Reef monitoring at Wake Island: preliminary results from fish surveys

By Dione Swanson

After departing Honolulu on March 5, the NOAA Ship Hi’ialakai arrived at Wake Island on March 14. It was the first stop for PIFSC cruise HA-14-01, a Pacific Reef Assessment and Monitoring Program (Pacific RAMP) expedition that also recently visited Guam and is currently focused on the southern islands of the Commonwealth of the Northern Marianas Islands. At Wake Island, staff members of the PIFSC Coral Reef Ecosystem Division (CRED) and partners conducted surveys of reef fish assemblages, coral populations, and benthic communities as well as deployed instruments and collected water samples to monitor effects of climate change and ocean acidification on coral reef ecosystems.

Our first 2 planned operational days on Wake Island were canceled because of poor weather conditions (strong winds and high seas). Relatively good weather returned by March 16, and we then were able to complete 4.5 days of small-boat operations before leaving for Guam on March 20. Over the course of our time at Wake Island, scientists accomplished the following field activities during a combined 229 dives: reef fish surveys at 45 Rapid Ecological Assessment (REA) sites; benthic surveys at 20 REA sites; collection of 12 water samples and 1 benthic sample for analysis of microbial communities; retrieval of 7 subsurface temperature recorders (STRs), 6 autonomous reef monitoring structures (ARMs), 15 calcification accretion units (CAUs), and 1 sea-surface temperature (SST) buoy; installation of 4 National Coral Reef Monitoring Plan climate stations—each of which includes 3 ARMs, 5 CAUs, 5 bioerosion monitoring units, and 3 STRs; and collection of 20 water samples for analysis of dissolved inorganic carbon; and completion of 11 shallow-water conductivity, temperature, and depth (CTD) casts.

Highlights of our research dives at Wake Island included incredible water visibility (>45 m), high coral cover that consisted of abundant large colonies with low partial mortality, overall low prevalence of coral disease and bleaching, and large patches of soft corals. There were only a few sightings of bumphead parrotfish (Bolbometopon muricatum) and Napoleon wrasse (Cheilinus undulatus).

Preliminary results from the surveys of reef fishes conducted by scuba divers at Wake Island (depth range: 0–30 m) during this cruise are provided in the below fish monitoring brief, which was issued on March 25 as PIFSC Data Report DR-14-007 (click here, to download a PDF file of this report). Wake Island is 1 of 7 islands, atolls, and reefs that make up the Pacific Remote Island Areas and, under the jurisdiction of the United States, are protected as the Pacific Remote Islands Marine National Monument.

Pacific Reef Assessment and Monitoring Program
Fish monitoring brief: Pacific Remote Island Areas 2014

By Adel Heenan

About this summary brief

The purpose of this document is to outline the most recent survey efforts conducted by the Coral Reef Ecosystem Division (CRED) of the NOAA Pacific Islands Fisheries Science Center as part of the long-term monitoring program known as the Pacific Reef Assessment and Monitoring Program (Pacific RAMP). More detailed survey results will be available in a forthcoming annual status report.

Sampling effort

  • Ecological monitoring took place in the Pacific Remote Island Areas from March 16 2014 to March20 2014.
  • Data were collected at 45 sites. Surveys were conducted at Wake Island.
  • At each site, the fish assemblage was surveyed by underwater visual census and the benthic community was assessed.

Overview of data collected

Primary consumers include herbivores (which eat plants) and detritivores (which bottom feed on detritus), and secondary consumers are largely omnivores (which mostly eat a variety of fishes and invertebrates) and invertivores (which eat invertebrates).

Figure 1. Mean total fish biomass at sites surveyed.

Figure 1. Mean total fish biomass at sites surveyed.

 

Figure 2. Mean hard coral cover at sites surveyed.

Figure 2. Mean hard coral cover at sites surveyed.

Figure 3. Mean consumer group fish biomass (± standard error). Primary consumers are herbivores and detritivores, and secondary consumers are omnivores and invertivores.

Figure 3. Mean consumer group fish biomass (± standard error). Primary consumers are herbivores and detritivores, and secondary consumers are omnivores and invertivores.

Figure 4. Mean fish biomass per size class (± standard error). Fish measured by total length (TL) in centimeters (cm).

Figure 4. Mean fish biomass per size class (± standard error). Fish measured by total length (TL) in centimeters (cm).

 

Spatial sample design

Survey site locations are randomly selected using a depth-stratified design. During cruise planning and the cruise itself, logistic and weather conditions factor into the allocation of monitoring effort around sectors of each island or atoll. The geographic coordinates of sample sites are then randomly drawn from a map of the area of target habitat per study area. The target habitat is hard-bottom reef, the study area is typically an island or atoll, or in the case of larger islands, sectors per island, and the depth strata are shallow (0–6 m), mid (6–18 m), and deep (18–30 m).

Sampling methods

A pair of divers surveys the fish assemblage at each site using a stationary-point-count method (Fig. 5). Each diver identifies, enumerates, and estimates the total length of fishes within a visually estimated 15-m-diameter cylinder with the diver stationed in the center.

These data are used to calculate fish biomass per unit area (g m-2) for each species. Mean biomass estimates per island are calculated by weighting averages by the area per strata. Island-scale estimates presented here represent only the areas surveyed during this cruise. For gaps or areas not surveyed during this cruise, data from this and other survey efforts will generally be pooled to improve island-scale estimates.

Each diver also conducts a rapid visual assessment of reef composition, by estimating the percentage cover of major benthic functional groups (encrusting algae, fleshy macroalgae, hard corals, turf algae and soft corals) in each cylinder. Divers also estimate the complexity of the surface of the reef structure, and they take photos along a transect at each site that are archived to allow for future analysis.

Figure 5. Method used to monitor fish assemblage and benthic communities at the Rapid Ecological Assessment (REA) sites.

Figure 5. Method used to monitor fish assemblage and benthic communities at the Rapid Ecological Assessment (REA) sites.

About the monitoring program

Pacific RAMP forms a key part of the National Coral Reef Monitoring Program of NOAA’s Coral Reef Conservation Program (CRCP), providing integrated, consistent, and comparable data across U.S. Pacific islands and atolls. CRCP monitoring efforts have these aims:

  • Document the status of reef species of ecological and economic importance
  • Track and assess changes in reef communities in response to environmental stressors or human activities
  • Evaluate the effectiveness of specific management strategies and identify actions for future and adaptive responses

In addition to the fish community surveys outlined here, Pacific RAMP efforts include interdisciplinary monitoring of oceanographic conditions, coral reef habitat assessments and mapping. Most data are available upon request.

For more information

Coral Reef Conservation Program: http://coralreef.noaa.gov

Pacific Islands Fisheries Science Center: http://www.pifsc.noaa.gov/

CRED publications: http://www.pifsc.noaa.gov/pubs/credpub.php

CRED fish team: http://www.pifsc.noaa.gov/cred/fish.php

Fish team lead and fish survey data requests: ivor.williams@noaa.gov

 

 

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