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Long term monitoring of Fagatele Bay National Marine Sanctuary, Tutuila Island, American Samoa: results of surveys conducted in 2007/8, including a re-survey of the historic Aua Transect


Douglas Fenner

Alison Green

Charles Birkeland

Cheryl Squair

Benjamin Carroll

2008

Report prepared for:


U.S. Department of Commerce American Samoa Government

National Oceanic and Atmospheric Administration Department of Commerce

National Ocean Service Environment Division

Office of National Marine Sanctuaries



Executive Summary
Corals:

  • The main finding of our survey of the corals in Fagatele Bay is that they are still resilient (capable of recovering from damage) and doing quite well. The abundance and population density of corals (14.5 colonies per m2) and the living coral cover (64%) in Fagatele Bay in August 2007 are typical of very healthy reefs. We encountered 94 species within the areas specifically within our transects, a small part of Fagatele Bay. A total of 164 species of corals were previously recorded from Fagatele Bay, but this latest survey found yet another four species not previously recorded: Acropora formosa, Montipora hispida, Fungia concinna and Fungia klunzingeri, bringing the total number of species in Fagatele Bay to 168. The number of species in Fagatele Bay is not yet decreasing.

  • The size distribution of coral colonies in Fagatele Bay also indicates a healthy situation with a few large colonies and an abundance of smaller colonies, indicating a healthy recruitment. However, some of the smaller colonies are of species that do not usually grow large, e.g., Porites sp. 2 and Galaxea fascicularis. The numerical pattern of relative abundance of species, the relative abundance of coral species representing the different families of corals, and the population densities of corals along the depth distribution are all fairly constant between 2004 and 2007, indicating that the population has reached a temporary equilibrium as a relatively healthy coral community. The proportion of corals in the smallest size category (< 5 cm diameter) has decreased and the proportion in the higher size classes have increased since 1995, showing that the coral community has grown in size distribution over the past decade.

  • The corals in Pago Pago Harbor were surveyed both along the permanent transect in front of Aua village and also in front of the Sadie’s by the Sea Hotel. There has been successful recruitment and growth of some colonies of Acropora hyacinthus at both sites. The coral cover typical of a fully normal and healthy reef community has returned to the area of the Aua transect wherever there are solid substrata, i.e., on the reef crest and on large coral blocks on the reef flat. The dominant species on the Aua reef crest is Acropora nana because of a major successful recruitment in 1999.

  • Surveys of Fagatele Bay should be shifted back to March/April for a better chance of having enough days with good sea state to get the surveys accomplished.

Benthic Communities



    • Percent cover of all algae has decreased from a high in 1985. Diversity also appears to have decreased. No obvious patterns are apparent in this survey year with respect to depth or position with FBMS. Hydrolithon onkodes appears to be the most common species of crustose coralline algae in FBMS and this is similar to what was reported in 1985.

    • Higher coral cover and lower turf cover at the Aua site compared with the Rainmaker site appear to indicate that the sites are recovering at different rates. The high turbidity, low coral cover and low macroalgal cover appear to indicate more restricted circulation or higher disturbance at the Rainmaker site.

    • Benthic communities at Fagasa appear to represent typical high disturbance communities with moderate coral cover, high encrusting algal species, moderate turf/fleshy algae species.

Fish communities




  • Changes in fish communities over time may be partly due to changes in coral communities as a result of habitat destruction by cots, hurricanes etc. This mostly affects small specialized species that are closely associated with Acropora and Pocillopora corals (eg. Plectroglyphidon dicki – see Green 2002).

  • Changes in density (particularly peaks in abundance in 1985 and 2001) were primarily due to surgeonfishes (see Fig 10, Green et al 2005). These pulses are associated with mass recruitment events of C. striatus (Birkeland et al 1987; Green et al 2005).

  • Coral reef fish communities in FB and elsewhere around Tutuila are still showing signs of overfishing. Several large species that are characteristic of unfished reefs in the Indo-Pacific remain conspicuous by their absence or small size. They include species such as maori wrasse (Chelinus undulatus), sharks, and larger species of serranids and scarids, all of which are known to be particularly vulnerable to fishing.

CONTENTS
EXECUTIVE SUMMARY………………………………………………………………2

CONTENTS……………………………………………………………………………...4

INTRODUCTION………………………………………………………………………..5

METHODS……………………………………………………………………………….5

Survey techniques- Fagatele Bay National Marine Sanctuary…………….....5

Corals……………………………………………………………………..5

Benthic……………………………………………………………………6

Reef Fishes………………………………………………………………..7



Survey techniques- Pago Pago Harbor………………………………………...8

Survey techniques- The Aua Transect…………………………………………8

Survey techniques- Historic fish transects around Tutuila…………………...8

Data analysis……………………………………………………………………..9

RESULTS………………………………………………………………………………..10



Fagatele Bay National Marine Sanctuary…………………………………….10

Corals in Fagatele Bay- 2007/8………………………………………….10

Trends in Fagatele Bay coral populations 2004-2007/8…………………14

Benthic Cover in Fagatle Bay…………………………………………....18

Fish in Fagatele Bay- 2007/8…………………………………………….23

Trends in Fagatele Bay fish populations 2004-2007/8…………………..25



Reefs around Tutuila…………………………………………………………...26

Corals in Pago Pago Harbor 2007………………………………………..26

Trends in coral populations in Pago Pago Harbor 2004-2007/8…………26

Benthic Cover in Pago Pago Harbor……………………………………..29

The Aua Transect………………………………………………………...30

Fagasa Bay Benthic Data………………………………………………...33

Historic Fish Transects 2004-2007………………………………………34

DISCUSSION……………………………………………………………………………38



Fagatele Bay National Marine Sanctuary……………………………………..38

Coral communities in Fagatele Bay……………………………………...38

Corals in Pago Pago Harbor……………………………………………...39

Fish communities in Fagatele Bay……………………………………….40

REFERENCES…………………………………………………………………………...41

APPENDIX 1 – Coral Data 2007/8 (Fagatele Bay)……………………………………...44

APPENDIX 2- Benthic Species Data……………………………………………………57

INTRODUCTION
The coral reefs of American Samoa have suffered many destructive events in the last few decades, including a major outbreak of the corallivorous starfish Acanthaster planci, several hurricanes varying from devastating to relatively mild, periods of high water temperature, and exposure during unusually low tides (Birkeland et al 1996, 2003, 2004, 2008, Green 1996, 1997, 2002, Green et al 1999). The reefs in some locations, such as Pago Pago Harbor, have also been subjected to chronic human influences including sedimentation, eutrophication, pollution and overfishing (Birkeland et al, 1996, 2003, 2004, Green 1996, 1997, 2002, Green et al 1997). As a direct result of these disturbances, the reefs of Fagatele Bay National Marine Sanctuary (FBMNS) and other locations around Tutuila Island have undergone some major changes in the last 30 years (Birkeland et al 1996, 2003, 2008, Green et al 1997, 2005). Of particular concern have been the physical and biological changes to the coral communities in some locations.
Coral communities provide important habitat for reef fishes and changes in their condition may have important consequences for the associated fish fauna. The coral reef communities of Fagatele Bay and other sites around Tutuila have been the subjects of a long term monitoring program since the late 1970’s, supported by the Fagatele Bay National Marine Sanctuary program. The purpose of the ongoing monitoring of coral reef communities is to document the recovery, or further decline, of coral and fish communities in Fagatele Bay, and elsewhere around Tutuila, and to determine if reef communities have changed substantially since the combined effects of A. planci outbreaks and hurricanes that devastated American Samoa reefs in the past 30 years.
The results of the monitoring program have been used to describe the changes in the coral and fish communities of American Samoa during the 26 years from 1978-2004 (Birkeland et al 1987, 1994, 1996, 2003, 2004, Green et al 1999). This report documents the results from surveys in Fagatele Bay National Marine Sanctuary conducted in November, 2007 and May, 2008.
In 1917, Alfred Mayor established the permanent transect across the reef flat in front of Aua village and it has become the oldest long-term coral-reef quantitative transect in the Pacific Ocean. In August 2007, with our assistance, the U.S. Geodetic Survey established an official benchmark at the offshore end of the transect. We replicated another survey of the corals and other aspects of the benthic community on its 90th year.

METHODS



Survey techniques – Fagatele Bay National Marine Sanctuary


Corals

From 1985 to 2001, corals were surveyed using point-quarter method (Birkeland et al 1987). In 2004, the coral survey method was changed to belt transects because they produce a much larger sample in an equivalent time period than the point-quarter method (Green et al 2005). This method is also directly compatible with archipelago-wide surveys (Mundy, 1996; Fisk and Birkeland, 2002). Belt transect methods were used to survey coral communities in 2007/2008.


We recorded all corals whose center occurred in a 0.5 m wide belt transect laid perpendicular to four of the six permanent transect lines in FBNMS (Transects 2-5, Figure 1). Transect tapes were 20 m long, but on occasion dive time did not allow the completion of the full 20 m. When that happened, the length that was recorded was noted and the area adjusted accordingly. Each coral was identified to species, and the maximum diameter measured. Corals were then categorized into one of seven size classes based on the maximum diameter of the colony; <5cm, 5-10cm, 10-20cm, 20-40cm, 40-80cm, 80-160cm, and >160cm. We collected data at Sites 2 to 5, at 3, 6, 9, and 12 m depth. Weather and time did not allow collecting data on transects 1 and 6. Coral data were collected in November, 2007 by Charles Birkeland and Douglas Fenner, and May, 2005 by Douglas Fenner.
Benthos

Few benthic surveys have been conducted in Fagatele Bay and for those that have been undertaken, methods, sampling intensity and time of year have all varied. These differences make it very difficult to draw conclusions about changes over time, especially for the algae, which are typically seasonal and show changes in diversity and biomass throughout the year. Therefore the goal in this survey was to provide data that could be easily compared to previous studies and in particular, the study undertaken by Green et al in 2004, where benthic organisms were identified to functional form. Consequently, for the purposes of this study, benthic organisms were also identified to functional form. Additionally, macroalgae were identified to the lowest taxonomic level possible, with the exception of crustose coralline algae (CCA) and turf.


Benthic surveys were undertaken for Fagatele Bay, Pago Pago Harbor (at Rainmaker and Aua) and for Fagasa (at Cape Larsen and Sita Bay). Following the method established by Green et al (2004), forty-eight points were sampled along the 30 m fish belt transects. The substrate under the tape was identified every two meters and the substrate at a point approximately 1 m on either side of, and perpendicular to the tape at 1m was also identified (NB: except at Fagasa, where three 30 m transects were laid end to end, for a total of 144 points per transect). The benthos was classified into one of the following 23 categories:
Corals (branching, digitate, encrusting, foliaceous, massive, mushroom, plate)

Macroalgae (encrusting, blue green, Halimeda, macroalgae, crustose coralline algae - CCA)

Invertebrate (ascidian, clam, hydrozoan, soft coral, sponge, urchin, zooanthid); and

Non-living (crevice/hole; reef matrix, rubble, sand)


Additionally, macroalgae were identified to the lowest level possible. For species that could not be identified in the field, representative voucher samples were collected. Representative samples of CCA were collected in the vicinity of the transects, when the surveys were complete. Coralline algae require extensive laboratory analysis in order to make definitive identifications. Tentative identifications of specimens collected in this survey are included in the report and final identifications will be will be submitted as an addendum when they are complete. Cheryl Squair collected the benthic data.
Reef Fishes

Reef fishes were surveyed using the same underwater visual census techniques used in previous surveys: 30 x 2m belt transects laid perpendicular to the four permanent transect lines in FBNMS (Transects 2-5, Figure 1). This method is described in detail by Birkeland et al. (1987, 1994). In addition to recording fish species and abundance on each transect as in all previous surveys, fish sizes have also been recorded since 1998.


Due to bad weather and limited boat access, only one of the permanent transect lines (Transect 2, depths 3, 6, 9, 12 and 18m) was surveyed by Alison Green in November 2007 (this report). The remaining permanent transect lines will be surveyed by Ben Carroll, and results of these surveys will be provided when they have been completed. Alison Green also conducted the fish surveys in 1995, 1998 and 2001, while two other observers conducted the surveys in 1985 and 1988 (Richard Wass and Steve Amesbury respectively).


Figure 1. Map of Fagatele Bay showing six permanent transects (T1 – T6) and the approximate locations of the coral and fish surveys at each depth along each transect. The locations of three reef flat sites (A-C) are also indicated.

Survey techniques – Pago Pago Harbor

The two sites in Pago Pago Harbor (Rainmaker Hotel and Aua, Figure 2), which provide useful information for management (Birkeland et al 2004), were resurveyed in 2007 in conjunction with the Fagatele Bay surveys. At these two sites, corals were surveyed at 3 m and 6 m depths on the reef slope. Survey methods were as described above, with corals surveyed in a single 30 x 0.5 m belt transect at each depth and with each colony identified to species and categorized into one of seven size classes.



The Aua Transect

The methods are described in detail in Green et al. (1997). The corals were counted in 0.25 m2 quadrats that were tossed haphazardly within about 10 m to either side of the transect, with an equal number of quadrats on each side, within a set of zones between the shore and the reef crest. The transect now began 91 m from shore because this was now the seaward extent of the burrow pit.



Survey techniques – Historic fish transects around Tutuila
Fish communities were surveyed on the reef slope at each of three sites (Fagatele Bay 12 m, Sita Bay 5-6 m and Cape Larsen 8-9 m) on eight occasions from 1977 to 2007. These sites were initially surveyed as part of an assessment of the impacts of the crown-of-thorns starfish, Acanthaster planci (see Birkeland et al. 1987, 2003). We have continued to survey these sites as part of the Fagatele Bay surveys, because they form the oldest continuous survey data for coral reef fishes from American Samoa. One large transect (100 m x 2 m) was surveyed at each site from 1977 to 2001, because they were originally designed as part of a different project (see Wass 1982). In 2004, survey methods were modified to include three replicate 30m x 2m transects at each site, rather than a continuous 100 m x 2 m transect. This allowed us to survey a similar area, while introducing replication into the survey design. The exact location of the start of each of the transects is described in Birkeland et al. (1987), and GPS co-ordinates were recorded at each site in 2004 to facilitate relocation (Appendix 1, Green et al 2004). Alison Green conducted the fish surveys in 1995, 1998, 2001, 2004 and 2007, while two other observers conducted the surveys in 1977 and 1985 (Richard Wass) and 1988 (Steve Amesbury).

Figure 2. Map of Tutuila showing the location of Fagatele Bay National Marine Sanctuary, the two coral survey sites in Pago Pago Harbour (Rainmaker and Aua), and the location of the three historic fish transects around the island (Cape Larsen, Sita Bay and Fagatele Bay).

Data analysis

Coral data from Fagatele Bay and the two sites in Pago Pago Harbor were summarized to determine the abundance and percent coral cover at each depth. Percent cover was calculated according to Mundy (1996), based on using the maximum diameter as the diameter of a circle, and using the mid-point of each size class.


Percent cover was calculated from benthic data by dividing the number of points of a given category, by the total number of points on the transect and multiplying by 100. To allow for comparison between years, data were grouped into the above categories, even where more detailed information was available.
Fish data from Fagatele Bay and the three historic fish transects (Fagatele Bay, Cape Larsen and Sita Bay) were summarised to determine the relative abundance and species richness at each site and each depth. Fish data from the historic transects were also converted to density estimates (no. individuals per hectare) to make the data among years more comparable (to adjust for the change in sampling area in the 2004 surveys), and to match international standards for fish survey data.
Long term trends in coral and fish communities in Fagatele Bay, Pago Pago Harbour and other sites around Tutuila were compared from 1977-1985 to 2007.
Fish size data in Fagatele Bay are only available for the three most recent surveys (2001, 2004 and 2007). These data will be summarised at the family level to determine the size-frequency of four important fisheries families over the last seven years once all the data have been collected: Acanthuridae (surgeonfishes), Scaridae (parrotfishes), Lujanidae (snappers) and Serranidae (groupers, see Green 2002 for further details). Size frequency of two important fisheries species will also be compared over the last seven years: Cephalopholis argus (Family Serranidae) and Ctenochaetus striatus (Family Acanthuridae).

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