Planktonic larval stages of many benthic marine invertebrates are especially susceptible to environmental stress, such as the presence of pollution. Recruitment of these larvae onto the seafloor frequently controls benthic community structure. We thus evaluated larval availability and recruitment of macrobenthos over a period of 14 months at 12 stations within Mamala Bay, to assess the ecosystem impacts of major point and non-point sources of pollution. The major point source of pollution in the Bay, the Sand Island outfall, had no detectable negative impact on larval recruitment, even though the sewage plume frequently bathed our stations nearest the outfall. In contrast, larval availability and recruitment were significantly reduced at two study sites located 1 km west of the Pearl Harbor Channel (1 and 3 km offshore respectively). These two sites are likely bathed by a larval- depleted water mass whose source is not presently known. Possible sources include: 1) Pearl Harbor, whose outflow may be larval-depleted due to larval mortality caused by non-point source pollution, or the settlement of larvae inside Pearl Harbor before they are advected offshore (recruitment shadow), 2) offshore waters, or 3) coastal waters west of Pearl Harbor. It is difficult to determine the source(s) of waters bathing our offshore Pearl Harbor study sites because circulation patterns in the area are complicated by the convergence of semi-diurnal tidal flows located offshore of the area between Keehi Lagoon and the Honouliuli outfall (MB-6). The scale of hydrographic observations conducted as part of MB-6 were spatially too coarse to determine the location of the convergence therefore making it impossible to determine the source of water that most frequently bathes our western offshore Pearl Harbor study sites. Outflow from Keehi Lagoon produced a distinct, low-clarity water mass which appeared to enhance larval availability and recruitment of some taxa (especially balanomorph barnacles). Coral recruitment rates were extremely low across the bay (6 x 10-5 cm-2). Low coral recruitment rates are most likely due to inadequate larval supply since percent cover of live adult coral (coral larval source) is less than 5% throughout most of the bay. Coral recruitment rates observed in earlier studies in Maunalua Bay (located east of Diamond Head), which has similar live coral cover and few significant inputs of pollution, are also extremely low. This suggests that pollution inputs to Mamala Bay are not responsible for the observed low coral recruitment rates.
Study of recruitment patterns of marine benthic invertebrates in Mamala Bay. It was a process-oriented measure of ecosystem response to pollution.
NOAASupplemental: Entry_ID: Unknown Sensor_Name: recruitment plates and larvae traps Originating_Center: University of Hawaii Storage_Medium: Lotus 1-2-3, MS Word, ASCII Reference: None Online_size: 600 kilobytes Resource Description: NODC Accession Number 9900151
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Mamala Bay Study MB-9 Department of Oceanography University of Hawaii
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SAMPLING STATIONS: SITE Latitude Longitude Depth (deg,min) (deg,min) (m) ----- ------------------- ----------------- -------- 1 21 16.808 N 157 58.754 W 72 2 21 16.770 N 157 54.333 W 72 3 21 14.988 N 157 49.744 W 72 4 21 17.471 N 157 58.952 W 16 5 21 17.908 N 157 57.090 W 16 6 21 17.611 N 157 55.032 W 16 7 21 17.317 N 157 52.035 W 16 8 21 16.411 N 157 50.682 W 16 9 21 15.146 N 157 49.405 W 16 METHODOLOGY Larval recruitment and distribution patterns were evaluated at moorings sites chosen according to three criteria. First, sites of maximal point-source influence (Sand Island outfall), maximal non-point source influence (off Pearl Harbor) and minimal pollution influence (off Diamond Head) were targeted along a single depth contour. These mooring sites allowed direct comparisons of larval availability and recruitment in point source, non-point source, and control areas; bottom depth at these sites (termed "deep sites") was set by the depth of the Sand-Island outfall diffuser (72 m). Second, areas near sources of non-point pollution ( Pearl Harbor, Keehi Lagoon, Honolulu Harbor and the Ala Wai Harbor) and an area with minimal pollution influence (off Diamond Head) were targeted along a depth contour (16 m) where recruitment rates should be representative of subtidal fauna. These sites (termed "shallow sites") allowed comparisons of larval availability and recruitment between areas presumed to be influenced by major non-point sources of pollution in Mamala Bay, and a control area. As a third criterion, settlement moorings were located within close enough range to Honolulu Harbor to allow diver sampling of all nine sites in a single day. To ensure environmental similarity across sites, controlled settlement substrates (ceramic plates) and larval traps were placed on midwater moorings. We chose not to conduct recruitment studies on the seafloor to avoid biases due to dramatically varying flow regimes (resulting from differences in seafloor topography), varying bottom types, and varying rates of demersal fish predation on larvae and recruits between sites. Recruitment plates and larval traps were placed at two water depths at deep sites; 15 meters (for spatial comparisons with shallow sites), and 35 meters (where plume models suggest that sewage concentrations from the Sand Island outfall are often maximal; Noda, pers. comm.). Recruitment plates and larval traps were placed at 10 m at shallow sites. Ideally, upper sampling depths would have been identical at shallow and deep sites. However, Coast Guard rules prevented subsurface moorings from being shallower than 15 meters in water depths exceeding 18 meters, and seafloor proximity precluded placing plates and traps deeper than 10 m at shallow (16-m bottom depth) sites. Larval recruitment rates were quantified using ceramic tiles as settlement substrates (dimensions, 20 x 9.5 x 1cm). Two to four replicate tiles, held in specially designed and fabricated aluminum frames (Figure 3.2), were used on each settlement mooring. Clean tiles were placed on frames by divers, allowed to collect recruits for 1-3 wk, and then recovered by carefully sealing each plate (while still underwater) in a separate tupperware container. In the lab, tiles were gently washed with tapwater over a 250 micrometer sieve. Animals remaining on tiles or retained in the sieve were then identified and enumerated under a dissecting microscope. Larval availability was quantified using two different methods. During initial stages of the study, larvae were sampled by conducting plankton tows at shallow stations, as initially proposed. Plankton tows were conducted with a 0.5 meter diameter, 202 micron Nytex) net. A General Oceanics flowmeter was rigged to the front of the net to quantify tow volumes. Two five-minute replicate tows were taken at stations 5, 6, 8 and 9. Plankton tow samples were immediately fixed in a 10% formalin solution, transferred in the laboratory to 80% ETOH, and then sorted under a dissecting microscope. Several months into the study, it became clear that larval numbers in plankton tows did not correlate well with recruitment at any mooring sites. A likely explanation was that plankton tows quantify larval concentrations at a particular point in time, but not the time-integrated flux of larvae past a stationary point; in contrast, recruitment tiles record larval availability or flux throughout their 1-3 wk deployment period literature that sediment traps with aspect ratios 10 record larval flux in flow regimes typical of shallow coastal waters. Therefore, after becoming aware of these new methods for measuring larval flux, we elected to evaluate larval availability at mooring sites using time-integrative, larval traps. Upward-facing plastic tubes (i.e., larval traps) with a diameter = 5 cm, and a height = 60 cm, were deployed 25 cm from the sides of moorings to sample the horizontal flux of larvae past stations 4 through 9. The bottom 10 cm of larval traps contained a 10% formalin solution for larval fixation. NaCl (100 ppt) was added to the formalin solution to form a high-density layer that generally remained undisturbed in the bottom of the traps throughout deployment and recovery. This solution was dyed with Rhodamine WT for sample-integrity verification. Recovered traps that did not contain an intact layer of dyed formalin solution were not analyzed. Two replicate traps were deployed at each station synchronously with deployment of settlement plates. After recovery, larval trap samples were transferred to 80% ETOH and larvae were identified and enumerated under a dissecting microscope. Smith, Craig R. and Parnell, Ed P., 1995. Recruitment Patterns of Marine Benthic Invertebrates in Mamala Bay: A Process-Oriented Measure of Ecosystem Response to Pollution. Mamala Bay Study, Project MB-9. Mamala Bay Study Commission. 1996. Mamala Bay Study Final Report.
FILE FORMATS: Lotus 1-2-3 (*.wk1) and corresponding ascii dumps (*.prn). Each wk1 file denotes a deployment period. The first file (recr1a.wk1) only lists expected taxa. recr1a.prn recr1a.wk1 recr1b.prn recr1b.wk1 recr1c.prn recr1c.wk1 recr1d.prn recr1d.wk1 recr1e.prn recr1e.wk1 recr1f.prn recr1f.wk1 recr1g.prn recr1g.wk1 recr1h.prn recr1h.wk1 recr1i.prn recr1i.wk1 recr1j.prn recr1j.wk1 recr1k.prn recr1k.wk1 recr1l.prn recr1l.wk1 recr1m.prn recr1m.wk1 recr1n.prn recr1n.wk1 recr1o.prn recr1o.wk1 recr1p.prn recr1p.wk1
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