Spatial patterns of coral reef benthic communities vary across a range of broad-scale biogeographical levels to fine-scale local habitat conditions. This study described spatial patterns of coral reef benthic communities spanning across the 536-km coast of Kenya. Thirty-eight reef sites representing different geographical zones within an array of habitats and management levels were assessed by benthic cover, coral genera and coral colony size classes. Three geographical zones were identified along the latitudinal gradient based on their benthic community composition. Hard coral dominated the three zones with highest cover in the south and Porites being the most abundant genus. Almost all 15 benthic variables differed significantly between geographical zones. The interaction of habitat factors and management levels created a localised pattern within each zone. Four habitats were identified based on their similarity in benthic community composition; 1. Deep-Exposed Patch reef in Reserve areas (DEPR), 2. Deep-Exposed Fringing reefs in Unprotected areas (DEFU), 3. Shallow Fringing and Lagoon reefs in Protected and Reserve areas (SFLPR) and 4. Shallow Patch and Channel reefs (SPC). DEPR was found in the north zone only and its benthic community was predominantly crustose coralline algae. DEFU was found in central and south zones mainly dominated by soft corals, Acropora, Montipora, juvenile corals and small colonies of adult corals. SFLPR was dominated by macroalgae and turf algae and was found in north and central zones. SPC was found across all geographical zones with a benthic community dominated by hard corals of mostly large colonies of Porites and Echinopora. The north zone exhibits habitat types that support resistance properties, the south supports recovery processes and central zone acts as an ecological corridor between zones. Identifying habitats with different roles in reef resilience is useful information for marine spatial planning and supports the process of designing effective marine protected areas.
Distributions of Species
Marine turtles are of conservation concern throughout their range, with past population declines largely due to exploitation through both legal and illegal take, and incidental capture in fisheries. Whilst much research effort has been focused on nesting beaches and elaborating migratory corridors, these species spend the vast majority of their life-cycle in foraging grounds, which are, in some species, quite discrete. To understand and manage these populations, empirical data are needed on distribution, space-use, and habitats to best inform design of protective measures. Here we describe space-use, occupancy, and wide-ranging movements derived from conventional flipper tagging and satellite tracking of sub-adult green turtles (Chelonia mydas) within the coastal waters of the Turks and Caicos Islands (TCI; 2011–2017). 623 turtles were fitted with flipper tags, with 69 subsequently recaptured, five of which in international waters. Sixteen individual turtles of between 63 and 81 cm curved carapace length were satellite tracked for a mean 226 days (range: 38–496). Data revealed extended periods of occupancy in the shallow coastal waters within a RAMSAR protected area. Satellite tracking and flipper tagging showed wide-ranging movements, with flipper tag recaptures occurring in waters off Nicaragua (n = 4), and Venezuela (n = 1). Also, four of 16 satellite tracked turtles exhibiting directed movements away (displaced >450 km) from TCI waters traveling through nine geo-political zones within the Caribbean-Atlantic basin, as well as on the High Seas. One turtle traveled to the Central American coast before settling on inshore habitat in Colombia’s waters for 162 days before transmission ceased, indicating ontogenetic dispersal to a distant foraging habitat. These data highlight connectivity throughout the region, displaying key linkages between countries that have previously only been linked by genetic evidence. This study also provides evidence of the importance of the Turks and Caicos Islands marine protected area network and importance of effective management of the sea turtle fishery for regional green turtle populations.
Satellite telemetry is a valuable tool for examining long-term, large scale movements of highly migratory species. Tracking data can be used by resource managers to protect habitat and ensure recovery of threatened and endangered species. Few tracking studies have focused on habitat use patterns of juvenile, neritic stage turtles. Satellite tracking surveys were conducted to assess juvenile green turtle movements in the northwestern Gulf of Mexico during 2006–2010. Fifteen turtles were equipped with platform terminal transmitters (PTT; 3 rehabilitated, 12 wild). Mean track duration was 129 days (range: 16–344 days). A hierarchical switching state-space model (hSSM) was applied to extrapolate population level foraging/resident versus migratory movements. All turtles displayed residency in Texas bays during summer months (March-November) while five individuals exhibited seasonal migrations into Mexican waters following passage of strong cold fronts in December and January. Winter (e.g., Mexico) versus summer (e.g., Texas) core areas were not significantly different. Winter 95% contours were significantly larger than summer (summer: 125.4 ± 47.5 km2, n = 15; winter: 274.4 ± 252.9 km2, n = 5). Space-time hot spot analysis provided a new and unique approach for conducting spatiotemporal cluster analysis, and was applied to migratory turtles to determine monthly changes in distribution and habitat associations. Changes in hot spots over time were detected within the lower regions of the Laguna Madre with punctuated intervals of hot spot activity. Upper regions of the Laguna Madre were identified as new hot spots in the later part of the year (e.g., Fall/Winter). Within core areas in Texas, seagrasses comprised an average density of 32.4% while 87.5% of the total available seagrass habitat occurred within the 95% KDE contour. Based on PTT and historic tide station surface water temperatures, all turtles tracked over winter migrations and residencies (n = 5) remained within waters > 15°C, suggesting a threshold temperature at which migration behavior may be initiated. Continued recovery of threatened and endangered sea turtle populations depends on a comprehensive examination of patterns in habitat use. These data suggest cooperation between the United States and Mexico is needed to protect critical habitat and enhance recovery of this species.
The Western North-Pacific (WNP) gray whale feeding grounds are off the northeastern coast of Sakhalin Island, Russia and is comprised of a nearshore and offshore component that can be distinguished by both depth and location. Spatial movements of gray whales within their foraging grounds were examined based on 13 years of opportunistic vessel and shore-based photo-identification surveys. Site fidelity was assessed by examining annual return and resighting rates. Lagged Identification Rates (LIR) analyses were conducted to estimate the residency and transitional movement patterns within the two components of their feeding grounds. In total 243 individuals were identified from 2002–2014, among these were 94 calves. The annual return rate over the period 2002–2014 was 72%, excluding 35 calves only seen one year. Approximately 20% of the individuals identified from 2002–2010 were seen every year after their initial sighting (including eight individuals that returned for 13 consecutive years). The majority (239) of the WNP whales were observed in the nearshore area while only half (122) were found in the deeper offshore area. Within a foraging season, there was a significantly higher probability of gray whales moving from the nearshore to the offshore area. No mother-calf pairs, calves or yearlings were observed in the offshore area, which was increasingly used by mature animals. The annual return rates, and population growth rates that are primarily a result of calf production with little evidence of immigration, suggest that this population is demographically self-contained and that both the nearshore and offshore Sakhalin feeding grounds are critically important areas for their summer annual foraging activities. The nearshore habitat is also important for mother-calf pairs, younger individuals, and recently weaned calves. Nearshore feeding could also be energetically less costly compared to foraging in the deeper offshore habitat and provide more protection from predators, such as killer whales.
Global oceans are absorbing over 90% of the heat trapped in our atmosphere due to accumulated anthropogenic greenhouse gases, resulting in increasing ocean temperatures. Such changes may influence marine ectotherms, such as sharks, as their body temperature concurrently increases toward their upper thermal limits. Sharks are high trophic level predators that play a key role in the regulation of ecosystem structure and health. Because many sharks are already threatened, it is especially important to understand the impact of climate change on these species. We used shark occurrence records collected by commercial fisheries within the Australian continental Exclusive Economic Zone (EEZ) to predict changes in future (2050–2099) relative to current (1956–2005) habitat suitability for pelagic sharks based on an ensemble of climate models and emission scenarios. Our predictive models indicate that future sea temperatures are likely to shift the location of suitable shark habitat within the Australian EEZ. On average, suitable habitat is predicted to decrease within the EEZ for requiem and increase for mackerel sharks, however, the direction and severity of change was highly influenced by the choice of climate model. Our results indicate the need to consider climate change scenarios as part of future shark management and suggest that more broad-scale studies are needed for these pelagic species.
In the Northwestern Mediterranean Sea, the European sardine (Sardina pilchardus) and the European anchovy (Engraulis encrasicolus) are the most important small pelagic fish in terms of biomass and commercial interest. During the last years, these species have experimented changes in their abundance and biomass trends in the Northwestern Mediterranean Sea, in addition to changes in growth, reproduction and body condition. These species are particularly sensitive to environmental fluctuations with possible cascading effects as they play a key role in connecting the lower and upper trophic levels of marine food webs. It is therefore essential to understand the factors that most profoundly affect sardine and anchovy dynamics. This study used a two-step approach to understand how the environment influences the adult stages of these species in the Northwestern Mediterranean Sea. First, we explored the effects of environmental change over time using Random Forests and available datasets of species occurrence, abundance, biomass and landings. We then applied species distribution models to test the impact of the extreme pessimistic and optimistic Intergovernmental Panel on Climate Change (IPCC) pathway scenarios, and to identify possible climate refuges: areas where these species may be able to persist under future environmental change. Findings from the temporal modeling showed mixed effects between environmental variables and for anchovy and sardine datasets. Future pathway projections highlight that both anchovy and sardine will undergo a reduction in their spatial distributions due to future climate conditions. The future climate refuges are the waters around the Rhone River (France) and the Ebro River (Spain) for both species. This study also highlights important knowledge gaps in our understanding of the dynamics of small pelagic fish in the region, which is needed to progress towards an ecosystem approach to fisheries management.
Coexistence of ecologically similar species occupying the same geographic location (sympatry) poses questions regarding how their populations persist without leading to competitive exclusion. There is increasing evidence to show that micro-variations in habitat use may promote coexistence through minimizing direct competition for space and resources. We used two sympatric marine predators that show high fidelity to a small, remote coral atoll as a model to investigate how temporally dynamic partitioning of space use may promote coexistence. Using novel methods (difference network analysis and dynamic space occupancy analysis), we revealed that even though blacktip reef sharks Carcharhinus melanopterus and sicklefin lemon sharks Negaprion acutidens both show focused use of the same atoll habitats, the spatio-temporal dynamics of their use was partitioned such that they only shared the same microhabitats 26% of the time. Moreover, the degree of overlap was strongly influenced by the tidal cycle, peaking at ∼35% at higher tides as both species appear to target similar intertidal micro-habitats despite the increase in available space. Our work provides a rare example of how two marine predators with similar ecological roles and habitat preferences may coexist in the same place through dynamic segregation of habitat use in space and time, potentially reflecting adaptive behavioral traits for minimizing interactions. The strong influence of small tidal variation on species habitat use and partitioning also raises concerns over how atoll ecosystem dynamics may be influenced by sea level rises that could alter tidal dynamics.
Glacier Bay National Park and Preserve (GBNPP) in Southeast Alaska is a system of glaciated fjords with a unique and recent history of deglaciation. As such, it can serve as a natural laboratory for studying patterns of distribution in marine communities with proximity to glacial influence. In order to examine the changes in fjord-based coral communities, underwater photo-quadrats were collected during multipurpose dives with a remotely operated vehicle (ROV) in March of 2016. Ten sites were chosen to represent the geochronological and oceanographic gradients present in GBNPP. Each site was surveyed vertically between 100 and 420 meters depth and photo-quadrats were extracted from the video strip transects for analysis. The ROV was equipped with onboard CTD which recorded environmental data (temperature and salinity), in order to confirm the uniformity of these characteristics at depth across the fjords. The percent cover and diversity of species were lowest near the glaciated heads of the fjords and highest in the Central Channel and at the mouths of the fjords. Diversity is highest where characteristics such as low sedimentation and increased tidal currents are predominant. The diverse communities at the mouths of the fjords and in the Central Channel were dominated by large colonies of the Red Tree Coral, Primnoa pacifica, as well as sponges, brachiopods, multiple species of cnidarians, echinoderms, molluscs and arthropods. The communities at the heads of the fjords were heavily dominated by pioneering species such as brachiopoda, hydrozoan turf, the encrusting stoloniferan coral Sarcodyction incrustans, and smaller colonies of P. pacifica. This research documents a gradient of species dominance from the Central Channel to the heads of the glaciated fjords, which is hypothesized to be driven by a combination of physical and biological factors such as glacial sedimentation, nutrient availability, larval dispersal, and competition.
Epizoic diatoms form an important part of micro-epibiota of marine vertebrates such as whales and sea turtles. The present study explores and compares the diversity and biogeography of diatom communities growing on the skin and shell of loggerhead sea turtles (Caretta caretta) from four different localities: Adriatic Sea (Croatia), Ionian Sea (Greece), South Africa and Florida Bay (USA) using both light and scanning electron microscopy. We observed almost 400 diatom taxa belonging to more than 100 genera. Diatom communities from Greece and Croatia showed the highest similarity and were statistically different from those recorded from South Africa and Florida. Part of this variation could be attributed to differences in sampling techniques; however, we believe that geography had an important role. In general, contrary to several previous observations from sea turtles, the presumably exclusively epizoic diatoms contributed less than common benthic taxa to the total diatom flora, which might have been related to the loggerhead feeding behavior. Moreover, skin samples differed from carapace samples in having a distinct diatom composition with a higher proportion of the putative true epizoonts. Our results indicate that epizoic diatom communities differ according to loggerhead geographical location and substrate (skin vs. carapace). The relative abundances of common benthic diatoms and putative exclusive epizoic taxa may inform about sea turtle habitat use or behavior though detailed comparisons among different host species have yet to be performed.
The decline in numbers of reef manta rays (Mobula alfredi) throughout their range has highlighted the need for improved information on their spatial ecology in order to design effective conservation strategies for vulnerable populations. To understand their patterns of movement in Seychelles, we used three techniques—archival pop-up satellite tags, acoustic tags, and photo-identification—and focussed on the aggregation at D’Arros Island and St. Joseph Atoll within the Amirantes Group. M. alfredi were photographed within six of the seven Island Groups of Seychelles, with 64% of individuals being resighted at least once between July 2006 and December 2019 over timeframes of 1–3,462 days (9.5 years; median = 1,018 days). Only three individuals from D’Arros Island were resighted at a second aggregation site located more than 200 km away at St. François Atoll during photo-identification surveys. Satellite-tracked M. alfredi (n = 5 tracks; maximum 180 days) remained within the boundary of the Seychelles Exclusive Economic Zone, where they spent the majority of their time (87%) in the upper 50 m of the water column in close proximity to the Amirantes Bank. The inclusion of acoustic tagging data in the models of estimated satellite-track paths significantly reduced the errors associated with the geolocation positions derived from archived light level data. The insights gained into the patterns of horizontal and vertical movements of M. alfredi using this multi-technique approach highlight the significance of D’Arros Island and St. Joseph Atoll, and the wider Amirantes Group, to M. alfredi in Seychelles, and will benefit future conservation efforts for this species within Seychelles and the broader Western Indian Ocean.