James E. Maragos

Baselines and degradation of coral reefs in the Northern Line Islands.

Effective conservation requires rigorous baselines of pristine conditions to assess the impacts of human activities and to evaluate the efficacy of management. Most coral reefs are moderately to severely degraded by local human activities such as fishing and pollution as well as global change, hence it is difficult to separate local from global effects. To this end, we surveyed coral reefs on uninhabited atolls in the northern Line Islands to provide a baseline of reef community structure, and on increasingly populated atolls to document changes associated with human activities. We found that top predators and reef-building organisms dominated unpopulated Kingman and Palmyra, while small planktivorous fishes and fleshy algae dominated the populated atolls of Tabuaeran and Kiritimati. Sharks and other top predators overwhelmed the fish assemblages on Kingman and Palmyra so that the biomass pyramid was inverted (top-heavy). In contrast, the biomass pyramid at Tabuaeran and Kiritimati exhibited the typical bottom-heavy pattern. Reefs without people exhibited less coral disease and greater coral recruitment relative to more inhabited reefs. Thus, protection from overfishing and pollution appears to increase the resilience of reef ecosystems to the effects of global warming.

Phase shift from a coral to a corallimorph-dominated reef associated with a shipwreck on Palmyra atoll.

Coral reefs can undergo relatively rapid changes in the dominant biota, a phenomenon referred to as phase shift. Various reasons have been proposed to explain this phenomenon including increased human disturbance, pollution, or changes in coral reef biota that serve a major ecological function such as depletion of grazers. However, pinpointing the actual factors potentially responsible can be problematic. Here we show a phase shift from coral to the corallimorpharian Rhodactis howesii associated with a long line vessel that wrecked in 1991 on an isolated atoll (Palmyra) in the central Pacific Ocean. We documented high densities of R. howesii near the ship that progressively decreased with distance from the ship whereas R. howesii were rare to absent in other parts of the atoll. We also confirmed high densities of R. howesii around several buoys recently installed on the atoll in 2001. This is the first time that a phase shift on a coral reef has been unambiguously associated with man-made structures. This association was made, in part, because of the remoteness of Palmyra and its recent history of minimal human habitation or impact. Phase shifts can have long-term negative ramification for coral reefs, and eradication of organisms responsible for phase shifts in marine ecosystems can be difficult, particularly if such organisms cover a large area. The extensive R. howesii invasion and subsequent loss of coral reef habitat at Palmyra also highlights the importance of rapid removal of shipwrecks on corals reefs to mitigate the potential of reef overgrowth by invasives.

2000-2002 Rapid Ecological Assessment of Corals (Anthozoa) on Shallow Reefs of the Northwestern Hawaiian Islands. Part 1: Species and Distribution

Rapid Ecological Assessment (REA) surveys at 465 sites on 11 reefs in the Northwestern Hawaiian Islands (NWHI) inventoried coral species, their relative abundances, and their distributions during 2000-2002. Surveys (462) around the 10 islands were in depths of a 20 m, and three surveys on the submerged Raita Bank were in depths of 30Ð35 m. Data from 401 REA sites met criteria for quantitative analysis. Results include 11 first records for stony coral species in the Hawaiian Archipelago and 29 range extensions to the NWHI. Several species may be new to science. There are now 57 stony coral species known in the shallow subtropical waters of the NWHI, similar to the 59 shallow and deep-water species known in the better-studied and more tropical main Hawaiian Islands. Coral endemism is high in the NWHI: 17 endemic species (30%) account for 37-53% of the abundance of stony corals on each reef of the NWHI. Three genera (Montipora, Porites, Pocillopora) contain 15 of the 17 endemic species and most of the endemic abundance. Seven Acropora species are now known from the central NWHI despite their near absence from the main Hawaiian Islands. Coral abundance and diversity are highest at the large, open atolls of the central NWHI (French Frigate, Maro, Lisianski) and decline gradually through the remaining atolls to the northwest (Pearl and Hermes, Midway, and Kure). Stony corals are also less abundant and less diverse off the exposed basalt islands to the southeast (Nihoa, Necker, La Perouse, Gardner), where soft corals (Sinularia, Palythoa) are more abundant. Exposure to severe wave action appears to limit coral development off these small islands and surrounding deep platforms. Temperature extremes and natural accumulation of lagoon sediments may contribute to decline of coral species and abundance at the northwestern end of the chain.

Modeling patterns of coral bleaching at a remote Central Pacific atoll.

A mild bleaching event (9.2% prevalence) at Palmyra Atoll occurred in response to the 2009 ENSO, when mean water temperature reached 29.8-30.1 degrees C. Prevalence among both abundant and sparse taxa varied with no clear pattern in susceptibility relating to coral morphology. Seven taxon-specific models showed that turbidity exacerbated while prior exposure to higher background temperatures alleviated bleaching, with these predictors explaining an average 16.3% and 11.5% variation in prevalence patterns, respectively. Positive associations occurred between bleaching prevalence and both immediate temperature during the bleaching event (average 8.4% variation explained) and increased sand cover (average 3.7%). Despite these associations, mean unexplained variation in prevalence equalled 59%. Lower bleaching prevalence in areas experiencing higher background temperatures suggests acclimation to temperature stress among several coral genera, while WWII modifications may still be impacting the reefs via shoreline sediment re-distribution and increased turbidity, exacerbating coral bleaching susceptibility during periods of high temperature stress.

Oil damages corals exposed to air

Abstract It has often been assumed that the tropical marine environment with its rich diversity of species is difficult to harm by pollution. This now seems quite untrue. Corals provide an important habitat for many creatures and are now exposed to oil pollution as never before. Here is evidence that some reef-building corals can be seriously damaged if coated with oil.

First record of mass coral bleaching in the Northwestern Hawaiian Islands

Mass bleaching events have become increasingly common on coral reefs throughout the world (Williams and Bunkley-Williams 1990; Berkelmans and Oliver 1999) and now, for the first time, have been observed in the Northwestern Hawaiian Islands (NWHI). During a September 2002 survey expedition to the NWHI, we observed substantial bleaching (greater than 20% of the corals) on reefs at the three northwestern-most atolls of the Hawaiian Archipelago: Kure, Midway, and Pearl and Hermes. There was lesser bleaching on reefs at two adjacent islands: Lisianski and Maro. In areas where bleaching was occurring, visual estimates of the extent of bleaching ranged from 20 to 100% of the most common corals (Fig. 1). Prior surveys in the NWHI between 1980 and 2001 found little evidence of bleaching, although minor bleaching of corals was reported in 1996 in the main Hawaiian Islands (Maragos 2000). Bleaching corals were predominantly in the scleractinian genera Montipora and Pocillopora, and to a lesser extent Porites. This differential susceptibility to bleaching is consistent with reports from other areas of the Indo-Pacific (Marshall and Baird 2000). According to NOAA sea surface temperature (SST) information (www.coris.noaa.gov), water temperatures at Midway rose to nearly 29 C at the beginning of August and remained elevated throughout the month. This is a 2 C increase over the usual summer maximum water temperature at Midway (27 C) and is therefore a likely explanation for the observed bleaching response. Much of the bleaching occurred in shallow back-reef habitats and so exposure to UV radiation may have also contributed to this bleaching event.

US Coral Reefs in the Line and Phoenix Islands, Central Pacific Ocean: Status, Threats and Significance

This is the second of two chapters on the coral reefs of the five US Line and Phoenix Islands, consisting of Baker, Howland and Jarvis Islands, Kingman Reef, ; and Palmyra Atoll (Fig. 16.1). The previous chapter (Chapter 15, Maragos et al.) covers the history, geology, oceanography and biology, while this chapter covers the status, threats and significance of the five. All are low reef islets or atolls in the central Pacific Ocean administered by the US Fish and Wildlife Service as National Wildlife Refuges. These 5 Refuges are among 20 within the tropical Pacific and among 10 that protect coral reefs. Together they are geographically a part of the largest series of fully protected marine areas under unified management in the world.

The Lagoon at Caroline/Millennium Atoll, Republic of Kiribati: Natural History of a Nearly Pristine Ecosystem

A series of surveys were carried out to characterize the physical and biological parameters of the Millennium Atoll lagoon during a research expedition in April of 2009. Millennium is a remote coral atoll in the Central Pacific belonging to the Republic of Kiribati, and a member of the Southern Line Islands chain. The atoll is among the few remaining coral reef ecosystems that are relatively pristine. The lagoon is highly enclosed, and was characterized by reticulate patch and line reefs throughout the center of the lagoon as well as perimeter reefs around the rim of the atoll. The depth reached a maximum of 33.3 m in the central region of the lagoon, and averaged between 8.8 and 13.7 m in most of the pools. The deepest areas were found to harbor large platforms of Favia matthaii, which presumably provided a base upon which the dominant corals (Acropora spp.) grew to form the reticulate reef structure. The benthic algal communities consisted mainly of crustose coralline algae (CCA), microfilamentous turf algae and isolated patches of Halimeda spp. and Caulerpa spp. Fish species richness in the lagoon was half of that observed on the adjacent fore reef. The lagoon is likely an important nursery habitat for a number of important fisheries species including the blacktip reef shark and Napoleon wrasse, which are heavily exploited elsewhere around the world but were common in the lagoon at Millennium. The lagoon also supports an abundance of giant clams (Tridacna maxima). Millennium lagoon provides an excellent reference of a relatively undisturbed coral atoll. As with most coral reefs around the world, the lagoon communities of Millennium may be threatened by climate change and associated warming, acidification and sea level rise, as well as sporadic local resource exploitation which is difficult to monitor and enforce because of the atolls remote location. While the remote nature of Millennium has allowed it to remain one of the few nearly pristine coral reef ecosystems in the world, it is imperative that this ecosystem receives protection so that it may survive for future generations.

Proximate environmental drivers of coral communities at Palmyra Atoll: establishing baselines prior to removing a WWII military causeway.

A management proposal aims to partly remove a WWII military causeway at Palmyra Atoll to improve lagoon water circulation and alleviate sedimentation stress on the southeast backreef, an area of high coral cover and diversity. This action could result in a shift in sedimentation across reef sites. To provide management advice, we quantified the proximate environmental factors driving scleractinian coral cover and community patterns at Palmyra. The proportion of fine sedimentation was the optimal predictor of coral cover and changes in community structure, explaining 23.7% and 24.7% of the variation between sites, respectively. Scleractinian coral cover was negatively correlated with increases in fine sedimentation. Removing the causeway could negatively affect the Montipora corals that dominate the western reef terrace, as this genus was negatively correlated with levels of fine sedimentation. The tolerance limits of corals, and sediment re-distribution patterns, should be determined prior to complete removal of the causeway.

The Occurrence of Coral Species Reported as Threatened in Federally Protected Waters of the US Pacific

A recent study reported that seventy-five species of reef-building corals, considered to be at elevated extinction risk when assessed by the criteria of the International Union for Conservation of Nature, occur in Pacific waters under United States jurisdiction. Closer examination substantiates records of occurrence for 66 species, while records for the other 9 species were based on misinterpretations or are otherwise uncertain. Of these, at least 55 have been reported from reef habitat under federal protection within National Parks, Marine National Monuments, National Marine Sanctuaries, and National Wildlife Refuges. The highest number of species (31) is found within the Ofu Island unit of the National Park of American Samoa, followed by Kingman Reef (24) and Palmyra Atoll (21), both within the Pacific Remote Islands Marine National Monument. Federally protected areas already in place serve as important habitats for resources whose stewardship needs and priorities may vary over time.