Southern California Bight 2003 Regional Monitoring Program: IV. Demersal Fishes and Megabenthic Invertebrates
V. Megabenthic Invertebrate Populations
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V. Megabenthic Invertebrate PopulationsIntroductionInvertebrates living on or in the surface sediment and large enough to be retained by a trawl net are termed megabenthos. Hundreds of megabenthic invertebrate species occur within the southern California Bight (SCB; Moore and Mearns 1978, Allen et al. 1998, Stull et al. 2001, Allen et al. 2002a). Because these species are relatively sedentary and respond to changes in the benthic environment, their populations have been used for decades to assess impacts resulting from human activities. Most information on the megabenthic invertebrate fauna of the southern California shelf has resulted from regular trawl surveys conducted near ocean outfalls to assess effects of wastewater discharge (e.g., Carlisle 1969a,b; Mearns and Greene 1974; CLAEMD 1994a,b; CSDMWWD 1995; Stull 1995; CSDOC 1996; CSDLAC 2000). While local areas have been well-studied for temporal and small-scale spatial variability, earlier regional assessments compiled trawl data gathered for various purposes (Allen and Voglin 1976, Thompson et al. 1993a), collected data in reference surveys of limited scope (Word et al. 1977, Thompson et al. 1987b, Thompson et al. 1993b), or provided composite assessment in wastewater discharge areas (Mearns and Greene 1974). A synoptic regional assessment was not conducted until 1994 (Allen et al. 1998, Stull et al. 2001). Although this study provided substantial information on the fauna of the mainland shelf (10-200 m depth), it did not cover bays and harbors, islands, or the slope of the SCB. A second regional survey was conducted in 1998 (Allen et al. 2002a) to provide additional region-wide information on the status of invertebrate populations. This study included bays, harbors, and offshore island habitats. The objectives of this section are 1) to describe the distribution, relative importance (areal coverage, abundance, and biomass) and health of the dominant invertebrates of the SCB in bays, at islands, on the shelf and slope, and in select geographic, depth, and human influence subpopulations in 2003; 2) to assess population changes between 1994, 1998, and 2003; and 3) to examine historical trends based on earlier studies. This information will provide context for local population patterns observed in monitoring studies. Other aspects of this fauna are presented in the Section VI – Assemblages and Biointegrity. ResultsPopulation AttributesAbundance per HaulA total of 157,326 invertebrates were collected during the survey (Table V-1). The number per haul ranged from 0 to 10,986. The lowest individual values occurred in the mainland region on the outer shelf and in bays, and the highest in the northern mainland region on the upper slope. The median for the Bight as a whole was 389 individuals per haul, with subpopulation medians ranging from 12 (inner shelf, small POTWs) to 1,701 (mainland upper slope). Abundance was higher (more area above the Bight median) on the mainland, although the southeast islands were higher than the southern mainland. Both island medians were below the Bight median. The warm islands had much higher numbers of invertebrates than did the cool islands, with median numbers of 268 and 84, respectively. On the mainland, the median abundance was highest in the north (683), followed by the central (486) and southern (151) regions. By depth zone, the upper slope had the highest median number, followed by the outer and middle shelf, bays/harbors, and lastly, the inner shelf; medians were 1,653, 174, 154, 94, and 18, respectively. On the upper slope, mainland catches were higher than at islands. On the outer shelf, large POTWs had the highest median abundances and other mainland sites had the lowest. On the middle shelf, median abundance was highest (196) at mainland non-POTW sites and lowest at small POTWs (37). Median abundance declined with decreasing depth from the upper slope to the inner shelf, but increased in bays. Slope median abundance was an order of magnitude greater than the outer shelf median, and two orders of magnitude higher than inner shelf median (Table V-2). More than 1,979 invertebrates per haul were caught at 21 stations (Figure V-1). All of these high abundance sites were on the outer shelf or upper slope. Most were located on either the mainland or island sides of the Santa Barbara Channel. The highest invertebrate catch of 10,986 individuals occurred at an upper slope site on the mainland side. Most (83) stations had invertebrate catches of 107 to 1,978 individuals, with nearly half the sites having more than 106 invertebrates in the catch. Biomass per HaulA total of 2214.3 kg of invertebrates were taken during the survey (Table V-3). The biomass of invertebrates per haul ranged from 0 to 186.7 kg. Lowest individual values occurred in all mainland regions at all shelf zones, although not in the upper slope zone or in all human influence subpopulations. The highest individual biomass occurred on the central region outer shelf. The Bight-wide median was 4.8 kg/haul, with subpopulation medians ranging from 0.2 kg (island upper slope, and inner shelf small POTW and “other mainland” sites) to 38.2 kg at the single outer shelf large POTW site. Invertebrate biomass was higher (more sites above the Bight median) at northern and central mainland regions than at either the northwest or southeast islands (Table V-3). All regions except the northern and central mainland had median biomass below that of the Bight as a whole, as did all subpopulations except outer shelf large POTWs, mainland non-POTWs, islands, and upper slope mainland. Island subpopulations had similar median biomass values, and both the cool and warm islands were lower than the median for mainland regions. This was a result of the almost complete lack of upper slope samples from the islands (only 1 upper slope station in the Island subpopulation). Among the mainland regions the northern region had a significantly higher median (42%) than the central region, which in turn had a higher median biomass (79%) than the southern mainland subpopulation. On the inner shelf small POTW sites had the same median biomass as other mainland non-POTW sites, while the median at large POTW sites was four times higher. On the middle shelf this relationship did not hold, with the island median being the highest, followed by mainland non-POTW, large POTW, and small POTW medians. By depth zone the inner shelf supported the lowest median biomass (0.2 kg/haul) and upper slope the highest (21.0 kg/haul; Table V-3). Inner shelf sites followed a regional trend with northern region > central region > southern region medians. Bay and harbor sites had double the median biomass/haul of the inner shelf, but were far lower than other shelf zones. Table V-1. Megabenthic invertebrate abundance by subpopulation at depths of 2-476 m on the southern California shelf and upper slope, July-October 2003. 
Table V-2. Megabenthic invertebrate abundance by region within shelf zone subpopulations at depths of 2-476 m on the southern California shelf and upper slope, July-October, 2003. 
Table V-3. Megabenthic invertebrate biomass by subpopulation at depths of 2-476 m on the southern California shelf and upper slope, July-October 2003. 
Figure V-1. Distribution of megabenthic invertebrate abundance per haul at depth of 2-476 m on the southern California shelf and upper slope, July-October 2003. Median biomass values increased with depth beyond the inner shelf; from 3.5 kg on the middle shelf, to 10.7 kg on the outer shelf, and 21 kg on the upper slope (Table V-4). Twenty-one stations, 11 of which were in the Santa Barbara Channel, had catches over 31.1 kg (Figure V-2). Of the remaining 10 high biomass sites, 9 were located on the central region mainland shelf, and one on the southern region shelf. Most stations (82) had biomass between 2.2 and 31 kg/haul, while 32 sites had invertebrate biomass of 0.1 kg or less. Directory: pub -> download pub -> Acm word Template for sig site pub -> The german unification, 1815-1870 pub -> Baltic Olympiads in Informatics: Challenges for Training Together pub -> Preparation of Papers for ieee transactions on medical imaging pub -> Forthcoming meetings and conferences pub -> Asilomar Conference on Circuits, Systems & Computers, Pacific Grove, ca, November 1978, pp. 55 58 pub -> Forthcoming meetings and conferences pub -> Harmonised compatibility and sharing conditions for video pmse in the 7 9 ghz frequency band, taking into account radar use Download 11.21 Mb. Share with your friends:
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