Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 126–132

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Palaeogeography, Palaeoclimatology, Palaeoecology

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Fish as paleo-indicators of ichthyofauna composition and climatic change in Malawi, Africa

Peter N. Reinthal a,⁎, Andrew S. Cohen b, David L. Dettman b a Department of Ecology and Evolutionary Biology, The University of Arizona, Tucson, AZ 85721, USA b Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA article info abstract

Article history: Numerous biological and chemical paleorecords have been used to infer paleoclimate, lake level fluctuation Received 27 February 2009 and faunal composition from the drill cores obtained from Lake Malawi, Africa. However, fish fossils have Received in revised form 23 October 2009 never been used to examine changes in African Great Lake vertebrate aquatic communities nor as indicators Accepted 1 January 2010 of changing paleolimnological conditions. Here we present results of analyses of a Lake Malawi core dating Available online 7 January 2010 back ∼144 ka that describe and quantify the composition and abundance of fish fossils and report on stable carbon isotopic data (δ13C) from fish scale, bone and fossils. We compared the δ13C values to δ13C Keywords: fi Lake Malawi values from extant sh communities to determine whether carbon isotope ratios can be used as indicators of inshore versus offshore pelagic fish assemblages. Fossil buccal teeth, pharyngeal teeth and mills, vertebra and fossils scales from the fish families Cichlidae and occur in variable abundance throughout the core. Carbon isotopes Carbon isotopic ratios from numerous fish fossils throughout the core range between −7.2 and −27.5‰, Cyprinid similar to those found in contemporary Lake Malawi benthic and pelagic fish faunas. These results are the core first paleo-record of fish fossils from a Lake Malawi sediment core and the first reported δ13C values from Lake Malawi fish fossils. This approach provides a new methodology and framework for interpreting pelagic versus inshore fish faunas, lake level fluctuations and the evolution of the Lake Malawi fish assemblages. © 2010 Elsevier B.V. All rights reserved.

1. Introduction Lake Malawi contains one of the most diverse freshwater fish faunas found anywhere in the world (Fryer and Iles, 1972; Ribbink et al., 1983) In 2005 a series of drill cores was collected from two sites in Lake and is dominated primarily by members of the family Cichlidae. Malawi/Nyasa, Africa (Scholz et al., 2006, 2007). Four cores were Ecologically, the fish fauna may be segregated into those members of retrieved from a deep-water, central basin Site 1 (11°17.66S, 34°26.15E, the inshore, rocky substrate fish assemblages versus the offshore pelagic 592 m water depth), one of which (MAL05-1C, 76 m in length) forms and sandy bottom species. The near shore , known as ‘mbuna’, the basis for this study. During other analyses of this core (Cohen et al., are well known for their adaptive radiation and are considered a model 2007), it was noted by one of the authors (ASC) that numerous fish system for evolutionary studies (Kocher, 2004). Morphologically, remains/fossils were present at all depths. These fossils included scales, mbuna body forms are very similar but most cichlids have species- bones and teeth. Whereas many types of chemical and biological specific oral (jaw or buccal) and pharyngeal dentition and neurocranial indicators have been previously used to assess climate, lake level and morphology that are indicative of diet and use (Reinthal, 1990a, faunal changes from Lake Malawi sediment cores, no one to date has b)(Fig. 1). Alternatively, in the pelagic community of Lake Malawi, quantified fossil fish remains or used these fossils as indicators of past four families are represented; Cichlidae, Cyprinidae, Clariidae and fish communities or paleolimnological conditions. We examined these Mochokidae. Only members from the first two families demonstrate fossils in order to 1) determine which components are most commonly predominantly pelagic life history strategies. The pelagic cichlids are recovered from each species, 2) quantify their composition and specifically represented by three non-mbuna genera: Rhamphochromis abundance at varying levels of the core and 3) use stable carbon Regan, Diplotaxodon Trewavas and Copidichromis Eccles and Trewavas isotopic ratios to assess inshore versus offshore fish assemblages. Here (Allison et al., 1995). The most abundant and widespread pelagic fish we report the preliminary results of these analyses and discuss the species, and the only Lake Malawi species of fish to have pelagic applicability of using fish fossils as a methodology to examine lake level planktonic larvae, is the cyprinid Engraulicypris sardella, a monospecific fluctuations and evolutionary changes in an important African fresh- genus of small neoboline cyprinid that spends its entire life in the pelagic water fish assemblage. zone of the lake (Thompson, 1995). Ecologically, the fish fauna of Lake Malawi is well known for its δ13 ⁎ Corresponding author. Tel.: +1 520 621 7518; fax: +1 520 621 9190. breadth of food resources. Stable isotopes (carbon C and nitrogen 15 E-mail address: [email protected] (P.N. Reinthal). δ N) have been used to determine food resource partitioning among

0031-0182/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2010.01.004 P.N. Reinthal et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 126–132 127

Fig. 1. Variation in buccal (oral) teeth and neurocrania morphology among six species of Lake Malawi cichlids. All taxa shown here are members of the nearshore, monophyletic species complex known as ‘mbuna’. Long, flexible bicuspid and tricuspid teeth are found in algae grazers and rock scrappers. Shorter, unicuspid teeth are found in pelagic feeders (drawing by D.S.C. Lewis).

Lake Malawi fishes by comparing isotopes of a variety of inshore et al., 2005, 2008), alewife (Dufour et al., 2005; Dufour et al., 2008) benthic versus pelagic species and their available resources (Bootsma and undescribed Jurassic species (Patterson, 1999). Lake sediment et al., 1996). Stable isotopes have also been used to look at niche records of δ15N and biological indicators were used to reconstruct segregation among Lake Malawi cichlids (Genner et al., 1999) and abundance in Alaska over the past 300 (Finney et al., 2000) ontogenetic variation in isotopic signatures related to body size and ∼2200 years (Finney et al., 2002). (Genner et al., 2003). These studies provide a large sampling of extant Preliminary examination of sediment from the Lake Malawi core inshore and pelagic fish isotopic signatures that may be used for revealed a wide variety of well preserved fish teeth, bones and scales comparative purposes. Species with δ13C values in the range of −6to from all depths. We hypothesized that δ13C values of fish fossils would −16‰ VPDB are primarily inshore mbuna species. Pelagic species, vary with fluctuations in lake level. ‘Mbuna’ fossils and/or fossils with like Engraulicypris sardella, and open water cichlids show lower δ13C more positive δ13C values (−6to−16‰ VPDB) might be indicative of values, in the range of −22 to −25‰ VPDB. an inshore, shallow water fauna during periods of decreased or low Fish have long been known to play a critical role in the function lake levels. Alternatively, fossils of pelagic species with more negative and structure of lake . It is only recently that scientists are δ13C values (−22 to −25‰) might be indicative of a deep-water beginning to assess the potential of fish fossils and stable isotope fauna and higher lake levels. values from sediment cores in paleoecological studies (Patterson and The present study attempted to assess the paleolimnological Smith, 2002). Scale and scale fragments have been used to examine potential of fish fossils from Lake Malawi cores by quantifying fossils percid–cyprinid faunal shifts in shallow English (Davidson et al., and comparing fossils with contemporary structures and isotopic 2003). Stable isotopic values found in fish fossils have also been used values. Specifically, we sought to quantitatively examine teeth, bones in a variety of studies to evaluate paleolimnological conditions and scale fish fossils found at different depths of the core, to identify (Patterson et al., 1993; Patterson, 1998; Smith and Patterson 1994; modern analogs of these fossils, to identify fish assemblages based on Wurster and Patterson, 2001, 2003). For example, Nd and Sr isotopes fossils found in the cores and to use stable isotopes (δ13C) to have been examined in Neogene fossil teeth to determine historical determine benthic versus pelagic food sources. We analyzed 467 values of seawater isotopic values (Martin and Haley, 2000), and in stratigraphic horizons for fish fossil abundance (#/g) from throughout archeological sites to determine the source of the fish (Dufour et al., the core. We then collected δ13C data from fish fossils from selected 2007). isotopes in have also been used to examine intervals in the core. Finally, based on independent data sets from the natal and adult temperature (Dufour et al., 2005; Zazzo et al., 2006), same core we then assessed the potential of fish fossils as predictors of and habitat preferences in Cynoscion othonopterus (Rowell lake level, fish communities and climatic conditions. 128 P.N. Reinthal et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 126–132

2. Materials and methods and tooth samples were acidified with sulfurous acid (H2SO3) in silver foil capsules to remove structural carbonate from the bone apatite. Core collection, and archiving methods are de- Two drops of acid were used followed by overnight drying in a 60 °C scribed elsewhere (Scholz et al., 2006, 2007). MAL05-1C provides a oven. This procedure was repeated once. Because the amount of record of Lake Malawi history from ∼144 to 10 ka. Because of core organic carbon in these samples was extremely small (pre-acidified over-penetration the most recent ∼10 ka are missing from the core weights ranged from .001 to 2.14 mg with most being .05 to .2 mg), record. Malawi core MAL05-1C was sampled at 16-cm intervals for a extra care was taken to eliminate carbon contamination. Silver foil total of 467 samples collected for wet-sieved residue analysis. For a capsules were heated to ∼500 °C in air to remove any carbon material discussion of wet-sieved residue analysis see Cohen et al. (2007). on the foil. Numbers of bone, scale and teeth fossils were counted from samples that had been disaggregated in deionized water and sieved using a 3. Results 125-um stainless steel sieve. Samples were sorted using an Olympus SZH stereomicroscope and separated for identification and isotopic Identifiable fish fossils of buccal teeth, pharyngeal teeth and mill, analysis. vertebrae, other bones and scales are all from the fish families Stable isotope data was collected on a continuous-flow gas-ratio Cichlidae and Cyprinidae. All fish fossils are extremely small (less than mass spectrometer (Finnigan Delta PlusXL). Samples were combusted one mm) and are found throughout the core with variation in using an elemental analyzer (Costech) coupled to the mass spec- abundance. More fossils were found in older sections than in younger trometer. Standardization is based on an acetanilide working standard sections (Fig. 2). In sections of the core between 10 ka (youngest) and calibrated against NBS-22 and USGS-24 for δ13C. A urea working 60 ka, only 34.9% (44 of 126) of the sample horizons contained fish standard was also used when processing extremely small samples. fossils, whereas in the older sections of the core (60–∼140 ka) this Precision is normally better than ±0.1 for δ13C(1σ), based on proportion rises to 78.7% (270 of 343 samples). Fish bones were the repeated internal standards. Samples that were extremely small most common fossils, being present in 96.2% of samples with fossils (marked with an asterisk in Table 1) have a higher uncertainty; present whereas fish scales were found in 36.0% and fish teeth in standards of equivalent size had a variability of ±0.25‰ (1σ). Bone 24.2% of samples with fossils present respectively. Fish bones were also the most numerically abundant fossils found in the samples; when any fossils (bones, teeth or scales) were present in a sample Table 1 (314 samples), fish bones accounted for 82.8% of all of the fossils fi Core section and depth (cm) within core section (included for sample identi cation), present. fossil descriptions, weights of sample or combined samples when available, estimated model age of sample (from Scholz et al., 2007), and δ13C value. Carbon isotope ratios Although it was impossible to taxonomically identify all of the followed by an asterisk have an uncertainty of ±0.25‰ (1σ) due to small sample size. bones to family and/or species, the cyprinid bones appeared to be dominated by, if not exclusively consist of ‘Usipa’, Engraulicypris Core Depth Fossil description Weight Model age Final δ13C sardella, the pelagic cyprinid found in modern Lake Malawi. Given the section (cm) (mg) (ybp) value taxonomic complexities of and limited morphological differentiation – − 1H1 2 3 Unicuspid pharyngeal .047 10,283 20.29 among the Lake Malawi cichlids, the cichlid bones were impossible to teeth 1H1 2–3 Four bone fragments .012 10,283 −25.10* identify beyond family. However there were certain structures, like 1H1 18–19 Three Cyprinid bones .009 10,662 −24.22* buccal (oral) teeth that are unmistakably from the family Cichlidae 1H1 50–51 Five bone fragments .025 11,433 −25.17 and most likely, from the mbuna group. – − 1H1 82 83 One scale .111 12,222 21.41 All of the bones were extremely small (less than 1 mm in length) 1H1 82–83 Three teeth .019 12,222 −23.73* and many of the bones were fragmented and therefore difficult to 1H1 82–83 Bone fragments .029 12,222 −24.70* 1H1 82–83 Bone fragments .133 12,222 −23.67 identify (Fig. 4A–B). This also complicated our isotopic analyses. Most 1H1 82–83 Bone .013 12,222 −24.35* samples were too small to have enough material from single bones for 1H2 41–42 Ten bone fragments .058 13,444 −24.05 isotopic analyses, requiring us to use multiple bones and bone – − 1H2 41 42 Bone fragments .031 13,444 23.44* fragments from the same sample to obtain enough organic material 1H2 41–42 Bone fragments .011 13,444 −23.50* 1H2 89–90 Four bone fragments .024 14,692 −24.55* for carbon isotope analyses. We were able to obtain isotopic ratios 1H2 82–83 Five bone fragments .049 14,692 −24.57 from scale samples as small as .008 mg. We were not able to obtain 4 H 3 51.6–52.6 Five bone fragments .041 39,224 −24.19 isotopes from small tooth (.007 mg and .003 mg) or small bone (.001 8 H 2 15.3–16.3 Two bones .023 61,576 −26.04* and .006 mg) samples. Taxonomic specific identifications of bones and 8 H 2 47.3–48.3 Eleven bone fragments .314 62,011 −23.90 teeth to species were possible in a few cases and we were able to 8 H 2 111.4–112.4 Five vertebrae .347 62,884 −22.71 8 H 2 111.4–112.4 Bone .129 62,884 −22.76* identify bone structures including abdominal and caudal vertebrae 8 H 2 111.4–112.4 Bone fragments .307 62,884 −16.21 (Figs. 3A and B). These are from the cyprinid, Engraulicypris sardella, 9 H 1 2.3–3.3 Eight vertebrae .135 63,500 −23.55 and in two cases we found fused preural and ural centra (compound 9 H 1 18.3–19.3 Three irregular bones .070 63,718 −23.59* – − centrum) with urodermal and hypural plates diagnostic of cyprinids. 9 H 1 50.3 51.3 Bone fragments .001 64,145 23.75 fi 10 H 3 76.9–77.9 Bone fragments .335 71,043 −21.29 We also identi ed upper pharyngeal tooth pads and pharyngeal 11 H 1 66–67 Six scale fragments .016 72,513 −20.96 teeth (Fig. 4A). Pharyngeal teeth are found in both cichlids and 11 H 1 66–67 Ten scales .030 72,513 −21.63 cyprinids, but most of these appeared to be cyprinids. Most of teeth 11 H 1 82–83 Five scales .037 72,731 −23.31 found in the core were identified as pharyngeal teeth but we also 11 H 1 82–83 Bone Fragments .253 72,731 −8.59 found oral (buccal) teeth from cichlids (Fig. 5A–B). Cyprinids have no 11 H 1 98–99 Bone Fragments .822 72,949 −11.95 12 H 2 85.2–86.2 Six bone fragments 2.14 78,519 −7.16 teeth in their oral jaws. The tricuspid oral teeth found in the core 12 H 2 85.2–86.2 Three vertebrae .283 78,519 −22.12* (Fig. 5A–5B) are from cichlids as they are found only in cichlid adult 14 H 1 97.4–98.4 Three vertebrae .276 85,181 −18.62* fishes from modern Lake Malawi and no other fishes. In adult cichlids, – − 14 H 3 17.9 18.9 Eight scale fragments .048 86,952 18.64* tricuspid oral teeth are found in certain species of algal scrapers in the 14 H 3 17.9–18.9 Nine scale fragments .011 86,952 −24.74* 15 H 2 21.9–22.9 Five scales fragments .008 88,301 −24.17* mbuna (inshore, benthic) group but little is known about tooth shape 17 H 1 53.6–54.6 Oral tooth .034 96,812 −18.25* development. Pharyngeal teeth were common and distinctive from 17 H 1 53.6–54.6 Bone .208 96,812 −21.66* oral teeth (Fig. 5C–D). 17 H 2 30–31 Two pharyngeal teeth .044 97,256 −27.51 Numerous scale and scale fragments were found and they 20 E 3 43–44 Bone .164 111,617 −23.46* appeared to primarily cycloid scales. Cyprinids have exclusively P.N. Reinthal et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 126–132 129

4. Discussion

The preliminary analyses presented here revealed that fish fossils are widespread throughout a sediment core from Lake Malawi and may provide valuable information regarding fish faunal composition and lake level fluctuations. In core sections between 10–60 ka, when the MAL-05-1C core site in Lake Malawi is thought to have been about the same depth as at present (∼580 m), fish fossils were present in less than half as many horizons as was the case from samples ranging between 60 and 135 ka, when the lake was often much shallower (and more broadly fluctuating in depth). This may reflect greater fish at the core site during periods of lower lake levels, when the core site would have been located closer to shore. We were able to identify a number of different structures; teeth, bones and scales, from various taxonomic groups. This is the first time Fig. 2. Log10 concentration per gram of the summation the number of bone, scale and such fossils have been identified and quantified from a Lake Malawi teeth fragments plus one. Data set starts at ∼10,000 BP due to core over-penetration. core. Unfortunately, many specimens are very small with limited diagnostic characteristics but we are able to identify some taxonomic groups. The results here are a preliminary analysis and it is expected that cycloid scales. Cichlids are thought to have ctenoid scales, but one of more complete quantification and identification will result in better us (PNR) has observed numerous cichlids, especially small juveniles, resolution of faunal composition over the recent history of Lake Malawi. with cycloid scales. However, even the data presented here provide insight into the We obtained a broad range of δ13C isotopic signatures from evolutionary history of an important group of endemic cichlid fishes numerous fish fossils, bone organic matter, teeth, and scales, found in often cited as examples of rapid and ‘explosive’ speciation Kocher, 2004. various sections throughout the core (Table 1, Fig. 6). Stable carbon For example, tricuspid teeth that are approximately 130,000 years old isotopic ratios range between −7.2 and −27.5‰ VPDB. Most of the δ13C (Fig. 5A–B) from ‘mbuna’ inshore benthic species, indicates that this values (34 of 41) were between −20 and −25‰ VPDB, indicative of a lineage is at least this age. Understanding dates of cichlid evolutionary pelagic fauna. Seven samples had δ13C values that fell between −7and events has proven problematic and attempts have focused on −19‰ VPDB, more typical of benthic inshore ‘mbuna’ cichlids. Multiple extrapolating rates of gene evolution (Meyer et al., 1990), lake level samples from within a single stratigraphic horizon (e.g. samples from fluctuation (Sturmbauer et al., 2001; Johnson et al., 2002; Verheyen et 1H1 (2–3 cm), model age ∼10.3 ka; 1H1 (82–83 cm), model age al., 2003) and employing calibration from cichlid fossils (Genner et al., ∼12.2 ka; 1H2 (41–42 cm), model age ∼13.4 ka; 8H2 (111.4– 2007). The fossils from the core can be used as calibration points for 112.4 cm), model age ∼62.8 ka; 9H1 (50.3–51.3 cm), model age estimating the timing of genetic divergence within the Lake Malawi ∼64.1 ka; 11H1 (66–67 cm), model age ∼72.5 ka; 12H2 (85.2– cichlid group. Also, the minimum lake level for Lake Malawi for the past 86.2 cm), model age ∼ 78.5 ka; 14H3 (17.9–18.9 cm), model 140,000 years is hypothesized to have occurred approximately age ∼86.9 ka; 17H1 (53.6–54.6 cm), model age ∼96.8 ka) displayed 108,500 ybp (Cohen et al., 2007). These 130,000 year old ‘mbuna’ fossils variable δ13C values throughout the core (Table 1). provide support that the lineage was present prior to this major period of

Fig. 3. A. Left lateral view of cyprinid (Engraulicypris sardella) preural centrum vertebrae from sample 5-H-2 (93.4–94.4 cm), 20.19 mblf (meters below lake floor), approximately 48,000 years old. Legend: ha — hemal arch, haz — hemal prezygapophysis, hpz — hemal postzygapophysis, hs — hemal spine, na — neural arch, naz — neural prezygapophysis, npz — neural postzygapophysis, ns — neural spine, pc — preural centrum. Fig. 3B. Three post Weberian vertebrae from sample 5-H-2 (93.4–94.4 cm), 20.19 mblf, approximately 48,000 years old. 130 P.N. Reinthal et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 126–132

Fig. 4. A. View of cyprinid (Engraulicypris sardella) left upper pharyngeal plate and teeth (630×) from sample 1-H-1 (82–83 cm), 7.33 mblf (meters below lake floor), approximately 12,000 years old. Fig. 4B. Series of bone fragments from sample 12-H-2 (85.2–86.2 cm), 41.02 mblf, approximately 79,000 years old (125×). desiccation and that at least some members of the lineage persisted there may have been significant reduction in the ‘mbuna’ diversity, through this major drying period. The presence of the ‘mbuna’ lineage various ‘mbuna’ lineages persisted and have undergone a prior to the 108.5 ka megadrought is consistent with nuclear (0.7 ma; subsequent species-level radiation as Lake Malawi reached its modern Won et al., 2006) and mitochondrial (0.57–1.0 ma; Sturmbauer et al., lake levels. 2001) molecular clock estimates for mbuna and non-mbuna cichlid These fossils can provide an important resource for future divergence. However, a lake level fall of at least 600 m for Lake Malawi complementary analyses. We were able to obtain δ13C isotopic ratios during the megadrought (∼108,500 ybp) would result in a major from extremely small fossils and such fossils may also provide raw reduction in rocky habitat for cichlids with a greatly reduced region of material for DNA studies, tooth wear analyses and/or other biogeo- the west coastline available as ‘mbuna’ habitat (Cohen et al., 2007). While chemical studies.

Fig. 5. A — Scanning electron microscope (SEM) image of cichlid oral (buccal) tricuspid tooth from sample 24-E-3 (58.1–59.1 cm), 78.67 mblf, approximately 444 µm in length and 130,000 years old. Fig. 5B — SEM image of oral tricuspid tooth from sample 24-E-3 (58.1–59.1 cm), 78.67 mblf (meters below lake floor), approximately 766 µm in length and 130,000 years old. Fig. 5C. SEM image of pharyngeal tooth from cichlid or cyprinid from sample 24-E-3 (58.1–59.1 cm), 78.67 mblf, which is approximately 826 µm in length and 130,000 years old. Fig. 5D. Light microscopy image of pharyngeal tooth from sample 24-E-3 (58.1–59.1 cm), 78.67 mblf, approximately 600 µm in length and 130,000 years old. P.N. Reinthal et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 303 (2011) 126–132 131

The lack of more benthic isotopic signatures (higher δ13C values) could also be the result of ontogenetic dietary shifts in cichlids. Juvenile cichlids are found to have a mainly phytoplankton-based diet while sub-adults and adults consumed more epilithic algae. The mean δ13C values of five ontogenetic classes of Lake Malawi cichlids changed considerably with increasing body size (Genner et al., 2003). The fossils used in this study were all extremely small and would be from juvenile cichlids. δ13C values of the juvenile cichlids feeding on phytoplankton would be difficult to distinguish from δ13C values from juvenile cyprinids feeding on a similar diet. This is the first paleo-record of fish fossils from Lake Malawi and the first reported examples of δ13C values from Lake Malawi fish fossils. Such data are not only useful in understanding Lake Malawi's paleo-ichthyofauna, lake level fluctuations and the evolution of cichlid fishes but also provides a new methodology and framework for interpreting pelagic versus inshore fish faunas and in the region.

Acknowledgements Fig. 6. δ13C values for fish fossils from Lake Malawi core (values on upper x axis and ● each value (n=41) represented by ) and principal component 1 scores (Stone. pers. We thank reviewers William Patterson, John Lundberg, and Chris com) (values on lower x axis and represented by ―) versus age (ypb) of samples based on the age model from Scholz et al. (2007). The principal components analysis Scholz for comments and suggestions that led to a greatly improved (PCA) included the relative abundance of major groups (see Stone et al., this manuscript. Initial core processing was carried out at LacCore, the volume, for further details), relative abundance of major ostracode groups, percentages National Lake Core Repository at the University of Minnesota. Funding of vivianite, terrigenous minerals, and carbonate-coated grains, and log-concentrations for the field program was provided by the U.S. National Science of chaoborid fragments and ostracode valves. PCA of 18 variables and 438 samples was Foundation–ESH Program and the International Continental Scientific performed using CANOCO 4.5 (ter Braak and Šmilauer, 2002); variables were centered and standardized but otherwise untransformed. PCA scores were re-sampled to 200-yr Drilling Program, with additional funding for AC from the Smithsonian intervals and smoothed by singular spectrum analysis, using AnalySeries 1.2 (Paillard Institution (ETE and Fellowship Programs). We also thank D. Gauggler, et al., 1996). Positive PC1 scores represent minimum lake levels and negative PC1 scores R. Markus and L. Brooke McDonough for help with sample preparation. 13 represent maximum lake levels. δ C values indicating a benthic inshore fish were not This work was supported by NSF EAR-0602350 to the three authors. found until Lake Malawi started undergoing significant lake level fluctuations older We thank the government of Malawi for permission to undertake this than 60,000 ybp. research and Dr. D.S.C. Lewis for drawing Fig. 1.

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