Fish settlement in the ocean vs. estuary: Comparison of pelagic larval and settled juvenile composition and abundance from southern New Jersey, U.S.A.

Transcription

1 Estuarine, Coastal and Shelf Science 66 (2006) 280e290 Fish settlement in the ocean vs. estuary: Comparison of pelagic larval and settled juvenile composition and abundance from southern New Jersey, U.S.A. Kenneth W. Able a, *, Michael P. Fahay b, David A. Witting c, Richard S. McBride d, Stacy M. Hagan a a Rutgers University, Institute of Marine and Coastal Sciences, Marine Field Station, 800 c/o 132 Great Bay Boulevard, Tuckerton, NJ , USA b NOAA/NMFS/NEFSC, Howard Marine Laboratory, 74 Magruder Road, Highlands, NJ 07732, USA c NOAA/MSRP 501 W. Ocean Boulevard. Suite 4200, Long Beach, CA , USA d Florida Marine Research Institute, 100 Eighth Avenue SE, St. Petersburg, FL 33701, USA Received 31 July 2003; accepted 2 September 2005 Available online 28 November 2005 Abstract To describe the larval and juvenile fish fauna and to evaluate the relative contribution of the ocean and the estuary as settlement areas for benthic species, we compared the composition and abundance of larval fish supply to that of recently settled juvenile fishes in both ocean and an adjacent estuary habitats in southern New Jersey. The study was conducted from May to November 1992 in the Great BayeLittle Egg Harbor estuary (<1e8 m sampling depth) and on the adjacent inner continental shelf in the vicinity of Beach Haven Ridge (8e16 m). During the study more larvae nearing settlement (postflexion) were captured in the estuary than in the ocean. Settlement occurred earlier in the estuary than in the ocean perhaps under the influence of earlier, seasonal warming of estuarine waters. There appeared to be two spatial patterns of settlement in the study area based on the dominant species (n ¼ 17) represented by a sufficient number of individuals (n 25 individuals). There were species that primarily settle in the estuary, as represented by both estuarine residents (n ¼ 3) and transients (n ¼ 4), and those that settle in both the estuary and the ocean (n ¼ 10). However, there were no species whose larvae were present in the estuary yet settle in the ocean. The fact that many of the species settle in both the estuary and the ocean indicates an overlap between these habitats because, at least for some species, these habitats may function in the same way. Further resolution of fish settlement patterns, and its influence on recruitment will need to rely on synoptic comparisons between estuaries and the ocean over multiple years. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: fishes; settlement; metamorphosis; benthic; estuarine; ocean 1. Introduction The period of settlement in the life history of fishes has received more attention in recent years because it is increasingly recognized that important morphological, physiological, and behavioral transitions occur simultaneously with the habitat transitions that are typical of this period (Moser, 1981; Balon, * Corresponding author. address: able@marine.rutgers.edu (K.W. Able). 1984; Youson, 1988; Kaufman et al., 1992; Keefe and Able, 1993, 1994; McCormick, 1998). In addition, predation may influence successful settlement. For example, the generally small size of individuals during and immediately after settlement makes these especially susceptible to predators (Carr and Hixon, 1995; Witting and Able, 1995; McCormick and Kerrigan, 1996; Modin and Pihl, 1996; Steele, 1997; Wennhage, 2000; Webster, 2002). Increasingly, empirical evidence has accumulated emphasizing the importance of metamorphosis and settlement for coral reef (Victor, 1991; Öhman et al., 1998; Doherty, 2002; Hixon and Webster, 2002; McCormick /$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi: /j.ecss

2 K.W. Able et al. / Estuarine, Coastal and Shelf Science 66 (2006) 280e et al., 2002 for reviews) and occasionally freshwater fishes (Geffen and Nash, 1992). However, for temperate marine fishes, especially those on the continental shelf, the importance of settlement effects on recruitment variation is less well-known with some exceptions (e.g. van der Veer and Bergman, 1987; Tanaka et al., 1989; Levin, 1991, 1993, 1994; Tupper and Boutilier, 1995a,b; Sullivan et al., 2000). The difficulty in studying settlement is magnified by the episodic nature of arriving competent larvae or recently settled juveniles over short time spans for a variety of taxa (e.g. Victor, 1986a,b; Doherty, 1987; Robertson et al., 1988; Milicich et al., 1992). While the importance of benthic habitat has been generally recognized for a variety of faunal groups (see Rosenzweig, 1991; Oksanen et al., 1992; Benaka, 1999; Rodwell et al., 2003) this recognition often does not extend to recently settled fishes and when it does, it is primarily for tropical reef fishes. However, recent investigations in temperate estuaries have highlighted the importance of settlement (Petrik et al., 1999; Amara et al., 2000), including our study estuary (e.g. Keefe and Able, 1994; McBride et al., 2002; Martino and Able, 2003) and occasionally the continental shelf (Steves et al., 1999; Sullivan et al., 2000, 2003) habitats. To our knowledge there are no studies that have examined settlement across the estuaryeocean transition. The objectives of this study were to (1) describe the larval and juvenile fish composition on the inner continental shelf site off southern New Jersey and in the adjacent Great Baye Little Egg Harbor estuary, and (2) determine the pattern of settlement between the estuary and the ocean. For these purposes, we took advantage of some existing sampling programs in the estuary and designed others in the ocean. We focused on this area, in part, because of the wealth of related studies of fishes in the region Study sites Our definition of estuary follows the definition of Pritchard (1967) and includes the semi-enclosed waters of Great Bay and Little Egg Harbor (Fig. 1). The ocean sampling sites are all seaward of this estuary (Fig. 1). These inner continental shelf sites were centered around Beach Haven Ridge, which is of Holocene age (Stahl et al., 1974) and representative of the abundant sand ridges along the east coast of the U.S. (McBride and Moslow, 1991; Trowbridge, 1995). This 7-km long ridge extends northeastward from the ebb tidal delta of Little Egg Inlet, New Jersey (Twichell and Able, 1993). It is about 1 km wide along its central and southern portions and broadens to 1.5 km at the northeastern end. It has a maximum relief of 8 m between the ridge crest and the trough on the seaward side and 4e5 m relief between the ridge crest and the trough on the shoreward side. A sidescan sonar mosaic based on observations in 1991 and subsequent ROV observations indicates that the surficial sediments are complex and heterogeneous (Twichell and Able, 1993; Craghan, 1995; Able et al., 2003). On the inner continental shelf in the vicinity of Little Egg Inlet (Fig. 1), there is a general southward flow that is modulated by buoyancy from freshwater (estuarine) inputs and wind stress (Wong, 1999; Munchow and Chant, 2000). Cross-shelf Fig. 1. Study sites for fish settlement in the coastal ocean around Beach Haven Ridge and the adjacent Great BayeLittle Egg Harbor estuaries. Locations for sampling of larvae and recently settled juveniles are indicated. See Table 1 for other details concerning sampling effort for these locations. transport is driven by the alongshore winds. There may be multiple water masses in the sampling region. Drifters on the inner shelf, deployed 1e2 km from the inlet, were drawn into the estuary on flood tides particularly from northeast and east of the inlet (Charlesworth, 1968). This shelf water reaches several kilometers into the estuary during flood tides (Witting et al., 1999; Chant et al., 2000). The adjacent Great Bay, a drowned river valley, and Little Egg Harbor, a barrier beach estuary, are relatively shallow (1.7 m at depth at mean low water) systems (Fig. 1) that are surrounded by extensive stands of Spartina alterniflora. These water bodies share many qualities with other estuaries on the east coast of the U.S. including a moderate tidal range from <0.7 m in Little Egg Harbor to 1.1 m (Chant et al., 2000) near the mouth of Great Bay (Chizmadia et al., 1984; Durand, 1984; Able et al., 1992; Chant, 2001; Kennish, 2001). The fishes of these estuaries have been the focus of intensive study for more than a decade (Able and Fahay, 1998; Jivoff and Able, 2001) with some emphasis on the larvae of resident and transient fishes (Witting et al., 1999). Together, these estuaries and the adjacent continental shelf in the vicinity of Beach Haven Ridge comprise a large portion of the Jacques Cousteau National Estuarine Research Reserve (Psuty et al., 1993; Kennish, 2004). 2. Materials and methods Larvae and recently settled juveniles were collected with plankton nets and beam trawls, respectively (Table 1). Sampling on the inner continental shelf, hereafter referred to as

3 282 K.W. Able et al. / Estuarine, Coastal and Shelf Science 66 (2006) 280e290 Table 1 Sampling effort for plankton larvae and recently settled fishes from the ocean (Beach Haven Ridge) and adjacent estuary (Great BayeLittle Egg Harbor) during MayeNovember See Fig. 1 for sampling locations Study area Sampling gear Depth range (m) Beach Haven Ridge Planktonic Benthic 11 m Tucker trawl (0.505 mm mesh) 2-m beam trawl (6 mm mesh) Great BayeLittle Egg Harbor estuary Planktonic 1 m plankton net (1 mm mesh) Benthic 1 m beam trawl (6 mm mesh) Sampling frequency Number of sampling locations Number of tows 5e15 Biweekly/monthly e15 Biweekly/monthly Weekly <1e8 Monthly Total number of fish collected the ocean, occurred at three fixed locations near Beach Haven Ridge (Fig. 1); one landward of the ridge (approximately 6e 10 m depth), one on the top of the ridge (approximately 8 m depth), and the other seaward of the ridge (approximately 12e14 m depth) (see Hales et al., 1995). Sampling frequency was every two to four weeks from May to November Larvae were sampled with a double, step-oblique tow, using a Tucker trawl, from the surface to the bottom (3 min) and from the bottom back to the surface (6 min) during the day. In the ocean, recently settled juveniles were collected with 2 m beam trawl (3 mm mesh cod end) with three replicate tows landward and seaward of the ridge and only two replicate tows on top of the ridge. In the estuary, larvae were sampled weekly on night flood tides from a bridge that spans Little Sheepshead Creek (Witting et al., 1999). The bridge is located approximately 5.5 km from Little Egg Inlet and 9.5 km from Beach Haven Ridge (Fig. 1). The plankton net was set in Little Sheepshead Creek for three separate 0.5 h hauls, once each week during the study period. This location affords the opportunity to sample larval fishes ingressing into this estuary as Atlantic Ocean water flows into the estuary through Little Egg Inlet during flood tides and some of this flow is directed into Little Sheepshead Creek, a thoroughfare through the peninsula behind Little Egg Inlet (Charlesworth, 1968; Chant et al., 2000). In the estuary, recently settled juveniles were collected with three replicate tows of a 1 m beam trawl (3 mm mesh cod end) at 12 fixed locations (Fig. 1, Table 1). For all sampling techniques, fish were identified to species, enumerated and all or a subsample (n ¼ 20 fish) measured after preservation. Fish > 25 mm standard length (SL) were measured to the nearest 1 mm, while fish < 25 mm SL were measured to the nearest 0.1 mm. Fish density was quantified by estimating volume or area sampled with a flow-meter (for both ichthyoplankton sampling techniques) or a meter wheel (for beam trawl collections). Density is presented as mean number of fish 1 standard error (SE). Further details of some sampling procedures and area covered in the ocean are provided by Hales et al. (1995) and McBride et al. (2002), and in the estuary by Witting et al. (1999). For the purpose of this study the term larva was used for all sizes and stages of fishes collected in plankton tows. Larvae were staged as preflexion, flexion, and postflexion, based on the position of the posterior portion of the notochord and development of the hypural bones (Kendall et al., 1984). Larvae were assigned to the flexion stage once cartilage began to form on the ventral edge of the notochord tip and as long as the tip remained posterior to the posterior edge of the hypurals. Specimens collected in beam trawls were referred to as recently settled juveniles. Age 1 and older juveniles were omitted from trawl collection data based on length, as presented in Able and Fahay (1998). Pelagic species, which do not settle, such as engraulids, clupeids, etc., were included in the faunal list for sake of completeness. However, only those that settle to benthic habitats are considered in detail. Rare species, i.e. those represented by <25 individuals across all samples, were also eliminated from further consideration. During all benthic collections temperature and salinity were measured from near bottom water samples, using a stem thermometer, and refractometer, respectively. Water depth was recorded at the beginning of all tows with an electronic depth sounder Analysis Because the assumptions (i.e. normality and homogeneity of variance) necessary for analysis of variance (ANOVA) were not met for some species, species-specific comparison of fish density were analyzed with nonparametric statistics. For each life stage (n ¼ 2 tests; larval and juvenile) and species, separate KruskaleWallis tests were used to test the effect of habitat (ocean and estuary) on fish density. Significant ( p < 0.003, Bonferroni adjusted) differences indicate higher density of a species in a particular habitat, while nonsignificant results indicate similar densities among habitats. Tests were not conducted on species that do not settle (i.e. pelagic juveniles). For each life stage, overall lengths collected were also tested for effect of habitat by KruskaleWallis (significance ¼ p < 0.05). To determine assemblage structure of recently settled juveniles, principal components analysis (PCA) was performed on the correlation matrix of log-transformed mean density of dominant fish (>25 individuals total). PCA is an iterative

4 K.W. Able et al. / Estuarine, Coastal and Shelf Science 66 (2006) 280e regression technique that seeks to reduce variation onto the few most important latent trends, i.e. gradients in species abundance (Pielou, 1984). After the important factors were determined, the eigenvector loadings for each species were examined for significant correlation ( p < 0.003, Bonferroni adjusted) with each factor. As a result, if species X is positively correlated with Factor Y and Factor Y separated ocean (positive) and estuarine (negative) assemblages, then species X is representative of the ocean assemblage. 3. Results and discussion 3.1. Physical characteristics During MayeNovember 1992, temperatures in the ocean and estuary sampling sites were generally overlapping at 13.5e21.8 C, 12.2e24.8 C, respectively, but they varied by month (Fig. 2). Temperatures were higher at the estuarine sites than the ocean from May to August and lower in the estuary than the ocean during September and October. Temperatures in the estuary showed a relatively abrupt decrease of approximately 10 C from August to September. A similar decrease occurred in the ocean from September to October. Because the average temperatures in the estuary were consistently warmer by several degrees during the spring and summer (MayeAugust), this may provide a metabolic advantage, by enhancing growth (Deegan et al., 2000), for species which settle in the estuary. The relationship between ocean and estuary temperatures in the summer was reversed from September to October due to the response of shallow estuarine waters to the seasonal cooling of air temperatures. This seasonal cooling, which occurs at approximately the same time every year (Kennish and O Donnell, 2002), may provide the cue for the seasonal egress of settled fishes from the estuary into the ocean, as frequently observed for a number of species (Able and Fahay, 1998). The salinities in the ocean were relatively constant (30e31) throughout the study, while salinities in the estuary fluctuated Fig. 2. Mean temperature ( C) and salinity 1 standard error at estuary and ocean sites during 1992 based on bottom sampling. (16e31). The lowest salinities encountered in the estuary in August were associated with a heavy rain event several days prior to sampling. The general patterns in estuary vs. ocean temperature and salinity observed are consistent with patterns observed in other years (McBride and Able, 1994; Martino and Able, 2003) Constraints of the sampling program Several factors could have influenced the interpretation of settlement patterns in this study. First, the sampling occurred during a single year and it is clear that annual variation in occurrence and abundance of many species occurs in the study estuary (Able and Fahay, 1998). Second, the monthly limits of the sampling period were constrained by the available data sets. Thus, sampling earlier in the spring (prior to May) or in the winter (after November) could influence our interpretation for the few species that use the study area in the winter (Able et al., 1996; Able and Fahay, 1998). Third, differences in gears between the estuary and the ocean, could bias the analyses but we doubt that this has profound effects (see below). Fourth, while most sampling occurred during the day, the sampling for larval fishes in the estuary occurred at night. This was necessary because day vs. night comparison collected very few larvae during the day (Able, unpubl. data) perhaps because of net avoidance by the larger postflexion larvae (see below) Size and stage composition The size of larval and recently settled juvenile fishes varied from planktonic to benthic samples and to some degree between the estuary and the ocean (Fig. 3). Planktonic larvae collected in the ocean (x ¼ 8.1 mm SL, median ¼ 5 mm SL) were significantly smaller than those in the estuary (x ¼ 20.4 mm SL, median ¼ 13 mm SL; KruskaleWallis: c 2 ¼ 247.1, p < ). Larvae < 20 mm SL dominated ocean and estuarine samples, however, fish of this size occurred more frequently (96%) in ocean than in the estuary (63%). The size of recently settled juveniles in the estuary (x ¼ 54.1 mm SL, median ¼ 40 mm SL) was larger than in the ocean (x ¼ 34.9 mm SL, median ¼ 23 mm SL; Kruskale Wallis: c 2 ¼ 358.4, p < ). Although the size range of juveniles was similar in ocean (9e200 mm SL) and estuary (10e195 mm SL), fish < 40 mm SL occurred more frequently in the ocean (78%) than the estuary (48%). While the sampling programs in the estuary and the ocean developed from different research needs, and slightly different gears, our ability to assess abundance of late-stage larvae nearing settlement and recently settled juveniles was largely successful. Collections from the estuary and the ocean frequently sampled larvae < 30 mm SL, a size range that would cover settlement sizes in many local species (see Able and Fahay, 1998). The collection of some larger larvae in estuarine ichthyoplankton collections is due, in part, to the occurrence of elongate forms such as Conger oceanicus, which are seldom collected in oceanic waters (Able and Fahay,

5 284 K.W. Able et al. / Estuarine, Coastal and Shelf Science 66 (2006) 280e290 Fig. 3. Length composition of fish from planktonic and benthic collections of fishes in the estuary and the ocean during MayeNovember Sample sizes based on number of measured individuals. 1998; Bell et al., 2003). The collections of recently settled juveniles from the estuary and the ocean had similar size ranges, with fish from 10 to 40 mm well-represented in the collections. The stages of larval fish collected varied dramatically from the estuary to the ocean (Table 2, Fig. 4). Most (77%) preflexion larvae were collected in the ocean and most (90%) postflexion larvae were collected in the estuary with flexion stage larvae nearly equally divided between the two habitats. Preflexion larvae in the ocean were dominated by Centropristis striata, Cynoscion regalis, Micropogonias undulatus, and Prionotus spp. All species analyzed from the estuary were predominantly postflexion stage with the exception of C. regalis, M. undulatus, and Pseudopleuronectes americanus, which were primarily at flexion stage (Table 2) Monthly abundance The density of larvae and recently settled juveniles was affected by both habitat and month (Fig. 5). The mean density of larvae in the estuary (118.2 fish 1000 m ÿ3 ) was higher than that in the ocean (41.6 fish 1000 m ÿ3 ). This pattern was most evident during June and early July but was similar thereafter except for one sampling date in late July. The high larval abundance in the estuary in June and July is characteristic of the summer assemblage (Witting et al., 1999) and was Table 2 Flexion stage and size of larvae for a subset of larvae collected in ocean and estuarine habitats during 1992 from MayeNovember Species Ocean Estuary Preflexion Flexion Postflexion Total Preflexion Flexion Postflexion Percent Size range Percent Size range Percent Size range measured Percent Size range Percent Size range Percent Size range Total measured Ammodytes americanus e e e e e e e 13 e e e e e42.9 Anchoa mitchilli e e e e e e4 Brevoortia tyrannus e9.2 e e e e e e25.1 Centropristis striata e e e e e e e22.4 Cynoscion regalis e e4.7 e e e e e10.8 Etropus microstomus e13 77 e e e e e21.1 Gobiosoma bosc e e e e e e e 86 e e e25 Gobiosoma ginsburgi 1 e e e e e e e16.7 Menidia menidia e e e e e e e 8 e e e e e33.2 Micropogonias undulatus e e e e e e e15.7 Pseudopleuronectes americanus e e e e e e e 7 e e e Prionotus carolinus e e9.5 2 e e e e e19.8 Prionotus evolans e e e e e e e 10 e e e e e14.5 Scophthalmus aquosus e e e e e e13.2 Symphurus plagiusa e e e e e e e 4 e e e e e11.5 Syngnathus fuscus 13 e e e e e88 12 e e e e e71.4 Tautoga onitis e e e e e e e21.8 Tautogolabrus adspersus e5.1 e e 3 e e e e e21.1

6 K.W. Able et al. / Estuarine, Coastal and Shelf Science 66 (2006) 280e program, while more extensive (3 years) but not as intensive temporally, found the same pattern of increased abundance of juveniles in the ocean in the fall (September) relative to the summer (July) (Martino and Able, 2003). The pattern of earlier occurrence of larvae and recently settled juveniles in the estuary relative to the ocean may be due to the earlier warming of the shallow estuary (Fig. 2) and earlier reproduction in the estuary vs. the ocean. Fig. 4. Stages of larvae of benthic species in estuary vs. ocean samples during MayeNovember Number over each bar indicates sample sizes. dominated in 1992 by Syngnathus fuscus, as in other years (Witting et al., 1999). The single peak in late July was due to Gobiosoma bosc (n ¼ 247), Tautoga onitis (n ¼ 210), and Etropus microstomus (n ¼ 128). Increasing numbers of recently settled individuals in the estuary began in late June and extended to a peak in late August (Fig. 5), presumably due to settlement by larvae by resident and ingressing individuals from the ocean. The abundance of recently settled fishes declined thereafter. In the ocean, the peaks in larval abundance were not as pronounced but the highest numbers occurred in late July and October, a pattern similar to that observed during 1972e1975 at the same site (Able and Hagan, 1995). The abundance of recently settled individuals in the ocean increased beginning in early August and reached a peak in late October and then declined thereafter (Fig. 5). This peak in abundance in October, which occurred at the same time as the fall peak in larvae, probably represented subsequent settlement but it might also be influenced by recently settled juveniles of some species leaving the estuary for the ocean. In an earlier study in the 1970s the peak in juvenile abundance occurred one month earlier (September; Able and Hagan, 1995) than in our 1992 observations. Regardless of the cause, peaks in larval and juvenile abundance were delayed from summer in the estuary to fall in the ocean. A more recent sampling Fig. 5. Monthly variation in mean density (1 standard error) of larvae and recently settled juveniles in ocean and estuarine sampling from May to November Species composition Larval fish The species composition of the dominant larvae collected in the ocean and estuary had a high degree of overlap as 62% of the species collected occurred in both habitats, while 24% and 14% were exclusively collected in the estuary and ocean, respectively (Table 3). In this study, the larvae in the estuary and ocean were dominated by pelagic species. In the estuary, these included Brevoortia tyrannus and Anchoa mitchilli which is consistent with other estuaries in the region (Vouglitois et al., 1987) and elsewhere along the east coast (McHugh, 1967; Morton, 1989). In the ocean, pelagic species/taxa included unidentified Engraulidae, A. mitchilli, and B. tyrannus. Among those larvae that are benthic as juveniles, there was considerable overlap between the ocean and estuary of the most abundant, including Syngnathus fuscus, Tautoga onitis, Etropus microstomus, and Cynoscion regalis. The latter does not settle but is available to benthic gears because it occurs near the bottom in an engybenthic behavior (Chao and Musick, 1977). Other abundant larvae in the estuary included Gobiosoma bosc, Gobiosoma ginsburgi, and Symphurus plagiusa; while in the ocean these included Scophthalmus aquosus, Tautogolabrus adspersus, and Micropogonias undulatus. The composition of larvae in 1992 appear to be representative of taxa for the estuary and the ocean at broader temporal and spatial scales. For instance, the dominant larval species collected in 1992 in the estuary were similar to the dominant forms identified over the 1989e1994 period at the same site (Witting et al., 1999) with the exception of Gobionellus boleosoma which was not abundant in In the ocean, the larval species composition was similar for the dominant species for the same months in 1972e1975 at this location (Able and Hagan, 1995) except that species with more northern distributions, e.g. Limanda ferruginea and Enchelyopus cimbrius, were more abundant or more consistently represented in the early 1970s. At a broader spatial scale, the species composition of the larvae collected in this study overlaps with the shallow coastal assemblage in the Middle Atlantic Bight (Cowen et al., 1993) Juvenile fish The species composition of the dominant juveniles collected in the ocean and estuary had a high degree of overlap with 47% of the species collected occurring in both habitats, while 32% and 21% were collected exclusively in the estuary and ocean, respectively (Table 3). In the estuary, the most abundant juvenile fish were pelagic individuals of Anchoa mitchilli and Menidia menidia. However, in the ocean collections, pelagic

7 286 K.W. Able et al. / Estuarine, Coastal and Shelf Science 66 (2006) 280e290 Table 3 Density of dominant larvae and juveniles in estuarine and ocean habitats. Significance indicates where there were significant ( p < 0.003) differences in Kruskale Wallis analysis comparing habitats (ns, not significant; e, test was not performed due to insufficient data or pelagic species). Settlement habitat indicates location of recently settled individuals based on Pearson s correlation of PCA eigenvector loadings for each species on factor 1 which separated ocean from estuarine assemblages (see Fig. 6) Species Larval abundance (number 1000 m ÿ3 ) Juvenile abundance (number 1000 m ÿ2 ) Settlement habitat Estuary Ocean Significant? Estuary Ocean Significant? Ammodytes americanus ns ns Estuary/ocean Anchoa mitchilli e e Pelagic Apeltes quadracus 0 0 e ns Estuary Brevoortia tyrannus e 0 0 e Pelagic Centropristis striata ns Ocean Estuary/ocean Cynoscion regalis ns ns Estuary Engraulidae sp e 0 0 e Pelagic Etropus microstomus ns Ocean Estuary/ocean Gobiosoma bosc Estuary Estuary Estuary Gobiosoma ginsburgi Estuary Ocean Estuary/ocean Menidia menidia e e Pelagic Micropogonias undulatus ns Ocean Estuary/ocean Prionotus carolinus ns Ocean Estuary/ocean Prionotus evolans ns Ocean Estuary/ocean Pseudopleuronectes americanus ns ns Estuary Scophthalmus aquosus ns Ocean Estuary/ocean Symphurus plagiusa ns 0 0 e? Syngnathus fuscus Estuary ns Estuary Tautogolabrus adspersus ns ns Estuary Tautoga onitis ns Estuary Estuary Urophycis chuss ns Ocean Estuary/ocean Urophycis regia ns Ocean Estuary/ocean juvenile fish were rarely collected which may have been the result of differences between habitats in the percentage of water column sampled by our primarily benthic gear. All the other abundant species were those with benthic or engybenthic juveniles. Abundant species in common among both the estuary and the ocean were Centropristis striata, Etropus microstomus, and Syngnathus fuscus. Abundant benthic or engybenthic juveniles in the estuary were Apeltes quadracus, Gobiosoma bosc, Cynoscion regalis, Tautoga onitis, Pseudopleuronectes americanus, and Ammodytes americanus; while in the ocean these include Micropogonias undulatus, Prionotus carolinus, Gobiosoma ginsburgi, Scophthalmus aquosus, Urophycis regia, and Urophycis chuss. The juveniles of A. americanus are somewhat of an exception to the benthic category in that they feed in the water column but are capable of burying in the substrate (Collette and Klein-MacPhee, 2002). The composition of juveniles in 1992 also appeared to be representative for the estuary and the ocean at broader temporal and spatial scales. The composition of recently settled juveniles in the estuary in 1992 is similar to earlier studies in the same estuary during 1988e1989 (Szedlmayer and Able, 1996) with the exception of large numbers of Leiostomus xanthurus and Sphoeroides maculatus as well as smaller numbers of Stenotomus chrysops and Bairdiella chrysoura which occurred in the late 1980s but not in this study. Some of these (e.g. S. maculatus, S. chrysops, B. chrysoura) were present in the Great Bay portion of the estuary in later years (1997e 1999) (Martino and Able, 2003). Several of the species not collected as juveniles in 1992, including L. xanthurus and S. maculatus, are annually variable (Able and Fahay, 1998; Witting et al., 1999) and this variability probably accounts for these differences. In general, the fauna of recently settled juveniles in this estuary during 1992 is similar to the same estuary in 1997e1999 (Martino and Able, 2003) and to other estuaries in the Middle Atlantic Bight (Able et al., 1996; Able and Fahay, 1998). Thus, the patterns observed here may be characteristic of a broader region. The oceanic species composition was similar to collections of juveniles in the ocean during 1972e1975 (Able and Hagan, 1995) with the exception of several pelagic species (Alosa spp., Engraulis eurystole) when a larger trawl (7.6 semi-balloon trawl) was used in the earlier study. Other exceptions were those that are annually variable in southern New Jersey such as Leiostomus and Bairdiella (Able and Fahay, 1998). More recent (1997e1999) (Martino and Able, 2003) surveys in the same approximate ocean study sites found a similar fauna as reported in Unexplained differences between earlier collections and our 1992 collections include the greater abundances of Merluccius bilinearis in the 1970s. The lack of Limanda ferruginea in our collections in 1992 is likely due to the decline in the populations of this species in southern New England, on Georges Bank (Collette and Klein-MacPhee, 2002) and more locally (Sullivan et al., 2003) Settlement habitats Based on the principal components analysis of recently settled juveniles, we were able to determine the species that settle in the estuary and/or the ocean (Table 3, Fig. 6). This analysis revealed that two factors account for 40% and 17% of the

8 K.W. Able et al. / Estuarine, Coastal and Shelf Science 66 (2006) 280e Fig. 6. Results of PCA on collection of benthic juvenile fish in estuary and ocean habitats (A). Species loading on factor 1 with a dashed line indicating transition between significant correlation with factor 1 indicating settlement habitat (B). variation, respectively, with factor 1 alone significantly (KruskaleWallis: c 1 2 ¼ 12.01, p ¼ ) accounting for the estuarine (positive) and ocean (negative) distribution of samples along this axis. There were seven species (41% of total) positively correlated (adjusted p < 0.003) with factor 1 and therefore representing estuarine settlement including Apeltes quadracus, Gobiosoma bosc, and Pseudopleuronectes americanus, which are resident estuarine species and which did not occur as larvae or juveniles in the ocean. This finding is consistent with other more detailed studies for P. americanus (Chant et al., 2000). Other, non-resident species, including Tautoga onitis, Syngnathus fuscus, Cynoscion regalis and Tautogolabrus adspersus, were positively correlated with factor 1 and thus also indicative of estuarine settlement. Cynoscion regalis may also settle in the ocean (Able and Fahay, 1998) although individuals were not collected in the beam trawl during this study. Other studies suggest that S. fuscus probably settles in the estuary but are collected in the ocean as the result of outwelling of estuarine water as sometimes occurs for larval P. americancus (Smith et al., 1975; Chant et al., 2000). None of the remaining species (n ¼ 10, 59% of total) had a significant (adjusted p < 0.003) correlation with factor 1, i.e. not exclusively representing ocean (negative) or estuary (positive) settlement. As a result, these species (Ammodytes americanus, Centropristis striata, Gobiosoma ginsburgi, Scophthalmus aquosus, Urophycis chuss, Micropogonias undulatus, Etropus microstomus, Prionotus carolinus, Urophycis regia and Prionotus evolans) were representative of settlement spanning both the estuary and the ocean (Fig. 6). Although all species, except A. americanus, were significantly more abundant in ocean habitats, they occurred in both the estuary and ocean which accounted for this settlement pattern (Table 3). These patterns were consistent with previous studies for C. striata (Able et al., 1995), G. ginsburgi (Duval and Able, 1998), S. aquosus (Neuman and Able, 2002), U. chuss (Pacheco, 1983; Wilk et al., 1992), E. microstomus (Able and Fahay, 1998), P. carolinus (McBride and Able, 1994), U. regia (Barans, 1972; Fahay, 1987; Able and Fahay, 1998) and P. evolans (McBride and Able, 1994; McBride et al., 2002), which were based on more extensive sampling over multiple years. The interpretation of settlement for U. regia is also potentially confounding because there are two cohorts in the Middle Atlantic Bight (Able and Fahay, 1998). This general pattern of use of both estuary and ocean habitats is evident for multiple species from the region from other data as well (Able, 2005). There are other species, not represented here, which are seldom collected in estuaries but occur in the coastal ocean and only use ocean habitats for settlement such as Lophius americanus (Able et al., in press), Limanda ferruginea (Sullivan et al., 2003), and many others such as those in the larval coastal assemblage of Cowen et al. (1993). This ability of larvae in the coastal assemblage to remain outside or enter estuaries implies that there may be behavioral mechanisms that accounts for species that find their way into estuaries and seldom, if ever, occur as small juveniles in the ocean (e.g. Conger oceanicus and Brevoortia tyrannus). The results from other studies assume that tidal stream transport is the mechanism responsible for the different distributions (Creutzberg, 1961; Rijnsdorp et al., 1985; Rowe and Epifanio, 1994; Jager, 1999). In our study there were no species that spawned in the estuary and settled in the ocean although this type of pattern has been reported for some South Africa fishes (Whitfield, 1998) Summary The pattern of distribution for pelagic larvae and recently settled juveniles in estuarine and coastal ocean habitats in southern New Jersey suggests that there are two basic patterns of settlement represented by species that (1) develop and settle in estuaries, and (2) those that settle in both estuarine and coastal ocean habitats. The results for the latter group suggest that among the species that spawn in the inshore ocean there are relative few, if any, that are estuarine dependent because they settle in and use both estuarine and ocean habitats. Other observations in the same study area indicate the general patterns observed here may vary between cohorts because of the relative contributions of different species with varying life histories (Able, 2005). For example, the distribution of recently settled individuals of Scophthalmus aquosus varies between cohorts. The spring-spawned cohort is abundant in both the estuary and the ocean while fall-spawned individuals are almost exclusively found in the ocean (Neuman and Able, 2002). It should be kept in mind that the data analyzed here are from a single year. Recent analysis suggests that longer-term changes such as climate effects may influence settlement habitats, as for

9 288 K.W. Able et al. / Estuarine, Coastal and Shelf Science 66 (2006) 280e290 Micropogonias undulatus, which has extended its range further north into Middle Atlantic Bight habitats (Hare and Able, in press). Further resolution of settlement patterns will need to rely on synoptic comparisons between the estuary and the ocean in this and other regions over multiple years. Acknowledgements A large number of individuals assisted in this sampling program. L.S. Hales, Jr. and R. Hoden were actively involved in the field sampling program in the ocean. In the estuary, numerous RUMFS technicians assisted in the sampling program there. This study was funded by Rutgers University Institute of Marine and Coastal Sciences (IMCS), NOAA/National Undersea Research Program, and the Rutgers University Marine Field Station. We are grateful to all of the above. 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