Locating a Mate in 3D: the Case of Temora Longicornis

Using laser optics to illuminate high–resolution video–recordings, we revealed behavioural mechanisms through which males of the calanoid copepod species Temora longicornis locate females. Males of T. longicornis swam at significantly faster speeds than females along more sinuous routes, possibly reflecting adaptations to increase encounter with females. Upon approaching within 2 mm (i.e. two bodylengths) of a female\u27s swimming path, males accelerated to significantly higher pursuit speeds. Pursuit trajectories closely traced the trajectories of females, suggesting that males were following detectable trails created by swimming females. Males of T. longicornis detected female trails up to at least 10 s old, and tracked trails for distances exceeding 13 cm, or 130 bodylengths. Females were positioned up to 34.2 mm away from males (i.e. reactive distance) when males initiated ‘mate–tracking’. It was always the males of T. longicornis that detected and pursued mates. In rare events, males pursued other males. Behavioural flexibility was exhibited by males during mate–tracking. Males generally tracked the trails of ‘cruising’ (i.e. fast–swimming) females with high accuracy, while the pursuits of ‘hovering’ (i.e. slow–swimming) females often included ‘casting’ behaviour, in which males performed sharp turns in zigzag patterns within localized volumes. This casting by males suggested that hovering females create more dispersed trails than cruising females. Casting behaviour also was initiated by males near locations where females had hopped, suggesting that rapid movements by females disrupt the continuity of their trails. Males were inefficient at choosing initial tracking directions, following trails in the incorrect direction in 27 of the 67 (40%) mating pursuits observed. Males usually attempted to correct misguided pursuits by ‘back–tracking’ along trails in the correct direction. Males were observed to detect and track their own previous trajectories without females present, suggesting the possibility that males follow their own trails during back–tracking. Observations of males tracking their own trails and the trails of other males bring into question the specificity of trails as a mechanism promoting reproductive isolation among co–occurring planktonic copepods

Climate change, precipitation and impacts on an estuarine refuge from disease

© The Author(s), 2011. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS One 6 (2011): e18849, doi:10.1371/journal.pone.0018849.Oysters play important roles in estuarine ecosystems but have suffered recently due to overfishing, pollution, and habitat loss. A tradeoff between growth rate and disease prevalence as a function of salinity makes the estuarine salinity transition of special concern for oyster survival and restoration. Estuarine salinity varies with discharge, so increases or decreases in precipitation with climate change may shift regions of low salinity and disease refuge away from optimal oyster bottom habitat, negatively impacting reproduction and survival. Temperature is an additional factor for oyster survival, and recent temperature increases have increased vulnerability to disease in higher salinity regions. We examined growth, reproduction, and survival of oysters in the New York Harbor-Hudson River region, focusing on a low-salinity refuge in the estuary. Observations were during two years when rainfall was above average and comparable to projected future increases in precipitation in the region and a past period of about 15 years with high precipitation. We found a clear tradeoff between oyster growth and vulnerability to disease. Oysters survived well when exposed to intermediate salinities during two summers (2008, 2010) with moderate discharge conditions. However, increased precipitation and discharge in 2009 reduced salinities in the region with suitable benthic habitat, greatly increasing oyster mortality. To evaluate the estuarine conditions over longer periods, we applied a numerical model of the Hudson to simulate salinities over the past century. Model results suggest that much of the region with suitable benthic habitat that historically had been a low salinity refuge region may be vulnerable to higher mortality under projected increases in precipitation and discharge. Predicted increases in precipitation in the northeastern United States due to climate change may lower salinities past important thresholds for oyster survival in estuarine regions with appropriate substrate, potentially disrupting metapopulation dynamics and impeding oyster restoration efforts, especially in the Hudson estuary where a large basin constitutes an excellent refuge from disease.Funding was provided by the Hudson River Foundation, grant number 00607A, and the New York State Department of Environmental Conservation (MOU 2008)

Seawater carbonate chemistry and growth of Saccharina latissima and herbivory of Lacuna vincta

The laminarialean kelp, Saccharina latissima, is a common macroalgae along rocky shorelines that is also frequently used in aquaculture. This study examined how ocean acidification may alter the growth of S. latissima as well as grazing on S. latissima by the gastropod, Lacuna vincta. Under elevated nutrients, S. latissima experienced significantly enhanced growth at pCO2 levels >1,200 µatm compared to ambient pCO2 (400 µatm). Elevated pCO2 (>830 µatm) also significantly reduced herbivory of L. vincta grazing on S. latissima relative to ambient pCO2. There was no difference in grazing of S. latissima previously grown under elevated or ambient pCO2, suggesting lowered herbivory was due to harm to the gastropods rather than alteration of the biochemical composition of the kelp. Decreased herbivory was specifically elicited when L. vincta were exposed to elevated pCO2 in the absence of food for >18 h prior to grazing, with reduced grazing persisting 72 h. Elevated growth of S. latissima and reduced grazing by L. vincta at 1,200 µatm pCO2 combined to increase net growth rates of S. latissima by more than four-fold relative to ambient pCO2. L. vincta consumed 70% of daily production by S. latissima under ambient pCO2 but only 38% and 9% at 800 µatm and 1,200 µatm, respectively. Collectively, decreased grazing by L. vincta coupled with enhanced growth of S. latissima under elevated pCO2 demonstrates that increased CO2 associated with climate change and/or coastal processes will dually benefit commercially and ecologically important kelps by both promoting growth and reducing grazing pressure

Growth and disease prevalence as a function of salinity.

<p>(a) Relationship of mean oyster shell height to salinity (r² = 0.89, in samples collected in October 2008, after 3 months of growth from a mean starting height of 51.7 mm);vertical bars show standard error. (b) Prevalence of Dermo in oysters (30 per site) from 9 sites taken from coastal and TZ-HB sites in September, 2008, and 4 sites from coastal and TZ-HB sites in August, 2009 (r² = 0.67).</p

Model simulations of salinity at TZ-HB site (river km 50).

<p>Shown are average conditions over the entire period 1918–2009, and average conditions during the 5 years of that period with the greatest annual precipitation. Model output is averaged by year-day and filtered with a 5-day running average, Daily average salinities from the model at the same location are shown for 2008 and 2009.</p

Survival patterns, salinity variation, and river discharge.

<p>(a) Left: Survivorship of oysters grown in summer 2008 at a series of coastal and oligohaline sites in Tappan Zee-Haverstraw Bay. The decline at Ossining, the lowest-salinity TZ-HB site, was associated with a drop of salinity while the decline at Pier 40 was associated with a major infection of MSX. Right: Survivorship of oysters grown in the summer of 2009 (only 5 of the 2008 sites were investigated), comparing TZ-HB with two of the coastal sites studied in 2008. (b) Salinities in 2008 (left) and 2009 (right). Continuous, tidally filtered surface salinities are shown for Sandy Hook NJ (NOAA station # 8531680, SH in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0018849#pone-0018849-g001" target="_blank">Figure 1</a>) and Hastings NY (USGS station # 01376304, HA in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0018849#pone-0018849-g001" target="_blank">Figure 1</a>) (grey and black lines, respectively); oyster sites were sampled biweekly. (c) River discharge in 2008 (left, dark line) and 2009 (right), as compared to average seasonal discharge pattern for the period 1918–2009 (light grey line).</p