-bottom profundal prey) are available. Apparently, this represents a case of incipient segregation by expansion to new resource types (niche invasion), and not by subdivision of one broad ancestral niche.

Trace Metals in Microcrustaceans and Brazilian Waterweed from a Contaminated Chilean Wetland Using Total Reflection X-Ray Fluorescence Spectrometry

The trace element content of individual copepod specimens and of the Brazilian water weed (Egeria densa) from a metal-contaminated wetland in Southern Chile were determined using total reflection X-ray fluorescence spectrometry. Sampling of the water and the organisms was carried out at three sampling sites during 2004. Enhanced concentrations of dissolved Fe and Mn were found in the column water and in the pore water. The Fe content in the benthic copepods was significantly elevated compared to other aquatic organisms from different Chilean lakes. Regarding E. densa, healthy (green coloured) plants showed mass fractions of Fe, Mn, Ni, Cu and Zn which were typical for uncontaminated systems. In contrast, damaged (brownish coloured) plants exhibited very high Fe and Mn concentrations indicative of contamination or processes which changed the element load from the environment to the plant.

Trophic interactions between benthic copepods and algal assemblages: a laboratory study

Meiofauna are potentially capable of controlling microphytobenthic biomass. Grazing by copepods in high densities has been hypothesized to lead to successional changes in algal assemblages toward less-edible algal species with consequent effects on copepod survival and growth. In our study, adult Attheyella trispinosa were offered monospecific algal films of 3 benthic diatom species and 1 benthic cyanobacterial species and algal assemblages consisting of different combinations of these species. Changes in abundances of algal species were observed over 17 d. Nauplii of A. trispinosa and Bryocamptus minutus were grown with a similar range of algal assemblages supplied as food, and their survival and development rates were measured. Feeding by A. trispinosa decreased the density of the diatom Nitzschia perminuta, whereas biomass of all other diatom species generally was unaffected by copepod feeding. The biomass of the cyanobacterium Leptolyngbya foveolarum was either unaffected or slightly enhanced by copepod feeding. Nevertheless, the architecture of the algal assemblages changed. Leptolyngbya foveolarum was ingested and partly digested by the copepods, and copepods were able to develop on this diet. However, L. foveolarum alone or combined with diatoms reduced the survival and development rate of nauplii and diminished copepodid sizes of A. trispinosa and B. minutus. Our results suggest that these algal species can exert a strong effect on harpacticoid copepods. Specific effects of copepod grazing on bispecific algal assemblages were masked to a large extent by the interactions among autotrophic species. In contradiction to our hypothesis, copepods grazing on L. foveolarum altered the physiognomy of algal assemblages and promoted the persistence of (edible) diatom species otherwise overgrown by L. foveolarum of lower food quality.

Comparative Ecology of the Gobies Nes longus and Ctenogobius saepepallens, Both Symbiotic with the Snapping Shrimp Alpheus floridanus

We re-examined the symbiotic association of the western Atlantic gobiid fishes Nes longus and Ctenogobius saepepallens with the snapping shrimp Alpheus floridanus on the basis of a critical literature review and new data. Our research confirms that N. longus interacts closely with the shrimp and is dependent on it for the cover provided by the burrow that the shrimp constructs; the goby serves as the sentinel at the burrow entrance. Ctenogobius saepepallens is often seen occupying a burrow of the alpheid, and the shrimp will leave the burrow to deposit sediment with the goby at the entrance, even pushing the goby aside at times. However, the shrimp does not make contact with the goby with its antennae, nor does the goby communicate with caudal fin fluttering at the approach of danger. We suggest that their relationship is a first step in an evolutionary process that may lead to the very close mutualistic association exhibited by N. longus and the alpheid, as well as Indo-Pacific shrimp gobies of 13 different genera and their alpheid partners. Nes longus remains close to the burrow entrance; it feeds mainly on small gastropods, decapod crustaceans, ostracods, and isopods. By contrast, C. saepepallens makes longer excusions from the shelter of the burrow; its diet is dominated by benthic copepods, followed by ostracods and lesser amounts of foraminiferans, isopods, and decapod crustaceans. By virture of its greater mobility, it can be more selective in its prey.

Intertidal and subtidal soft-bottom macro- and meiofauna of the Kongsfjord (Spitsbergen)

The intertidal and subtidal soft bottom macro- and meiofauna of a glacier fjord on Spitsbergen was studied after complete ice melt in June 2003. The abundances of the benthic fauna were within the range reported from estuaries and similar intertidal areas of boreal regions. The high proportion of juveniles in the eulittoral zone indicated larval recruitment from subtidal areas. The macrobenthic fauna can be divided into an intertidal and a subtidal community, both being numerically dominated by annelids. Deposit feeders were numerically predominant in intertidal sites, whereas suspension feeders were most abundant in the subtidal area. Among the meiofauna, only the benthic copepods were identified to species, revealing ecological adaptations typical for intertidal species elsewhere.

Seasonal patterns of reproductive activities among deep-sea benthic copepod species in the bathyal Sagami Bay, central Japan

Little is known about the life histories of the deep-sea metazoan meiobenthos. At a bathyal site (depth 1430 m) in Sagami Bay, central Japan, temporal changes in abundance and reproductive activity of deep-sea benthic copepods were investigated for eight abundant species that composed about 50% of total individuals, based on samples collected before fresh organic matter increased in the sediment (December 1996 and 1997), 1 month thereafter (June 1997 and May 1998), and a few months after the event (August 1997 and 1998). Densities of adults of these species fluctuated among samples (the total abundance was 5–30 individuals/10 cm2), but did not show any seasonal trend. Strong evidence for competitive relationships among species could not be detected, and there was no significant negative correlation in abundance between any species pair. The percentage of ovigerous females among total adult females of Schizopera sp. 1 differed significantly by month. Furthermore, the adult sex ratio of the species appeared to fluctuate temporally. These suggest a temporal change in reproductive activity and synchronized growth of Schizopera sp. 1. There was no temporal trend, however, in any parameter for the other species. Mean egg number per brood and egg diameter differed among species, but did not change seasonally in any species. Our study suggests the rarity of seasonal breeding species among the deep-sea benthic copepods, one of the major metazoan meiofaunal groups, as well as among other macro-megafaunal metazoans.

The timing of benthic copepod emergence

We investigated emergence of marine benthic harpacticoid and cyclopoid copepods from subtidal sediment into the bottom water. Previous studies that used traps in the field found that copepods emerged from the sediment within 2 h of dusk. We examined emergence in 20‐min sampling periods over 13 h from 1200 to 0100 h in a laboratory flume under conditions of constant flow speed. The light intensity was adjusted to field conditions every 20 min. We observed a peak in emergence during the 20‐min sampling period after the onset of darkness, greatly increasing the accuracy with which the timing of emergence is known. This result will help to set the stage for studies of emergence cues.

Temporal patterns in diversity and species composition of deep-sea benthic copepods in bathyal Sagami Bay, central Japan

Little is known about temporal changes in the diversity and species composition of deep-sea metazoan meiofauna and their relationships with changes in the food supply. Those changes were studied for benthic copepod assemblages based on 2-year time-series data at a bathyal site in Sagami Bay (1430 m depth), central Japan, where annual fluctuation in the abundance of benthic foraminiferans was previously observed. Species diversity of benthic copepods at the site was as high as, or slightly higher than, that observed at other deep-sea sites, but did not fluctuate temporally through the study period. Multivariate analyses did not reveal any clear seasonal or directional change occurring over the longer term in their species composition, although there was some consistent pattern. These results indicate a lack of, or only weak, seasonality in the diversity and species structure of the deep-sea benthic copepod assemblages, even though the fresh organic food supply fluctuates seasonally. They also suggest that there are differences between copepods and foraminiferans in the response to changes in environmental factors, and that spatial differences in the composition of copepod communities are greater than temporal ones at this deep-sea site.

Wind events and benthic-pelagic coupling in a shallow subtropical bay in Florida

During the winter months (December to April), the SE United States is influenced by continental air masses from the north or northwest which pass at approximately 4 to 7 d intervals. These wind events can cause suspension of bottom sediments in Florida Bay. Over a 9 d period in March 2001, we examined the effects of a wind-mixing event on the pelagic system within the NW part of Florida Bay, where water depth is 2 to 3 m. This event caused significant suspension of bottom materials, large increases in NH 4 and PO 4 , smaller increases in NO 3 +NO 2 and Si(OH) 4 , a decrease in microzooplankton abundance, and an increase in benthic copepods in the water column. As wind speeds declined, there was a rapid decline in PO 4 concentration, gradual declines in suspended sediment, NH 4 and Si(OH) 4 , an increase in chlorophyll a (chl a) stock, an increase in phytoplankton growth and productivity, an increase in microzooplankton grazing rate, and a settling of the benthic harpacticoid community. No grazing response was apparent in the mesozooplankton community. The wind event clearly injected dissolved and particulate benthic materials into the water column, where they directly stimulated the bacterioplankton, phytoplankton and microzooplankton communities within 1 to 2 d after the event. The water column was strongly net heterotrophic at this time, suggesting a large input of dissolved organic matter from the bottom. Stimulation of the pelagic food web continued at least until we completed our study 6 d after the event. By the end of our study, the water column was net autotrophic.

Lipids and fatty acids of the benthic marine harpacticoid copepod Heteropsyllus nunni Coull during diapause: a contrast to pelagic copepods

Many free-living copepods produce and store lipids prior to entering diapause (long-term dormancy). Heteropsyllus nunni Coull is the only marine harpacticoid copepod known to undergo any form of diapause. This study presents the first information on the types of lipids and fatty acids produced for long-term diapause in this benthic species. Sexually immature adults of H. nunni undergo diapause within a pliable self-made cyst. Prior to entering diapause (which lasts 3–4 months), they produce and store large amounts of orange lipid. The lipids apparently are utilized during diapause. Although some residual lipids remain, chiefly around the gonads, after the copepods emerge from their cysts, the lipid stores are visibly reduced. Typically, the copepods mate and produce eggs within 48 h after diapause is terminated. Light level and confocal laser scanning microscopy revealed that the lipid stores are distributed throughout the body in numerous oil droplets and not as a single oil sac, as seen in many marine calanoid copepods prior to overwintering (winter diapause). Transmission electron microscopy showed lipid spheres within the gut epithelium and large droplets of lipids stored extracellularly. Confocal laser scanning microscopy of copepods in pre-diapause, during diapause (encysted), post-diapause (recently excysted), and in reproductive condition, revealed that lipid stores are reduced following diapause, but are not totally absent. Analysis of lipid classes showed that H. nunni store predominantly wax esters/sterol esters (83% of total lipids) during diapause. The predominant lipid is most likely wax esters, as sterol esters typically are found only in small amounts in copepods. Fatty acid (FA) profiles of the copepods in diapause showed 16:0 to be most abundant followed by 16:1n-7 and 18:0; other FA occurred at concentrations <10% of total FA. Three polyunsaturated fatty acids (PUFA), 20:5n-3, 18:2n-6 and 20:4n-6, were found at concentrations <2% of total FA. These PUFA are "essential fatty acids" in H. nunni, obtained through dietary sources. The lipid classes and fatty acids present in H. nunni during diapause are compared to those of other copepods, some in a state of diapause and others not. It appears that lipid class and FA profiles are indicative of genetic makeup, type of diet or amount of food consumed prior to dormancy. Some classic paradigms of lipids and their association with copepod diapause are re-evaluated.

A microcosm system for the study of pollution effects in shallow, sandy, subtidal communities

The introduction of pollutants into the marine environment is inevitable, so an understanding of their effects is needed. Because shallow, coastal waters are at greatest risk and many of these shorelines are sandy, a test system for the shallow, sandy, subtidal environment is required. We developed a microcosm system for this purpose and tested it for three months to determine whether the benthic community remained healthy. Furthermore, because long-term effects on the environment occur primarily in the sediment, an experimental method for administering pollutants to the sediment is necessary. We administered a 1-mm layer of clean sand (simulating a technique of administering pollutants as a coating on sand) and tested the benthic community for artifactual effects of the sand itself. Fifteen metrics of community health, including the abundance of benthic microalgae, nematodes, and copepods, were measured. Most metrics were not significantly affected either by containment in the microcosms or by the addition of a 1-mm layer of clean sand. These microcosms are suitable as a test system for the shallow, sandy, subtidal environment.

Niche segregation and habitat specialisation of harpacticoid copepods in a tropical seagrass bed

Several harpacticoid copepod species are adapted to an epiphytic lifestyle. Previous studies on tropical seagrass meiofauna mainly focussed on the epiphytic communities and neglected the benthic component. The present study aims to document the benthic harpacticoid copepod communities sampled from different sediment depth horizons adjacent to five seagrass species in the intertidal and subtidal zone of a tropical seagrass bed (Gazi Bay, Kenya). Two benthic copepod communities could be identified mainly based on the tidal position of the samples: a first community was collected near the intertidal seagrasses Halophila ovalis and Halodule wrightii; a second community occurred near the subtidal seagrasses Thalassia hemprichii, Syringodium isoetifolium and Halophila stipulacea. The first community was mainly determined by sediment characteristics (e.g. skewness), while the second community was split off based on organic matter content (% TOM), nutrient and pigment values. A subtle combination of horizontal and vertical niche segregation was reported for the dominant copepod families. Species of the families Thalestridae, Laophontidae and Diosaccidae were structured by tidal position and showed a strong preference for the subtidal zone. The opposite strategy, i.e. a clear preference for the intertidal zone, was found for copepods belonging to the families Paramesochridae and Canuellidae. In addition, Apodopsyllus africanus (Paramesochridae) was well-adapted to stress and was concentrated in the deeper sediment layers near the subtidal seagrasses. On the other hand, Canuellidae, as filter feeders, were concentrated in the upper centimetres of the sediment. The families Ectinosomatidae and Cletodidae did not show any vertical or horizontal segregation. On the species level, however, clear horizontal niche segregation was detected for the family Cletodidae. In addition to the reported ecological results, the study material was used to evaluate different niche definitions. We found tidal position to be the most important factor forcing harpacticoids to specialise. Sediment depth horizon was less powerful in dividing the families into different guilds (from specialists to generalists) based on standardised niche breadth. The present study documents the subtle habitat partitioning of co-existing species in a limited area and its role in sustaining high biodiversity in the community.