PRD 00/01-07

Monitoring macroalgae: different pictures from different methods

1 2 2 M.W. Miller , RB. Aronson , T.J.T.Murdoch

1) NOAA-Fisheries, Southeast Science Center, 75 Virginia Beach Dr., Miami FL, 33149 USA phone: 305-361-4561, FAX: 305-361-4562, emai1: margaret.w.miller(2linoaa.gov

2) Dauphjn Island Sea Lab, 101 Bienville Blvd., Dauphin Island, AL 36528 USA; and Department of Marine Sciences, University of South Alabama, Mobile, AL 36688 USA

Running Head: Monitoring reef macroalgae

Keywords: macro algae, monitoring, video, biomass ABSTRACT

Despite the low coral abundance and high macroalgal abundance on many coral reefs worldwide, coral reef monitoring programs often focus narrowly on hard . As part ofa benthic monitoring program to assess the effects of no-take marine reserves in the Florida Keys

National Marine Sanctuary, we comptired two measures of macroalgal abundance: percent cover estimated from video trunsects and biomass estimated from harvested quadrats. The overall patterns of macroalgal abundance were sirnilar between the two methods, but the species-specific resolution of assemblage structure was much greater in the biomass sampling. Neither method provided adequate estimates of cristose nor algal turf abundance. Considering the present emphasis Gn improving and coordinating coral reef monitoring on both national and global scales, we advocate inclusion and standardization of the estimation and reporting of reef macroalgal abundance.

2 INTRODUC'nON

Monitoring is receiving increased emphasis as a means to improve the information on status and trends required for adaptive management and conservation of coral reefs. Examples include the activities of the US Coral Reef Task Force (USCRTF 2000, hLtp://coralreefgov/WG-reg2rts.htrni) and the 1999 International Conference on Scientific

Aspects of Coral Reef Monitoring, Assessment, and Restoration

(h4p://www.nova.edu/ocean/ncri/conf99. . While it is well-recognized. that proliferation of macroaigae is one of the major results of reef degradation (Ginsburg 1994, Wilkinson 2000), coral reef monitoring methods and ieporting almost always focus on corals. IvIacroalgae are counted incidentally andiumped, often into a single category xmiled "algae". Such lumping obscures important fimetional groupings (Steneck and Diether 1994) that could elucidate reef status and fimiction. As part of the benthic monitoring program of the no-take zones in the Florida Keys

National Marine Sanctuary (FKNMS), we compared results of a standard reef monitoring method

(video taping transects) with a macroalgal-focased method (harvesting and quant&f* biomass) to =mine the differences in macroalgal abundance and assemblage composition measured by the two methods.

METHODS

SWdy sites - Permanent sites were established in selected no-take zones and at nearby reference sites in October 1997. Study sites were established on six reefs within two depth ranges, 7.5-10.5 rn (25-35 ft) and 13.5-17.4 m (45-58 ft). Table I lists the sites and their characteristics. The sites were permanently marked and their DGPS coordinates were recorded.

3 Video transects - At each of the six fiked sites, ten haphazardly located transects were videotaped during May 1998 and again in May 1999. Each transect consisted of a 25 in x 0.4 in area. A reference arm was mounted on the camera housing to maintain a constant distance between the video camera and the substrate to standardize the size of the field of view at 0.4 ra width.

The video transects were analyzed according to welt-established protocols (Aronson et al.

1994; Aronson and Swanson 1997). Automated procedures were developed for video fi-ame capture using digital video equipment and commercially available hardware and software. Each transect was characterized with 50 non-overlapping frames. The captured images were analyzed using point-counting procedures (10 points per frame), and the frames and data were archived on

CD-ROK Quality assurance/quality control procedures were instituted, consisting of multiple, trained individuals doing the same point counts. These QA/QC assessments indicated that the , data are of high quality, with <1% error in the assignment of points to the following algal genera identifiable from the video: Dictywa, Lobophora, Stypopodium, Halimeda, Sargassum, and a category of "other macroalgae".

Macroalgal biomass - To quantify macroalgal biomass, a 40 x 40 cm quadrat was placed at random intervals along 25-m transects videotaped at the same time in Afay 1998. In 1999, the biomass samples were collected in June, approximately I mo following the video transect sampling. The quadrats were placed systematically around the permanent marker buoy at each site, at intervals of 5 fin-kicks along a long-shore heading. The 40-cm size of the quadrat was chosen to match the 40-cm path of the vkleo sample. All of the seaweed biomass that one could

4 grasp, pluck, and deliver into a sealed plastic bag in a 5-min span was harvested from each

quadrat. Back on the boat, each plastic bag was careffilly drained. The samples were placed in

larger, labeled plastic bags and frozen for storage.

In the laboratory, each quadrat sample was thawed, placed in a sieve and rinsed with tap

water to remove sediment, and then rinsed from the sieve into a sorting tray. Samples were

sorted to genus into pre-weighed aluminum weighing dishes, dried for at least 24 hr at 65-700C,

and weighed.

Data Apaiysis - Analysis of Ilariance (or non-parametric Y^ruskal-Wallis ANOVA, incasesof

violation of theassumptions of parametric statistics) was used io test for significant variation

among sites, as coral reef monitoring programs are often designed to do. Separate ANOVAs

were performed for each parameter, macroaigal cover and macroalgal biomass, for each year, and

for the deep and shallow depth strata. Significant parametric (or Kruskal-Wallis) ANOVAs were

followed by Tukey's (or Dunn's) aposteriori pairwise comparisons.

RESULTS

Macroalgal Abundance - In most cases, the pattern of relative macroalgal abundance among sites was similar when assessed as either cover or bio s (Fig. 1). For example, the deep sites in

1999 showed high macroalgal abundance at South Carydort and at Pelican Shoal and low abundance at the other sites, whether abundance was determined by video sampling for percent cover or by harvesting for bioma s (Fig 1). Although all 12 ANOVAs indicated sigifficant variation among sites, there were no consistent differences in macroalgal abundance between the

5 no-take reserves and the reference sites.

Macmalgal Cominunity Structure - While the video and biomass sampling methods showed consistent patterns in total macroalgal abundance, they provided sharply contrasting characterizations ofmacroalgal assemblage structure. The video transect sampling showed that the sampled reefs were strongly dominated by Dictyota spp. Almost half the video samples (I I out of 24 depth/year/site combinations) showed over 501/o of benthic cover to be Dictyota. All the video samples indicated that Diclyota comprised more than 78% of the macroalgal assemblage, and for most samples it was over 90% (Fig. 2). Four other macroalgal genera were disc2mable in the video sampling, but these included no red algal genera.

The biomass sampling yielded a more balanced picture of the macroalgal assemblage. The green calcareous Halimeda spp. were strongly represented at levels up to -40% of the macroalgal biomass. Numerous other genera were well-represented in the biomass sampling (Table 2) and represented up to 871/o of the macroaigae in a given sample (Fig. 2, PS Shallow 1999). Twenty- four genera were identified in the biomass sampling.

DISCUSSION

While video sampling and harvested biom s sampling yielded smi pictures of overall macroalgal abundance, there were sharp differences in the representation of macroalgal diversity and assemblage structure. The recommended method depends on the particular question one is trying to answer. In most coral reef monitoring programs, the primary questions are: 1) what is the status or "healff'of the monitored coral reef? and 2) is it changing over time? While patterns can be discerned in monitoring studies, questions of causation can be only partially answered.

6 Although the proliferation of macroalgal standing stock is widely recognized as a

manifestation of coral reef decline, the fact is that most major regional coral reef benthic

monitoring programs report solely on hard coral abundance (e.g., Haw*

htti2:/Icr=.wcc.hawaii.edu/Overview/ or Brown et al. 1999; Great Barrier Ree^ Australia,

httv..-//www.airns 9ov.au/i3aLres/research/reef-monito reef-monitorin a-index. or

Sweatman. 1999; the , Loya et al. 1999). In some cases, extensive effort has been

expended to devise a robust, powerfW, and reasonably priced sampling scheme for corals (e.g.,

Brown et al 1999). However, no mention is made of any analysis nor results fi)r macroalgae

despite often explicit intent to detect ^-.hanges related to impoi tant reef threats ^acluding invasive

algal species and algal outbreaksp.wcc.ha,,vaii.edu/Overviel,v/3. (e.g., ho://crarn P ethodsl). V

Many of these large-scale, integrated monitoring programs utilize video transect sampling. It

would appear that resource limitation simply precludes the extraction and/or reporting of

macroalgal data.

Biomass harvesting, while destructive, yields much better taxonomic resolution than video

sampling and can provide insights into the fimction of reef ecosystems. There is ongoing

controversy in the literature regarding the relative importance of top-down and bottom-up control

of macroalgal abundance on coral reefs (Hughes 1994, Lapointe 1997, Miller et al. 1999, Hughes

et al. 1999). The generic-level resolution of macroalgal composition, which does not require

excessive taxonomic effort, can suggest causal factors for spatial variation and temporal trends.

For example, in the current study, the biomass data suggest spatial patterns in the relative palatability of macroalgal communities to herbivores. Many of the red algal genera are relatively palatable (Paul and Hay 1986), and the biomass data show them to be at relatively low abundance at and Middle Sarnbo and high abundance at South Carysfort and Pelican Shoal

("other" algae in Fig. 2). This pattern may indicate variation in relative herbivory pressure and it certainly indicates that further investigation of spatial variation in herbivory processes is wan-anted. Such information is not available from the video transect data. Also, measurements of algal biomass in conjunction with assessments of tissue nutrient content allow determination of nutrient status and nutrient standing stocks in different reef areas.

Neither of the methods evaluated here adequately assessed the abundance and distribution of crustose coralline algae (CCA) or of algal turfs. Both of these functional groupings provide insights into reef status. they both indicate highly grazed substrates (Aronson and Prect 2000) and

CCA's supply chemical inducers that enhauce, coral settlement and metamorphosis (Mo rr et al.

1994). Direct, in-water observation is required to get accurate data regarding these groups.

In conclusion, we urge that greater emphasis be placed on quantifying and reporting macroalgal abundance, whatever monitoring method is used. Given the current low abundance of live coral on many reefs, the narrow focus on monitoring hard corals is not acceptable.

Moreover, the range of fimetional forms which can fit under the single label of "algae" (e.g. frondose macroalgae, algal turfs, CCA) renders the reporting of "algar' abundance per se ahnost meaningless. Reporting of macroalgal abundance, perhaps even specified as broad categories such as Halimeda spp, Diclyota spp, other frondose algae, etc. is feasible from standard monitoring methods and will provide valuable information for reef management.

ACKNOWLEDGEMENTS

This work was conducted with funding and logistical support from the Florida Keys

8 National Nhu-ine Sanctuary and the National Undersea Research Center ofthe University of North

Carolina - Wilmington under permit 4 FIQ^TMS-263-97. S. R Smith, 1. Baums, J. Barimo, M.k

Dardeau, L.Kellogg, and K.D. Kirsch assisted with field work- A- Medri, E. Goh, J. Barimo, and

A. Bourque assisted in sample and data processing. This is Contrihution # 30M from the

Dauphin Island Sea Lab.

9 LITERATURE CITED

Aronson, R. B., P. J. Edmunds, W. F. Precht, D. W. Swanson and D. R. Levitan. 1994. Large-

scale, long-term monitoring of coral reefs: simple, quick, inexpensive methods.

Atoll Res. Bull. 421:1-19.

Aronson, R. B. and W. F. Precht. 2000. Herbivory and algal dynamics on the coral reef at

Discovery Bay, Jamaica. Limnol. Oceanogr. 45:251-255.

Aronson, R. B. and D. W. Swanson. 1997. Video surveys of coral reefs: uni- and multivariate

applications. Proc. 8th Int. Coral Reef Symp. 2:1441-1446.

Brolmi, E.,_'E. F. Cox, 3. Tissot, K. Rodgers, and W. Smith. 1999. Evaluation of benthic sampling

methods considered for the coral reef assessment and monitoring program (CRAMP) in

Hawaii. Int. Conf. Scientific Aspects of Coral Reef Assessment, Monitoring, and

Restoration, National Coral Reef institute, Nova Southeastern University, Ft. Lauderdale,

FL, p. 61.

Ginsburg, R. N. (Compiler) 1994. Proceedings of the Colloquium. on Global Aspects of Coral

F,eef Health, Hazards, and History, 1993. Rosenstiel School of Marine and Atmospheric

Sciences, Univ. of MiamL Miami FL. 420 p.

Hughes, T. P. 1994. Catastrophes, phase shifts, and large-scale degradation of a Caribbean coral

reef. Science 265:1547-1551.

Hughes, T. P., A. M. Szrrm , R. Steneck, R. Carpenter, S. T^Iiller. 1999. Algal blooms on coral

reefs: what are the causes? Limnol. Oceanogr. 44:1583-1586.

Lapointe, B. E. 1997. Nutrient thresholds for bottom-up control of macroalgal blooms on coral

reefs in Jamaica and southeast Florida. Limnol. Oceanogr. 42:1119-113 1.

10 Loya, Y., S. M. Al-Moghrabi^ A Ilan, and M. P. Crosby. 1999. The Red Sea Marine Peace Park

coral reef benthic communities: ecology and biology monitoring program. Pages239-250

in iviaragos, J. E., and R. Grober-Dunsmore (Eds.), Proc. Hawaii Coral Reef Monitoring

Workshop, Honolulu, Hawaii..

Miller, A W., A E. Hay, S. L. Miller, D. Malone, E. Sotka, and A- A Szmant. 1999. A new

method for manipulating nutrients on coral reefs: effects of nutrients vs. herbivory on reef

algae. Limnol. Oceanogr. 44:1847-1861

Morse, D. E., A- N. C. Morse, P. T. Rairnondi, and N. Hooker. 1994. Morphogen-based chemical

flypaper for AgaHcia humilis coral ianae. Biol. Bull. 186: 172- 181

Paui, V. J., and M.. E. Hay. 1986. Seaweed susceptibility to lierbivory: chemical ^md

morphologicla correlates. Mar. Ecol. Prog. Ser. 33:255-264.

Steneck, R. S., and 1VL N. Dethier. 1994. A functional group approach to the structure of algal-

dominated communities. Oikos 69:476-498.

Sweatman, H. 1999. The Australian Institute of Marine Science's coral reef monitoring porgrams

on the Grew Barrier Reef. Pages 225-238 in Maragos, J. E., and R. Grober-Dunsmore

(Eds.), Proc. Hawaii Coral Reef Monitoring Workshop, Honolulu, Hawaii.

Wilkinson, C. (Ed.) 2000. Status of coral reefs of the world:2000. Australian Institute of Marine

Science, Cape Ferguson and Dampier. 363 p.

I I Table 1: Site ^haraeteristics for the Florida Keys National Marine Sanctuary No-Take Zones monitoring program Shallow sites were at a depth range of7.5-10.5 m and Deep sites ranged from 13.5-17.4 in Reference sites were chosen to be similar reef areas adjacent to each no-take zone. Diving activity at each site was inferred from the presence of recreational mooring buoys and the regulations for Research Only areas which prevent entry without a permit. The first pair of sites is located in the northern region of the FIC,4MS; the remaining four sites are in the southwest area, offshore from Key West.

Reef Site Coordinates Fishing Diving South Carystbrt (SC) Shallow 25'12.536'N; 80'13,126^W No Yes No-Take Zone Deep (buoys) 25'12.208'N; 80'11856'W Maitland (Ma) Shallow 25'1 1.784'N; 80013.594'W Yes No Reference Site Deep 25-11.614'N; 80013.324'W (no buoys) Western Sambo, (WS) Shallow 24'28.780'N; 8 1'42.799'W No Yes NO-Take Zone Deep 24'28.655N; 81'42.812'W (buoys) Middle Sambo (MS) Shallow 2429.263'N; 81'40.489'W Yes No Reference Site Deep 2429.134'N; 81'40.414'W (no buoys) Eastern Sambo (ES) Shallow 24029.519'N; 81039.575'W No* No (regs.) Research-Only (no-take) Deep 2429,.387'N; 81*39.597'W Pelican Shoal (PS) Shallow 24'29.954'N; 81'37.739'W Yes Yes Reference Site (buoys) Deep 2429.851'N; 81'37.651'W _J *ES Deep is just outside the Eastern Sambo Research-Only Area, which ends at 12-13 m depth.

12 Table 2: Macroalgal genera represented in the video and biomass sampling of macroalgae on

Florida Keys Reefs. The lesser taxonomic resolution of the video method overlooks anY representation by Rhodophyta.

Genus Video Biomass

Haluneda x x Acetabularia x 0 Udotea x Valonia x Rhipocephalus x Chladophora x COO Dietyota x x Lobophora X x Slypopodiwn x x Sargusswn x Galaxaura x Hypnea x Amphiroa x Gelidiella x Choni*ia x Bryothamnion x Laurencia x Halymenia x Bo"ocWia x Gracilaria x Sppldia x Champia x WngMella x Gelidium x syphonja x

13 FIGURE LEGEI'^TDS:

Fig. 1. Total -macroalgal abundance as derived from video transect sampling (percent cover) and harvested biomass sampling conducted in May1998 and May-Ame 1999. P-values from one-way

ANOVA (parametric or Kruskal-Wallace). Bars within one series with the same letter do not differ significantly (Tukey's or Dunn's post-hoc pairwise comparisons). Site codes inside a box represent no-take zones. SC=South Carysfort, MA=Makland, WS=Westem Sambo, MS=Afiddle

Sambo, ES=Eastern Sambo, PS=Pelican Shoal.

Fig.2. Macruaigal assemblage Qomposition as discQrned from video (percent cover) and biomass sawplimg. Site codes as in Figure 1.

14 Biomass p=0.029 90 I 35 90 35 Cover p<0.001 Biomass P<0.001 go I SHALLOW'98 DEEP'98 C= Cover 30 so 'clic p<0.001 30 70 1 -T 70 - 25 60 25 60 ^ -T- T 50 - 20 50 20

40 - 15 40 T T 15 T 30 30 ^ 10 10 20 20 5 '10 10 -A- M^LEE 0 Ic I 0 0 CS 90 - Biomassp=O.Oj2 35 090 35 0 SHALLOW'99 v-;= Biomass p<0.001 80 - Cover P<0.001 80 DEEP'99 i Cover p--0.001 30 300 70 - 0 70 PQ 25 60 - 25 >^ 20 60 5 50 - a) 50 20 40 15 40 15 -30 - 10 30 to 20 20 5 -10 V 10 5 113C 0 - Q2 j 0 0 ^m I 0 Fg-cl MA Pws- MS ES] VS Kc:l MA Fw--Sl MS ES PS C==::J Other macroalgae 0:0:::0::0 Halimeda spp. c:::z::::z::J Dictyota spp.

80 j SILt\LLOW, May 98 SHALLOW, May 98 70 IT/'l _ ~ I 25 I 60 j 20 50 I r/ 40 rg~~~~~ 15

30 1 10 20 .~~ 5 10 fa~ra~ o I v ,/1 I",,: I v ,''.' L/, A r ,/ 1 ~ I 0 80 j SHALLOW, May 99 SHALLOW, June 99 70 I 25 I 60 20 50 40 --~;... 15 ''0 30 ~ 10 0" ,~"'0 ~ 5 ~ 10 - ~ 00 >- 0 <00 0 80 ~ 3 DEEP, May 98 o I DEEP, May 98 ~ 70 - 25 ~ 60 ~ 20 50 40 ~ ~~~ Q 15

30 1 r/j r//J V/I f"'./1 V/~ I 10 20 lOJ r/J P71 VJ V/l V'/J V~ I 5

' ,~ ~ ", ' , ~;---' "," '," , o I 1 a 80 j DEEP, May 99 I DEEP, June 99 70 I 25 60 I I 20 50 40 J V~ V~ I 15 30 1 r/J t:0j I 10 20 101 r/J r/.,.l I 5 o I I , 1 , 1/,." V,/I r; II/, A I 0 Isc I MA IWSI 1\118IES I PS IsclMAlwSI M8 IESI PS SITE