Survey of aquatic macro-invertebrates in new dykes and a pond at Paull, East Yorkshire
Summary
Realignment of the Humber bank between Paull and Thorgumbald resulted in loss of a large borrow pit situated behind the original embankment which was known to support a rich assemblage of water beetles and other aquatic insects. At the same time, new aquatic habitats have been provided in the form of extensive dykes and a pond behind the new embankments. In July 2003, vegetation was transferred from the former borrow pit to the new water bodies and an attempt was also made to translocate invertebrates.
A survey of aquatic macroinvertebrates in the new water bodies was undertaken in April 2004, both to judge the effectiveness of the translocation work and to assess the overall fauna.
The new water bodies support several scarce water beetles. These include opportunistic colonists of raw ponds such as Hygrotus nigrolineatus and Scarodytes halensis as well as specialists of coastal / brackish water habitats including Haliplus apicalis, Agabus conspersus and Enochrus bicolor. Some of these species may be of ephemeral occurrence but others will hopefully have established resident populations. None of the specialist brackish water Corixid bugs were found but these had not been present in the former borrow pit. Caddis flies were represented by two larval taxa, one of which is typical of ion-rich waters. The brackish water amphipod Gammarus zaddachi is abundant. Most other aquatic invertebrates were ubiquitous freshwater or wide tolerance species.
It is difficult to evaluate the efficacy of translocation of vegetation and invertebrates from the former borrow pit to the new water bodies. However, the presence of species which do not normally colonise raw, early-successional habitats but favour richly-vegetated ponds and dykes and are known to have been translocated indicates some success. Almost certainly, the translocation of perennial water plants has been valuable in providing immediate vegetation structure and by introducing attached eggs, larvae, pupae or adults.
The presence of several brackish water invertebrates indicates that conditions in the new aquatic habitats are sufficiently ion-rich to support a specialised invertebrate fauna. This is probably due to aerial deposition and at least some of these species appear to have established breeding populations. Potentially, the establishment of a pond and connecting dykes with low-end brackish water could provide habitats of regional importance for the conservation of aquatic invertebrates.
1. Introduction
Realignment of the Humber bank between Paull and Thorgumbald resulted in loss of a large borrow pit situated behind the original embankment. At the same time, new aquatic habitats have been provided in the form of extensive soke dykes behind the new embankments and a pond close to South Pasture Drain. In July 2003, vegetation was transferred from the former borrow pit to the new water bodies and an attempt was also made to translocate invertebrates (the former borrow pit was known to support a rich assemblage of water beetles and other aquatic insects).
This survey was commissioned by the Environment Agency with the aims of:
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(a) providing baseline data on the aquatic invertebrates colonising the new water bodies within twelve months of construction, and
(b) assessing whether the attempt to translocate invertebrates from the former borrow pit had been successful.
Sampling was carried out on 14th April 2004 by Martin Hammond and Robert Merritt. Four sampling points were selected (see below) and each was worked vigorously with a pond net until no further species could be found. Care was taken to trawl all features of the water body at each sampling point, e.g. submerged and water-margin vegetation, exposed substrate. Collections of water plants were also examined in a bucket to look for attached invertebrates.
2. Sampling points
Sampling points were selected to represent the new water bodies constructed at Paull.
SP1 (National Grid Reference TA 1800 2512) is a rather steep-sided pond near the visitors’ car park. It contained very little vegetation apart from limited algal growth, a few clumps of a liner-leaved pondweed and occasional pieces of bladder wrack (presumably blown over the estuary wall during a storm). A small amount of woody debris was present.
SP2 (TA 1798 2515) is the dyke nearest the car park, to the west of the pond. A length of around 70 metres was sampled. Vegetation translocated from the former borrow pit is well-established including patches of sea club-rush (Bolboschoenus maritimus) and submerged stands of spiked water milfoil (Myriophyllum spicatum), thread-leaved water crowfoot (Ranunculus trichophyllos) and common stonewort (Chara vulgaris).
SP3 (TA 1819 2477) covers around 100 metres towards the western end of the new soke dyke east of South Pasture Drain. There are patches of grey club-rush (Schoenoplectus tabernaemontani) and submerged mixtures of spiked water milfoil, thread-leaved water crowfoot and a liner-leaved pondweed (probably Potamogeton pusillus). This section includes shallow water with trailing grasses at the westernmost end of the ditch.
SP4 (TA 1890 2411) covers a section of around 100 metres further east along the same dyke.
3. Invertebrates recorded
3.1 Aquatic Coleoptera (beetles)
Water beetles are often amongst the most abundant and speciose insects in standing water habitats. The ecology and distribution of British species is well-known and these insects are readily sampled throughout most of the year, making them very useful in conservation assessment.
38 water beetle taxa were recorded, which is diverse for a site with poorly-developed vegetation structure. By far the greatest diversity of species was found at SP3 where 29 taxa were found. This section of dyke has dense mats of floating grasses in very shallow water as well as submerged waterweeds and emergent monocots: a very favourable habitat structure for water beetles. This SP produced nearly double the number of species
2 found at SP2 (n =16), which has healthy growth of submerged macrophytes including Chara but little complex marginal vegetation in shallow water. The algivorous Haliplus confinis and H. obliquus recorded here are often associated with Chara. SP1 produced a significant suite of small diving beetles found in open, sparsely-vegetated standing waters, often in ponds or ditches which have recently been created or cleared. These have striped or highly patterned wing cases in contrast to the predominantly dark and uniform colouration of beetles found in richly-vegetated ponds and include Hydroglyphus pusillus, Hygrotus confluens, H. nigrolineatus and Scarodytes halensis. SP4 was poor in water beetles (n=10).
Of 41 aquatic beetles recorded from the former borrow pit in 2000-2003, 26 (63%) were present in the new habitats in April 2004. Allowing for chance and seasonal influences, it can be assumed that between two-thirds and three-quarters of the species present in the former borrow pit have been retained in the local area, either through translocation or spontaneous colonisation of the new water bodies.
Of eight Nationally Scarce water beetles recorded from the former borrow pit, three were found in the new habitats (Haliplus apicalis, Agabus conspersus and Dytiscus circumflexus). Larvae of Ilybius sp. were present in the dyke at SP3 and may represent a fourth scarce species, I. subaeneus (which had already colonised this dyke by July 2003). Three Nationally Scarce species not previously recorded in the vicinity were found (Hygrotus nigrolineatus, Scarodytes halensis and Enochrus bicolor).
The high turnover of species in this type of habitat can be illustrated by records of the genus Enochrus, which are known to be good fliers (e.g. Hammond, 2001). Four have been recorded at Paull, the most widespread species (E. testaceus) being found both in the former borrow pit and in one of the new dykes (SP2). Of the rarer Enochrus, E. halophilus was found in the borrow pit was not collected in the new water bodies; E. quadripunctatus was found in one of the new dykes in July 2003 but not before or since; E. bicolor, not previously known from the site, was found in April 2004. This suggests that records (especially of single specimens) do not necessarily demonstrate the presence of an established breeding population - but equally it shows that even some rarer species will migrate into the new habitats and, if conditions are suitable, may become established.
It is possible to assess the ‘quality’ of water beetle assemblages by calculating a Species Quality Index (SQI). This represents the mean Species Quality Score (SQS) for the species present; the SQS is based on the national and regional status of each species, using a logarithmic scale from 1 (ubiquitous) to 32 (nationally threatened). The SQI for the former borrow pit was 2.66, the SQI for the new habitats is 2.67. Consequently, the ‘quality’ of both assemblages is very similar. However, scarce brackish water species were better represented in the former borrow pit, whereas the SQI for the new habitats is boosted by the presence of scarce pioneer species such as Hygrotus nigrolineatus and Scarodytes halensis. An SQI score above 2.0 indicates a good quality site for water beetles.
3.2 Aquatic Hemiptera - Heteroptera (water bugs)
The water bugs are a diverse group including water crickets, pond-skaters, water- measurers, saucer bugs, water scorpions, backswimmers and lesser water-boatmen. Many water bugs show distinct preferences in terms of water chemistry and habitat structure (e.g. amount of vegetation or successional stage).
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A total of 16 species were recorded, which is good for this type of habitat especially as a number of common species were not found. The most diverse sampling points was SP2 (nine species), the other locations producing six or seven species each. As would be expected, most are insects which move rapidly into new habitats (e.g. the three common pond-skaters) or are associated with early successional conditions (e.g. the lesser water- boatmen Sigara falleni, S. lateralis and Arctocorisa germari). Two bugs typical of more vegetated ponds - the saucer bug Ilyocoris and the lesser backswimmer Plea - were only found in two and one locations respectively.
None of the true brackish water species (Corixa affinis, Sigara selecta and S. stagnalis) were found, but equally none had been recorded from the former borrow pit. Sigara concinna (SP1) favours ponds of high ionic status, though not extending into the more strongly brackish conditions preferred by S. stagnalis. The rather uncommon water boatman Cymatia bonsdorfii was thought to have been seen in the net at SP3 but none were found when material was examined in the laboratory. This species was present in the former borrow pit. Arctocorisa germari is an infrequent species in Yorkshire, previously recorded from a small number of gravel pits and sparsely-vegetated lakes.
3.3 Trichoptera (caddis flies) and Ephemeroptera (mayflies)
Although numerous cased caddis larvae of varying appearance were collected, these proved to be of just two (possibly three) species. Some Limnephilid caddis larvae change the construction of their cases as they develop, so can appear quite dissimilar at different developmental stages. Limnephilus affinis / incisus1 probably refers to the former, a widespread species associated with coastal dykes which extends into brackish water.
Both taxa were present at SP 1 & 2 with L. ?affinis at SP3. The water bodies are probably too new for many caddis to have been able to colonise. The dyke at SP3/4 has minimal flow and a rather uniformly silty clay bed; these conditions are not suitable for many caddis.
Small numbers of mayfly nymphs were collected at SP3 but had disappeared from samples examined in the laboratory.
3.4 Odonata (damselflies and dragonflies)
Mayfly nymphs were recorded at SP 2 & 3, consisting of Blue-tailed Damselfly (Ischnura elegans) and Coenagrion sp. (very probably Azure Damselfly, C. puella ).
3.5 Molluscs
The only mollusc found was the ubiquitous Wandering Snail (Lymnaea peregra), present in some quantity at SP 2, 3 & 4. Sediment samples failed to reveal any small bivalves such as Pisidium spp.
3.6 Leeches
A single species of leech, the common Glossiphonia complanata, was found at SP2.
1 This pair of species cannot be separated in the larval stage
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3.7 Amphipods and Isopods (Crustacea)
Samples were taken of amphipods (Gammaridae) and water-slaters (Asellidae). The amphipod Gammarus zaddachi, a brackish water species, was present in good numbers at SP 1,2 & 4 with immature indet Gammarus at SP3 presumably being the same species. According to Fryer (1993), this species has been found in Yorkshire at Blacktoft Sands, Thorne Quay and nearby warping drains and in the River Ouse; it may, however, be widespread around the Humber.
The only Isopod was the ubiquitous Asellus aquaticus.
3.8 Fish and amphibians
Small numbers of Ten-spined Stickleback were present at each location.
Common Toad spawn was noted in the dyke at SP2. Several adult Smooth Newts were caught at SP3.
4. Assessment of the translocation initiative
It is very difficult to assess the effectiveness of the attempt to translocate invertebrates from the former borrow pit into the new water bodies. A number of species had spontaneously colonised the new dykes beforehand and even those known to have been transferred may also have arrived under their own steam. However, aquatic insects characteristic of well-vegetated ponds such as the saucer bug Ilyocoris cimicoides, the lesser backswimmer Plea leachi and the water beetle Noterus clavicornis are rarely found in water bodies of very recent origin. These three species are known to have been transferred from the former borrow pit in good numbers and are present at least locally in the new water bodies.
Of eight Nationally Scarce water beetles recorded from the former borrow pit, three were found in the new habitats (Haliplus apicalis, Agabus conspersus and Dytiscus circumflexus). All these species were believed to have been translocated2, although it cannot be assumed that they have not established unassisted.
The weevil Lictodactylis leucogaster was not found despite having been translocated in large numbers and its food plant (spiked water-milfoil) being well-established and vigorous. However, the phenology of this species is not well known and it may not be present in adult form this early in the year. Larvae of Ilybius sp/spp were present in the dyke at SP3 and may include I. subaeneus, a species which had already colonised this dyke by July 2003.
A very obvious benefit of translocating vegetation from the former borrow pit has been to provide food and shelter for invertebrates in the new habitats. Vegetation has established very well, particularly in the dyke at SP2, where there are fine stands of spiked water- milfoil, thread-leaved water-crowfoot, common stonewort and sea club rush. Lesser pondweed is more dominant in the dyke at SP3/4, with water-milfoil and water-crowfoot more patchy. In this dyke submerged macrophytes were coated in clayey silt, presumably washed in from agricultural field drains.
2 Large numbers of adult Haliplus were moved from the old borrow pit but cannot be distinguished in the field; Dytiscus sp. larvae were most likely to be D. circumflexus
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Table 1 Nationally scarce water beetles recorded from the former borrow pit
Species Translocated Present in new habitat Haliplus apicalis ? y Hygrotus parallelogramus N N Agabus conspersus y Y Ilybius subaeneus N nc Dytiscus circumflexus y y Enochrus halophilus N N Ochthebius marinus N N Lictodactylis leucogaster Y nc
Y – yes, in large numbers (y = in small numbers); N – not found; nc – not confirmed but may be present
5. Species of conservation concern
Six of the beetles recorded during the current survey are listed as Nationally Scarce (Foster, in prep).
Haliplus apicalis (Nationally Scarce, NSb) A small ovoid algivorous water beetle associated with brackish or otherwise very ion-rich ponds and dykes. There are recent records from nine hectads (10 km. squares) in the Yorkshire and Humber region. Sites are scattered along the Humber from Broomfleet to Welwick, including Barton clay pits on the south bank. It also occurs at two sites inland, a single outpost on the east coast and around the Tees estuary.
This beetle occurs in well-vegetated standing or slow-flowing water and requires no specific management measures at this site.
Hygrotus nigrolineatus (Nationally Scarce, NSa) A small diving beetle which has only colonised Britain within the last 20 years. It is a pioneer species of early successional ponds and gravel pits. Hygrotus nigrolineatus has been recorded from six other widely scattered sites in the Yorkshire and Humber region. Given the high level of recent recording effort, this indicates a genuinely rare species, albeit opportunist and highly mobile; it could occur in some of the many gravel pits in the Hull Valley.
H. nigrolineatus is a fugitive species which appears to establish relatively short-lived populations. It is not found in very shallow water bodies and will probably remain restricted to the pond until successional conditions become unsuitable. Although rare, site specific management is not really appropriate for this species since new water bodies are continuous created.
Scarodytes halensis (Nationally Scarce, NSb) A small diving beetle with broken markings on its pale wing cases, a common feature of dytiscids inhabiting sparsely-vegetated sandy or gravelly substrates. It is a southern and eastern species, at the northern edge of its British range in Yorkshire: there are a handful of recent records including one other from South Holderness.
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S. halensis could benefit from rotational clearance of vegetation in the new water bodies so that there are always some areas of sparsely-vegetated substrate.
Agabus conspersus (Nationally Scarce, NSb) A medium-sized, spotted brown diving beetle restricted to shallow brackish waters. Although it can be plentiful where it occurs, A. conspersus in very local in the Yorkshire and Humber region. It is restricted to a small number of sites between North Ferriby and Easington, with records from six hectads.
Agabus conspersus tolerates a range of successional conditions and would presumably benefit from rotational clearance of the dykes at Paull.
Dytiscus circumflexus (Nationally Scarce, NSb) A Great Diving Beetle found in larger ponds and drains, most frequently near the coast; it has spread northwards and inland in recent decades, in contrast to the decline of some other members of the genus. Dytiscus species prey on invertebrates, amphibian tadpoles and small fish, and are often top predators in ponds.
There are recent records from 17 hectads in the Yorkshire and Humber region, mostly clustered along the north bank of the Humber, in the central Vale of York and in the western Vale of Pickering. D. circumflexus still has a restricted distribution in Britain but is not threatened. No specific conservation measures are suggested at Paull but this species would presumably benefit from richly-vegetated (though not reed-choked) conditions with abundant prey.
Enochrus bicolor (Nationally Scarce, NSb) This scavenger water beetle is restricted to brackish pools and dykes. It has been recorded over a range of salinity values up to 63 ppt (Greenwood & Wood, 2003) and can be found in more saline conditions than most water beetles tolerate. A single specimen was collected from the dyke at SP2 so it is unclear whether a breeding population has established; E. bicolor has not been detected previously at Paull.
Enochrus bicolor has a very restricted distribution in the Yorkshire and Humber region, with recent records for a handful of sites along the outer Humber estuary and one location on Teeside. The record from the present survey is the most westerly apart from an isolated inland population near Thorne. At the latter site it has been associated with saline mine water pumped to the surface, and may not persist now this practice has ceased.
6. Brackish water indicators
Many specialist invertebrates of coastal or brackish waters are of conservation interest in the sense that their habitat is highly restricted and many have quite exacting requirements. The water beetles Haliplus apicalis, Agabus conspersus and Enochrus bicolor, the caddis fly Limnephilus affinis and the amphipod Gammarus zaddachi are all associated with coastal or brackish standing waters; the lesser water boatman Sigara concinna is also characteristic of ion-rich waters. The presence of several such species suggests that the new water bodies at Paull are sufficiently ion-rich to develop a specialised coastal invertebrate fauna. Since the new water bodies are hydrologically isolated from the estuary, it is likely that salt spray provides the main brackish influence.
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Assuming that caddis larvae identified as Limnephilus affinis / incisus are the former, this species is obviously breeding. This caddis occurs in both coastal and inland ponds, pools and ditches of high ionic content (Wallace, 1991). Gammarus zaddachi is said not to be able to breed in freshwater (Fryer, 1993) so the good numbers of both sexes present suggest that conditions are sufficiently brackish to allow reproduction. Haliplus apicalis and Enochrus bicolor were only recorded as single individuals which does not prove the establishment of breeding populations, though it should be noted that the former species is only identifiable by dissection of males so it could be present in significant numbers. Agabus conspersus was common and probably breeding.
It should be noted that although some ‘brackish’ water invertebrates tolerate high salinities, many seem to favour low-end brackish conditions. Such communities are quite distinct from those of saline lagoons or estuarine habitats subject to frequent tidal incursions. Long-term studies of an Essex saltmarsh subject to rare episodes of tidal flooding have indicated that most brackish water beetles only reappeared when salinity fell below about 15 ppt and electrical conductivity was less than 15 mScm-1 (Greenwood & Wood, 2002).
7. References
FOSTER, G.N. (In prep.) The scarce and threatened Coleoptera of Great Britain, 3: Aquatic Coleoptera. Joint Nature Conservation Committee: Peterborough.
FRYER, G. (1993). The freshwater Crustacea of Yorkshire. Yorkshire Naturalists’ Union & Leeds Philosophical and Literary Society.
GREENWOOD, M.T. & WOOD, P.J. (2003). Effects of seasonal variation in salinity on a population of Enochrus bicolor Fabricius 1792 (Coleoptera: Hydrophilidae) and implications for other beetles of conservation interest. Aquatic Conservation: Marine and Freshwater Ecosystems, 12: 21-34.
HAMMOND, M. (2001). Flight records for Yorkshire water beetles. Latissimus 13: 1-3
HUXLEY, T. (2003). Provisional Atlas of the British aquatic bugs (Hemiptera, Heteroptera). Biological Records Centre: Monks Wood.
MERRITT, R. & HAMMOND, M. (in prep.) Atlas of the aquatic Coleoptera of the Yorkshire and Humber region [draft maps].
WALLACE, I.D. (1991). A review of the Trichoptera of Great Britain. Research & Survey in Nature Conservation No. 32. Nature Conservancy Council: Peterborough.
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APPENDIX: SPECIES LISTS
Sampling Point 1: Pond at TA 1800 2512
Trichoptera (caddis-flies)
Limnephilidae Limnephilus affinis / incisus larvae Limnephilus marmoratus larvae
Coleoptera (beetles)
Haliplidae (algivorous water beetles) Haliplus lineatocollis several Haliplus ruficollis agg.
Noteridae (burrowing water beetles) Noterus clavicornis several
Dytiscidae (diving beetles) Hydroglyphus pusillus Hygrotus confluens several Hygrotus inaequalis Hygrotus nigrolineatus four caught Hydroporus palustris two Scarodytes halensis one collected Agabus conspersus four caught
Hydrophilidae (scavenger water beetles) Hydrobius fuscipes
Hemiptera - Heteroptera (water bugs)
Gerridae (pond skaters) Gerris odontogaster
Notonectidae (backswimmers) Notonecta viridis
Corixidae (lesser water boatmen) Arctocorisa germari Callicorixa praeusta Sigara concinna Sigara distincta Sigara dorsalis Sigara lateralis Sigara nigrolineata
Amphipoda (freshwater shrimps and sandhoppers)
Gammaridae Gammarus zaddachi
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Sampling point 2: Dyke at TA 1798 2515
Amphipoda
Gammaridae Gammarus zaddachi
Isopoda
Asellidae Asellus aquaticus
Annelida (leeches)
Glossiphoniidae Glossiphonia complanata
Mollusca
Lymnaeidae (pond snails) Lymnaea peregra
Odonata (damselflies and dragonflies)
Ischnura elegans larvae
Trichoptera (caddis-flies)
Limnephilidae Limnephilus affinis / incisus larvae Limnephilus marmoratus larvae
Coleoptera (beetles)
Haliplidae (algivorous water beetles) Haliplus confinis Haliplus lineatocollis Haliplus obliquus Haliplus ruficollis
Noteridae (burrowing water beetles) Noterus clavicornis
Dytiscidae (diving beetles) Laccophilus minutus Hydroglyphus pusillus Hygrotus confluens Hygrotus inaequalis Hydroporus palustris Agabus conspersus Colymbetes fuscus
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Hydrophilidae (scavenger water beetles) Megasternum concinnum Hydrobius fuscipes Laccobius colon Enochrus testaceus
Hemiptera - Heteroptera (water bugs)
Gerridae (pond skaters) Gerris odontogaster Gerris thoracicus
Naucoridae (saucer bugs) Ilyocoris cimicoides
Pleidae (lesser backswimmers) Plea leachi
Corixidae (lesser water boatmen) Corixa punctata Callicorixa praeusta Sigara dorsalis Sigara lateralis Sigara nigrolineata
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Sampling point 3: Dyke at TA 1819 2477
Amphipoda
Gammaridae Gammarus sp. immatures
Mollusca
Lymnaeidae Lymnaea peregra
Araneae (spiders)
Paradosa sp. immature Pirata sp. immature Tetragnatha extensa Pachygnatha clerki Oedothorax fuscus Lepthyphantes gracilis
Odonata (damselflies and dragonflies)
Coenagrion sp. larva Ischnura elegans larvae
Trichoptera (caddis-flies)
Limnephilidae Limnephilus affinis / incisus larvae
Coleoptera (beetles)
Haliplidae (algivorous water beetles) Haliplus apicalis one male collected Haliplus immaculatus numerous
Noteridae (burrowing water beetles) Noterus clavicornis
Dytiscidae (diving beetles) Laccophilus minutus Hydroglyphus pusillus Hygrotus confluens Hygrotus inaequalis Hydroporus palustris Hydroporus planus Hydroporus tessellatus Agabus bipustulatus Agabus conspersus Ilybius sp. indet larvae Colymbetes fuscus
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Dytiscus circumflexus one caught
Helophoridae Helophorus aequalis Helophorus grandis Helophorus obscurus
Hydrophilidae Cercyon marinus one collected Megasternum concinnum Hydrobius fuscipes Anacaena limbata Laccobius colon Helochares lividus Enochrus bicolor one collected Enochrus testaceus Cymbiodyta marginella
Hydraenidae Ochthebius minimus
Heteroceridae Heterocerus fenestratus
Hemiptera - Heteroptera (water bugs)
Gerridae Gerris lacustris Gerris odontogaster Gerris thoracicus
Corixidae Hesperocorixa linnaei Sigara lateralis Sigara nigrolineata
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Sampling Point 4: Dyke at TA 1890 2411
Amphipoda
Gammaridae Gammarus zaddachi
Odonata (damselflies and dragonflies)
Ischnura elegans
Coleoptera (beetles)
Dytiscidae (diving beetles) Hygrotus impressopunctatus Agabus bipustulatus Agabus conspersus Colymbetes fuscus Dytiscus marginalis
Helophoridae Helophorus grandis
Hydrophilidae (scavenger water beetles) Laccobius colon Cymbiodyta marginella
Hydraenidae Ochthebius dilatatus Ochthebius minimus
Hemiptera - Heteroptera (water bugs)
Gerridae (pond skaters) Gerris thoracicus Gerris odontogaster
Naucoridae (saucer bugs) Ilyocoris cimicoides
Notonectidae (backswimmers) Notonecta viridis
Corixidae (lesser water boatmen) Sigara dorsalis Sigara falleni Sigara lateralis
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Appendix 2: combined species list
Annelida (leeches)
Glossiphonia complanata
Mollusca
Lymnaeidae Lymnaea peregra
Amphipoda
Gammaridae Gammarus zaddachi
Isopoda
Asellidae Asellus aquaticus
Odonata (damselflies and dragonflies)
Coenagrion sp. (indet larvae) Ischnura elegans
Trichoptera (caddis-flies)
Limnephilidae Limnephilus affinis / incisus Limnephilus marmoratus
Coleoptera (beetles)
Haliplidae (algivorous water beetles) Haliplus apicalis Haliplus confinis Haliplus immaculatus Haliplus lineatocollis Haliplus obliquus Haliplus ruficollis
Noteridae (burrowing water beetles) Noterus clavicornis
Dytiscidae (diving beetles) Laccophilus minutus Hydroglyphus pusillus Hygrotus confluens Hygrotus impressopunctatus Hygrotus inaequalis Hygrotus nigrolineatus
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Hydroporus palustris Hydroporus planus Hydroporus tessellatus Scarodytes halensis Agabus bipustulatus Agabus conspersus Ilybius sp. (indet larvae) Colymbetes fuscus Dytiscus circumflexus Dytiscus marginalis
Helophoridae Helophorus aequalis Helophorus grandis Helophorus obscurus
Hydrophilidae (scavenger water beetles) Cercyon marinus Megasternum concinnum Hydrobius fuscipes Anacaena limbata Laccobius colon Helochares lividus Enochrus bicolor Enochrus testaceus Cymbiodyta marginella
Hydraenidae Ochthebius dilatatus Ochthebius minimus
Heteroceridae Heterocerus fenestratus
Hemiptera - Heteroptera (water bugs)
Gerridae (pond skaters) Gerris lacustris Gerris thoracicus Gerris odontogaster
Naucoridae (saucer bugs) Ilyocoris cimicoides
Pleidae (lesser backswimmers) Plea leachi
Notonectidae (backswimmers) Notonecta viridis
Corixidae (lesser water boatmen) Corixa punctata
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Callicorixa praeusta Arctocorisa germari Hesperocorixa linnaei Sigara concinna Sigara distincta Sigara dorsalis Sigara falleni Sigara lateralis Sigara nigrolineata
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ment), inoculated (received three vegetation/sediment Does Facilitation of cores from a natural wetland), and stocked inocu- lated (received three cores and were stocked with a poorly dispersing invertebrate group—gastropods). Faunal Recruitment All mesocosms were placed 100 m from a natural wet- land and allowed to colonize for 82 days. Facilitation Benefit Ecosystem of invertebrate colonization led to communities in in- oculated and stocked inoculated treatments that contrasted strongly with those in the unaided control Restoration? An treatment. Control mesocosms had the highest taxa richness but the lowest diversity due to high densities and dominance of Tanytarsini (Diptera: Chironomidae). Experimental Study Community structure in inoculated and stocked in- oculated mesocosms was more similar to that of a of Invertebrate nearby natural wetland, with abundance more evenly distributed among taxa, leading to diversity that was higher than in the control treatment. Inoculated and Assemblages in stocked inoculated communities were dominated by non-aerial invertebrates, whereas control meso- cosms were dominated by aerial invertebrates. These Wetland Mesocosms results suggest that facilitation of invertebrate recruit- ment does indeed alter invertebrate community de- Valerie J. Brady1,2,3 velopment and that facilitation may lead to a more 1,4 natural community structure in less time under condi- Bradley J. Cardinale tions simulating wetland restoration. Joseph P. Gathman1,5 Key words: 1,6 aquatic insects, colonization, Gastropoda, Thomas M. Burton inoculation, macroinvertebrates, marsh, recruitment, restoration, stocking, wetland. Abstract We used wetland mesocosms (1) to experimentally as- Introduction sess whether inoculating a restored wetland site with vegetation/sediment plugs from a natural wetland fforts to restore the community structure of degraded would alter the development of invertebrate commu- E systems are often based on the untested assumption nities relative to unaided controls and (2) to determine that providing the correct habitat structure will naturally if stocking of a poor invertebrate colonizer could fur- lead to recovery of the appropriate community (i.e., the “If ther modify community development beyond that you build it, they will come” tenet, Palmer et al. 1997). due to simple inoculation. After filling mesocosms However, recovery of a community may be limited by re- with soil from a drained and cultivated former wet- cruitment of organisms, and recruitment limitation can act land and restoring comparable hydrology, mesocosms as a control on local community structure (e.g., Ricklefs were randomly assigned to one of three treatments: 1987; Palmer et al. 1996). Indeed, barriers to dispersal are control (a reference for unaided community develop- now known to limit the success of many restoration efforts (e.g., Bradshaw 1996), especially when the restored system is isolated or has only limited connectivity to a functioning Departments of 1Zoology and 6Fisheries and Wildlife, Michi- ecosystem. gan State University, East Lansing, Michigan 48824, U.S.A. Practices that enhance recruitment may increase the 2Present address: Natural Resources Research Institute, Uni- chances of restoration success. Establishment of direct versity of Minnesota Duluth, 5013 Miller Trunk Highway, connections between natural and restored areas are in- Duluth, MN 55804. creasingly being used in restoration plans to facilitate 3 Corresponding author. ecosystem recovery (Keesing & Wratten 1998). But when 4Present address: Department of Zoology, University of Wis- degraded sites are isolated from a natural source of colo- consin–Madison, Madison, WI 53706. 5Present address: 854 Inglehart Avenue, St. Paul, MN 55104. nists and it is impractical to establish connectivity, how does one maximize the potential for normal community © 2002 Society for Ecological Restoration development? Two procedures, stocking and inocula-
DECEMBER 2002 Restoration Ecology Vol. 10 No. 4, pp. 617–626 617
Aquatic Invertebrate Recruitment in Wetland Restoration tion, have been used to facilitate the establishment of the non-insect invertebrates, are usually underrepre- poorly dispersing taxa in restored areas. Direct stocking sented in isolated restored wetlands (Barnes 1983; of target taxa has been successful and can allow restored Brown et al. 1997). The lack of these taxa can lead to areas to function like natural systems more quickly by fa- structural differences in the food web that may have cilitating the establishment of key species (Bradshaw important consequences for the recovery of ecosystem 1996). However, stocking is often impractical because of function (Palmer et al. 1997). A few pond and wetland (1) the difficulty of collecting all the fauna that should projects have attempted inoculation with sediments occur in an ecosystem; (2) the lack of knowledge about from natural ponds and wetlands (Howick et al. 1992; what species are most important to ecosystem recovery; Ferrington et al. 1994; Brown et al. 1997). The results of (3) the lack of knowledge about the dispersal abilities of these studies, however, have been ambiguous because various species; and (4) the cost that direct stocking can of experimental design constraints, including low repli- entail. A second method for enhancing establishment of cation and/or the inability to control sources of natural poor colonizers involves inoculating a site with small variation. pieces of a similar natural ecosystem (Touart 1987; In the present study we used mesocosms to test Bradshaw 1996; Brown et al. 1997). In many instances whether inoculation only or inoculation plus stocking inoculation is more practical and cost effective than of a poorly dispersing taxa could alter the development stocking because it has the potential to transplant many of invertebrate communities in restored wetland sites. of the smaller and more ubiquitous members of a com- Our use of mesocosms allowed increased replication and munity in a single effort. reduced the number of confounding factors that have Stocking and inoculation through planting seeds and been associated with prior studies. The objectives of our transplanting rhizomes and seedlings are common pro- study were (1) to determine whether inoculating a re- cedures in restoration of plant communities in wetlands stored site with plugs of natural wetland vegetation and (e.g., Reinartz & Warne 1993). Although some of these sediments would alter development of macroinvertebrate activities (e.g., use of plugs of rhizomes and soil) may community structure relative to unassisted controls and also inoculate restoration areas with invertebrates, few (2) to determine whether inoculation plus deliberate stock- studies have documented this inoculation. Stocking and ing of a restored site with poorly dispersing taxa would inoculation of macroinvertebrates have recently been modify invertebrate community development beyond applied in wetland restoration projects in an effort to that from simple inoculation. assist biological recovery (e.g., Brown et al. 1997). Al- though studies have assessed how these methods influ- Methods ence the recovery of target populations, there have been few rigorous tests to determine whether either method The study site was located in southeastern Michigan of facilitation (stocking or inoculation) has any affect on just inland from Saginaw Bay, Lake Huron. Histori- the development of entire communities. Because the cally, this area was an extensive wetland complex char- functioning of a restored site will depend at least in part acterized by wet prairies, coastal and inland emergent on community structure, it is important to determine marshes, and forested swamps, bogs, and fens (Prince whether these methods actually alter community devel- & Burton 1994). Over the past 150 years 70% of the in- opment or are useful only in the recovery of individual land wetlands have been diked, drained, and converted target populations. to farmland (Prince & Burton 1994). Because patches of Attention is currently being focused on invertebrate natural wetlands remain as sources of colonists for re- communities during wetland restoration because inver- stored areas, much of the area was being considered for tebrates are known to have an important influence on wetland restoration by Michigan’s Department of Natu- the rates of nutrient cycling, primary productivity, de- ral Resources (Prince & Burton 1994). Thus, we chose composition, and the flux of energy between trophic this site for determining the influence of inoculation levels in these ecosystems (Merritt et al. 1984; Murkin & and stocking on the development of wetland inverte- Wrubleski 1988; Batzer & Wissinger 1996). Invertebrate brate communities. communities similar to those found in natural wetlands Plastic wading pools (1.5 m diameter 0.25 m deep) develop rapidly in restored wetlands when restoration were used to create 15 wetland mesocosms alongside a sites are adjacent to a remnant natural ecosystem corn field that was cultivated by local farmers through a (Paterson & Fernando 1969; Streever et al. 1996; Chov- cooperative agreement with the Michigan Department anec & Raab 1997). Restored wetlands that are more iso- of Natural Resources Fish Point Wildlife Management lated, however, may develop invertebrate communities Area (with parts of the crop left for waterfowl feeding dominated by highly mobile taxa having aerial dis- during migration). The mesocosms were approximately persal capabilities (Barnes 1983; Layton & Voshell 1991; 100 m from a remnant natural wetland. Topsoil from Brown et al. 1997). Poorer dispersers, including most of the corn field was used for soil in our mesocosms to
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Aquatic Invertebrate Recruitment in Wetland Restoration simulate wetland restoration of drained agricultural On the final day of the experiment, basic chemical soils. The soil was contoured to form a water depth gra- and physical parameters (dissolved oxygen, turbidity, dient that ranged from saturated soil with no overlying conductivity, alkalinity, temperature, and pH) were water to 15 cm water depth in each mesocosm. Meso- measured to determine whether environmental condi- cosms were filled with filtered water (approximately tions were similar among treatments, the natural wet- 150 m mesh) from a nearby agricultural ditch and land, and the source of water. Only turbidity differed were refilled one to two times weekly during the exper- among treatments, and conductivity was somewhat iment to replace evaporative losses. higher in mesocosms than in the ditch due to evaporation Five replicate mesocosms were randomly assigned to (V. Brady, unpublished data). We then sampled the inver- one of three treatments: control, inoculated, or stocked tebrate community in each mesocosm by sweeping inoculated. Control mesocosms received only agricul- 250- m mesh nets through the water column, the sub- tural soils and filtered water to simulate the unaided mersed portion of the vegetation, and the top 5 mm of in- development of invertebrate communities on a reflooded undated sediment. Netting in each mesocosm continued agricultural field. The only nearby sources of wetland in- until we could capture no additional animals. The in- vertebrate colonists for these mesocosms were a drainage vertebrate community in the natural wetland was also ditch and the remnant wetland—a palustrine emergent sampled with a 250- m mesh dip net. Five 1-m sweeps marsh with wet meadow zones dominated by Carex spp. were made through the water column, submersed veg- (sedges) and deeper water areas containing islands of etation, and surficial sediments in each of four shallow Typha latifolia (broadleaf cattail). The inoculated meso- water habitats. The contents of all 20 sweeps were com- cosms received agricultural soil and water as described bined to form one composite sample from the natural for control mesocosms but were also inoculated with wetland. three vegetation/sediment cores (10 cm diameter 10 Invertebrates were subsampled (one sixth of each sam- cm depth) taken from the wet meadow zone of the rem- ple by volume) and identified to lowest operational taxo- nant natural wetland and embedded into the soil of the nomic unit (Thorp & Covich 1991; Merritt & Cummins mesocosms. Our assumption was that these cores would 1996). Chironomidae were subsampled again (one fifth contain a representation of the natural wetland fauna of chironomids by volume) if there were more than 200 and/or their propagules and would facilitate the estab- chironomid larvae and were identified to tribe. We tested lishment of populations of poorly dispersing non-aerial for differences in the taxonomic composition of inverte- taxa. Stocked inoculated mesocosms received agri- brate communities among treatments with one-way cultural soil, water, and the vegetation/soil cores (as analysis of variance (least-squares means procedure us- described for inoculated mesocosms) but in addition ing SAS [SAS Institute 2000]). Dependent variables in- were stocked with 25 snails added according to their cluded the number of taxa, Simpson’s diversity index, relative abundances in the remnant natural wetland (18 richness and abundance of non-aerial taxa, total inverte- Stagnicola and/or Fossaria, 5 Physa, 2 Helisoma). Snails brate abundance, and abundances of individual taxa. Be- were selected as representative poor dispersers because cause abundance data were not normally distributed, they were the most abundant non-aerial invertebrates densities were log(x 1) transformed before testing. in the natural wetland. Thus, stocked inoculated me- Taxa whose distributions were non-normal after trans- socosms were used to discern whether direct addition formation were tested non-parametrically (Kruskal-Wal- of a poorly dispersing invertebrate would alter commu- lis test). An alpha level of 0.05 was used for all analyses. nity development relative to both unaided recovery (i.e., We used two similarity indices, the percent similarity control mesocosms) and/or relative to mesocosms receiv- index (PSI) and Morisita’s index, to compare the commu- ing an inoculum only (i.e., inoculated mesocosms). nities in each of the mesocosms with the community in The experiment began on 30 May 1995 and continued the natural wetland. Each of the two indices emphasizes until 20 August 1995. Thus, invertebrates were allowed a different aspect of community structure. The PSI com- to naturally colonize all mesocosms for 82 days. Al- pares the relative abundance of taxa shared between two though this duration was probably sufficient to allow communities. Morisita’s index also compares commu- colonization and establishment of most strongly dis- nity structure between two communities, but it is more persing taxa (Williams 1987; de Moor 1992), our study sensitive than the PSI to differences in rare taxa and is did ignore those species having seasonal emergence in relatively insensitive to differences in total abundance the fall or spring. Emergent and wet meadow macro- between samples (Brower et al. 1990). We calculated phytes grew rapidly in all the mesocosms. We did not community similarity between each mesocosm and the quantitatively sample the vegetation in this experiment composite natural wetland sample, resulting in five rep- due to time constraints; however, we could observe no licate measures of similarity for each treatment from qualitative differences in vegetation density or compo- each index. These five replicate measures were com- sition between treatments after only a few weeks. pared among treatments using analysis of variance (fol-
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Table 1. Taxa collected from wetland mesocosms and a nearby natural wetland.
Taxon Control Inoculated Stocked Inoculated p Natural Wetland Gastropoda (snails; total) 18.8 (0–64)a 213.1 (71–514)b 168.8 (75–382)b 0.0012 54 Lymnaeidae Fossaria a 42.0 (0–71)b 7.5(0–30)a 0.022* 15 Stagnicola 0.8 (0–4)a 5.3 (0–19)a 51.0 (15–79)b 0.0002 15 Physidae Physa 18.0 (0–60)a 165.0 (23–424)b 102.0 (4–311)b 0.035 6 Planorbidae Helisoma a 0.8 (0–4)a 8.3 (0–19)b 0.022* 18 Bivalvia (clams) Sphaeriidae 168 Annelidae (segmented worms) Oligochaeta Naididae 98 (0–480) 126.8 (0–555) 13 Hirudinea (leeches) Erpobdellidae 6 Hydracarina (mites) 1.5 (0–8) 1.5 (0–8) 3 Collembola (springtails) 1.5 (0–4) 0.8 (0–4) Ephemeroptera (mayflies) Baetidae 30.2 (0–64) 38.4 (8–90) 48.0 (4–98) 30 Caenidae Caenis 30 Odonata (dragonflies and damselflies; total) 297.0 (97–671)a 64.6 (15–142)b 30.8 (4–45)b 0.0012 18 Aeshnidae 0.8 (0–4) Libellulidae Orthemis 18.0 (0–49) 10.5 (0–23) 0.8 (0–4) 6 Coenagrionidae 279.0 (71–626)a 53.3 (11–124)b 30.0 (15–41)b 0.0022 12 Hemiptera (true bugs; total) 48.8 (19–117)a 7.6 (4–12)b 10.5 (4–22)b 0.003 25 Veliidae 18.8 (0–52.5)a b b 0.032* Corixidae 7.5 (0–11) 2.3 (0–8) 1.5 (0–4) 18 Notonectidae 9.0 (0–26) 1.5 (0–4) 3.0 (0–11) 6 Mesoveliidae Mesovelia 13.5 (4–30) 3.8 (0–11) 6.0 (0–11) 1 Trichoptera (caddisflies) Hydroptilidae 4 Coleoptera (beetles; total) 110.4 (41–187)a 21.3 (18–34)b 18.9 (4–45)b 0.0016 1 Haliplidae Haliplus 78.8 (11–143)a 11.3 (4–26)b 13.5 (4–34)b 0.007 Dytiscidae Hydroporus 1.5 (0–8) 0.8 (0–4) Laccophilus 7.5 (0–19) 5.3 (4–8) 3.0 (0–8) Rhantus 14.3 (0–38) 0.8 (0–4) Unidentified 0.8 (0–4) 1 Hydrophilidae Berosus 3.8 (0–15) 0.8 (0–4) Laccobeus 0.8 (0–4) Tropisternus 1.5 (0–4) 0.8 (0–4) 0.8 (0–4) Unidentified 3 (0–15) 1.5 (0–8) Diptera (flies) Ceratopogonidae (biting midges) 79.6 (15–146)a 0.8 (0–4)b 4.4 (0–11)b 0.0001 2 Chironomidae (midges; total) 2,008.5 (705–3,375)a 45.9 (0–199)b 12.8 (0–30)b 0.0001 27 Tanypodinae 21.8 (0–36)a 0.8 (0–4)b b 0.016* 2 Orthocladiinae 2.4 (0–8) 0.8 (0–4) 18 Chironomini 44.4 (0–84)a b b 0.016* Tanytarsini 1,939.9 (611–3,220)a 44.3 (0–184)b 12.0 (0–26)b 0.0001 3 Culicidae (mosquitoes; total) 11.3 (4–19)a b b 0.001* Anopheles 6.8 (0–19)a b b 0.007* Culicinae 4.5 (0–11) Tabanidae (deer and horse flies) 0.8 (0–4) Isopoda (sowbugs) 6 Total invertebrates 2,702.9 (1,549–4,339) 393.2 (229–638) 424.3 (180–810) 512
Different letters denote significant differences among means at the given p value. Treatment values are means/m2 (range) and wetland values are number per sample. *Kruskal-Wallis test statistic.
lowing arcsine transformation; Sokal & Rohlf 1995). Be- land. Because all mesocosms were sampled identically cause the mesocosms and the natural wetland were and were compared with the same composite sample sampled differently, it is important to note that accurate from the natural wetland, any differences among treat- estimates of similarity were not possible. However, our ments in their relative similarity to the natural wetland interest was in making relative comparisons among the must represent real effects of the treatments, rather than treatments regarding their similarity to the natural wet- differences in sampling methodology.
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Aquatic Invertebrate Recruitment in Wetland Restoration
Figure 1. (A) Richness, (B) diversity, and (C) abundance of macroinvertebrate communities in wetland mesocosms (mean SE). C, control; I, inoculated; S I, stocked inoculated. Different superscripts denote significant differences among means (p 0.01).