This article was downloaded by: [University of York]On: 27 April 2013, At: 23:56Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

OpheliaPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/smar19

COmparison of biomass and percentage cover of sessileepibiota on the Poole Bay Artificial ReefAlison M. Hatcher a ba FAWLEY arl Ltd., Marine Biology Unit, Fawley, Southampton, SO45 1TW, UKb Department of Oceanography, Southampton University, Southampton OceanographyCentre, European Way, Southampton, SO14 3ZH, UKVersion of record first published: 21 Mar 2012.

To cite this article: Alison M. Hatcher (1997): COmparison of biomass and percentage cover of sessile epibiota on the PooleBay Artificial Reef, Ophelia, 47:1, 55-62

To link to this article: http://dx.doi.org/10.1080/00785326.1997.10433390

PLEASE SCROLL DOWN FOR ARTICLE

Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form toanyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses shouldbe independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly inconnection with or arising out of the use of this material.

OPHELIA 47 (1): 55-62 (October 1997)

COMPARISON OF BIOMASS AND PERCENTAGECOVER OF SESSILE EPIBIOTA ON THE POOLE

BAYARTIFICIAL REEF

Alison M. HatcherFAWLEYarl Ltd., Marine Biology Unit, Fawley,Southampton, S045 ITW, UK

&

Department of Oceanography, Southampton University, Southampton Oceanography Centre,European Way,Southampton, S014 3ZH, UK

Correspondence address: Ecology Centre, Sunderland University, Sunderland, SRI 3SD, UK

ABSTRACT

The Poole Bay Artificial Reef (deployed June 1989) was the first artificial reef made of concreteand stabilised coal-waste blocks in the UK. In this study, percentage cover (determined by a labor­atory-based random point method) and biomass (ash-free dry weight) of sessile epibiota on reefblocks were recorded every 5-7 weeks from April to November, in 1990 and 1991.

Biomass, ui, was compared with percentage cover, L, for five categories of sessile epibiota onthe 400 x 200 mm faces of the reef blocks. This resulted in the following regression equations (allp < 0.01): w= 1.70 (arcsin ~L /100)1.91, r2 =0.47 for ascidians; w= 7.94 (arcsin ~L/ 100)2.10, r2

=0.88 for eggs; w = 2.09 (arcsin ~L / 100)3.26, r2 =0.71 for erect organisms; and w =3.02 (arcsin~L / 100)2.65, r2 = 0.60 for sponges. The slopes of these regression lines were not significantly dif­ferent, however, the elevation for the eggs was significantly different to the other elevations. Thusa general relationship could not be derived. A significant regression could not be derived forencrusting organisms (barnacles, tube worms, molluscs and encrusting bryozoans).

INTRODUCTION

Colonisation of sessile epibiota on artificial substrata, in particular artificialreefs, has commonly been documented in terms of percentage cover (seeHatcher, 1993 for review). Only relatively recently have artificial reef studiesreported biomass, and then, usually as wet weight (WW) (for example, Wendtet al. 1989, Foster et al. 1994, Relini et al. 1994, Badalamenti & D'Anna 1995).The use of WW and dry weight (DW) values of epibiotic communities can,however, lead to inaccurate comparisons between studies where one commu­nity has a lower inorganic content than the other.

A few studies have reported biomass as ash-free dry weight (AFDW) (forexample, Leewis & Waardenburg 1991, Hatcher, in press). Although AFDWsare species-specific and can vary, for example, during the reproductive cycle, a

Dow

nloa

ded

by [

Uni

vers

ity o

f Y

ork]

at 2

3:56

27

Apr

il 20

13

56 ALISON M. HATCHER

general relationship between percentage cover and AFDW could be used toestimate AFDW values from existing percentage cover data, especially wherebiomass was not measured (for example, Humphries et al. 1985, Woodhead etal. 1985, Nelson et al. 1994). Comparison of living tissue (as AFDW) betweencommunities may be the most appropriate method for future use, especially asa major goal of artificial reef research is to construct energy budgets in orderto understand how artificial reefs function. .

The aim of this study was to investigate possible relationships between bio­mass (g AFDW) and colonisation (percentage cover), of sessile epibiota onstabilised coal-waste and concrete blocks from the Poole Bay artificial reef(PBAR). Previous studies have reported no significant differences in epibioticcolonisation on either block type from PBAR (Hatcher 1993, Jensen & Collins1995).

Thanks to Mark Davies for criticism of the manuscript. The help of FAWLEY ad Ltd., Frank Els­ton (Skipper) and the SUDO dive team was also appreciated. This work was funded by a dona­tion made to Southampton University by National Power pIc.

METHODS

Eight reef units (2 each, of concrete and 3 different fly ash mixes) weredeployed at a depth of 12 m on the PBAR site in Poole Bay, Dorset(50039'72"N 01°54'79"W) inJune 1989. The PBAR site and reef complex isdescribed in more detail elsewhere (Hatcher 1993, Hatcher, in press). Oneblock (400 x 200 x 200 mm) was randomly selected and removed from the low­er region of each of two artificial reef units, one concrete and one fly ash(30% gravel, 10% cement, 40% pulverised fuel ash, 17.5% gypsum and 2.5%flue-gas desulphurisation sludge), from the Poole Bay artificial reef complex,every 5 to 7 weeks from April to November, in 1990 and 1991 (with the excep­tionof a concrete block in April 1990).

The blocks were placed within mesh bags which retained the whole sessileepibiotic community, and were raised to the surface using lifting bags. Oncelifted, the bagged blocks were placed in plastic boxes and covered with seawa­ter to keep them wet during transportation. These were then stored overnightin seawater with aeration prior to examination in the laboratory.

The epibiotic percentage cover was analysed by first adjusting the water levelin the box to suspend the canopies of the erect species on the uppermost 400x 200 mm face of a block. A 400 x 200 mm Perspex (Plexiglas) sheet, markedwith a grid of 20 x 20 mm squares, was then held 30-50 mm over the block­face. Using a minimum of 108 randomly chosen points out of the 144 intersec­tion points on the grid (75%; confirmed as adequate by chi-squared test;Hatcher 1993), the organisms under each point were identified to species levelwhere possible. Care was also taken not to use points within 20 mm of the

Dow

nloa

ded

by [

Uni

vers

ity o

f Y

ork]

at 2

3:56

27

Apr

il 20

13

EPIBIOTIC BIOMASS AND PERCENTAGE COVER 57

perimeter of a face, to avoid any edge effect which can occur either as a resultof damage to a block, or because of preferential larval settlement at edges(Humphries et al. 1985). In cases where overgrowth had occurred the compe­tition pattern was noted but only secondary cover, i.e. that of the overgrowers,was measured. In the case of the erect organisms, the percentage cover wasmeasured over the canopy of the organism rather than over the area of basalattachment, so as to avoid underestimation of percentage cover for these epi­biota (as was done by the Coal-Waste Artificial Reef Project team, for example,Woodhead et al. 1985).

After percentage cover had been determined and mobile organismsremoved, the sessile epibiota were scraped from the block-face using a house­hold scraper and sorted into categories. The samples were washed with freshwater in a 0.5 mm mesh sieve to remove traces of block material, silt and salt.This procedure was repeated on all block-faces.

Sessile epibiota were separated into five categories: ascidians, eggs, erectorganisms (algae, hydroids and erect bryozoans), encrusting organisms (mol­luscs, barnacles, tube worms and encrusting bryozoans) and sponges. The per­centage cover of each category per block-face was calculated by dividing thenumber of grid points recorded for that category by the total number ofpoints analysed.

The samples of each category on each block-face were dried to a constantweight at 80°C. A homogenised (using pestle and mortar) subsample of eachcategory per block was weighed into a crucible, decalcified overnight by aciddigestion (6% (v/v) HCI), washed in distilled water and re-dried to a constantweight at 80°C. The subsamples were then ashed at 600°C, until a constantweight was achieved.

The methods used in the present study produced some biomass values great­er than zero, with a corresponding percentage cover value of zero. This dem­onstrates the limitations in using a point contact/percentage cover technique,as this type of method relies upon organisms falling under points on a grid:the percentage cover of any organisms which do not lie under a point aretherefore not recorded. Thus, all zero percentage cover values and corre­sponding biomass values were discarded from the regression analyses. All per­centage cover values were greater than zero for the encrusting organisms. Dis­carded values represented 5%, 6%, 11% and 25% of the total data for ascid­ians, erect organisms, eggs and sponges on the 400 x 200 mm block-faces,respectively. On the 200 x 200 mm faces, zero percentage cover values wereonly discarded for 14% and 25% of the eggs and sponge data sets, respectively.

The estimated biomass, w (g AFDW) and the percentage cover, L, (for L >0) for the ascidians, eggs, sponges, erect and encrusting organisms, on eachface, of both the fly ash and concrete PBAR blocks, for all sample dates, werecompared by log-log regression (percentage cover values were first subjectedto a (arcsin --J [L / 100J) transformation, results determined in radians. The

Dow

nloa

ded

by [

Uni

vers

ity o

f Y

ork]

at 2

3:56

27

Apr

il 20

13

58 ALISON M. HATCHER

general format of the regression equations is as follows: log w = m log (arcsin.;,f [L / 100]) + log cor w = c (arcsin :v [L / 100])m.

Analysis of covariance (ANCOVA) was used to establish whether regressionswere statistically homogeneous. Significant differences were further analysedby Tukey test.

Data collected for epibiota on the ends (200 x 200 mm) of the blocks wereonly analysed where a relationship between percentage cover and biomassdata on the 400 x 200 mm block-faces was statistically significant. This wasbecause the sampling regime used on the ends of blocks was different to thatused on the four 400 x 200 mm block-faces as 60 out of 81 points were used todetermine percentage cover on the ends of the blocks. In addition, the area ofthe ends of the blocks, and thus the ratio of basal area of organism to area ofblock-face, was also different to the other block faces.

RESULTS

The double-logarithmic relationships between estimated biomass, w (gAFDW), and percentage cover, L, for the four categories, from the 400 x 200mm block-faces, which showed significant correlations are shown in Fig. 1.Regression data are given in Table 1.

Comparison of the regressions in Table 1 by ANCOVA showed that therewas no significant difference between the slopes of the regressions (F3, III =

2.71, p> 0.05) but that the elevations of the regressions were significantly dif­ferent (F3, 114 = 16.13, P < 0.001). Thus, a standard cross-category relationshipdoes not exist between biomass and percentage cover.

Further analysis by Tukey test (Table 1) showed that there was no significantdifference between the regression elevations for the ascidians, sponges anderect organisms, however, these were significantly different from the regres­sion elevation for the eggs. The relationship between estimated biomass and

Table 1. Summary of regression analyses between biomass (AFDW), w, and percentage cover, L,for four sessile epibiotic categories on the 400 x 200 mm block-faces, which showed a significantrelationship at the p = 0.05 level. All exponents (slopes) are not significantly different (see text).

Tukey test for intercepts (elevations): underlined intercepts are not significantly different.

Category Regression equation n r2 p

Ascidians w = 1.70 (arcsin" [L / 100]) 1.91 53 0.47 < 0.001Eggs W= 7.94 (arcsin "[L/ 100])2.10 8 0.88 < 0.001Erect organisms W= 2.09 (arcsin "[L/ 100])3.26 46 0,71 < 0.001Sponges w = 3.02 (arcsin" [L / 100])2.65 12 0.60 <omTukey test for intercepts

Ascidians Erects Sponges Eggs

0.23 0.32 0.48 0.90

Dow

nloa

ded

by [

Uni

vers

ity o

f Y

ork]

at 2

3:56

27

Apr

il 20

13

EPIBIOTIC BIOMASS AND PERCENTAGE COVER 59

.0.1.0.3.0.5.0.7.0.9

••• ••Ascidians I !a ••• • 1. •. . .... . .... + .. ..1•

1

Q

S -1

~ -2

-3

-4 I I-1.1 I I I I

T" ~o e_e.

~".. ...Q -2

-3

-4 I I I I

-1.1 .0.9 .0.7 -0.5 .0.3 -0.1

l~"'~ • • •S -1

8'-2 ~ •- -3 , •

-4 I I

-1.1 .0.9 .0.7 .0.5 .0.3 .0.1

log (arcsin [L /100)112)

Fig. 1. Double-logarithmic relationships between biomass, w (g AFDW) , and percentage cover, L,for four epibiotic categories on the 400 x 200 mm faces of the reef blocks.

percentage cover for the encrusting organisms on the PBAR was not signifi­cant.

The double-logarithmic relationships between estimated biomass, w (gAFDW), and percentage cover, L, for the two categories, from the 200 x 200mm block-faces, which showed significant correlations are shown in Fig. 2.Regression data are given in Table 2. The relationships between estimated bio­mass and percentage cover for the erect organisms and sponges, on the 200 x200 mm block-faces, were not significant.

Comparison of the significant regressions on the 400 x 200 mm and 200 x200 mm block-faces by ANCOVA (Table 2) for both ascidians and eggs showedthat there were no significant differences between the slopes of the regressions

Dow

nloa

ded

by [

Uni

vers

ity o

f Y

ork]

at 2

3:56

27

Apr

il 20

13

60 ALISON M. HATCHER

-0.1-0.3-0.5-0.7

• •• • I •••• •.-. .. . .'.-•

-0.9

Ascidianso

'" -1OJ

..Q -2

-3

-4 I I I-1.1 I I I

Tw' -",-1 ~ •OJ _

..Q -2

-3

-4 I I I I

-1.1 -0.9 -0.7 -0.5 -0.3 -0.1

log (arcsin [L /1 OOl,n)

Fig. 2. Double-logarithmic relationships between biomass, w (g AFDW) , and percentage cover, L,for two epibiotic categories on the 200 x 200 mm faces of the reef blocks.

(Fl , 82 = 0.10, p> 0.05 for ascidians and Fl , 10 = 1.01, p> 0.05 for eggs). The ele­vations of the regressions, however, were significantly different (Fl , 83 = 13.59,P < 0.001 for ascidians and Fl , 11 = 12.67, P < 0.01 for eggs).

DISCUSSION

A number of problems arose in determining biomass in this study. Many of theorganisms began to decay on removal from the blocks and it was thereforenecessary to prepare them for the oven as quickly as possible. The use of pre­servatives was considered unsuitable as formalin and alcohol have been foundto alter organic content unpredictably (Atkinson & Wacasey 1983). Further­more it was not time-efficient to separate the organisms even into phyla.Wendt et al. (1989) also experienced problems in the separation of bryozoansfrom hydroids and of tube worms from their host organisms. These problemswere overcome in this study by choosing broad, morphologically similar cate­gories.

Table 2. Summary of regression analyses between biomass (AFDW), w, and percentage cover, L,for two sessile epibiotic categories on the 200 x 200 mm block-faces, which showed a significant

relationship at the p = 0.05 level.

Category Regression equation n r 2 p

AscidiansEggs

w= 0.83 (arcsin"; [L / 100])2.06w = 4.79 (arcsin"; [L / 100])2.57

336

0.470.92

< 0.001< O.oI

Dow

nloa

ded

by [

Uni

vers

ity o

f Y

ork]

at 2

3:56

27

Apr

il 20

13

EPIBIOTIC BIOMASS AND PERCENTAGE COVER 61

Biomass, when measured as AFDW indicates the amount of living tissuepresent in a community. Percentage cover estimates, however, are theoreticallymade only on living organisms although difficulties can arise in determiningwhether some organisms are alive, for example, serpulids and barnacles.There is a weakness in the data set which resulted from the discarding of bio­mass values, where percentage cover estimates were equal to zero. This had amuch greater effect on the smaller data sets, eggs and sponges, than on thelarger data sets, ascidians, erect organisms and encrusting organisms.

Given isometry, the relationship between biomass, w, and the square-root ofpercentage cover, ."j L, is a cubic function of growth, w = c xb (where x is theaxial length of cover which approximates to ."j L, c is a constant and b is thecoefficient of growth which equals three). In the present study, the relation­ship between biomass and percentage cover varied between categories, suchthat the growth coefficient ranged from 1.91 to 3.26. These empirically­derived values were not statistically compared with the theoretical value, as thiswould involve comparing a coefficient with variance to one of zero variance.The resulting growth coefficients for the ascidians and the erect organisms, ofabout 2 and 3, respectively, may be explained in terms of the morphology ofthe categories. Most of the ascidians found on PBAR during this study wereessentially two-dimensional, i.e. had little depth, whereas many of the erectorganisms were arborescent species, the canopies of which were more three­dimensional.

The similarity of the relationships between biomass and percentage cover,on the 400 x 200 mm block-faces, for ascidians, sponges and erect organismssuggests that these categories could be consolidated into one category infuture studies. However, analysis of the data from the 200 x 200 mm ends ofthe blocks only supported the relationships observed for ascidians and eggs.Without further investigation, it would therefore be unwise to consolidate theascidians, sponges and erect organisms into one category. It would be pru­dent, however, to re-assess this relationship once a larger data set has beenobtained for the sponges.

By contrast, no correlation was evident between biomass and percentagecover for the encrusting organisms, as the pattern associated with these organ­isms in the community was more complex. Initially, there was a large percent­age cover of barnacles and serpulids which had a relatively high biomass,whilst with time, the number of these organisms declined, both as a result ofhaving a relatively short life-span (1-1.5 years) and of being good recruits tofresh substrata but poor competitors (Butler 1991). The encrusting organismswere later dominated by bryozoans, which had a large percentage cover with arelatively low biomass, compared with the earlier species assemblage.

Owing to the limitations of the percentage cover determination method it ispossible that small organisms, such as barnacles and hydroids, may have beenunder-represented if they were hidden under the canopies of larger erect

Dow

nloa

ded

by [

Uni

vers

ity o

f Y

ork]

at 2

3:56

27

Apr

il 20

13

62 ALISON M. HATCHER

organisms. It is probably better to record colonisation of a community as totalcover, which may be greater than 100%, as the percentage cover of every ses­sile epibiotic organism should be measured regardless of whether it occupiesprimary or secondary space.

The present study has produced a series of regression equations for the esti­mation of biomass (g AFDW) from percentage cover data for the categories,ascidians, eggs, sponges and erect organisms on the PBAR. Whether theseapply to other sublittoral, hard substrate, epibiotic communities has yet to bedetermined. If a series of similar relationships could be formulated for all epi­biotic categories in all major biogeographic areas, then the wealth of existingepibiotic percentage cover data could be used to estimate the biomass, andultimately energy flow of these communities. This would then aid our under­standing of the functioning of artificial reefs.

REFERENCES

Atkinson, E. G. &]. W. Wacasey, 1983. Caloric equivalents for benthic marine organisms from theCanadian Arctic. - Can. Tech. Rep. Fish. Aquatic Sci. 1216, 32pp.

Badalamenti, F. & G. D'Anna, 1995. Esperienze di barriere artificiali nel Golfo di Castellammare(Sicilia Nord-Occidentale). - BioI. Mar. Medit. 2:165-173.

Butler, A. J., 1991. Effect of patch size on communities of sessile invertebrates in Gulf St Vincent,South Australia. - ]. Exp. Mar. BioI. Ecol. 153:255-280.

Foster, K L., F. W. Steimle, W. C. Muir, R. K. Kropp & B. E. Conlin, 1994. Mitigation potential ofhabitat replacement: concrete artificial reef in Delaware Bay - preliminary results. - Bull. Mar.Sci. 55:783-795.

Hatcher, A. M., 1993. Epifaunal development on an artificial reef. - Ph. D. Thesis, SouthamptonUniversity, 263pp.

Hatcher, A. M., in press. Sessile epibiotic biomass on stabilised coal-waste and concrete artificialreefs. - In L. E Hawkins, S. Hutchinson, A. C. Jensen, M. Sheader &]. A. Williams (eds): Theresponses of marine organisms to their environments (Proceedings of the 30th EuropeanMarine Biology Symposium). University of Southampton Press.

Humphries, E.M., I. W. Duedall & S.]. Jordan, 1985. Coal-waste blocks as a fouling substrate inestuarine water.·- In I. W. Duedall, D. R. Kester, P. K. Park & B. H. Ketchum (eds): Wastes inthe ocean. Vol. 4. Energy wastes in the ocean, pp.613-649.John Wiley & Sons, New York.

Jensen, A. C. & K]. Collins, 1995. The Poole Bay artificial reef project 1989 to 1994. - BioI. Mar.Medit. 2:111-122.

Leewis, R.]. & H. W. Waardenburg, 1991. Environmental impact of ship wrecks in the North Sea.I. Positive effects: epifauna of North Sea ship wrecks. - Wat. Sci. Tech. 24:297-298.

Nelson, W. G., D. M. Savercool, T. E. Neth &]. R. Rodda, 1994. A comparison of the fouling com­munity development on stabilized oil-ash and concrete reefs. - Bull. Mar. Sci. 55:1303-1315.

Relini, G., N. Zamboni, F. Tixi & G. Torchia, 1994. Patterns of sessile macrobenthos communitydevelopment on an artificial reef in the Gulf of Genoa (Northwestern Mediterranean). - Bull.Mar. Sci. 55:745-771.

Wendt, P. H., D. M. Knott & R. F. Van Dolah, 1989. Community structure of the sessile biota onfive artificial reefs of different ages. - Bull. Mar. Sci. 44:1106-1122.

Woodhead, P. M.].,]. H. Parker, H. R. Carleton & I. W. Duedall, 1985. Coal Waste Artificial ReefProgram, Phase 4B. - Electric Power & Research Institute, Palo Alto, CA., 272 pp.

Dow

nloa

ded

by [

Uni

vers

ity o

f Y

ork]

at 2

3:56

27

Apr

il 20

13