On a Reef Far, Far Away: Anthropogenic Impacts Following Extreme Storms Affect Sponge Health and Bacterial Communities

Terrestrial runoff can negatively impact marine ecosystems through stressors including excess nutrients, freshwater, sediments, and contaminants. Severe storms, which are increasing with global climate change, generate massive inputs of runoff over short timescales (hours to days); such runoff impacted offshore reefs in the northwest Gulf of Mexico (NW GoM) following severe storms in 2016 and 2017. Several weeks after coastal flooding from these events, NW GoM reef corals, sponges, and other benthic invertebrates ∼185 km offshore experienced mortality (2016 only) and/or sub-lethal stress (both years). To assess the impact of storm-derived runoff on reef filter feeders, we characterized the bacterial communities of two sponges, Agelas clathrodes and Xestospongia muta, from offshore reefs during periods of sub-lethal stress and no stress over a three-year period (2016—2018). Sponge-associated and seawater-associated bacterial communities were altered during both flood years. Additionally, we found evidence of wastewater contamination (based on 16S rRNA gene libraries and quantitative PCR) in offshore sponge samples, but not in seawater samples, following these flood years. Signs of wastewater contamination were absent during the no-flood year. We show that flood events from severe storms have the capacity to reach offshore reef ecosystems and impact resident benthic organisms. Such impacts are most readily detected if baseline data on organismal physiology and associated microbiome composition are available. This highlights the need for molecular and microbial time series of benthic organisms in near- and offshore reef ecosystems, and the continued mitigation of stormwater runoff and climate change impacts.

Density, group composition and encounter rates of humpback whales (Megaptera novaeangliae) in the eastern Comoros Archipelago (C2)

The Comoros Archipelago is an assemblage of oceanic islands, banks and offshore reef systems that longitudinally span the northern MozambiqueChannel. The greater Comoros Archipelago has been designated by the IWC as Wintering sub-Region C2 for humpback whales and is currentlyconsidered data deficient. Since 1997, annual marine mammal surveys of varying length and objective have been carried out in the waters surroundingMayotte, the eastern most island in the Comoros Archipelago. The humpback whales component of these surveys focused effort in and around thelagoon surrounding Mayotte. While it is expected that humpback whales can found throughout Comoros Archipelago it still remains unknown asto what degree humpback whales utilise specific banks and offshore reef systems within this area. Surveys conducted in 2002 and 2003 includedpassing mode and closing mode components intended to examine the density, group composition and encounter rates of humpback whales in anoffshore reef complex and a bank adjacent to the lagoon surround Mayotte. The densities of humpback whales, out to one nautical mile from thesurveyed transects, ranged from 0.027 to 0.618 whales/n.mile2 across three study sites. Females with calves were the most frequently encounteredgroup type. Encounter rates ranged from 0.98 to 2.36 groups per hour of search effort. These results, while exploratory in nature, indicate that theeastern region of the Comoros may be an important area for humpback whales during the late austral winter months and that additional, moreintensive systematic research is warranted.

Environmental DNA metabarcoding for biodiversity monitoring of a highly-diverse tropical fish community in a coral-reef lagoon: Estimation of species richness and detection of habitat segregation

An environmental DNA (eDNA) metabarcoding approach has been widely used for biodiversity monitoring of fishes, although it has rarely been applied to tropical and subtropical aquatic ecosystems, where species diversity is remarkably high. This study examined the extent to which species richness can be estimated in a small coral reef lagoon (1500 × 900 m) near Okinawa Island, southern Japan, where the surrounding waters are likely to harbor more than 1500 species of fish. During 2015–2017, a total of 16 capture-based surveys were conducted to create a faunal list of fish species, followed by eDNA metabarcoding based on seawater samples taken from 11 sites in the lagoon on a day in May 2019. We also tested whether eDNA metabarcoding could detect differences between adjacent fish communities inhabiting the offshore reef edge and shore-side seagrass beds within the lagoon. A total of 217 fish species were confirmed by the capture-based samplings, while 291 fish species were detected by eDNA metabarcoding, identifying a total of 410 species distributed across 119 families and 193 genera. Of these 410 species, only 96 (24% of the total) were commonly identified by both methods, indicating that capture-based surveys failed to collect a number of species detected by eDNA metabarcoding. Interestingly, two different approaches to estimate species richness based on eDNA data yielded values close to the 410 species, including one that suggested an additional three or more eDNA surveys from 11 sites (36 samples) would detect 90% of the 410 species. In addition, non-metric multi-dimensional scaling for fish assemblages clearly distinguished between the fish communities of the offshore reef edge and those of the shore-side seagrass beds.

Offshore transport of floodwaters following extreme storms impacts sponge health and associated microbial communities

Terrestrial runoff can negatively impact marine ecosystems through stressors including excess nutrients, freshwater, sediments, and contaminants. Severe storms, which are increasing with global climate change, generate massive inputs of runoff over short timescales (hours to days); such runoff impacted offshore reefs in the northwest Gulf of Mexico (NW GoM) following severe storms in 2016 and 2017. Several weeks after coastal flooding from these events, NW GoM reef corals, sponges, and other benthic invertebrates experienced mortality (2016 only) and/or sub-lethal stress (both years). To assess the impact of storm-derived runoff on reef filter feeders, we characterized the microbiomes of two sponges, Agelas clathrodes and Xestospongia muta, during periods of lethal stress, sub-lethal stress, and no stress over a three-year period (2016-2018). Increased anaerobes during lethal stress indicate hypoxic conditions were associated with the 2016 mortality event. Additionally, we found evidence of wastewater contamination (based on 16S rRNA gene libraries and quantitative PCR) in sponges 185 km offshore following storms (2016 and 2017), but not during the non-flooding year (2018). We show that flooding after severe storms reaches offshore reef ecosystems and may impact offshore benthic organisms, highlighting the need for molecular and microbial time series from near- and offshore reef ecosystems, and for the continued mitigation of stormwater runoff and climate change impacts.ImportanceStressors associated with terrestrial runoff have contributed to substantial population declines in nearshore marine ecosystems worldwide over the last three decades. It has been assumed that offshore marine ecosystems (>100 km from land) are largely unaffected by terrestrial runoff. Our findings, however, suggest that flooding events can significantly impact offshore marine organisms, based on the detection of shifted microbiomes and human pathogens in offshore sponges after extreme storm events across two separate years, and lack of detection in a non-flooding year.

Assessing the Resilience Potential of Inshore and Offshore Coral Communities in the Western Gulf of Thailand

Coral reefs in the Gulf of Thailand have experienced severe coral bleaching events and anthropogenic disturbances during the last two decades. This study assessed the resilience potential of coral communities at Ko Losin offshore reef sites and Mu Ko Chumphon nearshore coral reefs, in the south of Thailand, by conducting field surveys on the live coral cover, hard substratum composition and diversity and density of juvenile corals. Most study sites had higher percentages of live coral cover compared to dead coral cover. Some inshore and offshore reef sites showed low resilience to coral bleaching events. The total densities of juvenile corals at the study sites were in the range of 0.89–3.73 colonies/m2. The density of the juvenile corals at most reef sites was not dependent on the live coral cover of adult colonies in a reef, particularly for the Acropora communities. We suggest that Ko Losin should be established as a marine protected area, and Mu Ko Chumphon National Park should implement its management plans properly to enhance coral recovery and promote marine ecotourism. Other measures, such as shading, should be also applied at some coral reefs during bleaching periods.

REASON OF FIXATION OF MOUTH OF A SMALL RIVER BEHIND NATURAL REEF

The mechanism by which the mouth of a small river is stably fixed in the wave-shelter zone behind an offshore reef composed of natural rocks was studied, taking a small river flowing into the Moriya coast together with two other small rivers as examples. The beach topography around the river mouth and the shape of the stream behind the reef were measured on this coast, and the wave height distribution around the reef was calculated using the angular spreading method, and the reason why the river mouth is stably fixed at this location was considered. Furthermore, the numerical simulation of beach changes using the BG model when an offshore breakwater was installed as a model of a natural reef was carried out to study the longshore change in the berm height. The primary cause for the fixation of a river mouth behind a reef was found to be the decrease in wave height behind the reef, which in turn decreases in the berm height.