Marine macroecology: evidence from patterns in soft sediment fauna in the UK

Marine macroecology: evidence from patterns in soft sediment fauna in the UK

Macroecology is the search for repeated, large-scale, statistically significant patterns in ecology such as latitudinal trends in diversity, or relationships between species’ abundance and frequency of site occupancy or geographical range size. It also represents an attempt to adopt a less reductionist approach to elucidating the underlying theoretical explanations for these patterns, and ultimately may provide the framework for predictive models and experimentation into these fundamental properties of assemblages.

Macroecological studies predate the naming of this branch of Ecology by 30 years or so, but there has a recent surge of interest in macroecological patterns in the terrestrial ecology in the last decade. To date this surge has not been mirrored as strongly in marine ecology.

Here I review some major macroecological patterns revealed in terrestrial studies, and use the extensive conservation database of the Marine Nature Conservation Review of the United Kingdom to search for replication of some of these patterns in British soft-sediment infauna. I draw some tentative conclusions on the use of such surveys in marine macroecological studies, and explore the theoretical implications of the evidence from comparison of marine and terrestrial macroecological patterns.

Kinsey Frick.* Department of Zoology, University of New Hampshire, Durham, NH 03824, USA; e-mail kinseym@cisunix.unh.edu.

Aeolid nudibranchs maintain functional stinging nematocysts for protection against predators such as fish and crabs. Nematocysts are sequestered from the nudibranch’s cnidarian prey, and selection for incorporation is largely a function of availability in the diet. However, nematocyst ratios vary within nudibranchs feeding on a given diet, indicating that other factors may be involved in determining nematocyst selection. I propose that predator presence influences nematocyst incorporation from those available in the diet, as nematocysts are a primary defense mechanism for combating predation. Nematocyst uptake in the nudibranch Flabellina verrucosa collected from the southern Gulf of Maine was examined in response to various predators, including Crossaster papposus, Tautogalubrus adspersus, and Carcinus maenas, and compared to uptake due to diet alone. F. verrucosa is a potential prey source for these predators, though not all are present in the collection area, thus nudibranch experience with these predators spanned the range of common exposure to no possible exposure to the experimental predator. Nudibranchs in individual flow-through containers feeding on a provided diet of the hydroids Tubularia crocea and Obelia spp. were subjected to tanks containing a predator, then the nematocyst distribution within the nudibranch cerata was examined. While the majority of the changes over the experimental period were attributable to diet as previously shown, nudibranchs responded to both the cunner T. adspersus and the sea star C. papposus stimulus by significantly increasing incorporation of microbasic mastigophores, a penetrating type of nematocyst. No differential uptake was seen with C. maenas; however, response was evident in the nudibranchs both for predators present in the collection area, and those with which they could have had no previous exposure. This indicates that in addition to diet, F. verrucosa, and possibly other aeolid nudibranchs, modulate nematocyst incorporation in response to the presence of predators in the area.


Factors determining the composition of infaunal beach communities at large scales

M. T. Frost,¹ M. J. Attrill,¹ A. A. Rowden,^{1,2 1}Benthic Ecology Research Group, University of Plymouth, United Kingdom; ²present address: Marine Biodiversity Group, National Institute of Water & Atmospheric Research (NIWA), Wellington, New Zealand.

Leslie J. Gallagher* and Kenneth L. Heck, Jr. Dauphin Island Sea Lab and University of South Alabama, Dauphin Island, AL 36528, USA.

Despite their well-known potential to produce significant artefacts, caging experiments remain a staple item in the benthic ecologist’s toolbox. We used field studies to evaluate the significance of several potential artefacts associated with conducting caging experiments in low energy seagrass beds. This work demonstrated that cage structure significantly influenced velocity of water flow and sediment composition. Such alterations in physical properties were associated with a change in the number and community composition of new recruits settling inside cages. However, cage structure had little effect on overall densities and species composition of macrofauna (> 500 um), and inclusion/exclusion of predatory pinfish (>8 cm) had no significant effect on the immigration and emigration rates of potential prey species. These results suggests that short-term (~ 1 month) caging experiments in low energy seagrass habitats that focus on macrofauna can be an effective tool in understanding the ecology of these systems, and that careful planning can limit the impact of caging artefacts.


Seed dispersal and landscape-scale dispersal limitation in the cobble beach plant metacommunity

Jacqueline L. P. Gamiño,* Margaret A. Dolan, and John F. Bruno. The University of North Carolina at Chapel Hill, Department of Marine Sciences CB#3300, 12-2 Venable Hall, Chapel Hill, NC, 27599-3300, USA.

Dispersal is a key process in marine communities and can have profound effects on population- and community-level parameters. Several new lines of inquiry within marine ecology are largely dependent on an ability to quantify dispersal characteristics. Since dispersal can have a large influence on population connectivity, the implications for population management and reserve design are obvious. Additionally, dispersal has been described as the key variable in metapopulation ecology. For example, the details of migration essentially dictate the effects that landscape attributes will have on large-scale species distributions and dynamics. Unfortunately, it is very difficult to obtain even basic dispersal data for most species. We quantified the dispersal-distance function of several plant species that inhabit the cobble beach plant metacommunity. We sampled seed supply as a function of distance from the parental source population over four years at a number of sites. We found a surprising degree of seed retention that is suggestive of very low rates of emigration and evidence of relatively long distance dispersal (≈500 m). When combined with data on the spatial arrangement of habitat patches and patterns of patch occupancy and colonization, our results indicate that patch isolation is a significant cause of dispersal limitation in this system. In this metacommunity, frequencies of patch occupancy are quite low (0.01 to 0.40) and many habitable patches remain unoccupied. Thus, dispersal limitation and patch isolation appear to significantly affect the dynamics of this metacommunity.


The distributional ecology of Johnson’s seagrass (Halophila johnsonii), in southeastern Florida

Adam Gelber,¹* Donald R. Deis,² and William F. Precht.^{1 1}PBS&J, 2001 N.W. 107th Ave., Miami, FL 33172, USA; ²PBS&J, 7785 Baymeadows Way, Suite 202, Jacksonville, FL 32256, USA.

M. L. Gielazyn,¹* A. H. Ringwood,² S. E. Stancyk,¹ and W. W. Piegorsch.^{1 1}University of South Carolina, Columbia, SC, USA; ²Marine Resources Research Institute, Charleston, SC, USA.

Elevated levels of chromium are found in marine water and sediment near urban and industrial areas worldwide. Hexavalent chromium, Cr(VI), the predominant valence state in seawater, readily passes through cellular membranes. Once inside the cell Cr(VI) is reduced to trivalent chromium, Cr(III), by cellular reductants. Exposure to Cr(VI) can result in numerous forms of DNA damage. A portion of the DNA damage is thought to be oxidative, due to reactive oxygen intermediates and Cr species produced during Cr(VI) reduction. Single cell gel electrophoresis or the comet assay is a simple and sensitive technique used to examine DNA damage in single cells. Endogenous enzymes that repair DNA can be used in conjunction with the comet assay to identify different types of DNA damage. For example, the lesion-specific enzyme formamidopyrimidine glycosylase (FPG) recognizes 8-oxyguanine and other damaged bases, which are products of oxidative damage. Experimental objectives were to use the comet assay to quantify DNA damage (single strand breaks and alkali-labile sites) and oxidative DNA damage in bivalve tissues. Oyster (Crassostrea virginica) hemocytes were exposed to Cr(VI) (as K₂Cr₂O₇) and H₂O₂ under controlled laboratory conditions. The comet assay was used with and without FPG to determine the amount of DNA damage in oyster tissues. We have found an increase in single strand DNA breaks and alkali-labile sites in hemocytes after exposure. FPG studies indicate that oxidative damage is contributing to observed DNA damage. DNA damage can lead to necrosis, apoptosis, or heritable mutations, and therefore has the potential to impact populations as well as individuals. Recent studies using a similar experimental design with clam (Mercenaria mercenaria) hemocytes suggest that clams are more sensitive than oysters.


Life at the edge: examination of the northern geographic range limit of an intertidal snail

S. E. Gilman.* Center for Population Biology, University of California, Davis, CA 95616, USA.

For many terrestrial species the poleward edges of ranges are determined by climate and physiological stress while the equatorward edge is determined by species interactions. There is significantly less evidence for this paradigm among marine species, and only a few studies have examined the range limits of any intertidal species from the Northeastern Pacific. For species with a planktonic larval stage, ocean currents could also determine the location of range limits. The intertidal limpet Macclintockia scabra is distributed from Mexico to Cape Mendocino, CA. I am studying the northern range limit of M. scabra to compare the relative influence of physiological stress and recruitment limitation on this range limit. Preliminary results from transplanting M. scabra north of Cape Mendocino do not show a consistent relationship between latitude and survival or growth rates. In contrast, a study of recruitment shows a decline in recruitment rates with latitude. I will discuss possible factors determining the northern range limit of M. scabra in light of this data.


Chemical ecology of reef and cave sponges of the Bahamas: predator deterrent vs. antimicrobial activity

D. J. Gochfeld¹* and M. Slattery.^{1,2 1}National Center for Natural Products Research and ²Department of Pharmacognosy, University of Mississippi, University, MS 38677, USA.

The sponge Plakortis sp. is common on reefs throughout the Caribbean; in the Bahamas it is found on shallow and deep fore-reefs, as well as in marine caves. We compared the chemical ecology of the sponge Plakortis sp. from both reef and cave habitats near Lee Stocking Island, Bahamas. These habitats differ considerably in both physical and biological parameters, including light, water motion, and microbial and predator communities. Reef sponges are potentially subject to high levels of predation, and both the sponges and their extracts were more deterrent to fish than were cave sponges. Whereas marine caves are free of predatory fishes, they do act as microbial sinks that concentrate a microbial community on the cave substratum, although the associated sponge fauna is relatively free of microbial overgrowth. By comparison, reef sponge surfaces harbor significantly more microbes than do their cave counterparts. Extracts of cave sponges exhibited greater antimicrobial activity against cultured marine microbes than did reef sponge extracts, and phytagel discs embedded with cave sponge extracts were significantly less susceptible to fouling than were those containing reef sponge extracts. There appears to be a tradeoff between predator deterrent and antimicrobial chemical defenses in the reef vs. cave habitats.


Grazing preferences of marine isopods, amphipods, and gastropods on three prominent algal species of the Baltic Sea

M. E. Goecker¹* and S. E. Kåll.^{2 1}Dauphin Island Sea Lab/University of South Alabama, 101 Bienville Blvd., Dauphin Island, AL 36528, USA; ²Åbo Akademi University, Department of Biology/Environmental and Marine Biology, Åbo, Finland 20500.

Preference tests were performed over a two-week period in September 2001 in which isopods (Idotea spp.), amphipods (Gammarus spp.), and gastropods (Theodoxus fluviatilis) were offered choices of three common algal species from the Baltic Sea: Enteromorpha intestinalis, Cladophora spp., and Fucus vesiculosus. After a 48-hour starvation period, 20 of each grazer species were placed in aquaria containing ~1.0 g of each algal species. Fifteen trials for each grazer were run for 20 hours. We found that Gammarus spp. ate significantly more Cladophora spp. and E. intestinalis than F. vesiculosus (p < 0.001). Similarly, Idotea spp. ate significantly more of both filamentous green algae than F. vesiculosus (p < 0.001). T. fluviatilis showed no preferences among algal species with almost no consumption. With the preference of isopods and amphipods for filamentous green algae, we would expect these algae to be maintained at low biomass levels, but this is not the case in the Baltic Sea. We suggest two factors that may be promoting accumulation of algal biomass. Clearly, bottom-up effects of high nutrient loading have caused high growth rates of filamentous algae, negating effects of preferential grazing. Second, removal of piscivorous fish may be producing a top-down effect on herbivore abundance, and thus herbivore ability to control filamentous algal biomass. More likely a combination of factors plays a role in grazer regulation of fast growing, filamentous algae. With further study on grazing rates, densities of animals, and growth rates of algae, more insight can be gained on grazer influence of algal overgrowth.