Mesh-Size Matters in Epibenthic Surveys

J. Mar. Biol. Ass. U. K. 12002), 82,1^8 Printed in the United Kingdom Mesh-size matters in epibenthic surveys Ruth Callaway*P, Simon JenningsP, John Lancaster* and John CotterO *University ofWales Swansea, School ofBiological Sciences, Singleton Park, Swansea, Wales, SA2 8PP. OCentre for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Lowestoft, Norfolk, NR33 0HT. PCorresponding author 1ne¨ eR.Zu« hlke): e-mail: [email protected] This study aimed to identify the e¡ects of di¡erent sieve mesh-sizes on processing time, the number of species retained, diversity measures and multivariate community analysis in the North Sea. Samples were collected at 63 sites throughout the North Sea and washed through two successive sieves, 10-mm and 5-mm mesh respectively. Processing time for whole samples 15- and 10-mm fraction) averaged 91 Æ25 min compared with 55 Æ16 min for the 10-mm mesh fraction. Altogether 40% of free-living species and 9% of attached species were recorded exclusively in the 5-mm fraction. The majority of these species were rare. Spatial gradients of species diversity and community structure were identical, independent ofthe mesh-size used. Multivariate community analysis showed no signi¢cant di¡erence between descriptions ofcommunity structure based on fauna from 10-mm or 5-mm mesh. The use ofcoarser sieving mesh would save time and money, ifthe aims ofan epibenthic survey were to describe broad patterns ofcommunity structure and relative diversity. It would be possible to process approximately 50% more samples, ifthe time saved with 10-mm mesh were allocated to additional sampling. However, ifinformation on single species is required, then sorting with the ¢ner sieve mesh will yield crucial information. It was decided to employ a 5-mm mesh for epibenthic monitoring of the North Sea. INTRODUCTION or temporal replication. The aspiration to use ¢nancial resources and time as productively as possible initiated Currently ¢ve European countries 1Germany, England, research on e¡ects ofmesh-size on infauna studies 1Reish, Norway, the Netherlands and Denmark) contribute to an 1959; Rees, 1984; Bachelet, 1990; James et al., 1995; epibenthic monitoring programme in the North Sea Schlacher & Wooldridge, 1996). Most studies assessed 1Jennings et al., 1999; Zu« hlke et al., 2001). The aim is to 1-mm and 0.5-mm mesh while Schlacher & Wooldridge describe spatial diversity patterns based on univariate and 11996) and Reish 11959) evaluated e¡ects ofeven smaller multivariate data analysis, to analyse the distribution of sizes. individual species and to provide a baseline study for Although studies ofepibenthic invertebrates were future analysis oftemporal changes ofthese patterns. Two among the ¢rst faunal investigations in the North Sea hundred and forty-one stations in 143 ICES rectangles 1e.g. Peterson, 1914; Peterson, 1918), sampling methods 1International Council for the Exploration of the Sea, have not been widely standardized 1Dyer et al., 1983; boxes 0.58 latitudeÂ18 longitude) were sampled in 1999. Reise & Bartsch, 1990; Basford & Ra¡aelli, 1990; Clearly, on such a large, multi-participant survey, a stand- Bergmann & Hup, 1992). Beside the variation in sampling ardized sampling protocol that speeds sample processing equipment 1dredges and several di¡erent types oftrawls), without losing the required biological information can processing ofsamples di¡ered considerably between the provide crucial cost and time savings. Such a concern studies. Some samples were not sieved 1Basford et al., prompted the research described in this paper. 1989; Hosten, 2000), while others were sieved with Studies ofthe distribution and diversity ofmarine meshes from 5-mm 1Rees et al., 1999) to 14-mm benthic invertebrates generally require that samples are 1Frauenheim et al., 1989). collected and sieved through mesh screens. The choice of The aims ofthis study were to determine how 10-mm mesh-size depends on the objectives ofa study, the compo- mesh, in comparison to 5-mm mesh, a¡ects: 1i) the time nent of fauna investigated 1meiofauna, macrofauna), the required to sort and identify epibenthic invertebrate coarseness ofthe sediment and the importance of samples; 1ii) the range ofspecies sampled; and 1iii) esti- collecting juveniles or smaller species. Finer meshes will mations ofspecies diversity and community structure. retain a larger number ofindividuals and species, providing more complete information of the community and populations. However, they will increase the time MATERIALS AND METHODS and cost ofprocessing 1Rees, 1984; Schlacher & Sampling Wooldridge, 1996). Larger meshes should allow more samples to be processed per unit time, which releases time Epibenthic invertebrates were sampled at 63 stations and ¢nancial resources that can be used to increase spatial throughout the North Sea 1528N^618N) from August to Journal of the Marine Biological Association of the United Kingdom 2002) 2 R. Callaway et al. Mesh-size matters in epibenthic surveys Table 1. Time needed to sort and identify samples sieved September 1996. At each station one sample was collected through two hierarchically ordered mesh sizes 10- and 5-mm). with a 2-m-beam trawl, equipped with a 2-mm mesh liner. Times are given as mean minutes ÆSE, N63. The precise locations ofstations and the beam trawl design were described in Jennings et al. 11999). 10-mm 5-mm Total sample Each catch was sieved through two successive metal fraction fraction 15- and 10-mm) sieves, the ¢rst with 10-mm square mesh, the second with 5-mm mesh 1internal measurement). The material Free-living fauna 34 Æ724Æ956Æ15 retained on each sieve, referred to as 5-mm and 10-mm Attached fauna 20 Æ10 3 Æ425Æ13 fractions respectively, was treated separately. All Total fauna 55 Æ16 32 Æ12 91 Æ25 epibenthic species were sorted from the retained material Table 2. Species unique to 5-mm fraction. Ubiquity indicates the number of sites a species was found. Abundance is the total number of individuals found throughout the study. For attached species abundance was not recorded. Ubiquity Abundance Attached species Hydrozoa Obelia longissima 1Pallas, 1766) 1 ^ Halecium baenii 1Johnston, 1838) 1 ^ Amphisbetia operculata 1Linnaeus, 1758) 1 ^ Diphasia pinaster Hincks, 1861 1 ^ Bryozoa Amphiblestrum auritum 1Hincks, 1877) 1 ^ Amphiblestrum £emingii 1Busk, 1854) 1 ^ Palmiskenea lorea 1Alder, 1864) 1 ^ Hexacorallia Caryophyllia smithii var. clavus Stokes & Broderip, 1828 2 ^ Free-living species Polychaeta Laetmonice ¢licornis Kinberg, 1855 1 1 Gattyana cirrosa 1Pallas, 1766) 1 1 Lepidonotus squamata 1Linnaeus, 1758) 1 1 Amphipoda Lophogaster typicus M. Sars, 1857 1 3 Epimeria cornigera 1Fabricius, 1779) 2 2 Tmetonyx cicada 1Fabricius, 1779) 3 7 Ampelisca macrocephala Liljeborg, 1852 2 8 Ampelisca spinipes Boeck, 1861 2 2 Maera loveni 1Brucellius, 1859) 1 1 Melita dentata 1KrÖyer, 1842) 2 3 Isopoda Rocinela damnoniensis Leach, 1815 1 1 Astacilla longicornis 1Sowerby, 1806) 2 2 Decapoda Pandalina brevirostris 1Rathke, 1837) 3 3 Philoceras bispinosus 1Hailstone, 1835) 2 5 Philoceras echinulatus 1M. Sars, 1861) 1 1 Philoceras trispinosus 1Hailstone, 1835) 2 15 Philoceras sculptus 1Bell, 1847) 1 1 Anapagurus chiroacanthus 1Liljeborg, 1856) 1 2 Anapagurus hyndmanni 1Bell, 1845) 2 2 Munida rugosa 1Fabricius, 1775) 1 1 Ebalia cranchii Leach, 1817 7 12 Gastropoda Emarginula ¢ssura 1Linnaeus, 1758) 1 1 Trivia arctica 1Pulteney, 1799) 1 1 Velutina velutina 1O.F. Mu« ller, 1776) 4 4 Polinices pulchellus 1Risso, 1826) 1 1 Polinices fuscus 1de Blainville, 1825) 2 5 Polinices montagui 1Forbes, 1838) 1 1 Opisthobranchia Archidoris pseudoargus 1Rapp, 1827) 1 1 Aeolidia papillosa 1Linnaeus, 1761) 1 1 Bivalvia Nucula nitidosa Winckworth, 1930 4 28 Palliolum tigerinum 1O.F. Mu« ller, 1776) 1 1 Palliolum striatum 1O.F. Mu« ller, 1776) 1 1 Turtonia minuta 1Fabricius, 1780) 1 1 Corbula gibba 1Olivi, 1792) 3 56 Cuspidaria cuspidata 1Olivi, 1792) 1 3 Cephalopoda Sepiola atlantica Orbigny, 1840 5 7 Rossia macrosoma 1delle Chiaje, 1830) 1 1 Ophiuroidae Amphiura brachiata 1Montagu, 1804) 1 1 Amphiura chiajei Forbes, 1845 2 21 Amphiura ¢liformis 1O.F. Mu« ller 1776) 1 1 Holothuriidae Leptopentacta elongata 1Dueben & Koren, 1844) 1 2 Ocnus lacteus 1Forbes & Goodsir, 1839) 1 1 Pseudothyone raphanus 1Dueben & Koren, 1845) 1 1 Journal of the Marine Biological Association of the United Kingdom 2002) Mesh-size matters in epibenthic surveys R. Callaway et al. 3 onboard. The majority ofspecies were identi¢ed un- samples. Time to remove formalin and wash the sample preserved, but some were kept in 4% formalin for sub- was not included. sequent identi¢cation in the laboratory. Species were classi¢ed as `free-living' or `attached', the latter being recorded as present/absent only. Lists ofspecies assigned Diversity indices to free-living and attached categories are given in Jennings Diversity offree-living epibenthos was measured using et al. 11999).Todetermine species composition and abund- the Hill's indices N0 and N1 1Hill, 1973), where ance for 5-mm mesh, data for the 5-mm and the 10-mm N0number ofspecies 1species richness) and N1 exp fractions were combined. 1H), where H is Shannon^Wiener diversity. Hill's N0 is the total number ofspecies in a sample, while N1 incorpo- Sorting and identi¢cation time rates individual abundance. Analysis ofvariance The time required to sort and identify free-living and 1ANOVA) was applied to test for signi¢cant di¡erences attached species in each fraction was recorded for all between latitudes. Table 3. Presence

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