Southern California Bight 2003 Regional Monitoring Program: IV. Demersal Fishes and Megabenthic Invertebrates
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DiscussionBiointegrity AssessmentThe biointegrity indices that were applied to the SCB as a whole (i.e., FRI, MIRI, and TRI) showed that 81-96% of the SCB area was classified as reference (normal) with 4-19% being nonreference (abnormal or disturbed). These indices could not be calculated in 0-14% of the stations. For the middle shelf zone, the FFG index indicated that 41% of the area (primarily on the Channel Island Shelf) was classified as nonreference. For the SCB-wide indices, the highest percent of nonreference area were found in the bay/harbor and in the inner shelf river mouth subpopulation (particularly near the Santa Clara River mouth). Most of the sites where the MIRI could not be calculated were in San Diego Bay, with others in LA/LB Harbor and river mouth areas (Figure VI-23). These areas had insufficient index species because species richness was greatly reduced (e.g., river mouth areas) or the fauna was dramatically different from the coastal fauna upon which the indices are based (e.g., San Diego Bay). All of the response indices (FRI, MIRI, and TRI) were developed from fish data collected on the mainland shelf from 10-200 m from 1973 to 1994 (Allen et al. 2001a). Since the bay fauna differs from the coast, the indices become less effective in this region. However, nonreference assemblages also occurred in LA/LB Harbor, and on the Santa Barbara Shelf, suggesting that other explanations are needed. 
Figure VI-22. Percent of nonreference area by subpopulation on the southern California shelf and upper slope at depths of 2-476 m) for the Megabenthic Invertebrate Response Index (MIRI), July-October 2003. 
Figure VI-23. Percent of nonreference area by shelf zone subpopulation on the southern California shelf and upper slope at depths of 2-476 m for the Megabenthic Invertebrate Response Index (MIRI), July-October 2003. 
Figure VI-24. Distribution of response levels for Megabenthic Invertebrate Response Index (MIRI) on the southern California shelf at depths of 2-476 m, July-October 2003. 
Figure VI-25. Percent of nonreference area by subpopulation on the southern California shelf and upper slope at depths of 2-476 m for the Trawl Response Index (TRI), July-October 2003. 
Figure VI-26. Percent of nonreference area by shelf zone subpopulation on the southern California shelf and upper slope at depths of 2-476 m for the Trawl Response Index (TRI), July-October 2003. 
Figure VI-27. Distribution of response levels for Trawl Response Index (TRI) on the southern California shelf at depths of 2-476 m, July-October 2003. Although in 1998, the MIRI showed many nonreference shelf sites in the Santa Barbara Channel and the FRI and TRI did not (Allen et al. 2002a), all three indices identified nonreference areas in this area in 2003 (Figures VI-19, VI-24, and VI-27). Similar to the MIRI, the TRI showed nonreference areas in bays/harbors whereas the FRI did not. River mouths (particularly the Santa Clara River area) had relatively high numbers of nonreference sites for all three indices. Whereas the response indices are based on the relative distribution of many species to a pollution gradient regardless of their biology, the FFG index is based on relative abundances of three foraging guilds. These are the generalists (benthic pelagobenthivores, sanddab guild), polychaete feeders (benthic extracting benthivores, turbot guild), and nekton ambushers (benthic pelagivores, lizardfish guild; Allen et al. 2001a). Typically, turbot guild species are abundant near wastewater discharge sites and sanddab and lizardfish guild species are not. Thus, the index addresses ecological conditions in polluted areas, such as food type availability and sediment type (as this often determines food type availability). Nonreference areas (e.g., near outfalls discharging particulates) are typically those with higher organic sediments, more polychaetes, and fewer epibenthic pericarid crustacea; Cross et al. 1985) whereas reference areas have sediments with lower organic content and higher crustacean abundance. Whereas both sanddab guild and turbot guild species are widespread on the shelf, lizardfish guild species (e.g., California lizardfish, bigmouth sole, California halibut) were less common and abundant in 1994, equally common in 1998, and less common in 2003. In this survey, nonreference areas for this index were primarily on the middle shelf of the Channel Islands, perhaps related to increased organic fallout to sediments from cold-regime upwelling in the California Current, perhaps resulting in a benthic polychaete fauna suitable for turbot-guild species (Figures VI-20 and VI-21). These indices were developed using (in part) nearly three decades of trawl data from the Palos Verdes Shelf in the early 1970s (Allen et al. 2001a), the most contaminated sites along the southern California coast (Mearns et al. 1976). Heavily impacted sites occurred in this area, particularly in the middle shelf zone, but also in the outer shelf zone. However, sites of similar high impact were not identified in the inner shelf zone (or subsequently for bays and harbors, where fish assemblage sampling was done along with sediment chemistry sampling). These indices, while not perfect, performed nearly as well as the BRI (Smith et al. 1998) in following improving conditions over time on the Palos Verdes Shelf. Their real value is likely to become apparent when applied to historical data with clearly defined impact sites (CSDLAC 2002; Montagne 2002a,b; Allen 2006b). Although impact levels were not defined for the response indices, such a level was defined for the FFG index (Allen et al. 2001a). It should be noted that no site in the middle shelf zone was classified as impacted for the FFG index in 1998. Overall, the condition of the fish and invertebrate assemblages on the southern California shelf in 2003 was generally good, except perhaps in river mouth areas (particularly near the Santa Clara River) and LA/LB Harbor. The four indices were based on the most contaminated site (Palos Verdes Shelf) in the early 1970s and all four indices showed that site to have abnormal or disrupted (i.e., nonreference) assemblages of fishes, invertebrates, combined fishes and invertebrates, and fish foraging guilds relative to those typical of the southern California shelf. This was apparent in gradients of species or guild abundances relative to the outfall area (Allen et al. 2001a). Although these gradients existed, the cause of each gradient is not known. Certainly concentrations of contaminants (e.g., DDT, PCBs, other organochlorines, and trace metals) were higher there than elsewhere on the shelf. In addition, there were also high levels of total organics, anaerobiosis, and different infaunal assemblages in the sediments near the outfall than further away. All or some of these may have influenced the species gradients there. However, the MIRI and TRI have there own value in identifying abnormal megabenthic invertebrate assemblages and combined fish and invertebrate assemblages. The FFG index has value in showing the distribution of alternative natural soft-bottom habitat states (low organics, high epibenthic crustacea, lower polychaete abundance; high organics, low epibenthic crustacea, and high polychaete abundance) independent of contaminant concentrations, and has value in ecological studies of the demersal fish fauna of the shelf. The cause of the high organic sediment state may be due to natural phenonema (e.g., upwelling, depositional conditions) or anthropogenic activity (e.g., discharge of organic particulates). Based on its relative performance along historical spatial and temporal gradients in contamination, Allen et al. (2001a) recommended the FRI as the best index for use in assessing effects on fish assemblages. Based on that index, 97% of the area of the southern California shelf had relatively normal fish assemblages in 1998 (Allen et al. 2002a) and 96% in 2003. 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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