Harmful Algae 10 (2010) 19–29
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Gulf menhaden (Brevoortia patronus): A potential vector of domoic acid in coastal Louisiana food webs Ross Del Rio a, Sibel Bargu a,*, Donald Baltz a, Spencer Fire b, Gary Peterson a, Zhihong Wang b a
Department of Oceanography and Coastal Sciences, School of the Coast and Environment, 1235 Energy, Coast & Environment Building, Louisiana State University, Baton Rouge, LA 70803, USA b Marine Biotoxins Program, NOAA/NOS Center for Coastal Environmental Health & Biomolecular Research, 219 Fort Johnson Road, Charleston, SC 29412, USA
A R T I C L E I N F O
A B S T R A C T
Article history: Received 9 February 2010 Received in revised form 25 May 2010 Accepted 26 May 2010
Harmful algal blooms are an increasing problem for coastal waters world-wide. The presence of the toxigenic diatom genus Pseudo-nitzschia is of concern in the Gulf of Mexico, due to the potential for several species in this genus to produce the neurotoxin domoic acid (DA). Louisiana coastal waters are of particular interest due to the presence of both toxin-producing species of Pseudo-nitzschia and abundant potential vectors. While trophic transfer of DA to consumers has repeatedly occurred along the California coast, little is known about trophic transfer of recently detected DA in the Gulf of Mexico. In this study, the presence of DA was investigated in filter-feeding gulf menhaden (Brevoortia patronus) and in seawater where high abundances of these fish reside. Pseudo-nitzschia presence and enumeration was determined using light microscopy, species identification in seawater and gulf menhaden gut contents was conducted with transmission electron microscopy (TEM), and DA quantification in corresponding seawater and tissue samples was determined by competitive enzyme-linked immunosorbent assay (cELISA). Examination of the phytoplankton revealed the presence of four species of Pseudo-nitzschia: P. calliantha for the first time, P. pseudodelicatissima, P. pungens, and P. americana, with P. calliantha as the dominant Pseudo-nitzschia species. Low levels of DA were detected in both seawater and fish samples, with a significant correlation between the two (n = 22, p = 0.043). Thus, for the first time in the Gulf of Mexico, a potential vector of DA has been identified, revealing the possibility of DA contamination in coastal Louisiana food webs. Published by Elsevier B.V.
Keywords: Pseudo-nitzschia Domoic acid Gulf menhaden Brevoortia patronus Louisiana Gulf of Mexico
1. Introduction Harmful algal blooms (HABs) are accumulations of algal biomass to ‘‘sufficient’’ levels for negative impacts to occur in the environment through their morphology, sheer biomass, or toxin production (Hallegraeff, 1993; Smayda, 1997; Glibert et al., 2005a). Incidents of HABs have increased with escalating eutrophication of coastal water bodies around the world (e.g. Glibert et al., 2005b). The negative consequences of a HAB pose a significant threat to the environment and human health which can damage ecosystem function (Glibert et al., 2005a). Despite the threat, the link between HABs and upper trophic level consumers has yet to be adequately investigated for many coastal systems. Due to increasing eutrophication from Mississippi River discharge, HAB species pose a threat to Louisiana coastal waters (Turner and Rabalais, 1994). Exacerbating this threat is the abundance of potential food web vectors in coastal Louisiana
* Corresponding author. Tel.: +1 225 578 0029; fax: +1 225 578 6326. E-mail address:
[email protected] (S. Bargu). 1568-9883/$ – see front matter . Published by Elsevier B.V. doi:10.1016/j.hal.2010.05.006
including oysters and planktivorous fishes. These conditions create a region that has a high potential for the rapid transfer of algal toxins to upper trophic level consumers. The dominant harmful algal group in coastal Louisiana is the pennate diatom genus Pseudo-nitzschia, of which some species are capable of producing a powerful neurotoxin called domoic acid (DA). Although these diatoms have been identified in the northern Gulf of Mexico since the 1910s, abundances of Pseudo-nitzschia have been increasing since the 1950s (Parsons et al., 2002). Currently, these diatoms are frequently detected at bloom concentrations (e.g. Dortch et al., 1997). Previous examinations of the Pseudo-nitzschia community in Louisiana coastal waters revealed six different species with two confirmed DA producers, Pseudo-nitzschia multiseries and P. pseudodelicatissima, two potentially toxic species, P. delicatissima and P. pungens, and two nontoxic species, P. subfraudulenta and P. americana, in abundances that have been documented to reach intense bloom concentrations of 108 cells l1 on the Louisiana continental shelf and 106 cells l1 in Terrebonne Bay, an inshore Louisiana estuary (Dortch et al., 1997; Parsons et al., 1999; Pan et al., 2001). Although presence of Pseudo-nitzschia has been well documented in Louisiana’s coastal
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waters, no studies have characterized the extent of its role in marine food webs of the northern Gulf of Mexico. DA has been responsible for both human and marine animal deaths around the world (Bates et al., 1989; Wright et al., 1989; Perl et al., 1990; Work et al., 1993; Scholin et al., 2000; Fire et al., 2009). Several major marine animal mass mortality events have occurred on the west coast of the U.S. including hundreds of brown pelicans (Pelecanus occidentalis), Brant’s cormorants (Phalacrocorax penicillatus), and California sea lions (Zalophus californianus) (Work et al., 1993; Scholin et al., 2000). In these instances, the main vector of DA was identified as a planktivorous fish, the northern anchovy (Engraulis mordax) (Work et al., 1993; Lefebvre et al., 1999, 2002; Scholin et al., 2000). Many other DA vectors including krill (Euphausia pacifica and Thysanoessa spinifera), market squid (Loligo opalescens), razor clams (Siliqua patula), and blue mussels (Mytilus edulis) have also been identified (Bates et al., 1989; Wright et al., 1989; Wekell et al., 1994; Bargu et al., 2002, 2003, 2008), but planktivorous fishes represent the most effective pathway for toxin transfer to these higher level organisms (Lefebvre et al., 2002). The efficiency of transfer is due, in part, to planktivorous fishes being highly mobile. They are able to potentially accumulate toxin from large geographic areas, can ingest high numbers of toxic phytoplankton due to their high filtration efficiency (Durbin and Durbin, 1975; Friedland et al., 1984), and are a direct link from toxic algae to large predators. In Louisiana, the gulf menhaden (Brevoortia patronus) represents a likely vector for the transmission of DA since it shares the same characteristics as the planktivorous fishes mentioned above. As a filter-feeding clupeid fish, gulf menhaden also occupy a similar niche (Ahrenholz, 1991) to the northern anchovy of California food webs. The gulf menhaden is an abundant, estuarine-dependent fish (Lassuy, 1983) that can filter the water column at, potentially, a high rate (as measured in the congener Atlantic menhaden, Brevoortia tyrannus, by Durbin and Durbin, 1975). Thus, it may be capable of accumulating large amounts of contaminants. Additionally, gulf menhaden are one of the most abundant fishes in the northern Gulf of Mexico, with Louisiana providing up to 52% of the juvenile abundance for the nation’s second largest fishery in terms of landings (Vaughan et al., 2007). They are also identified as a prominent prey item for several upper trophic level predators that are common in Louisiana estuaries, such as brown pelicans, bottlenose dolphins (Tursiops truncatus), and several species of shark (Hildebrand, 1963; Snelson et al., 1984; Ahrenholz, 1991; Hoffmayer and Parsons, 2003; Bethea et al., 2004; Barry et al., 2008; US Fish and Wildlife Service, 2008). One estuary that is at a particularly high risk of DA contamination of the food web in Louisiana is Terrebonne Bay. High amounts of Pseudo-nitzschia (106 cells l1) have been reported in this bay and adjacent Gulf of Mexico waters (Dortch et al., 1997), and like most Louisiana estuaries, there is a high abundance of gulf menhaden that reside in and around the Bay. Additionally, many upper trophic level predators (brown pelicans, bottlenose dolphins, sharks, etc.) use this area for foraging and nursery functions (Neer et al., 2007; Barry et al., 2008; US Fish and Wildlife Service, 2008; Miller and Baltz, 2010). Based on previous research and knowledge concerning DA and its vectors, the goal of the present study was to identify whether the gulf menhaden is a potential vector of DA to such higher trophic levels in Terrebonne Bay, Louisiana. 2. Materials and methods 2.1. Water and gulf menhaden sampling and initial processing Samples were acquired in Terrebonne Bay, Louisiana (298090 N, 908380 W) which is a typical representation of a Louisiana estuary
with shallow (50%).
Water samples collected from nearby Gulf of Mexico Stations C1, C3, and C4, during the month of April 2008 were also analyzed to determine Pseudo-nitzschia species identification. TEM revealed P. pseudodelicatissima (Fig. 6a) to be the dominant species for the selected samples, but P. americana (Fig. 6b) was also present.
Fig. 4. Counts of Pseudo-nitzschia abundance from the nearby Gulf of Mexico (Stations C1, C3, C4) over the entire study period. All of the points were transformed to fit the log scale by adding one.
3.4.1. Domoic acid in Terrebonne Bay and nearby Gulf of Mexico water DA was present in most of the Terrebonne Bay water samples over the entire study period. The frequency of detection was 72% for all particulate samples, and the extraction efficiency was 107.6%. Particulate DA in water samples from all the study sites ranged from below the detection limit (10 ng l1 methanolic extract) to 43.4 ng l1 (Fig. 7a). Highest particulate DA values in Terrebonne Bay were observed in April 2008 (Set 18), but corresponded to only moderate cell numbers of Pseudo-nitzschia (5 104 cells l1) in the nearby Gulf of Mexico waters. Particulate DA was not detected in some of the stations in Terrebonne Bay including Set 1 (July 2007), Sets 13 and 16 (September 2007), Sets 20 and 21 (April 2008), and Sets 23 and 24 (June 2008). Despite non-detectable levels of DA at some stations, Pseudo-nitzschia spp. was consistently present in the plankton community, and DA values were obtained in all months. Nearby Gulf of Mexico samples revealed variable, but higher levels of DA during the study period. The frequency of detection was 76%, and the concentrations of particulate DA ranged from below the detection limit (10 ng l1 methanolic extract) to 371 ng l1 (Fig. 7c). DA was highest in April 2008 with a mean value of 309 47 ng l1. No DA was detected during the entire month of August in 2007 or at Station C1 in July 2007 and June 2008. When combined with cell counts from the same samples, cellular quotas of DA ranged from below detection to 11 pg DA cell1. 3.4.2. Domoic acid in gulf menhaden visceral tissue Results from the cELISA revealed the presence of DA in gulf menhaden visceral tissue and had an extraction efficiency of 127% for gulf menhaden. Neither a dilution series assay nor a negative control were used in this analysis due to the lack of a clean sample, but the results of the LC–MS/MS substantiate the findings of the present study (see Section 3.4.3). Appropriate dilutions were made to obtain results within a valid working range for the assay
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Fig. 6. Pseudo-nitzschia specimens from nearby Gulf of Mexico water from April 2008 (a) Pseudo-nitzschia pseudodelicatissima, width = 2.29 mm, stria = 33 in 10 mm, fibulae = 19 in 10 mm. The poroids are arranged in one row with 6 in 1 mm. Inset photo is to show the poroid structure, (b) Pseudo-nitzschia americana, width = 1.79 mm, stria = 30 in 10 mm, fibulae = 20 in 10 mm. The poroids are arranged in 2–3 rows with 9 in 1 mm.
(10–300 pg ml methanolic extract1). DA concentrations ranged from below the detection limit to 0.31 mg DA g fish visceral tissue1 (Fig. 8), and were present in 96% of the samples tested. Maximum DA tissue concentrations were found during April 2008 (Set 17), temporally corresponding to highest particulate and dissolved DA in Terrebonne Bay (Set 18) and nearby Gulf of Mexico waters (Fig. 7). A Pearson’s correlation between gulf menhaden visceral DA concentration and Terrebonne Bay particulate DA concentration for all sampling sets was performed to investigate an observed relationship between particulate DA
in water and DA in gulf menhaden visceral tissue (n = 22, R2 = 0.189, p = 0.043). 3.4.3. LC–MS/MS confirmation of domoic acid in gulf menhaden visceral tissue Confirmation of DA by LC–MS/MS gave concentrations of 0.03 mg DA g1 for a gulf menhaden visceral tissue sample from April 2008 (Set 18) and 0.1 mg DA g1 for another individual visceral tissue sample from May 2008 (Set 22). The LC–MS/MS results corroborate those of the cELISA since the results were similar. Both menhaden visceral tissue samples showed higher abundance of DA isomers than those present in NRC standards (Fig. 9). The limit of quantification (LOQ) of this method using gulf menhaden viscera was 1.0 ng DA ml1 extract, and clearly distinguishable signal peaks were more than ten times greater than background noise for standards. 3.5. Gulf menhaden gut contents analysis A total of seven fish GIs were examined for the presence of Pseudo-nitzschia spp., as well as other planktonic groups that were consumed. The samples were chosen from April 2008 (Sets 17 and 18) and June 2008 (Set 25). The April samples were chosen due to their high DA concentrations either in menhaden viscera (Set 17) or the water (Set 18). The June sample (Set 25) was chosen because of its moderate DA values for water and fish viscera samples (to contrast the higher April DA concentrations), and it provides more temporal scaling since both of the other samples examined were taken in April.
Fig. 7. Domoic acid concentrations over the entire study from (a) particulate water samples (ng l1) from Terrebonne Bay, Louisiana and (b) particulate water samples (ng l1) from the nearby Gulf of Mexico.
Fig. 8. Domoic acid concentrations from Brevoortia patronus visceral tissue (mg g1) from Terrebonne Bay, Louisiana.
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Fig. 9. LC–MS/MS extracted ion chromatograms of the two major MRM transitions of DA: (a) a DA NRC standard (20 ng ml1) with MRM transitions at m/z 312 ! 161 and (b) m/z 312 ! 266, and a menhaden visceral tissue sample with MRM transitions at (c) m/z 312 ! 161 and (d) m/z 312 ! 266.
From each set, a maximum of three GIs were examined in triplicate using a light microscope; however, April 2008 (Set 17, FL = 20.5 cm) only had one GI to examine. Zooplankton was the most prevalent food item in April 2008 (Set 17), followed by centric diatoms, pennate diatoms (including P. calliantha), and finally dinoflagellates. The dominant members of the qualitative groups were copepods, Rhizsolenia spp. (identified by an end spike only), Navicula sp., and Prorocentrum spp., respectively. Menhaden from April 2008 (Set 18, FL = 19, 19.5, 19.5 cm) had a different diet composition with centric diatoms as the most dominant group. The dietary discrepancy may be due to the fact that they were sampled at a different location 6.4 km away from
Set 17. Dinoflagellates were the next most abundant, followed by pennate diatoms (including P. calliantha, P. pungens, and P. pseudodelicatissima), and zooplankton comprising only a small part of the diet. Rhizosolenia spp. (identified by an end spike only), other centrics, Prorocentrum spp., Protoperidinium spp., Pleurosigma spp., and copepods were the main constituents of their groups in the diet. The composition of the gut contents for these fish closely corresponded with the composition of both Terrebonne Bay and nearby Gulf of Mexico waters at the selected stations. Fish from June 2008 (Set 25, FL = 17.5, 20, 20 cm) had a diet composition different from both of the April 2008 menhaden samples and did not match with the corresponding water plankton community composition. Dinoflagellates were the main gut component found for this set, followed by centric diatoms, pennate diatoms (including Pseudo-nitzschia spp.), and zooplankton. The most prevalent members of the dinoflagellate community were Prorocentrum spp. and Ceratium spp., while Rhizosolenia spp. (identified by an end spike only) and Coscinodiscus spp. were the most frequently seen centric diatoms. Abundant pennate diatoms included Pleurosigma spp. and Navicula spp., and copepods and tintinnids comprised the majority of the zooplankton component in the gut. Pseudo-nitzschia frustules were found in all gut contents examined; however, attempts to conclusively verify the species present using light microscopy were unsuccessful. Therefore, TEM was used to identify the species of Pseudo-nitzschia in the gut contents from April 2008. However, most of the frustules found in the gulf menhaden gut contents were broken, likely a result of the gizzard-induced grinding of food particles. This made identification of specific epithet difficult in most cases. Gulf menhaden stomach contents from April 2008 revealed a dominant presence of P. calliantha (Sets 17 and 18, Fig. 10a and b, respectively), with P. pungens (Set 18, Fig. 10c) and P. pseudodelicatissima (Set 18, Fig. 10d) found equally at lower relative abundance. 4. Discussion In this study, toxic Pseudo-nitzschia has been shown to be a persistent member of the coastal Louisiana plankton community by being observed at all times sampled in Terrebonne Bay and in nearby Gulf of Mexico waters. Furthermore, the discovery of DA in
Fig. 10. Pseudo-nitzschia from Brevoortia patronus gut contents from April 2008 (a) Pseudo-nitzschia calliantha from Set 17, width = 1.8 mm, fibulae = 16 in 10 mm, stria = 38 in 10 mm. The poroids are arranged in one row with 5 in 1 mm, and are subdivided in the interior, (b) Pseudo-nitzschia calliantha from Set 18, width = 1.81 mm, stria = 40 in 10 mm, fibulae = 20 in 10 mm. The poroids are arranged in one row with 5 in 1 mm, and are subdivided in the interior, (c) Pseudo-nitzschia pungens from Set 18, width = 2.23 mm, stria = 20 in 10 mm, fibulae = 20 in 10 mm. The poroids are arranged in two rows with 3 in 1 mm, and (d) Pseudo-nitzschia pseudodelicatissima from Set 18, width = 1.4 mm, stria = 70 in 10 mm, fibulae = 10 in 10 mm. The poroids are arranged in one row with 8 in 1 mm.
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gulf menhaden viscera signifies the potential DA contamination into higher trophic levels in the area. Coastal Louisiana waters like Terrebonne Bay and the adjacent Gulf of Mexico are nourished by the input of nutrient-rich waters from the Mississippi River, and are capable of supporting a large and diverse plankton community. Both previous research in the area (e.g. Dortch et al., 1997) and the results of the present study show Louisiana coastal waters as home to a large, mixed assemblage of plankton including the toxigenic diatom genus Pseudo-nitzschia. As shown by the environmental parameters, the coastal Louisiana habitat is within Pseudo-nitzschia physiological tolerances (Bates et al., 1998). However, the results of the present study indicate that Pseudo-nitzschia made up a small portion of the highly diverse plankton community in Terrebonne Bay during July 2007–September 2007 and April 2008–June 2008. This dilution amongst many other plankton species may cause a reduction in the negative consequences usually associated with toxic Pseudonitzschia, although a more detailed examination of the plankton community structure in coastal Louisiana may be necessary to understand this issue. When examining the toxicity of Pseudo-nitzschia, speciesspecific identification is important because not all members of this genus produce DA. Moestrup and Lundholm (2007) have identified 11 species as being capable of producing DA from areas around the world. Previously in Louisiana, two toxic species have been identified: P. multiseries and P. cf. pseudodelicatissima, and two potentially toxic species: P. delicatissima and P. pungens (Parsons et al., 1999; Pan et al., 2001). In the present study, similar Pseudonitzschia species that are capable of producing DA were also found in Terrebonne Bay and nearby Gulf of Mexico waters such as P. pseudodelicatissima and P. pungens, but for the first time, P. calliantha was also identified. Previous studies in coastal Louisiana indicated that some of the morphologically similar species within the P. pseudodelicatissima/cuspidata complex (e.g. P. calliantha) were present, but inadequacies in morphological data may have prevented their species-specific identification. However, Lundholm et al. (2003) have allowed for the differentiation of P. calliantha from other species within the complex, allowing it to be identified for the first time in the Gulf of Mexico in Florida (Lundholm et al., 2003) and with this study, in Louisiana waters. Species identifications in this study were determined during periods of high DA levels in an attempt to identify the causative toxic species. However, some samples had high Pseudo-nitzschia cell counts that corresponded to low toxin levels. The lack of DA in the presence of Pseudo-nitzschia in August 2007 water samples reinforces the need for further and more detailed species-specific identification. These results suggest the presence of a non-toxic species for this month, but could also be a toxin-producing species not generating DA. DA levels detected in coastal Louisiana waters were generally low during the present study. A possible reason for this may be due to low cellular abundance within Terrebonne Bay at the times sampled. Pseudo-nitzschia was found to compose only part of the Terrebonne Bay plankton community which consisted of many different types of diatoms, dinoflagellates, and zooplankton. DA in nearby Gulf of Mexico water samples was generally similar to levels detected in Terrebonne Bay except in April 2008, where it was elevated by an order of magnitude, and in August 2007, when none was detected. Water DA concentrations found in this study were typically a few orders of magnitude lower, and cellular DA quotas were also less than previous animal mortality events (Work et al., 1993; Scholin et al., 2000). Despite being lower than previous events, the cellular DA from the present study were typically in the same range as those previously described for field and cultured cells from this region (Parsons et al., 1999; Pan et al., 2001). However, in April 2008 DA levels reached over double the
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maximum reported by Parsons et al. (1999), and the samples were dominated by P. calliantha. Generally for trophic transfer of algal toxins to occur, a filterfeeding intermediary is likely to act as a vector. In Louisiana, one vector candidate is the gulf menhaden. This study demonstrated that when DA was present in the water, gulf menhaden did contain the toxin in their visceral tissue relative to the water concentrations. These concentrations are far lower than the FDA regulatory limit for human consumption (20 mg DA g1 fish tissue), and several orders of magnitude lower than those found in California fish vectors, northern anchovy and Pacific sardine (Sardinops sagax), during acute marine animal mortality events (Work et al., 1993; Scholin et al., 2000; Lefebvre et al., 2002). However, one potential cause for the low DA values in the menhaden could be the lower cellular DA quotas found in this study, and at these low levels of cellular DA, much larger blooms of Pseudo-nitzschia would be required in order to see the same effects that have been observed in California. A significant correlation found between water and fish DA values suggests that when DA is found in the water, it would likely be found in gulf menhaden. The spring blooms of Pseudonitzschia coincide with the reoccurrence of gulf menhaden into the estuaries of Louisiana, like Terrebonne Bay, after the winter spawning season. This timing potentially exposes these fish to higher concentrations of DA in coastal Louisiana, which is then available to be transferred to upper trophic level predators such as brown pelicans, bottlenose dolphins, sharks, and other marine wildlife. Further research into DA production by local species of Pseudo-nitzschia during the spring could better show the potential risk of coastal Louisiana to DA contamination. More research is also needed to identify, for example, if gulf menhaden actively feed on Pseudo-nitzschia blooms or if there is avoidance, since they do not feed continuously. The concept of prey avoidance has previously been suggested by Friedland et al. (1989) when they found a lack of correlation in menhaden distribution around blooms of dinoflagellates and cyanobacteria, both of which are known to be associated with the production of toxic substances. These suggested studies could also provide an explanation for the low DA concentrations found in the fish in this study. Gulf menhaden are highly mobile fishes which can affect their toxin accumulation and distribution potential. Menhaden can migrate as far as 80 km offshore in winter (Vaughan et al., 2007), and the closely related Atlantic menhaden is capable of swimming up to 41 cm s1 (Durbin et al., 1980). This mobility can give menhaden the opportunity to take up or transport toxin from different locations in and around Terrebonne Bay. As an example, there was a spatial discrepancy in the data from the present study between the highest DA in the water and highest DA in gulf menhaden visceral tissue. Additionally, gut contents from June 2008 (Set 25) revealed a different qualitative composition from the water where it was captured showing that menhaden have the potential to transport DA throughout the estuarine system. These results show that gulf menhaden can transport dietary components from outside areas, and that they have the ability to transfer toxin from blooms not in their immediate area. As a moderately sized filter-feeding fish, gulf menhaden utilize a feeding strategy that results in the consumption of bulk suspended matter in the water column, and are therefore capable of consuming large quantities of toxic Pseudo-nitzschia when present. A study by Durbin and Durbin (1975) of the closely related Atlantic menhaden found the filtration rate of large specimens (25 cm FL) to be up to 34.8 l min1 fish1. Another study on juvenile Atlantic menhaden (13.8 cm FL) by Friedland et al. (1984) showed that filtration efficiency increased with increases in phytoplankton size or chain length, and that detritus presence aided filtration. The potentially toxic Pseudo-nitzschia species observed in the present study (P. pseudodelicatissima, P. pungens,
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and P. calliantha) have documented valve lengths in the range of 41–142 mm (Hasle and Syvertsen, 1996; Lundholm et al., 2003) which would be efficiently filtered by menhaden. Additionally, filtration of Pseudo-nitzschia species is enhanced by the formation of chains that can be in excess of 20 cells (pers. obs.), and the high amount of detritus present in estuarine systems. With such potentially rapid and efficient filtration rates, gulf menhaden could accumulate a large amount of DA during a Pseudo-nitzschia bloom which it could then transfer to a predator. Additionally, the gut contents analysis revealed copepods as a prey item which can serve as an important secondary pathway for DA uptake by gulf menhaden. Several studies have shown no differences in copepod feeding on toxic vs. non-toxic species of Pseudo-nitzschia, and that copepods can accumulate DA in their tissues (Lincoln et al., 2001; Maniero et al., 2005; Leandro et al., 2010). These studies indicate that copepods will feed on toxic Pseudo-nitzschia, if present, and may concentrate DA in their tissues prior to ingestion by menhaden which could increase the amount of toxin available for upper trophic level consumers in Louisiana. Other physical factors along the Louisiana coast that may enhance the gulf menhaden’s DA accumulation are wind patterns and current flow that control the exchange of water between Terrebonne Bay and the nearby Gulf of Mexico (Marmer, 1954; Prager, 1992; Inoue and Wiseman, 2000). By controlling the exchange of water into and out of the bay, these physical parameters control the distribution of phytoplankton. The example of April 2008 wind and wave patterns illustrate that the higher DA concentrations detected could have been from increased Pseudo-nitzschia presence in the Bay due to physical forcing. Therefore, gulf menhaden within Terrebonne Bay could be more likely to consume toxic Pseudo-nitzschia and normally low DA concentrations in the Bay could have been elevated due to the incoming Gulf water. The high abundance of gulf menhaden in coastal Louisiana clearly provides many opportunities for large amounts of DA to be taken up and potentially transferred to higher trophic levels. Gulf menhaden have been identified in many other studies as an important prey item for upper trophic level predators such as brown pelicans (Ahrenholz, 1991; US Fish and Wildlife Service, 2008), bottlenose dolphins (Barros and Wells, 1998), and many species of coastal shark (Snelson et al., 1984; Bethea et al., 2004; Barry et al., 2008). An investigation into this potential for several shark species is already underway, and preliminary data indicate that sharks do contain measurable amounts of DA in their tissues, i.e. GI, liver, and gills (Del Rio et al., unpublished data). This finding is in somewhat contrast to another study which investigated the effects of DA on leopard sharks (Triakis semifasciata) (Schaffer et al., 2006). In that study the sharks were found to completely depurate DA within two hours of intracoelomic injection. In light of the Schaffer et al. (2006) study, the presence of DA in natural populations of sharks warrants further investigation. Samples from a bottlenose dolphin mortality event during 2004 in the Florida panhandle were also found to contain DA (S. Fire, unpublished data). However, DA concentrations detected were relatively low and food web vectors have yet to be identified. As a common prey item, gulf menhaden have the ability to transfer DA to important apex predators by providing direct and indirect (zooplankton) links for toxic Pseudo-nitzschia. This study represents a significant first step in understanding the role of Pseudo-nitzschia in Louisiana coastal food webs. To more fully understand the threat DA poses to Louisiana food webs, research is needed to further investigate DA – gulf menhaden interactions (i.e. uptake rate, effects of DA) and to identify other potential vectors of DA in Gulf of Mexico food webs.
Acknowledgements This study was funded by the Louisiana Board of Regents under award number LEQSF (2007-10)-RD-A-02 to Sibel Bargu and the Louisiana State University Department of Oceanography and Coastal Sciences. We would like to thank Dr. Cindy Henk for her help with the TEM, and Dr. Gregory Stone for granting access to WAVCIS data and its interpretation. Finally, we would also like to thank Brian Milan, Elin Sandy, Jessica Czubakowski, Dr. Kari Galvan, Ana Cristina Garcia, and Benjamin Von Korff for their assistance either in the field or lab.[SS] References Ahrenholz, D.W., 1991. Population biology and life history of the North American menhadens, Brevoortia spp. Mar. Fish. Rev. 53 (4), 3–19. Bargu, S., Powell, C.L., Coale, S.L., Busman, M., Doucette, G.J., Silver, M.W., 2002. Krill: a potential vector for domoic acid in marine food webs. Mar. Ecol. Prog. Ser. 237, 209–216. Bargu, S., Marinovic, B., Mansergh, S., Silver, M.W., 2003. Feeding responses of krill to the toxin-producing diatom Pseudo-nitzschia. J. Exp. Mar. Biol. Ecol. 284, 87– 104. Bargu, S., Powell, C.L., Wang, Z., Doucette, G.J., Silver, M.W., 2008. Note on the occurrence of Pseudo-nitzschia australis and domoic acid in squid from Monterey Bay, CA (USA). Harmful Algae 7, 45–51. Barros, N.B., Wells, R.S., 1998. Prey and feeding patterns of resident bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, Florida. J. Mamm. 79 (3), 1045– 1059. Barry, K.P., Condrey, R.E., Driggers, W.B., Jones, C.M., 2008. Feeding ecology and growth of neonate and juvenile blacktip sharks Carcharhinus limbatus in the Timbalier-Terrebonne Bay complex, LA, USA. J. Fish. Biol. 73, 650–662. Bates, S.S., Bird, C.J., de Freitas, A.S.W., Foxall, R., Gilgan, M., Hanic, L.A., Johnson, G.R., McCulloch, A.W., Odense, P., Pocklington, R., Quilliam, M.A., Sim, P.G., Smith, J.C., Subba Rao, D.V., Todd, E.C.D., Walter, J.A., Wright, J.L.C., 1989. Pennate diatom Nitzschia pungens as the primary source of domoic acid, a toxin in shellfish from eastern Prince Edward island, Canada. Can. J. Fish. Aquat. Sci. 46, 1203–1215. Bates, S.S., Garrison, D.L., Horner, R.A., 1998. Bloom dynamics and physiology of domoic-acid-producing Pseudo-nitzschia species. In: Anderson, D.M., Cembella, A.D., Hallegraeff, G.M. (Eds.), Physiological Ecology of Harmful Algal Blooms. Springer-Verlag, Heidelberg, pp. 267–292. Bethea, D.M., Buckel, J.A., Carlson, J.K., 2004. Foraging ecology of the early life stages of four sympatric shark species. Mar. Ecol. Prog. Ser. 268, 245–264. Carlson, J.K., Brusher, J.H., 1999. An index of abundance for coastal species of juvenile sharks from the northeast Gulf of Mexico. Mar. Fish. Rev. 61 (3), 37–45. Dortch, Q., Robichaux, R., Pool, S., Milsted, D., Mire, G., Rabalais, N., Soniat, T., Fryxell, G.A., Turner, R.E., Parsons, M.L., 1997. Abundance and vertical flux of Pseudonitzschia in the northern Gulf of Mexico. Mar. Ecol. Prog. Ser. 146, 249–264. Durbin, A.G., Durbin, E.G., 1975. Grazing rates of the Atlantic menhaden Brevoortia tyrannus as a function of particle size and concentration. Mar. Biol. 33, 265–277. Durbin, A.G., Durbin, E.G., Verity, P.G., Smayda, T.J., 1980. Voluntary swimming speeds and respiration rates of a filter-feeding planktivore, the Atlantic menhaden, Brevoortia tyrannus (Pisces: Clupeidae). Fish. Bull. 78 (4), 877–886. Fire, S.E., Wang, Z., Leighfield, T.A., Morton, S.L., McFee, W.E., McLellan, W.A., Litaker, R.W., Tester, P.A., Hohn, A.A., Lovewell, G., Harms, C., Rotstein, D.S., Barco, S.G., Costidis, A., Sheppard, B., Bossart, G.D., Stolen, M., Durden, W.N., Van Dolah, F.M., 2009. Domoic acid exposure in pygmy and dwarf sperm whales (Kogia spp.) from southeastern and mid-Atlantic U.S. waters. Harmful Algae 8, 658–664. Friedland, K.D., Haas, L.W., Merriner, J.V., 1984. Filtering rates of the juvenile Atlantic menhaden Brevoortia tyrannus (Pisces: Clupeidae), with consideration of the effects of detritus and swimming speed. Mar. Biol. 84, 109–117. Friedland, K.D., Ahrenholz, D.W., Guthrie, J.F., 1989. Influence of plankton on distribution patterns of the filter-feeder Brevoortia tyrannus (Pisces: Clupeidae). Mar. Ecol. Prog. Ser. 54, 1–11. Glibert, P.M., Anderson, D.M., Gentien, P., Graneli, E., Sellner, K.G., 2005a. The global, complex phenomena of harmful algal blooms. Oceanography 18, 136–147. Glibert, P.M., Seitzinger, S., Heil, C.A., Burkholder, J.M., Parrow, M.W., Codispoti, L.A., Kelly, V., 2005b. The role of eutrophication in the global proliferation of harmful algal blooms: new perspectives and new approaches. Oceanography 18, 198–209. Hallegraeff, G.M., 1993. A review of harmful algal blooms and their apparent global increase. Phycologia 32, 79–99. Hasle, G.R., Syvertsen, E.E., 1996. Marine diatoms. In: Tomas, C.R. (Ed.), Identifying Marine Diatoms and Dinoflagellates. Academic Press, San Diego, USA, pp. 5– 385. Hildebrand, S.F., 1963. Family clupeidae. In: Olsen, Y.H. (Ed.), Fishes of the Western North Atlantic. Sears Found. Mar. Res., vol. 3. pp. 257–454. Hoffmayer, E.R., Parsons, G.R., 2003. Food habits of three shark species from Mississippi Sound in the northern Gulf of Mexico. Southeastern Naturalist 2, 271–280. Inoue, M., Wiseman, W.J., 2000. Transport, mixing and stirring processes in a Louisiana estuary: a model study. Est. Coast Shelf Sci. 50, 449–466.
R. Del Rio et al. / Harmful Algae 10 (2010) 19–29 Lassuy, D.R., 1983. Species Profiles: Life Histories and Environmental Requirements (Gulf of Mexico) – Gulf Menhaden. U.S. Fish and Wildlife Service. Division of Biological Sciences, FWS/OBS-82/11.2 U.S. Army Corps of Engineers, TR FL-82-4, p. 13. Leandro, L.F., Teegarden, G.J., Roth, P.B., Wang, Z., Doucette, G.J., 2010. The copepod Calanus finmarchicus: a potential vector for trophic transfer of the marine algal biotoxin, domoic acid. J. Exp. Mar. Biol. Ecol. 382, 88–95. Lefebvre, K.A., Powell, C.L., Busman, M., Doucette, G.J., Moeller, P.D.R., Silver, J.B., Miller, P.E., Hughes, M.P., Singaram, S., Silver, M.W., Tjeerdema, R.S., 1999. Detection of domoic acid in northern anchovies and California sea lions associated with an unusual mortality event. Nat. Toxins 7, 85–92. Lefebvre, K.A., Silver, M.W., Coale, S.L., Tjeerdema, R.S., 2002. Domoic acid in planktivorous fish in relation to toxic Pseudo-nitzschia cell densities. Mar. Biol. 140, 625–631. Lincoln, J.A., Turner, J.T., Bates, S.S., Leger, C., Gauthier, D.A., 2001. Feeding, egg production, and egg hatching success of the copepods Acartia tonsa and Temora longicornis on diets of the toxic diatom Pseudo-nitzschia multiseries and the non-toxic diatom Pseudo-nitzschia pungens. Hydrobiologia 453/454, 107–120. Lundholm, N., Moestrup, Ø., Hasle, G.R., Hoef-Emden, K., 2003. A study of the Pseudo-nitzschia pseudodelicatissima/cuspidata complex (Bacillariophyceae): what is P. pseudodelicatissima? J. Phycol. 39, 797–813. Maniero, I., Iglesias, P., Guisande, C., Riveiro, I., Barreiro, A., Zervoudaki, S., Grane´li, E., 2005. Fate of domoic acid ingested by the copepod Acartia clausi. Mar. Biol. 148 (1), 123–130. Marmer, H.A., 1954. Tides and sea level in the Gulf of Mexico. Fish. Bull. 55, 101– 118. Miller, C.E., Baltz, D.M., 2010. Environmental characterization of seasonal trends and foraging habitat of bottlenose dolphins (Tursiops truncatus) in northern Gulf of Mexico bays. Fish. Bull. 108 (1), 79–86. Moestrup, Ø., Lundholm, N., 2007. Intergovernmental Oceanographic Commission Taxonomic Reference List of Toxic Plankton Algae. , accessed 30 March:http:// www.bi.ku.dk/ioc/group1.asp. Neer, J.A., Blackburn, J.K., Thompson, B.A., 2007. Shark nursery areas of central Louisiana’s nearshore coastal waters. Am. Fish. Soc. Symp. 50, 317–330. Pan, Y.L., Parsons, M.L., Busman, M., Moeller, P.D.R., Dortch, Q., Powell, C.L., Doucette, G.J., 2001. Pseudo-nitzschia sp. cf. pseudodelicatissima – a confirmed producer of domoic acid from the northern Gulf of Mexico. Mar. Ecol. Prog. Ser. 220, 83–92. Parsons, M.L., Scholin, C.A., Miller, P.E., Doucette, G.J., Powell, C.L., Fryxell, G.A., Dortch, Q., Soniat, T.M., 1999. Pseudo-nitzschia species (Bacillariophyceae) in Louisiana coastal waters: molecular probe field trials, genetic variability, and domoic acid analyses. J. Phycol. 35, 1368–1378. Parsons, M.L., Dortch, Q., Turner, R.E., 2002. Sedimentological evidence of an increase in Pseudo-nitzschia (Bacillariophyceae) abundance in response to coastal eutrophication. Limnol. Oceanogr. 47, 551–558.
29
Parsons, T.R., Maita, Y., Lali, C.M., 1984. A Manual of Chemical and Biological Methods for Seawater Analysis. Pergamon, Oxford. Perl, T.M., Bedard, L., Kosatsky, T., Hockin, J.C., Todd, E.C.D., Remis, R.S., 1990. An outbreak of toxic encephalopathy caused by eating mussels contaminated with domoic acid. N. Engl. J. Med. 322, 1775–1780. Prager, E.J., 1992. Modeling of circulation and transport in Terrebonne Bay, Louisiana, and its implications for oyster harvesting management. Ph.D. dissertation. Louisiana State University, Baton Rouge, LA. Schaffer, P., Reeves, C., Casper, D.R., Davis, C.R., 2006. Absence of neurotoxic effects in leopard sharks, Triakis semifasciata, following domoic acid exposure. Toxicon 47, 747–752. Scholin, C.A., Gulland, F., Doucette, G.J., Benson, S., Busman, M., Chavez, F.P., Cordaro, J., DeLong, R., De Vogelaere, A., Harvey, J., Haulena, M., Lefebvre, K., Lipscomb, T., Loscutoff, S., Lowenstine, L.J., Marin, R., Miller, P.E., McLellan, W.A., Moeller, P.D.R., Powell, C.L., Rowles, T., Silvagni, P., Silver, M.W., Spraker, T., Trainer, V., Van Dolah, F.M., 2000. Mortality of sea lions along the central California coast linked to a toxic diatom bloom. Nature 403, 80–84. Smayda, T.J., 1997. What is a bloom? A commentary. Limnol. Oceanogr. 42, 1132– 1136. Snelson, F.F., Mulligan, T.J., Williams, S.E., 1984. Food habits, occurrence, and population structure of the bull shark, Carcharhinus leucas, in Florida coastal lagoons. Bull. Mar. Sci. 34, 71–80. Turner, R.E., Rabalais, N.N., 1994. Coastal eutrophication near the Mississippi river delta. Nature 368, 619–621. US Environmental Protection Agency, 1999. Ecological Condition of Estuaries in the Gulf of Mexico. EPA 620-R-98-004. U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Gulf Ecology Division, Gulf Breeze, Florida. US Fish and Wildlife Service, 2008. Brown Pelican Pelecanus occidentalis. Dept. Interior, p. 2. Vaughan, D.S., Shertzer, K.W., Smith, J.W., 2007. Gulf menhaden (Brevoortia patronus) in the US. Gulf of Mexico: fishery characteristics and biological reference points for management. Fish. Res. 83, 263–275. Wekell, J.C., Gauglitz, E.J., Barnett, H.J., Hatfield, C.L., Eklund, M., 1994. The occurrence of domoic acid in razor clams (Siliqua patula). Dungeness crab (Cancer magister), and anchovies (Engraulis mordax). J. Shellfish Res. 13, 587–593. Work, T.M., Beale, A.M., Fritz, L., Quilliam, M.A., Silver, M.W., Buck, K., Wright, J.L.C., 1993. Domoic acid intoxication of brown pelicans and cormorants in Santa Cruz, California. In: Smayda, T.J., Shimizu, Y. (Eds.), Toxic Phytoplankton Blooms in the Sea. Elsevier Science Publishers, pp. 643–649. Wright, J.L.C., Boyd, R.K., de Fritas, A.S.W., Falk, M., Foxall, R.A., Jamieson, W.D., Laycock, M.V., McCulloch, A.W., McInnes, A.G., Odense, P., Pathak, V.P., Quilliam, M.A., Ragan, M.A., Sim, P.G., Thibault, P., Walter, J.A., Gilgan, M., Richard, D.J.A., Dewar, D., 1989. Identification of domoic acid, a neuroexcitatory amino acid, in toxic mussels from eastern Prince Edward Island. Can. J. Chem. 67, 481–490.
