Feeding habits and competitive abilities of Pterois volitans and Holocentrus rufus in Caribbean reef ecosystems.
There have been many instances in the past where people have jumped to conclusions and taken the wrong measures trying to solve a problem. Currently the invasion of lionfish (Pterois volitans) in Caribbean waters is being viewed as a major problem and people are being told that this fish will destroy the reef ecosystem by significantly reducing native reef fish populations. Papers published claiming lionfish eating over twenty Wrasse in an hour portray the fish as a “super predator” that will rid the waters of any small fish. Just like the movie “Jaws” left no remorse for sharks in the 1970's, scientists are giving lionfish a terrible reputation by stressing extreme examples of their predation.
This experiment was designed to demonstrate and compare the feeding habits of lionfish to other native reef species. Maximum consumption rates for lionfish (Pterois volitans) and squirrelfish (Holocentrus rufus) were recorded and showed that squirrelfish can consume almost four times as much as lionfish. When put in direct competition for a single food source, squirrelfish consumed the prey 71.4% of the time. Stomach contents of 34 lionfish caught in the wild were also analyzed and three Wrasse weighing a total of 2.9g was the most any of them contained. Considering both of these species consume the same prey, reproduce year round and have very few predators, maybe people should reconsider the true impacts lionfish have on Caribbean reefs.
Aggressiveness of Stegastes adustus towards humans and other S. adustus
Four sites were assessed in Discovery Bay, Jamaica to monitor the aggressive behavior of the Dusky damselfish, Stegastes adustus: two sites by the jetty, one by the limestone rock area and one by the mangrove. All four sites were specifically chosen because of its sufficiency in its food supply, algae. The purpose of this study is to observe the territorial behavior of S. adustus and recording whether the damselfish reacts more aggressively to humans or to its own kind. Within all of the four sites, two controls were performed using an empty plastic jar, as well as seven trials of human interaction, and seven trials of another damselfish placed in the container. On a reaction scale that measures the level of aggression from 1 to 5, the damselfish were most aggressive towards another damselfish in all of the four sites. The first site of the jetty experienced the highest level of aggression. Its aggression level reached a level 5 (physically attacking the object), when the object was within zero feet of its territory. This area also showed a higher level of aggressiveness towards humans as compared to the other three sites – an average of a level 4 behavior. The damselfish were least aggressive towards another damselfish in the limestone rock area and the mangrove. Both sites encountered an average of level 3 behavior (flapping of their fins). This project suggests that the S. adustus are highly aggressive. Regardless of the ample food supply that is has in its territory, it still reacts more aggressively to its own kind than it does to humans.
Jenna and Paulie
An observation of brittle stars Ophiothrix suensonii, Ophinoreis reticulata, and Ophiocoma enchinata, and their preference in sponge selection among Alypsina fistularis and Niphates digitalis.
Brittle stars are naturally a negatively phototaxic species; therefore the species we tested were placed in a closed tank covered from light. This enabled them to attach to a particular sponge species for reasons other than avoiding light. By positioning a selected species of Brittle stars in an assigned pre-measured area, we were able to observe their final location after three hours in the dark tank. After conducting 4 trials for each star species it was observed that the majority of Brittle stars were found not attached. Sponge Brittle Stars were the first to be selected for testing and were found to have low attachment to any of the sponges in the controlled environment. This was peculiar since all of the Sponge Brittle stars collected in the wild were found attached to Niphates digitalis. They were mostly found in the middle showing the least activity, low tolerance for stress, and very susceptible to de-attaching their podia. Reticulated Stars were more active than the Sponge stars, and were never found at their initial position (the center), but mass numbers were found compressed in corners where the net divider and tank wall met. Those found on sponges were mostly found on Niphates digitalis and Aplysina fistularis. Blunt Spined Brittle Stars have shown to be the most active when seeking out sponges in the tank. The majority of these stars were found on the cover of the tank, and on the other side of the net divider. This species seemed to be attracted to Aplysina fistularis the most compared to the other species.
– Kasey and Brooks
A study of territory loyalty
Organisms choose a home based on its needs. When those needs are removed, the organism has two options. The organism can either move and look for a new home that meets its needs, or it can stay and facilitate rehabilitation of the resources to the territory. Stegastes adustus is well known for protecting their territory. Inside of a S. adustus territory, the fish maintains an algae patch that it takes care of and protects from other grazers. The hypothesis of this paper is that at a critical reduced algal level, S. adustus will move on to a new site. This is a problem because when the S. adustus moves on, any algae left is open to grazing and will also be lost. The drop in biomass can then lead to a decreased productivity level of the area. After testing 13 sites by gradually removing percentages as well as taking all of the algal mass on an area at once, only 7.7% of fish abandon their sites. This data suggests that S. adustus in fact does not abandon their territories in a number that would make a difference to productivity.
The Effect of Algal Diet on Ink Production in the Spotted Sea Hare (Aplysia dactylomela).
Spotted Sea Hares (Aplysia dactylomela) are slow moving, herbivorous opisthobranchs common to Discovery Bay, Jamaica. As a defensive mechanism, they are able to release a vivid purple ink which can disorient potential predators. In our study, we looked at the effect of three algal types – green, red, and brown – on the Sea Hares’ ability to produce ink. To determine this, four groups of eight Sea Hares each were isolated and each group fed a strictly monitored diet. One group with only green algae (Derbesia sp.), one group with only red algae (Jania adherens, Coelothrix irregularis, and Gracilaria cervicornis), one group with only brown algae (Dictyota divaricota), and a fourth control group which was fed all types. Each day, we gently handled the Sea Hares over a container to collect the ink and measured it with a syringe. Our results show that the Sea Hares which were fed red algae were the only ones that could still produce a substantial amount of ink after seven days of testing. The implications of this are that if red algae were to be outcompeted by green or brown algae, the Sea Hares may lose their defensive inking ability, potentially leading to more successful predation upon them and, eventually, their disappearance from the area.
– Megan and Kathleen
Difference in predation deterrence behavior and evisceration frequency between two holothurian species: Holothuria mexicana and Euapta lappa.
Driving the high productivity characteristic of coral reefs, holothurians play an integral role in maintaining the reef ecosystem: mixing substrates, recycling detritus, nutrients, consuming sediment, and increasing oxygenation. Two of the most common holothurian species are the diurnal Holothuria mexicana (aspidochirote) and nocturnal Euapta lappa (apodaceates). These sediment feeding organisms, although of different species, have adapted similar strategies to deter predators and thereby sustain high productivity. Holothuria mexicana and Euapta lappa incapacitate predators using evisceration (expulsion of internal organs), leading to entanglement and confusion. The objective of this study was to determine species more adept at evisceration. Differences in evisceration frequency between Holothuria mexicana and Euapta lappa were assessed. Additional predation deterrence strategies, as well as the effect of volume on reaction rates were also taken into account. Specimens were submerged in cold (~ 8° C) seawater to attain maximum contraction length. Volumetric measurements were then taken before and after placement under uniform mass (1.12 x 104 g). Repeated observations were conducted in 20 minute intervals to assess types of predation deterrence reaction as well as volumetric changes in both species. The relationship between volume and predation reaction rate was analyzed using regression correlation. Regression equations correlating biometric characteristics for both species were determined. While Holothuria mexicana showed a higher percentage of evisceration than Euapta lappa did, the latter exhibited a wider variety of predation deterrence strategies. There was not a strong correlation between volume and reaction rate in both Holothuria mexicana and Euapta lappa. However, it should be noted Euapta lappa trials were capped at 180 minutes to maximize sample size over the five day period.
The effects of light and food consumption on the deflation on Diodon holocanthus
Diodon holocanthus have a unique defense mechanism against predation. The balloonfish are able to inflate their bodies with water and air if necessary, enlarging themselves and protruding their spines. The purpose of this study is to see how food consumption and light affect the rate of deflation, or returning to their normal state from inflation. The study was conducted using 20 balloonfish over a six day period. Two tanks were used to house the subjects, which were each split into halves for a total of four sections, representing a different environment. Each tank was separated into fed and non-fed sides, in which one whole tank represented a light environment, and the other a dark environment. The fed subjects were given a limitless supply of food while the non-fed sections were starved. A net was used to apply consistent disturbance in order to stimulate maximum inflation in the balloonfish. Time measurements were taken every twelve hours at 11:00AM and 11:00PM. The experiment consisted of 149 total trials of which 27 trials led to no inflation. The results for the study showed that the fed balloonfish deflated at a faster rate than the non-fed subjects. Furthermore, on average, the balloonfish that were placed in the dark environment would deflate at a faster rate than the subjects in the light environment. It was also observed that balloonfish in the wild would deflate at a slower rate than those in captivity. Further implications may explain that Diodon holocanthus would be able to best protect itself using this predatory defense mechanism when starved and in a light environment.
Aron and Oded
Measuring The Flow Rates of Sponges In a Reef Ecosystem
The method I use of measuring how fast a sponge circulates.
Sponges are animals in the phylum Porifera, which means they have pores that they use to filter the water around them. These pores are tiny holes in the wall of the sponge, lined with many collar cells. Collar cells have flagella that they beat to create a current of water that passes through the entire sponge. Nutrients and particles are then taken from the water and used. All filtered water is then expelled through the osculum at the top of the sponge. The amount of water that a sponge circulates can be measured by injecting fluorescine dye into the water surrounding the base, and then counting how many seconds it takes for the dye to exit the osculum and travel to the end of a tube 10 centimeters long. I am using this process of measurement in my research project. I’m answering the question “Do sponges of the same species circulate water at the same speed at different parts of a reef ecosystem?” My hypothesis is that sponges found in shallower water circulate faster than those that are found in deeper water. My reasoning behind this hypothesis is that several other filter-feeding animals, which cause competition for particles suspended in water, surround sponges living in the shallow mangrove area. Sponges that are found in deep water are surrounded by much more water, and compete far less for resources.
Sea anemones and their inhabitants: Field surveys and laboratory experiments
Sea anemones host a wide variety of symbiotic inhabitants. The animals that seek shelter in anemones benefit by avoiding predation in the form of a physical camouflage, as well as the defense system offered by the anemone’s nematocysts. Anemones are thought to benefit by being cleaned as the inhabitants feed. This study explored the factors that affect the types and numbers of species and individuals that inhabit sea anemones in Discovery Bay, Jamaica. Field surveys of anemones were carried out in three areas of the bay including mangrove, limestone area; a jetty; and patch reefs bordering the ocean side of the lagoon and continuing into the reef crest. Size and species of anemone, and all inhabitants were recorded. Condylactis gigantaea, giant anemone, had greater species inhabitant diversity and abundance than Rhodactis lucida, knobby anemone. The greatest number of inhabitant species were found in the patch reefs and the least in the mangrove, limestone area. This is likely due to the high diversity of species supported by reef structure. Also, these organisms may avoid predation by escaping to higher ground on mangrove roots or exposed rock. Based on personal observation, more individuals and species were found in larger Condylactis gigantaea than smaller. Ten sea anemones were tagged during the day and revisited at night to observe any changes in inhabitants based on time of day. Some of the inhabitants were removed prior to revisiting to determine if new individuals would move in. There tended to be fewer or no species present in anemones at night than during the day. Organisms may be able to forage at night, protected from predators by the low light. Of the anemones where inhabitants were removed, some were left empty at night and others were filled by new individuals. Of the anemones where inhabitants were not removed, some had the same species at night and some had become occupied by other individuals. Finally, laboratory experiments were carried out to determine the patterns by which common inhabitants disperse among large and small anemones. There does not seem to be a preference for larger anemones by larger, presumably dominant crabs. The banded cling crabs either preferred or outcompeted the green clinging crabs for anemone space. Smaller individuals tended to share anemones more than larger ones. Further study is needed to determine the patterns of species dispersal across anemones based on size, species, and time of day.
Well, all good things must come to an end. And in this case, they came to a freezing cold, screeching halt as we returned to a New York covered in snow. It's taken some of us a little extra time to dig out our cars, repair frozen pipes, or adjust to wearing socks and shoes when outdoors; but we're all acclimating to our regular life in a temperate (not-tropical) environment.
The next set of posts will be the project abstracts for the student research projects. They gave us their final oral presentation in Jamaica and in two weeks will be submitting their final paper for the course.
Hope everybody had a great time and learned a lot. Brad and I (and Amber) enjoyed the course immensely.