Marine Biology

Abstract
Photosynthesizers face a trade-off regarding light: they need enough to maintain high photosynthetic rates, yet excess leads
to oxidative stress. Despite this, light and its detrimental effects are chronically underestimated. Solar-powered sea slugs
(Sacoglossa: Gastropoda) provide the ideal lens with which to study this trade-off, since they steal chloroplasts from algae
but do not inherit photoacclimation and photorepair capacities. We collected three slug species in Curaçao during March
and December 2022, comparing the amount of light they received in nature to their optimal light intensities for photosynthesis,
and their preferred light intensities. We then investigated behavioral and physiological photoprotection mechanisms
to determine if and how they limit light. Finally, we examined oxidative activity under optimal and excess light. All three
species were naturally exposed to more light (> 1000 μmol m−2 s−1) than is optimal or preferred. Elysia crispata (kleptoplast
retention for > 3 months) is fully exposed to light in nature but reduces the light reaching its kleptoplasts via parapodial
shading. Elysia velutinus retains kleptoplasts for ~ 2 weeks and hides in its macroalgal food, limiting light exposure. Both
species displayed low amounts of oxidative activity under optimal light, which increased slightly under excess light. Elysia
ornata retained chloroplasts for ~ 3 days, lacked observable photoprotection and always displayed high levels of oxidative
activity, potentially explaining its limited capacity for kleptoplast retention. Furthermore, both E. velutinus and E. ornata
display strong light-avoidance behaviors. This study clearly demonstrates links between high light intensities, photoprotection,
and oxidative stress, highlighting the need for future studies that examine aquatic photosynthesizers under natural lighting.

Reef-dwelling Christmas tree worms (Spirobranchus spp.) are common coral associates. Their calcareous tubes are usually embedded in the coral skeleton and can be closed by an operculum. Tubes not overgrown by coral tissue either remain bare or become covered by algae. Despite their widespread distribution, high abundance and striking appearance, little is known about the impact of these worms on their hosts. We quantifed visible coral damage caused by Spirobranchus in Curaçao (Southern Caribbean) and found that 62.6% of worm opercula (n = 1323) caused abrasions and tissue loss in their hosts. Filamentous turf algae, known to be potentially harmful to corals, covered 76.9% of the opercula. Examination of the six most frequently inhabited host species showed a variation in the damage percentages, although this was independent of the presence of epibiotic algae on 78.4% of all opercula. Since injured corals are more susceptible to diseases, the overall negative impact of Spirobranchus worms on their hosts may be more severe than previously assumed.

Bulk stable isotope analysis was used to assess the trophic level and foraging habitats of Caribbean reef sharks (Carcharhinus perezi) compared to three large sympatric predatory teleosts (the Nassau grouper Epinephelus striatus, black grouper Mycteroperca bonaci, and great barracuda Sphyraena barracuda) in an isolated Caribbean coral reef ecosystem. Models and empirical studies have suggested that the depletion of large-bodied sharks in coral reef ecosystems triggers a trophic cascade that could affect the benthic community, favoring algae over coral. The hypothesized cascade is based on the premise that sharks prey on large piscivorous teleost fish that in turn prey on key herbivorous fish. Analysis of nitrogen-stable isotopes (δ15N) from white muscle tissue revealed neither adult or juvenile Caribbean reef sharks were significantly enriched in 15N compared with sympatric predatory teleost species. Linear regression found no evidence of an ontogenetic increase in nitrogen with increasing body size for Caribbean reef sharks; however, there was a significant positive relationship between body size and carbon isotope (δ13C) values. These results suggest that Caribbean reef sharks in isolated systems do not act as the apex predator in coral reef ecosystems primarily feeding on large-bodied sympatric teleosts. Instead, Caribbean reef sharks form part of an upper trophic-level predator guild alongside large-bodied teleosts, which makes the predicted trophic cascade as a result of the removal of reef sharks unlikely. Moreover, the body size–δ13C relationship suggests Caribbean reef sharks exhibit ontogenetic and individual variation in where they feed. The ecological role of this species is, therefore, complex and contextual, similar to carcharhinid species in the Indo-Pacific, emphasizing the need to further elucidate the interactions between reef sharks and the overall coral reef ecosystem so as to best inform effective conservation and management of the species.

Octocorals have increased in abundance on a number of Caribbean reefs, but this trend has largely been reported with functional group or genus resolution. A species-level analysis of octocoral communities in St. John, US Virgin Islands was conducted to better understand how this taxon will respond to changing conditions based on their synecology at two sites that are 1.5 km apart and differ in physical conditions. East Cabritte is characterized by moderate wave energy, low sedimentation, and clear water, while contrasting conditions characterize Europa Bay. Surveys conducted in 2014 and 2015 showed that the abundance and size of adult octocorals differed between sites, with taller and denser communities at East Cabritte than Europa Bay (mean height of 32 versus 20 cm; 18 versus 8 colonies m−2). Octocoral diversity and evenness were similar between sites, although multivariate octocoral community structure differed between sites regardless of whether octocorals were resolved to genera or species. Genus-resolution masked differences between sites for speciose genera like Eunicea. The broad overlap in species representation at both sites suggests that diversity is less responsive than community structure to differing environmental conditions, perhaps because the ecological niches of these species are broad. With 35 octocoral species, and diversity and abundances comparable to those studied > 40 years ago on shallow Caribbean reefs, the dense octocoral communities appearing on some present-day reefs reflect expanded benthic occupancy by a well-known (rather than a novel) community type.

Abstract In response to a call from the US National Research Council for research programs to combine their data to improve sea turtle population assessments, we analyzed somatic growth data for Northwest Atlantic (NWA) loggerhead sea turtles (Caretta caretta) from 10 research programs. We assessed growth dynamics over wide ranges of geography (9–33°N latitude), time (1978–2012), and body size (35.4–103.3 cm carapace length). Generalized additive models revealed significant spatial and temporal variation in growth rates and a sig- nificant decline in growth rates with increasing body size. Growth was more rapid in waters south of the USA (\24°N) than in USA waters. Growth dynamics in southern waters in the NWA need more study because sample size was small. Within USA waters, the significant spatial effect in growth rates of immature loggerheads did not exhibit a consistent latitudinal trend. Growth rates declined signifi- cantly from 1997 through 2007 and then leveled off or increased. During this same interval, annual nest counts in Florida declined by 43 % (Witherington et al. in Ecol Appl 19:30–54, 2009) before rebounding. Whether these simul- taneous declines reflect responses in productivity to a common environmental change should be explored to determine whether somatic growth rates can help interpret population trends based on annual counts of nests or nesting females. Because of the significant spatial and temporal variation in growth rates, population models of NWA loggerheads should avoid employing growth data from restricted spatial or temporal coverage to calculate demographic metrics such as age at sexual maturity. 

The distribution and abundance of juvenile corals were examined at depths from 3 to 37 m on the reefs of Curaçao and Bonaire (Netherlands Antilles). Juveniles of Agaricia agaricites were most abundant (60.6%), followed by Helioseris cucullata (8.3%). The large massive corals such as Montastrea annularis, M. cavernosa and branched species such as Madracis mirabilis and Acropora palmata had few juveniles. This, combined with species characteristics, shows that these species employ very different life history strategies. In some species the abundance of juveniles over the reef paralleled that of larger colonies, but not for example in Agaricia agaricites. The composition of the coral community was apparently no direct function of juvenile abundance. A change in angle of settlement of A. agaricites juveniles with increasing depth, from vertical to horizontal surfaces, seems to reflect the preferred light intensity. We studied the survival of juvenile corals during a half-year period. One-third remained unharmed, one-third died or disappeared, and one-third was limited in growth by factors such as spatial competition. This was the same for all depths, but factors influencing survival varied with depth.

Abstract
Satellite transmitters were deployed on three green turtles, Chelonia mydas, and two hawksbill turtles, Eretmochelys imbricata, nesting in the Lesser Antilles islands, Caribbean, between 2005 and 2007 to obtain pre- liminary information about the inter-nesting, migratory and foraging habitats in the region. Despite the extremely small dataset, both year-round residents and migrants were iden- tified; specifically, (1) two green turtles used local shallow coastal sites within 50 km of the nesting beach during all of their inter-nesting periods and then settled at these sites on completion of their breeding seasons, (2) one hawksbill turtle travelled 200 km westward before reversing direction and settling within 50 km of the original nesting beach and (3) one green and one hawksbill turtle initially nested at the proximate site, before permanently relocating to an alter- native nesting site over 190 km distant. A lack of nesting beach fidelity was supported by flipper tag datasets for the region. Tagging datasets from 2002 to 2012 supported that some green and hawksbill individuals exhibit low fidelity to nesting beaches, whereas other females exhibited a high degree of fidelity (26 turtles tagged, 40.0 km maximum distance recorded from original nesting beach). Individual turtles nesting on St Eustatius and St Maarten appear to exhibit behavioural plasticity in their inter-nesting behav- iour and post-nesting migration routes in the eastern Carib- bean. The tracking and tagging data combined indicate that some of the green and hawksbill females that nest in the Lesser Antilles islands are year-round residents, whilst oth- ers may nest and forage at alternative sites. Thus, continued year-round protection of these islands and implementation of protection programmes in nearby islands could contrib- ute towards safeguarding the green and hawksbill popula- tions of the region. 

The red lionfish (Pterois volitans) is an invasive predatory marine fish that has rapidly expanded its pres- ence in the Western Hemisphere. We collected 214 invasive red lionfish samples from nine countries and territories, including seven unpublished locations. To more compre- hensively evaluate connectivity, we compiled our d-loop sequence data with 846 published sequences, resulting in 1,060 samples from 14 locations. We found low nucleo- tide diversity (π = 0.003) and moderate haplotype diversity (h = 0.59). Using haplotype population pairwise ΦST tests, we analyzed possible phylogeographic breaks that were pre- viously proposed based on other reef organisms. We found support for the Bahamas/Turks/Caicos versus Caribbean break (ΦST = 0.12) but not for the Northwestern Carib- bean, Eastern Caribbean, or US East Coast versus Bahamas breaks. The Northern Region had higher variation and more haplotypes, supporting introductions of at least five haplo- types to the region. Our wide-ranging samples showed that a lower-frequency haplotype in the Northern Region domi- nated the Southern Region and suggested multiple introduc- tions, possibly to the south. We tested multiple scenarios of phylogeographic structure with analyses of molecular vari- ance and found support for a Northern and Southern Region split at the Bahamas/Turks/Caicos versus Caribbean break (percentage of variation among regions = 8.49 %). We found that Puerto Rico clustered with the Southern Region more strongly than with the Northern Region, as opposed to previous reports. We also found the rare haplotype H03 for the first time in the southern Caribbean (Panama), indicat- ing that either secondary releases occurred or that the low- frequency haplotypes have had time to disperse to extreme southern Caribbean locations. 

Abstract: 

Numerous marine invertebrates form endosymbiotic relationships with dinoflagellates in the genus Symbiodinium. However, few studies have examined the fine-scale population structure of these symbionts. Here, we describe the genetic structure of Symbiodinium type ‘‘B1/B184’’ inhabiting the gorgonian Gorgonia ventalina along the Florida Keys. Six polymorphic microsatellite loci were utilized to examine 16 populations along the Upper, Middle, and Lower Keys spanning a range of *200 km. Multiple statistical tests detected significant differentiation in 54–92% of the 120 possible pairwise comparisons between localities, suggesting low levels of gene flow in these dinoflagellates. In general, populations clustered by geographic region and/or reefs in close proximity. Some of the sharpest population differentiation was detected between Symbiodinium from deep and shallow sites on the same reef. In spite of the high degree of population structure, alleles and genotypes were shared among localities, indicating some connectivity between Symbiodinium populations associated with G. ventalina. 

The recent intensification of human disturbances in the Caribbean has increased the prevalence of partial mortality on coral colonies. Partial mortality can change colony size by directly shrinking colonies or by splitting colonies into fragments. A reduction in colony size can also adversely affect fecundity and fitness as internal resources shift away from reproduction toward colony maintenance. This study aimed to determine whe- ther three Caribbean coral species, Siderastrea siderea, Montastraea faveolata, and Diploria strigosa, along the reef tract in Puerto Morelos, Mexico (20'52'N, 86'51'W), continued to dedicate resources to reproduction when colonies were fragmented to pre-maturation size. Contrary to expectations, eggs were found in colonies that were smaller than the maturation size and had been subjected to partial mortality. The continued dedication of resources toward reproduction, even in the smallest colonies, suggests that resource trade-offs away from reproduction are not as rigid as previously suggested in stressed corals.