The Community Composition, Distribution, and Nutrient Status of Epilithic Periphyton at Five Rocky Littoral Zone Sites in Lake Malawi, Africa

J. Great Lakes Res. 29 (Supplement 2):181–189 Internat. Assoc. Great Lakes Res., 2003

The Community Composition, Distribution, and Nutrient Status of Epilithic Periphyton at Five Rocky Littoral Zone Sites in Lake Malawi, Africa Scott N. Higgins*,1, Hedy J. Kling2, Robert E. Hecky1, William D. Taylor1, and Harvey A. Bootsma3 1Dept.

of Biology University of Waterloo Waterloo, Ontario N2L 3G1 231

Laval Dr. Winnipeg, Manitoba R3T 2X8 3Great

Lakes WATER Institute University of Wisconsin-Milwaukee 600 E. Greenfield Ave. Milwaukee, Wisconsin 53204 ABSTRACT. The epilithic periphyton of Lake Malawi is dominated by heterocystous cyanoprokaryotes (blue-green algae/cyanophytes) and diatoms containing endosymbionts capable of nitrogen fixation, though in some locations impacts such as sediment and nutrient loading have shifted the algal community structure towards dominance by diatoms and chlorophytes. Overall, diazotrophic (capable of N2 fixation) Calothrix spp. dominated the littoral periphyton communities at almost all sites/depths located within this study. The biovolume of associated heterocysts tended to decline with depth and was similar between sites. Diazotrophic endosymbionts within Rhopalodia spp. were a common feature of the algal community at all sites/depths, although they have not previously been reported in the literature for Lake Malawi. While the use of stoichiometric C:N:P ratios to determine the nutrient status of naturally-occurring periphyton communities was confounded by detrital and non-living portions of the algal matrix, the dominance of diazotrophic algae suggests that the rocky littoral zones are N-limited systems. INDEX WORDS: Lake Malawi.

Periphyton, epilithon, epilithic algae, nutrient, littoral zone, tropical, endosymbionts,

INTRODUCTION Much of the interest in the community structure and nutrient dynamics of the epilithic periphyton community in Lake Malawi stems from the importance of epilithic algae as a food source for a dense and diverse group of cichlid fishes (known locally as “mbuna”) which inhabit the rocky littoral zones. The most recent estimates suggest that over one half of Lake Malawi’s 700+ species of fishes reside in the rocky littoral zone, and that fish density often reaches 5 individuals per square meter of lake bottom (Reinthal 1990, Ribbink et al. 1983). The majority of “mbuna,” though facultative omnivores, are primarily herbivorous and intensively graze the *Corresponding

epilithic algal communities that blanket rocky surfaces in the littoral zone (Hecky and Hesslein 1995, Reinthal 1990). High rates of primary productivity (near 1 g C/m 2 /day; Bootsma 1993) maintain the algal biomass, creating a strong demand for nutrients. Ambient concentrations of nitrogen and phosphorus are low in the surface waters of Lake Malawi, with dissolved inorganic nitrogen (DIN) concentrations below 3 µM and soluble reactive phosphorus concentrations (SRP) below 0.4 µM (Bootsma and Hecky 1999, Guildford et al. 1999). Overall, Lake Malawi is considered N-deficient (Guildford et al. 1999), and through fish-mediated processes (Andre 1999) high rates of epilithic nitrogen fixation may supply up to 30% of pelagic nitrogen demand (Hig-

author. E-mail: [email protected]

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gins et al. 2001). However, despite the importance of the epilithic periphyton communities in maintaining high densities and diversity of cichlid fishes, and in whole-lake nutrient processes (Higgins et al. 2001), very few studies on the taxonomy or ecology exist (Haberyan and Mhone 1991, Reinthal 1990). The purpose of this study was to describe the spatial patterns of community composition and nutrient composition of the epilithic periphyton community within Lake Malawi, and to discuss the potential impact of sediment and nutrient loading. SITE DESCRIPTIONS The five sites chosen for algal sampling were located in the central and southern portions of Lake Malawi (Fig. 1). All sites were located on islands, and dominated by rocky substrata over the entire depth gradient sampled. The Thumbi West Island sampling site was located on the northern, exposed, portion of the island, away from potential anthropogenic nutrient inputs from Chembe village (approx. 1.5 km from the southern tip of the island). Maleri Island has a predominantly rocky shoreline with smaller zones of sandy beach, and is impacted annually by sediment-laden, nutrient-rich water that flows from the Linthipe River during the rainy season (Kingdon et al. 1998). The Maleri South site is located on the southerly side of Maleri Island, within a small bay opening to the southeast. The “Maleri South” site is relatively unprotected from wave action caused by the predominantly southeasterly wind (known locally as “mwera”), which during the windy season (June through August) can become quite strong causing 4 to 5 m swells. Likoma Island is located in the central eastern portion of Lake Malawi. The island is the site of a relatively large fishing village, and virtually no large terrestrial vegetation remains. Agriculture is restricted to small areas near the village, as much of the island is steep sloped (30 to 50 degrees) with large boulders and little topsoil. The two Likoma Island sampling sites, Membe point (LI-Membe) and Makalawe point (LI-Makalawe), were chosen off steep sloping rocky shorelines well away from development or potential for soil erosion. These sites are discussed in more detail in Higgins (1999) and Ribbink et al. (1983). METHODS Algal samples were taken in triplicate at five sites and three discrete depths (2 m, 5 m, 10 m) during the windy seasons (May through October) of

FIG. 1. Locations of nearshore sampling sites in Lake Malawi, Africa. A = Likoma Island; B = Maleri Island; C = Thumbi West Island. X’s represent the approximate sampling location in the littoral zones around each island. 1997 and 1998 using SCUBA and a periphytonscraping device described by Loeb (1981). Samples were taken from horizontal rocky surfaces. All sites within this study were also used for studies on nitrogen fixation (Higgins et al. 2001) and fish ecology (Ribbink et al. 1983), and some were used for studies on the role of fishes in nutrient cycling (Andre 1999), macro-invertebrates (Abdallah 2000), and primary production (Bootsma 1993). Samples collected from a 5 cm2 surface area were diluted to 250 mL with filtered lake water, and immediately sub-sampled for algal and heterocyst enumeration, chlorophyll a, particulate nutrients (C, N, P), and total epilithic mass. Algal composition/

Periphyton Community Structure in Lake Malawi heterocyst sub-samples were preserved in 20 mL scintillation vials using Lugol’s solution until analysis. Triplicate algal samples were pooled to form one composite sample from which 2 mL was placed in an Utermöl chamber. Algal identification and enumeration were conducted using a Wild M40 inverted microscope. Taxonomic guides included Dickie (1879), Klee and Casper (1992), Müller (1895, 1903, 1904, 1905, 1911), Shmidle (1902a, 1902b), and Vyverman and Cocquyt (1993). Cell estimates were made by counting a 200 µm diagonal strip under 940× magnification and half of a 2 mL chamber at 234× for each sub-sample (Hecky and Kling 1987, Nauwerck 1963). For each site/depth five algal samples were chosen randomly for heterocyst enumeration (of filamentous cyanoprokaryotes) and endosymbiont biovolume (in Rhopalodia). For each homogenized sample a 2 mL subsample was placed in a Utermöhl chamber, and at least 50 fields (or 100 heterocysts and 100 endosymbionts) were counted using an Zeiss Axioinvert 35 inverted phase microscope under 400× magnification. Each sample to be counted was selected randomly, such that the person counting did not know the site or depth from which it originated. Both heterocysts and endosymbionts were enumerated in three size classes. Biovolume was calculated using lengths and widths from at least 50 individuals randomly selected in each size class, and equations for the appropriate geometric shapes (Wetzel and Likens 1991). The total biovolume for heterocysts and endosymbionts were then calculated by multiplying the average biovolume for each size class by the number of individuals in that class, then adding the size classes together. Chlorophyll a was extracted using an alkaline acetone solution at –5°C for at least 12 hours before filtering and fluorometric analysis (Stainton et al. 1977). Particulate nutrients (C, N, P) were collected on GF/C filters, desiccated, and kept frozen until analyzed following the methods of Stainton et al. (1977). Epilithic mass was determined as the difference in mass between the weight of a desiccated ashed filter without particulate material, and the weight of the filter with particulate material after desiccation for at least 48 hr. RESULTS Periphyton Composition With the exception of the Maleri Island sites, particularly Maleri South, cyanoprokaryotes (bluegreen algae/cyanophytes) dominated the biomass

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within periphyton communities at all sites/depths (Fig. 2). Within the cyanoprokaryote group members of the genus Calothrix, particularly C.cf paretina Thuret, comprised at least one half of the biomass (Table 1). Calothrix is a heterocystous cyanoprokaryote capable of nitrogen fixation. Heterocyst biovolume was similar between sites at similar depth, and followed a general decreasing trend as depth increased (Fig. 3a). Other filamentous cyanoprokaryotes, that may have been juvenile forms from the genus Calothrix, were small and non-identifiable and comprised approximately 20% of the biomass within the cyanoprokaryotic grouping. Tychonema, Planktolyngbya, and Chroococcoid taxa were also important genera in terms of biomass, each composing 5 to 11% of the biomass. All other taxa combined comprised approximately 3% of the total cyanophyte biomass at all sites. A major difference between the composition of the cyanophytes at Maleri Island South and other sites was the increased importance of other genera in the Oscillatoriaceae such as Lyngbya, Leptolyngyba (approximately 20% of cyanophyte biomass) at Maleri South, replacing previously mentioned taxa. Diatoms were the second most important component of the total periphyton biomass at most sites/depths. However, their biomass reached high proportions of the total epilithic biomass only at the Maleri Island sites. At Maleri Island sites Navicula spp. comprised over 50% of the diatom biomass. Rhopalodia, particularly R. cf. stuhlmanii O. Müller, R. hirundiformis, and R. cf. rhopala O. Müller, comprised approximately 25% of the diatom biomass. Rhopalodia spp. at all sites often contained endosymbionts capable of nitrogen fixation (Higgins 1999, DeYoe et al. 1992). The endosymbiont biovolume at each site showed no site/depth trends, and was typically an order of magnitude lower than heterocyst biovolume (Fig. 3b). The mean number of endosymbionts per Rhopalodia cell was 1.8 and showed no site/depth trends. Cymbella and Encyonema together comprised approximately 15% of the diatom biomass at Maleri South. At non-Maleri Island sites the diatom community was dominated by members of the genus Rhopalodia, particularly R. gibba (Ehrenberg) O. Müller, R. gracilis O. Müller, R. hirundiformis, O. Müller and R. cf. rhopala which is probably a morphotype of R. hirundiformis, and together contributed over 45% of the diatom biomass (Table 1). Cymbella contributed nearly 30% of the diatom biomass, and was dominated by C. cf. minuta Hilse ex Rabenorst syn Encyonema minutum (Hilse ex Rabenhorst)

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FIG. 2. The composition of epilithic periphyton on horizontal rock surfaces at five sites in the littoral zone of Lake Malawi, Africa. Each site/depth represents one pooled triplicate sample taken over the windy season (May to Oct).

Mann, and C. cf. tumida (Brébisson in Kütz) Grunow. The genera Gomphocymbella and Nitzchia each contributed approximately 10% of the total diatom biomass. Gomphonema and Navicula were also important genera and each contributed nearly 5% of the total diatom biomass. Chlorophytes, though present at all sites/depths, were most notable at the Maleri Island sites. At non-Maleri Island sites Coelastrum reticulatum dominated the chlorophyte biomass, with members of the genera Mougeotia, Pediastrum, and Cladophora making important contributions (Tables 1 and 2). The Coelastrum and Pediastrum are primarily planktonic taxa that may have settled on to the rocks from the overlying water column. Mougeotia spp. also appeared to be planktonic (without holdfasts and unattached), and identical to those described as Oedegonium sp. by Schmidle (1902a). Cladophora, on the other hand, was permanently attached and growing on the rocks. At the Maleri Island sites two macroscopically distinct algal patches were easily discernable. These patches were termed “Calothrix” and “Cladophora”

for their dominant constituents. Cladophora patches (dull green in color) were found in depths from 1 to 5 m, while Calothrix patches (dark brown) were noted throughout the sampling range (1 to 10 m), and were always spatially dominant. More detailed taxonomy of the algae in these benthic habitats is underway and will be published elsewhere. Elemental Composition of Periphyton The total mass of C, N, and P within the epilithic mass was similar between sites/depths with the exception of Maleri South 10 m depth, where values of each were approximately 4 to 6 times all other sites/depths (Table 2). Measured stoichiometric C:P and N:P ratios were much higher than the typical “Redfield” ratio (106C:16N:1P) for non-nutrient limited phytoplankton, and perhaps for benthic micro-algae (Hillebrand and Sommer 1999). Epilithic carbon to nitrogen (C:N) ratios were similar between all sites/depths, however C:P and N:P ratios were much lower at all depths of the Maleri Island South site relative to other sites/depths, re-

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Periphyton Community Structure in Lake Malawi TABLE 1. The percent composition of dominant algal genera in the epilithic periphyton of Lake Malawi, Africa. The percent biomass within each algal group, and percentage of the total algal biomass were determined by pooling all sites and depths for each group. NonMaleri sites were Makalawe, Membe, and Thumbi West. Maleri sites were Maleri S. and Maleri N.

Cyanophytes Calothrix Chroococcoid species Unidentified filamentous Lyngbya Tychonema Planktolyngbya Schizothrix Other non-filamentous

Maleri sites % of group % of total 36.0 74.9 27.0 3.3 1.2 — 20.6 7.4 — — — — — — 1.2 0.4

Non-Maleri sites % of group % of total 82.8 49.1 40.6 6.6 5.5 21.4 17.7 — — 10.2 8.5 5.9 4.9 3.4 2.8 3.4 2.9

Diatoms Rhopalodia Navicula Cymbella + Encyonema Nitzschia Gyrosigma Other

24.4 54.6 12.9 1.4 3.5 3.3

60.3 14.7 32.9 7.8 0.8 2.1 1.9

45.2 3.7 28.9 9.7 — 16.2

15.1 6.6 0.5 4.2 1.4 — 2.4

Chlorophytes Coelastrum Mougeotia Choricystis/chlorella Euastrum Other

— — — 93.0 7.0

3.7 — — — 3.4 0.3

62.6 14.4 11.7 — 11.3

2.7 1.7 0.4 0.3 — 0.3

flecting the relative increase in phosphorus at the Maleri Island South site. Chlorophyll and Total Epilithon Mass Chlorophyll a concentrations in periphyton samples did not show distinct patterns between sites, though they sometimes tended to increase with depth, presumably because the algae increased their chlorophyll a:cell ratio under low light conditions (Lowe and Pillsbury 1995) (Fig. 3c). Although the Maleri South site had high chlorophyll a values and high epilithon mass (dry weight of all material including the silt layer) (Fig. 3c) at 10 m depth, algal biomass (as determined from algal cell counts) was much lower than other sites at similar depths (Fig. 2). DISCUSSION Cyanoprokaryote and diatom species capable of nitrogen fixation dominated the epilithic algal bio-

mass. Within the cyanoprokaryotes, epilithic Calothix spp. contributed 50 to 75% of the biomass, and within the diatoms Rhopalodia spp. (epiphytic on Cladophora and within mucilage of Calothrix), containing endosymbionts capable of N2 fixation (DeYoe et al. 1992, Higgins 1999), contributed approximately 45% of the biomass. Overall, Calothrix spp. contributed approximately 50% of the total algal biomass at all site/depths except Maleri South. Within the diatom taxa, the dominance of Rhopalodia spp. with diazotrophic endosymbionts has not previously been reported for the epilithon of Lake Malawi. Due to high algal productivity and low ambient concentrations of inorganic nitrogen in Lake Malawi, the ability to fix atmospheric N2 likely provides Rhopalodia spp. a competitive advantage over other diatoms and other non-diazotrophic algae. Rates of epilithic nitrogen fixation for these epilithic algal communities are among the highest recorded for freshwater or marine systems and an important contributer to the whole lake nitrogen

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FIG. 3. Depth distribution of a) heterocyst biovolume, b) endosymbiont biovolume, c) chlorophyll a, and d) total epilithic mass sampled from horizontal rock surfaces in the littoral zone of Lake Malawi, Africa. Heterocyst and endosymbiont biovolumes represent the mean value of five samples counted for each site/depth (see text). Chlorophyll and epilithic mass represent the mean value of at least five samples collected from each depth.

cycle (Higgins et al. 2001). Interestingly, diazotrophic algae are only an important component of the phytoplankton during a few months of the year (Patterson and Kachinjika 1995) despite total nitrogen concentrations that are among the lowest recorded for freshwater or marine systems (Guildford and Hecky 2000). Other studies have also noted the dominance of N2 fixing cyanoprokaryotes in the littoral benthos of N-deficient oligotrophic systems, despite their relative unimportance in pelagic phytoplankton communities (Bergmann and Welch 1990, Capone 1983, Haberyan and Mhone 1991, Reuter et al. 1986). These studies originate from polar to tropical latitudes, in both freshwater and marine environments; additional studies may reveal that phytobenthos are often N-limited in oligotrophic lakes. Cyanoprokaryotes have a high requirement for phosphorus and other essential nutrients (Mo, Fe) which are often unavailable, or inaccessible, to the phytoplankton community in oligotrophic systems. Conversely, concentrations and residence times of these same nutrients are likely higher within benthic regions, where sediment and detrital sources of critical elements occur, allowing for dominance by diazotrophic cyanoprokaryotes (Howarth et al. 1988, Reuter et al. 1986). Furthermore, studies on grazer-periphyton interactions on coral reefs have demonstrated that high densities of fish grazers can: 1) increase primary productivity by keeping algae in an early successional stage (Wilkinson and Sammarco 1983); 2) shift the periphyton community

TABLE 2. Biomass and elemental ratios for epilithic periphyton samples in the littoral zone of Lake Malawi. All values are expressed as the mean of triplicate samples, which were collected during the windy season (May to Oct). Maleri samples from 1997, all others from 1998. Depth (m) 2 5 10

C 6,677 7,130 5,744

Mg/m2 N 635 609 524

LI-Makalawe LI-Makalawe LI-Makalawe

2 5 10

5,865 6,719 9,199

449 571 709

16 21 29

911 771 799

15 14 15

60 56 53

LI-Membe LI-Membe LI-Membe

2 5 10

5,071 7,925 8,141

400 725 647

24 28 24

758 700 833

14 13 15

52 55 57

Maleri S Maleri S Maleri S

2 5 10

5,684 8,330 30,451

502 726 2,432

37 97 231

401 340 374

14 13 15

30 27 26

Site Thumbi W Thumbi W Thumbi W

P 19 37 26

C:P 800 642 585

molar C:N 12 14 13

N:P 61 47 45

Periphyton Community Structure in Lake Malawi structure toward dominance by nitrogen fixing species (Larkum 1988); and 3) increase rates of nitrogen fixation through a combination of the first two points (Larkum 1988). Indeed, the epilithic algal community of Lake Malawi is heavily grazed (Andre 1999); and rates of primary production and nitrogen fixation are among the highest recorded for freshwater systems, and similar to those occurring on coral reefs (Bootsma 1993, Higgins et al. 2001). The nutrient stoichiometry of phytoplankton has long been used to assess the limitation of algal production by particular nutrients (Healy and Hendzel 1980), and recently these principles have been applied to benthic microalgae (Hillebrand and Sommer 1999). The mean C:N:P ratio from algal scrapings at non-Maleri Island sites was 755:54:1 (molar), compared to the optimal 119C:17N:1P ratio for benthic microalgae, and well above the 22N:1P threshold indicating P limitation (Hillebrand and Sommer 1999). These results, however, appear to contradict the current understanding of the nutrient status of Lake Malawi’s periphyton communities. The epilithic algae in Lake Malawi are dominated by heterocystous cyanoprokaryotes fixing nitrogen at high rates (Higgins et al. 2001), which would be considered unusual for strongly P limited algae. Also, the difference between the N:P ratio of herbivorous fishes in the rocky littoral zone of Lake Malawi and their excretory products suggests that their food source (primarily epilithic algae) has an N:P ratio near 16:1 molar (Andre 1999). Therefore, it is unlikely that particulate nutrient ratios measured in situ on naturally occurring algal populations using Loeb’s (1981) sampling technique (as used here), or Stockner and Armstrong’s (1971), are useful in assessing nutrient limitation. Stoichiometric ratios of periphyton sampled using these methods can be influenced by detrital and non-living portions of the algal matrix. Therefore, the measured stoichiometric ratios of the algal matrix may not accurately reflect the living, growing portion that is of interest when discussing nutrient limitation or nutrient fluxes. The epilithic algae in Lake Malawi are fast growing and heavily grazed by cichlid fishes, and relative to most temperate lakes there is little accumulation of detrital material. The inability to use stoichiometry to infer the nutrient status of periphyton in Lake Malawi (where the detrital contribution is at a minimum) suggests that it will prove even more difficult in temperate locations using similar sampling procedures. The total amount of sediment and nutrient loading from individual rivers flowing into Lake

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Malawi has only recently been quantified (Kingdon et al. 1999). This information, combined with qualitative evidence that the Maleri Islands often become engulfed in a sediment plume extending from the Linthipe River during the rainy season (December through March), allowed an excellent opportunity to examine the effect of point source sediment and nutrient loading on algal biomass and community structure. Visual observations using SCUBA revealed that a 1 to 2 cm layer of silt was present over nearly all rocky surfaces below 8 m depth at the protected Maleri South site throughout the sampling season (May through October), although was not present at any other sites in this study. Quantitatively, the sediment layer was associated with a high total epilithon mass (Fig. 3d), and high chlorophyll. The biomass of the epilithic algae (as determined by algal enumeration), however, was much reduced at this site/depth relative to other sites at similar depth (Fig. 2). The combination of high chlorophyll values and low algal biomass suggests that the few remaining algal cells had increased their chlorophyll concentrations to compensate for low light conditions in the sediment layer. Although the majority of the nitrogen and phosphorus that enters into Lake Malawi through the Linthipe River, as with all rivers in Malawi, is bound in particulate form (Kingdon et al. 1999), the dissolved fractions are likely the most accessible to nearshore benthic algae. The Linthipe River supplies approximately 600 metric tons of DIN and 90 metric tons of SRP to the epilimnion of Lake Malawi annually (the vast majority during the rainy season) at a DIN:SRP ratio of approximately 3:1 molar. The algal community structure at the Maleri Island South site, which is co-dominated by diatoms, cyanoprokaryotes and chlorophytes, differs substantially from other sites in this study which were dominated by cyanoprokaryotes alone. Among the diatoms, Rhopalodia spp., that contained endosymbionts capable of N2 fixation, decreased in relative importance to other diatoms. The increased importance of non-nitrogen fixing algae at the Maleri Island South site suggests, despite the low N:P ratio of nutrient inputs from the Linthipe River, that the epilithic algae do not experience the severe nitrogen limitation compared to all other sites/depths in this study. It is interesting to note that the observations of algal patches at the Maleri South site are similar to those reported by Reinthal (1990) and Haberyan and Mhone (1991) on the southern portion of Thumbi West island. At the Thumbi West site, lo-

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cated on the northeastern portion of the island, no such algal patches were found within the sampling depths (2 to 16 m). The differences between these sites may be due to the close proximity of the southern portion of Thumbi West to the mainland village of Chembe, where nutrient and sediment loading may be more important. The distinction between impacted and non-impacted sites in Lake Malawi is important for two reasons. First, the ability to determine point source nutrient loading from the characteristics of the epilithic algal community may be a useful tool in monitoring water quality in Lake Malawi. Second, the use of sites potentially impacted by sediment and nutrient loading (the southern portion of Thumbi West Island) to describe periphyton community structure on a lakewide basis may have led to incorrect conclusions regarding algal community structure and its interaction with herbivorous fishes (Reinthal 1990). CONCLUSION The results of this study suggest that algae and cyanoprokaryotes capable of N2 fixation dominate the epilithic periphyton community of Lake Malawi, supporting the mounting evidence that Lake Malawi is currently a nitrogen deficient system (Guildford 2000, Hecky and Bugenyi 1992, Hecky et al. 1996). These results also suggest that sediment and nutrient loading have the ability to shift the periphyton community structure and reduce the effective habitat for algal grazing cichlids within Lake Malawi. Previous studies have highlighted the importance of periphyton to littoral and whole lake nutrient processes (Andre 1999, Higgins et al. 2001), and as a food source for rocky shore fishes (Fryer and Illes 1972, Hecky and Hesslein 1995, Bootsma et al. 1996, Reinthal 1990). Considering that the rocky littoral zones contribute only 30% of Lake Malawi’s shoreline, yet sustain over 50% of the lakes 700+ fish species (Reinthal 1990, Ribbink et al. 1983), changes in the epilithic periphyton community structure or depth of the effective littoral zone could potentially affect fish abundance, diversity, and whole-lake nutrient processes. ACKNOWLEDGMENTS We gratefully thank the governments of Malawi, Tanzania, and Mozambique and the SADC/GEF Lake Malawi Biodiversity Conservation Project for enabling us to complete this research. Funding was provided through the Canadian International Devel-

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