Reef monitoring cruise in the main Hawaiian Islands completed: preliminary results from fish surveys

Last Friday afternoon, Aug. 23, the NOAA Ship Hi`ialakai returned to Honolulu from a Pacific Reef Assessment and Monitoring Program (Pacific RAMP) cruise (HA-13-04) during which staff of the PIFSC Coral Reef Ecosystem Division (CRED) and partners conducted surveys of reef fish assemblages and benthic communities at the islands of Hawai`i, Lāna`i, Kaua`i, Maui, Moloka`i, Ni`ihau, and O`ahu and deployed instruments and collected water samples to monitor effects of climate change and ocean acidification on the coral reef ecosystems of those islands.

Over the course of this expedition, which began on Aug. 1, CRED staff and partners accomplished the following field activities: 1031 dives, reef fish surveys at 237 Rapid Ecological Assessments (REA) sites, benthic surveys at 104 REA sites, collections of 30 water samples and 42 benthic samples for analysis of microbial communities, retrieval of 18 and deployment of 12 autonomous reef monitoring structures, installation of 120 calcification accretion units and 30 bioerosion monitoring units, recovery of 4 ecological acoustic recorders, retrieval of 18 and deployment of 32 subsurface temperature recorders, and completion of 71 shallow-water conductivity, temperature, and depth (CTD) casts and 69 deepwater (shipboard) CTD casts. Additional water samples were collected for analyses of dissolved inorganic carbon, total alkalinity, and salinity.

Preliminary results from the surveys of reef fishes conducted by scuba divers at depths of 0–30 m during the PIFSC cruise HA-13-04 are provided in the fish monitoring brief below.

Pacific Reef Assessment and Monitoring Program
Fish monitoring brief: main Hawaiian Islands 2013

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 status report.

Sampling effort

  • Ecological monitoring took place in main Hawaiian Islands from August 2 2013 to August 22 2013.
  • Data were collected at 237 Rapid Ecological Assessments (REA) sites. Surveys were conducted at Hawai`i (n=58), Kaua`i (n=37), Lāna`i (n=29), Maui (n=34), Moloka`i (n=39), Ni`ihau (n=26) and O`ahu (n=14).
  • At each REA site, the fish assemblage was surveyed by underwater visual census and the benthic community was assessed.

Overview of data collected

Figure 1. Mean total fish biomass (g m–2)  at sites surveyed.

Figure 1. Mean total fish biomass (g m–2) 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 (±1 standard error). Primary consumers are herbivores and detritivores, and secondary consumers are omnivores and invertivores.

Figure 4. Mean fish biomass per size class (±1 standard error). Fish measured by total length (TL) in centimeters (cm).

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).

Spatial sample design

Locations of REA sites 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, eshy 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:

Pacific Islands Fisheries Science Center:

CRED publications:

CRED fish team:

Fish team lead and fish survey data requests:

Follow this link for a PDF version of this main Hawaiian Islands 2013 fish monitoring brief.

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